Technical Support
Document for the
Clean Water Rule:
Definition of Waters
of the United States
May 27, 2015
U.S. Environmental Protection
Agency
U.S. Department of the Army
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Technical Support Document for the Clean Water Rule: Definition of Waters of the United States May 2015
This Technical Support Document addresses in more detail the legal basis and the existing
scientific literature in support of the significant nexus determinations underpinning the Clean
Water Rule. The Preamble, the Science Report, this Technical Support Document, the Response
to Comments, and the rest of the administrative record provide the basis for the definition of
"waters of the United States" established in the rule. Where this Technical Support Document does
not reflect the language in the preamble and final rule, the language in the final preamble and rule
controls and should be used for purposes of understanding the scope, requirements, and basis of the
final rule.
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Table of Contents
I. Statute, Regulations and Caselaw: Legal Issues 6
A. The Clean Water Act 6
i. Background 6
ii. The Rule is Consistent with the Statute 9
B. Historic Scope of Regulatory Definition of "Waters of the United States" 18
i. Existing Regulation 18
ii. Caselaw 22
iii. The Rule is Narrower in Scope than Existing Regulation 30
C. Supreme Court Decisions Concerning "Waters of the United States" 34
i. Supreme Court Decisions 34
ii. Post-Rapanos Appellate Court Decisions 40
iii. The Rule is Consistent with Supreme Court Decisions 47
iv. The Rule is Consistent with the Constitution 83
II. Significant Nexus Analysis 92
A. Science Report and Scientific Review 93
i. Science Report: Synthesis of Peer-Reviewed Scientific Literature 93
1. Summary of Major Conclusions 96
2. Discussion of Major Conclusions 102
3. Key Findings for Major Conclusions 105
4. Science Report: Framework for Analysis 118
5. Science Report Executive Summary Closing Comments 155
6. Emerging Science 156
ii. Scientific Review 158
1. Peer Review of the Connectivity Report 158
2. SAB Review of the Proposed Rule 160
B. Scope of Significant Nexus Analysis: "Similarly Situated" 164
i. Analyzing "Similarly situated" Waters in Combination 164
ii. Rationale for Conclusion 171
C. "In the Region" 174
i. Identifying "In the Region" As the Point of Entry Watershed 174
ii. Rationale for Conclusion 175
D. "Significant Nexus" 177
i. Scope of Significant Nexus Analysis 180
ii. Rationale for Conclusion 184
III. Traditional Navigable Waters 190
IV. Interstate Waters 197
A. The Language of the Clean Water Act, the Statute as a Whole, and the Statutory
History Demonstrate Congress' Clear Intent to Include Interstate Waters as
"Navigable Waters" Subject to the Clean Water Act 197
i. The Federal Water Pollution Control Act Prior to 1972 202
ii. The Refuse Act 204
iii. The Federal Water Pollution Control Act Amendments of 1972 205
B. Supreme Court Precedent Supports CWA Jurisdiction over Interstate Waters
Without Respect to Navigability 207
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May 2015
C. The Supreme Court's Decisions in SWANCC and Rapanos Do Not Limit or
Constrain Clean Water Act Jurisdiction Over Non-navigable Interstate Waters . 211
D. The Agencies' Longstanding Interpretation of the Term "Navigable Waters" to
Include "Interstate Waters" 215
V. Territorial Seas 223
VI. Impoundments of "Waters of the United States" 224
A. Impoundments Have a Significant Nexus 224
B. Rationale for Conclusion 229
VII. Tributaries 232
A. Definition of Tributary 234
i. Bed and Banks and Ordinary High Water Mark 235
ii. Rationale for Conclusion 241
B. The Agencies Have Concluded that Tributaries, as Defined, Have a Significant
Nexus 243
i. Tributaries as Defined Are "Similarly Situated" 245
ii. Tributaries Significantly Affect the Physical Integrity of (a)(1) through (a)(3)
Waters 246
iii. Tributaries Significantly Affect the Chemical Integrity of (a)(1) through (a)(3)
Waters 249
iv. Tributaries Significantly Affect the Biological Integrity of (a)(1) through (a)(3)
Waters 254
v. Man-made or Man-altered Tributaries Significantly Affect the Physical, Chemical
and Biological Integrity of (a)(1) through (a)(3) Waters 256
vi. Ephemeral and Intermittent Tributaries Significantly Affect the Chemical,
Physical, or Biological Integrity of (a)(1) through (a)(3) Waters 259
C. Rationale for Conclusions 271
VIII. Adjacent Waters 275
A. Definition of "Adjacent Waters" 275
i. Bordering and Contiguous Waters 277
ii. Waters Separated by a Berm 284
iii. Neighboring Waters 293
1. Waters within 100 Feet of the Ordinary High Water Mark 295
2. Waters in the Floodplain within 1,500 Feet of the Ordinary High Water Mark
299
3. Waters within 1,500 Feet of the High Tide Line 302
B. Adjacent Waters, As Defined, Have a Significant Nexus 305
i. Adjacent Waters as Defined are "Similarly Situated" 305
ii. Adjacent Waters Significantly Affect the Physical Integrity of (a)(1) through (a)(3)
Waters 306
iii. Adjacent Waters Significantly Affect the Chemical Integrity of (a)(1) through
(a)(3) Waters 311
iv. Adjacent Waters Significantly Affect the Biological Integrity of (a)(1) through
(a)(3) Waters 315
C. Rationale for Conclusions 321
IX. Case-Specific Significant Nexus Determinations 327
A. Five Subcategories of Waters are "Similarly Situated" 330
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i. Prairie Potholes 332
ii. Carolina and Delmarva Bays 336
iii. Pocosins 339
iv. Western Vernal Pools in California 342
v. Texas Coastal Prairie Wetlands 348
B. Waters within the 100-Year Floodplain of a Traditional Navigable Water, Interstate
Water, or the Territorial Sea and Waters within 4,000 Feet of the High Tide Line or
Ordinary High Water Mark 349
i. Waters within the 100-Year Floodplain of a Traditional Navigable Water,
Interstate Water, or the Territorial Sea 350
ii. Waters within 4,000 Foot of the High Tide Line or Ordinary High Water Mark of
a Traditional Navigable Water, Interstate Water, the Territorial Sea,
Impoundment, or Covered Tributary 353
C. Rationale for Conclusions 369
Appendices
Appendix 1: References
Appendix 2: Traditional Navigable Waters ("Appendix D")
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I. Statute, Regulations and Caselaw: Legal Issues
A. The Clean Water Act
i. Background
Congress enacted the Federal Water Pollution Control Act Amendments of 1972, Pub. L.
No. 92-500, 86 Stat. 816, as amended, Pub. L. No. 95-217, 91 Stat. 1566, 33 U.S.C. 1251 et seq.
(Clean Water Act or CWA or Act) "to restore and maintain the chemical, physical and biological
integrity of the Nation's waters." Section 101(a). One of the goals of the CWA is to attain
"water quality which provides for the protection and propagation of fish, shellfish, and wildlife."
Section 101(a)(2). A major tool in achieving that purpose is a prohibition on the discharge of any
pollutants, including dredged or fill material, into "navigable waters" except in accordance with
the Act. Section 301(a).
The CWA provides that "[t]he term 'navigable waters' means the waters of the United
States, including the territorial seas." Section 502(7). The Conference Report accompanying the
CWA explained that "[t]he conferees fully intend that the term 'navigable waters' be given the
broadest possible constitutional interpretation unencumbered by agency determinations which
have been made or may be made for administrative purposes." S. Conf. Rep. No. 1236, 92d
Cong., 2d Sess. 144 (1972). The House and Senate Committees expressed concern that
"navigable waters" might be given an unduly narrow reading. Thus, the House Report observed:
"One term that the Committee was reluctant to define was the term "navigable waters." The
reluctance was based on the fear that any interpretation would be read narrowly. However, this
is not the Committee's intent. The Committee fully intends that the term "navigable waters" be
given the broadest possible constitutional interpretation unencumbered by agency determinations
which have been made or may be made for administrative purposes." H.R. Rep. No. 911, 92d
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Cong., 2d Sess. 131 (1972). Referring to the term "integrity" in the statutory goals, the House
Report stated: "[T]he word 'integrity' ... refers to a condition in which the natural structure and
function of ecosystems [are] maintained." H.R. Rep. No. 92-911, 92nd Cong. 2d Sess. 76 (1972)
(iquoted in United States v. Riverside Bayview Homes, Inc., 474 U.S. 121, 132-33 (1985)).
The Senate Report stated that "[t]hrough a narrow interpretation of the definition of
interstate waters the implementation [of the] 1965 Act was severely limited. Water moves in
hydrologic cycles and it is essential that discharge of pollutants be controlled at the source." S.
Rep. No. 414, 92d Cong., 1st Sess. 77 (1971).
The Conference Committee deleted the word "navigable" from the definition of
"navigable waters," broadly defining the term to include "the waters of the United States." As
noted above, the Conference Report explained that the definition was intended to repudiate
earlier limits on the reach of federal water pollution efforts: "The conferees fully intend that the
term 'navigable waters' be given the broadest possible constitutional interpretation
unencumbered by agency determinations which have been made or may be made for
administrative purposes." S. Conf. Rep. No. 1236, 92d Cong., 2d Sess. 144 (1972). See Section
I.C. below for discussion of Supreme Court decisions regarding the scope of the CWA.
The Environmental Protection Agency (EPA) administers the CWA except as otherwise
explicitly provided. Section 101(d). The Attorney General has determined that the "ultimate
administrative authority to determine the reach of the term 'navigable waters' for purposes of §
404" resides with EPA. 43 Op. Att'y Gen. 197 (1979). EPA has had a consistent view as to the
broad scope of the jurisdiction conferred by the CWA.
In 1977, Congress considered a legislative proposal that would have limited the class of
waters subject to the U.S. Army Corps of Engineers' (Corps) permitting authority under Section
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404 of the CWA. A bill passed by the House of Representatives provided that for purposes of
Section 404, the Corps' permitting authority would extend to navigable waters "and adjacent
wetlands," with the term "navigable waters" defined to mean waters navigable in fact, or capable
of being made so by "reasonable improvement." 123 Cong. Rec. 10,420 (1977); see id. at 10,434
(passage of bill). A similar amendment was defeated in the Senate, however, see id. at 26,728,
and the provision to redefine the term "navigable waters" was eliminated by the Conference
Committee, see H.R. Conf. Rep. No. 830, 95th Cong., 1st Sess. 97-105 (1977). Congress rejected
the proposal to limit the geographic reach of section 404 because it wanted a permit system with
"no gaps" in its protective sweep. 123 Cong. Rec. 26707 (1977) (remarks of Sen. Randolph).
Rather than alter the geographic reach of section 404, Congress amended the statute by
exempting certain activities — most notably certain agricultural and silvicultural activities — from
the permit requirements of section 404. See Section 404(f). Congress also established a
mechanism by which a State may assume responsibility for administration of the Section 404
program with respect to waters "other than" traditional navigable waters and their adjacent
wetlands. Section 404(g)(1).
Other evidence abounds to support the conclusion that when Congress rejected the
attempt to limit the geographic reach of Section 404, it was well aware of the jurisdictional scope
of EPA and the Corps' definition of "waters of the United States." For example, Senator Baker
stated:
Interim final regulations were promulgated by the [CJorps [on] July 25, 1975. . . .
Together the regulations and [EPA] guidelines established a management
program that focused the decisionmaking process on significant threats to aquatic
areas while avoiding unnecessary regulation of minor activities. On July 19,
1977, the [C]orps revised its regulations to further streamline the program and
correct several misunderstandings. . . .
Continuation of the comprehensive coverage of this program is essential for the
protection of the aquatic environment. The once seemingly separable types of
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aquatic systems are, we now know, interrelated and interdependent. We cannot
expect to preserve the remaining qualities of our water resources without
providing appropriate protection for the entire resource.
Earlier jurisdictional approaches under the [Rivers and Harbors Act] established
artificial and often arbitrary boundaries ....
123 Cong. Rec. 26718 (1977).
ii. The Rule is Consistent with the Statute
The U.S. Environmental Protection Agency (EPA) and the Department of the Army
(collectively referred to as "the agencies") have promulgated a rule designed to implement
Congress' foundational goal for the CWA "to restore and maintain the chemical, physical and
biological integrity of the Nation's waters." Section 101(a). Some commenters stated that the
proposed rule was inconsistent with the CWA because it impinged on the role of States to
"prevent, reduce and eliminate pollution, to plan the development and use (including restoration,
preservation, and enhancement) of land and water resources." Section 101(b). To the contrary,
the agencies recognize that States and tribes play a vital role in the implementation and
enforcement of the CWA. Nothing in this rule limits or impedes any existing or future state or
tribal efforts to further protect their waters. States and tribes, consistent with the CWA, retain
full authority to implement their own programs to more broadly and more fully protect the
waters in their jurisdiction. Under Section 510 of the CWA, unless expressly stated, nothing in
the CWA precludes or denies the right of any state or tribe to establish more protective standards
or limits than the CWA. Many states and tribes, for example, regulate groundwater, and some
others protect wetlands that are vital to their environment and economy but which are outside the
scope of the CWA.
In addition, when Congress passed the Federal Water Pollution Control Act Amendments
of 1972 it was not acting on a blank slate. It was amending existing law that provided for a
federal/state program to address water pollution. The Supreme Court has recognized that
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Congress, in enacting the CWA in 1972, "intended to repudiate limits that had been placed on
federal regulation by earlier water pollution control statutes and to exercise its powers under the
Commerce Clause to regulate at least some waters that would not be deemed 'navigable' under
the classical understanding of that term." Riverside Bayview Homes v. U.S., 474 U.S. 121,133
(1985); see also International Paper Co. v. Ouellette, 479 U.S. 481, 486, n.6 (1987). The final
rule interprets the term "waters of the United States" consistent with the stated goals on policies
of the CWA as a whole.
Other commenters stated that the proposed rule was inconsistent with Sections 101(g)
and 510(2) of the CWA, because it interfered with States' rights over waters and will impinge
upon allocation and movement of State waters. Section 101(g) of the CWA states, "It is the
policy of Congress that the authority of each State to allocate quantities of its water within its
jurisdiction shall not be superseded, abrogated or otherwise impaired by [the CWA and] that
nothing in [the CWA] shall be construed to supersede or abrogate rights to quantities of water
which have been established by any State." Similarly, Section 510(2) provides that nothing in
the Act shall "be construed as impairing or in any manner affecting any right or jurisdiction of
the States with respect to the waters ... of such States." The rule is entirely consistent with these
policies. The rule does not impact or diminish State authorities to allocate water rights or to
manage their water resources. Nor does the rule alter the CWA's underlying regulatory process.
Having been enacted with the objective of restoring and maintaining the chemical, physical, and
biological integrity of our nation's waters, the CWA serves to protect water quality. Neither the
CWA nor the rule impairs the authorities of States to allocate quantities of water. Instead, the
CWA and the rule serve to enhance the quality of the water that the States allocate.
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Even if the rule were to have an incidental effect on water quantity or allocation, which it
does not, the rule would still be consistent with Section 101(g) of the CWA. In PUD No. 1 of
Jefferson County v. Washington Dept. of Ecology, 511 U.S. 700, 720, 114 S.Ct. 1900, 1913,
128 L.Ed.2d 716, 733 (1994) the United States Supreme Court held, "Sections 101(g) and 510(2)
[of the CWA] preserve the authority of each State to allocate water quantity as between users;
they do not limit the scope of water pollution controls that may be imposed on users who have
obtained, pursuant to state law, a water allocation." First, the Court stated: "The Federal Water
Pollution Control Act, commonly known as the Clean Water Act, 86 Stat. 816, as amended, 33
U.S.C. § 1251 etseq., is a comprehensive water quality statute designed to 'restore and maintain
the chemical, physical, and biological integrity of the Nation's waters.' § 1251(a). The Act also
seeks to attain 'water quality which provides for the protection and propagation of fish, shellfish,
and wildlife.' § 1251(a)(2). To achieve these ambitious goals, the Clean Water Act establishes
distinct roles for the Federal and State Governments. Under the Act, the Administrator of the
Environmental Protection Agency (EPA) is required, among other things, to establish and
enforce technology-based limitations on individual discharges into the country's navigable
waters from point sources. See §§ 1311, 1314. Section 303 of the Act also requires each State,
subject to federal approval, to institute comprehensive water quality standards establishing water
quality goals for all intrastate waters. §§ 1311(b) (1)(C), 1313. These state water quality
standards provide 'a supplementary basis ... so that numerous point sources, despite individual
compliance with effluent limitations, may be further regulated to prevent water quality from
falling below acceptable levels.' EPA v. California ex rel. State Water Resources ControlBd.,
426 U.S. 200, 205, n. 12, 48 L. Ed. 2d 578, 96 S. Ct. 2022 (1976)." 511 U.S. at 704.
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Petitioners in the case argued that the Clean Water Act is only concerned with water
"quality," and does not allow the regulation of water "quantity." The Court held: "This is an
artificial distinction. In many cases, water quantity is closely related to water quality; a sufficient
lowering of the water quantity in a body of water could destroy all of its designated uses, be it for
drinking water, recreation, navigation or, as here, as a fishery. In any event, there is recognition
in the Clean Water Act itself that reduced stream flow, i.e., diminishment of water quantity, can
constitute water pollution. First, the Act's definition of pollution as 'the man-made or man
induced alteration of the chemical, physical, biological, and radiological integrity of water'
encompasses the effects of reduced water quantity. 33 U.S.C. § 1362(19). This broad conception
of pollution — one which expressly evinces Congress' concern with the physical and biological
integrity of water — refutes petitioners' assertion that the Act draws a sharp distinction between
the regulation of water 'quantity' and water 'quality.' Moreover, § 304 of the Act expressly
recognizes that water 'pollution' may result from 'changes in the movement, flow, or circulation
of any navigable waters . . ., including changes caused by the construction of dams.' 33 U.S.C. §
1314(f)." 511 U.S. at 719-20.
Petitioners also argued that Sections 101(g) and 510(2) exclude the regulation of water
quantity from the coverage of the Act. The Supreme Court held: "we read these provisions more
narrowly than petitioners. Sections 101(g) and 510(2) preserve the authority of each State to
allocate water quantity as between users; they do not limit the scope of water pollution controls
that may be imposed on users who have obtained, pursuant to state law, a water allocation. In
California v. FERC, 495 U.S. 490, 498, 109 L. Ed. 2d 474, 110 S. Ct. 2024 (1990), construing an
analogous provision of the Federal Power Act, we explained that "minimum stream flow
requirements neither reflect nor establish 'proprietary rights'" to water. Cf. First Iowa Hydro-
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Electric Cooperative v. FPC, 328 U.S. 152, 176, 90 L. Ed. 1143, 66 S. Ct. 906, and n. 20 (1946).
Moreover, the certification itself does not purport to determine petitioners' proprietary right to
the water of the Dosewallips. In fact, the certification expressly states that a "State Water Right
Permit (Chapters 90.03.250 RCW and 508-12 WAC) must be obtained prior to commencing
construction of the project." App. to Pet. for Cert. 83a. The certification merely determines the
nature of the use to which that proprietary right may be put under the Clean Water Act, if and
when it is obtained from the State. Our view is reinforced by the legislative history of the 1977
amendment to the Clean Water Act adding § 101(g). See 3 Legislative History of the Clean
Water Act of 1977 (Committee Print compiled for the Committee on Environment and Public
Works by the Library of Congress), Ser. No. 95-14, p. 532 (1978) ('The requirements [of the
Act] may incidentally affect individual water rights. ... It is not the purpose of this amendment
to prohibit those incidental effects. It is the purpose of this amendment to insure that State
allocation systems are not subverted, and that effects on individual rights, if any, are prompted
by legitimate and necessary water quality considerations')." 511 U.S. at 720-21. The rule is
consistent with the Supreme Court's reading of these provisions consistent with the "ambitious
goals" of the Act.
Under the rule, States, tribes, and local governments, consistent with the CWA, retain full
authority to implement their own CWA programs to protect their waters more broadly or more
fully than under the CWA. According to Section 510 of the CWA, unless expressly stated in the
CWA, nothing in the CWA precludes or denies the right of any State, tribe, or political
subdivision to establish its own standards or limits, as long as these standards and limits are at
least as protective as those under the federal CWA. Many States and tribes, for example, protect
groundwater. Others protect wetlands that are vital to their environment and economy but are
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outside the regulatory coverage of the CWA. Nothing in the rule limits or impedes any existing
or future State, tribal, or local efforts to further protect waters. In fact, by providing greater
clarity regarding what waters are subject to the CWA, the rule will assist States and tribes
authorized Section 402 and 404 CWA permitting programs, because it will reduce the need for
case-specific jurisdictional determinations.
Some commenters stated that the proposed rule was inconsistent with the Clean Water
Act because the agencies considered biological effects on downstream traditional navigable
waters, interstate waters, or the territorial seas. Again, the objective of the Act, and, therefore, the
scope of the significant nexus under the statute and Justice Kennedy's standard is "to restore and
maintain the chemical, physical, and biological integrity of the Nation's waters." Section
101(a)(emphasis added). Among the means to achieve the CWA's objective to restore and
maintain the chemical, physical, and biological integrity of the Nation's waters, Congress
established an interim national goal to achieve wherever possible "water quality which provides
for the protection and propagation of fish, shellfish, and wildlife and provides for recreation in
and on the water." Section 101(a)(2). Therefore, the agencies disagree that consideration of
biological effects on downstream waters is inconsistent with the CWA.
First, the agencies considered biological functions for purposes of the significant nexus
determinations in support of the rule only to the extent that the functions provided by tributaries
and adjacent water affected the biological integrity of the downstream traditional navigable
waters, interstate waters, or the territorial seas. For example, to protect Pacific and Atlantic
salmon in traditional navigable waters (and their associated commercial and recreational fishing
industries), headwater streams must be protected. Pacific and Atlantic salmon require both
freshwater and marine habitats over their life cycles and therefore migrate along river networks,
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providing one of the clearest illustrations of biological connectivity. Many Pacific salmon
species spawn in headwater streams, where their young grow for a year or more before migrating
downstream, living their adult life stages in the ocean, and then migrating back upstream to
spawn. These species thereby create a biological connection along the entire length of the river
network. Science Report at 2-40.
Second, as is clear from the CWA's objective of protecting the "biological integrity" of
the Nation's waters and the interim goal of achieving wherever possible water quality which
provides for the protection and propagation of fish, shellfish, and wildlife, the statute is clear that
protection of aquatic wildlife is an important aspect of protecting water quality and is addressed
by the CWA. Among the many other provisions in which the CWA addresses wildlife are
Section 102, comprehensive programs for water pollution control, "[i]n the development of such
comprehensive programs due regard shall be given to the improvements which are necessary to
conserve such waters for the protection and propagation of fish and aquatic life and wildlife;"
Section 104, the Administrator will conduct continuing "comprehensive studies of the effects of
pollution, including sedimentation, in the estuaries and estuarine zones of the United States on
fish and wildlife, on sport and commercial fishing, on recreation, on water supply and water
power, and on other beneficial purposes"; Section 301(h) provide that "[n]o permit issued under
this subsection shall authorize the discharge of any pollutant into saline estuarine waters which at
the time of application do not support a balanced indigenous population of shellfish, fish and
wildlife"; Section 302, requiring effluent limitations for, among other things, "protection and
propagation of a balanced population of shellfish, fish and wildlife"; Section 303(d) requiring
States to "identify those waters or parts thereof within its boundaries for which controls on
thermal discharges under section 301 are not stringent enough to assure protection and
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propagation of a balanced indigenous population of shellfish, fish, and wildlife"; Section 304,
requiring the Administrator to develop criteria for water quality accurately reflecting the latest
scientific knowledge: "(A) on the kind and extent of all identifiable effects on health and welfare
including, but not limited to, plankton, fish, shellfish, wildlife, plant life, shorelines, beaches,
esthetics, and recreation which may be expected from the presence of pollutants in any body of
water, including ground water; (B) on the concentration and dispersal of pollutants, or their
byproducts, through biological, physical, and chemical processes; and (C) on the effects of
pollutants on biological community diversity, productivity, and stability, including information
on the factors affecting rates of eutrophication and rates of organic and inorganic sedimentation
for varying types of receiving waters"; and, Section 404, authorizing the Administrator to
prohibit the specification of any defined area as a disposal site, if, among other considerations,
the discharge of dredged or fill material will have an unacceptable adverse effect on "shellfish
beds and fishery areas (including spawning and breeding areas), wildlife."
Some commenters stated that the exclusion of groundwater from the rule is inconsistent
with the CWA and that the rule should instead include groundwater in the definition of "waters
of the United States." EPA has never interpreted "waters of the United States" to include
groundwater. This interpretation is reflected in the existing regulation, and all previous
regulations, which does not define "waters of the United States" to include groundwater. The
courts which have considered the issue generally agree that "waters of the United States" do not
include groundwater. Idaho Rural Council v. Bosma, 143 F.Supp. 2d. 1169, 1179 (D.Id. 2001).
Those courts reach this conclusion based largely upon the legislative history of the CWA which
indicates that Congress specifically chose not to regulate groundwater, largely because "the
jurisdiction regarding groundwaters is so complex and varied from State to State." S. Rep. No.
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414, 92d Cong., 1st Sess. 73 (1971), U.S. Code Cong. & Admin. News 1972, pp. 3668, 3749,
reprinted in 2 Congressional Research Service of the Library of Congress, A Legislative History
of the Water Pollution Control Act Amendments of1972, 93d Cong., 1st Sess., at 1491 (Comm.
Print 1973). The majority of courts have also concluded that this interpretive history "does not
suggest that Congress intended to exclude from regulation discharges into hydrologically
connected groundwater which adversely affect surface water." Bosma at 1180. While EPA has
never interpreted the CWA to include groundwater as a "water of the United States," EPA's
longstanding interpretation is that point source discharges of pollutants to "waters of the United
States" via groundwater with a direct hydrologic connection to surface waters are discharges
subject to the CWA. See Concentrated Animal Feeding Operation Proposed Rule, 66 FR 2960,
3015 (Jan. 12, 2001). The exclusion for groundwater in the rule does not affect this longstanding
interpretation as the agency has never considered the groundwater itself to be a "water of the
United States."
Several commenters cited to Hawai 'i Wildlife Fund v. County of Maui to argue the
agencies should include groundwater as "waters of the United States." The court there held that
groundwater was a "conduit" through which pollutants were being discharged into the ocean,
requiring an NPDES permit. This finding is consistent with agency interpretation that discharges
of pollutants to "waters of the United States" via groundwater with a direct hydrologic
connection to surface waters to be subject to the CWA. While the court analyzed whether a
discharge of pollutant into groundwater itself would require a permit, the court acknowledged the
agencies' interpretation, including citing to the proposed rule. The court further acknowledged
that if the agencies promulgated a final rule that reflected their interpretation, it would be entitled
to Chevron deference.
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May 2015
B. Historic Scope of Regulatory Definition of "Waters of the United States"
i. Existing Regulation
The existing regulatory definition of "waters of the United States" is:1
The term waters of the United States means:
1. All waters which are currently used, or were used in the past, or may be susceptible to
use in interstate or foreign commerce, including all waters which are subject to the ebb
and flow of the tide;
2. All interstate waters including interstate wetlands;
3. All other waters such as intrastate lakes, rivers, streams (including intermittent streams),
mudflats, sandflats, wetlands, sloughs, prairie potholes, wet meadows, playa lakes, or
natural ponds, the use, degradation or destruction of which could affect interstate or
foreign commerce including any such waters:
a. Which are or could be used by interstate or foreign travelers for recreational or other
purposes; or
b. From which fish or shellfish are or could be taken and sold in interstate or foreign
commerce; or
c. Which are used or could be used for industrial purposes by industries in interstate
commerce;
4. All impoundments of waters otherwise defined as waters of the United States under this
definition;
5. Tributaries of waters identified in paragraphs (s)(l) through (4) of this section;
1 There are some minor differences between the regulations for the various CWA programs that utilize the term
"waters of the United States," but they are fundamentally consistent.
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6. The territorial sea;
7. Wetlands adjacent to waters (other than waters that are themselves wetlands) identified in
paragraphs (s)(l) through (6) of this section; waste treatment systems, including
treatment ponds or lagoons designed to meet the requirements of CWA (other than
cooling ponds as defined in 40 CFR 423.1 l(m) which also meet the criteria of this
definition) are not waters of the United States.
Waters of the United States do not include prior converted cropland. Notwithstanding the
determination of an area's status as prior converted cropland by any other federal agency, for the
purposes of the Clean Water Act, the final authority regarding Clean Water Act jurisdiction
remains with EPA.
Discharges of dredged or fill material into "waters of the United States" may be
authorized by a permit issued by the Corps pursuant to Section 404 of the CWA. Regulations
implementing the Corps' Section 404 permitting authority were first published in 1974. 39 Fed.
Reg. 12,115. Those regulations defined the term "navigable waters" to mean "those waters of the
United States which are subject to the ebb and flow of the tide, and/or are presently, or have been
in the past, or may be in the future susceptible for use for purposes of interstate or foreign
commerce." 33 C.F.R. 209.120(d)(1) (1974); see also 33 C.F.R. 209.260(e)(1) (1974)
(explaining that "[i]t is the water body's capability of use by the public for purposes of
transportation or commerce which is the determinative factor"). Discharges of all other
pollutants from a point source to a "water of the United States" may be authorized by, most
often, a Section 402 permit issued by EPA or an authorized state. While the Corps' initial
regulations implementing the CWA limited its jurisdiction under Section 404 to traditional
navigable waters, EPA's implementing regulations were clear that "waters of the United States"
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were distinct from and broader than traditional navigable waters. 38 Fed. Reg. 13528, 13528-29
(May 3, 1973).
The Corps' initial view of the scope of its Section 404 jurisdiction met with substantial
opposition. Several federal courts considering the coverage of wetlands adjacent to other waters
held that the Corps had given Section 404 an unduly restrictive reading. See, e.g., United States
v. Holland, 373 F. Supp. 665, 670-676 (M.D. Fla. 1974). EPA and the House Committee on
Government Operations expressed agreement with the decision in Holland.2 In Natural
Resources Defense Council, Inc. v. Callaway, 392 F. Supp. 685, 686 (D.D.C. 1975), the court
held that in the CWA Congress had "asserted federal jurisdiction over the nation's waters to the
maximum extent permissible under the Commerce Clause of the Constitution. Accordingly, as
used in the Water Act, the term ['navigable waters'] is not limited to the traditional tests of
navigability." The court ordered the Corps to publish new regulations "clearly recognizing the
full regulatory mandate of the Water Act." Id.
In response to the district court's order in Callaway, the Corps promulgated interim final
regulations providing for a phased-in expansion of its Section 404 jurisdiction. 40 Fed. Reg.
31,320 (1975); see 33 C.F.R. 209.120(d)(2) and (e)(2) (1976). The interim regulations revised
9
EPA expressed the view that "the Holland decision provides a necessary step for the preservation of our limited
wetland resources," and that "the [Holland] court properly interpreted the jurisdiction granted under the [CWA] and
Congressional power to make such a grant." See Section 404 of the Federal Water Pollution Control Act
Amendments of 1972: Hearings Before the Senate Comm. on Pub. Works, 94th Cong., 2d Sess. 349 (1976) (letter
dated June 19, 1974, from Russell E. Train, Administrator of EPA, to Lt. Gen. W.C. Gribble, Jr., Chief of Corps of
Engineers). EPA explained that it "firmly believe[d] that the Conference Committee deleted 'navigable' from the
[CWA] definition of 'navigable waters' in order to free pollution control from jurisdictional restrictions based on
'navigability.' " Id. at 350. Shortly thereafter, the House Committee on Government Operations discussed the
disagreement between the two agencies (as reflected in EPA's June 19 letter) and concluded that the Corps should
adopt the broader view of the term "waters of the United States" taken by EPA and by the court in Holland. See
H.R. Rep. No. 1396, 93d Cong., 2d Sess. 23-27 (1974). The Committee urged the Corps to adopt a new definition
that "complies with the congressional mandate that this term be given the broadest possible constitutional
interpretation." Id. at 27 (internal quotation marks omitted).
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the definition of "waters of the United States" to include, inter alia, waters (sometimes referred
to as "isolated waters") that are not connected by surface water or adjacent to traditional
navigable waters. 33 C.F.R. 209.120(d)(2)(i) (1976).3 On July 19, 1977, the Corps published its
final regulations, in which it revised the 1975 interim regulations to clarify many of the
definitional terms. 42 Fed. Reg. 37,122. The 1977 final regulations defined the term "waters of
the United States" to include, inter alia, "isolated wetlands and lakes, intermittent streams, prairie
potholes, and other waters that are not part of a tributary system to interstate waters or to
navigable waters of the United States, the degradation or destruction of which could affect
interstate commerce." 33 C.F.R. 323.2(a)(5) (1978).4 The Corps' current regulation contains
similar language, see 33 C.F.R. 328.3(a)(3),5 and EPA has promulgated regulations that include
a substantially identical definition of the term "waters of the United States." See 40 C.F.R.
230.3(s)(3); 40 C.F.R. 232.2; 40 C.F.R. 122.2.
In 1986, the Corps consolidated and recodified its regulatory provisions defining "waters
of the United States" for purposes of the Section 404 program. See 51 Fed. Reg. 41,216-41,217
(1986). The Corps explained that the new regulations neither reduced nor expanded its
jurisdiction. Id. at 41,217. Rather, their "purpose was to clarify the scope of the 404 program by
defining the terms in accordance with the way the program is presently being conducted." Id. In
3 Phase I, which was immediately effective, included coastal waters and traditional inland navigable waters and their
adjacent wetlands. 40 Fed. Reg. 31,321, 31,324, 31,326 (1975). Phase II, which took effect on July 1, 1976,
extended the Corps' jurisdiction to lakes and primary tributaries of Phase I waters, as well as wetlands adjacent to
the lakes and primary tributaries. Id. Phase III, which took effect on July 1, 1977, extended the Corps' jurisdiction to
all remaining areas encompassed by the regulations, including "intermittent rivers, streams, tributaries, and perched
wetlands that are not contiguous or adjacent to navigable waters." Id. at 31,325; see also 42 Fed. Reg. 37,124 (1977)
(describing the three phases).
4 An explanatory footnote published in the Code of Federal Regulations stated that "[paragraph (a)(5) incorporates
all other waters of the United States that could be regulated under the Federal government's Constitutional powers to
regulate and protect interstate commerce." 33 C.F.R. 323.2(a)(5), at 616 n.2 (1978).
5 The current regulation defines "waters of the United States" to include, inter alia, "[a]ll other waters such as
intrastate lakes, rivers, streams (including intermittent streams), mudflats, sandflats, wetlands, sloughs, prairie
potholes, wet meadows, playa lakes, or natural ponds, the use, degradation or destruction of which could affect
interstate or foreign commerce." 33 C.F.R. 328.3(a)(3).
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the preamble to the regulations, the Corps observed that EPA had "clarified that waters of the
United States" include waters "[wjhich are or would be used as habitat by birds protected by
Migratory Bird Treaties," as well as waters "[wjhich are or would be used as habitat by other
migratory birds which cross state lines." Id.
Note that as early as 1975 the Corps stated that "[wjetlands considered to perform
functions important to the public interest include * * * [wjetlands which serve important natural
biological functions, including food chain production, general habitat, and nesting, spawning,
rearing and resting sites for aquatic or land species." 40 Fed. Reg. 31,328 (1975).
ii. Caselaw
As discussed in Section I. A. above, with the enactment of the Clean Water Act, Congress
adopted a comprehensive approach to regulating pollution and improving the quality of the
nation's waters, expressly stating its goal "to restore and maintain the chemical, physical, and
biological integrity of the Nation's waters." Section 101(a).
The expression of statutory goals combined with the legislative history of the CWA
historically was interpreted as evincing an intent by Congress to extend application of the Clean
Water Act broadly to the fullest extent allowed by the Constitution. The earliest court decisions
established two principles that would become the bedrock for interpreting the extent of CWA
applicability. The first is that the CWA embodies Congress' understanding that water flows into
traditionally navigable waters from upstream sources; pollution added to non-navigable upstream
waters ultimately will cause harmful effects on downstream traditionally navigable waters; and
consequently, it would be futile to regulate direct discharges into traditionally navigable waters
without also regulating discharges to upstream waters. For example, in an early decision
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construing the applicability of the CWA, the U.S. Court of Appeals for the Sixth Circuit stated in
United States v. Ashland Oil and Transportation Co., 504 F.2d 1317, 1326 (6th Cir. 1974):
It would, of course, make a mockery ... if authority [under the Clean Water Act] to
control pollution was limited to the bed of the navigable stream itself. The tributaries
which join to form the river could then be used as open sewers as far as federal regulation
was concerned. The navigable part of the river could become a mere conduit for
upstream waste.
The Sixth Circuit went on to state: "Pollution control of navigable streams can only be
exercised by controlling pollution of their tributaries." Id. at 1327.
The second principle derived by early court decisions from the language and legislative
history of the 1972 Act is a distinction between traditional navigable waters and the broader term
"waters of the United States," which describes the waters subject to the CWA. This distinction
consistently has been acknowledged by nearly every court to consider the issue, including the
Supreme Court in Riverside Bayview Homes, Solid Waste Agency of Northern Cook County v.
U.S. Army Corps of Engineers, 531 U.S. 159 (2001) C'SWANCC"), and Rapanos v. United
States, 547 U.S. 715 (2006).
This distinction found early judicial expression in Natural Resources Defense Council v.
Callaway, 392 F. Supp. 685 (D.D.C. 1975). In striking Corps regulations limiting the Corps'
jurisdiction under Section 404 of the CWA to traditional navigable waters, that decision held that
Congress intended the CWA to extend beyond waters that are traditional navigable waters:
Congress by defining the term 'navigable waters' in Section 502(7) of the Federal Water
Pollution Control Act Amendments of 1972, 86 Stat. 816, 33 U.S.C. § 1251 et seq. (the
'Water Act') to mean 'the waters of the United States, including the territorial seas,'
asserted federal jurisdiction over the nation's waters to the maximum extent permissible
under the Commerce Clause of the Constitution. Accordingly, as used in the Water Act,
the term is not limited to the traditional tests of navigability.
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As discussed earlier, in response to the Callaway decision, the Corps in 1975 issued
interim regulations (to be phased in over three periods of time) that defined navigable waters for
purposes of the Clean Water Act to include non-navigable tributaries, freshwater wetlands
adjacent to primary navigable waters, and lakes and all other waters covered under the statute,
including "intermittent rivers, streams, tributaries, and perched wetlands that are not contiguous
or adjacent to navigable waters" whenever the Corps determines the regulation is necessary for
the protection of water quality. 40 Fed. Reg. 31320 (July 25, 1975). In 1977, the Corps issued a
final rule that included isolated wetlands and waters whose degradation or destruction could
affect interstate commerce. 42 Fed. Reg. 37,122 (July 19, 1977).
During the late 1970s and early 1980s, the courts that considered the issue gave broad
application to the CWA. For example, in QuiviraMining Co. v. EPA, 765 F.2d 126, 130 (10th
Cir. 1985), the U.S. Court of Appeals for the Tenth Circuit held that the CWA applied to creeks
and arroyos that were connected to streams during intense rainfall. During the late 1970s and
early 1980s, the courts that considered the issue gave broad application to the CWA. Similarly,
the court in United States v. Phelps Dodge Corp., 391 F. Supp. 1181, 1187 (D. Ariz. 1975)
stated: "Thus a legal definition of 'navigable waters' or 'waters of the United States' within the
scope of the Act includes any waterway within the United States also including normally dry
arroyos through which water may flow, where such water will ultimately end up in public waters
such as a river or stream, tributary to a river or stream, lake, reservoir, bay, gulf, sea or ocean
either within or adjacent to the United States."
The court in United States v. Byrd, 609 F.2d 1204, 1210-11 (7th Cir. 1979) (footnotes
omitted), held:
The recreational use of inland lakes has a significant impact on interstate commerce, as is
testified to by the number of out-of-state visitors to Lake Wawasee in particular. The
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value of these lakes depends, in part, on the purity of their water for swimming, or the
abundance of fish and other wildlife inhabiting them or the surrounding wetland and land
areas. The Corps, among other authorities, has come to recognize the importance of
wetlands adjacent to lakes in preserving the biological, chemical, and physical integrity
of the lakes they adjoin. Destruction of all or most of the wetlands around Lake
Wawasee, for example, could significantly impair the attraction the lake holds for
interstate travelers by degrading the water quality of the lake, thereby indirectly affecting
the flow of interstate commerce. We conclude that Congress constitutionally may extend
its regulatory control of navigable waters under the Commerce Clause to wetlands which
adjoin or are contiguous to intrastate lakes that are used by interstate travelers for water-
related recreational purposes as defined by 33 C.F.R. § 209.120(d)(2)(i) (G) and (H)
(1977). Furthermore, these regulatory definitions promulgated by the Corps are
reasonably related to Congress' purpose: "The objective of this chapter is to restore and
maintain the chemical, physical, and biological integrity of the Nation's waters". 33
U.S.C. § 125l(aY
Other courts also relied upon a connection with interstate commerce as a basis to apply
the CWA. In Utah v. Marsh, 740 F.2d 799, 803-804 (10th Cir. 1984), the Tenth Circuit held that
the CWA could apply to an intrastate lake:
Waters from the Lake are used to irrigate crops which are sold in interstate commerce,
and the lake supports the State's most valuable warm water fishery which markets most
of the catch out of state. The lake also provides recreationists with opportunities to fish,
hunt, boat, water ski, picnic, and camp, as well as the opportunity to observe, photograph,
and appreciate a variety of bird and animal life.... Finally, the lake is on the flyway of
several species of migratory waterfowl....
In United States v. Eidson, 108 F.3d 1336 (11th Cir. 1997), the United States Court of
Appeals for the Eleventh Circuit held that the CWA applies to a discharges to a sewer drain that
flows to a drainage ditch that flows to a drainage canal that empties into a tributary to Tampa
Bay. The Eleventh Circuit held: "There is no reason to suspect that Congress intended to regulate
only the natural tributaries of navigable waters. Pollutants are equally harmful to this country's
water quality whether they travel along man-made or natural routes. The fact that bodies of water
are 'man-made makes no difference.... That the defendants used them to convey the pollutants
without a permit is the matter of importance.' United States v. Holland, 373 F. Supp. 665, 673
(M.D.Fla. 1974); see also Leslie Salt Co. v. United States, 896 F.2d 354, 358 (9th Cir. 1990)
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(noting that protection of the CWA "does not depend on the how the property at issue became a
water of the United States"), cert, denied, 498 U.S. 1126, 111 S. Ct. 1089, 112 L. Ed. 2d 1194
(1991). Consequently, courts have acknowledged that ditches and canals, as well as streams and
creeks, can be "waters of the United States" under 1362(7). See, e.g., United States v. Velsicol
Chemical Corp., 438 F. Supp. 945, 947 (W.D.Tenn.1976) (sewers that lead to Mississippi
River); Holland, 373 F. Supp. at 673 (mosquito canals that empty into bayou arm of Tampa
Bay)." 108F.3dat 1342.
The United States Court of Appeals for the Second Circuit in United States v. TGR Corp.,
171 F.3d 762 (2d Cir. 1999), held that a drain to a storm water discharge system that flowed to a
tributary of a traditionally navigable water is within the scope of the CWA. See also United
States v. Banks, 115 F.3d 916, 920-21 (11th Cir. 1997) (affirming district court's conclusion that
wetlands located at least one-half mile away from any navigable channels were adjacent in light
of the district court's conclusion that water from the wetlands reached navigable channels
through both groundwater and surface water connections and because there was "ecological
adjacency"); United States v. Pozsgai, 999 F.2d 719, 727-32 (3d Cir. 1993) (wetlands adjacent to
a non-navigable in fact tributary that flows into traditionally navigable waters are within the
scope of the CWA); Conant v. United States, 786 F.2d 1008 (11th Cir. 1986) (per curiam)
(affirming a district court's finding that wetlands were adjacent even though they did not directly
abut a navigable river because the wetlands served as filters for the river and thus had a
hydrological connection).
At least one appellate court, however, clarified that jurisdiction under the CWA was not
unlimited. In United States v. Wilson, 133 F. 3d 251 (4th Cir. 1997), the U.S. Court of Appeals
for the Fourth Circuit reversed criminal convictions under the CWA for unauthorized discharges
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to wetlands because the Corps relied in part on 33 C.F.R. § 328.3(a)(3), the regulatory provision
covering isolated wetlands and waters whose degradation or destruction could affect interstate
commerce. The verdict did not identify the basis on which the jury had found CWA
applicability, and it was possible, therefore, that the jury had found CWA applicability based
solely upon Section 328.3(a)(3). The Fourth Circuit reasoned that the term "navigable" was a
limiting term, and therefore Section 328.3(a)(3) was invalid on its face because it purported to
extend applicability of the CWA to waters that had no connection or nexus with traditionally
navigable or interstate waters. The matter ultimately was remanded to the district court for
retrial to allow the United States to assert other bases for jurisdiction.
Even after the Supreme Court addressed the scope of the CWA in SWANCC, see
discussion in I.C. below, the majority of federal appellate and district courts, along with EPA and
the Corps, ultimately construed SWANCC narrowly and continued to view a broad interpretation
of the applicability of the CWA as necessary to and consistent with Congressional goals.6 The
majority of courts viewed most pre-SWANCC cases such as Eidson and Ashland Oil as good law
and unaffected by SWANCC.
Most courts that considered the issue held that the SWANCC decision was limited either
to the Migratory Bird Rule or to isolated waters where the only basis for an assertion of
jurisdiction was a connection to interstate commerce pursuant to 33 U.S.C. § 328.3(a)(3). These
courts held that SWANCC did not affect the ability of the Corps or EPA to assert jurisdiction
under the CWA pursuant to any other subsection of the regulations. See, e.g., United States v.
Krilich, 393F.3d 784 (7th Cir. 2002) (rejecting motion to vacate consent decree, finding that
6 A minority of court decisions, primarily in the U.S. Court of Appeals for the Fifth Circuit, construed the reasoning
of SWANCC broadly as a basis for interpreting the scope of applicability of the CWA narrowly See In re Needham,
354 F.3d 340 (5th Cir. 2003); Rice v. Harken Exploration Co., 250 F.3d 264 (5th Cir. 2001); FD&P Enterprises, Inc.
v. U.S. Army Corps ofEng'rs, 239 F. Supp. 2d 509 (D.N.J. 2003).
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SWANCC did not alter regulations interpreting "waters of the U.S." other than 33 C.F.R. §
328.3(a)(3)) and the cases cited infra. See also Robert E. Fabricant, General Counsel, U.S.
Environmental Protection Agency & Stephen J. Morello, General Counsel, U.S. Department of
the Army, Joint Memorandum, 68 Fed. Reg. 1995-1998 (Jan. 15, 2003).
The majority of federal appellate and district court decisions following SWANCC
coalesced around the view that CWA jurisdiction extends to all waters that have a hydrologic
connection to and form part of the tributary system of a traditionally navigable water, including
streams that flow intermittently or ephemerally, and roadside ditches. "In sum, the Corps'
unremarkable interpretation of the term 'waters of the United States' as including wetlands
adjacent to tributaries of navigable waters is permissible under the CWA because pollutants
added to any of these tributaries will inevitably find their way to the very waters that Congress
has sought to protect." Treacy v. Newdunn Assoc., LLP, 344 F. 3d 407, 416-17 (4th Cir. 2003),
cert, denied sub nom, Newdunn Assoc., LLP v. U.S. Army Corps o/Eng'rs, 541 U.S. 972 (2004)
(upholding Corps' assertion of jurisdiction over wetlands connected to a traditionally navigable
water through approximately 2.4 miles of ditches and streams). See, e.g., United States v.
Interstate General Co., No. 01-4513, slip op. at 7 (2002 WL 1421411 (4th Cir. July 2, 2002)
(refusing to grant a writ of coram nobis, rejecting an argument that SWANCC eliminated
jurisdiction over wetlands adjacent to non-navigable tributaries); Headwaters v. Talent Irrigation
Dist., 243 F.3d 526, 534 (9th Cir. 2001) ("Even tributaries that flow intermittently are 'waters of
the United States'"); Idaho Rural Council v. Bosma, 143 F. Supp. 2d 1169, 1178 (D. Idaho 2001)
("waters of the United States include waters that are tributary to navigable waters"); Aiello v.
Town of Brookhaven, 136 F. Supp. 2d 81, 118 (E.D. N.Y. 2001) (non-navigable pond and creek
determined to be tributaries of navigable waters, and therefore "waters of the United States under
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the CWA"); United States v. RuethDev. Co., No. 2:96CV540, 2001 WL 17580078 (N.D. Ind.
Sept. 26, 2001) (refusing to reopen a consent decree in a CWA case and determining that
jurisdiction remained over wetlands adjacent to a non-navigable (manmade) waterway that flows
into a navigable water).
The lower courts generally held that CWA jurisdiction was present even when the
tributaries in question flowed for a significant distance before reaching a navigable water or were
several times removed from the navigable waters (i.e., "tributaries of tributaries"). See, e.g.,
United States v. Deaton, 332 F.3d 698 (4th Cir. 2003), cert, denied, 541 U.S. 972 (2004) (Corps
had authority to regulate wetlands bordering a "roadside ditch" that took a "winding, thirty-two
mile path to the Chesapeake Bay," including flow through roadside ditches, culverts, Beaverdam
Creek and the Wicomico River, a traditionally navigable water); Community Ass 'n for
Restoration of the Env't v. Henry Bosma Dairy, 305 F. 3d 953 (9th Cir. 2002) (drain that flowed
into a canal that flows into a river is jurisdictional); United States v. Hummel, 2003 WL
1845365 (N.D. 111. Apr. 8, 2003) (wetlands adjacent to a tributary to a traditionally navigable
water are jurisdictional: "Although the [wetlands are] two steps removed from an actually
navigable water, the Court finds a significant nexus to exist to establish jurisdiction"); North
Carolina Shellfish Growers Ass 'n v. Holly Ridge Associates, LLC, 278 F. Supp. 2d 654
(E.D.N.C. 2003) (intermittent streams and tributaries are capable of carrying pollutants
downstream during rain events and therefore fall within the jurisdiction of the CWA); California
Sportfishing Protection Alliance v. Diablo Grande, Inc., 209 F. Supp. 2d 1059 (E.D. Cal. 2002)
(CWA jurisdiction extends to a tributary that flows through an underground pipeline prior to
reaching a traditionally navigable water); United States v. Lamplight Equestrian Ctr., No. 00 C
6486, 2002 WL 360652, at *8 (ND. 111. Mar. 8, 2002) ("Even where the distance from the
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tributary to the navigable water is significant, the quality of the tributary is still vital to the
quality of navigable waters"); United States v. Buday, 138 F. Supp. 2d 1282, 1291-92 (D.Mont.
2001) ("water quality of tributaries . . . distant though the tributaries may be from navigable
streams, is vital to the quality of navigable waters").
iii. The Rule is Narrower in Scope than Existing Regulation
In light of the broad provisions of the existing regulatory definition and the expansive
historic interpretation of the existing regulation, and as a result of the Supreme Court decisions in
SWANCC and Rapanos, the scope of "waters of the United States" in this rule is narrower than
that under the existing regulations. The most substantial change is the deletion of the existing
regulatory provision that defines "waters of the United States" as all other waters such as
intrastate lakes, rivers, streams (including intermittent streams), mudflats, sandflats, wetlands,
sloughs, prairie potholes, wet meadows, playa lakes, or natural ponds, the use, degradation or
destruction of which could affect interstate or foreign commerce including any such waters:
which are or could be used by interstate or foreign travelers for recreational or other purposes;
from which fish or shellfish are or could be taken and sold in interstate or foreign commerce; or
which are used or could be used for industrial purposes by industries in interstate commerce. 33
CFR § 328.3(a)(3); 40 CFR § 122.2. Under the final rule, an interstate commerce connection is
not sufficient to meet the definition of "waters of the United States." Further, waters in a
watershed in which there is no connection to a traditional navigable water, interstate water or the
territorial seas would not be "waters of the United States." In addition, the rule would, for the
first time, explicitly exclude some features and waters over which the agencies have not
generally asserted jurisdiction and in so doing eliminates the authority of the agencies to
determine in case-specific circumstances that some such waters are jurisdictional "waters of the
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United States." The rule also provides new limitations on the scope of tributaries by establishing
a definition of "tributary" for the first time. Together all of these changes serve to narrow the
scope of the rule in comparison to the existing regulation.
Some commenters argued that the proposed rule provides for even broader jurisdiction
than the existing rule, including jurisdiction over non-navigable features such as isolated
wetlands, ephemeral drainages, and isolated ponds, that lack any meaningful connection to
navigable waters and that have previously been non-jurisdictional. Those commenters argued
that the proposed rule allowed for sweeping jurisdiction based on connections as tenuous as the
Migratory Bird Rule that was rejected in SWANCC, and essentially amounts to the "any
connection" theory that was rejected in Rapanos. The agencies disagree. The rule does not
establish jurisdiction based on the Migratory Bird Rule. In fact, the agencies have explicitly
deleted the (a)(3) provision from the existing regulation that was interpreted by the Migratory
Bird Rule. In addition, the agencies' conclusions that certain categories of waters are
jurisdictional are not based on an "any connection" theory; instead they are based on careful
examinations of the science and the law to conclude that particular categories of waters
significantly affect the chemical, physical, and biological integrity of a traditional navigable
water, interstate water, or the territorial seas. Further, for those limited waters for which the
agencies will perform a case-specific significant nexus analysis, there is no authorization for
considering migratory birds in the rule and the preamble is explicit that non-aquatic species or
species such as non-resident migratory birds do not demonstrate a life cycle dependency on the
identified aquatic resources and are not evidence of biological connectivity for purposes of the
rule. Finally, while commenters argued that under the proposed rule the agencies' authority to
assert jurisdiction is limitless, the final rule provides explicit limitations on the agencies' authority
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to make case-specific determinations. Case-specific determinations of jurisdiction are only
authorized for five specific types of waters under (a)(7), and for waters located within the 100-
year floodplain of a traditional navigable water, interstate water, or the territorial seas and waters
located within 4,000 feet of the ordinary high water mark or high tide line of an (a)(1) through
(a)(5) water under (a)(8).
Based on the history of the existing regulations and the caselaw discussed above, the
agencies disagree that all such waters were previously non-jurisdictional. The agencies further
disagree that the final rule provides for jurisdiction over waters "that lack any meaningful
connection." To the contrary, the rule and its supporting documentation demonstrate that
agencies are asserting jurisdiction over traditional navigable waters, interstate waters, the
territorial seas, and those waters that have a significant nexus to them. Consistent with SWANCC
and Rapanos, the agencies have narrowed the definition of "waters of the United States"
compared to the longstanding, existing definition.
Some commenters stated that the proposed rule is an expansion of jurisdiction because it
would change the provision for "adjacent wetlands" to "adjacent waters." The agencies
acknowledge that under the existing rule, the adjacency provision applied only to wetlands
adjacent to "waters of the United States." As noted in San Francisco Baykeeper v. Cargill Salt,
481 F.3d 700 (9th Cir. 2007), this provision of the agencies' regulations only defines adjacent
wetlands, not adjacent ponds, as "waters of the United States." However, under the existing
regulations, "other waters" (such as intrastate rivers, lakes and wetlands that are not otherwise
jurisdictional under other sections of the rule) could be determined to be jurisdictional if the use,
degradation or destruction of the water could affect interstate or foreign commerce. This
provision reflected the agencies' interpretation at the time of the jurisdiction of the CWA to
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extend to the maximum extent permissible under the Commerce Clause of the Constitution.
Therefore, while the language of the specific adjacency provision may have expanded from
wetlands to waters, that does not represent an expansion of jurisdiction as a whole, since adjacent
non-wetland waters would have been subject to jurisdiction under the "other waters" provision.
Moreover, as a matter of practice in the past, the agencies generally relied on the presence of
migratory birds to indicate an effect on interstate commerce and conclude that waters, such as
adjacent ponds, were jurisdictional. In 2001, the Supreme Court in SWANCC rejected the use of
migratory birds as a sole basis to establish jurisdiction over such "isolated" intrastate
nonnavigable waters. The rule does not protect all waters that were protected under the "other
waters" provision of the existing rule, and therefore the inclusion of adjacent ponds, for example,
in the adjacent waters provision of the rule does not reflect an overall expansion of jurisdiction
when compared to the existing rule.
Some commenters also express confusion that the agencies conclude that the scope of
jurisdiction of the CWA in this rule is narrower than that under the existing regulations while at
the same time concluding in an economic analysis that a percentage of negative jurisdictional
determinations would change to positive jurisdictional determinations under the new rule. This
apparent inconsistency is simply the result of comparing the scope of the rule to different
baselines - compared to the historic scope of the existing rule, the final rule is narrower;
compared to agency practice in light of guidance issued after SWANCC and Rapanos, the final
rule is generally broader, but not broader than the existing rule. The scope of waters covered by
the CWA today is considerably smaller than the scope of waters historically covered prior to the
2001 and 2006 Supreme Court decisions. Based on the reduction in the scope of CWA
jurisdiction, the agencies conclude that the new rule would impose no additional costs when
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compared to historic application of the regulation it replaces. For purposes of the economic
analysis, however, the agencies evaluated costs and benefits associated with the difference in
assertions of jurisdiction in jurisdictional determinations between the new rule and current field
practice, which is based on the 2008 EPA and Corps jurisdiction guidance. Compared to this
baseline, the agencies anticipate the new rule will result in an increase in the number of positive
jurisdictional determinations and an associated increase in both costs and benefits that derive
from the implementation of CWA programs.
C. Supreme Court Decisions Concerning "Waters of the United States"
i. Supreme Court Decisions
The U.S. Supreme Court first addressed the scope of "waters of the United States"
protected by the CWA in United States v. Riverside Bayview Homes, 474 U.S. 121 (1985), which
involved wetlands adjacent to a traditional navigable water in Michigan. In a unanimous
opinion, the Court deferred to the Corps' ecological judgment that adjacent wetlands are
"inseparably bound up" with the waters to which they are adjacent, and upheld the inclusion of
adjacent wetlands in the regulatory definition of "waters of the United States." Id. at 134. The
Court observed that the broad objective of the CWA to restore and maintain the integrity of the
Nation's waters "incorporated a broad, systemic view of the goal of maintaining and improving
water quality .... Protection of aquatic ecosystems, Congress recognized, demanded broad
federal authority to control pollution, for '[wjater moves in hydrologic cycles and it is essential
that discharge of pollutants be controlled at the source.' In keeping with these views, Congress
chose to define the waters covered by the Act broadly." Id. at 132-33 (citing Senate Report 92-
414).
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The Court also recognized that "[i]n determining the limits of its power to regulate
discharges under the Act, the Corps must necessarily choose some point at which water ends and
land begins. Our common experience tells us that this is often no easy task: the transition from
water to solid ground is not necessarily or even typically an abrupt one. Rather, between open
waters and dry land may lie shallows, marshes, mudflats, swamps, bogs — in short, a huge array
of areas that are not wholly aquatic but nevertheless fall far short of being dry land. Where on
this continuum to find the limit of 'waters' is far from obvious." Id. The Court then deferred to
the agencies' interpretation: "In view of the breadth of federal regulatory authority contemplated
by the Act itself and the inherent difficulties of defining precise bounds to regulable waters, the
Corps' ecological judgment about the relationship between waters and their adjacent wetlands
provides an adequate basis for a legal judgment that adjacent wetlands may be defined as waters
under the Act." Id. at 134.
In a footnote, the Court stated that to achieve the goal of preserving and improving
adjacent wetlands that have significant ecological and hydrological impacts on navigable waters,
it was appropriate for the Corps to regulate all adjacent wetlands, even though some might not
have any impacts on navigable waters. Id. at 135 n.9. The Court acknowledged that some
adjacent wetlands might not have significant hydrological and biological connections with
navigable waters, but concluded that the Corps' regulation was valid in part because such
connections exist in the majority of cases. Id.
Notably, while integral to its holding, the Court did not precisely define the meaning of
"adjacent" in terms of distance from or impact on navigable waters. The Court left in place the
Corps' 1985 definition of "adjacent": "The term adjacent means bordering, contiguous, or
neighboring. Wetlands separated from other waters of the United States by man-made dikes or
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barriers, natural river berms, beach dunes and the like are 'adjacent wetlands.'" The Court
expressly reserved the question of whether the Act applies to "wetlands that are not adjacent to
open waters." Id. at 131 n.8.
The issue of CW A jurisdiction over "waters of the United States" was addressed again by
the Supreme Court in Solid Waste Agency of Northern Cook County v. U.S. Army Corps of
Engineers, 531 U.S. 159 (2001) (SWANCC). In SWANCC, the Court (in a 5-4 opinion) held that
the use of "isolated" nonnavigable intrastate ponds by migratory birds was not by itself a
sufficient basis for the exercise of federal regulatory authority under the CWA. The SWANCC
Court noted that in Riverside it had "found that Congress' concern for the protection of water
quality and aquatic ecosystems indicated its intent to regulate wetlands 'inseparably bound up'
with the 'waters of the United States'" and that "it was the significant nexus between the
wetlands and 'navigable waters' that informed our reading of the CWA" in that case. Id. at 167.
While recognizing that in Riverside Bayview Homes, it had found the term "navigable" to be of
limited import, the Court in SWANCC noted that the term "navigable" could not be read entirely
out of the Act. Id. at 172. The Court stated: "We said in Riverside Bayview Homes that the word
'navigable' in the statute was of 'limited effect' and went on to hold that § 404(a) extended to
nonnavigable wetlands adjacent to open waters. But it is one thing to give a word limited effect
and quite another to give it no effect whatever. The term 'navigable' has at least the import of
showing us what Congress had in mind as its authority for enacting the CWA: its traditional
jurisdiction over waters that were or had been navigable in fact or which could reasonably be so
made. See, e.g., United States v. Appalachian Elec. Power Co., 311 U.S. 377, 407-408, 85 L. Ed.
243, 61 S. Ct. 291 (1940)." SWANCC did not invalidate (a)(3) or other parts of the regulatory
definition of "waters of the United States."
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Five years after SWANCC, the Court again addressed the CWA term "waters of the
United States" in Rapanosv. United States, 547 U.S. 715 (2006). Rapanos involved two
consolidated cases in which the CWA had been applied to wetlands adjacent to nonnavigable
tributaries of traditional navigable waters. All Members of the Court agreed that the term
"waters of the United States" encompasses some waters that are not navigable in the traditional
sense. A four-Justice plurality in Rapanos interpreted the term "waters of the United States" as
covering "relatively permanent, standing or continuously flowing bodies of water . . id. at
739, that are connected to traditional navigable waters, id. at 742, as well as wetlands with a
"continuous surface connection . . " to such water bodies, id. (Scalia, J., plurality opinion). The
Rapanos plurality noted that its reference to "relatively permanent" waters did "not necessarily
exclude streams, rivers, or lakes that might dry up in extraordinary circumstances, such as
drought," or "seasonal rivers, which contain continuous flow during some months of the year but
no flow during dry months ..." Id. at 732 n.5 (emphasis in original).
Justice Kennedy's concurring opinion took a different approach. Justice Kennedy
concluded that "to constitute 'navigable waters' under the Act, a water or wetland must possess a
'significant nexus' to waters that are or were navigable in fact or that could reasonably be so
made." Id. at 759 (citing SWANCC, 531 U.S. at 167, 172). He concluded that wetlands possess
the requisite significant nexus if the wetlands "either alone or in combination with similarly
situated [wet]lands in the region, significantly affect the chemical, physical, and biological
integrity of other covered waters more readily understood as 'navigable.'" 547 U.S. at 780.
Justice Kennedy's opinion notes that such a relationship with navigable waters must be more
than "speculative or insubstantial." Id. at 780. For additional discussion of Justice Kennedy's
standard see sections II, VII, and VIII below.
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In Rapanos, the four dissenting Justices in Rapanos, who would have affirmed the court
of appeals' application of the agencies' regulation, also concluded that the term "waters of the
United States" encompasses, inter alia, all tributaries and wetlands that satisfy "either the
plurality's [standard] or Justice Kennedy's." Id. at 810 & n.14 (Stevens, J., dissenting). The four
dissenting Justices stated: "the proper analysis is straightforward. The Army Corps has
determined that wetlands adjacent to tributaries of traditionally navigable waters preserve the
quality of our Nation's waters by, among other things, providing habitat for aquatic animals,
keeping excessive sediment and toxic pollutants out of adjacent waters, and reducing
downstream flooding by absorbing water at times of high flow. The Corps' resulting decision to
treat these wetlands as encompassed within the term "waters of the United States" is a
quintessential example of the Executive's reasonable interpretation of a statutory provision. See
Chevron U.S.A., Inc. v. NRDC, 467 U.S. 837, 842-845, 104 S. Ct. 2778, 81 L. Ed. 2d 694 (1984).
Our unanimous decision in United States v. Riverside Bayview Homes, Inc., 474 U.S. 121, 106 S.
Ct. 455, 88 L. Ed. 2d 419 (1985), was faithful to our duty to respect the work product of the
Legislative and Executive Branches of our Government." Id at 788.
Further, the four dissenting Justices stated: "As we recognized in Riverside Bayview, the
Corps has concluded that such wetlands play important roles in maintaining the quality of their
adjacent waters, see id, at 134-135, 106 S. Ct. 455, 88 L. Ed. 2d 419, and consequently in the
waters downstream. Among other things, wetlands can offer 'nesting, spawning, rearing and
resting sites for aquatic or land species'; 'serve as valuable storage areas for storm and flood
waters'; and provide 'significant water purification functions.' 33 CFR § 320.4(b)(2) (2005); 474
U.S., at 134-135, 106 S. Ct. 455, 88 L. Ed. 2d 419. These values are hardly 'independent
ecological considerations as the plurality would have it, ante, at 741, 165 L. Ed. 2d, at 179-
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instead, they are integral to the 'chemical, physical, and biological integrity of the Nation's
waters,' 33 U.S.C. § 1251(a). Given that wetlands serve these important water quality roles and
given the ambiguity inherent in the phrase 'waters of the United States,' the Corps has
reasonably interpreted its jurisdiction to cover nonisolated wetlands. See 474 U.S., at 131-135,
106 S. Ct. 455, 88 L. Ed. 2d 419." Id. at 796.
The four dissenting Justices went on to state: "The Corps' exercise of jurisdiction is
reasonable even though not every wetland adjacent to a traditionally navigable water or its
tributary will perform all (or perhaps any) of the water quality functions generally associated
with wetlands. Riverside Bayview made clear that jurisdiction does not depend on a wetland-by-
wetland inquiry. 474 U.S., at 135, n. 9, 106 S. Ct. 455, 88 L. Ed. 2d 419. Instead, it is enough
that wetlands adjacent to tributaries generally have a significant nexus to the watershed's water
quality. If a particular wetland is 'not significantly intertwined with the ecosystem of adjacent
waterways,' then the Corps may allow its development 'simply by issuing a permit.' Ibid." Id. at
797.
The dissent was clear that it found the existing regulations reasonable and worthy of
deference: "The Corps defines 'adjacent' as 'bordering, contiguous, or neighboring,' and
specifies that '[wjetlands separated from other waters of the United States by man-made dikes or
barriers, natural river berms, beach dunes and the like are 'adjacent wetlands.'" 33 CFR §
328.3(c) (2005). This definition is plainly reasonable, both on its face and in terms of the
purposes of the Act. While wetlands that are physically separated from other waters may perform
less valuable functions, this is a matter for the Corps to evaluate in its permitting decisions. We
made this clear in Riverside Bayview, 474 U.S., at 135, n. 9, 106 S. Ct. 455, 88 L. Ed. 2d 419."
Id. at 805-6.
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Finally, the dissent opined on significant nexus, stating: "I think it clear that wetlands
adjacent to tributaries of navigable waters generally have a 'significant nexus' with the
traditionally navigable waters downstream. Unlike the 'nonnavigable, isolated, intrastate waters'
in SWANCC, 531 U.S., at 171, 121 S. Ct. 675, 148 L. Ed. 2d 576, these wetlands can obviously
have a cumulative effect on downstream water flow by releasing waters at times of low flow or
by keeping waters back at times of high flow. This logical connection alone gives the wetlands
the 'limited' connection to traditionally navigable waters that is all the statute requires, see id, at
172, 121 S. Ct. 675, 148 L. Ed. 2d 576; 474 U.S., at 133, 106 S. Ct. 455, 88 L. Ed. 2d 419 --and
disproves Justice Kennedy's claim that my approach gives no meaning to the word "'navigable,'"
ante, at 779, 165 L. Ed. 2d, at 202 (opinion concurring in judgment). Similarly, these wetlands
can preserve downstream water quality by trapping sediment, filtering toxic pollutants,
protecting fish-spawning grounds, and so forth." Id. at 808.
Neither the plurality nor the Kennedy opinions invalidated any of the regulatory
provisions defining "waters of the United States."
ii. Yost-Rapanos Appellate Court Decisions
The earliest post-Rapcmos decisions by the United States Courts of Appeals
focused on which standard to apply, fulfilling Chief Justice Roberts' observation in his
concurring opinion:
It is unfortunate that no opinion commands a majority of the Court on precisely how to
read Congress' limits on the reach of the Clean Water Act. Lower courts and regulated
entities will now have to feel their way on a case-by-case basis.
547 U.S. at 758 (Roberts, Chief J., concurring).
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Chief Justice Roberts went on to cite as applicable precedent Marks v. United States, 430
U.S. 188 (1977) ("When a fragmented Court decides a case and no single rationale explaining
the result enjoys the assent of five Justices, the holding of the Court may be viewed as the
position taken by those Members who concurred in the judgments on the narrowest grounds").
The dissenting Justices in Rapanos also spoke to future application of the divided decision.
While Justice Stevens stated that he assumed Justice Kennedy's significant nexus standard would
apply in most instances, the dissenting Justices noted that they would find the CWA extended to
waters meeting either the standard articulated by Justice Scalia or the "significant nexus"
standard described by Justice Kennedy. 547 U.S. at 810 & n. 14 (Stevens, J., dissenting).
That the standards articulated by the plurality and Justice Kennedy are premised on
entirely different analyses with little analytical overlap has presented a challenge for the lower
courts in identifying which standard should apply and more particularly, which represents "the
narrowest grounds" under Marks. All nine of the United States Courts of Appeals to have
considered the issue have stated that Justice Kennedy's significant nexus standard may be used
to establish applicability of the CWA. Precon Dev. Corp. v. U.S. Army Corps ofEng'rs, 633
F.3d 278 (4th Cir. 2011); United States v. Donovan, 661 F.3d 174 (3d Cir. 2011), cert, denied,
132 S. Ct. 2409 (2012); United States v. Bailey, 571 F.3d 791 (8th Cir. 2009); United States v.
Cundiff, 555 F.3d 200 (6th Cir.), cert, denied, 130 S. Ct. 74 (2009); United States v. Lucas, 516
F.3d 316 (5th Cir.), cert, denied, 555 U.S. 822 (2008); United States v. Robison, 505 F.3d 1208
(11th Cir. 2007), cert, denied sub nom McWane v. United States, 555 U.S. 1045 (2008); Northern
California River Watch v. City of Healdsburg,496 F.3d 993 (9th Cir. 2007) (superseding the
original opinion published at 457 F.3d 1023 (9th Cir. 2006)), cert, denied, 552 U.S. 1180 (2008);
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United States v. Johnson, 467 F.3d 56 (1st Cir. 2006), cert, denied, 552 U.S. 948 (2007); United
States v. Gerke Excavating, Inc., 464 F.3d 723 (7th Cir. 2006), cert, denied, 552 U.S. 810 (2007).
Of these, only the Eleventh Circuit in Robison has held that only Justice Kennedy's
standard applies. The First, Third and Eighth Circuits, consistent with the Rapanos dissent's
reasoning, have held that the CWA applies where a water meets either the plurality's standard or
Justice Kennedy's standard. Bailey, 571 F.3d at 799; Donovan, 661 F.3d at 182; Johnson, 467
F.3d at 62-64. The Fifth and Sixth Circuits did not reach the question of which standard would
be controlling because, in the cases before them, the waters satisfied both standards. Cundiff,
555 F.3d at 210; Lucas, 516 F.3d at 327. The Seventh and Ninth Circuits applied Justice
Kennedy's standard to the facts before them, but left open whether the plurality's standard could
be applicable in appropriate circumstances. Northern California River Watch, 496 F.3d at 999-
1000; Gerke Excavating, 464 F.3d at 725; see also Northern California River Watch v. Wilcox,
633 F.3d 766 (9th Cir. Aug. 25, 2010, amended Jan. 26, 2011). In United States v. Vierstra, 2012
U.S. App. LEXIS 16876 (9th Cir. Aug. 13, 2012) (unpublished opinion), the Ninth Circuit upheld
a district court opinion (803 F. Supp. 2d 1166 (D. Idaho 2011)) that applied both standards. The
Fourth Circuit in Precon did not determine the applicability of the plurality standard because the
parties in that case had agreed that Justice Kennedy's standard applied. Precon, 633 F.3d at 278.
The Fourth Circuit later upheld a district court's application of both standards. Deerfield
Plantation Phase II-B Property Owners Ass'n, Inc. v. U.S. Army Corps of Engineers, 2012 U.S.
App. LEXIS 26402 (4th Cir. Dec. 26, 2012) (unpublished decision).
Those appellate courts that have applied the standard articulated by the plurality have
found a variety of waters to be "relatively permanent" waters meeting that standard. In
Deerfield, the Fourth Circuit upheld the Corps finding that two non-navigable tributaries were
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"relatively permanent waters" because they "'typically flow year-round or have continuous flow
at least seasonally (e.g., typically 3 months).... [E]ach had a firm sandy bottom with a clearly-
defined channel that was free of vegetation, which 'demonstrates continuous flow more than
seasonally, because vegetation will not have a chance to establish itself due to the water's
flow'... evidence of a clearly-defined ordinary high water mark, groundwater influx, and the
degree of curvature (or 'sinuousity') of the tributaries." Deerfield Plantation Phase II-B
Property Owners Ass'n, 2012 U.S. App. LEXIS 26402 *6 (citations omitted).
In Cundiff, the Sixth Circuit held that wetlands with surface connections to relatively
permanent waters flowing ultimately to a traditionally navigable water satisfied the plurality
standard. 555 F.3d at 211-13. Among other things, the Sixth Circuit rejected an argument that
wetlands at a different elevation than the receiving creeks lacked a continuous surface
connection. The court interpreted the plurality standard's concept of "continuous surface
connection" as requiring a surface hydrologic connection, but not limited to perpetually flowing
creeks. "In other words, the [plurality's standard] requires a topical flow of water between a
navigable-in-fact waterway or its tributary with a wetland and that connection requires some
kind of dampness such that polluting a wetland would have a proportionate effect on the
traditional waterway." Id. at 212. In addition, the Sixth Circuit found the existence of
"additional (and substantial) surface connections between the wetlands and permanent water
bodies 'during storm events, bank full periods, and/or ordinary high flows' provides additional
evidence of a continuous surface connection." Id. The court also found whether or not the
channel forming the hydrologic connection was man-made to be of no import. Id. at 213.
In Donovan, the Third Circuit found that wetlands with continuous surface connection to
two perennial streams flowing to traditionally navigable waters satisfied the plurality standard.
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661 F.3d at 185-86. In United States v. Vierstra, 2012 U.S. LEXIS 16876 (9th Cir. Aug. 13,
2012) (unpublished decision), the Ninth Circuit upheld a district court decision (803 F. Supp. 2d
1166 (D. Idaho 2011)) holding that a man-made canal that flowed six to eight months per year
was a relatively permanent water that satisfied the plurality standard. The Fifth Circuit in Lucas
held that a site that drained in three directions through various tributaries to traditionally
navigable waters satisfied the plurality standard based on qualitative evidence including
government testimony, photographs, maps and aerial photographs. 516 F.3d at 326-27.
The lower courts also have applied Justice Kennedy's significant nexus standard with
some consistency. The Eighth Circuit emphasized there is no need to perform a case-specific
determination of significant nexus where the waters at issue are adjacent to a traditionally
navigable water because significant nexus can be presumed as a matter of law in that
circumstance. Bailey, 571 F.3d at 799 ("Justice Kennedy's opinion holds that when a wetland is
adjacent to the navigable-in-fact waters, then a significant nexus exists as a matter of law"). All
of the courts of appeals that have addressed the issue have agreed that a nexus is formed between
a non-navigable water and a traditionally navigable water when the non-navigable water, alone
or in combination with other similarly situated waters in the region, performs a function or
otherwise has an effect on a downstream traditionally navigable water that is neither speculative
nor insubstantial. The types of functions found to form a significant nexus with a downstream
traditionally navigable water have included contribution of flow (Donovan, 661 F.3d at 186),
runoff or floodwater storage (Precon Dev. Corp., Inc. v. U.S. Army Corps o/Eng'rs, 2015 U.S.
App. LEXIS 3704 (4th Cir. March 10, 2015) (unpublished decision); Cundiff, 555 F.3d at 210-11;
Lucas, 516 F.3d at 327), nutrient recycling {Precon Dev. Corp., Inc. v. U.S. Army Corps of
Eng'rs, 2015 U.S. App. LEXIS 3704 (4th Cir. March 10, 2015) (unpublished decision); Donovan,
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661 F.3d at 186), pollutant trapping or filtering {Donovan, 661 F.3d at 186; Cundiff, 555 F.3d at
211; Lucas, 516 F.3d at 327), export of organic matter and/or food resources as part of the
aquatic food web {Donovan, 661 F.3d at 186), pollutant transport {Northern California
Riverwatch, 496 F.3d at 1001) and fish and wildlife habitat {Donovan, 661 F.3d at 186; Cundiff,
555 F.3d at 211; Northern California Riverwatch, 496 F.3d at 1000-1001)).
The Fourth Circuit has considered application of Justice Kennedy's statement that the
significant nexus inquiry should focus on whether "wetlands, either alone or in combination with
similarly situated lands in the region, significantly affect the chemical, physical, and biological
integrity of other covered waters more readily understood as 'navigable.'" Rapanos, 547 U.S. at
780 (Kennedy, J., concurring in the judgment) (emphasis added)." Precon, 633 F.3d at 290. In
Precon, the Corps had analyzed as "similarly situated" wetlands that either directly abutted two
tributary ditches or were adjacent to those tributaries and separated from them by a berm. Id. at
291. Noting that "Justice Kennedy's instruction that 'similarly situated lands in the region' can
be evaluated together is a broad one," id. at 292, the Fourth Circuit rejected Precon's argument
that it was inappropriate to treat abutting and adjacent wetlands as similarly situated: "[W]e find
no evidence that Justice Kennedy ... intended to differentiate between abutting and other
adjacent wetlands. To the contrary, his concurrence explicitly approved of the Corps' regulatory
definition of 'adjacent,' which includes both those wetlands that directly abut waters of the
United States and those separated from other waters 'by man-made dikes or barriers, natural
river berms, beach dunes, and the like.'" Id. at 291. The court accepted the Corps' explanation
that a berm separating 4.8 acres of wetlands from one of the tributary ditches did not inhibit the
functions being performed by those wetlands. Id. at 291-92. The Fourth Circuit also accepted
the Corps' determination to consider as similarly situated wetlands adjacent to two tributary
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ditches because the two ditches together had been part of the same naturally defined wetland
drainage before being altered by man. Id. at 292 ("There is both logical and practical appeal to
treating man-made ditches that would naturally be part of the same drainage feature together").
While the lower courts generally have agreed on the types of function that can form a
nexus, they have had a harder time describing when such a nexus is "significant." Justice
Kennedy simply stated that a significant nexus is one that is neither speculative nor insubstantial.
Rapanos, 547 U.S. at 780. The term "significant" as used by Justice Kennedy was not intended
to require statistical significance. Precon Dev. Corp., Inc. v. U.S. Army Corps o/Eng'rs, 2015
U.S. App. LEXIS 3704 * 6 (4th Cir. March 10, 2015) (Precon II) (unpublished decision). The
Fourth Circuit has noted that the standard "is a 'flexibly ecological inquiry,'" and that
"[quantitative or qualitative evidence may support [applicability of the CWA]" Precon II, 2015
U.S. App. LEXIS 3704 * 6 (4th Cir. March 10, 2015). The same court also has clarified that the
burden of establishing applicability of the CWA should not be "unreasonable." Precon, 633
F.3d at 297. While the appellate courts have accepted laboratory analysis or quantitative or
empircal data (Donovan, 661 F.3d at 186); Northern California Riverwatch, 496 F.3d at 1000-
1001), the appellate courts have not required such quantitative evidence. Precon, 633 F.3d at
294 ("We agree that the significant nexus test does not require laboratory tests or any particular
quantitative measurements in order to establish significance"); Cundiff, 555 F.3d at 211
("Though no doubt a district court could find such evidence persuasive, the Cundiffs point to
nothing - no expert opinion, no research report or article, and nothing in any of the various
Rapanos opinions - to indicate that [laboratory analysis] is the sole method by which a
significant nexus may be proved"). The appellate courts have accepted a variety of evidence,
including but not limited to, photographs, visual observation of stream condition, flow and
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morphology, studies, dye tests, scientific literature, maps, aerial photographs, and remote sensing
data. Lucas, 516 F. 3d at 326-21. See also Deer field Plantation Phase II-B Property Owners
Ass 'n, 2012 U.S. App. LEXIS 26402 *5 (in addition to conducting two site visits, Corps relied
upon infrared aerial photography, agency records, a county soil survey, a topographic map and a
wetland inventory); Donovan, 661 F. 3d at 185-86.
Waters have been found to be relatively permanent under the plurality standard or
sufficient to form a significant nexus under Justice Kennedy's standard even when they flow less
than year round. Cundiff, 555 F.3d at 211-12 (waters forming hydrologic connection flow for
"all but a few weeks a year"); Moses, 496 F.3d at 989-91 (portion of stream that receives flow
two months of the year is within the scope of the Act); see also United States v. Vierstra, 2012
U.S. LEXIS 16876 (9th Cir. Aug. 13, 2012) (unpublished decision) (upholding district court
opinion that canal that flows seasonally for six to eight months of the year is a relatively
permanent water). The appellate courts generally have not distinguished between naturally
occurring and man-made waters that meet the standards laid out by the plurality or Justice
Kennedy. Cundiff, 555 F.3d at 213 ("[I]n determining whether the Act confers jurisdiction, it
does not make a difference whether the channel by which water flows from a wetland to a
navigable-in-fact waterway or its tributary was man-made or formed naturally"); Moses, 496
F.3d at 988-89 (man-made diversion does not change the character of a water of the U.S.); see
also United States v. Vierstra, 2012 U.S. LEXIS 16876 (9th Cir. Aug. 13, 2012) (unpublished
decision) (upholding district court opinion that relatively permanent water can be man-made),
iii. The Rule is Consistent with Supreme Court Decisions
With this rule, the agencies interpret the scope of the "waters of the United States" for the
CWA in light of the goals, objectives, and policies of the statute, the Supreme Court case law,
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the relevant and available science, and the agencies' technical expertise and experience. The key
to the agencies' interpretation of the CWA is the significant nexus standard as informed by the
ecological and hydrological connection the Supreme Court noted in Rverside Bayview,
established by the Supreme Court in SWANCC, and refined in Justice Kennedy's opinion in
Rapanos. Waters are "waters of the United States" if they, either alone or in combination with
similarly situated waters in the region, significantly affect the chemical, physical, or biological
integrity of traditional navigable waters, interstate waters or the territorial seas. The agencies
have also utilized the plurality standard by establishing boundaries and primarily in support of
the exclusions from the definition of "waters of the United States." The plurality opinion in
Rapanos noted that there were certain features that were not primarily the focus of the CWA.
See 547 U.S. at 734. In the rule, the agencies are drawing lines and concluding that certain
waters and features are not subject to the jurisdiction of the Clean Water Act. The Supreme
Court has recognized that clarifying the lines of jurisdiction is a difficult task: "Our common
experience tells us that this is often no easy task: the transition from water to solid ground is not
necessarily or even typically an abrupt one. Rather, between open waters and dry land may lie
shallows, marshes, mudflats, swamps, bogs — in short, a huge array of areas that are not wholly
aquatic but nevertheless fall far short of being dry land. Where on this continuum to find the
limit of 'waters' is far from obvious." Riverside Bayview at 132-33. The exclusions reflect the
agencies' determinations of the lines of jurisdiction based on science, the case law and the
agencies' experience and expertise. The position of the United States is that a water is
jurisdictional if it meets either the plurality's standard or the Kennedy standard. Upon the
effective date of this rule, a water will be jurisdictional if it meets the rule's definition of "waters
of the United States."
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Some commenters argue that to comply with Supreme Court precedent, the rule should only
find jurisdiction where both the plurality's and Justice Kennedy's standards are satisfied. Those
commenters further argue that the agencies cannot rely solely on Justice Kennedy's significant
nexus standard. While the Courts of Appeals are split on the proper interpretation of Rapanos,
none has adopted the position that the agencies cannot rely on Justice Kennedy's standard or that
jurisdiction exists only where both the plurality's and Justice Kennedy's standards are satisfied.
The Third Circuit in United States v. Donovan rejected that interpretation of Rapanos and
provided a detailed analysis of the proper interpretation of Rapanos. 661 F.3d 174 (3d Cir.
2011), cert, denied, 132 S. Ct. 2409 (2012). The agencies' rule is consistent with every Circuit
Court decision to address this issue. The Third Circuit's thorough analysis states:
The Courts of Appeals for the Seventh and Eleventh Circuits have concluded that
Justice Kennedy's test alone creates the applicable standard for CW A jurisdiction
over wetlands. United States v. Gerke Excavating, Inc., 464 F.3d 723, 724-25
(7th Cir.2006); United States v. Robison, 505 F.3d 1208, 1221-22 (11th
Cir.2007). These courts based their conclusions on an analysis of the Supreme
Court's decision in United States v. Marks, in which the Court directed that,
"[w]hen a fragmented Court decides a case and no single rationale explaining the
result enjoys the assent of five Justices, the holding of the Court may be viewed as
that position taken by those Members who concurred in the judgments on the
narrowest grounds." 430 U.S. 188, 193, 97 S.Ct. 990, 51 L.Ed.2d 260 (1977)
(citation and internal quotation marks omitted). In their view, Justice Kennedy's
opinion in Rapanos controls because, among those Justices concurring in the
judgment, Justice Kennedy's view is the least restrictive of federal jurisdiction.
Gerke, 464 F.3d at 724-25; Robison, 505 F.3d at 1221-22.
The Courts of Appeals for the First and Eighth Circuits have taken a different
view. These courts examined the Supreme Court's directive in Marks, but found
that the Rapanos opinions did not lend themselves to a Marks analysis because
neither the plurality opinion nor Justice Kennedy's opinion relied on "narrower"
grounds than the other. United States v. Johnson, 467 F.3d 56, 62-64 (1st
Cir.2006); United States v. Bailey, 571 F.3d 791, 799 (8th Cir.2009). Judge Lipez,
writing for the majority of the panel in Johnson, disagreed that the "narrowest
grounds" in the Marks sense necessarily means those grounds least restrictive of
federal jurisdiction. The court in Johnson stated that "it seems just as plausible to
conclude that the narrowest ground of decision in Rapanos is the ground most
restrictive of government authority. . . because that ground avoids the
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constitutional issue of how far Congress can go in asserting jurisdiction under the
Commerce Clause." 467 F.3d at 63 (emphasis added). Even if one were to
conclude that the opinion resting on the narrowest grounds is the one that relies on
"less sweeping reasons than the other"—meaning that it requires the same
outcome (here, the presence of federal regulatory jurisdiction) in only a subset of
the cases that the other opinion would, and in no other cases—the court in
Johnson concluded that Marks is unhelpful in determining which Rapanos test
controls. Id. at 64. This is because Justice Kennedy's test would find federal
jurisdiction in some cases that did not satisfy the plurality's test, and vice versa.
Id. For example, if there is a small surface water connection between a wetland
and a remote navigable water, the plurality would find jurisdiction, while Justice
Kennedy might not. Furthermore, a wetland that lacks a surface connection with
other waters, but significantly affects the chemical, physical, and biological
integrity of a nearby river would meet Justice Kennedy's test but not the
plurality's. See id. It is therefore difficult, if not impossible, to identify the
"narrowest" approach.
Accordingly, the Johnson Court looked to Justice Stevens's approach in
Rapanos and found it to provide "a simple and pragmatic way to assess what
grounds would command a majority of the Court." Id. According to the Johnson
Court, following Justice Stevens's instructions and looking to see if either
Rapanos test is satisfied "ensures that lower courts will find jurisdiction in all
cases where a majority of the Court would support such a finding." Id.6 Therefore,
the Courts of Appeals for the First and Eighth Circuits held that federal regulatory
jurisdiction can be established over wetlands that meet either the plurality's or
Justice Kennedy's test from Rapanos. Id. at 66; Bailey, 571 F.3d at 799.7
6 The Johnson Court also suggested that the Supreme Court has moved
away from the Marks formulation, citing several instances in which
"members of the Court have indicated that whenever a decision is
fragmented such that no single opinion has the support of five Justices,
lower courts should examine the plurality, concurring and dissenting
opinions to extract the principles that a majority has embraced." 467 F.3d
at 65-66 (citing cases). Moreover, the Johnson Court stated that "the fact
that Justice Stevens does not even refer to Marks indicates that he found its
framework inapplicable." Id. at 66.
7 Several Circuit Courts of Appeals have expressly reserved the issue of
which Rapanos test, or tests, governs CWA enforcement actions. See
Precon Dev. Corp. v. U.S. Army Corps of Eng'rs, 633 F.3d 278, 288 (4th
Cir. 2011) (reserving judgment on whether Corps jurisdiction can be
established under either Rapanos test); N. Cal. River Watch v. Wilcox, 633
F.3d 766, 781 (9th Cir. 2011) (same); United States v. Cundiff, 555 F.3d
200, 210 (6th Cir. 2009) (declining to decide which Rapanos test or tests
govern because jurisdiction was proper under both); United States v. Lucas,
516 F.3d 316, 325-27 (5th Cir. 2008) (upholding Corps jurisdiction over
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wetlands where evidence at trial supported jurisdiction under the reasoning
of the plurality, Justice Kennedy, and Justice Stevens).
We agree with the conclusion of the First Circuit Court of Appeals that neither
the plurality's test nor Justice Kennedy's can be viewed as relying on narrower
grounds than the other, and that, therefore, a strict application of Marks is not a
workable framework for determining the governing standard established by
Rapanos. We also agree with its conclusion that each of the plurality's test and
Justice Kennedy's test should be used to determine the Corps' jurisdiction under
the CWA.
As we have stated in discussing Marks, our goal in analyzing a fractured
Supreme Court decision is to find "a single legal standard ... [that] when
properly applied, produce[s] results with which a majority of the Justices in the
case articulating the standard would agree." Planned Parenthood of Southeastern
Pa. v. Casey, 947 F.2d 682, 693 (3d Cir. 1991), modified on other grounds, 505
U.S. 833, 112 S.Ct. 2791, 120 L.Ed.2d 674 (1992). To that end, we have looked
to the votes of dissenting Justices if they, combined with votes from plurality or
concurring opinions, establish a majority view on the relevant issue. See United
States v. Richardson, No. 11-1202, F.3d , 2011 WL 4430808, at *5 (3d
Cir. Sept.23, 2011) (viewing as "persuasive authority" the shared view of a four-
Justice dissent and a single-Justice concurrence); Horn v. Thoratec Corp., 376
F.3d 163, 176 & n. 18 (3d Cir.2004) ("Thus, on the state requirement issue,
Justice Breyer joined with the four-member dissent to make a majority."); Student
Pub. Interest Research Grp. of N.J., Inc. v. AT & T Bell Labs, 842 F.2d 1436,
1451 (3d Cir. 1988) (deriving holding from one Justice concurrence and four
dissenting Justices).
The Supreme Court has also employed this mode of analysis. In United States
v. Jacobsen, 466 U.S. 109, 111, 104 S.Ct. 1652, 80 L.Ed.2d 85 (1984), the
Supreme Court determined that the rule of law established by its prior decision in
Walter v. United States, 447 U.S. 649, 100 S.Ct. 2395, 65 L.Ed.2d 410 (1980),
could be divined by combining the opinion of the Walter Court (which garnered
only two votes) with the opinion of four dissenting Justices. Justice Stevens,
writing for a majority of the Justices in Jacobsen, downplayed its reliance on the
votes of the dissenting Justices in extrapolating a legal standard from Walter,
saying that "the disagreement between the majority and the dissenters in {Walter]
with respect to the [application of law to fact] is less significant than the
agreement on the standard to be applied." Jacobsen, 466 U.S. at 117 n. 12; see
also Vasquez v. Hillery, 474 U.S. 254, 261 n. 4, 106 S.Ct. 617, 88 L.Ed.2d 598
(1986) (describing as "unprecedented" the argument that "a statement of legal
opinion joined by five Justices"—including some Justices in dissent—"does not
carry the force of law"), Alexander v. Choate, 469 U.S. 287, 293 & nn. 8-9, 105
S.Ct. 712, 83 L.Ed.2d 661 (1985) (deriving holdings from opinion of the Court,
concurring opinions, and dissenting opinions); Moses H. Cone Mem. Hosp. v.
Mercury Const. Corp., 460 U.S. 1, 17, 103 S.Ct. 927, 74 L.Ed.2d 765 (1983) ("On
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remand, the Court of Appeals correctly recognized that the four dissenting
Justices and Justice Blackmun formed a majority to require application of the
Colorado River test").
Thus, we are to examine the dissenting Justices' views to see if there is
common ground. Here, there is more than just common ground. While our sister
Courts of Appeals have struggled to divine the proper approach, we conclude that
the struggle is greatly lessened because Justice Stevens, along with the other three
Justices who joined his opinion, have actually told us what jurisdictional test is to
be applied.
As we noted above, Justice Stevens specifically states:
I would affirm the judgments in both cases, and respectfully dissent
from the decision of five Members of this Court to vacate and remand. I
close, however, by noting an unusual feature of the Court's judgments in
these cases. It has been our practice in a case coming to us from a lower
federal court to enter a judgment commanding that court to conduct any
further proceedings pursuant to a specific mandate. That prior practice has,
on occasion, made it necessary for Justices to join a judgment that did not
conform to their own views. In these cases, however, while both the
plurality and Justice Kennedy agree that there must be a remand for
further proceedings, their respective opinions define different tests to be
applied on remand. Given that all four Justices who have joined this
opinion would uphold the Corps' jurisdiction in both of these cases—and
in all other cases in which either the plurality's or Justice Kennedy's test is
satisfied—on remand each of the judgments should be reinstated if either
of those tests is met.
Rapanos, 547 U.S. at 810 (Stevens, J., dissenting) (footnotes omitted). And,
lest there be any confusion, he adds, "in these and future cases the United States
may elect to prove jurisdiction under either test." Id. at 810 n. 14. Recognizing
that the plurality and Justice Kennedy had failed to give a mandate to the Court of
Appeals on remand, Justice Stevens and the dissenters provided the mandate.
Were we to disregard this key aspect of his opinion we would be ignoring the
directive of the dissenters. They have spoken and said that, while they would have
chosen a broader test, they nonetheless agree that jurisdiction exists if either the
pluralitys or Justice Kennedys test is met.
Accordingly, Donovan's invocation of our decision in Rappa is unavailing. In
Rappa, we confronted a Supreme Court case in which the three opinions "share[d]
no common denominator" and each failed to garner a majority of the Justices'
votes. Rappa, 18 F.3d at 1060 (analyzingMetromedia, Inc. v. San Diego, 453
U.S. 490, 101 S.Ct. 2882, 69 L.Ed.2d 800 (1981)). Faced with precedent in which
there was no majority and no point of agreement whatsoever among the disparate
opinions, we determined that the Supreme Court failed to establish a governing
standard, and we therefore looked to prior case law to determine the relevant rule
of law. Id. That is not the case here. Instead, in Rapanos there is a point of
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agreement and no basis for disregarding the Supreme Court's directive that two
new tests should apply.8 Because each of the tests for Corps jurisdiction laid out
in Rapanos received the explicit endorsement of a majority of the Justices,
Rapanos creates a governing standard for us to apply: the CWA is applicable to
wetlands that meet either the test laid out by the plurality or by Justice Kennedy in
Rapanos.
8 Because the four Rapanos dissenters explicitly endorsed both the
plurality's and Justice Kennedy's jurisdictional tests, we are not faced with
a concern, like in Rappa, that combining the votes of Justices who joined in
different opinions would lead to unprincipled outcomes. . . . Rapanos
creates no such dilemma. We need not "combine" the votes of Justices
relying on different rationales to find that a majority of the Rapanos Justices
would come out a particular way in a given case. Two separate rationales
each independently enjoy the support of five or more Rapanos Justices,
without any need to "count[] the votes" of Justices relying on different
rationales. See id.
In any given case, this disjunctive standard will yield a result with which a
majority of the Rapanos Justices would agree. See Casey, 947 F.2d at 693. If the
wetlands have a continuous surface connection with "waters of the United States,"
the plurality and dissenting Justices would combine to uphold the Corps'
jurisdiction over the land, whether or not the wetlands have a "substantial nexus"
(as Justice Kennedy defined the term) with the covered waters. If the wetlands
(either alone or in combination with similarly situated lands in the region)
significantly affect the chemical, physical, and biological integrity of "waters of
the United States," then Justice Kennedy would join the four dissenting Justices
from Rapanos to conclude that the wetlands are covered by the CWA, regardless
of whether the wetlands have a continuous surface connection with "waters of the
United States." Finally, if neither of the tests is met, the plurality and Justice
Kennedy would form a majority saying that the wetlands are not covered by the
CWA.
In sum, we find that Rapanos establishes two governing standards and
Donovan's reliance on pre-Rapanos case law is misplaced. We hold that federal
jurisdiction to regulate wetlands under the CWA exists if the wetlands meet either
the plurality's test or Justice Kenned's test from Rapanos.
661 F.3rd at 180-184.
Some commenters argued that the significant nexus standard should not be applied to
non-wetlands. Based on the statute, its goals and objectives, and the Supreme Court caselaw, the
agencies conclude that the significant nexus standard applies to non-wetland waters and that
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Justice Kennedy's explication of the significant nexus standard applies to non-wetlands waters as
well. In Rapanos, Justice Kennedy reasoned that Riverside Bayview and SWANCC "establish the
framework for" determining whether an assertion of regulatory jurisdiction constitutes a
reasonable interpretation of "navigable waters" - "the connection between a non-navigable water
or wetland and a navigable water may be so close, or potentially so close, that the Corps may
deem the water or wetland a 'navigable water' under the Act;" and "[ajbsent a significant nexus,
jurisdiction under the Act is lacking." 547 U.S. at 767. "The required nexus must be assessed in
terms of the statute's goals and purposes. Congress enacted the law to 'restore and maintain the
chemical, physical, and biological integrity of the Nation's waters,' 33 U.S.C. § 1251(a), and it
pursued that objective by restricting dumping and filling in 'navigable waters,' §§ 1311(a),
1362(12)." Id. at 779. Justice Kennedy concluded that the term "waters of the United States"
encompasses wetlands and other waters that "possess a 'significant nexus' to waters that are or
were navigable in fact or that could reasonably be so made." Id. at 759. While Justice Kennedy's
discussion of the application of the significant nexus standard focused on adjacent wetlands in
light of the facts of the cases before him, his opinion is clear that he does not conclude that the
significant nexus analysis only applies to adjacent wetlands. As he explicitly states "the
connection between a non-navigable water or wetland and a navigable water may be so close, or
potentially so close, that the Corps may deem the water or wetland a 'navigable water' under the
Act." Id. at 767 (emphases added). Fundamentally, Justice Kennedy's significant nexus analysis
is about the fact, long-acknowledged by Supreme Court caselaw, that protection of waters from
pollution can only be achieved by controlling pollution of upstream waters. It would be
inconsistent with Justice Kennedy's opinion as a whole, science, and common sense to apply
Justice Kennedy's significant nexus standard to wetlands adjacent to tributaries and not to the
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tributaries themselves. Moreover, commenters appear to assume that if Justice Kennedy's
significant nexus analysis does not apply to tributaries the result would be that each individual
tributary must be determined alone to have a significant nexus. Nowhere in Justice Kennedy's
opinion does he state or imply that is the result of his opinion. In fact, Justice Kennedy's opinion
did not reject the existing regulation's definition of "waters of the United States" to include
tributaries.
The assertion of jurisdiction over tributaries as defined in the rule is consistent with
Justice Kennedy's opinion in Rapanos. Justice Kennedy concluded that "a water or wetland
must possess a 'significant nexus' to waters that are or were navigable in fact or that could
reasonably be so made. Id., at 167, 172." Rapanos at 759 (citing .Y^A'CCXernphasis added).
Therefore, the agencies disagree that Justice Kennedy's opinion reflects an intention that his
significant nexus standard applies only to wetlands. With respect to tributaries, Justice Kennedy
rejected the plurality's approach that only "relatively permanent" tributaries are within the scope
of CWA jurisdiction. He stated that the plurality's requirement of "permanent standing water or
continuous flow, at least for a period of 'some months' . . . makes little practical sense in a
statute concerned with downstream water quality." Id. at 769. Instead, Justice Kennedy
concluded that "Congress could draw a line to exclude irregular waterways, but nothing in the
statute suggests it has done so;" in fact, he stated that Congress has done "[qjuite the opposite . . .
." Id. at 769. Further, Justice Kennedy concluded, based on "a full reading of the dictionary
definition" of "waters," that "the Corps can reasonably interpret the Act to cover the paths of
such impermanent streams" Id. at 770 (emphasis added). Most fundamentally, the scientific
literature demonstrates that tributaries, as a category and as the agencies propose to define them,
play a critical role in the integrity of aquatic systems comprising traditional navigable waters and
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interstate waters, and therefore are "waters of the United States" within the meaning of the Clean
Water Act.
Moreover, as noted above, Justice Kennedy's opinion did not reject the agencies' existing
regulations governing tributaries. The consolidated cases in Rapanos involved discharges into
wetlands adjacent to nonnavigable tributaries and, therefore, Justice Kennedy's analysis focused
on the requisite showing for wetlands. Justice Kennedy described the Corps' standard for
asserting jurisdiction over tributaries: "the Corps deems a water a tributary if it feeds into a
traditional navigable water (or a tributary thereof) and possesses an ordinary high water mark . . .
." Id. at 781, see also id at 761. He acknowledged that this requirement of a perceptible ordinary
high water mark for ephemeral streams, 65 FR 12828, March 9, 2000, "[ajssuming it is subject to
reasonably consistent application, . . . may well provide a reasonable measure of whether
specific minor tributaries bear a sufficient nexus with other regulated waters to constitute
navigable waters under the Act." 547 U.S. at 781, see also id. at 761. With respect to wetlands,
Justice Kennedy concluded that the breadth of this standard for tributaries precluded use of
adjacency to such tributaries as the determinative measure of whether wetlands adjacent to such
tributaries "are likely to play an important role in the integrity of an aquatic system comprising
navigable waters as traditionally understood." Id. at 781. He did not, however, reject the Corps'
use of "ordinary high water mark" to assert regulatory jurisdiction over tributaries themselves.
Id.
In the foregoing passage regarding the existing regulatory standard for ephemeral
streams, Justice Kennedy also provided a "but see" citation to a 2004 U.S. General Accounting
Office (now the U.S. Government Accountability Office) (GAO) report "noting variation in
results among Corps district offices." Id. In 2005, the Corps issued a regulatory guidance letter
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(RGL 05-05) to Corps districts on OHWM identification that was designed to ensure more
consistent practice. U.S. Army Corps of Engineers 2005b. The Corps has also issued documents
to provide additional technical assistance for problematic OHWM delineations. See, e.g.,
Lichvar and McColley 2008; Mersel and Lichvar 2014. Moreover, the agencies' rule for the first
time provides a regulatory definition of "tributary." The definition expressly addresses some of
the issues with respect to identification of an OHWM that caused many of the inconsistencies
reported by the GAO. For example, this regulation clearly provides that a water that otherwise
meets the definition of tributary remains a jurisdictional tributary even if there are natural or
man-made breaks in the OHWM. The definition also provides a non-exclusive list of examples
of breaks in the OHWM to assist in clearly and consistently determining what meets the
definition of tributary. The preamble to the rule also includes extensive discussion of the tools
and information available to clearly and consistently implement the definition of tributary.
Some commenters also argued that Justice Kennedy's significant nexus standard does not
apply to non-wetland waters based on a statement by the Ninth Circuit in San Francisco
Baykeeper v. Cargill Salt Division, 481 F.3d 700,707 (9th Cir. 2007) ("No Justice, even in
dictum, addressed the question whether all waterbodies with a significant nexus to navigable
waters are covered by the Act."). First, to the extent the Ninth Circuit is stating that Justice
Kennedy's significant nexus standard is limited to wetlands, the statement is wrong. Justice
Kennedy stated: "to constitute 'navigable waters' under the Act, a water or wetland must
possess a 'significant nexus' to waters that are or were navigable in fact or that could reasonably
be so made." Rapanos at 759 (citing SWANCC, 531 U.S. at 167, 172) (emphasis added).
Second, in the context of the case, the statement is about the interplay between the existing
regulatory definition of "waters of the United States" and the Rapanos case. The existing
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provision of the regulations regarding adjacency applies only to wetlands and the water at issue
in the case was a pond. As the Ninth Circuit stated, "Under the controlling regulations, therefore,
the only areas that are defined as waters of the United States by reason of adjacency to other such
waters are 'wetlands.' . . . Disregarding the unambiguous regulations limiting to wetlands the
areas subject to the CWA because of adjacency, the district court determined that the Pond is
covered by the Act because 'the same characteristics that justif[y] protection of adjacent
wetlands . . . apply as well to adjacent ponds.' This analysis was improper." 481 F.3d at 705.
Because the adjacency provision did not cover the pond at issue, the citizen's group argued that
it was a "water of the United States" under Rapanos because it had a significant nexus. And the
Ninth Circuit held "Baykeeper's reliance on Rapanos v. United States, 126 S. Ct. 2208, 165 L.
Ed. 2d 159 (2006), is similarly misplaced." In that context, the Ninth Circuit was holding that
Rapanos did not establish jurisdiction for waters that did not first meet a provision in the
agencies' regulations.
The Ninth Circuit's decisions after Baykeeper further demonstrate that commenters' view
of the decision is erroneous; the Ninth Circuit did not hold that Kennedy's standard does not
apply to non-wetland waters. In Northern California River Watch v. City of Healdsburg, 496
F.3d 993, 998 (9fe Cir. 2007), the Ninth Circuit stated "The Basalt Pond and its surrounding area
are therefore regulable under the Clean Water Act, because they qualify as wetlands under the
regulatory definition. The district court explicitly found that the Pond is not only surrounded by
extensive wetlands, which connect to the Russian River, but also that the Pond's shoreline has
receded so substantially that much of the area that was originally Basalt Pond has turned into
wetland. This case is thus different than our recent decision in San Francisco Baykeeper v.
Cargill SaltDiv., 481 F.3d 700 (9th Cir. 2007), because here, the Pond is not isolated; it contains
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and is surrounded by wetlands, rendering it regulable under the CWA." And in United States v.
Vierstra, 2012 U.S. Appeal LEXIS 16876, **3 (9th Cir. Aug. 9, 2012), the Ninth Circuit upheld a
finding of jurisdiction over a tributary based on the significant nexus standard: "Sufficient
evidence supported the jury's verdict because, viewing the evidence in the light most favorable to
the government, United States v. Ramirez, 537 F.3d 1075, 1081 (9th Cir. 2008), a rational jury
could have concluded that a 'significant nexus' existed between the Low Line Canal and the
Snake River. Rapanos v. United States, 547 U.S. 715, 767, 126 S. Ct. 2208, 165 L. Ed. 2d 159
(2006) (Kennedy, J., concurring in the judgment); see TV. Cal. River Watch v. City of Healdsburg,
496 F.3d 993, 999-1000 (9th Cir. 2007) (describing the effect of the Supreme Court's various
opinions). For six to eight months a year, the Low Line Canal flows continuously and directly
into a tributary of the Snake River, a traditionally navigable water. Additionally, the canal has a
significant flow of water, an ordinary high water mark, and a defined bed and bank."
Finally, the Ninth Circuit did not view its opinion as establishing limitations on the
authority of the agencies and clearly stated that they would defer to the agencies' definition of
"waters of the United States": "it is most appropriate to defer to the administering agencies in
construing the statutory term 'waters of the United States,' which establishes the reach of the
CWA. Deference is especially suitable because this borderline determination of non-navigable
areas to be made subject to the CWA is one that involves 'conflicting policies' and expert factual
considerations for which the agencies are especially well suited. See Wash., Dep't of Ecology,
752 F.2d at 1469. Because we do not want to undermine or throw into chaos the EPA's and the
Corps' construction of the statute that establishes the reach of the CWA, Chevron deference is
required, even in this citizen suit." Id. at 706. Even if the Ninth Circuit had held that Justice
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Kennedy's significant nexus standard was inapplicable to non-wetland waters, such a holding
would not be binding on the agencies nationwide.
Some commenters also argued that the proposed rule's aggregation approach is
inconsistent with Justice Kennedy's opinion, stating that Justice Kennedy imposed limitations on
what is "similarly situated" based on proximity to navigable water, regularity of flow, or duration
of the function being performed. While Justice Kennedy discussed some of these as possible
factors in significant nexus generally, Justice Kennedy did not define either "similarly situated"
or "in the region," and no Circuit Court has held that the limitations commenters identify exist in
Justice Kennedy's opinion. As the Fourth Circuit stated, while Justice Kennedy's significant
nexus test clearly allows for aggregation of wetlands in determining whether a significant nexus
exists, "his concurrence provided no further explanation of what 'similarly situated,' or, for that
matter, 'region,' should be taken to mean in this context." Precon, 633 F.3d at 291. Moreover, a
number of Circuit Courts have noted that this is precisely the type of issue to which deference
would be due when the agency proceeds through notice and comment rulemaking. The Fourth
Circuit, for instance, recognizing the Corps' expertise in administering the CWA, gave some
deference to its interpretation and application of Justice Kennedy's test where appropriate, citing
United States v. Mead Corp., 533 U.S. 218, 234, 121 S. Ct. 2164, 150 L. Ed. 2d 292 (2001)
("[A]n agency's interpretation may merit some deference whatever its form, given the
'specialized experience and broader investigations and information' available to the agency
(quoting Skidmore v. Swift, 323 U.S. 134, 140, 65 S. Ct. 161, 89 L. Ed. 124 (1944)), and noted
that greater deference would be accorded under Chevron U.S.A. Inc. v. Natural Resources
Defense Council, Inc., 467 U.S. 837, 104 S. Ct. 2778, 81 L. Ed. 2d 694 (1984), once the agencies
adopted an interpretation of navigable waters" that incorporates the concept of significant nexus
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through notice-and-comment rulemaking, but instead has interpreted the term only in a non-
binding guidance document. 633 F.3d at n. 10. The Fourth Circuit noted further that "Justice
Kennedy's instruction that 'similarly situated lands in the region' can be evaluated together is a
broad one." Id. at 292.
The agencies have determined that tributaries, as defined, are "similarly situated,"
adjacent waters, as defined, are "similarly situated," and the five subcategories of waters
identified in (a)(7) are "similarly situated," for the reasons articulated in the preamble at Sections
III and IV and in the relevant sections of this Technical Support Document. The agencies have
also provided a definition of "significant nexus," including a definition of "similarly situated" for
purposes of case-specific significant nexus determinations under (a)(8) of the rule. The SAB
found that the available science provides an adequate scientific basis for the key components of
the proposed rule. The SAB noted that although water bodies differ in degree of connectivity that
affects the extent of influence they exert on downstream waters {i.e., they exist on a
"connectivity gradient"), the available science supports the conclusion that the types of water
bodies identified as "waters of the United States" in the proposed rule exert strong influence on
the chemical, physical, and biological integrity of downstream waters. In particular, the SAB
expressed support for the proposed rule's inclusion of tributaries and adjacent waters as
categorical waters of the United States and the inclusion of "other waters" on a case-specific
basis, though noting that certain "other waters" can be determined as a subcategory to be
similarly situated. Thus, the agencies determinations with respect to "similarly situated" and the
final rule are supported by the science and consistent with Justice Kennedy's standard.
Some commenters also stated that the proposed rule's definition of significant nexus, that
establishes that for an effect to be significant it must be more than speculative or insubstantial, is
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inconsistent with Justice Kennedy's opinion. These commenters cite to dictionary definitions of
the word "significant" in support of their contention that the agencies' definition is inconsistent
with Justice Kennedy's opinion. The agencies' definition of the term "significant nexus" in the
rule is consistent with language in SWANCC and Rapanos, and with the goals, objectives, and
policies of the CWA. The definition reflects that not all waters have a requisite connection to
traditional navigable waters, interstate waters, or the territorial seas sufficient to be determined
jurisdictional. Justice Kennedy was clear that to be covered, waters must significantly affect the
chemical, physical, or biological integrity of a downstream navigable water and that the requisite
nexus must be more than "speculative or insubstantial," Rapanos, at 780. The agencies define
significant nexus in precisely those terms. Under the rule a "significant nexus" is established by
a showing of a significant chemical, physical, or biological effect. Since the agencies have used
the precise language Justice Kennedy used in his opinion, the agencies disagree that this
definition is inconsistent with Justice Kennedy's opinion. Further, the agencies disagree that a
dictionary definition of the word "significant" is more representative of Justice Kennedy's
opinion than Justice Kennedy's opinion itself. In Rapanos, Justice Kennedy stated that in both
the consolidated cases before the Court the record contained evidence suggesting the possible
existence of a significant nexus according to the principles he identified. See id. at 783. Justice
Kennedy concluded that "the end result in these cases and many others to be considered by the
Corps may be the same as that suggested by the dissent, namely, that the Corps' assertion of
jurisdiction is valid." Id. Justice Kennedy remanded the cases because neither the agency nor the
reviewing courts properly applied the controlling legal standard - whether the wetlands at issue
had a significant nexus. See id. Justice Kennedy was clear however, that "[m]uch the same
evidence should permit the establishment of a significant nexus with navigable-in-fact waters,
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particularly if supplemented by further evidence about the significance of the tributaries to which
the wetlands are connected." Id. at 784.
With respect to one of the wetlands at issue in the consolidated Rapanos cases, Justice
Kennedy stated:
In Carabell, No. 04-1384, the record also contains evidence bearing on the jurisdictional
inquiry. The Corps noted in deciding the administrative appeal that "[bjesides the effects
on wildlife habitat and water quality, the [district office] also noted that the project would
have a major, long-term detrimental effect on wetlands, flood retention, recreation and
conservation and overall ecology. . . . The Corps' evaluation further noted that by
'eliminat[ing] the potential ability of the wetland to act as a sediment catch basin," the
proposed project "would contribute to increased runoff and . . . accretion along the drain
and further downstream in Auvase Creek.' .... And it observed that increased runoff
from the site would likely cause downstream areas to "see an increase in possible
flooding magnitude and frequency."
Id. at 785-86. Justice Kennedy also expressed concern that "[t]he conditional language in
these assessments—'potential ability,' 'possible flooding'—could suggest an undue degree of
speculation." Mat 786. Justice Kennedy's observations regarding the underlying case provide
guidance as to what it means for a nexus to be more than merely speculative or insubstantial and
inform the definition of "significant nexus."
Some commenters also stated that Justice Kennedy's significant nexus standard requires
chemical, physical, and biological effects. The agencies' definition of the term "significant
nexus" in the rule is consistent with language in SWANCC and Rapanos, and with the goals,
objectives, and policies of the CWA. The definition reflects that not all waters have a requisite
connection to traditional navigable waters, interstate waters, or the territorial seas sufficient to be
determined jurisdictional. Justice Kennedy was clear that to be covered, waters must
significantly affect the chemical, physical, or biological integrity of a downstream navigable
water and that the requisite nexus must be more than "speculative or insubstantial," Rapanos, at
780. The agencies define significant nexus in precisely those terms. Under the rule a
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"significant nexus" is established by a showing of a significant chemical, physical, or biological
effect. In characterizing the significant nexus standard, Justice Kennedy stated: "[t]he required
nexus must be assessed in terms of the statute's goals and purposes. Congress enacted the
[CWA] to 'restore and maintain the chemical, physical, and biological integrity of the Nation's
waters' . . . ." 547 U.S. at 779. It is clear that Congress intended the CWA to "restore and
maintain" all three forms of "integrity," Section 101(a), so if any one is compromised then that is
contrary to the statute's stated objective. It would subvert the objective if the CWA only
protected waters upon a showing that they had effects on every attribute of the integrity a
traditional navigable water, interstate water, or the territorial sea.
Some commenters stated that because the agencies did not provide metrics to quantify
when chemical, physical, or biological effects amount to a significant nexus, the proposed rule is
based on simple identification of the presence of connections and is therefore inconsistent with
Justice Kennedy's opinion. First, neither Justice Kennedy's opinion nor any Circuit Court to
address this issue required metrics or quantification of the waters' effects on the downstream
chemical, physical or biological integrity. As noted above, the Circuit Courts have held that the
term "significant" as used by Justice Kennedy was not intended to require statistical significance.
Precon Dev. Corp., Inc. v. U.S. Army Corps ofEng'rs, 2015 U.S. App. LEXIS 3704 * 6 (4th Cir.
March 10, 2015) (Precon II) (unpublished decision). The Fourth Circuit has noted that the
standard "is a 'flexibly ecological inquiry,"' and that "[quantitative or qualitative evidence may
support [applicability of the CWA]." Precon II, 2015 U.S. App. LEXIS 3704 * 6 (4th Cir. March
10, 2015). The same court also has clarified that the burden of establishing applicability of the
CWA should not be "unreasonable." Precon, 633 F.3d at 297. While the appellate courts have
accepted laboratory analysis or quantitative or empircal data (Donovan, 661 F.3d at 186);
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Northern California Riverwatch, 496 F.3d at 1000-1001), the appellate courts have not required
such quantitative evidence. Precon, 633 F.3d at 294 ("We agree that the significant nexus test
does not require laboratory tests or any particular quantitative measurements in order to establish
significance"); Cundiff, 555 F.3d at 211 ("Though no doubt a district court could find such
evidence persuasive, the Cundiffs point to nothing - no expert opinion, no research report or
article, and nothing in any of the various Rapanos opinions - to indicate that [laboratory
analysis] is the sole method by which a significant nexus may be proved"). The appellate courts
have accepted a variety of evidence, including but not limited to, photographs, visual observation
of stream condition, flow and morphology, studies, dye tests, scientific literature, maps, aerial
photographs, and remote sensing data. Lucas, 516 F.3d at 326-27. See also DeerfieldPlantation
Phase II-B Property Owners Ass 'n, 2012 U.S. App. LEXIS 26402 *5 (in addition to conducting
two site visits, Corps relied upon infrared aerial photography, agency records, a county soil
survey, a topographic map and a wetland inventory); Donovan, 661 F. 3d at 185-86.
With respect to the comment that without quantifying "significant" the agencies are
asserting jurisdiction based on the presence of connections that are the equivalent of "any
hydrologic connection," the agencies disagree with both the characterization of the science and
the suggestion that the jurisdictional conclusions reflected in the rule are based on mere
hydrologic connections. First, the science did not assess a mere nexus to downstream waters, but
also examined the degree of connection and effect. Some commenters may have been confused
by the terminology of the Science Report - "connectivity" does not mean a mere hydrologic
connection. The term connectivity is defined in the Science Report as the degree to which
components of a watershed are joined and interact by transport mechanisms that function across
multiple spatial and temporal scales. Connectivity is determined by the characteristics of both the
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physical landscape and the biota of the specific system. The Science Report found strong
evidence supporting the central roles of the physical, chemical, and biological connectivity of
streams, wetlands, and open waters—encompassing varying degrees of both connection and
isolation—in maintaining the structure and function of downstream waters, including rivers,
lakes, estuaries, and oceans. The Science Report also found strong evidence demonstrating the
various mechanisms by which material and biological linkages from streams, wetlands, and open
waters affect downstream waters, classified here into five functional categories (source, sink,
refuge, lag, and transformation; discussed below), and modify the timing of transport and the
quantity and quality of resources available to downstream ecosystems and communities. Thus,
the currently available literature provides a large body of evidence for assessing the types of
connections and functions by which streams and wetlands produce the range of observed effects
on the integrity of downstream waters. Regarding tributaries, the SAB found, "[t]here is strong
scientific evidence to support the EPA's proposal to include all tributaries within the jurisdiction
of the Clean Water Act. Tributaries, as a group, exert strong influence on the physical, chemical,
and biological integrity of downstream waters, even though the degree of connectivity is a
function of variation in the frequency, duration, magnitude, predictability, and consequences of
physical, chemical, and biological process." SAB 2014b at 2. Regarding adjacent waters and
wetlands, the SAB stated, "[t]he available science supports the EPA's proposal to include
adjacent waters and wetlands as a waters of the United States. .. .because [they] have a strong
influence on the physical, chemical, and biological integrity of navigable waters." Id.
In the rule, the agencies have also provided more detail in the definition of significant
nexus as to the functions to be considered for the purposes of determining significant nexus:
sediment trapping, nutrient recycling, pollutant trapping transformation, filtering and transport,
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retention and attenuation of floodwaters, runoff storage, contribution of flow, export of organic
matter, export of food resources, or provision of life-cycle dependent aquatic habitat (such as
foraging, feeding, nesting, breeding, spawning, use as a nursery area) for species located in
traditional navigable waters, interstate waters, or the territorial seas. These functions are
consistent with the agencies' scientific understanding of the functioning of aquatic ecosystems.
A water does not need to perform all of the functions listed in paragraph (c)(5) in order to have a
significant nexus. Depending upon the particular water and the functions it provides, if a water,
either alone or in combination with similarly situated waters, performs just one function, and that
function has a significant impact on the integrity of a traditional navigable water, interstate
water, or the territorial seas, that water would have a significant nexus.
Some commenters stated that the proposed rule's definition of tributary is inconsistent
with the Rapanos plurality and Justice Kennedy's opinion and sweeps in waters beyond the reach
of the CWA. The agencies agree that some tributaries as defined in the final rule may not be
"relatively permanent" under the plurality's test, but as addressed above, no court has held that
waters must meet the plurality test or must meet both the plurality test and the Kennedy test. The
agencies disagree that the definition of tributary is inconsistent with Justice Kennedy's opinion.
First, as discussed earlier, Justice Kennedy did not raise concerns with the agencies' existing
jurisdiction over tributaries themselves; rather, Justice Kennedy's concern arose with respect to
wetlands adjacent to those tributaries without case-specific significant nexus analysis until the
agencies undertook a rulemaking. Second, the final rule requires tributaries to have both a bed
and banks and another indicatory of ordinary high water mark. This narrows the waters that
meet the definition of tributary compared to current practice that simply requires one indicator of
ordinary high water mark.
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Some commenters stated that the proposed definition was inconsistent with Justice
Kennedy's opinion because it did not require consideration of frequency or duration of flow.
Justice Kennedy's opinion reflected that he thought that a significant nexus analysis for
jurisdiction over adjacent wetlands should consider duration and frequency of flow of the
tributaries to which the wetlands were adjacent. Moreover, the definition of tributary in the rule
is based on considerations of duration and frequency of flow because those are demonstrated by
the physical indicators of an ordinary high water mark. By requiring two indicators of an
ordinary high water mark, the agencies defined tributary to require more flow and be more
limited than existing practice which determined waters were tributary based on just one indicator
of ordinary high water mark. In fact, the SAB commented that not all tributaries have ordinary
high water marks, and any such waters will not be tributaries under the rule. The rule explicitly
excludes any ephemeral features that do not meet the definition of tributary. Finally, contrary to
some commenters assertions that the proposed rule's assertion of jurisdiction over tributaries
amounts to the "any hydrological connection standard," as discussed in the preamble and further
below, the agencies carefully evaluated the extensive science on the significant effects that
tributaries have on chemical, physical, and biological integrity. Therefore, the rule's jurisdiction
over tributaries is consistent with Justice Kennedy's opinion.
Some commenters stated the proposed rule's protection of small intermittent and
ephemeral streams and their adjacent waters, as defined in the rule, is inconsistent with Justice
Kennedy's opinion. Justice Kennedy stated:
As applied to wetlands adjacent to navigable-in-fact waters, the Corps' conclusive
standard for jurisdiction rests upon a reasonable inference of ecologic
interconnection, and the assertion of jurisdiction for those wetlands is sustainable
under the Act by showing adjacency alone. That is the holding of Riverside
Bayview. Further, although the Riverside Bayview Court reserved the question of
the Corps' authority over "wetlands that are not adjacent to bodies of open water,"
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474 U.S., at 131-132, n. 8, 106 S. Ct. 455, 88 L. Ed. 2d 419, and in any event
addressed no factual situation other than wetlands adjacent to navigable-in-fact
waters, it may well be the case that Riverside Bayview's reasoning—supporting
jurisdiction without any inquiry beyond adjacency—could apply equally to
wetlands adjacent to certain major tributaries. Through regulations or
adjudication, the Corps may choose to identify categories of tributaries that, due
to their volume of flow (either annually or on average), their proximity to
navigable waters, or other relevant considerations, are significant enough that
wetlands adjacent to them are likely, in the majority of cases, to perform
important functions for an aquatic system incorporating navigable waters.
547 U.S. at 780-81.
With the rule, the agencies interpret the scope of the "waters of the United States" for the
CWA in light of the goals, objectives, and policies of the statute, the Supreme Court case law,
the relevant and available science, and the agencies' technical expertise and experience. In the
rule, the agencies determine that tributaries, as defined, have a significant nexus to downstream
traditional navigable waters, interstate waters, and the territorial seas and therefore are "waters of
the United States." Informed by science, the agencies identified a category of tributaries that
were "waters of the United States" based on those waters having sufficient volume, duration, and
frequency of flow to form two physical indicators of flow - a bed and banks and another
indicator of ordinary high water mark. The science demonstrates how valuable these tributaries
are for the chemical, physical or biological integrity of downstream traditional navigable waters,
interstate waters, or the territorial seas. Commenters appear to view Justice Kennedy's opinion
as foreclosing protection under the CWA of small streams at the head of the tributary system and
therefore also foreclosing protection of any waters adjacent to those streams. The agencies do
not interpret the statute, or view Justice Kennedy's opinion, to foreclose protection of such
waters; in fact, based on the science and consistent with Justice Kennedy's opinion, the agencies
have determined that those small streams at the beginning of the tributary system are key to the
chemical, physical or biological integrity of the downstream traditional navigable water,
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interstate water, or the territorial seas, and waters adjacent to them similarly protect those
important tributaries and through them the downstream waters.
The agencies therefore disagree with commenters that state the rule is inconsistent with
Justice Kennedy's opinion. In light of the statute, the available science, and Justice Kennedy's
opinion, the agencies defined tributaries based on their flow (demonstrated by physical indicators
of flow), consideration of proximity (effects on the closest traditional navigable water, interstate
water, or the territorial seas), and other relevant considerations (the importance of the functions
provided by the tributaries, as defined, to the closest downstream traditional navigable water
interstate water or the territorial seas). Once these tributaries were identified, the agencies
assessed the effects of waters and wetlands on the tributaries and downstream and concluded that
tributaries as defined "are significant enough that wetlands adjacent to them are likely, in the
majority of cases, to perform important functions for an aquatic system incorporating navigable
waters." Id.
The Science Report found that those small, farther away streams, headwater streams,
which are the smallest channels where streamflows begin, are the cumulative source of
approximately 60% of the total mean annual flow to all northeastern U.S. streams and rivers. In
addition to downstream transport, headwaters convey water into local storage compartments such
as ponds, shallow aquifers, or stream banks, and into regional and alluvial aquifers which
important sources of water for maintaining baseflow in rivers. Headwater streams, including
ephemeral and intermittent streams, shape river channels by accumulating and gradually or
episodically releasing stored materials such as sediment and large woody debris. These materials
help structure stream and river channels by slowing the flow of water through channels and
providing substrate and habitat for aquatic organisms. There is strong evidence that headwater
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streams function as nitrogen sources (via export) and sinks (via uptake and transformation) for
river networks. For example, one study estimated that rapid nutrient cycling in small streams
with no agricultural or urban impacts removed 20-40% of the nitrogen that otherwise would be
delivered to downstream waters. Nutrients are necessary to support aquatic life, but excess
nutrients lead to eutrophication and hypoxia, in which over-enrichment causes dissolved oxygen
concentrations to fall below the level necessary to sustain most aquatic animal life in the stream
and streambed. Thus, the influence of streams on nutrient loads can have significant
repercussions for hypoxia in downstream waters. Headwaters provide habitat that is critical for
completion of one or more life-cycle stages of many aquatic and semiaquatic species capable of
moving throughout river networks. Use of headwater streams as habitat is especially critical for
the many species that migrate between small streams and marine environments during their life
cycles (e.g., Pacific and Atlantic salmon, American eels, certain lamprey species). The presence
of these species within river networks provides robust evidence of biological connections
between headwaters and larger rivers; because these organisms also transport nutrients and other
materials as they migrate, their presence also provides evidence of biologically mediated
chemical connections. The Science Report concludes that streams, regardless of their flow
regime, have important effects on larger downstream waters. The Science Advisory Board's final
review of the Science Report strongly supports this conclusion. In their comments, the SAB
found, "[t]here is strong scientific evidence to support the EPA's proposal to include all
tributaries within the jurisdiction of the Clean Water Act. Tributaries, as a group, exert strong
influence on the physical, chemical, and biological integrity of downstream waters, even though
the degree of connectivity is a function of variation in the frequency, duration, magnitude,
predictability, and consequences of physical, chemical, and biological process."
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In light of these scientific conclusions about the importance of these smaller intermittent
and ephemeral streams, the agencies did not subcategorize tributaries, but rather focused on
defining tributary to reasonably ensure that tributaries, as defined, had a significant nexus to
downstream traditional navigable waters, interstate waters, or the territorial seas. The agencies
then focused on defining adjacent waters to ensure that they, too, "perform[ed] important
functions for an aquatic system." Adjacent waters, as defined, function together to maintain the
chemical, physical, or biological health of traditional navigable waters, interstate waters, and the
territorial seas to which they are directly adjacent or to which they are connected by the tributary
system. This functional interaction can result from hydrologic connections or because adjacent
waters can act as water storage areas holding damaging floodwaters or filtering harmful
pollutants. These chemical, physical, and biological connections affect the integrity of
downstream traditional navigable waters, interstate waters, and the territorial seas through the
temporary storage and deposition of channel-forming sediment and woody debris, temporary
storage of local groundwater sources of baseflow for downstream waters and their tributaries,
and transformation and transport of organic matter. Covered adjacent waters improve water
quality through the assimilation, transformation, or sequestration of pollutants, including excess
nitrogen and phosphorus and chemical contaminants such as pesticides and metals that can
degrade downstream water integrity. In addition to providing effective buffers to protect
downstream waters from pollution, covered adjacent waters form integral components of
downstream food webs, providing nursery habitat for breeding fish and amphibians, colonization
opportunities for stream invertebrates, and maturation habitat for stream insects. Covered
adjacent waters serve an important role in the integrity of traditional navigable waters, interstate
waters, and the territorial seas by subsequently releasing (desynchronizing) floodwaters and
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retaining large volumes of stormwater, sediment, nutrients, and contaminants that could
otherwise negatively impact the condition or function of traditional navigable waters, interstate
waters, and the territorial seas. Therefore, the agencies disagree that the rule is inconsistent with
Justice Kennedy's opinion.
Some commenters stated that ditches should be excluded from regulation and that the
proposed rule's inclusion of ditches would subject ditches to regulation for the first time and was
contrary to Rapanos. The agencies disagree that the rule subjects ditches to regulation for the
first time. The courts of appeals have consistently held that, for purposes of the regulatory
definition of "waters of the United States," a man-made ditch can be a "tributary" of the
downstream waters to which the ditch ultimately contributes flow. See, e.g., United States v.
Gerke Excavating, Inc., 412 F.3d 804, 805-806 (7th Cir. 2005); Parker v. Scrap Metal
Processors, Inc., 386 F.3d 993, 1009 (11th Cir. 2004); Treacy v. Newdunn Assocs., 344 F.3d 407,
417 (4th Cir. 2003), cert, denied, 541 U.S. 972 (2004); United States v. Rapanos, 339 F.3d 447,
449, 451-452 (6th Cir. 2003), cert, denied, 541 U.S. 972 (2004); United States v. Deaton, 332
F.3d 698, 710-712 (4th Cir. 2003), cert, denied, 541 U.S. 972 (2004); Headwaters, Inc. v. Talent
Irrigation Dist., 243 F.3d 526, 533 (9th Cir. 2001); United States v. Eidson, 108 F.3d 1336, 1341-
1342 (11th Cir.), cert, denied, 522 U.S. 899 and 1004 (1997); United States v. Ashland Oil &
Transp. Co., 504 F.2d 1317, 1325 (6th Cir. 1974). But cf. In re Needham, 354 F.3d 340, 347 (5th
Cir. 2003) ("[T]he term 'adjacent' cannot include every possible source of water that eventually
flows into a navigable-in-fact waterway.").
In fact, the rule for the first time explicitly excludes certain ditches from the definition of
waters of the United States. First, excluding all ditches from CW A jurisdiction would be
inconsistent with the CWA and Congressional intent by nullifying a provision of the statute.
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Section 404(f)(1)(C) of the CWA states that, with some exceptions, the discharge of dredge or
fill material "for the purpose of construction or maintenance of farm or stock ponds or irrigation
ditches, or the maintenance of drainage ditches" is not prohibited by or otherwise subject to
regulation under the CWA. There would be no need for such a permitting exemption if ditches
were excluded from "waters of the United States." To be clear, under the rule a ditch may be a
"water of the United States" only if it meets the definition of tributary and is not otherwise
excluded under section (b) of the rule.
In addition, the agencies' longstanding interpretation of the CWA is that it is not relevant
whether a water is man-altered or man-made for purposes of determining whether a water is
jurisdictional under the CWA. The agencies' long-standing regulations defining "waters of the
United States," for example, did not distinguish between "natural" and "man-made" waters,
except to explicitly exclude only one category of man-made or man-altered waters - waste
treatment systems designed to meet the requirements of the CWA. In 1975, the General Counsel
of EPA issued an opinion interpreting the CWA: "it should be noted that what is prohibited by
section 301 is 'any addition of any pollutant to navigable waters from any point source.' It is
therefore my opinion that, even should the finder of fact determine that any given irrigation ditch
is a navigable water, it would still be permittable as a point source where it discharges into
another navigable water body, provided that the other point source criteria are also present." In
re Riverside Irrigation District at 4 (emphasis in original). The opinion stated that "to define the
waters here at issue as navigable waters and use that as a basis for exempting them from the
permit requirement appears to fly directly in the face of clear legislative intent to the contrary."
Id.
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In S. I). Warren v. Maine Board of Envt'l Protection, Justice Stevens, writing for a
unanimous Court, stated: "nor can we agree that one can denationalize national waters by
exerting private control over them." Cf. United States v. Chandler-Dunbar Water Power Co.,
229 U.S. 53, 69, 33 S. Ct. 667, 57 L. Ed. 1063 (1913) ("[T]hat the running water in a great
navigable stream is capable of private ownership is inconceivable"). 126 S.Ct. 1843, 1849 n.5
(2006). In Rapanos, all members of the Court generally agreed that "it is also true that highly
artificial, manufactured, enclosed conveyance systems — such as 'sewage treatment plants,' post,
at 15 (opinion of Kennedy, J.), and the 'mains, pipes, hydrants, machinery, buildings, and other
appurtenances and incidents' of the city of Knoxville's 'system of waterworks,' Knoxville Water
Co. v. Knoxville, 200 U.S. 22, 27, 26 S. Ct. 224, 50 L. Ed. 353, 3 Ohio L. Rep. 572 (1906), cited
post, at 17, n. 12 (opinion of Stevens, J.) — likely do not qualify as "waters of the United States,"
despite the fact that they may contain continuous flows of water. See post, at 15 (opinion of
Kennedy, J.); post, at 17, n. 12 (opinion of Stevens, J.)." 547 U.S. at 737 (opinion of Scalia, J.).
But there was also agreement that certain waters that are man-made or man-altered, such as
canals with relatively permanent flow, are waters of the United States. 547 U.S. at 736, at n. 7
(opinion of Scalia J.). Justice Kennedy and the dissent rejected the conclusion that because the
word "ditch" was in the definition of "point source" a ditch could never be a water of the United
States: "certain water bodies could conceivably constitute both a point source and a water." Id.
at 772 (opinion of Kennedy, J.); see also, Id. at 802 (dissent of Stevens, J.) ("The first provision
relied on by the plurality—the definition of "point source" in 33 U.S.C. § 1362(14) —has no
conceivable bearing on whether permanent tributaries should be treated differently from
intermittent ones, since 'pipe[s], ditch[es], channels], tunnel[s], conduit[s], [and] well[s]' can
all hold water permanently as well as intermittently.") While the plurality, Justice Kennedy, and
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the dissent formulated different standards for determining what is a "water of the United States,"
no test based jurisdiction on a distinction between "natural" versus "man-made" or "man-
altered" waters or excluded ditches in their entirety.
No Circuit Court has interpreted Rapanos to exclude ditches from the CWA. The
discussion of caselaw above demonstrates that ditches have long been subject to regulation as
"waters of the United States." The D.C. Circuit recently confirmed that ditches are not
categorically rendered non-jurisdictional for purposes of the CWA. In National Association of
Home Builders (NAHB) v. Corps of Engineers (No. 10-5169), the NAHB sought a declaratory
judgment that ditches are not waters of the United States. The D.C. Circuit did not grant the
motion for a declaratory judgment and instead held that NAHB did not have standing to
challenge the nationwide permit for certain ditches that NAHB sought to have overturned.
Upland ditches are, by their very nature, man-made. The D.C. Circuit concluded that the Corps'
permit for activities in certain upland ditches did not injure NAHB's members because "The risk
of sanctions attendant on filling upland ditches without Corps approval predates, and is in no
way aggravated by, the issuance of [the permit]" Slip op. at 5. The court did not question the
underlying premise of the permit that certain upland ditches would be "waters of the United
States."
Some commenters also cite to Justice Kennedy's critique that "the dissent would permit
federal regulation whenever wetlands lie alongside a ditch or drain, however remote and
insubstantial, that eventually may flow into traditional navigable waters," 547 at 778, to
demonstrate that the proposed rule's regulation of ditches and of adjacent waters is inconsistent
with Justice Kennedy's opinion. First, with this statement Justice Kennedy is expressing concern
about the categorical regulation of wetlands adjacent to remote and insubstantial ditches and
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drains. Second, the agencies' final rule explicitly excludes ephemeral ditches (that are not
constructed in tributaries themselves), so wetlands will not be jurisdictional under the rule based
on their adjacency to such ditches. In addition, "ditches and drainages" that do not meet the
definition of tributary in the final rule - including having a bed and banks and another indicator
of ordinary high water mark—are not jurisdictional and wetlands will not be jurisdictional under
the rule based on their adjacency to such ditches and drainages.
Some commenters stated that the proposed rule's regulation of adjacent waters expands
CWA jurisdiction over such waters for the first time and is inconsistent with SWANCC and
Rapanos. As stated in the preamble to the proposed rule, and as demonstrated by the discussion
above of caselaw prior to the SWANCC decision, while the rule reflects a change from the
existing regulation by addressing adjacent waters in one provision rather than adjacent wetlands
and adjacent other waters in two separate provisions, this would not be the first time the agencies
asserted jurisdiction over such waters. For the reasons discussed in this preamble, the agencies
do not interpret the SWANCC decision as prospectively invalidating the regulation of adjacent
open waters along with adjacent wetlands. Nor did the Ninth Circuit's decision in Baykeeper
reject the possibility of the agencies in rulemaking asserting jurisdiction over adjacent waters.
Some commenters stated the proposed rule's assertion of jurisdiction over "isolated
waters" violates SWANCC. These commenters contended that SWANCC invalidated the use of
the existing regulation's (a)(3) other waters provision and that it is unlawful to assert jurisdiction
over waters that are not tributaries or adjacent waters. The Supreme Court did not vacate (a)(3)
of the existing regulation. Rather, in SWANCC, the Court held that the use of "isolated"
nonnavigable intrastate ponds by migratory birds was not by itself a sufficient basis for the
exercise of federal regulatory authority under the CWA. The SWANCC Court noted that in
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Riverside it had "found that Congress' concern for the protection of water quality and aquatic
ecosystems indicated its intent to regulate wetlands 'inseparably bound up' with the 'waters of
the United States'" and that "it was the significant nexus between the wetlands and 'navigable
waters' that informed our reading of the CWA" in that case. Id. at 167. No Circuit Court has
interpreted SWANCC to have vacated the other waters provision of the existing regulation.
Justice Kennedy concluded that SWANCC held that "to constitute 'navigable waters' under the
Act, a water or wetland must possess a 'significant nexus' to waters that are or were navigable in
fact or that could reasonably be so made." Rapanos at 759 {citing SWANCC, 531 U.S. at 167,
172). And the Supreme Court in SWANCC did not prospectively invalidate a regulation that
authorizes case-specific significant nexus determinations for some waters.
Other commenters expressed concern about the proposed rule's deletion of the existing
provision covering other waters where "the use, degradation or destruction of' such waters
"could affect interstate or foreign commerce," stating that this change is not compelled by either
SWANCC or Rapanos. Presented with an assertion of jurisdiction under that provision of teh
existing rule and based on the effects of migratory birds' on interstate or foreign commerce, the
Court stated in SWANCC that "[t]he term 'navigable' has at least the import of showing us what
Congress had in mind as its authority for enacting the CWA: its traditional jurisdiction over
waters that were or had been navigable in fact or which could reasonably be so made. See, e.g.,
United States v. Appalachian Elec. Power Co., 311 U.S. 377, 407-408, 85 L. Ed. 243, 61 S. Ct.
291 (1940)," SWANCC at 172. In light of that statement, the agencies concluded that the general
other waters provision in the existing regulation that asserted jurisdiction based on a different
aspect of Congress' Commerce Clause authority - authority over activities that "could affect
interstate or foreign commerce" - was not consistent with Supreme Court precedent. The final
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rule provides for case-specific analysis of certain waters to determine whether they are "waters
of the U.S.," but that determination will be based on the significant nexus standard and not
whether "the use, degradation or destruction of' such waters "could affect interstate or foreign
commerce."
Some commenters stated that in the 2008 Guidance the United States interpreted Rapanos
to convey jurisdiction when either Justice Kennedy's or the plurality's standard is met and the
agencies failed to explain their basis for dispensing with that interpretation and taking a very
different approach in the 2014 Proposed Rule. In the rule, the agencies are establishing a binding
definition of the "waters of the United States" in light of the goals, objectives, and policies of the
statute, the Supreme Court case law, the relevant and available science, and the agencies'
technical expertise and experience, whereas the guidance was simply a practical guide to field
staff on how to proceed, in the absence of rulemaking, with case-specific jurisdictional
determinations, permitting actions, and other relevant actions in light of the split opinions in
Rapanos. While the agencies' interpretation and rulemaking is most informed by the significant
nexus standard as informed by the ecological and hydrological connections the Supreme Court
noted in Riverside Bayview, SWANCC, and Justice Kennedy's opinion, particularly in light of
Justice Kennedy's recognition that the agencies could identify categorically jurisdictional waters,
and in light of the available science, the agencies are also informed by the plurality opinion, as
discussed in the preamble, with respect to drawing lines to exclude features. The agencies do not
view the 2008 Guidance as an interpretation of the Clean Water Act, but to the extent the
agencies have changed their interpretation, they disagree that they failed to explain their basis.
Further, to the extent the agencies have changed an interpretation in a guidance document, they
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can do so under the Administrative Procedure Act (APA), and they can especially do so where,
as here, the agencies have proceeded through notice and comment rulemaking.
The 2008 Guidance was clearly guidance, as the agencies stated: "The CWA provisions
and regulations described in this document contain legally binding requirements. This guidance
does not substitute for those provisions or regulations, nor is it a regulation itself. It does not
impose legally binding requirements on EPA, the Corps, or the regulated community, and may
not apply to a particular situation depending on the circumstances. Any decisions regarding a
particular water will be based on the applicable statutes, regulations, and case law. Therefore,
interested persons are free to raise questions about the appropriateness of the application of this
guidance to a particular situation, and EPA and/or the Corps will consider whether or not the
recommendations or interpretations of this guidance are appropriate in that situation based on the
statutes, regulations, and case law." 2008 Guidance at 4 n.16. Further, the agencies were clear
that the guidance was an interim step and that the agencies intended to proceed through
rulemaking, as appropriate: "The agencies are issuing this memorandum in recognition of the
fact that EPA regions and Corps districts need guidance to ensure that jurisdictional
determinations, permitting actions, and other relevant actions are consistent with the decision and
supported by the administrative record. Therefore, the agencies have evaluated the Rapanos
opinions to identify those waters that are subject to CWA jurisdiction under the reasoning of a
majority of the justices. This approach is appropriate for a guidance document. The agencies
intend to more broadly consider jurisdictional issues, including clarification and definition of key
terminology, through rulemaking or other appropriate policy process." 2008 Guidance at 3.
The goals of the 2008 Guidance were: "To ensure that jurisdictional determinations,
administrative enforcement actions, and other relevant agency actions are consistent with the
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Rapanos decision, the agencies in this guidance address which waters are subject to CWA § 404
jurisdiction. Specifically, this guidance identifies those waters over which the agencies will
assert jurisdiction categorically and on a case-by-case basis, based on the reasoning of the
Rapanos opinions. EPA and the Corps will continually assess and review the application of this
guidance to ensure nationwide consistency, reliability, and predictability in our administration of
the statute." Id. at 4. In the proposed rule, the agencies explained that one of the reasons they
were promulgating a rule was that the 2008 Guidance had failed to achieve its goals. As the
agencies stated in the preamble to the proposed rule: "The SWANCC and Rapanos decisions
resulted in the agencies evaluating the jurisdiction of waters on a case-specific basis far more
frequently than is best for clear and efficient implementation of the CWA. This approach results
in confusion and uncertainty to the regulated public and results in significant resources being
allocated to these determinations by federal and state regulators. The agencies are proposing this
rule to fully carry out their responsibilities under the Clean Water Act. The agencies are
providing clarity to regulated entities as to whether individual water bodies are jurisdictional and
discharges are subject to permitting, and whether individual water bodies are not jurisdictional
and discharges are not subject to permitting." 79 FR at 22188. The agencies further stated: "The
proposed rule will reduce documentation requirements and the time currently required for
making jurisdictional determinations. It will provide needed clarity for regulators, stakeholders
and the regulated public for identifying waters as 'waters of the United States,' and reduce time
and resource demanding case-specific analyses prior to determining jurisdiction and any need for
permit or enforcement actions." 79 FR at 22191. The agencies also noted some inconsistencies
in practice in implementing the 2008 guidance.
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The 2008 Guidance is nothing more than an internal guidance document that does not
carry the "force and effect of law." Perez v. Mortgage Bankers Ass'n, 135 S. Ct. 1199, 1204
(2015). As the Supreme Court in Perez makes clear, "the APA permit[s] agencies to promulgate
freely [interpretive] rules — whether or not they are consistent with earlier interpretations" of the
agency's regulations. Id. at 1207; see also Hudson v. FAA, 192 F.3d 1031, 1035-36 (D.C. Cir.
1999) (holding that an agency may change its policy statements as it sees fit without following
APA notice and comment procedures). As noted in Perez, "[o]ne would not normally say that a
court 'amends' a statute when it interprets its text. So too can an agency 'interpret' a regulation
without 'effectively amending]' the underlying source of law." Id. at 1208 (alteration in
original). And "[bjecause an agency is not required to use notice-and-comment procedures to
issue an initial interpretive rule, it is also not required to use those procedures when it amends or
repeals that interpretive rule." Id. at 1206. Thus, to the extent there is a change, the agencies of
course may proceed by rulemaking.
Even if the agencies had reversed the approach they took in guidance, they agencies
disagree with commenters that the rule is therefore arbitrary or unreasonable. The Supreme
Court has held: "We find no basis in the Administrative Procedure Act or in our opinions for a
requirement that all agency change be subjected to more searching review. The Act mentions no
such heightened standard. And our opinion in State Farm neither held nor implied that every
agency action representing a policy change must be justified by reasons more substantial than
those required to adopt a policy in the first instance. That case, which involved the rescission of a
prior regulation, said only that such action requires 'a reasoned analysis for the change beyond
that which may be required when an agency does not act in the first instance.' 463 U. S., at 42
(emphasis added). . . . The statute makes no distinction, however, between initial agency action
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and subsequent agency action undoing or revising that action." FCC v. Fox, 556 U.S. 502, 514-
15 (2009). The Supreme Court continued: "To be sure, the requirement that an agency provide
reasoned explanation for its action would ordinarily demand that it display awareness that it is
changing position. An agency may not, for example, depart from a prior policy sub silentio or
simply disregard rules that are still on the books. See United States v. Nixon, 418 U. S. 683, 696
(1974). And of course the agency must show that there are good reasons for the new policy. But
it need not demonstrate to a court's satisfaction that the reasons for the new policy are better than
the reasons for the old one; it suffices that the new policy is permissible under the statute, that
there are good reasons for it, and that the agency believes it to be better, which the conscious
change of course adequately indicates. This means that the agency need not always provide a
more detailed justification than what would suffice for a new policy created on a blank slate."
Id. As noted above, with this rule the agencies are interpreting the statute in light the goals of the
statute, the science, and the opinions in SWANCC and Rapanos. To the extent this reflects a
change, it is not a silent one and the agencies have articulated good reasons for it.
iv. The Rule is Consistent with the Constitution
Some commenters argued that the proposed rule asserts expansive jurisdiction that is beyond
the commerce authority Congress exercised in enacting the CWA. In particular, commenters
argued that the Constitution allows for the CWA to reach more than "navigable in fact" waters,
but that asserting jurisdiction over a water based on a mere connection to a "navigable in fact"
water raises serious constitutional concerns. The final rule does not assert jurisdiction over a
water based on a "mere connection." Again, as demonstrated in the rule and its supporting
documentation, the agencies are asserting jurisdiction over traditional navigable waters, interstate
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May 2015
waters, the territorial seas, and those waters that have a significant nexus to them. Some
commenters argued that the proposed rule exceeds the limits of Congress' authority under the
Constitution by encroaching on the traditional power of the States to regulate land and water.
Justice Kennedy explicitly addressed these Constitutional concerns in Rapanos, stating "In
SWANCC, by interpreting the Act to require a significant nexus with navigable waters, the Court
avoided applications—those involving waters without a significant nexus—that appeared likely,
as a category, to raise constitutional difficulties and federalism concerns." 547 at 776.
Justice Kennedy further stated, "As for States' 'responsibilities and rights,' §1251(b), it is
noteworthy that 33 States plus the District of Columbia have filed an amici brief in this litigation
asserting that the Clean Water Act is important to their own water policies. See Brief for States
of New York et al. 1-3. These amici note, among other things, that the Act protects downstream
States from out-of-state pollution that they cannot themselves regulate. Ibid." Id. at 777.
Finally, Justice Kennedy concluded of the significant nexus standard:
This interpretation of the Act does not raise federalism or Commerce Clause concerns
sufficient to support a presumption against its adoption. To be sure, the significant nexus
requirement may not align perfectly with the traditional extent of federal authority. Yet in
most cases regulation of wetlands that are adjacent to tributaries and possess a significant
nexus with navigable waters will raise no serious constitutional or federalism difficulty.
Cf. Pierce County v. Guillen, 537 U. S. 129, 147 (2003) (upholding federal legislation
"aimed at improving safety in the channels of commerce"); Oklahoma ex rel. Phillips v.
Guy F. Atkinson Co., 313 U. S. 508, 524-525 (1941) ("[J]ust as control over the non-
navigable parts of a river may be essential or desirable in the interests of the navigable
portions, so may the key to flood control on a navigable stream be found in whole or in
part in flood control on its tributaries .... [T]he exercise of the granted power of
Congress to regulate interstate commerce may be aided by appropriate and needful
control of activities and agencies which, though intrastate, affect that commerce"). As
explained earlier, moreover, and as exemplified by SWANCC, the significant-nexus test
itself prevents problematic applications of the statute. See supra, at 19-20; 531 U. S., at
174. The possibility of legitimate Commerce Clause and federalism concerns in some
circumstances does not require the adoption of an interpretation that departs in all cases
from the Act's text and structure. See Gonzales v. Raich, 545 U. S. 1, (2005) (slip op.,
at 14) ("[W]hen a general regulatory statute bears a substantial relation to commerce, the
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de minimis character of individual instances arising under that statute is of no
consequence" (internal quotation marks omitted)).
Id. at 782-83.
Justice Stevens, in his dissent on behalf of four Justices, also addressed the issue of
Commerce Clause concerns and stated: "the plurality suggests that the canon of constitutional
avoidance applies because the Corps' approach might exceed the limits of our Commerce Clause
authority. Setting aside whether such a concern was proper in SWANCC, 531 U.S., at 173, 121 S.
Ct. 675, 148 L. Ed. 2d 576; but see id., at 192-196, 121 S. Ct. 675, 148 L. Ed. 2d 576 (Stevens,
J., dissenting), it is plainly not warranted here. The wetlands in these cases are not 'isolated' but
instead are adjacent to tributaries of traditionally navigable waters and play important roles in the
watershed, such as keeping water out of the tributaries or absorbing water from the tributaries.
'There is no constitutional reason why Congress cannot, under the commerce power, treat the
watersheds as a key to flood control on navigable streams and their tributaries." Oklahoma ex
rel. Phillips v. Guy F. Atkinson Co., 313 U.S. 508, 525, 61 S. Ct. 1050, 85 L. Ed. 1487 (1941).'"
Rapanos at 803-4.
Some commenters raise due process concerns with respect to case-specific significant
nexus determinations for one water in a watershed to bind other "similarly situated" waters in the
watershed. Justice Kennedy's standard itself establishes that whether a water significantly effects
the downstream water must be determined "alone or in combination" with other "similarly
situated" waters, so any consequences for "similarly situated" waters are a result of the
significant nexus standard. In addition, jurisdictional determinations are not final agency actions
so due process is not implicated. Any subsequent jurisdictional determinations with respect to
other "similarly situated" waters in the same region by an agency cannot be inconsistent with an
existing jurisdictional determination without explanation, but once the agency has taken a final
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agency action such as issuing a permit or denying a permit, a recipient has administrative and
judicial processes available to challenge the action including any underlying jurisdictional
determination. The Fifth and Ninth Circuits have held that a Corps' jurisdictional determination
was not a "final agency action" subject to judicial review under the Administrative Procedure
Act (APA). Belle Co. LLC v. Corps (retitled as Kent Recycling), 761 F.3d 383 (5th Cir. 2014);
Fairbanks N. Star Borough v. United States Army Corps ofEng'rs, 543 F.3d 586 (9th Cir. 2008),
cert, denied, 557 U.S. 919 (2009); but see Hawkes Co. v. U.S. Army Corps of Engineers, No. 13-
3067, 2015 WL 1600465 (8th Cir. Apr. 10, 2015).
The APA authorizes judicial review of "final agency action for which there is no other
adequate remedy in a court." 5 U.S.C. 704. Two conditions must be met for agency action to be
"final." Bennett, 520 U.S. at 177-178. "First, the action must mark the consummation of the
agency's decision making process—it must not be of a merely tentative or interlocutory nature.
And second, the action must be one by which rights or obligations have been determined, or
from which legal consequences will flow." Id. (internal citations and quotation marks omitted).
In Belle, the Fifth Circuit held that the Corps' jurisdictional determination was not "final agency
action" subject to judicial review under the APA. 761 F.3d 383. In reaching that conclusion, the
court applied the two requirements for "final agency action" identified by the Supreme Court in
Bennett v. Spear. 761 F.3d at 387. The Fifth Circuit concluded that the Corps' determination
satisfied the first Bennett requirement because "the Corps has asserted its final position on the
facts underlying jurisdiction—that is, the presence or absence on Belle's property of waters of
the United States as defined in the CWA." Id. The Fifth Circuit concluded, however, that the
Corps' jurisdictional determination did not satisfy Bennett's second requirement because it did
not impose obligations or legal consequences on petitioner and Belle. Id. The court explained
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that, when '"the action sought to be reviewed may have the effect of forbidding or compelling
conduct on the part of the person seeking to review it, but only if some further action is taken by
the [agency],' that action is nonfinal and nonreviewable because it 'does not of itself adversely
affect complainant but only affects his rights adversely on the contingency of future
administrative action.' " Id. (quoting Rochester Tel. Corp. v. United States, 307 U.S. 125, 129-
130 (1939), and citing FTC v. Standard Oil Co., 449 U.S. 232, 240- 241 (1980)). The court also
observed that it had previously held that a jurisdictional determination was not final. Id. at 388
(citing Greater Gulfport Props., LLC v. United States Army Corps o/Eng'rs, 194 Fed. Appx.
250, 250 (2006) (per curiam)). Therefore, the rule does not raise due process concerns.
Some commenters stated that the proposed rule, and the CWA itself, is void for vagueness
and fails to meet Constitutional requirement for due process. The Clean Water Act is not void
for vagueness. The Supreme Court has found that the term "waters of the United States" is
ambiguous in some respects, but has never found that the phrase "waters of the United States" is
void for vagueness. See Rapanos, 547 U.S. at 752 (plurality opinion), 804 (dissent). Indeed, in
light of that ambiguity, Chief Justice Roberts' concurrence in Rapanos emphasized that
"[ajgencies delegated rulemaking authority under a statute such as the Clean Water Act are
afforded generous leeway by the courts in interpreting the statute they are entrusted to
administer." Id. at 758.
The final rule also is not vague, clearly identifying waters that are jurisdictional, waters
that are not jurisdictional, and a limited set of waters for which case-specific significant nexus
analyses will be performed. Preamble, IV. Some commenters expressed concern that the terms
and definitions in the proposed rule were unclear or inadequately defined or requested additional
definitions of terms used in the proposed rule. The agencies responded to the suggestions for new
and amended definitions in various ways. In some cases, the terms are not used in the rule;
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therefore, the agencies did not provide definitions (e.g., riparian area, uplands). Other
clarifications were added to the preamble (e.g., ephemeral, intermittent, and perennial). In some
cases, the agencies also made changes directly to the rule to clarify definitions (e.g., significant
nexus). While the agencies considered other requests for definitions, the agencies reasonably
concluded that the rule and the preamble provide definitions and clarifications of the key terms
that demarcate the boundaries of CW A jurisdiction and provide for increased clarity, certainty
and consistent implementation. The agencies also concluded that attempting to add new
definitions for some terms, such as ditches, would actually introduce confusion. Preamble, IV.
Moreover, a regulation will not be deemed impermissibly vague as long as the standard is sufficient
to put the regulated party on notice as to what conduct is required. Brock v. L.R Willson & Sons,
Inc., 773 F.2d 1377, 1387 (D.C. Cir. 1985); see Komjathy v. National Transportation Safety Bd.,
832 F.2d 1294, 1296 (D.C. Cir. 1987), cert, denied, 486 U.S. 1057 (1988). This standard does not
require a precise definition for each phrase used. Thus, the Supreme Court has upheld statutes
prohibiting "excess profits," providing for "just and reasonable rates," proscribing "unfair methods of
competition," and requiring "fair and reasonable rent." Montgomery National Bank v. Clarke, 882
F.2d 87, 90 (3d Cir. 1989) (citing Lichter v. United States, 334 U.S. 742, 786 (1948) (collecting
cases). In Nat'I Oilseed Processors Ass'n v. OSHA, 769 F.3d 1173 (D.C. Cir 2014), the D.C.
Circuit rejected a challenge that OSHA violated the Due Process Clause because a final rule was
unconstitutionally vague on its face, holding: "The Final Rule satisfies Due Process because the
term 'combustible dust' is clear enough to provide fair warning of enforcement, and OSHA has
provided additional guidance on how the revised Hazard Communication Standard will be
enforced. 'If, by reviewing the regulations and other public statements issued by the agency, a
regulated party acting in good faith would be able to identify, with "ascertainable certainty," the
standards with which the agency expects parties to conform, then the agency has fairly notified a
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petitioner of the agency's interpretation.' Gen. Elec. Co. v. EPA, 53 F.3d 1324, 1329, 311 U.S.
App. D.C. 360 (D.C. Cir. 1995) (quoting Diamond Roofing Co. v. OSHRC, 528 F.2d 645, 649
(5th Cir. 1976)); see also Aeronautical Repair Station Ass 'n, Inc. v. FAA, 494 F.3d 161, 174, 377
U.S. App. D.C. 329 (D.C. Cir. 2007)." Again, by identifying waters that are jurisdictional,
waters that are not jurisdictional, and a limited set of waters for which case-specific significant
nexus analyses will be performed, the rule fairly notifies a regulated party acting in good faith of
the agencies' interpretation of "waters of the United States."
Some commenters stated that the proposed rule would result in regulatory takings, in
violation of the Fifth Amendment. The rule does not constitute a taking of private property in
violation of the Fifth Amendment. As a matter of law, an agency's determination of jurisdiction
cannot constitute a taking. See, e.g., United States v. Riverside Bayview Homes, 474 U.S. 121
(1985). Even if a finding of jurisdiction means that a property owner must obtain a permit, such a
requirement, by itself, does not constitute a taking. The existence of a permit system leaves open
the possibility that a landowner may be permitted to use the property as he or she wishes. Even
where a permit is denied, other economically viable uses of the land may be available to the
owner. Because the permit system leaves open a number of potential outcomes at any given
property, challenging the agency's permit requirement in the abstract is premature (or "unripe").
Under the CWA, any person discharging a pollutant from a point source into navigable waters
must obtain a permit. The rule clarifies which navigable waters trigger the permit requirement.
As stated by a unanimous Supreme Court in Riverside Bayview Homes, supra, "A requirement
that a person obtain a permit before engaging in a certain use of his or her property does not
itself 'take' the property in any sense: after all, the very existence of a permit system implies that
permission may be granted, leaving the landowner free to use the property as desired. Moreover,
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even if the permit is denied, there may be other viable uses available to the owner. Only when a
permit is denied and the effect of the denial is to prevent 'economically viable' use of the land in
question can it be said that a taking has occurred." 474 U.S. at 127, 106 S.Ct. at 459, 88 L.Ed.2d
419 (1985).
Some commenters also argued that the proposed rule violates Executive Order 12630,
takings assessments. EPA has fully complied with E.O. 12630. Moreover, by its terms, E.O.
12630 creates no right enforceable at law by a party against the agency. The Order is intended
"only to improve the internal management of the Executive Branch...."
Some commenters asserted that the rule violates the Tenth Amendment of the U.S.
Constitution. This rule does not violate the Tenth Amendment. Under the Tenth Amendment,
the Supreme Court has stated that for a federal activity to be limited under the commerce clause,
the "federal statute at issue must regulate 'the States as States.'" Garcia v. San Antonio
Metropolitan Transit Authority et al., 469 U.S. 528, 537 (1985), citing Hodel v. Virginia Surface
Mining & Recla. Assn., 452 U.S. 264 (1981). In New York v. United States, and specifically
citing the CWA as an example, the Court held that' [t]the Constitution enables the Federal
Government to pre-empt state regulation contrary to federal interests, and it permits the Federal
Government to hold out incentives to the States as a means of encouraging them to adopt
suggested regulatory schemes." However, "[t]he federal government may not compel the States
to enact or administer a federal regulatory program." New York v. United States, 505 U.S. 144,
158 (1992). The Court continued:
Where Congress has the authority to regulate private activity under the Commerce
Clause, we have recognized Congress' power to offer States the choice of regulating that
activity according to federal standards or having state law pre-empted by federal
regulation. . . . These include the Clean Water Act, 86 Stat. 816, as amended, 33 U.S.C. §
1251 et seq., see Arkansas v. Oklahoma, 503 U.S. 91, 101, 112 S.Ct. 1046, 1054, 117
L.Ed.2d 239 (1992) (Clean Water Act "anticipates a partnership between the States and
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the Federal Government, animated by a shared objective"); . . Id. at 166-167. See
also, Printz v. United States, 521 U.S. 898, 925 (1997).
Here, neither the rule nor the Act compel action on the part of the states to implement the
regulatory definition promulgated in the rule. Implementation programs such as permitting
programs under 402 or 404 of the Act, all of which are unchanged by and outside the scope of
the rule, will continue to be conducted by both the states and the agencies. Under Section 510 of
the CWA, the states may have other definitions than the federal definition subject to the
limitations in Section 510. While this rule does not compel the states to conform their definition
to the federal definition, the agencies recognize that the existence of a federal definition may
persuade the state to implement the federal definition, but this does not violate the Tenth
Amendment. Under New York, "there are a variety of methods, short of outright coercion, by
which Congress may urge a State to adopt a legislative program consistent with federal interests.
New York at 144. After citing two methods of persuasion, pre-emption or holding out incentives
to the States as a means of encouraging them to adopt suggested regulatory approaches, the
Court stated, "By either of these two methods, as by any other permissible method of
encouraging a State to conform to federal policy choices, the residents of the State retain the
ultimate decision as to whether or not the State will comply." New York at 145. In the case of
the Clean Water Rule, the existence of a federal definition may persuade some states to adopt the
same regulatory definition, but this is state action under state law; and therefore, the rule is
consistent with the Tenth Amendment. Because this rule does not regulate the "States as States,"
See e.g., Garcia at 537, or "compel the States to enact or administer a federal regulatory
program" see New York at 158, it does not violate the Tenth Amendment.
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II. Significant Nexus Analysis
With the rule, the agencies interpret the scope of the "waters of the United States" for the
CWA in light of the goals, objectives, and policies of the statute, the Supreme Court caselaw, the
relevant and currently available science, and the agencies' technical expertise and experience.
The key to the agencies' interpretation of the CWA is the significant nexus standard, as
established and refined in Supreme Court opinions: waters are "waters of the United States" if
they, either alone or in combination with similarly situated waters in the region, significantly
affect the chemical, physical, and biological integrity of traditional navigable waters, interstate
waters or the territorial seas. The agencies interpret specific aspects of the significant nexus
standard in light of the science, the law, and the agencies' technical expertise: the scope of the
region to assess when making a significant nexus determination; the waters to evaluate in
combination with each other; and the functions provided by waters and strength of those
functions, and when such waters significantly affect the chemical, physical, or biological
integrity of the downstream traditional navigable waters, interstate waters, or the territorial seas.
In the rule, the agencies determine that tributaries, as defined ("covered tributaries"), and
adjacent waters, as defined ("covered adjacent waters"), have a significant nexus to downstream
traditional navigable waters, interstate waters, and the territorial seas and therefore are "waters of
the United States." In the rule, the agencies also establish that defined sets of additional waters
may be determined to have a significant nexus on a case-specific basis: (1) five types of waters
that the agencies conclude are "similarly situated" and therefore must be analyzed "in
combination" in the watershed that drains to the nearest traditional navigable water, interstate
water, or the territorial seas when making a case-specific significant nexus analysis; and (2)
waters within the 100-year floodplain of traditional navigable waters, interstate waters, or the
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territorial seas and waters within 4,000 feet of the high tide line or ordinary high water mark of
traditional navigable waters, interstate waters, the territorial seas, impoundments or covered
tributaries. The rule establishes a definition of significant nexus, based on Supreme Court
opinions and the science, to use when making these case-specific determinations.
Significant nexus is not purely a scientific determination. Further, the opinions of the
Supreme Court have noted that as the agencies charged with interpreting the statute, EPA and the
Corps must develop the outer bounds of the scope of the CWA, while science does not provide
bright lines with respect to where "water ends" for purposes of the CWA. Therefore, the
agencies' interpretation of the CWA is informed by the Science Report and the review and
comments of the SAB, but not dictated by them.
With this context, this section of the Technical Support Document addresses in more
detail the relevant scientific conclusions reached by analysis of existing scientific literature and
the agencies' significant nexus determinations underpinning the rule. Specific sections of the
Technical Support Document below address in more detail the precise definitions of the covered
waters promulgated by the agencies to provide the bright lines identifying "waters of the United
States."
A. Science Report and Scientific Review
i. Science Report: Synthesis of Peer-Reviewed Scientific Literature
In preparation for this rule, more than 1,200 peer-reviewed scientific papers and other
data and information including jurisdictional determinations, relevant agency guidance and
implementation manuals, and federal and state reports that address connectivity of aquatic
resources and effects on downstream waters were reviewed and considered. EPA's Office of
Research and Development (ORD) prepared a peer-reviewed synthesis of published peer-
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reviewed scientific literature discussing the nature of connectivity and effects of tributaries and
wetlands on downstream waters. U.S. Environmental Protection Agency 2015, hereinafter,
"Science Report." The Science Report was directly considered in the development of this rule, as
was the peer review of the Science Report led by EPA's Scientific Advisory Board (SAB), and is
available at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=296414. The SAB peer review
is discussed in detail in section II. The Science Report also underwent an earlier external
independent peer review, and the results of both peer reviews are available in the docket for the
rule. Prior to the earlier peer review, the Science Report also underwent a peer consultation.
The Science Report summarizes and assesses relevant and currently available scientific
literature that is part of the administrative record for this rule. In addition, the agencies
considered other sources of scientific information and literature, particularly for topics that were
not addressed in the Science Report. This includes peer reviewed literature, federal and state
government reports, and other relevant information. As anticipated, additional data and
information became available during the rulemaking process, including that provided during the
public comment process, and by additional research, studies, and investigations that took place
before the rulemaking process concluded. The agencies have reviewed the entirety of the
completed administrative record, including the final Science Report reflecting SAB review, and
have made adjustments to the rule, as further described in the preamble. Section Il.a. of this
document provides the conclusions of the Science Report. Sections VI through IX provide
additional detail of the scientific literature and the agencies' reasoning in support of the rule.
The Science Report reviews and synthesizes the peer-reviewed scientific literature on the
connectivity or isolation of streams and wetlands relative to large water bodies such as rivers,
lakes, estuaries, and oceans. The purpose of the review and synthesis is to summarize current
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scientific understanding about the connectivity and mechanisms by which streams and wetlands,
singly or in aggregate, affect the physical, chemical, and biological integrity of downstream
waters. Specific types of connections considered in the Science Report include transport of
physical materials and chemicals such as water, wood, and sediment, nutrients, pesticides, and
mercury; movement of organisms or their seeds or eggs; and hydrologic and biogeochemical
interactions occurring in surface and groundwater flows, including hyporheic zones and alluvial
aquifers. A hyporheic zone is the area next to and beneath a stream or river in which hyporheic
flow (water from a stream or river channel that enters subsurface materials of the stream bed and
bank and then returns to the stream or river) occurs. Science Report at A-6. An alluvial aquifer is
an aquifer with geologic materials deposited by a stream or river (alluvium) that retains a
hydraulic connection with the depositing stream. Id. at A-l.
The Science Report consists of six chapters. Chapter 1 outlines the purpose, scientific
context, and approach of the report. Chapter 2 describes the components of a river system and
watershed; the types of physical, chemical, and biological connections that link those
components; the factors that influence connectivity at various temporal and spatial scales; and
methods for quantifying connectivity. Chapter 3 reviews literature on connectivity in stream
networks in terms of physical, chemical, and biological connections and their resulting effects on
downstream waters. Chapter 4 reviews literature on the connectivity and effects of nontidal
wetlands and certain open waters on downstream waters. Chapter 5 applies concepts and
evidence from previous chapters to six case studies from published literature on Carolina and
Delmarva bays, oxbow lakes, prairie potholes, prairie streams, southwestern streams, and vernal
pools. Chapter 6 summarizes key findings and conclusions, identifies data gaps, and briefly
discusses research approaches that could fill those gaps. A glossary of scientific terms used in the
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report and detailed case studies of selected systems (summarized in Chapter 5) are included in
Appendix A and Appendix B, respectively.
1. Summary of Major Conclusions
Based on the review and synthesis of more than 1,200 publications from the peer
reviewed scientific literature, the evidence supports five major conclusions. Citations have been
omitted from the text to improve readability; please refer to individual chapters of the Science
Report for supporting publications and additional information.
Conclusion 1: Streams
The scientific literature unequivocally demonstrates that streams, individually or
cumulatively, exert a strong influence on the integrity of downstream waters. All tributary
streams, including perennial, intermittent, and ephemeral streams, are physically, chemically,
and biologically connected to downstream rivers via channels and associated alluvial deposits
where water and other materials are concentrated, mixed, transformed, and transported. Streams
are the dominant source of water in most rivers, and the majority of tributaries are perennial,
intermittent, or ephemeral headwater streams. Headwater streams also convey water into local
storage compartments such as ponds, shallow aquifers, or stream banks, and into regional and
alluvial aquifers; these local storage compartments are important sources of water for
maintaining baseflow in rivers. In addition to water, streams transport sediment, wood, organic
matter, nutrients, chemical contaminants, and many of the organisms found in rivers. The
literature provides robust evidence that streams are biologically connected to downstream waters
by the dispersal and migration of aquatic and semiaquatic organisms, including fish, amphibians,
plants, microorganisms, and invertebrates, that use both upstream and downstream habitats
during one or more stages of their life cycles, or provide food resources to downstream
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communities. In addition to material transport and biological connectivity, ephemeral,
intermittent, and perennial flows influence fundamental biogeochemical processes by connecting
channels and shallow ground water with other landscape elements. Physical, chemical, and
biological connections between streams and downstream waters interact via integrative processes
such as nutrient spiraling, in which stream communities assimilate and chemically transform
large quantities of nitrogen and other nutrients that otherwise would be transported directly
downstream, increasing nutrient loads and associated impairments due to excess nutrients in
downstream waters.
Conclusion 2: Riparian/Floodplain Wetlands and Open Waters
The literature clearly shows that wetlands and open waters in riparian areas and
floodplains are physically, chemically, and biologically integrated with rivers via functions that
improve downstream water quality, including the temporary storage and deposition of channel-
forming sediment and woody debris, temporary storage of local ground water that supports
baseflow in rivers, and transformation and transport of stored organic matter. Riparian/floodplain
wetlands and open waters improve water quality through the assimilation, transformation, or
sequestration of pollutants, including excess nutrients and chemical contaminants such as
pesticides and metals, that can degrade downstream water integrity. In addition to providing
effective buffers to protect downstream waters from point source and nonpoint source pollution,
these systems form integral components of river food webs, providing nursery habitat for
breeding fish and amphibians, colonization opportunities for stream invertebrates, and
maturation habitat for stream insects. Lateral expansion and contraction of the river in its
floodplain result in an exchange of organic matter and organisms, including fish populations that
are adapted to use floodplain habitats for feeding and spawning during high water, that are
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critical to river ecosystem function. Riparian/floodplain wetlands and open waters also affect the
integrity of downstream waters by subsequently releasing (desynchronizing) floodwaters and
retaining large volumes of stormwater, sediment, and contaminants in runoff that could
otherwise negatively affect the condition or function of downstream waters.
Wetlands and open waters in non-floodplain landscape settings (hereafter called "non-
floodplain wetlands") provide numerous functions that benefit downstream water integrity.
These functions include storage of floodwater; recharge of ground water that sustains river
baseflow; retention and transformation of nutrients, metals, and pesticides; export of organisms
or reproductive propagules (e.g., seeds, eggs, spores) to downstream waters; and habitats needed
for stream species. This diverse group of wetlands (e.g., many prairie potholes, vernal pools,
playa lakes) can be connected to downstream waters through surface-water, shallow subsurface-
water, and groundwater flows and through biological and chemical connections.
In general, connectivity of non-floodplain wetlands occurs along a gradient (Conclusion
4), and can be described in terms of the frequency, duration, magnitude, timing, and rate of
change of water, material, and biotic fluxes to downstream waters. These descriptors are
influenced by climate, geology, and terrain, which interact with factors such as the magnitudes of
the various functions within wetlands (e.g., amount of water storage or carbon export) and their
proximity to downstream waters to determine where wetlands occur along the connectivity
gradient. At one end of this gradient, the functions of non-floodplain wetlands clearly affect the
condition of downstream waters if a visible (e.g., channelized) surface-water or a regular shallow
subsurface-water connection to the river network is present. For non-floodplain wetlands lacking
a channelized surface or regular shallow subsurface connection (i.e., those at intermediate points
along the gradient of connectivity), generalizations about their specific effects on downstream
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waters from the available literature are difficult because information on both function and
connectivity is needed. Although there is ample evidence that non-floodplain wetlands provide
hydrologic, chemical, and biological functions that affect material fluxes, to date, few scientific
studies explicitly addressing connections between non-floodplain wetlands and river networks
have been published in the peer-reviewed literature. Even fewer publications specifically focus
on the frequency, duration, magnitude, timing, or rate of change of these connections. In
addition, although areas that are closer to rivers and streams have a higher probability of being
connected than areas farther away when conditions governing the type and quantity of flows—
including soil infiltration rate, wetland storage capacity, hydraulic gradient, etc.—are similar,
information to determine if this similarity holds is generally not provided in the studies we
reviewed. Thus, current science does not support evaluations of the degree of connectivity for
specific groups or classes of wetlands (e.g., prairie potholes or vernal pools). Evaluations of
individual wetlands or groups of wetlands, however, could be possible through case-by-case
analysis.
Some effects of non-floodplain wetlands on downstream waters are due to their isolation,
rather than their connectivity. Wetland "sink" functions that trap materials and prevent their
export to downstream waters (e.g., sediment and entrained pollutant removal, water storage)
result because of the wetland's ability to isolate material fluxes. To establish that such functions
influence downstream waters, we also need to know that the wetland intercepts materials that
otherwise would reach the downstream water. The literature reviewed does provide limited
examples of direct effects of wetland isolation on downstream waters, but not for classes of
wetlands (e.g., vernal pools). Nevertheless, the literature reviewed supports the conclusion that
sink functions of non-floodplain wetlands, which result in part from their relative isolation, will
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affect a downstream water when these wetlands are situated between the downstream water and
known point or nonpoint sources of pollution, and thus intersect flowpaths between the pollutant
source and downstream waters.
Conclusion 4: Degrees and Determinants of Connectivity
Watersheds are integrated at multiple spatial and temporal scales by flows of surface
water and ground water, transport and transformation of physical and chemical materials, and
movements of organisms. Although all parts of a watershed are connected to some degree—by
the hydrologic cycle or dispersal of organisms, for example—the degree and downstream effects
of those connections vary spatially and temporally, and are determined by characteristics of the
physical, chemical, and biological environments and by human activities.
Stream and wetland connections have particularly important consequences for
downstream water integrity. Most of the materials—broadly defined as any physical, chemical,
or biological entity—in rivers, for example, originate from aquatic ecosystems located upstream
or elsewhere in the watershed. Longitudinal flows through ephemeral, intermittent, and perennial
stream channels are much more efficient for transport of water, materials, and organisms than
diffuse overland flows, and areas that concentrate water provide mechanisms for the storage and
transformation, as well as transport, of materials.
Connectivity of streams and wetlands to downstream waters occurs along a continuum
that can be described in terms of the frequency, duration, magnitude, timing, and rate of change
of water, material, and biotic fluxes to downstream waters. These terms, which are referred to
collectively as connectivity descriptors, characterize the range over which streams and wetlands
vary and shift along the connectivity gradient in response to changes in natural and
anthropogenic factors and, when considered in a watershed context, can be used to predict
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probable effects of different degrees of connectivity over time. The evidence unequivocally
demonstrates that the stream channels and riparian/floodplain wetlands or open waters that
together form river networks are clearly connected to downstream waters in ways that
profoundly influence downstream water integrity. The connectivity and effects of non-floodplain
wetlands and open waters are more variable and thus more difficult to address solely from
evidence available in peer-reviewed studies.
Variations in the degree of connectivity influence the range of functions provided by
streams and wetlands, and are critical to the integrity and sustainability of downstream waters.
Connections with low values of one or more descriptors (e.g., low-frequency, low-duration
streamflows caused by flash floods) can have important downstream effects when considered in
the context of other descriptors (e.g., large magnitude of water transfer). At the other end of the
frequency range, high-frequency, low-magnitude vertical (surface-subsurface) and lateral flows
contribute to aquatic biogeochemical processes, including nutrient and contaminant
transformation and organic matter accumulation. The timing of an event can alter both
connectivity and the magnitude of its downstream effect. For example, when soils become
saturated by previous rainfall events, even low or moderate rainfall can cause streams or
wetlands to overflow, transporting water and materials to downstream waters. Fish that use
nonperennial or perennial headwater stream habitats to spawn or rear young, and invertebrates
that move into seasonally inundated floodplain wetlands prior to emergence, have life cycles that
are synchronized with the timing of flows, temperature thresholds, and food resource availability
in those habitats.
Conclusion 5: Cumulative Effects
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The incremental effects of individual streams and wetlands are cumulative across entire
watersheds and therefore must be evaluated in context with other streams and wetlands.
Downstream waters are the time-integrated result of all waters contributing to them. For
example, the amount of water or biomass contributed by a specific ephemeral stream in a given
year might be small, but the aggregate contribution of that stream over multiple years, or by all
ephemeral streams draining that watershed in a given year or over multiple years, can have
substantial consequences on the integrity of the downstream waters. Similarly, the downstream
effect of a single event, such as pollutant discharge into a single stream or wetland, might be
negligible but the cumulative effect of multiple discharges could degrade the integrity of
downstream waters.
In addition, when considering the effect of an individual stream or wetland, all
contributions and functions of that stream or wetland should be evaluated cumulatively. For
example, the same stream transports water, removes excess nutrients, mitigates flooding, and
provides refuge for fish when conditions downstream are unfavorable; if any of these functions is
ignored, the overall effect of that stream would be underestimated.
2. Discussion of Major Conclusions
The Science Report synthesizes a large body of scientific literature on the connectivity
and mechanisms by which streams, wetlands, and open waters, singly or in aggregate, affect the
physical, chemical, and biological integrity of downstream waters. The major conclusions reflect
the strength of evidence currently available in the peer-reviewed scientific literature for assessing
the connectivity and downstream effects of water bodies identified in Chapter 1 of the Science
Report.
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The conclusions of the Science Report were corroborated by two independent peer
reviews by scientists identified in the front matter of the Science Report.
The term connectivity is defined in the Science Report as the degree to which
components of a watershed are joined and interact by transport mechanisms that function across
multiple spatial and temporal scales. Connectivity is determined by the characteristics of both the
physical landscape and the biota of the specific system. ORD's review found strong evidence
supporting the central roles of the physical, chemical, and biological connectivity of streams,
wetlands, and open waters—encompassing varying degrees of both connection and isolation—in
maintaining the structure and function of downstream waters, including rivers, lakes, estuaries,
and oceans. ORD's review also found strong evidence demonstrating the various mechanisms by
which material and biological linkages from streams, wetlands, and open waters affect
downstream waters, classified here into five functional categories (source, sink, refuge, lag, and
transformation; discussed below), and modify the timing of transport and the quantity and quality
of resources available to downstream ecosystems and communities. Thus, the currently available
literature provided a large body of evidence for assessing the types of connections and functions
by which streams and wetlands produce the range of observed effects on the integrity of
downstream waters.
ORD identified five categories of functions by which streams, wetlands, and open waters
influence the timing, quantity, and quality of resources available to downstream waters:
• Source: the net export of materials, such as water and food resources;
• Sink: the net removal or storage of materials, such as sediment and contaminants;
• Refuge: the protection of materials, especially organisms;
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• Transformation: the transformation of materials, especially nutrients and chemical
contaminants, into different physical or chemical forms; and
• Lag: the delayed or regulated release of materials, such as stormwater.
These functions are not mutually exclusive; for example, the same stream or wetland can
be both a source of organic matter and a sink for nitrogen. The presence or absence of these
functions, which depend on the biota, hydrology, and environmental conditions in a watershed,
can change over time; for example, the same wetland can attenuate runoff during storm events
and provide groundwater recharge following storms. Further, some functions work in
conjunction with others; a lag function can include transformation of materials prior to their
delayed release. Finally, effects on downstream waters should consider both actual function and
potential function. A potential function represents the capacity of an ecosystem to perform that
function under suitable conditions. For example, a wetland with high capacity for denitrification
is a potential sink for nitrogen, a nutrient that becomes a contaminant when present in excessive
concentrations. In the absence of nitrogen, this capacity represents the wetland's potential
function. If nitrogen enters the wetland (e.g., from fertilizer in runoff), it is removed from the
water; this removal represents the wetland's actual function. Both potential and actual functions
play critical roles in protecting and restoring downstream waters as environmental conditions
change.
The evidence unequivocally demonstrates that the stream channels and
riparian/floodplain wetlands or open waters that together form river networks are clearly
connected to downstream waters in ways that profoundly influence downstream water integrity.
The body of literature documenting connectivity and downstream effects was most abundant for
perennial and intermittent streams, and for riparian/floodplain wetlands. Although less abundant,
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the evidence for connectivity and downstream effects of ephemeral streams was strong and
compelling, particularly in context with the large body of evidence supporting the physical
connectivity and cumulative effects of channelized flows that form and maintain stream
networks.
As stated in Conclusion 3, the connectivity and effects of wetlands and open waters that
lack visible surface connections to other water bodies are more difficult to address solely from
evidence available in the peer-reviewed literature. The limited evidence currently available
shows that these systems have important hydrologic, water-quality, and habitat functions that can
affect downstream waters where connections to them exist; the literature also provides limited
examples of direct effects of non-floodplain wetland isolation on downstream water integrity.
Currently available peer-reviewed literature, however, does not identify which types or classes of
non-floodplain wetlands have or lack the types of connections needed to convey the effects on
downstream waters of functions, materials, or biota provided by those wetlands.
3. Key Findings for Major Conclusions
This section summarizes key findings for each of the five major conclusions, above and
in Chapter 6 of the Science Report. Citations have been omitted from the text to improve
readability; please refer to individual chapters of the Science Report for supporting publications
and additional information.
Conclusion 1, Streams: Key Findings
• Streams are hydrologically connected to downstream waters via channels that convey
surface and subsurface water either year-round {i.e., perennial flow), weekly to
seasonally {i.e., intermittent flow), or only in direct response to precipitation (i.e.,
ephemeral flow). Streams are the dominant source of water in most rivers, and the
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majority of tributaries are perennial, intermittent, or ephemeral headwater streams. For
example, headwater streams, which are the smallest channels where streamflows begin,
are the cumulative source of approximately 60% of the total mean annual flow to all
northeastern U.S. streams and rivers.
• In addition to downstream transport, headwaters convey water into local storage
compartments such as ponds, shallow aquifers, or stream banks, and into regional and
alluvial aquifers. These local storage compartments are important sources of water for
maintaining baseflow in rivers. Streamflow typically depends on the delayed (i.e.,
lagged) release of shallow ground water from local storage, especially during dry periods
and in areas with shallow groundwater tables and pervious subsurfaces. For example, in
the southwestern United States, short-term shallow groundwater storage in alluvial
floodplain aquifers, with gradual release into stream channels, is a major source of annual
flow in rivers.
• Infrequent, high-magnitude events are especially important for transmitting materials
from headwater streams in most river networks. For example, headwater streams,
including ephemeral and intermittent streams, shape river channels by accumulating and
gradually or episodically releasing stored materials such as sediment and large woody
debris. These materials help structure stream and river channels by slowing the flow of
water through channels and providing substrate and habitat for aquatic organisms.
• There is strong evidence that headwater streams function as nitrogen sources (via export)
and sinks (via uptake and transformation) for river networks. For example, one study
estimated that rapid nutrient cycling in small streams with no agricultural or urban
impacts removed 20-40% of the nitrogen that otherwise would be delivered to
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downstream waters. Nutrients are necessary to support aquatic life, but excess nutrients
lead to eutrophication and hypoxia, in which over-enrichment causes dissolved oxygen
concentrations to fall below the level necessary to sustain most aquatic animal life in the
stream and streambed. Thus, the influence of streams on nutrient loads can have
significant repercussions for hypoxia in downstream waters.
• Headwaters provide habitat that is critical for completion of one or more life-cycle stages
of many aquatic and semiaquatic species capable of moving throughout river networks.
Evidence is strong that headwaters provide habitat for complex life-cycle completion;
refuge from predators, competitors, parasites, or adverse physical conditions in rivers
(e.g., temperature or flow extremes, low dissolved oxygen, high sediment); and reservoirs
of genetic- and species-level diversity. Use of headwater streams as habitat is especially
critical for the many species that migrate between small streams and marine
environments during their life cycles (e.g., Pacific and Atlantic salmon, American eels,
certain lamprey species). The presence of these species within river networks provides
robust evidence of biological connections between headwaters and larger rivers; because
these organisms also transport nutrients and other materials as they migrate, their
presence also provides evidence of biologically mediated chemical connections. In prairie
streams, many fishes swim upstream into tributaries to release eggs, which develop as
they are transported downstream.
• Human alterations affect the frequency, duration, magnitude, timing, and rate of change
of connections between headwater streams, including ephemeral and intermittent streams,
and downstream waters. Human activities and built structures (e.g., channelization, dams,
groundwater withdrawals) can either enhance or fragment longitudinal connections
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between headwater streams and downstream waters, while also constraining lateral and
vertical exchanges and tightly controlling the temporal dimension of connectivity. In
many cases, research on human alterations has enhanced our understanding of the
headwater stream-downstream water connections and their consequences. Recognition of
these connections and effects has encouraged the development of more sustainable
practices and infrastructure to reestablish and manage connections, and ultimately to
protect and restore the integrity of downstream waters.
Conclusion 2, Riparian/Floodplain Wetlands and Open Waters: Key Findings
• Riparian areas and floodplains connect upland and aquatic environments through both
surface and subsurface hydrologic flowpaths. These areas are therefore uniquely situated
in watersheds to receive and process waters that pass over densely vegetated areas and
through subsurface zones before the waters reach streams and rivers. When pollutants
reach a riparian or floodplain wetland, they can be sequestered in sediments, assimilated
into wetland plants and animals, transformed into less harmful or mobile forms or
compounds, or lost to the atmosphere. A wetland's potential for biogeochemical
transformations (e.g., denitrification) that can improve downstream water quality is
influenced by local factors, including anoxic conditions and slow organic matter
decomposition, shallow water tables, wetland plant communities, permeable soils, and
complex topography.
• Riparian/floodplain wetlands can reduce flood peaks by storing and desynchronizing
floodwaters. They can also maintain river baseflows by recharging alluvial aquifers.
Many studies have documented the ability of riparian/floodplain wetlands to reduce flood
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pulses by storing excess water from streams and rivers. One review of wetland studies
reported that riparian wetlands reduced or delayed floods in 23 of 28 studies. For
example, peak discharges between upstream and downstream gaging stations on the
Cache River in Arkansas were reduced 10-20% primarily due to floodplain water
storage.
• Riparian areas and floodplains store large amounts of sediment and organic matter from
upstream and from upland areas. For example, riparian areas have been shown to remove
80-90% of sediments leaving agricultural fields in North Carolina.
• Ecosystem function within a river system is driven in part by biological connectivity that
links diverse biological communities with the river system. Movements of organisms that
connect aquatic habitats and their populations, even across different watersheds, are
important for the survival of individuals, populations, and species, and for the functioning
of the river ecosystem. For example, lateral expansion and contraction of the river in its
floodplain result in an exchange of matter and organisms, including fish populations that
are adapted to use floodplain habitats for feeding and spawning during high water.
Wetland and aquatic plants in floodplains can become important seed sources for the
river network, especially if catastrophic flooding scours vegetation and seed banks in
other parts of the channel. Many invertebrates exploit temporary hydrologic connections
between rivers and floodplain wetland habitats, moving into these wetlands to feed,
reproduce, or avoid harsh environmental conditions and then returning to the river
network. Amphibians and aquatic reptiles commonly use both streams and
riparian/floodplain wetlands to hunt, forage, overwinter, rest, or hide from predators.
Birds can spatially integrate the watershed landscape through biological connectivity.
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Conclusion 3, Non-floodplain Wetlands and Open Waters: Key Findings
• Water storage by wetlands well outside of riparian or floodplain areas can affect
streamflow. Hydrologic models of prairie potholes in the Starkweather Coulee subbasin
(North Dakota) that drains to Devils Lake indicate that increasing the volume of prairie
pothole storage across the subbasin by approximately 60% caused simulated total annual
streamflow to decrease 50% during a series of dry years and 20% during wet years.
Similar simulation studies of watersheds that feed the Red River of the North in North
Dakota and Minnesota demonstrated qualitatively comparable results, suggesting that the
ability of prairie potholes to modulate streamflow could be widespread across eastern
portions of the prairie pothole region. This work also indicates that reducing water
storage capacity of wetlands by connecting formerly isolated prairie potholes through
ditching or drainage to the Devils Lake and Red River basins could increase stormflow
and contribute to downstream flooding. In many agricultural areas already crisscrossed
by extensive drainage systems, total streamflow and baseflow are increased by directly
connecting prairie potholes to stream networks. The impacts of changing streamflow are
numerous, including altered flow regime, stream geomorphology, habitat, and ecology.
The presence or absence of an effect of prairie pothole water storage on streamflow
depends on many factors, including patterns of precipitation, topography, and degree of
human alteration. For example, in parts of the prairie pothole region with low
precipitation, low stream density, and little human alteration, hydrologic connectivity
between prairie potholes and streams or rivers is likely to be low.
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• Non-floodplain wetlands act as sinks and transformers for various pollutants, especially
nutrients, which at excess levels can adversely impact human and ecosystem health and
pose a serious pollution problem in the United States. In one study, sewage wastewaters
were applied to forested wetlands in Florida for 4.5 years; more than 95% of the
phosphorus, nitrate, ammonium, and total nitrogen were removed by the wetlands during
the study period, and 66-86% of the nitrate removed was attributed to the process of
denitrification (chemical and biological processes that remove nitrogen from water). In
another study, sizeable phosphorus retention occurred in marshes that comprised only 7%
of the lower Lake Okeechobee basin area in Florida. A non-floodplain bog in
Massachusetts was reported to sequester nearly 80% of nitrogen inputs from various
sources, including atmospheric deposition, and prairie pothole wetlands in the upper
Midwest were found to remove >80% of the nitrate load via denitrification. A large
prairie marsh was found to remove 86% of nitrate, 78% of ammonium, and 20% of
phosphate through assimilation and sedimentation, sorption, and other mechanisms.
Together, these and other studies indicate that onsite nutrient removal by non-floodplain
wetlands is substantial and geographically widespread. The effects of this removal on
rivers are generally not reported in the literature.
• Non-floodplain wetlands provide unique and important habitats for many species, both
common and rare. Some of these species require multiple types of waters to complete
their full life cycles, including downstream waters. Abundant or highly mobile species
play important roles in transferring energy and materials between non-floodplain
wetlands and downstream waters.
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• Biological connections are likely to occur between most non-floodplain wetlands and
downstream waters through either direct or stepping stone movement of amphibians,
invertebrates, reptiles, mammals, and seeds of aquatic plants, including colonization by
invasive species. Many species in those groups that use both stream and wetland habitats
are capable of dispersal distances equal to or greater than distances between many
wetlands and river networks. Migratory birds can be an important vector of long-distance
dispersal of plants and invertebrates between non-floodplain wetlands and the river
network, although their influence has not been quantified. Whether those connections are
of sufficient magnitude to impact downstream waters will either require estimation of the
magnitude of material fluxes or evidence that these movements of organisms are required
for the survival and persistence of biota that contribute to the integrity of downstream
waters.
• Spatial proximity is one important determinant of the magnitude, frequency and duration
of connections between wetlands and streams that will ultimately influence the fluxes of
water, materials and biota between wetlands and downstream waters. However,
proximity alone is not sufficient to determine connectivity, due to local variation in
factors such as slope and permeability.
• The cumulative influence of many individual wetlands within watersheds can strongly
affect the spatial scale, magnitude, frequency, and duration of hydrologic, biological and
chemical fluxes or transfers of water and materials to downstream waters. Because of
their aggregated influence, any evaluation of changes to individual wetlands should be
considered in the context of past and predicted changes (e.g., from climate change) to
other wetlands within the same watershed.
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• Non-floodplain wetlands can be hydrologically connected directly to river networks
through natural or constructed channels, nonchannelized surface flows, or subsurface
flows, the latter of which can travel long distances to affect downstream waters. A
wetland surrounded by uplands is defined as "geographically isolated." Our review found
that, in some cases, wetland types such as vernal pools and coastal depressional wetlands
are collectively—and incorrectly—referred to as geographically isolated. Technically, the
term "geographically isolated" should be applied only to the particular wetlands within a
type or class that are completely surrounded by uplands. Furthermore, "geographic
isolation" should not be confused with functional isolation, because geographically
isolated wetlands can still have hydrologic, chemical, and biological connections to
downstream waters.
• Non-floodplain wetlands occur along a gradient of hydrologic connectivity-isolation with
respect to river networks, lakes, or marine/estuarine water bodies. This gradient includes,
for example, wetlands that serve as origins for stream channels that have permanent
surface-water connections to the river network; wetlands with outlets to stream channels
that discharge to deep groundwater aquifers; geographically isolated wetlands that have
local groundwater or occasional surface-water connections to downstream waters; and
geographically isolated wetlands that have minimal hydrologic connection to other water
bodies (but which could include surface and subsurface connections to other wetlands).
This gradient can exist among wetlands of the same type or in the same geographic
region.
• Caution should be used in interpreting connectivity for wetlands that have been
designated as "geographically isolated" because (1) the term can be applied broadly to a
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heterogeneous group of wetlands, which can include wetlands that are not actually
geographically isolated; (2) wetlands with permanent channels could be miscategorized
as geographically isolated if the designation is based on maps or imagery with inadequate
spatial resolution, obscured views, etc.; and (3) wetland complexes could have
connections to downstream waters through stream channels even if individual wetlands
within the complex are geographically isolated. For example, a recent study examined
hydrologic connectivity in a complex of wetlands on the Texas Coastal Plain. The
wetlands in this complex have been considered to be a type of geographically isolated
wetland; however, collectively they are connected both geographically and
hydrologically to downstream waters in the area: During an almost 4-year study period,
nearly 20% of the precipitation that fell on the wetland complex flowed out through an
intermittent stream into downstream waters. Thus, wetland complexes could have
connections to downstream waters through stream channels even when the individual
wetland components are geographically isolated.
Conclusion 4, Degrees and Determinants of Connectivity: Key Findings
• The surface-water and groundwater flowpaths (hereafter, hydrologic flowpaths), along
which water and materials are transported and transformed, determine variations in the
degree of physical and chemical connectivity. These flowpaths are controlled primarily
by variations in climate, geology, and terrain within and among watersheds and over
time. Climate, geology, and terrain are reflected locally in factors such as rainfall and
snowfall intensity, soil infiltration rates, and the direction of groundwater flows. These
local factors interact with the landscape positions of streams and wetlands relative to
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downstream waters, and with functions (such as the removal or transformation of
pollutants) performed by those streams and wetlands to determine connectivity gradients.
• Gradients of biological connectivity (i.e., the active or passive movements of organisms
through water or air and over land that connect populations) are determined primarily by
species assemblages, and by features of the landscape (e.g., climate, geology, terrain) that
facilitate or impede the movement of organisms. The temporal and spatial scales at which
biological pathways connect aquatic habitats depend on characteristics of both the
landscape and species, and overland transport or movement can occur across watershed
boundaries. Dispersal is essential for population persistence, maintenance of genetic
diversity, and evolution of aquatic species. Consequently, dispersal strategies reflect
aquatic species' responses and adaptations to biotic and abiotic environments, including
spatial and temporal variation in resource availability and quality. Species' traits and
behaviors encompass species-environment relationships over time, and provide an
ecological and evolutionary context for evaluating biological connectivity in a particular
watershed or group of watersheds.
• Pathways for chemical transport and transformation largely follow hydrologic flowpaths,
but sometimes follow biological pathways (e.g., nutrient transport from wetlands to
coastal waters by migrating waterfowl, upstream transport of marine-derived nutrients by
spawning of anadromous fish, uptake and removal of nutrients by emerging stream
insects).
• Human activities alter naturally occurring gradients of physical, chemical, and biological
connectivity by modifying the frequency, duration, magnitude, timing, and rate of change
of fluxes, exchanges, and transformations. For example, connectivity can be reduced by
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dams, levees, culverts, water withdrawals, and habitat destruction, and can be increased
by effluent discharges, channelization, drainage ditches and tiles, and impervious
surfaces.
Conclusion 5, Cumulative Effects: Key Findings
• Structurally and functionally, stream-channel networks and the watersheds they drain are
fundamentally cumulative in how they are formed and maintained. Excess water from
precipitation that is not evaporated, taken up by organisms, or stored in soils and geologic
layers moves downgradient by gravity as overland flow or through channels carrying
sediment, chemical constituents, and organisms. These channels concentrate surface-
water flows and are more efficient than overland (i.e., diffuse) flows in transporting water
and materials, and are reinforced over time by recurrent flows.
• Connectivity between streams and rivers provides opportunities for materials, including
nutrients and chemical contaminants, to be transformed chemically as they are
transported downstream. Although highly efficient at the transport of water and other
physical materials, streams are dynamic ecosystems with permeable beds and banks that
interact with other ecosystems above and below the surface. The exchange of materials
between surface and subsurface areas involves a series of complex physical, chemical,
and biological alterations that occur as materials move through different parts of the river
system. The amount and quality of such materials that eventually reach a river are
determined by the aggregate effect of these sequential alterations that begin at the source
waters, which can be at some distance from the river. The opportunity for transformation
of material (e.g., biological uptake, assimilation, or beneficial transformation) in
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intervening stream reaches increases with distance to the river. Nutrient spiraling, the
process by which nutrients entering headwater streams are transformed by various
aquatic organisms and chemical reactions as they are transported downstream, is one
example of an instream alteration that exhibits significant beneficial effects on
downstream waters. Nutrients (in their inorganic form) that enter a headwater stream
(e.g., via overland flow) are first removed from the water column by streambed algal and
microbial populations. Fish or insects feeding on algae and microbes take up some of
those nutrients, which are subsequently released back into the stream via excretion and
decomposition (i.e., in their organic form), and the cycle is repeated. In each phase of the
cycling process—from dissolved inorganic nutrients in the water column, through
microbial uptake, subsequent transformations through the food web, and back to
dissolved nutrients in the water column—nutrients are subject to downstream transport.
Stream and wetland capacities for nutrient cycling have important implications for the
form and concentration of nutrients exported to downstream waters.
• Cumulative effects across a watershed must be considered when quantifying the
frequency, duration, and magnitude of connectivity, to evaluate the downstream effects of
streams and wetlands. For example, although the probability of a large-magnitude
transfer of organisms from any given headwater stream in a given year might be low (i.e.,
a low-frequency connection when each stream is considered individually), headwater
streams are the most abundant type of stream in most watersheds. Thus, the overall
probability of a large-magnitude transfer of organisms is higher when considered for all
headwater streams in a watershed—that is, a high-frequency connection is present when
headwaters are considered cumulatively at the watershed scale, compared with
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probabilities of transport for streams individually. Similarly, a single pollutant discharge
might be negligible but the cumulative effect of multiple discharges could degrade the
integrity of downstream waters. Riparian open waters (e.g., oxbow lakes), wetlands, and
vegetated areas cumulatively can retain up to 90% of eroded clays, silts, and sands that
otherwise would enter stream channels. The larger amounts of snowmelt and
precipitation cumulatively held by many wetlands can reduce the potential for flooding at
downstream locations. For example, wetlands in the prairie pothole region cumulatively
stored about 11-20% of the precipitation in one watershed.
• The combination of diverse habitat types and abundant food resources cumulatively
makes floodplains important foraging, hunting, and breeding sites for fish, aquatic life
stages of amphibians, and aquatic invertebrates. The scale of these cumulative effects can
be extensive; for example, coastal ibises travel up to 40 km to obtain food from
freshwater floodplain wetlands for nesting chicks, which cannot tolerate salt levels in
local food resources until they fledge.
4. Science Report: Framework for Analysis
In support of the conclusions addressed above in this section, Chapter 2 of the Science
Report essentially provides the framework for the analysis by describing the components of a
river system and watershed; the types of physical, chemical, and biological connections that link
those components; the factors that influence connectivity at various temporal and spatial scales;
and methods for quantifying connectivity. In addition, Chapter 1 of the Science Report
introduces the approach used for the analysis of the peer-reviewed literature. Justice Kennedy's
opinion in Rapanos established the framework for a significant nexus analysis that mirrors the
framework through which scientists assess a river system - examining how the components of
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the system (e.g., wetlands), in the aggregate (in combination), in the watershed (in the region),
contribute and connect to the river (significantly affect the chemical, physical, or biological
integrity of the river). While some commenters stated that the agencies' proposed rule asserted
jurisdiction simply based on "any hydrologic connection," this framework, and the Science
Report and preamble, demonstrate that the agencies instead undertook a very thorough analysis
of the complex interactions between upstream waters and wetlands and the downstream river in
order to reach the significant nexus conclusions underlying the provisions of the rule.
To identify connections and effects of streams, wetlands, and other water bodies on
downstream waters, the Science Report used two types of evidence from peer-reviewed,
published literature: (1) direct evidence that demonstrated a connection or effect (e.g., observed
transport of materials or movement of organisms from streams or wetlands to downstream
waters) and (2) indirect evidence that suggested a connection or effect (e.g., presence of
environmental factors known to influence connectivity, a gradient of impairment associated with
cumulative loss of streams or wetlands). In some cases, an individual line of evidence
demonstrated connections along the entire river network (e.g., from headwaters to large rivers).
In most cases, multiple sources of evidence were gathered and conclusions drawn via logical
inference—for example, when one body of evidence shows that headwater streams are connected
to downstream segments, another body of evidence shows those downstream segments are linked
to other segments farther downstream, and so on. This approach, which borrows from weight-of-
evidence approaches in causal analysis is an effective way to synthesize the diversity of evidence
needed to address questions at larger spatial and longer temporal scales than are often considered
in individual scientific studies. Science Report at 1-14, 1-16 (citing Suter etal. 2002; Suter and
Cormier 2011).
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A river is the time-integrated result of all waters contributing to it, and connectivity is the
property that spatially integrates the individual components of the watershed. In discussions of
connectivity, the watershed scale is the appropriate context for interpreting technical evidence
about individual watershed components. Science Report at 2-1 (citing Newbold et al. 1982b;
Stanford and Ward 1993; Bunn and Arthington 2002; Power and Dietrich 2002; Benda et al.
2004; Naiman et al. 2005; Nadeau and Rains 2007; Rodriguez-Iturbe et al. 2009). Such
interpretation requires that freshwater resources be viewed within a landscape—or systems—
context. Id. (citing Baron et al. 2002). Addressing the questions asked in the Science Report,
therefore, requires an integrated systems perspective that considers both the components
contributing to the river and the connections between those components and the river.
Components of the River System
In the Science Report, the term river refers to a relatively large volume of flowing water
within a visible channel, including subsurface water moving in the same direction as the surface
water and lateral flows exchanged with associated floodplain and riparian areas. Id. at 2-2
(Naiman and Bilby 1998). Channels are natural or constructed passageways or depressions of
perceptible linear extent that convey water and associated materials downgradient. They are
defined by the presence of continuous bed and bank structures, or uninterrupted (but permeable)
bottom and lateral boundaries. Although bed and bank structures might in places appear to be
disrupted (e.g., bedrock outcrops, braided channels, flow-through wetlands), the continuation of
the bed and banks downgradient from such disruptions is evidence of the surface connection with
the channel that is upgradient of the perceived disruption. Such disruptions are associated with
changes in the gradient and in the material over and through which the water flows. If a
disruption in the bed and bank structure prevented connection, the area downgradient would lack
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a bed and banks, be colonized with terrestrial vegetation, and be indiscernible from the nearby
land. The concentrated longitudinal movement of water and sediment through these channels
lowers local elevation, prevents soil development, selectively transports and stores sediment, and
hampers the colonization and persistence of terrestrial vegetation. Streams are defined in a
similar manner as rivers: a relatively small volume of flowing water within a visible channel,
including subsurface water moving in the same direction as the surface water and lateral flows
exchanged with associated floodplain and riparian areas. Id. (citing Naiman and Bilby 1998).
A river network is a hierarchical, interconnected population of channels that drains
surface and subsurface water from a watershed to a river and includes the river itself. Watershed
boundaries traditionally are defined topographically, such as by ridges. These channels can
convey water year-round, weekly to seasonally, or only in direct response to rainfall and
snowmelt. Id. (citing Frissell et al. 1986; Benda et al. 2004). The smallest of these channels,
where streamflows begin, are considered headwater streams. Headwater streams are first- to
third-order streams, where stream order is a classification system based on the position of the
stream in the river network. Id. (citing Strahler 1957; Vannote et al. 1980; Meyer and Wallace
2001; Gomi et al. 2002; Fritz et al. 2006b; Nadeau and Rains 2007). The point at which stream
or river channels intersect within a river network is called a confluence. The confluence of two
streams with the same order results in an increase of stream order {i.e., two first-order streams
join to form a second-order stream, two second-order streams join to form a third-order stream,
and so on); when streams of different order join, the order of the larger stream is retained.
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Terminal and lateral source streams7 typically originate at channel heads, which occur
where surface-water runoff is sufficient to erode a definable channel. Id. at 2-3 (citing Dietrich
and Dunne 1993). The channel head denotes the upstream extent of a stream's continuous bed
and banks structure. Channel heads are relatively dynamic zones in river networks, as their
position can advance upslope by overland or subsurface flow-driven erosion, or retreat
downslope by colluvial infilling. Source streams also can originate at seeps or springs and
associated wetlands.
When two streams join at a confluence, the smaller stream (i.e., that with the smaller
drainage area or lower mean annual discharge) is called a tributary of the larger stream, which is
referred to as the mainstem. A basic way of classifying tributary contributions to a mainstem is
the symmetry ratio, which describes the size of a tributary relative to the mainstem at their
confluence, in terms of their respective discharges, drainage areas, or channel widths. Id. at 2-4
(citing Roy and Woldenberg 1986; Rhoads 1987; Benda 2008).
Surface-water hydrologic connectivity within river network channels occurs, in part,
through the unidirectional movement of water from channels at higher elevations to ones at
lower elevations—that is, hydrologic connectivity exists because water flows downhill. In
essence, the river network represents the aboveground flow route and associated subsurface-
water interactions, transporting water, energy, and materials from the surrounding watershed to
downstream rivers, lakes, estuaries, and oceans (The River Continuum Concept). Id. (citing
(Vannote et al. 1980).
H
Mock (1971) presented a classification of the streams comprising stream or river networks. He designated first-
order streams that intersect other first-order streams as sources. We refer to these as terminal source streams. Mock
defined first-order streams that flow into higher order streams as tributary sources, and we refer to this class of
streams as lateral source streams.
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Streamflow and the quantity and character of sediment—interacting with watershed
geology, terrain, soils and vegetation—shape morphological changes in the stream channel that
occur from river network headwaters to lower rivers. Id. (citing Montgomery 1999; Church
2002). Headwater streams are typically erosion zones in which sediment from the base of
adjoining hillslopes moves directly into stream channels and is transported downstream. As
stream channels increase in size and decrease in slope, a mixture of erosion and deposition
processes usually is at work. At some point in the lower portions of river networks, sediment
deposition becomes the dominant process and floodplains form. Floodplains are level areas
bordering stream or river channels that are formed by sediment deposition from those channels
under present climatic conditions. These natural geomorphic features are inundated during
moderate to high water events. Id. (citing Leopold 1994; Osterkamp 2008). Floodplain and
associated river channel forms (e.g., meandering, braided, anastomosing) are determined by
interacting fluvial factors, including sediment size and supply, channel gradient, and streamflow.
Id. (citing Church 2002; Church 2006).
Both riparian areas and floodplains are important components of river systems. Riparian
areas are transition zones between terrestrial and aquatic ecosystems that are distinguished by
gradients in biophysical conditions, ecological processes, and biota. They are areas through
which surface and subsurface hydrology connect water bodies with their adjoining uplands, and
they include those portions of terrestrial ecosystems that significantly influence exchanges of
energy and matter with aquatic ecosystems. Id. (citing National Research Council 2002).
Riparian areas often have high biodiversity. Id. (citing Naiman et al. 2005). They occur near
lakes and estuarine-marine shorelines and along river networks, where their width can vary from
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narrow bands along headwater streams to broad zones that encompass the floodplains of large
rivers.
Floodplains are also considered riparian areas, but not all riparian areas have floodplains.
All rivers and streams within river networks have riparian areas, but small streams in constrained
valleys are less likely to have floodplains than larger streams and rivers in unconstrained valleys.
The "100-year floodplain" is the area with a one percent annual chance of flooding. Id. at 2-5
(citing Federal Emergency Management Agency); U.S. Geological Survey. The 100-year
floodplain can but need not coincide with the geomorphic floodplain.
Wetlands are transitional areas between terrestrial and aquatic ecosystems. Wetlands
include areas such as swamps, bogs, fens, marshes, ponds, and pools. Science Report at 2-6
(citing Mitsch et al. 2009).
Many classification systems have been developed for wetlands. Id. (citing Mitsch and
Gosselink 2007). These classifications can focus on vegetation, hydrology, hydrogeomorphic
characteristics, or other factors. Id. (citing Cowardin et al. 1979; Brinson 1993; Tiner 2003a;
Comer et al. 2005). Because the Science Report focuses on downstream connectivity, it
considered two landscape settings in which wetlands occur based on directionality of hydrologic
flows. Directionality of flow also is included as a component of hydrodynamic setting in the
hydrogeomorphic approach and as an element of water flowpath in an enhancement of National
Wetlands Inventory data (the National Wetlands Inventory is a mapping dataset of the U.S. Fish
and Wildlife Service regarding the extent and types of wetlands and deepwater habitats across
the country). Id. (citing Brinson 1993; Smith et al. 1995, Tiner 2011). This emphasis on
directionality of flow is necessary because hydrologic connectivity plays a dominant role in
determining the types of effects wetlands have on downstream waters.
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A non-floodplain wetland setting is a landscape setting where a potential exists for
unidirectional, lateral hydrologic flows from wetlands to the river network through surface water
or ground water. Such a setting would include upgradient areas such as hillslopes or upland
areas outside of the floodplain. Any wetland setting where water could only flow from the
wetland toward a river network would be considered a non-floodplain setting, regardless of the
magnitude and duration of flows and of travel times. The Science Report refers to wetlands that
occur in these settings as non-floodplain wetlands.
A riparian/floodplain wetland setting is a landscape setting (e.g., floodplains, most
riparian areas, lake and estuarine fringes) that is subject to bidirectional, lateral hydrologic flows.
Wetlands in riparian/floodplain settings can have some of the same types of hydrologic
connections as those in non-floodplain settings. In addition, wetlands in these settings also have
bidirectional flows. For example, wetlands within a riparian area are connected to the river
network through lateral movement of water between the channel and riparian area (e.g., through
overbank flooding, hyporheic flow). Given the Science Report's interest in addressing the effects
of wetlands on downstream waters, it focused in particular on the subset of these wetlands that
occur in riparian areas with and without floodplains (collectively referred to hereafter as
riparian/floodplain wetlands); the Science Report generally does not address wetlands at lake and
estuarine fringes. Riparian wetlands are portions of riparian areas that meet the Cowardin et al.
(1979) three-attribute wetland criteria (i.e., having wetland hydrology, hydrophytic vegetation, or
hydric soils); floodplain wetlands are portions of the floodplain that meet these same criteria. Id.
at 2-7. Given that even infrequent flooding can have profound effects on wetland development
and function, the Science Report considers such a wetland to be in a riparian/floodplain setting.
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Note that the scientific definition of "wetland" used in the Science Report is not the same
as the longstanding Clean Water Act regulatory definition of "wetland," retained in the final rule.
Only aquatic resources that meet the regulatory definition of wetland at paragraph (c)(4) are
considered to be wetlands for Clean Water Act purposes under the final rule. The agencies are
not changing their longstanding regulation that requires that an aquatic resource must meet all
three parameters under normal circumstances to be considered a wetland in the regulatory sense.
As noted above, Cowardin wetlands need to have only one of the parameters. Conclusions in the
Science Report apply to the Cowardin wetlands, and the Cowardin definition of wetlands
encompasses a larger universe of wetlands than the regulatory definition. Therefore, the Science
Report conclusions regarding Cowardin wetlands apply to the wetlands meeting the regulatory
definition because those wetlands are a subset of the Cowardin wetlands. All wetlands that meet
the regulatory definition also meet the Cowardin definition of wetlands. Because wetlands under
the regulatory definition of wetland must meet all three parameters, it is even more likely that
they provide the many functions described in the Science Report due to the conditions in the
waters that make them wetlands - that is, their hydric soils (inundated or saturated soils),
hydrophytic vegetation (plants that thrive in wet conditions), and wetland hydrology (inundation
or saturation at the surface at some time during the growing season). In addition, many of the
Cowardin wetland types are in fact open waters, as the Cowardin definition encompasses open
waters like ponds, and the Science Report utilizes many references that includes such open
waters when discussing floodplain and nonfloodplain wetlands. Thus, open waters also provide
the many functions described in the Science Report and throughout this document. The Science
Report acknowledges that its conclusions apply to open waters as well as wetlands, stating,
"although the literature review did not address other non-floodplain water bodies to the same
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extent as wetlands, our overall conclusions also apply to these water bodies (e.g., ponds and
lakes that lack surface water inlets) because the same principles govern hydrologic connectivity
between these water bodies and downstream waters." Id. at 4-41. Wetlands and open waters are
only jurisdictional when they meet the definition of "waters of the United States."
A major consequence of the two different landscape settings (non-floodplain versus
riparian/floodplain) is that waterborne materials can be transported only from the wetland to the
river network for a non-floodplain wetland, whereas waterborne materials can be transported
from the wetland to the river network and from the river network to the wetland for a
riparian/floodplain wetland. In the latter case, there is a mutual, interacting effect on the structure
and function of both the wetland and river network. In contrast, a non-floodplain wetland can
affect a river through the transport of waterborne material, but the opposite is not true. Note that
the Science Report limits use of riparian/floodplain and non-floodplain landscape settings to
describe the direction of hydrologic flow; the terms cannot be used to describe directionality of
geochemical or biological flows. For example, mobile organisms can move from a stream to a
non-floodplain wetland. Id. at 2-8 (citing, e.g., Subalusky etal. 2009a; Subalusky etal. 2009b).
Both non-floodplain and riparian/floodplain wetlands can include geographically isolated
wetlands, or wetlands completely surrounded by uplands. Id. (citing Tiner 2003b). These
wetlands have no apparent surface-water outlets, but can hydrologically connect to downstream
waters through spillage or groundwater. The Science Report defines an upland as any area not
meeting the Cowardin et al. (1979) three-attribute wetland criteria, meaning that uplands can
occur in both terrestrial and riparian areas.8 Id. Thus, a wetland that is located on a floodplain but
is surrounded by upland would be considered a geographically isolated, riparian/floodplain
8 Note that this definition of upland is the one that is used in the Science Report. The agencies are not promulgating
a definition of upland in the final rule.
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wetland that is subject to periodic inundation from the river network. Although the term
"geographically isolated" could be misconstrued as implying functional isolation, the term has
been defined in the peer-reviewed literature to refer specifically to wetlands surrounded by
uplands. Furthermore, the literature explicitly notes that geographic isolation does not imply
functional isolation. Id. (citing Leibowitz 2003; Tiner 2003b). Discussion of geographically
isolated wetlands is essential because hydrologic connectivity (an element of connectivity, which
is the focus of the Science Report) is generally difficult to characterize for these wetlands.
River System Hydrology
River system hydrology is controlled by hierarchical factors that result in a broad
continuum of belowground and aboveground hydrologic flowpaths connecting river basins and
river networks. Id. (citing Winter 2001; Wolock et al. 2004; Devito el al. 2005; Poole el al.
2006; Wagener et al. 2007; Poole 2010; Bencala et al. 2011; Jencso and McGlynn 2011). At the
broadest scale, regional climate interacts with river-basin terrain and geology to shape inherent
hydrologic infrastructure that bounds the nature of basin hydrologic flowpaths. Different climate-
basin combinations form identifiable hydrologic landscape units with distinct hydrologic
characteristics. Id. at 2-8 to 2-9 (Winter, 2001; Wigington et al. 2013). Buttle (2006) posited
three first-order controls of watershed streamflow generated under specific hydroclimatic
conditions: (1) the ability of different landscape elements to generate runoff by surface or
subsurface lateral flow of water; (2) the degree of hydrologic linkage among landscapes by
which surface and subsurface runoff can reach river networks; and (3) the capacity of the river
network itself to convey runoff downstream to the river-basin outlet. Id. at 2-9. River and stream
waters are influenced by not only basin-scale or larger ground-water systems, but also local-
scale, vertical and lateral hydrologic exchanges between water in channels and sediments
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beneath and contiguous with river network channels. Id. at 2-9 (citing Ward 1989; Woessner
2000; Malard et al. 2002; Bencala 2011). The magnitude and importance of river-system
hydrologic flowpaths at all spatial scales can radically change over time at hourly to yearly
temporal scales. Id. (citing Junk etal. 1989; Ward 1989; Malard et al. 1999; Poole etal. 2006).
Because interactions between groundwater and surface waters are essential processes in
rivers, knowledge of basic groundwater hydrology is necessary to understand the interaction
between surface and subsurface water and their relationship to connectivity within river systems.
Subsurface water occurs in two principal zones: the unsaturated zone and the saturated zone. Id.
(citing Winter et al. 1998). In the unsaturated zone, the spaces between soil, gravel, and other
particles contain both air and water. In the saturated zone, these spaces are completely filled with
water. Ground water refers to any water that occurs and flows (saturated groundwater flow) in
the saturated zone beneath a watershed surface. Id. (citing Winter et al. 1998). Rapid flow
(interflow) of water can occur through large pore spaces in the unsaturated zone. Id. (citing
Beven and Germann 1982).
Other hydrologic flowpaths are also significant in determining the characteristics of river
systems. The most obvious is the downstream water movement within stream or river channels,
or open-channel flow. River water in stream and river channels can reach riparian areas and
floodplains via overbank flow, which occurs when floodwaters flow over stream and river
channels. Id. at 2-12 (citing Mertes 1997). Overland flow is the portion of streamflow derived
from net precipitation that flows over the land surface to the nearest stream channel with no
infiltration. Id. (citing Hewlett 1982). Overland flow can be generated by several mechanisms.
Infiltration-excess overland flow occurs when the rainfall rates exceed the infiltration rates of
land surfaces. Id. (citing Horton 1945). Saturation-excess overland flow occurs when
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precipitation inputs cause water tables to rise to land surfaces so that precipitation inputs to the
land surfaces cannot infiltrate and flow overland. Id. (citing Dunne and Black 1970). Return flow
occurs when water infiltrates, percolates through the unsaturated zones, enters saturated zones,
and then returns to and flows over watershed surfaces, commonly at hillslope-floodplain
transitions. Id. (citing Dunne and Black 1970).
Alluvium consists of deposits of clay, silt, sand, gravel, or other particulate materials that
running water has deposited in a streambed, on a floodplain, on a delta, or in a fan at the base of
a mountain. These deposits occur near active river systems but also can be found in buried river
valleys—the remnants of relict river systems. Id. (citing Lloyd and Lyke 1995). The Science
Report was concerned primarily with alluvium deposited along active river networks.
Commonly, alluvium is highly permeable, creating an environment conducive to groundwater
flow. Alluvial groundwater (typically a mixture of river water and local, intermediate, and
regional groundwater) moves through the alluvium. Together, the alluvium and alluvial ground
water comprise alluvial aquifers. Alluvial aquifers are closely associated with floodplains and
have high levels of hyporheic exchange. Id. (citing Stanford and Ward 1993; Amoros and
Bornette 2002; Poole et al. 2006). Hyporheic exchange occurs when water moves from stream or
river channels into alluvial deposits and then returns to the channels. Id. at 2-12, 4-8 (citing
Sjodin et al. 2001; Bencala 2005;Gooseff et al. 2008; Leibowitz et al. 2008; Bencala 2011).
Hyporheic exchange allows for the mixing of surface water and groundwater. It occurs during
both high- and low-flow periods, and typically has relatively horizontal flowpaths at scales of
meters to tens of meters and vertical flowpaths with depths ranging from centimeters to tens of
meters. Science Report at 2-12 (citing Stanford and Ward 1988; Woessner 2000 and references
therein; Bencala 2005).
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Riparian areas and floodplains can have a diverse array of hydrologic inputs and outputs,
which, in turn influence riparian/floodplain wetlands. Riparian areas and floodplains receive
water from precipitation; overland flow from upland areas; local, intermediate, regional ground
water; and hyporheic flows. Id. at 4-14 (National Research Council 2002; Richardson etal.
2005; Vidon et al. 2010). Water flowing over the land surface in many situations can infiltrate
soils in riparian areas. Id. If low permeability subsoils or impervious clay layers are present,
water contact with the plant root zone is increased and the water is subject to ecological
functions such as denitrification before it reaches the stream channel. Id. (citing National
Research Council 2002; Naiman et al. 2005; Vidon et al. 2010).
The relative importance of the continuum of hydrologic flowpaths among river systems
varies, creating streams and rivers with different flow duration (or hydrologic permanence)
classes. Perennial streams or stream reaches typically flow year-round. They are maintained by
local or regional ground-water discharge or streamflow from higher in the stream or river
network. Intermittent streams or stream reaches flow continuously, but only at certain times of
the year (e.g., during certain seasons such as spring snowmelt); drying occurs when the water
table falls below the channel bed elevation. Ephemeral streams or stream reaches flow briefly
(typically hours to days) during and immediately following precipitation; these channels are
above the water table at all times. Streams in these flow duration classes often transition
longitudinally, from ephemeral to intermittent to perennial, as drainage area increases and
elevation decreases along river networks. Many headwater streams, however, originate from
permanent springs and flow directly into intermittent downstream reaches. At low flows,
intermittent streams can contain dry segments alternating with flowing segments. Transitions
between flow duration classes can coincide with confluences or with geomorphic discontinuities
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within the network. Id. at 2-14 (citing May and Lee 2004; Hunter et al. 2005). Variation of
streamflow within river systems occurs in response to hydrologic events resulting from rainfall
or snowmelt. Stormflow is streamflow that occurs in direct response to rainfall or snowmelt,
which might stem from multiple groundwater and surface-water sources. Id. (citing Dunne and
Leopold 1978). Baseflow is streamflow originating from groundwater discharge or seepage
(locally or from higher in the river network), which sustains water flow through the channel
between hydrologic events. Perennial streams have baseflow year-round; intermittent streams
have baseflow seasonally; ephemeral streams have no baseflow. All three stream types convey
stormflow. Thus, perennial streams are more common in areas receiving high precipitation,
whereas intermittent and ephemeral streams are more common in the more arid portions of the
United States. Id. (citing NHD 2008). The distribution of headwater streams (perennial,
intermittent, or ephemeral) as a proportion of total stream length is similar across geographic
regions and climates.
Similar to streams, the occurrence and persistence of riparian/floodplain wetland and
non-floodplain wetland hydrologic connections with river networks, via surface water (both
channelized and nonchannelized) or groundwater, can be continuous, seasonal, or ephemeral,
depending on the overall hydrologic conditions in the watershed. For example, a non-floodplain
wetland might have a direct groundwater connection with a river network during wet conditions
but an indirect regional ground-water connection (via groundwater recharge) under dry
conditions. Geographically isolated wetlands can be hydrologically connected to the river
network via nonchannelized surface flow (e.g., swales or overland flow) or groundwater.
The portions of river networks with flowing water expand and contract longitudinally (in
an upstream-downstream direction) and laterally (in a stream channel-floodplain direction) in
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response to seasonal environmental conditions and precipitation events. Id. at 2-18 (citing
Hewlett and Hibbert 1967; Gregory and Walling,1968; Dunne and Black 1970; Day 1978; Junk
et al. 1989; Hunter et al. 2005; Wigington et al. 2005; Rains et al. 2006; Rains et al. 2008). The
longitudinal expansion of channels with flowing water in response to major precipitation events
represents a transient increase in the extent of headwater streams. Intermittent and perennial
streams flow during wet seasons, whereas ephemeral streams flow only in response to rainfall or
snowmelt. During dry periods, flowing portions of river networks are limited to perennial
streams; these perennial portions of the river network can be discontinuous or interspersed with
intermittently flowing stream reaches. Id. (citing Stanley et al. 1997; Hunter et al. 2005; Larned
et al. 2010). Thus, stream reaches can be perennial even if the entire stream channel is not. As
discussed previously, perennial streams typically flow year-round, intermittent streams flow
continuously only at certain times of the year (e.g., when they receive water from a spring,
groundwater source, or surface snow such as melting snow), and ephemeral streams flow briefly
in direct response to precipitation. In perennial streams, baseflow (the portion of flow
contributed by groundwater) is typically present year-round. The definition of "perennial" allows
for infrequent periods of severe drought to cause some perennial streams to not have flow year-
round. Leopold 1994. Some studies have noted that perennial flow is present greater than 90% of
the time, except in periods of severe drought, or greater than 80% of the time, and these
definitions are consistent with the one used in the Science Report. Hedman and Osterkamp 1982;
Hewlett 1982.
The dominant sources of water to a stream can shift during river network expansion and
contraction. Id. (citing Malard et al. 1999; McGlynn and McDonnell 2003; McGlynn et al. 2004;
Malard et al. 2006). Rainfall and snowmelt cause a river network to expand in two ways. First,
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local aquifers expand and water moves into dry channels, which increases the total length of the
wet channel; the resulting intermittent streams will contain water during the entire wet season.
Id. (citing Winter et al. 1998). Second, stormflow can cause water to enter ephemeral and
intermittent streams. The larger the rainfall or snowmelt event, the greater the number of
ephemeral streams and total length of flowing channels that occur within the river network.
Ephemeral flows cease within days after rainfall or snowmelt ends, causing the length of wet
channels to decrease and river networks to contract. The flowing portion of river networks
further shrinks as the spatial extent of aquifers with ground water in contact with streams
contract and intermittent streams dry. In many river systems across the United States, stormflow
comprises a major portion of annual streamflow. Id. (citing Hewlett et al. 1977; Miller et al.
1988; Turton et al. 1992; Goodrich et al. 1997; Vivoni et al. 2006). In these systems, intermittent
and ephemeral streams are major sources of river water. When rainfall or snowmelt induces
stormflow in headwater streams or other portions of the river network, water flows downgradient
through the network to its lower reaches. As water moves downstream through a river network,
the hydrograph for a typical event broadens with a lower peak. This broadening of the
hydrograph shape results from transient storage of water in river network channels and nearby
alluvial aquifers. Id. (citing Fernald et al. 2001).
During very large hydrologic events, aggregate flows from headwaters and other tributary
streams can result in overbank flooding in river reaches with floodplains; this occurrence
represents lateral expansion of the river network. Id. (citing Mertes 1997). Water from overbank
flows can recharge alluvial aquifers, supply water to floodplain wetlands, surficially connect
floodplain wetlands to rivers, and shape the geomorphic features of the floodplain. Id. at 2-18 to
2-19 (citing Wolman and Miller 1960; Hammersmark et al. 2008). Bidirectional exchanges of
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water between ground water and river networks, including hyporheic flow, can occur under a
wide range of streamflows, from flood flows to low flows. Id. at 2-19 to 2-20 (citing National
Research Council 2002; Naiman et al. 2005; Vivoni et al. 2006).
Many studies have documented the fact that riparian/floodplain wetlands can attenuate
flood pulses of streams and rivers by storing excess water from streams and rivers. Bullock and
Acreman (2003) reviewed wetland studies and reported that wetlands reduced or delayed floods
in 23 of 28 studies. Id. at 2-21. For example, Walton et al. (1996) found that peak discharges
between upstream and downstream gaging stations on the Cache River in Arkansas were reduced
10-20% primarily due to floodplain water storage. Id. Locations within floodplains and riparian
areas with higher elevations likely provide flood storage less frequently than lower elevation
areas.
The interactions of high flows with floodplains and associated alluvial aquifers of river
networks are important determinants of hydrologic and biogeochemical conditions of rivers. Id.
at 2-21 (citing Ward 1989; Stanford and Ward 1993; Boulton et al. 1998; Burkart et al. 1999;
Malard et al. 1999; Amoros and Bornette 2002; Malard et al. 2006; Poole 2010). Bencala (1993;
2011) noted that streams and rivers are not pipes; they interact with the alluvium and geologic
materials adjoining and under channels. Id. In streams or river reaches constrained by
topography, significant floodplain and near-channel alluvial aquifer interactions are limited. In
reaches with floodplains, however, stormflow commonly supplies water to alluvial aquifers
during high-flow periods through the process of bank storage. Id. at 2-22 (citing Whiting and
Pomeranets 1997; Winter et al. 1998; Chen and Chen 2003). As streamflow decreases after
hydrologic events, the water stored in these alluvial aquifers can serve as another source of
baseflow in rivers.
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In summary, the extent of wetted channels is dynamic because interactions between
surface water in the channel and alluvial ground water, via hyporheic exchange, determine open-
channel flow. The flowing portion of river networks expands and contracts in two primary
dimensions: (1) longitudinally, as intermittent and ephemeral streams wet up and dry; and (2)
laterally, as floodplains and associated alluvial aquifers gain (via overbank flooding, bank
storage, and hyporheic exchange) and lose (via draining of alluvial aquifers and
evapotranspiration) water. Vertical ground-water exchanges between streams and rivers and
underlying alluvium are also key connections, and variations in these vertical exchanges
contribute to the expansion and contraction of the portions of river networks with open-channel
flow. Numerous studies have documented expansion and contraction of river systems; the
temporal and spatial pattern of this expansion and contraction varies in response to many factors,
including interannual and long-term dry cycles, climatic conditions, and watershed
characteristics. Id. (citing Gregory and Walling 1968; Cayan and Peterson 1989; Fleming etal.
2007).
Influence of Streams and Wetlands on Downstream Waters
The structure and function of rivers are highly dependent on the constituent materials
stored in and transported through them. Most of these materials, broadly defined here as any
physical, chemical, or biological entity, including water, heat energy, sediment, wood, organic
matter, nutrients, chemical contaminants, and organisms, originate outside of the river; they
originate from either the upstream river network or other components of the river system, and
then are transported to the river by water movement or other mechanisms. Thus, the fundamental
way in which streams and wetlands affect river structure and function is by altering fluxes of
materials to the river. This alteration of material fluxes depends on two key factors: (1) functions
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within streams and wetlands that affect material fluxes, and (2) connectivity (or isolation)
between streams and wetlands and rivers that allows (or prevents) transport of materials between
the systems. Id.
Streams and wetlands affect the amounts and types of materials that are or are not
delivered to downstream waters, ultimately contributing to the structure and function of those
waters. Leibowitz et al. (2008) identified three functions, or general mechanisms of action, by
which streams and wetlands influence material fluxes into downstream waters: source, sink, and
refuge. Id. at 2-22 to 2-23. The Science Report expanded on this framework to include two
additional functions: lag and transformation. These five functions provide a framework for
understanding how physical, chemical, and biological connections between streams and wetlands
and downstream waters influence river systems.
These five functions are neither static nor mutually exclusive, and often the distinctions
between them are not sharp. A stream or wetland can provide different functions at the same
time. These functions can vary with the material considered (e.g., acting as a source of organic
matter and a sink for nitrogen) and can change over time (e.g., acting as a water sink when
evapotranspiration is high and a water source when evapotranspiration is low). The magnitude of
a given function also is likely to vary temporally; for example, streams generally are greater
sources of organic matter and contaminants during high flows. Id. at 2-24.
Leibowitz et al. (2008) explicitly focused on functions that benefit downstream waters,
but these functions also can have negative effects—for example, when streams and wetlands
serve as sources of chemical contamination. Id. In fact, benefits need not be linear with respect
to concentration; a beneficial material could be harmful at higher concentrations due to nonlinear
and threshold effects. For example, nitrogen can be beneficial at lower concentrations but can
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reduce water quality at higher concentrations. Although the Science Report focused primarily on
the effects of streams and wetlands on downstream waters, these same functions can describe
effects of downstream waters on streams and wetlands (e.g., downstream rivers can serve as
sources of colonists for upstream tributaries). Id.
Because many of these functions depend on import of materials and energy into streams
and wetlands, distinguishing between actual function and potential function is instructive. For
example, a wetland with appropriate conditions (e.g., a reducing environment and denitrifying
bacteria) is a potential sink for nitrogen: If nitrogen is imported into the wetland, the wetland can
remove it by denitrification. The wetland will not serve this function, however, if nitrogen is not
imported. Thus, even if a stream and wetland do not currently serve a function, it has the
potential to provide that function under appropriate conditions (e.g., when material imports or
environmental conditions change). These functions can be instrumental in protecting those
waters from future impacts. Ignoring potential function also can lead to the paradox that
degraded streams and wetlands (e.g., those receiving nonpoint-source nitrogen inputs) receive
more protection than less impacted systems. Id. (citing Leibowitz etal. 2008).
Three factors influence the effect that material and energy fluxes from streams and
wetlands have on downstream waters: (1) proportion of the material originating from (or reduced
by) streams and wetlands relative to the importance of other system components, such as the
river itself; (2) residence time of the material in the downstream water; and (3) relative
importance of the material. Id. In many cases, the effects on downstream waters need to be
considered in aggregate. For example, the contribution of material by a particular stream and
wetland (e.g., a specific ephemeral stream) might be small, but the aggregate contribution by an
entire class of streams and wetlands (e.g., all ephemeral streams in the river network) might be
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substantial. Integrating contributions over time also might be necessary, taking into account the
frequency, duration, and timing of material export and delivery. Considering the cumulative
material fluxes that originate from a specific stream and wetland, rather than the individual
materials separately, is essential in understanding the effects of material fluxes on downstream
waters. Id. at 2-26.
In general, the more frequently a material is delivered to the river, the greater its effect.
The effect of an infrequently supplied material, however, can be large if the material has a long
residence time in the river. Id. (citing Leibowitz et al. 2008). For example, woody debris might
be exported to downstream waters infrequently but it can persist in downstream channels. In
addition, some materials are more important in defining the structure and function of a river. For
example, woody debris can have a large effect on river structure and function because it affects
water flow, sediment and organic matter transport, and habitat. Id. (citing Harmon et al. 1986;
Gurnell et al. 1995). Another example is salmon migrating to a river: They can serve as a
keystone species to regulate other populations and as a source of marine-derived nutrients. Id.
(citing Schindler et al. 2005).
The functions discussed above represent general mechanisms by which streams and
wetlands influence downstream waters. For these altered material and energy fluxes to affect a
river, however, transport mechanisms that deliver (or could deliver) these materials to the river
are necessary. Connectivity describes the degree to which components of a system are connected
and interact through various transport mechanisms; connectivity is determined by the
characteristics of both the physical landscape and the biota of the specific system. Id. This
definition is related to, but is distinct from, definitions of connectivity based on the actual flow of
materials between system components. Id. (citing, e.g., Pringle 2001). That connectivity among
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river-system components, including streams and wetlands, plays a significant role in the structure
and function of these systems is not a new concept. In fact, much of the theory developed to
explain how these systems work focuses on connectivity and linkages between system
components. Id. (citing, e.g., Vannote etal. 1980; Newbold etal. 1982a; Newbold etal. 1982b;
Junk etal. 1989; Ward 1989; Benda et al. 2004; Thorp etal. 2006).
In addition to its central role in defining river systems, water movement through the river
system is the primary mechanism providing physical connectivity both within river networks and
between those networks and the surrounding landscape. Id. (citing Fullerton et al. 2010).
Hydrologic connectivity results from the flow of water, which provides a "hydraulic highway"
along which physical, chemical, and biological materials associated with the water are
transported (e.g., sediment, woody debris, contaminants, organisms). Id. (citing Fausch et al.
2002)
Ecosystem functions within a river system are driven by interactions between the river
system's physical environment and the diverse biological communities living within it. Id.
(Wiens 2002; Schroder 2006). Thus, river system structure and function also depend on
biological connectivity among the system's populations of aquatic and semiaquatic organisms.
Biological connectivity refers to the movement of organisms, including transport of reproductive
materials (e.g., seeds, eggs, genes) and dormant stages, through river systems. Id. at 2-26 to 2-27.
These movements link aquatic habitats and populations in different locations through several
processes important for the survival of individuals, populations, and species. Id. at 2-27.
Movements include dispersal, or movement away from an existing population or parent
organism; migration, or long-distance movements occurring seasonally; localized movement
over an organism's home range to find food, mates, or refuge from predators or adverse
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conditions; and movement to different habitats to complete life-cycle requirements. Biological
connectivity can occur within aquatic ecosystems or across ecosystem or watershed boundaries,
and it can be multidirectional. For example, organisms can move downstream from perennial,
intermittent, and ephemeral headwaters to rivers; upstream from estuaries to rivers to
headwaters; or laterally between floodplain wetlands, geographically isolated wetlands, rivers,
lakes, or other water bodies.
As noted above, streams and rivers are not pipes; they provide opportunities for water to
interact with internal components (e.g., alluvium, organisms) through the five functions by which
streams and wetlands alter material fluxes. Id. (citing Bencala 1993; Bencala et al. 2011).
Connectivity between streams and wetlands provides opportunities for material fluxes to be
altered sequentially by multiple streams and wetlands as the materials are transported
downstream. The aggregate effect of these sequential fluxes determines the proportion of
material that ultimately reaches the river. The form of the exported material can be transformed
as it moves down the river network, however, making quantitative assessments of the importance
of individual stream and wetland resources within the entire river system difficult. For example,
organic matter can be exported from headwater streams and consumed by downstream
macroinvertebrates. Those invertebrates can drift farther downstream and be eaten by juvenile
fish that eventually move into the mainstem of the river, where they feed further and grow.
The assessment of stream and wetland influence on rivers also is complicated by the
cumulative time lag resulting from these sequential transformations and transportations. For
example, removal of nutrients by streambed algal and microbial populations, subsequent feeding
by fish and insects, and release by excretion or decomposition delays the export of nutrients
downstream.
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The opposite of connectivity is isolation, or the degree to which transport mechanisms
(i.e., pathways between system components) are lacking; isolation acts to reduce material fluxes
between system components. Id. at 2-28. Although the Science Report primarily focused on the
benefits that connectivity can have on downstream systems, isolation also can have important
positive effects on the condition and function of downstream waters. For example, waterborne
contaminants that enter a wetland cannot be transported to a river if the wetland is hydrologically
isolated from the river, except by non-hydrologic pathways. Id. at 2-28 to 2-29. Increased
isolation can decrease the spread of pathogens and invasive species, and increase the rate of local
adaptation. Id. at 2-29 (citing, e.g., Hess 1996; Bodamer and Bossenbroek 2008; Fraser etal.
2011). Thus, both connectivity and isolation should be considered when examining material
fluxes from streams and wetlands, and biological interactions should be viewed in light of the
natural balance between these two factors.
Spatial and Temporal Variability of Connectivity
Connectivity is not a fixed characteristic of a system, but varies over space and time. Id.
(citing Ward 1989; Leibowitz 2003; Leibowitz and Vining 2003). Variability in hydrologic
connectivity results primarily from the longitudinal and lateral expansion and contraction of the
river network and transient connection with other components of the river system. The variability
of connectivity can be described in terms of frequency, duration, magnitude, timing, and rate of
change. When assessing the effects of connectivity or isolation and the five general functions
(sources, sinks, refuges, lags, and transformations) on downstream waters, dimensions of time
and space must be considered. Id. Water or organisms transported from distant headwater
streams or wetlands generally will take longer to travel to a larger river than materials
transported from streams or wetlands near the river. This can introduce a lag between the time
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the function occurs and the time the material arrives at the river. In addition, the distribution of
streams and wetlands can be a function of their distance from the mainstem channel. For
example, in a classic dendritic network, there is an inverse geometric relationship between
number of streams and stream order. In such a case, the aggregate level of function could be
greater for terminal source streams, compared to higher order or lateral source streams. This is
one reason why watersheds of terminal source streams often provide the greatest proportion of
water for major rivers. Connectivity, however, results from many interacting factors. For
example, the relationship between stream number and order can vary with the shape of the
watershed and the configuration of the network.
The expansion and contraction of river networks affects the extent, magnitude, timing,
and type of hydrologic connectivity. For example, intermittent and ephemeral streams flow only
during wetter seasons or during and immediately following precipitation events. Thus, the spatial
extent of connectivity between streams and wetlands and rivers increases greatly during these
high-flow events because intermittent and ephemeral streams are estimated to account for 59%
of the total length of streams in the contiguous United States. Id. (citing Nadeau and Rains
2007). Changes in the spatial extent of connectivity due to expansion and contraction are even
more pronounced in the arid and semiarid Southwest, where more than 80% of all streams are
intermittent or ephemeral. Id. at 2-29 to 2-30 (citing Levick et al. 2008). Expansion and
contraction also affect the magnitude of connectivity because larger flows provide greater
potential for material transport. Id. at 2-30.
Besides affecting the spatial extent and magnitude of hydrologic connectivity, expansion
and contraction of the stream network also affect the duration and timing of flow in different
portions of the network. Perennial streams have year-round connectivity with a downstream
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river, while intermittent streams have seasonal connectivity. The temporal characteristics of
connectivity for ephemeral streams depend on the duration and timing of storm events. Similarly,
connectivity between wetlands and downstream waters can range from permanent to seasonal to
episodic.
The expansion and contraction of river systems also affect the type of connectivity. For
example, during wet periods when input from precipitation can exceed evapotranspiration and
available storage, non-floodplain wetlands could have connectivity with other wetlands or
streams through surface spillage. Id. (citing Leibowitz and Vining 2003; Rains etal. 2008).
When spillage ceases due to drier conditions, hydrologic connectivity could only occur through
groundwater. Id. (citing Rains et al. 2006; Rains et al. 2008).
When the flow of water mediates dispersal, migration, and other forms of biotic
movement, biological and hydrologic connectivity can be tightly coupled. For example, seasonal
flooding of riparian/floodplain wetlands creates temporary habitat that fish, aquatic insects, and
other organisms use. Id. (citing Junk et al. 1989; Smock 1994; Tockner et al. 2000; Robinson et
al. 2002; Tronstad et al. 2007). Factors other than hydrologic dynamics also can affect the
temporal and spatial dynamics of biological connectivity. Such factors include movement
associated with seasonal habitat use and shifts in habitat use due to life-history changes, quality
or quantity of food resources, presence or absence of favorable dispersal conditions, physical
differences in aquatic habitat structure, or the number and sizes of nearby populations. Id. (citing
Moll 1990; Smock 1994; Huryn and Gibbs 1999; Lamoureux and Madison 1999; Gibbons etal.
2006; Gamble et al. 2007; Grant et al. 2007; Subalusky et al. 2009a; Schalk and Luhring 2010).
For a specific river system with a given spatial configuration, variability in biological
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connectivity also occurs due to variation in the dispersal distance of organisms and reproductive
propagules. Id. (citing Semlitsch and Bodie 2003).
Finally, just as connectivity from temporary or seasonal wetting of channels can affect
downstream waters, temporary or seasonal drying also can affect river networks. Riverbeds or
streambeds that temporarily dry up are used by aquatic organisms that are specially adapted to
wet and dry conditions, and can serve as egg and seed banks for several organisms, including
aquatic invertebrates and plants. Uat 2-30 (citing Steward el al. 2012). These temporary dry
areas also can affect nutrient dynamics due to reduced microbial activity, increased oxygen
availability, and inputs of terrestrial sources of organic matter and nutrients. Id. (citing Steward
et al. 2012).
Numerous factors affect physical, chemical, and biological connectivity within river
systems. These factors operate at multiple spatial and temporal scales, and interact with each
other in complex ways to determine where components of a system fall on the connectivity-
isolation gradient at a given time. Id. at 2-30 to 2-31. The Science Report focused on five key
factors: climate, watershed characteristics, spatial distribution patterns, biota, and human
activities and alterations. Id. at 2-31. These are by no means the only factors influencing
connectivity, but they illustrate how many different variables shape physical, chemical, and
biological connectivity.
Climate-watershed Characteristics
The movement and storage of water in watersheds varies with climatic, geologic,
physiographic, and edaphic characteristics of river systems. Id. (citing Winter 2001; Wigington
et al. 2013). At the largest spatial scale, climate determines the amount, timing, and duration of
water available to watersheds and river basins. Key characteristics of water availability that
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influence connectivity include annual water surplus (precipitation minus evapotranspiration),
timing (seasonality) of water surplus during the year that is heavily influenced by precipitation
timing and form (e.g., rain, snow), and rainfall intensity.
Annual runoff generally reflects water surplus and varies widely across the United States.
Seasonality of water surplus during the year determines when and for how long runoff and
ground-water recharge occur. Precipitation and water surplus in the eastern United States is less
seasonal than in the West. Id. (Finkelstein and Truppi 1991). The Southwest experiences summer
monsoonal rains, while the West Coast and Pacific Northwest receive most precipitation during
the winter season. Id. (citing Wigington et al. 2013). Throughout the West, winter precipitation
in the mountains occurs as snowfall, where it accumulates in seasonal snowpack and is released
during the spring and summer melt seasons to sustain streamflow during late spring and summer
months. Id. (citing Brooks et al. 2012). The flowing portions of river networks tend to have their
maximum extent during seasons with the highest water surplus, when conditions for flooding are
most likely. Typically, the occurrence of ephemeral and intermittent streams is greatest in
watersheds with low annual runoff and high water surplus seasonality but also is influenced by
watershed geologic and edaphic features. Id. (citing Gleeson et al. 2011).
Rainfall intensity can affect hydrologic connectivity in localities where watershed
surfaces have low infiltration capacities relative to rainfall intensities. Infiltration-excess
overland flow occurs when rainfall intensity exceeds watershed surface infiltration, and it can be
an important mechanism in providing water to wetlands and river networks (Goodrich et al.
1997; Levick et al. 2008). Overland flow is common at low elevations in the Southwest, due to
the presence of desert soils with low infiltration capacities combined with relatively high rainfall
intensities. The Pacific Northwest has low rainfall intensities, whereas many locations in the
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Mid-Atlantic, Southeast, and Great Plains have higher rainfall intensities. The prevalence of
impermeable surfaces in urban areas can generate overland flow in virtually any setting. Id.
(citing Booth et al. 2002).
River system topography and landscape form can profoundly influence river network
drainage patterns, distribution of wetlands, and ground-water and surface-water flowpaths.
Winter (2001) described six generalized hydrologic landscape forms common throughout the
United States. Id. Mountain Valleys and Plateaus and High Plains have constrained valleys
through which streams and rivers flow. Id. at 2-31, 2-33. The Mountain Valleys form has
proportionally long, steep sides with narrow to nonexistent floodplains resulting in the rapid
movement of water downslope. In contrast, Riverine Valleys have extensive floodplains that
promote strong surface-water, hyporheic water, and alluvial ground-water connections between
wetlands and rivers. Id. at 2-33 to 2-34. Small changes in water table elevations can influence the
water levels and hydrologic connectivity of wetlands over extensive areas in this landscape form.
Local ground-water flowpaths are especially important in Hummocky Terrain. Constrained
valleys, such as the Mountain Valley landform, have limited opportunities for the development
of floodplains and alluvial aquifers, whereas unconstrained valleys, such as the Riverine Valley
landform, provide opportunities for the establishment of floodplains. Some river basins can be
contained within a single hydrologic landscape form, but larger river basins commonly comprise
complexes of hydrologic landscape forms. For example, the James River in Virginia, which
flows from mountains through the Piedmont to the Coastal Plain, is an example of a Mountain
Valley-High Plateaus and Plains-Coastal Terrain-Riverine Valley complex.
Floodplain hydrologic connectivity to rivers and streams occurs primarily through
overbank flooding, shallow ground-water flow, and hyporheic flow. Water-table depth can
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influence connectivity across a range of hydrologic landscape forms, but especially in
floodplains. Rivers and wetlands can shift from losing reaches (or recharge wetlands) during dry
conditions to gaining reaches (or discharge wetlands) during wet conditions. Wet, high water-
table conditions influence both ground-water and surface-water connectivity. When water tables
are near the watershed surface, they create conditions in which swales and small stream channels
fill with water and flow to nearby water bodies. Id. at 2-34 (Wigington et al. 2003; Wigington el
a\. 2005). Nanson and Croke (1992) noted that a complex interaction of fluvial processes forms
floodplains, but their character and evolution are essentially a product of stream power (the rate
of energy dissipation against the bed and banks of a river or stream) and sediment characteristics.
Id. They proposed three floodplain classes based on the stream power-sediment characteristic
paradigm: (1) high-energy noncohesive, (2) medium-energy noncohesive, and (3) low-energy
cohesive. The energy term describes stream power during floodplain formation, and the
cohesiveness term depicts the nature of material deposited in the floodplain. In addition,
hyporheic and alluvial aquifer exchanges are more responsive to seasonal discharge changes in
floodplains with complex topography. Id. (citing Poole et al. 2006).
Within hydrologic landscape forms, soil and geologic formation permeabilities are
important determinants of hydrologic flowpaths. Permeable soils promote infiltration that results
in ground-water hydrologic flowpaths, whereas the presence of impermeable soils with low
infiltration capacities is conducive to overland flow. In situations in which ground-water
outflows from watersheds or landscapes dominate, the fate of water depends in part on the
permeability of deeper geologic strata. The presence of an aquiclude (a confining layer) near the
watershed surface leads to shallow subsurface flows through soil or geologic materials.
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These local ground-water flowpaths connect portions of watersheds to nearby wetlands or
streams. Id. at 2-35. Alternatively, if a deep permeable geologic material (an aquifer) is present,
water is likely to move farther downward within watersheds and recharge deeper aquifers. Id. at
2-35 to 2-36. The permeability of soils and geologic formations both can influence the range of
hydrologic connectivity between non-floodplain wetlands and river networks. Id. at 2-36.
Climate and watershed characteristics directly affect spatial and temporal patterns of
connectivity between streams and wetlands and rivers by influencing the timing and extent of
river network expansion and contraction. Id. at 2-38. They also influence the spatial distribution
of water bodies within a watershed, and in particular, the spatial relationship between those water
bodies and the river. Id. (citing, e.g., Tihansky 1999)
Hydrologic connectivity between streams and rivers can be a function of the distance
between the two water bodies. Id. (Bracken and Croke 2007; Peterson et al. 2007). If channels
functioned as pipes, this would not be the case, and any water and its constituent materials
exported from a stream eventually would reach the river. Because streams and rivers are not
pipes, water can be lost from the channel through evapotranspiration and bank storage and
diluted through downstream inputs. Id. (Bencala 1993). Thus, material from a headwater stream
that flowed directly into the river would be subject to less transformation or dilution. On the
other hand, the greater the distance a material travels between a particular stream reach and the
river, the greater the opportunity for that material to be altered (e.g., taken up, transformed, or
assimilated) in intervening stream reaches; this alteration could reduce the material's direct effect
on the river, but it could also allow for beneficial transformations. For example, organic matter
exported from a headwater stream located high in a drainage network might never reach the river
in its original form, instead becoming reworked and incorporated into the food chain. Similarly,
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higher order streams generally are located closer to rivers and, therefore, can have higher
connectivity than upstream reaches of lower order. Note that although an individual low-order
stream can have less connectivity than a high-order stream, a river network has many more low-
order streams, which can represent a large portion of the watershed; thus, the magnitude of the
cumulative effect of these low-order streams can be significant.
The relationship between streams and the river network is a function of basin shape and
network configuration. Elongated basins tend to have trellis networks where relatively small
streams join a larger mainstem; compact basins tend to have dendritic networks with tree-like
branching, where streams gradually increase in size before joining the mainstem. This network
configuration describes the incremental accumulation of drainage area along rivers, and therefore
provides information about the relative contributions of streams to downstream waters. Streams
in a trellis network are more likely to connect directly to a mainstem, compared with a dendritic
network. The relationship between basin shape, network configuration, and connectivity,
however, is complex. A mainstem in a trellis network also is more likely to have a lower stream
order than one in a dendritic network. Id. at 2-38 to 2-39.
Distance also affects connectivity between non-floodplain and riparian/floodplain
wetlands and downstream waters. Id. at 2-39. Riverine wetlands that serve as origins for lateral
source streams that connect directly to a mainstem river have a more direct connection to that
river than wetlands that serve as origins for terminal source streams high in a drainage network.
This also applies to riparian/floodplain wetlands that have direct surface-water connections to
streams or rivers. If geographically isolated non-floodplain wetlands have surface-water outputs
(e.g., depressions that experience surface-water spillage or ground-water seeps), the probability
that surface water will infiltrate or be lost through evapotranspiration increases with distance. For
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non-floodplain wetlands connected through ground-water flows, less distant areas are generally
connected through shallower flowpaths, assuming similar soil and geologic properties. These
shallower ground-water flows have the greatest interchange with surface waters and travel
between points in the shortest amount of time. Although elevation is the primary factor
determining areas that are inundated through overbank flooding, connectivity with the river
generally will be higher for riparian/floodplain wetlands located near the river's edge compared
with riparian/floodplain wetlands occurring near the floodplain edge.
Distance from the river network also influences biological connectivity among streams
and wetlands. For example, mortality of an organism due to predators and natural hazards
generally increases with the distance it has to travel to reach the river network. The likelihood
that organisms or propagules traveling randomly or by diffusive mechanisms such as wind will
arrive at the river network decreases as distance increases.
The distribution of distances between wetlands and river networks depends on both the
drainage density of the river network (the total length of stream channels per unit area) and the
density of wetlands. Id. at 2-40. Climate and watershed characteristics influence these spatial
patterns, which can vary widely.
Biota
Biological connectivity results from the interaction of physical characteristics of the
environment—especially those facilitating or restricting dispersal—and species' traits or
behaviors, such as life-cycle requirements, dispersal ability, or responses to environmental cues.
Id. Thus, the types of biota within a river system are integral in determining the river system's
connectivity, and landscape features or species traits that necessitate or facilitate movement of
organisms tend to increase biological connectivity among water bodies.
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Diadromous fauna (e.g., Pacific and Atlantic salmon, certain freshwater shrimps and
snails, American eels), which require both freshwater and marine habitats over their life cycles
and therefore migrate along river networks, provide one of the clearest illustrations of biological
connectivity. Many of these taxa are either obligate or facultative users of headwater streams,
meaning that they either require (obligate) or can take advantage of (facultative) these habitats;
these taxa thereby create a biological connection along the entire length of the river network. Id.
(citing Erman and Hawthorne 1976; Wigington et al. 2006). For example, many Pacific salmon
species spawn in headwater streams, where their young grow for a year or more before migrating
downstream, living their adult life stages in the ocean, and then migrating back upstream to
spawn. Many taxa also can exploit temporary hydrologic connections between rivers and
floodplain wetland habitats caused by flood pulses, moving into these wetlands to feed,
reproduce, or avoid harsh environmental conditions and then returning to the river network. Id. at
2-40, 2-43 (citing Copp 1989; Junk et al. 1989; Smock 1994; Tockner et al. 2000; Richardson et
al. 2005).
Biological connectivity does not solely depend on diadromy, however, as many non-
diadromous organisms are capable of significant movement within river networks. Id. at 2-40.
For example, organisms such as pelagic-spawning fish and mussels release directly into the
water eggs or larvae that disperse downstream with water flow; many fish swim significant
distances both upstream and downstream; and many aquatic macroinvertebrates move or drift
downstream. Id. at 2-40 (citing, e.g., Elliott 1971; Miiller 1982; Gorman 1986; Brittain and
Eikeland 1988; Platania and Altenbach 1998; Elliott, 2003; Hitt and Angermeier 2008; Schwalb
et al. 2010). Taxa capable of movement over land, via either passive transport (e.g., wind
dispersal or attachment to animals capable of terrestrial dispersal) or active movement (e.g.,
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terrestrial dispersal or aerial dispersal of winged adult stages), can establish biotic linkages
between river networks and wetlands, as well as linkages across neighboring river systems.
Science Report at 2-40 (citing Hughes et al. 2009).
Human Activities and Alterations
Human activities frequently alter connectivity between headwater streams,
riparian/floodplain wetlands, non-floodplain wetlands, and downgradient river networks. Id. at 2-
44. In doing so, they alter the transfer and movement of materials and energy between river
system components. In fact, the individual or cumulative effects of headwater streams and
wetlands on river networks often become discernible only following human-mediated changes in
degree of connectivity. These human-mediated changes can increase or decrease hydrologic and
biological connectivity (or, alternatively, decrease or increase hydrologic and biological
isolation). Id at 2-44 to 2-45. For example, activities and alterations such as dams, levees, water
abstraction, piping, channelization, and burial can reduce hydrologic connectivity between
streams and wetlands and rivers, whereas activities and alterations such as wetland drainage,
irrigation, impervious surfaces, interbasin transfers, and channelization can enhance hydrologic
connections. Id. at 2-45. Biological connectivity can be affected similarly: For example, dams
and impoundments might impede biotic movement, whereas nonnative species introductions
artificially increase biotic movement. Further complicating the issue is that a given activity or
alteration might simultaneously increase and decrease connectivity, depending on which part of
the river network is considered. For example, channelization and levee construction reduce
lateral expansion of the river network (thereby reducing hydrologic connections with
floodplains), but might increase this connectivity downstream due to increased frequency and
magnitude of high flows.
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The greatest human impact on riparian/floodplain wetlands and non-floodplain wetlands
has been through wetland drainage, primarily for agricultural purposes. Estimates show that, in
the conterminous United States, states have lost more than half their original wetlands (50%),
with some losing more than 90%; wetland surface areas also have declined significantly. Id.
(citing Dahl 1990).
Drainage causes a direct loss of function and connectivity in cases where wetland
characteristics are completely lost. Id. at 2-45. In the Des Moines lobe of the prairie pothole
region, where more than 90% of the wetlands have been drained, a disproportionate loss of
smaller and larger wetlands has occurred. Accompanying this loss have been significant
decreases in perimeter area ratios—which are associated with greater biogeochemical processing
and groundwater recharge rates—and increased mean distances between wetlands, which
reduces biological connectivity. Id. at 2-45 to 2-46 (citing Van Meter and Basu 2015). Wetland
drainage also increases hydrologic connectivity between the landscape—including drained areas
that retain wetland characteristics—and downstream waters. Effects of this enhanced hydrologic
connectivity include (1) reduced water storage and more rapid conveyance of water to the
network, with subsequent increases in total runoff, baseflows, stormflows, and flooding risk; (2)
increased delivery of sediment and pollutants to downstream waters; and (3) increased transport
of water-dispersing organisms. Id. at 2-46 to 2-47 (citing Babbitt and Tanner 2000; Baber et al.
2002; Mulhouse and Galatowitsch 2003; Wiskow and van der Ploeg 2003; Blann et al. 2009).
Biological connectivity, however, also can decrease with drainage and ditching, as average
distances between wetlands increase and limit the ability of organisms to disperse between
systems aerially or terrestrially. Id. at 2-47 (citing Leibowitz, 2003). Groundwater withdrawal
also can affect wetland connectivity by reducing the number of wetlands. Of particular concern
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in the arid Southwest is that ground-water withdrawal can decrease regional and local water
tables, reducing or altogether eliminating ground-water-dependent wetlands. Id. (citing Patten et
al. 2008). Groundwater withdrawal, however, also can increase connectivity in areas where that
ground water is applied or consumed.
5. Science Report Executive Summary Closing Comments
The structure and function of downstream waters highly depend on materials—broadly
defined as any physical, chemical, or biological entity—that originate outside of the downstream
waters. Most of the constituent materials in rivers, for example, originate from aquatic
ecosystems located upstream in the drainage network or elsewhere in the drainage basin, and are
transported to the river through flowpaths illustrated in the introduction to this report. Thus, the
effects of streams, wetlands, and open waters on rivers are determined by the presence of (1)
physical, chemical, or biological pathways that enable (or inhibit) the transport of materials and
organisms to downstream waters; and (2) functions within the streams, wetlands, and open
waters that alter the quantity and quality of materials and organisms transported along those
pathways to downstream waters.
The strong hydrologic connectivity of river networks is apparent in the existence of
stream channels that form the physical structure of the network itself. Given the evidence
reviewed in the Science Report, it is clear that streams and rivers are much more than a system of
physical channels for efficiently conveying water and other materials downstream. The presence
of physical channels, however, is a compelling line of evidence for surface-water connections
from tributaries, or water bodies of other types, to downstream waters. Physical channels are
defined by continuous bed-and-banks structures, which can include apparent disruptions (such as
by bedrock outcrops, braided channels, flow-through wetlands) associated with changes in the
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material and gradient over and through which water flows. The continuation of bed and banks
downgradient from such disruptions is evidence of the surface connection with the channel that
is upgradient of the perceived disruption.
Although currently available peer-reviewed literature does not identify which types of
non-floodplain wetlands have or lack the types of connections needed to convey functional
effects to downstream waters, additional information (e.g., field assessments, analysis of existing
or new data, reports from local resource agencies) could be used in case-by-case analysis of non-
floodplain wetlands. Importantly, information from emerging research into the connectivity of
non-floodplain wetlands, including studies of the types identified in Section 4.5.2 of the Science
Report, could close some of the current data gaps in the near future. Recent scientific advances in
the fields of mapping, assessment, modeling, and landscape classification indicate that increasing
availability of high-resolution data sets, promising new technologies for watershed-scale
analyses, and methods for classifying landscape units by hydrologic behavior can facilitate and
improve the accuracy of connectivity assessments. Emerging research that expands our ability to
detect and monitor ecologically relevant connections at appropriate scales, metrics to accurately
measure effects on downstream integrity, and management practices that apply what we already
know about ecosystem function will contribute to our ability to identify waters of national
importance and maintain the long-term sustainability and resiliency of valued water resources.
6. Emerging Science
The agencies will continue a transparent review of the science, and gain experience and
expertise as the agencies implement the rule. If evolving science and the agencies' experience
lead to a need for action to alter the jurisdictional categories, any such action will be conducted
as part of a rule-making process. As stated in Conclusion 3 of the Science Report, the
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connectivity and effects of wetlands and open waters that are not structurally linked to other
waters by stream channels and their lateral extensions into riparian areas and floodplains are
more difficult to address solely from evidence available in peer-reviewed studies. The literature
on non-floodplain wetlands shows that these systems have important hydrologic, water-quality,
and habitat functions that can affect downstream waters where connections to them exist; the
literature also provides limited examples of direct effects of non-floodplain wetland isolation on
downstream water integrity. Currently available peer-reviewed literature, however, does not
identify which types of non-floodplain wetlands have or lack the types of connections needed to
convey the effects on downstream waters of functions, materials, or biota provided by those
wetlands. These limitations of the literature, considered in context with the relatively small
number of studies examining the relationships of non-floodplain wetlands to downstream waters
and with comments from the Science Advisory Board on an external review draft of the Science
Report, are reflected in the lower strength of evidence expressed in the conclusions of the
Science Report.
The relatively small body of literature currently available could reflect either a lack of
downstream connections and effects from non-floodplain wetlands, or a lack of peer-reviewed
published studies focused on the connections to and effects of these systems on downstream
waters. Information from other sources, including state and local reports, can be used in case-by-
case analysis of non-floodplain wetlands. Importantly, data from emerging research not yet
published in the peer-reviewed literature could close current data gaps in the near future. Recent
scientific advances in the fields of mapping (e.g., Heine et al. 2004; Tiner 2011; Lang et al.
2012), assessment (e.g., McGlynn and McDonnell 2003; Gergel 2005; McGuire et al. 2005; Ver
Hoef et al. 2006; Leibowitz et al. 2008; Moreno-Mateos et al. 2008; Lane and D'Amico 2010;
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Ver Hoef and Peterson 2010; Shook and Pomeroy 2011; Powers et al. 2012; McDonough et al.
2015), modeling (e.g., Golden etal. 2013; McLaughlin et al. 2014), and landscape classification
(e.g., Wigington et al. 2013) indicate that increasing availability of high-resolution data sets,
promising new technologies for watershed-scale analyses, and methods for classifying landscape
units by hydrologic behavior can facilitate such assessments by broadening their scope and
improving their accuracy. Id. at 6-13. Emerging research that expands our ability to detect and
monitor ecologically relevant connections at appropriate scales, metrics to accurately measure
effects on downstream integrity, and management practices that apply what we already know
about ecosystem function, will contribute to our ability to identify waters of national importance
and maintain the long-term sustainability and resiliency of valued water resources.
ii. Scientific Review
1. Peer Review of the Connectivity Report
The process for developing the Science Report followed standard information quality
guidelines for EPA. In September 2013, EPA released a draft of the Science Report for an
independent SAB review and invited submissions of public comments for consideration by the
SAB panel. In October 2014, after several public meetings and hearings, the SAB completed its
peer review of the draft Science Report. The SAB was highly supportive of the draft Science
Report's conclusions regarding streams, riparian and floodplain wetlands, and open waters, and
recommended strengthening the conclusion regarding non-floodplain waters to include a more
definitive statement that reflects how numerous functions of such waters sustain the integrity of
downstream waters. SAB 2014a. The final peer review report is available on the SAB website, as
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well as in the docket for this rulemaking. EPA revised the draft Science Report based on
comments from the public and recommendations from the SAB panel.
The SAB was established in 1978 by the Environmental Research, Development, and
Demonstration Authorization Act (ERDDAA), to provide independent scientific and technical
advice to the EPA Administrator on the technical basis for Agency positions and regulations.
Advisory functions include peer review of EPA's technical documents, such as the Science
Report. At the time the peer review was completed, the chartered SAB comprised more than 50
members from a variety of sectors including academia, non-profit organizations, foundations,
state governments, consulting firms, and industry. To conduct the peer review, EPA's SAB staff
formed an ad hoc panel based on nominations from the public to serve as the primary reviewers.
The panel consisted of 27 technical experts in array of relevant fields, including hydrology,
wetland and stream ecology, biology, geomorphology, biogeochemistry, and freshwater science.
Similar to the chartered SAB, the panel members represented sectors including academia, a
federal government agency, non-profit organizations, and consulting firms. The chair of the
panel was a member of the chartered SAB.
The SAB process is open and transparent, consistent with the Federal Advisory
Committee Act, 5 U.S.C., App 2, and agency policies regarding Federal advisory committees.
Consequently, the SAB has an approved charter, which must be renewed biennially, announces
its meetings in the Federal Register, and provides opportunities for public comment on issues
before the Board. The SAB staff announced via the Federal Register that they sought public
nominations of technical experts to serve on the expert panel: SAB Panel for the Review of the
EPA Water Body Connectivity Report (via a similar process the public also is invited to
nominate chartered SAB members). The SAB staff then invited the public to comment on the list
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of candidates for the panel. Once the panel was selected, the SAB staff posted a memo on its
website addressing the formation of the panel and the set of determinations that were necessary
for its formation (e.g., no conflicts of interest). In the public notice of the first public meetings
interested members of the public were invited to submit relevant comments for the SAB Panel to
consider pertaining to the review materials, including the charge to the Panel. Over 133,000
public comments were received by the Docket. Every meeting was open to the public, noticed in
the Federal Register, and had time allotted for the public to present their views. In total, the
Panel held a two-day in-person meeting in Washington, DC, in December 2013, and three four-
hour public teleconferences in April, May, and June 2014. The SAB Panel also compiled four
draft versions of its peer review report to inform and assist the meeting deliberations that were
posted on the SAB website. In September 2014, the chartered SAB conducted a public
teleconference to conduct the quality review of the Panel's final draft peer review report. The
peer review report was approved at that meeting, and revisions were made to reflect the chartered
SAB's review. The culmination of that public process was the release of the final peer review
report in October 2014. All meeting minutes and draft reports are available on the SAB website
for public access.
2. SAB Review of the Proposed Rule
In addition to its peer review of the draft Science Report, in a separate effort the SAB
also reviewed the adequacy of the scientific and technical basis of the proposed rule and
provided its advice and comments on the proposal in September 2014. SAB 2014b.The same
SAB Panel that reviewed the draft Science Report met via two public teleconferences in August
2014 to discuss the scientific and technical basis of the proposed rule. The Panel submitted
comments to the Chair of the chartered SAB. SAB 2014c. A work group of chartered SAB
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members considered comments provided by panel members, agency representatives, and the
public on the adequacy of the science informing the rule. This work group then led the
September 2014 public teleconference discussion of the chartered SAB. The public had an
opportunity to submit oral or written comments during these two public meetings. The SAB's
final letter to the EPA Administrator can be found on the SAB website and in the docket for this
rule.
The SAB found that the available science provides an adequate scientific basis for the
key components of the proposed rule. The SAB noted that although water bodies differ in degree
of connectivity that affects the extent of influence they exert on downstream waters (i.e., they
exist on a "connectivity gradient"), the available science supports the conclusion that the types of
water bodies identified as "waters of the United States" in the proposed rule exert strong
influence on the chemical, physical, and biological integrity of downstream waters. In particular,
the SAB expressed support for the proposed rule's inclusion of tributaries and adjacent waters as
categorical waters of the United States and the inclusion of "other waters" on a case-specific
basis, though noting that certain "other waters" can be determined as a subcategory to be
similarly situated.
Regarding tributaries, the SAB found, "[tjhere is strong scientific evidence to support the
EPA's proposal to include all tributaries within the jurisdiction of the Clean Water Act.
Tributaries, as a group, exert strong influence on the physical, chemical, and biological integrity
of downstream waters, even though the degree of connectivity is a function of variation in the
frequency, duration, magnitude, predictability, and consequences of physical, chemical, and
biological process." SAB 2014b at 2. The Board advised the agencies to reconsider the definition
of tributaries because not all tributaries have ordinary high water marks (e.g., ephemeral streams
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with arid and semi-arid environments or in low gradient landscapes where the flow of water is
unlikely to cause an ordinary high water mark). The SAB also advised the agencies to consider
changing the wording in the definition to "bed, bank, and other evidence of flow." Id. at 2. In
addition, the SAB suggested that the agencies reconsider whether flow-through lentic systems
should be included as adjacent waters and wetlands, rather than as tributaries.
Regarding adjacent waters and wetlands, the SAB stated, "[t]he available science
supports the EPA's proposal to include adjacent waters and wetlands as a waters of the United
States. .. .because [they] have a strong influence on the physical, chemical, and biological
integrity of navigable waters." Id. In particular, the SAB noted, "the available science supports
defining adjacency or determination of adjacency on the basis of functional relationships," rather
than "solely on the basis of geographical proximity or distance to jurisdictional waters." Id. at 2-
3.
In the evaluation of "other waters" the SAB found that "scientific literature has
established that 'other waters' can influence downstream waters, particularly when considered in
aggregate." Id. at 3. The SAB thus found it "appropriate to define 'other waters' as waters of the
United States on a case-specific basis, either alone or in combination with similarly situated
waters in the same region." Id. The SAB found that distance could not be the sole indicator used
to evaluate the connection of "other waters" to jurisdictional waters. The SAB also expressed
support for language in one of the options discussed in the preamble to the proposed rule.
Specifically, the SAB stated there is "also adequate scientific evidence to support a
determination that certain subcategories and types of 'other waters' in particular regions of the
United States (e.g., Carolina and Delmarva Bays, Texas coastal prairie wetlands, prairie
potholes, pocosins, western vernal pools) are similarly situated (i.e., they have a similar influence
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on the physical, chemical, and biological integrity of downstream waters and are similarly
situated on the landscape) and thus could be considered waters of the United States." Id. The
Board noted that other sets of wetlands could be identified as "similarly situated" as the science
continues to develop and that science does not support excluding groups of "other waters" or
subcategories thereof from jurisdiction.
The exclusions paragraph of the proposed rule generated the most comments from the
SAB. The SAB noted, "[t]he Clean Water Act exclusions of groundwater and certain other
exclusions listed in the proposed rule and the current regulation do not have scientific
justification." Id. With regard to ditches, the Board found that there is a lack of scientific
knowledge to determine whether ditches should be categorically excluded. For example, some
ditches that would be excluded in the Midwest may drain Cowardin wetlands and may provide
certain ecosystem services, while gullies, rills, and non-wetland swales can be important
conduits for moving water between jurisdictional waters. The SAB also noted that artificial lakes
or ponds, or reflection pools, can be directly connected to jurisdictional waters via either shallow
or deep groundwater. The SAB also recommended that the agencies clarify in the preamble to
the final rule that "significant nexus" is a legal term, not a scientific one.
In finalizing the rule, the agencies took the SAB's advice into careful consideration and
made some changes in response, as well as in response to public comments. These changes
included removing in-stream wetlands and open waters from the tributary category and including
them in the adjacent waters category instead, as well as determining by rule that the five
subcategory waters are similarly situated when located in the same point of entry watershed.
Although the available science is an important factor in the agencies' decision-making, policy
and legal considerations were also carefully contemplated when finalizing the rule.
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B. Scope of Significant Nexus Analysis: "Similarly Situated"
Under the significant nexus standard, waters possess the requisite significant nexus if
they "either alone or in combination with similarly situated [wetjlands in the region, significantly
affect the chemical, physical, and biological integrity of other covered waters more readily
understood as 'navigable.'" Rapanos at 780. Several terms in this standard were not defined. In
this rule the agencies interpret these terms and the scope of "waters of the United States" based
on the goals, objectives, and policies of the statute, the scientific literature, the Supreme Court
opinions, and the agencies' technical expertise and experience. Therefore, for purposes of a
significant nexus analysis, the agencies have determined (1) which waters are "similarly
situated," and thus should be in analyzed in combination in (2) the "region," for purposes of a
significant nexus analysis, and (3) the types of functions that should be analyzed to determine if
waters significantly affect the chemical, physical, and biological integrity of traditional navigable
waters, interstate waters and the territorial seas. These determinations underpin many of the key
elements of the rule and are reflected in the definition of "significant nexus" in the rule,
i. Analyzing "Similarly situated" Waters in Combination
For purposes of the rule, waters are "similarly situated" where they function alike and are
sufficiently close to function together in affecting downstream waters. This approach of
assessing the functions of identified waters in combination is consistent with the science.
Streams, wetlands, and other surface waters interact with ground water and terrestrial
environments throughout the landscape, "from the mountains to the oceans." Id. at 1-2 (citing
Winter et al. 1998). Thus, an integrated perspective of the landscape, provides the appropriate
scientific context for evaluating and interpreting evidence about the physical, chemical, and
biological connectivity of streams, wetlands, and open waters to downstream waters.
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Connectivity has long been a central tenet for the study of aquatic ecosystems. The River
Continuum Concept viewed the entire length of rivers, from source to mouth, as a complex
hydrologic gradient with predictable longitudinal patterns of ecological structure and function.
Id. (citing Vannote et al. 1980). The key pattern is that downstream communities are organized,
in large part, by upstream communities and processes. Id. (citing Vannote et al. 1980; Battin et
al. 2009). The Serial Discontinuity Concept built on the River Continuum Concept to improve
our understanding of how dams and impoundments disrupt the longitudinal patterns of flowing
waters with predictable downstream effects. Id. (Ward and Stanford 1983). The Spiraling
Concept described how river network connectivity can be evaluated and quantified as materials
cycle from dissolved forms to transiently stored forms taken up by living organisms, then back to
dissolved forms, as they are transported downstream. Id. at 1-3 (citing Webster and Patten 1979;
Newbold et al. 1981; Elwood etal. 1983). These three conceptual frameworks focused on the
longitudinal connections of river ecosystems, whereas the subsequent flood pulse concept
examined the importance of lateral connectivity of river channels to floodplains, including
wetlands and open waters, through seasonal expansion and contraction of river networks. Id.
(citing Junk et al. 1989). Ward (1989) summarized the importance of connectivity to lotic
ecosystems along four dimensions: longitudinal, lateral, vertical (surface-subsurface), and
temporal connections; he concluded that running water ecosystems are open systems that are
highly interactive with both contiguous habitats and other ecosystems in the surrounding
landscape. Id. As these conceptual frameworks illustrate, scientists have long recognized the
hydrologic connectivity the physical structure of river networks represents.
More recently, scientists have incorporated this connected network structure into
conceptual frameworks describing ecological patterns in river ecosystems and the processes
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linking them to other watershed components, including wetlands and open waters. Id. (citing
Power and Dietrich 2002; Benda et al. 2004; Nadeau and Rains 2007; Rodriguez-Iturbe et al.
2009). Sheaves (2009) emphasized the key ecological connections—which include process-
based connections that maintain habitat function (e.g., nutrient dynamics, trophic function) and
movements of individual organisms—throughout a complex of interlinked freshwater, tidal
wetlands, and estuarine habitats as critical for the persistence of aquatic species, populations, and
communities over the full range of time scales. Id.
Scientists routinely aggregate the effects of groups of waters, multiplying the known
effect of one water by the number of similar waters in a specific geographic area, or to a certain
scale. This kind of functional aggregation of non-adjacent (and other types of waters) is well-
supported in the scientific literature. See, e.g., Stevenson and Hauer 2002; Leibowitz 2003;
Gamble etal. 2007; Lane and D'Amico 2010; Wilcox etal. 2011. Similarly, streams and rivers
are routinely aggregated by scientists to estimate their combined effect on downstream waters in
the same watershed. This is because chemical, physical, or biological integrity of downstream
waters is directly related to the aggregate contribution of upstream waters that flow into them,
including any tributaries and connected wetlands. As a result, the scientific literature and the
Science Report consistently document that the health of larger downstream waters is directly
related to the aggregate health of waters located upstream, including waters such as wetlands that
may not be hydrologically connected but function together to prevent floodwaters and
contaminants from reaching downstream waters.
Stream and wetland connectivity to downstream waters, and the resulting effects on
downstream water integrity, must be considered cumulatively. Science Report at 1-10. First,
when considering the effect of an individual stream or wetland, including the cumulative effect
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of all the contributions and functions that a stream or wetland provides is essential. For example,
the same stream transports water, removes excess nutrients, mitigates flooding, and provides
refuge for fish when conditions downstream are unfavorable; ignoring any of these functions
would underestimate the overall effect of that stream.
Secondly, and perhaps more importantly, stream channel networks and the watersheds
they drain are fundamentally cumulative in how they are formed and maintained. Excess
precipitation that is not evaporated, taken up by organisms, or stored in soils and geologic layers
moves downgradient as overland flow or through channels, which concentrate flows and carry
sediment, chemical constituents, and organisms. As flows from numerous headwater channels
combine in larger channels, the volume and effects of those flows accumulate as they move
through the river network. As a result, the incremental contributions of individual streams and
wetlands accumulate in the downstream waters. Important cumulative effects are exemplified by
ephemeral flows in arid landscapes, which are key sources of baseflow for downgradient waters,
and by the high rates of denitrification in headwater streams. Id. (citing Schlesinger and Jones
1984; Baillie et al. 2007; Izbicki 2007). The amount of nutrients removed by any one stream
over multiple years or by all headwater streams in a watershed in a given year can have
substantial consequences for downstream waters. Id. (citing Alexander et al. 2007; Alexander et
al. 2009; Bohlke et al. 2009; Helton et al. 2011). Similar cumulative effects on downstream
waters have been documented for other material contributions from headwater streams in the
Science Report. For example, although the probability of a large-magnitude transfer of
organisms from any given headwater stream in a given year might be low {i.e., a low-frequency
connection when each stream is considered individually), headwater streams are the most
abundant type of stream in most watersheds. Thus, the overall probability of a large-magnitude
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transfer of organisms is higher when considered for all headwater streams in a watershed—that
is, there is a high-frequency connection when considered cumulatively at the watershed scale,
compared with probabilities of transport for streams individually. Similarly, a single pollutant
discharge might be negligible but the cumulative effect of multiple discharges could degrade the
integrity of downstream waters.
Evaluating cumulative contributions over time is critical in streams and wetlands with
variable degrees of connectivity. Id. at 1-11. For example, denitrification in a single headwater
stream in any given year might affect downstream waters; over multiple years, however, this
effect could accumulate. Western vernal pools provide another example of cumulative effects
over time. These pools typically occur as complexes in which the hydrology and ecology are
tightly coupled with the local and regional geological processes that formed them. When
seasonal precipitation exceeds wetland storage capacity and wetlands overflow into the river
network and generate stream discharge, the vernal pool basins, swales, and seasonal streams
function as a single surface-water and shallow ground-water system connected to the river
network.
In the aggregate, similarly situated wetlands may have significant effects on the quality of
water many miles away, particularly in circumstances where numerous similarly situated waters
are located in the region and are performing like functions that combine to influence downstream
waters. See, e.g., Jansson et al. 1998; Mitsch etal. 2001; Forbes etal. 2012. Cumulatively, many
small wetlands can hold a large amount of snowmelt and precipitation, reducing the likelihood of
flooding downstream. Science Report at 4-24 (citing Hubbard and Linder 1986).
Scientists can and do routinely classify similar waters and wetlands into groups for a
number of different reasons; because of their inherent physical characteristics, because they
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provide similar functions, because they were formed by similar geomorphic processes, and by
their level of biological diversity, for example. Classifying wetlands based on their functions is
also the basis for the U.S. Army Corps of Engineers hydrogeomorphic (HGM) classification of
wetlands. Brinson 1993. The HGM method is a wetlands assessment approach pioneered by the
Corps in the 1990s, and extensively applied via regional handbooks since then. The Corps HGM
method uses a conceptual framework for identifying broad wetland classes based on common
structural and functional features, which includes a method for using local attributes to further
subdivide the broad classes into regional subclasses. Assessment methods like the HGM provide
a basis for determining if waters provide similar functions based on their structural attributes and
indicator species. Scientists also directly measure attributes and processes taking place in
particular types of waters during in-depth field studies that provide reference information that
informs the understanding of the functions performed by many types of aquatic systems
nationwide.
Consideration of the aggregate effects of wetlands and other waters often gives the most
complete information about how such waters influence the chemical, physical, or biological
integrity of downstream waters. In many watersheds, wetlands have a disproportionate effect on
water quality relative to their surface area because wetland plants slow down water flow,
allowing suspended sediments, nutrients, and pollutants to settle out. They filter these materials
out of the water received from large areas, absorbing or processing them, and then releasing
higher quality water. National Research Council 1995. For an individual wetland, this is most
pronounced where it lies immediately upstream of a drinking water intake, for example. See, e.g.,
Johnston et al. 1990. The cumulative influence of many individual wetlands within watersheds
can strongly affect the spatial scale, magnitude, frequency, and duration of hydrologic, biological
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and chemical fluxes or transfers of water and materials to downstream waters. Science Report at
ES-11.
For example, as discussed in section VII.B., excess nutrients discharged into small
tributary streams in the aggregate can cause algal blooms downstream that reduce dissolved
oxygen levels and increase turbidity in traditional navigable waters, interstate waters, and the
territorial seas. This oxygen depletion in waters, known as hypoxia, has impacted commercial
and recreational fisheries in the northern Gulf of Mexico, as water low in dissolved oxygen
cannot support living aquatic organisms. Committee on Environment and Natural Resources
2000; Freeman etal. 2007. In this instance, the cumulative effects of nutrient export from the
many small headwater streams of the Mississippi River have resulted in large-scale ecological
and economically harmful impacts hundreds of miles downstream. See, e.g., Goolsby etal. 1999.
In their review of the scientific and technical adequacy of the rule, the SAB panel
members "generally agreed that aggregating 'similarly situated' waters is scientifically justified,
given that the combined effects of these waters on downstream waters are often only measurable
in aggregate. Panelists also were generally comfortable with the idea of using "similarly
situated" waters to guide aggregation." SAB 2014c at 4 to 5. One of the main conclusions of the
Science Report is that the incremental contributions of individual streams and wetlands are
cumulative across entire watersheds, and their effects on downstream waters should be evaluated
within the context of other streams and wetlands in that watershed. For example, the Science
Report finds, "[t]he amount of nutrients removed by any one stream over multiple years or by all
headwater streams in a watershed in a given year can have substantial consequences for
downstream waters." Science Report at 1-10. Cumulative effects of streams, wetlands, and open
waters across a watershed must be considered because "[t]he downstream consequences (e.g., the
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amount and quality of materials that eventually reach a river) are determined by the aggregate
effect of contributions and sequential alterations that begin at the source waters and function
along continuous flowpaths to the watershed outlet." Id. at 1-19.
ii. Rationale for Conclusion
As reflected in the rule's definition of "significant nexus," the agencies determined that it
is reasonable to consider waters as "similarly situated" where they function alike and are
sufficiently close to function together in affecting downstream waters. Since the focus of the
significant nexus standard is on protecting and restoring the chemical, physical, and biological
integrity of the nation's waters, the agencies interpret the phrase "similarly situated" in terms of
whether particular waters are providing common, or similar, functions for downstream waters
such that it is reasonable to consider their effect together. Regarding covered tributaries and
covered adjacent waters, the agencies define each water type such that the functions provided are
similar and the waters are situated so as to provide those functions together to affect downstream
traditional navigable waters as a landscape unit.
The science demonstrates that covered tributaries provide many common vital functions
important to the chemical, physical, and biological integrity of downstream waters, regardless of
the size of the tributaries. The science also demonstrates that tributaries within a single point of
entry watershed act together as a system in affecting downstream waters. Structurally and
functionally, tributary networks and the watersheds they drain are fundamentally cumulative in
how they are formed and maintained. Science Report at ES-13. The science also supports the
conclusion that sufficient volume, duration, and frequency of flow are required to create a bed
and banks and ordinary high water mark. The agencies conclude that covered tributaries with a
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bed and banks and ordinary high water mark are similarly situated for purposes of the agencies'
significant nexus analysis.
For covered adjacent waters, the science demonstrates that these waters provide many
similar vital functions to downstream waters, and the agencies defined adjacent waters with
distances limitations to ensure that the waters are providing similar functions to downstream
waters and that the waters are located comparably in the landscape such that the agencies'
reasonably judged them to be similarly situated. In addition, the science supports that interacting
wetland complexes might best be understood as a functional unit, supporting their evaluation in
combination due to their close proximity to each other. Id. at 4-22.
For waters for which a case-specific significant nexus determination is required the
agencies have determined that some waters in specific regions are similarly situated; for other
specified waters, the determination of whether there are any other waters providing similar
functions in a similar situation in the region must be made as part of a case-specific
determination. See preamble and discussion below.
For purposes of analyzing the significant nexus of tributaries and adjacent waters,
tributaries that meet the definition of "tributary" in a watershed draining to an (a)(1) through
(a)(3) water are similarly situated, and adjacent waters that meet the definition of "adjacent" in a
watershed draining to an (a)(1) through (a)(3) water are similarly situated. That is reasonable
because the agencies are identifying characteristics of these waters through the regulation and
documenting the science that demonstrates that these defined tributaries and defined adjacent
waters provide similar functions in the watershed. Assessing the functions of identified waters in
combination is consistent not only with Justice Kennedy's significant nexus standard, but with
the science. As stated above, the functions of the tributaries are inextricably linked and have a
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cumulative effect on the integrity of the downstream traditional navigable water or interstate
water. There is also an obvious locational relationship between the (a)(1), (a)(2) or (a)(3) water
and the streams, lakes, and wetlands that meet the definition of tributaries and the definition of
adjacent waters; these waters have a clear linear relationship resulting from the simple existence
of the channel itself and the direction of flow.
For waters for which a case-specific significant nexus analysis is required, numerous
factors affect chemical, physical, and biological connectivity, operating at multiple spatial and
temporal scales, and interacting with each other in complex ways, to determine where
components of aquatic systems fall on the connectivity-isolation gradient at a given time. Some
of these factors include climate, watershed characteristics, spatial distribution patterns, biota, and
human activities and alterations. Id. at 3-33. Recognizing the limits on the ability to observe or
document all of these interacting factors, it is reasonable to look for visible patterns in the
landscape and waters that are often indicative of the connectivity factors, in determining what
waters to aggregate. Due to relative similarity of soils, topography, or groundwater connections,
for example, there may be a group of wetlands scattered throughout a watershed, at similar
distances from the tributaries in the watershed and performing similar functions. It is appropriate
to assess the significance of the nexus of those waters in the aggregate, consistent with Justice
Kennedy's standard.
The agencies conclude, consistent with the science and the goals and purposes of the
CWA, that it is reasonable to assess the effects of waters in combination based on the similarity
of the functions they provide to the downstream water and their location in the watershed.
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C. "In the Region"
i. Identifying "In the Region" As the Point of Entry Watershed
The watershed that drains to the single point of entry to a traditional navigable water,
interstate water or territorial sea is a logical spatial framework for the evaluation of the nexus.
Scientists utilize watersheds to evaluate the connections and strength of those connections that
are fundamental to the significant nexus inquiry. The Science Report stated that watersheds are
integrated at multiple spatial and temporal scales by flows of surface water and ground water,
transport and transformation of physical and chemical materials, and movements of organisms.
Science Report at 6-8.
The watershed is also the most reasonable region within which to assess significant nexus
from a water quality management perspective, because the traditional navigable water, interstate
water, or the territorial sea is the downstream affected water whose quality is dependent on the
condition of the contributing upstream waters, including streams, lakes, and wetlands. To restore
or maintain the health of the downstream affected water, it is standard practice to evaluate the
condition of the waters that are in the contributing watershed and to develop a plan to address the
issues of concern. The functions of the contributing waters are inextricably linked and have a
cumulative effect on the integrity of the downstream traditional navigable water, interstate water,
or territorial sea. The size of that watershed can be determined by identifying the geographic
area that drains to the nearest traditional navigable water, interstate water or the territorial seas,
and then using that point of entry watershed to conduct a significant nexus evaluation. See, e.g.,
Black 1997.
The Corps has used watershed framework approaches for water resources and navigation
approaches for over 100 years, and in the regulatory program since its inception. Also, using a
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watershed framework is consistent with over two decades of practice by EPA and many other
governmental, academic, and other entities which recognize that a watershed approach is the
most effective framework to address water resource challenges. See, e.g., U.S. Environmental
Protection Agency 1996; U.S. Environmental Protection Agency 2010; U.S. Environmental
Protection Agency 2014. The agencies both recognize the importance of the watershed approach
by investing in opportunities to advance watershed protection and in developing useful
watershed tools and services. Applying a watershed approach continues to be a priority of EPA,
and is embedded in the agency's most recent strategic plans, which are used to drive progress
toward the EPA's health and environmental goals. U.S. Environmental Protection Agency 2010;
U.S. Environmental Protection Agency 2014.
ii. Rationale for Conclusion
The agencies have determined that because the movement of water from watershed
drainage basins to river networks and lakes shapes the development and function of these
systems in a way that is critical to their long term health, the watershed is reasonable and
technically appropriate to use for purposes of interpreting "waters of the United States," in light
of the phrase "in the region" in Justice Kennedy's standard. See, e.g., Montgomery 1999. The
agencies have reasonably limited the region to the watershed that drains to the nearest traditional
navigable water, interstate water, or the territorial seas to ensure that the area for analysis is
determined by those foundational waters protected by the CWA.
Using a watershed as the framework for conducting significant nexus evaluations is
scientifically supportable. Watersheds are generally regarded as the most appropriate spatial unit
for water resource management. See, e.g., Omernik and Bailey 1997; Montgomery 1999; Winter
2001; Baron et al. 2002; Allan 2004; U.S. Environmental Protection Agency 2008; Wigington el
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al. 2013. Anthropogenic actions and natural events can have widespread effects within the
watershed that collectively impact the quality of the relevant traditional navigable water,
interstate water or territorial sea. Levick et al. 2008. For these reasons, it is more appropriate to
conduct a significant nexus determination at the watershed scale than to focus on a specific site,
such as an individual stream segment. The watershed size reflects the specific water management
objective, and is scaled up or down as is appropriate to meet that objective. If the objective is to
manage the water quality in a particular receiving water body (the "target" water body), the
watershed should include all those waters that are contributing to that target water since they will
primarily determine the quality of the receiving water.
The agencies recognize that the point of entry watershed will vary in size depending upon
the region of the country and the distance a particular tributary network is from the nearest
traditional navigable water, interstate water, or the territorial seas. That variation appropriately
reflects regional variation in climate, geology, and terrain and also ensures that the "region" for
purposes of a significant nexus evaluation represents a functioning aquatic system. In the arid
West, the agencies recognize there may be situations where the single point of entry watershed is
very large, and it may be reasonable to evaluate all similarly situated waters in a smaller
watershed.
In addition, the Science Report also supports evaluating waters on a watershed scale,
concluding, " [cumulative effects across a watershed must be considered when quantifying the
frequency, duration, and magnitude of connectivity, to evaluate the downstream effects of
streams and wetlands. Science Report at ES-14 (emphasis added). In addition, the Science
Report notes, "[a] river is the time-integrated result of all waters contributing to it, and
connectivity is the property that spatially integrates the individual components of the watershed.
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In discussions of connectivity, the watershed scale is the appropriate context for interpreting
technical evidence about individual watershed components." Id. at 2-1 (citing Newbold etal.
1982b; Stanford and Ward 1993; Bunn and Arthington 2002; Power and Dietrich 2002; Benda et
al. 2004; Naiman et al. 2005; Nadeau and Rains 2007; Rodriguez-Iturbe et al. 2009). In light of
the scientific literature, the longstanding approach of the agencies' implementation of the CWA,
and the statutory goals underpinning Justice Kennedy's significant nexus framework, the
watershed draining to the nearest traditional navigable water, interstate water, or the territorial
sea, is the appropriate "region" for a significant nexus analysis.
D. "Significant Nexus"
The agencies are defining the term "significant nexus" to mean "that a water, including
wetlands, either alone or in combination with other similarly situated waters in the region,
significantly affects the chemical, physical, or biological integrity" of a traditional navigable
water, interstate water, or the territorial sea. For an effect to be significant, it must be more than
speculative or insubstantial. For purposes of determining whether or not a water has a significant
nexus, the water's effect on downstream (a)(1) through (a)(3) waters shall be assessed by
evaluating the aquatic functions listed in the definition, which are highlighted below. A water
has a significant nexus when any single function or combination of functions performed by the
water, alone or together with similarly situated waters in the region, contributes significantly to
the chemical, physical, or biological integrity of the nearest traditional navigable water, interstate
water, or the territorial seas. Functions relevant to the significant nexus evaluation are the
following: (A) sediment trapping, (B) nutrient recycling, (C) pollutant trapping, transformation,
filtering, and transport, (D) retention and attenuation of flood waters, (E) runoff storage, (F)
contribution of flow, (G) export of organic matter, (H) export of food resources, or (I) provision
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of life cycle dependent aquatic habitat (such as foraging, feeding, nesting, breeding, spawning, or
use as a nursery area) for species located in an (a)(1) through (3) water.
The agencies' definition of the term "significant nexus" in the rule is consistent with
language in SWANCC and Rapanos, and with the goals, objectives, and policies of the CWA.
The definition reflects that not all waters have a requisite connection to traditional navigable
waters, interstate waters, or the territorial seas sufficient to be determined jurisdictional. Justice
Kennedy was clear that to be covered, waters must significantly affect the chemical, physical, or
biological integrity of a downstream navigable water and that the requisite nexus must be more
than "speculative or insubstantial," Rapanos, at 780. The agencies define significant nexus in
precisely those terms. Under the rule a "significant nexus" is established by a showing of a
significant chemical, physical, or biological effect.
Since the Rapanos decision, the agencies have extensive experience making significant
nexus determinations, and that experience and expertise has informed the judgment of the
agencies as reflected in the provisions of the rule. The agencies, most often the Corps, have
made more than 400,000 CWA jurisdictional determinations since 2008. Of those, more than
120,000 have been case-specific significant nexus determinations. The agencies have made
determinations in every state in the country, from the arid West to the tropics of Hawaii, from the
Appalachian Mountains in the East to the lush forests of the Northwest. With field staff located
across 38 Corps District offices and 10 EPA regional offices, the agencies have almost a decade
of nationwide experience in making significant nexus determinations. Through this experience,
the agencies developed wide-ranging technical expertise in assessing the hydrologic flowpaths
along which water and materials are transported and transformed that determine the degree of
chemical, physical, or biological connectivity, as well as the variations in climate, geology, and
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terrain within and among watersheds and over time that affect the functions (such as the removal
or transformation of pollutants) performed by streams, wetlands, and open waters for
downstream traditional navigable waters, interstate waters, or the territorial seas.
In addition, these individual jurisdictional determinations have been for waters ranging
from an intermittent stream that provides flow to a drinking water source to a group of floodplain
wetlands in North Dakota that provide important protection from floodwaters to downstream
communities alongside the Red River to headwater mountain streams that provide high quality
water that supplies baseflow and reduces the harmful concentrations of pollutants in the
mainstem river below. The agencies utilized many tools and many sources of information to
help make these determinations, including U.S. Geological Survey (USGS) and state and local
topographic maps, aerial photography, National Wetlands Inventory data from the U.S. Fish and
Wildlife Service, soil surveys, watershed studies, scientific literature and references, and field
work. See, e.g., U.S. Army Corps of Engineers 2007a. For example, USGS and state and local
stream maps and datasets, aerial photography, gage data, flood predictions, historic records of
water flow, statistical data, watershed assessments, monitoring data, and field observations are
often used to help assess the contributions of flow of tributary streams, including intermittent and
ephemeral streams, to downstream traditional navigable waters, interstate waters, or the
territorial seas. M; U.S. Army Corps of Engineers 2005b. Similarly, floodplain and topographic
maps of federal, state, and local agencies, modeling tools, and field observations can be used to
assess how wetlands are trapping floodwaters that might otherwise affect downstream waters.
Further, the agencies utilize the large body of scientific literature regarding the functions of
tributary streams, regardless of their flow permanence, and of wetlands and open waters to
inform their evaluations of significant nexus. In addition, the agencies have experience and
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expertise for decades prior to and since the SWANCC and Rapanos decisions with making
jurisdictional determinations, and consider hydrology, ordinary high water mark, biota, and other
technical factors in implementing Clean Water Act programs. This immersion in the science
along with the practical expertise developed through case-specific determinations across the
country and in diverse settings is reflected in the agencies' conclusions with respect to waters
that have a significant nexus, as well as where the agencies have drawn lines demarking where
"waters of the United States" end.
i. Scope of Significant Nexus Analysis
Under the significant nexus standard, waters possess the requisite significant nexus if
they "either alone or in combination with similarly situated [wetjlands in the region, significantly
affect the chemical, physical, and biological integrity of other covered waters more readily
understood as 'navigable.'" Rapanos at 780. Several terms in this standard were not defined. In
this rule the agencies interpret these terms and the scope of "waters of the United States" based
on the goals, objectives, and policies of the statute, the scientific literature, the Supreme Court
opinions, and the agencies' technical expertise and experience. Therefore, for purposes of a
significant nexus analysis, the agencies have determined: (1) which waters are "similarly
situated," and thus should be in analyzed in combination in (2) the "region," for purposes of a
significant nexus analysis, and (3) the types of functions that should be analyzed to determine if
waters significantly affect the chemical, physical, and biological integrity of traditional navigable
waters, interstate waters and the territorial seas. These determinations underpin many of the key
elements of the rule and are reflected in the definition of "significant nexus" in the rule.
In the rule's definition of "significant nexus," the agencies identify the functions that
waters provide that can significantly affect the chemical, physical, or biological integrity of
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traditional navigable waters, interstate waters and the territorial seas. Functions to be considered
for the purposes of determining significant nexus are sediment trapping; nutrient recycling;
pollutant trapping, transformation, filtering, and transport; retention and attenuation of
floodwaters; runoff storage; contribution of flow; export of organic matter; export of food
resources; and provision of life-cycle dependent aquatic habitat (such as foraging, feeding,
nesting, breeding, spawning, use as a nursery area) for species located in traditional navigable
waters, interstate waters, or the territorial seas. The effect of an upstream water can be significant
even when a water, alone or in combination, is providing a subset, or even just one, of the
functions listed. In addition to the scientific support mentioned in this section for including these
functions in the definition of significant nexus, sections VI, VII, and VIII also provide additional
information on how impoundments, tributaries, and adjacent waters in providing these functions
significantly affect (a)(1) through (a)(3) waters, while section XI highlights how the waters
specified at (a)(7) and (a)(8) can provide such functions for a case-specific significant nexus
determination.
Science demonstrates that these aquatic functions provided by smaller streams, ponds,
wetlands and other waters are important for protecting the chemical, physical, and biological
integrity of downstream traditional navigable waters, interstate waters, and the territorial seas.
For example, States identify sediment and nutrients among the primary contaminants in the
nation's waters. See, e.g., U.S. Environmental Protection Agency 2003; U.S. Environmental
Protection Agency 2008. Sediment storage and export via streams to downstream waters is
critical for maintaining the river network, including the formation of channel features. Science
Report at 3-13. Although sediment is essential to river systems, excess sediment can impair
ecological integrity by filling interstitial spaces, reducing channel capacity, blocking sunlight
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transmission through the water column, and increasing contaminant and nutrient concentrations.
Id. (citing Wood and Armitage 1997). Streams and wetlands can prevent excess deposits of
sediment downstream and reduce pollutant concentrations in downstream waters. Id. at ES-2 to
ES-3; ES-8. Thus the function of trapping of excess sediment, along with export of sediment, has
a significant effect on the chemical, physical, and biological integrity of downstream waters.
Nutrient recycling results in the uptake and transformation of large quantities of nitrogen
and other nutrients that otherwise would be transported directly downstream, thereby decreasing
nutrient loads and associated impairments due to excess nutrients in downstream waters. Id. at
ES-8. Streams, wetlands, and open waters improve water quality through the assimilation,
transformation, or sequestration of pollutants, including excess nutrients and chemical
contaminants such as pesticides and metals that can degrade downstream water integrity. Id. at
ES-2 to ES-3, ES-13. Nutrient transport exports nutrients downstream and can degrade water
quality and lead to stream impairments. Id. at ES-2. Nutrients are necessary to support aquatic
life, but excess nutrients lead to excessive plant growth and hypoxia, in which over-enrichment
causes dissolved oxygen concentrations to fall below the level necessary to sustain most aquatic
animal life in the downstream waters. Id. at ES-8. Nutrient recycling, retention, and export can
significantly affect downstream chemical integrity by impacting downstream water quality.
The contribution of flow downstream is an important function, as upstream waters can be
a cumulative source of the majority of the total mean annual flow to bigger downstream rivers
and waters, including via the recharge of baseflow. Id. at ES-8. Streams, wetlands, and open
waters contribute surface and subsurface water downstream, and are the dominant sources of
water in most rivers. Id. at ES-2, ES-7, ES-9, ES-11. Contribution of flow can significantly affect
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the physical integrity of downstream waters, helping to sustain the volume of water in larger
waters.
Small streams and wetlands are particularly effective at retaining and attenuating
floodwaters. Id. atES-2, ES-8, ES-9, ES-10. By subsequently releasing (desynchronizing)
floodwaters and retaining large volumes of stormwater that could otherwise negatively affect the
condition or function of downstream waters, streams and adjacent wetlands and open waters
affect the physical integrity of downstream traditional navigable waters, interstate waters, or the
territorial seas. Id. at ES-3. This function can reduce flood peaks downstream and can also
maintain downstream river baseflows by recharging alluvial aquifers.
Streams, wetlands, and open waters supply downstream waters with dissolved and
particulate organic matter (e.g., leaves, wood), which support biological activity throughout the
river network. Id. at ES-2, ES-3. In addition to organic matter, streams, wetlands, and open
waters can also export other food resources downstream, such as aquatic insects that are the food
source for fish in downstream waters. Id. The export of organic matter and food resources
downstream is important to maintaining the food webs and thus the biological integrity of
traditional navigable waters, interstate waters, and the territorial seas.
Streams, wetlands, and open waters provide life-cycle dependent aquatic habitat (such as
foraging, feeding, nesting, breeding, spawning, and use as a nursery area) for species located in
traditional navigable waters, interstate waters, or the territorial seas. Id. at ES-2, ES-3, ES-8, ES-
9, ES-11. Many species require different habitats for different resources (e.g., food, spawning
habitat, overwintering habitat), and thus move throughout the river network over their life-
cycles. Id. at ES-11, 3-38 (citing Schlosser 1991; Fausch et al. 2002). For example, headwater
streams can provide refuge habitat under adverse conditions, enabling fish to persist and
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recolonize downstream areas once conditions have improved. Id. at 3-38 (citing Meyer and
Wallace 2001; Meyer et al. 2004; Huryn et al. 2005). These upstream systems form integral
components of downstream food webs, providing nursery habitat for breeding fish and
amphibians, colonization opportunities for stream invertebrates, and maturation habitat for
stream insects, including for species that are critical to downstream ecosystem function. Id. at
ES-3. The provision of life-cycle dependent aquatic habitat for species located in downstream
waters significantly affects the biological integrity of those downstream waters.
Tributaries, adjacent wetlands, and open waters can perform multiple functions, including
functions that change depending upon the season. Id. at 2-24. For example, the same stream can
contribute flow when evapotranspiration is low and can retain water when evapotranspiration is
high. Id. These functions, particularly when considered in aggregate with the functions of
similarly situated waters in the region, can significantly affect the chemical, physical, or
biological integrity of a traditional navigable water, interstate water, or the territorial seas. When
considering the effect of an individual stream, wetland, or open water, all contributions and
functions that the water provides should be evaluated cumulatively. Id. at 6-10. For example, the
same wetland retains sediment, removes excess nutrients, mitigates flooding, and provides
habitat for amphibians that also live downstream; if any of these functions is ignored, the overall
effect of that wetland would be underestimated. See, e.g., id. at ES-7, 6-10. It is important to
note, however, that a water or wetland can provide just one function that may significantly affect
the chemical, physical or biological integrity of the downstream water,
ii. Rationale for Conclusion
The agencies' definition of the term "significant nexus" in the rule is consistent with
language in Riverside Bayview, SWANCC, and Rapanos, and with the goals, objectives, and
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policies of the CWA. The definition reflects that not all waters have a requisite connection to
traditional navigable waters, interstate waters, or the territorial seas sufficient to be determined
jurisdictional. Justice Kennedy was clear that to be covered, waters must significantly affect the
chemical, physical, or biological integrity of a downstream navigable water and that the requisite
nexus must be more than "speculative or insubstantial," Rapanos, at 780. The agencies define
significant nexus in precisely those terms. Under the rule a "significant nexus" is established by
a showing of a significant chemical, physical, or biological effect. In characterizing the
significant nexus standard, Justice Kennedy stated: "[t]he required nexus must be assessed in
terms of the statute's goals and purposes. Congress enacted the [CWA] to 'restore and maintain
the chemical, physical, and biological integrity of the Nation's waters' . . . ." 547 U.S. at 779. It
is clear that Congress intended the CWA to "restore and maintain" all three forms of "integrity,"
33 U.S.C. § 1251(a), so if any one of these forms is compromised then that is contrary to the
statute's stated objective. It would subvert the objective if the CWA only protected waters upon
a showing that they had effects on every attribute of the integrity a traditional navigable water,
interstate water, or the territorial sea.
The agencies define the term "significant nexus" consistent with language in Riverside
Bayview, SWANCC, and Rapanos. The definition of "significant nexus" at (c)(7) relies most
significantly on Justice Kennedy's Rapanos opinion which recognizes that not all waters have
this requisite connection to waters covered by paragraphs (a)(1) through (a)(3) of the regulations.
Riverside Bayview also informs the agencies' interpretation of the statute as the Court stated "to
achieve the goal of preserving and improving adjacent wetlands that have significant ecological
and hydrological impacts on navigable waters, it was appropriate for the Corps to regulate all
adjacent wetlands, even though some might not have any impacts on navigable waters."
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Riverside Bayview at 135 n.9. Justice Kennedy was clear that the requisite nexus must be more
than "speculative or insubstantial. . . Rapanos, 547 U.S. at 780, in order to be significant and
the rule defines significant nexus in precisely those terms. In Rapanos, Justice Kennedy stated
that in both the consolidated cases before the Court the record contained evidence suggesting the
possible existence of a significant nexus according to the principles he identified. See id. at 783.
Justice Kennedy concluded that "the end result in these cases and many others to be considered
by the Corps may be the same as that suggested by the dissent, namely, that the Corps' assertion
of jurisdiction is valid." Id. Justice Kennedy remanded the cases because neither the agency nor
the reviewing courts properly applied the controlling legal standard - whether the wetlands at
issue had a significant nexus. See id. Justice Kennedy was clear however, that "[m]uch the same
evidence should permit the establishment of a significant nexus with navigable-in-fact waters,
particularly if supplemented by further evidence about the significance of the tributaries to which
the wetlands are connected." Id. at 784.
With respect to one of the wetlands at issue in the consolidated Rapanos cases, Justice
Kennedy stated:
In Carabell, No. 04-1384, the record also contains evidence bearing on the jurisdictional
inquiry. The Corps noted in deciding the administrative appeal that "[bjesides the effects
on wildlife habitat and water quality, the [district office] also noted that the project would
have a major, long-term detrimental effect on wetlands, flood retention, recreation and
conservation and overall ecology. . . . The Corps' evaluation further noted that by
'eliminat[ing] the potential ability of the wetland to act as a sediment catch basin," the
proposed project "would contribute to increased runoff and . . . accretion along the drain
and further downstream in Auvase Creek.' .... And it observed that increased runoff
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from the site would likely cause downstream areas to "see an increase in possible
flooding magnitude and frequency."
Id. at 785-86. Justice Kennedy also expressed concern that "[t]he conditional language in
these assessments—'potential ability,' 'possible flooding'—could suggest an undue degree of
speculation." Mat 786.
Justice Kennedy's observations regarding the underlying case provide guidance as to
what it means for a nexus to be more than merely speculative or insubstantial and inform the
definition of "significant nexus." It is important to note, however, that certain terms used in a
scientific context do not have the same implications that they have in a legal or policy context.
For example, discussion in the scientific literature of a wetland's "potential" to act as a sink for
floodwater and pollutants, means that wetlands in general do indeed perform those functions, but
whether a particular wetland performs that function is dependent upon there is a flood in the
watershed. That does not mean, however, that this nexus to downstream waters is "speculative;"
indeed the wetland will provide these functions when there is a flood or pollutants flow into the
wetland.
The agencies' significant nexus determinations are informed by the Science Report's
synthesis in Chapter 5. Based on the evidence presented in Chapters 3 and 4, ordering the three
broad categories of water bodies considered in the Science Report—streams, floodplain
wetlands, and non-floodplain wetlands—along a connectivity gradient is possible. Of these three
water body types, streams are, in general, more connected to and have better-documented effects
on downstream waters than either wetland category. Floodplain wetlands (and open waters), in
turn, tend to be more connected to downstream waters, and have better-documented downstream
effects, than non-floodplain wetlands (and open waters). This ordering must be recognized as a
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broad generalization, and considerable overlap can occur among the types, given the spatial and
temporal variability in connectivity documented in these habitats. Nevertheless, several key lines
of evidence support this hypothesized ordering of water body types along the gradient.
1. Streams are connected to rivers by a continuous channel, which is a physical reflection
of surface connectivity. Formation of a channel indicates that connectivity, in terms of its
combined descriptors (frequency, duration, magnitude, timing) is sufficiently strong (or
"effective") and outweighs terrestrialization processes (e.g., revegetation, wind-mediated
processes, soil formation processes).
2. Within-channel flows are more efficient for moving water, sediment, pollutants, and
other materials than overland flow; for some aquatic organisms, channels are the only possible
transport routes. Channels are places where excess water and materials from the landscape are
concentrated as they are transmitted downstream. Recurrent flow of sufficient magnitude over a
given area of landscape selects routes with least resistance, which develop into branched channel
networks with a repeating, cumulative pattern of smaller channels that join at confluences to
form larger channels.
3. The continuous channels connecting streams to rivers also represent areas of relatively
high shallow subsurface connectivity (shallow ground-water recharge and upwelling). Channels
are typically more permeable than surrounding soils, lack dense terrestrial vegetation (and thus
have lower uptake and evapotranspiration loss), and are topographic low points closer to
concentrated shallow ground water.
4. Floodplain wetlands and open waters are connected to rivers by historical and recurrent
surface connectivity. Riparian and floodplain wetlands are maintained by the recurrent
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inundation and deposition of materials from streams and rivers during the peak and recession of
flood flows.
5. Riparian and floodplain wetlands and open waters are close to river networks and thus
more likely to have strong connectivity with the downstream water than more distant wetlands,
when all other conditions are similar.
6. Non-floodplain wetlands are positioned outside the floodplain, and so are not subject
to direct flooding from the river or stream. Any hydrologic connections to the river system are
therefore unidirectional (from wetland to downstream water and not vice-versa). They are also
likely to be more distant from the network, increasing the flowpath lengths and travel time to it.
7. Because of their large numbers, headwater streams and associated wetlands
cumulatively represent a large portion of the land interface with a downstream water. These
areas provide functions that enhance both exchanges with and buffering of the downstream
water, making them critical to mediating the recognized relationship between the integrity of
downstream waters and the land use and stressor loadings from the surrounding landscape.
8. Connectivity to downstream waters is reflected in the distribution of aquatic organisms
and their dependence on particular aquatic habitats across different stages of their life cycles. For
example, the recurrent presence of completely aquatic organisms (i.e., organisms that lack
terrestrial life stages, overland dispersal, stages resistant to drying) in streams and wetlands that
periodically dry provides indirect evidence for surface-water connections. Because many aquatic
species can move and disperse overland, aquatic habitats can be highly connected biologically in
the absence of hydrologic connectivity.
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III. Traditional Navigable Waters
EPA and the Corps are proposing no changes to the existing regulation related to
traditional navigable waters and at paragraph (a)(1) will continue to assert jurisdiction over all
waters which are currently used, or were used in the past, or may be susceptible to use in
interstate or foreign commerce, including all waters which are subject to the ebb and flow of the
tide. See e.g., 33 CFR § 328.3(a)(1); 40 CFR § 230.3(s)(l); 40 CFR § 122.2 ("waters of the
U.S.")). These "(a)(l)waters" are the "traditional navigable waters." These (a)(1) waters include
all of the waters defined in 33 CFR Part 329, which implements sections 9 and 10 of the Rivers
and Harbors Act, and by numerous decisions of the federal courts, plus all other waters that are
navigable-in-fact (e.g., the Great Salt Lake, UT and Lake Minnetonka, MN).
To determine whether a water body constitutes an (a)(1) water under the regulations,
relevant considerations include Corps regulations, prior determinations by the Corps and by the
federal courts, and case law. Corps districts and EPA regions would determine whether a
particular water body is a traditional navigable water based on application of those
considerations to the specific facts in each case.
As noted above, the (a)(1) waters include, but are not limited to, waters that meet any of
the tests set forth in 33 CFR Part 329 (e.g., the water body is (a) subject to the ebb and flow of
the tide, and/or (b) the water body is presently used, or has been used in the past, or may be
susceptible for use (with or without reasonable improvements) to transport interstate or foreign
commerce). The Corps districts have made determinations in the past under these regulations for
purposes of asserting jurisdiction under sections 9 and 10 of the Rivers and Harbors Act of 1899
(33 U.S.C. §§ 401 and 403). Pursuant to 33 CFR § 329.16, the Corps maintains lists of final
determinations of navigability for purposes of Corps jurisdiction under the Rivers and Harbors
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Act of 1899. While absence from the list should not be taken as an indication that the water is not
navigable (329.16(b)), Corps districts and EPA Regions rely on any final Corps determination
that a water body meets any of the tests set forth in Part 329.
If the federal courts have determined that a water body is navigable-in-fact under federal
law for any purpose, that water body qualifies as a "traditional navigable water" subject to CWA
jurisdiction under 33 CFR § 328.3(a)(1) and 40 CFR § 230.3(s)(l). Corps districts and EPA
regions are guided by the relevant opinions of the federal courts in determining whether such
water bodies are "currently used, or were used in the past, or may be susceptible to use in
interstate or foreign commerce" (33 CFR § 328.3(a)(1); 40 CFR § 230.3(s)(l)) or "navigable-in-
fact."
The definition of "navigable-in-fact" derives from a long line of cases originating with
The Daniel Ball, 77 U.S. 557 (1870). The Supreme Court stated:
Those rivers must be regarded as public navigable rivers in law which are
navigable in fact. And they are navigable in fact when they are used, or are
susceptible of being used, in their ordinary condition, as highways for commerce,
over which trade and travel are or may be conducted in the customary modes of
trade and travel on water.
The Daniel Ball, 77 U.S. at 563.
In The Montello, the Supreme Court clarified that "customary modes of trade and travel
on water" encompasses more than just navigation by larger vessels:
The capability of use by the public for purposes of transportation and commerce
affords the true criterion of the navigability of a river, rather than the extent and
manner of that use. If it be capable in its natural state of being used for purposes
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of commerce, no matter in what mode the commerce may be conducted, it is
navigable in fact, and becomes in law a public river or highway.
The Montello, 87 U.S. 430, 441-42 (1874). In that case, the Court held that early fur trading
using canoes sufficiently showed that the Fox River was a navigable water of the United States.
The Court was careful to note that the bare fact of a water's capacity for navigation alone is not
sufficient; that capacity must be indicative of the water's being "generally and commonly useful
to some purpose of trade or agriculture." Id. at 442.
In Economy Light & Power, the Supreme Court held that a waterway need not be
continuously navigable; it is navigable even if it has "occasional natural obstructions or
portages" and even if it is not navigable "at all seasons ... or at all stages of the water."
Economy Light & Power Co. v. U.S., 256 U.S. 113, 122(1921).
In United States v. Holt State Bank, 270 U.S. 49 (1926), the Supreme Court summarized
the law on navigability as of 1926 as follows:
The rule long since approved by this court in applying the Constitution and laws
of the United States is that streams or lakes which are navigable in fact must be
regarded as navigable in law; that they are navigable in fact when they are used,
or are susceptible of being used, in their natural and ordinary condition, as
highways for commerce, over which trade and travel are or may be conducted in
the customary modes of trade and travel on water; and further that navigability
does not depend on the particular mode in which such use is or may be had -
whether by steamboats, sailing vessels or flatboats- nor on an absence of
occasional difficulties in navigation, but on the fact, if it be a fact, that the stream
in its natural and ordinary condition affords a channel for useful commerce.
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Holt State Bank, 270 U.S. at 56.
In U.S. v. Utah, 283 U.S. 64 (1931) and U.S. v. AppalachianElec. Power Co, 311 U.S.
377 (1940), the Supreme Court held that so long as a water is susceptible to use as a highway of
commerce, it is navigable-in-fact, even if the water has never been used for any commercial
purpose. U.S. v. Utah, at 81-83 ("The question of that susceptibility in the ordinary condition of
the rivers, rather than of the mere manner or extent of actual use, is the crucial question."); U.S.
v. Appalachian Elec. Power Co., 311 U.S. at 416 ("Nor is lack of commercial traffic a bar to a
conclusion of navigability where personal or private use by boats demonstrates the availability of
the stream for the simpler types of commercial navigation.") Appalachian Power further held
that a water is navigable-in-fact even if it is not navigable and never has been but may become so
by reasonable improvements. 311 U.S. at 407-08.
In 1971, in Utah v. United States, 403 U.S. 9 (1971), the Supreme Court held that the
Great Salt Lake, an intrastate water body, was navigable under federal law even though it "is not
part of a navigable interstate or international commercial highway." Id. at 10. In doing so, the
Supreme Court stated that the fact that the Lake was used for hauling of animals by ranchers
rather than for the transportation of "water-borne freight" was an "irrelevant detail." Id. at 11.
"The lake was used as a highway and that is the gist of the federal test." Id.
Most recently, the Supreme Court explained:
The Daniel Ball formulation has been invoked in considering the navigability of
waters for purposes of assessing federal regulatory authority under the
Constitution, and the application of specific federal statutes, as to the waters and
their beds. See, e.g., ibid.; TheMontello, 20 Wall. 430, 439, 22 L.Ed. 391 (1874);
United States v. Appalachian Elec. Power Co., 311 U.S. 377, 406, and n. 21, 61
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S.Ct. 291, 85 L.Ed. 243 (1940) (Federal Power Act); Rapanos v. United States,
547 U.S. 715, 730-731, 126 S.Ct. 2208, 165 L.Ed.2d 159 (2006) (plurality
opinion) (Clean Water Act); id., at 761, 126 S.Ct. 2208 (KENNEDY, J.,
concurring in judgment) (same). It has been used as well to determine questions
of title to water beds under the equal-footing doctrine. See Utah, supra, at 76, 51
S.Ct. 438; Oklahoma v. Texas, 258 U.S. 574, 586, 42 S.Ct. 406, 66 L.Ed. 771
(1922); Holt State Bank, supra, at 56, 46 S.Ct. 197. It should be noted, however,
that the test for navigability is not applied in the same way in these distinct types
of cases.
Among the differences in application are the following. For state title under the
equal-footing doctrine, navigability is determined at the time of statehood, see
Utah, supra, at 75, 51 S.Ct. 438, and based on the "natural and ordinary
condition" of the water, see Oklahoma, supra, at 591, 42 S.Ct. 406. In contrast,
admiralty jurisdiction extends to water routes made navigable even if not formerly
so, see, e.g., Ex parte Boyer, 109 U.S. 629, 631-632, 3 S.Ct. 434, 27 L.Ed. 1056
(1884) (artificial canal); and federal regulatory authority encompasses waters that
only recently have become navigable, see, e.g., Philadelphia Co. v. Stimson, 223
U.S. 605, 634-635, 32 S.Ct. 340, 56 L.Ed. 570 (1912), were once navigable but
are no longer, see Economy Light & Power Co. v. United States, 256 U.S. 113,
123-124, 41 S.Ct. 409, 65 L.Ed. 847 (1921), or are not navigable and never have
been but may become so by reasonable improvements, see Appalachian Elec.
Power Co., supra, at 407-408, 61 S.Ct. 291. With respect to the federal commerce
power, the inquiry regarding navigation historically focused on interstate
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commerce. See The Daniel Ball, 1229*1229 supra, at 564. And, of course, the
commerce power extends beyond navigation. See Kaiser Aetna v. United States,
444 U.S. 164, 173-174, 100 S.Ct. 383, 62 L.Ed.2d 332 (1979). In contrast, for title
purposes, the inquiry depends only on navigation and not on interstate travel. See
Utah, supra, at 76, 51 S.Ct. 438. This list of differences is not exhaustive. Indeed,
"[e]ach application of [the Daniel Ball] test... is apt to uncover variations and
refinements which require further elaboration." Appalachian Elec. Power Co.,
supra, at 406, 61 S.Ct. 291.
PPL Montana v. Montana, 565 U.S. (2012).
Also of note are two decisions from the courts of appeals. In FPL Energy Marine Hydro,
a case involving the Federal Power Act, the D.C. Circuit reiterated the fact that"actual use is not
necessary for a navigability determination" and repeated earlier Supreme Court holdings that
navigability and capacity of a water to carry commerce could be shown through "physical
characteristics and experimentation " FPL Energy Marine Hydro LLC v. FERC, 287 F.3d 1151,
1157 (D.C. Cir. 2002). In that case, the D.C. Circuit upheld a FERC navigability determination
that was based upon three experimental canoe trips taken specifically to demonstrate the river's
navigability. Id. at 1158-59.
The 9th Circuit has also implemented the Supreme Court's holding that a water need only
be susceptible to being used for waterborne commerce to be navigable-in-fact. Alaska v. Ahtna,
Inc., 891 F.2d 1404 (9th Cir. 1989). In Ahtna, the 9th Circuit held that current use of an Alaskan
river for commercial recreational boating was sufficient evidence of the water's capacity to carry
waterborne commerce at the time that Alaska became a state. Id. at 1405. It was found to be
irrelevant whether or not the river was actually being navigated or being used for commerce at
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the time, because current navigation showed that the river always had the capacity to support
such navigation. Id. at 1404.
In summary, when determining whether a water body qualifies as a "traditional navigable
water" (i.e., an (a)(1) water), relevant considerations include whether the water body meets any
of the tests set forth in Part 329, or a federal court has determined that the water body is
"navigable-in-fact" under federal law for any purpose, or the water body is "navigable-in-fact"
under the standards that have been used by the federal courts.
Some commenters argued that although the proposed rule would not change the
regulatory text for traditional navigable waters from the existing regulations, the agencies'
interpretation of the scope of waters that are considered traditional navigable waters broadly
expands the concept of traditional navigable waters and is inconsistent with the definition relied
on by the Rapanos plurality and Justice Kennedy's concurrence. The final rule makes no change
to the agencies' longstanding regulatory text for traditional navigable waters. The agencies
disagree that the interpretation and guidance in the preamble to the proposed rule and in this
section represents an expansion of the concept of traditional navigable waters. The interpretation
and guidance is not an expansion from that given by the agencies in 2008, and is simply based on
existing caselaw. See Appendix B. Further, while the 2008 attachment, the preamble to the
proposed rule, and this section reflect the considerations the agencies will use when making
traditional navigable waters determinations, when such a determination is part of a final agency
action, if challenged, the federal courts will decide whether a particular water is a traditional
navigable water for purposes of the Clean Water Act.
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IV. Interstate Waters
The agencies made no change to the interstate waters section of the existing regulations,
and the agencies will continue to assert jurisdiction over interstate waters, including interstate
wetlands. The language of the CWA is clear that Congress intended the term "navigable waters"
to include interstate waters, and the agencies' interpretation, promulgated contemporaneously
with the passage of the CWA, is consistent with the statute and legislative history. The Supreme
Court's decisions in SWANCC and Rapanos did not address the interstate waters provision of the
existing regulation.
The CWA was enacted in 1972. EPA's contemporaneous regulatory definition of
"waters of the United States," promulgated in 1973, included interstate waters. The definition
has been EPA's interpretation of the geographic jurisdictional scope of the CWA for
approximately 40 years. Congress has also been aware of and has supported the Agency's
longstanding interpretation of the CWA. "Where 'an agency's statutory construction has been
fully brought to the attention of the public and the Congress, and the latter has not sought to alter
that interpretation although it has amended the statute in other respects, then presumably the
legislative intent has been correctly discerned.'" North Haven Board of Education v. Bell, 102
456 U.S. 512, 535 (1982) (iquoting United States v. Rutherford, 442 U.S. 544 n. 10 (1979)
(internal quotes omitted)).
A. The Language of the Clean Water Act, the Statute as a Whole, and the
Statutory History Demonstrate Congress' Clear Intent to Include Interstate
Waters as "Navigable Waters" Subject to the Clean Water Act
While as a general matter, the scope of the terms "navigable waters" and "waters of the
United States" is ambiguous, the language of the CWA, particularly when read as a whole,
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demonstrates that Congress clearly intended to continue to subject interstate waters to federal
regulation. The statutory history of federal water pollution control places the terms of the CWA
in context and provides further evidence of Congressional intent to include interstate waters
within the scope of the "navigable waters" protected by the Act. Congress clearly intended to
subject interstate waters to CWA jurisdiction without imposing a requirement that they be water
that is navigable for purposes of federal regulation under the Commerce Clause themselves or be
connected to water that is navigable for purposes of federal regulation under the Commerce
Clause.9 The CWA is clear that interstate waters that were previously subject to federal
regulation remain subject to federal regulation. The text of the CWA, specifically the CWA's
provision with respect to interstate waters and their water quality standards, in conjunction with
the definition of navigable waters, provides clear indication of Congress' intent. Thus, interstate
waters are "navigable waters" protected by the CWA.
(I) The Plain Language of the Clean Water Act and the Statute as a Whole
Clearly Indicate Congress' Intent to Include Interstate Waters within the Scope of
"Navigable Waters" for Purposes of the Clean Water Act
Under well settled principles, the phrase "navigable waters" should not be read in
isolation from the remainder of the statute. As the Supreme Court has explained:
The definition of words in isolation, however, is not necessarily controlling in
statutory construction. A word in a statute may or may not extend to the outer
9 For purposes of the CWA, EPA and the Corps have interpreted the term "traditional navigable waters" to include
all of the "navigable waters of the United States," defined in 33 CFR Part 329 and by numerous decisions of the
federal courts, plus all other waters that are navigable-in-fact (e.g., the Great Salt Lake, UT and Lake Minnetonka
MN). This section explains why EPA and the Corps do not interpret the CWA or the Supreme Court's decisions in
Solid Waste Agency of Northern Cook County (SWANCC) v. U.S. Army Corps of Engineers, 531 U.S. 159 (2001)
and Rapanos v. United States, 547 U.S. 715 (2006), to restrict CWA jurisdiction over interstate waters to only those
interstate waters that are traditional navigable waters or that connect to traditional navigable waters.
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May 2015
limits of its definitional possibilities. Interpretation of a word or phrase depends
upon reading the whole statutory text, considering the purpose and context of the
statute, and consulting any precedents or authorities that inform the analysis.
Dolan v. U.S. Postal Service, 546 U.S. 481, 486 (2006); see also United States Nat'l. Bank of
Oregon v. Indep. Ins. Agents of Am., Inc., 508 U.S. 439, 455 (1993).
While the term "navigable waters" is ambiguous, interstate waters are waters that are
clearly covered by the plain language of the definition of "navigable waters."10 Congress
defined "navigable waters" to mean "the waters of the United States, including the territorial
seas." Interstate waters are waters of the several States and, thus, the United States. While the
1972 Act was clearly not limited to interstate waters, it was clearly intended to include interstate
waters.
Furthermore, the CWA does not simply define "navigable waters." Other provisions of
the statute provide additional textual evidence of the scope of this term of the Act. Most
importantly, there is a specific provision in the 1972 CWA establishing requirements for those
interstate waters which were subject to the prior Water Pollution Control Acts.
The CWA requires states to establish water quality standards for navigable waters and
submit them to the Administrator for review.11 Under section 303(a) of the Act, in order to
carry out the purpose of this Act, any water quality standard applicable to interstate waters
which was adopted by any State and submitted to, and approved by, or is awaiting approval by,
10 The Supreme Court has found that the term "waters of the United States" is ambiguous in some respects.
Rapanos, 547 U.S. at 752 (plurality opinion), 804 (dissent).
11 Section 303 of the Act requires the states to submit revised and new water quality standards to the Administrator
for review. CWA section 303(c)(2)(A). Such revised or new water quality standards "shall consist of the
designated uses of the navigable waters involved and the water quality criteria for such waters." Id. If the
Administrator determines that a revised or new standard is not consistent with the Act's requirements, or determines
that a revised or new standard is necessary to meet the Act's requirements, and the state does not make required
changes, "[t]he Administrator shall promptly prepare and publish proposed regulations setting forth a revised or new
water quality standard for the navigable waters involved." CWA section 303(c)(4).
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the Administrator pursuant to this Act as in effect immediately prior to the date of enactment of
the Federal Water Pollution Control Act Amendments of 1972, shall remain in effect unless the
Administrator determined that such standard is not consistent with the applicable requirements of
the Act as in effect immediately prior to the date of enactment of the Federal Water Pollution
Control Act Amendments of 1972. If the Administrator makes such a determination he shall,
within three months after the date of enactment of the Federal Water Pollution Control Act
Amendments of 1972, notify the State and specify the changes needed to meet such
requirements. If such changes are not adopted by the State within ninety days after the date of
such notification, the Administrator shall promulgate such changes in accordance with
subsection (b). CWA section 303(a)(1) {emphasis added).
Under the 1965 Act, as discussed in more detail below, states were directed to develop
water quality standards establishing water quality goals for interstate waters. By the early 1970s,
all the states had adopted such water quality standards. Advanced Notice of Proposed
Rulemaking, Water Quality Standards Regulation, 63 FR 36742, 36745, July 7, 1998. In section
303(a), Congress clearly intended for existing federal regulation of interstate waters to continue
under the amended CWA. Water quality standards for interstate waters were not merely to
remain in effect, but EPA was required to actively assess those water quality standards and even
promulgate revised standards for interstate waters if states did not make necessary changes. By
the plain language of the statute, these water quality standards for interstate waters were to
remain in effect "in order to carry out the purpose of this Act." The objective of the Act is "to
restore and maintain the chemical, physical, and biological integrity of the Nation's waters."
CWA section 101(a). It would contravene Congress' clearly stated intent for a court to impose
an additional jurisdictional requirement on all rivers, lakes, and other waters that flow across, or
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form a part of, state boundaries ("interstate waters" as defined by the 1948 Act, § 10, 62 Stat.
1161), such that interstate waters that were previously protected were no longer protected
because they lacked a connection to a water that is navigable for purposes of federal regulation
under the Commerce Clause. Nor would all the existing water quality standards be "carrying]
out the purpose of this Act," if the only water quality standards that could be implemented
through the Act (through, for example, National Pollutant Discharge Elimination System
permits under section 402) were those water quality standards established for interstate waters
that are also waters that are navigable for purposes of federal regulation under the Commerce
Clause or that connect to waters that are navigable for purposes of federal regulation under the
Commerce Clause. Nowhere in section 303(a) does Congress make such a distinction.
(2) The Federal Water Pollution Control Statute That Became the Clean Water Act
Covered Interstate Waters
In 1972, when Congress rewrote the law governing water pollution, two federal statutes
addressed discharges of pollutants into interstate waters and water that is navigable for purposes
of federal regulation under the Commerce Clause, and tributaries of each: the Water Pollution
Control Act of 1948, as amended, and section 13 of the Rivers and Harbors Act of 1899 (known
as the "Refuse Act"). The Water Pollution Control Act extended federal authority over interstate
waters and their tributaries, while the Refuse Act extended federal jurisdiction over the
"navigable waters of the United States" and their tributaries. These two separate statutes
demonstrate that Congress recognized that interstate waters and "navigable waters of the United
States" were independent lawful bases of federal jurisdiction.
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i. The Federal Water Pollution Control Act Prior to 1972
From the outset, and through all the amendments pre-dating the 1972 Amendments, the
federal authority to abate water pollution under the Water Pollution Control Act, and the Federal
Water Pollution Control Act (FWPCA) as it was renamed in 1956, extended to interstate waters.
In addition, since first enacted in 1948, and throughout all the amendments, the goals of the Act
have been, inter alia, to protect public water supplies, propagation of fish and aquatic life,
recreation, agricultural, industrial, and other legitimate uses. See 62 Stat. 1155 and 33 U.S.C. §
466 (1952), 33 U.S.C. § 466 (1958), 33 U.S.C. § 466 (1964), 33 U.S.C. § 1151 (1970).
In 1948, Congress enacted the Water Pollution Control Act in connection with the
exercise of jurisdiction over the waterways of the Nation and in the consequence of the benefits
to public health and welfare by the abatement of stream pollution. See Pub. L. No. 80-845, 62
Stat. 1155 (June 30, 1948). The Act authorized technical assistance and financial aid to states for
stream pollution abatement programs, and made discharges of pollutants into interstate waters
and their tributaries a nuisance, subject to abatement and prosecution by the United States. See §
2(d)(1),(4), 62 Stat, at 1156-1157 (section 2(d)(1) of the Water Pollution Control Act of 1948, 62
Stat, at 1156, stated that the "pollution of interstate waters" in or adjacent to any State or States
(whether the matter causing or contributing to such pollution is discharged directly into such
waters or reaches such waters after discharge into a tributary of such waters), which endangers
the health or welfare of persons in a State other than that in which the discharge originates, is
declared to be a public nuisance and subject to abatement as provided by the Act. (emphasis
added)); § 2(a), 62 Stat. 1155 (requiring comprehensive programs for "interstate waters and
tributaries thereof'); § 5, 62 Stat. 1158 (authorizing loans for sewage treatment to abate
discharges into "interstate waters or into a tributary of such waters"). Under the statute,
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"interstate waters" were defined as all rivers, lakes, and other waters that flow across, or form a
part of, state boundaries. § 10, 62 Stat. 1161.
In 1956, Congress strengthened measures for controlling pollution of interstate waters
and their tributaries. Pub. L. No. 84-660, 70 Stat. 498 (1956) (directing further cooperation
between the federal and state governments in development of comprehensive programs for
eliminating or reducing "the pollution of interstate waters and tributaries" and improving the
sanitary condition of surface and underground waters, and authorizing the Surgeon General to
make joint investigations with States into the conditions of and discharges into "any waters of
any State or States").
In 1961, Congress amended the FWPCA to substitute the term "interstate or navigable
waters" for "interstate waters." See Pub. L. No. 87-88, 75 Stat. 208 (1961). Accordingly,
beginning in 1961, the provisions of the FWPCA applied to all interstate waters and navigable
waters and the tributaries of each, see 33 U.S.C. §§ 466a, 466g(a) (1964).12
In 1965, Congress approved a second set of major legislative changes, requiring each
state to develop water quality standards for interstate waters within its boundaries by 1967. Pub.
L. No. 89-234, 79 Stat. 908 (1965).13 Failing establishment of adequate standards by the state,
the Act authorized establishment of water quality standards by federal regulation. Id. at 908.
The 1965 Amendments provided that the discharge of matter "into such interstate waters or
portions thereof," which reduces the quality of such waters below the water quality standards
12
Congress did not define the term "navigable waters" in the 1961 Amendments, or in subsequent FWPCA
Amendments, until 1972.
1 3
In 1967, the state of Arizona created the Water Quality Control Council (Council) to implement the requirements
of the 1965 FWPCA. The Council adopted water quality standards for those waters that were considered "interstate
waters" pursuant to the existing federal law. The Council identified the Santa Cruz River as an interstate water and
promulgated water quality standards for the river in accordance with federal law.
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established under this subsection (whether the matter causing or contributing to such reduction is
discharged directly into such waters or reaches such waters after discharge into tributaries of
such waters), is subject to abatement through procedures specified in the Act, including (after
conferences and negotiations and consideration by a Hearing Board) legal action in the courts.
Id. at 909.14
ii. The Refuse Act
Since its original enactment in 1899, the Refuse Act has prohibited the discharge of
refuse matter "into any navigable water of the United States, or into any tributary of any
navigable water." Ch. 425, 30 Stat. 1152 (1899). It also has prohibited the discharge of such
material on the bank of any tributary where it is liable to be washed into a navigable water. Id.
Violators are subject to fines and imprisonment. Id. at 1153 (codified at 33 U.S.C. § 412). In
1966, the Supreme Court upheld the Corps' interpretation of the Refuse Act as prohibiting
discharges that pollute the navigable waters, and not just those discharges that obstruct
navigation. United States v. Standard Oil Co., 384 U.S. 224, 230 (1966). In 1970, President
Nixon signed an Executive Order directing the Corps (in consultation with the Federal Water
Pollution Control Administration15) to implement a permit program under section 13 of the RHA
"to regulate the discharge of pollutants and other refuse matter into the navigable waters of the
United States or their tributaries and the placing of such matter upon their banks." E.O. 11574,
35 F R 19627, Dec. 25, 1970. In 1971, the Corps promulgated regulations establishing the
Refuse Act Permit Program. 36 FR 6564, 6565, April 7, 1971. The regulations made it unlawful
14 The 1966 Amendments authorized civil fines for failing to provide information about an alleged discharge
causing or contributing to water pollution. Pub. L. No. 89-753, 80 Stat. 1250 (1966); see also S. Rep. No. 414, 92d
Congress, 1st Sess. 10 (1972) (describing the history of the FWPCA).
15 In December 1970, administration of the Federal Water Pollution Control Administration was transferred from
the Secretary of the Interior to EPA. S. Rep. No. 414, 92d Congress, 1st Sess. (1972).
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to discharge any pollutant (except those flowing from streets and sewers in a liquid state) into a
navigable waterway or tributary, except pursuant to a permit. Under the permit program, EPA
advised the Corps regarding the consistency of a proposed discharge with water quality standards
and considerations, and the Corps evaluated a permit application for impacts on anchorage,
navigation, and fish and wildlife resources. Id. at 6566.
iii. The Federal Water Pollution Control Act Amendments of 1972
When Congress passed the Federal Water Pollution Control Act Amendments of 1972
(referred to hereinafter as the CWA or CWA), it was not acting on a blank slate. It was
amending existing law that provided for a federal/state program to address water pollution. The
Supreme Court has recognized that Congress, in enacting the CWA in 1972, "intended to
repudiate limits that had been placed on federal regulation by earlier water pollution control
statutes and to exercise its powers under the Commerce Clause to regulate at least some waters
that would not be deemed 'navigable' under the classical understanding of that term." Riverside
Bayview Homes, 474 U.S. at 133; see also International Paper Co. v. Ouellette, 479 U.S. 481,
486, n.6 (1987).
The amendments of 1972 defined the term "navigable waters" to mean "the waters of the
United States, including the territorial seas." 33 U.S.C. § 1362(7). While earlier versions of the
1972 legislation defined the term to mean "the navigable waters of the United States," the
Conference Committee deleted the word "navigable" and expressed the intent to reject prior
geographic limits on the scope of federal water-protection measures. Compare S. Conf. Rep. No.
1236, 92d Cong., 2d Sess. 144 (1972), withH.R. Rep. No. 911, 92 Cong., 2d Sess. 356 (1972)
(bill reported by the House Committee provided that "[t]he term 'navigable waters' means the
navigable waters of the United States, including the territorial seas"); see also S. Rep. No. 414,
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92d Cong., 1st Sess. 77 ("Through a narrow interpretation of the definition of interstate waters
the implementation of the 1965 Act was severely limited. . . . Therefore, reference to the control
requirements must be made to the navigable waters, portions thereof, and their tributaries.").
Thus, Congress intended the scope of the 1972 Act to include, at a minimum, the waters already
subject to federal water pollution control law - both interstate waters and waters that are
navigable for purposes of federal regulation under the Commerce Clause. Those statutes covered
interstate waters, defined interstate waters without requiring that they be a traditional navigable
water or be connected to water that is a traditional navigable water, and demonstrated that
Congress knew that there are interstate waters that are not navigable for purposes of federal
regulation under the Commerce Clause.
In fact, Congress amended the Federal Water Pollution Control Act in 1961 to substitute
the term "interstate or navigable waters" for "interstate waters," demonstrating that Congress
wanted to be very clear that it was asserting jurisdiction over both types of waters: interstate
waters even if they were not navigable for purposes of federal regulation under the Commerce
Clause, and traditional navigable waters even if they were not interstate waters. At no point were
the interstate waters already subject to federal water pollution control authority required to be
navigable or to connect to a traditional navigable water. Further, as discussed above, the
legislative history clearly demonstrates that Congress was expanding jurisdiction - not
narrowing it - with the 1972 amendments. Thus, it is reasonable to conclude that by defining
"navigable waters" as "the waters of the United States" in the 1972 amendments, Congress
included not just traditionally navigable waters, but all waters previously regulated under the
Federal Water Pollution Control Act, including non-navigable interstate waters.
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Based on the statutory definition of navigable waters, the requirement of section 303(a)
for water quality standards for interstate waters to remain in effect, the purposes of the Act, and
the more than three decades of federal water pollution control regulation that provides a context
for reading those provisions of the statute, the intent of Congress is clear that the term "navigable
waters" includes "interstate waters" as an independent basis for CWA jurisdiction, whether or
not they themselves are traditional navigable waters or are connected to a traditional navigable
water.
B. Supreme Court Precedent Supports CWA Jurisdiction over Interstate
Waters Without Respect to Navigability
In two seminal decisions, the Supreme Court established that resolving interstate water
pollution issues was a matter of federal law and that the CWA was the comprehensive regulatory
scheme for addressing interstate water pollution. Illinois v. Milwaukee, 406 U.S. 91 (1972); City
of Milwaukee v. Illinois, 451 U.S. 304 (1981). In both of these decisions, the Court held that
federal law applied to interstate waters. Moreover, these cases analyzed the applicable federal
statutory schemes and determined that the provisions of the Federal Water Pollution Control Act
and the CWA regulating water pollution applied generally to interstate waters. The holdings of
these cases recognized the federal interest in interstate water quality pollution; and City of
Milwaukee recognized that CWA jurisdiction extends to interstate waters without regard to
navigability.
In Illinois v. Milwaukee, the Court considered a public nuisance claim brought by the
state of Illinois against the city of Milwaukee to address the adverse effects of Milwaukee's
discharges of poorly treated sewage into Lake Michigan, "a body of interstate water." 406 U.S.
at 93. In relevant part, the Court held that the federal common law of nuisance was an
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appropriate mechanism to resolve disputes involving interstate water pollution. 406 U.S. at 107
("federal courts will be empowered to appraise the equities of suits alleging creation of a public
nuisance by water pollution"). The Court further noted that in such actions the Court could
consider a state's interest in protecting its high water quality standards from "the more degrading
standards of a neighbor." Id.
In reaching this conclusion, the Court examined in detail the scope of the federal
regulatory scheme as it existed prior to the October, 1972 FWPCA amendments. In its April,
1972 decision, the Court concluded that the Federal Water Pollution Control Act "makes clear
that it is federal, not state, law that in the end controls the pollution of interstate or navigable
waters." 406 U.S. at 102 {emphasis added). The Court, in this case, concluded that the
regulatory provisions of the Federal Water Pollution Control Act did not address the right of a
state to file suit to protect water quality. However, this was not because this statute did not reach
interstate waters. The Court specifically noted that section 10(a) of the Federal Water Pollution
Control Act "makes pollution of interstate or navigable waters subject 'to abatement'" 406 U.S.
at 102 {emphasis added). Rather, the Court noted that the plaintiff in this action was seeking
relief outside the scope of the Federal Water Pollution Control Act and that statute explicitly
provided that independent "state and interstate action to abate pollution of interstate or navigable
waters shall be encouraged and shall not... be displaced by Federal enforcement action." 406
U.S. at 104 {citing section 10(b) of the Federal Water Pollution Control Act).
In addition, in Illinois v. Milwaukee, the Court acknowledged that it was essential for
federal law to resolve interstate water pollution disputes, citing with approval the following
discussion from Texas v. Pankey:
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Federal common law and not the varying common law of the individual states is, we
think, entitled and necessary to be recognized as a basis for dealing in uniform standard
with the environmental rights of a State against improper impairment by sources outside
its domain.... Until the field has been made the subject of comprehensive legislation or
authorized administrative standards, only a federal common law basis can provide an
adequate means for dealing with such claims as alleged federal rights.
406 U.S. at 107 n. 9, citing Texas v. Pankey, 441 F.2d 236, 241-242.
In City of Milwaukee, the Court revisited this dispute and addressed the expanded
statutory provisions of the CWA regulating water pollution. The scope of the CWA amendments
led the Court to reverse its decision in Illinois v. Milwaukee.
Congress has not left the formulation of appropriate federal standards to the courts
through application of often vague and indeterminate nuisance concepts and maxims of
equity jurisprudence, but rather has occupied the field through the establishment of a
comprehensive regulatory program supervised by an expert administrative agency. The
1972 Amendments to the Federal Water Pollution Control Act were not merely another
law "touching interstate waters".... Rather, the Amendments were viewed by Congress as
a "total restructuring" and "complete rewriting" of the existing water pollution legislation
considered in that case.
451 U.S. at 317.
The Court's analysis in Illinois v. Milwaukee made clear that federal common law was
necessary to protect "the environmental rights of States against improper impairment by sources
outside its domain." 406 U.S. at 107, n. 9. In the context of interstate water pollution, nothing in
the Court's language or logic limits the reach of this conclusion to only navigable interstate
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waters. In City of Milwaukee, the Court found that the CWA was the "comprehensive regulatory
program" that "occupied the field" (451 U.S. 317) with regard to interstate water pollution,
eliminating the basis for an independent common law of nuisance to address interstate water
pollution. Since the federal common law of nuisance (as well as the statutory provisions
regulating water pollution in the Federal Water Pollution Control Act) applied to interstate
waters whether navigable or not, the CWA could only occupy the field of interstate water
pollution if it too extended to non-navigable as well as navigable interstate waters.
With regard to the specifics of interstate water pollution, the City of Milwaukee Court
noted that, in Illinois v. Milwaukee, it had been concerned that Illinois did not have a forum in
which it could protect its interests in abating water pollution from out of state, absent the
recognition of federal common law remedies. 451 U.S. at 325. The Court then went on to
analyze in detail the specific procedures created by the CWA "for a State affected by decisions
of a neighboring State's permit-granting agency to seek redress." 451 U.S. at 326. The Court
noted that "any State whose waters may be affected by the issuance of a permit" is to receive
notice and the opportunity to comment on the permit. Id. (citing to CWA section 402(b)(3)(5).
In addition the Court noted provisions giving EPA the authority to veto and issue its own permits
"if a stalemate between an issuing and objecting state develops." Id. (citing to CWA sections
402(d)(2)(A),(4)). In light of these protections for states affected by interstate water pollution,
the court concluded that
[t]he statutory scheme established by Congress provides a forum for the pursuit of such
claims before expert agencies by means of the permit-granting process. It would be quite
inconsistent with this scheme if federal courts were in effect to "write their own ticket"
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under the guise of federal common law after permits have already been issued and
permittees have been planning and operating in reliance on them.
451 U.S. at 326.
Nothing in the language or the reasoning of this discussion limits the applicability of
these protections of interstate waters to navigable interstate waters or interstate waters connected
to navigable waters. If these protections only applied to navigable interstate waters, a
downstream state would be unable to protect many of its waters from out of state water pollution.
This would hardly constitute a comprehensive regulatory scheme that occupied the field of
interstate water pollution.
For these reasons, the holdings and the reasoning of these decisions establish that the
regulatory reach of the CWA extends to all interstate waters without regard to navigability.16
C. The Supreme Court's Decisions in SWANCC and Rapanos Do Not Limit or
Constrain Clean Water Act Jurisdiction Over Non-navigable Interstate
Waters
As noted above, the Supreme Court recognized that Congress, in enacting the CWA,
"intended to repudiate limits that had been placed on federal regulation by earlier water pollution
control statutes and to exercise its powers under the Commerce Clause to regulate at least some
waters that would not be deemed 'navigable' under the classical understanding of that term."
Riverside Bayview, 474 U.S. at 133; see also International Paper Co. v. Ouellette, 479 U.S. 481,
16 Nothing in subsequent Supreme Court case law regarding interstate waters in any way conflicts with the
agencies'interpretation. See International Paper v. Ouellette, 479 U.S. 481 (1987); Arkansas v. Oklahoma, 503
U.S. 91 (1992). In both of these cases, the Court detailed how the CWA had supplanted the federal common law of
nuisance to establish the controlling statutory scheme for addressing interstate water pollution disputes. Nothing in
either decision limits the applicability of the CWA to interstate water pollution disputes involving navigable
interstate waters or interstate waters connected to navigable waters.
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486 n.6, (1987). In Riverside Bayview, and subsequently in SWANCC and Rapanos, the Court
addressed the construction of the CWA terms "navigable waters" and "the waters of the United
States." In none of these cases did the Supreme Court address interstate waters, nor did it
overrule prior Supreme Court precedent which addressed the interaction between the CWA and
federal common law to address pollution of interstate waters. Therefore, the statute, even in light
of SWANCC and Rapanos, does not impose an additional requirement that interstate waters must
be water that is navigable for purposes of federal regulation under the Commerce Clause or
connected to water that is navigable for purposes of federal regulation under the Commerce
Clause to be jurisdictional waters for purposes of the CWA.
At the outset, it is worth noting that neither SWANCC nor Rapanos dealt with the
jurisdictional status of interstate waters. Repeatedly in the SWANCC decision the Court
emphasized that the question presented concerned the jurisdiction status of nonnavigable
intrastate waters located in two Illinois counties. SWANCC 531 U.S. at 165-166, 171 ("we thus
decline to... hold that isolated ponds, some only seasonal, wholly located within two Illinois
counties fall under § 404(a) definition of navigable waters...") {emphasis added). Nowhere in
Justice Rehnquist's majority opinion in SWANCC does the Court discuss the Court's interstate
water case law.17 The Court does not even discuss the fact that CWA jurisdictional regulations
identify interstate waters as regulated "waters of the United States." In fact, the repeated
emphasis on the intrastate nature of the waters at issue can be read as an attempt to distinguish
SWANCC from the Court's interstate water jurisprudence.
In Rapanos, the properties at issue were located entirely within the State of Michigan.
547 U.S. 715, 762-764. Thus, the Court had no occasion to address the text of the CWA with
17
It is worth noting the Justice Rehnquist was also the author of City of Milwaukee.
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respect to interstate waters or the agencies' regulatory provisions concerning interstate waters.
In addition, neither Justice Kennedy nor the plurality discusses the impact of their opinions on
the Court's interstate waters jurisprudence. The plurality decision acknowledges that CWA
jurisdictional regulations include interstate waters. 547 U.S. 715, 724. However, the plurality
did not discuss in any detail its views as to the continued vitality of regulations concerning such
waters.
Moreover, one of the analytical underpinnings of the SWANCC and Rapanos decisions is
irrelevant to analysis of regulations asserting jurisdiction over interstate waters. In SWANCC,
the Court declined to defer to agency regulations asserting jurisdiction over isolated waters
because
[wjhere an administrative interpretation of a statute invokes the outer limits of Congress'
power, we expect a clear indication that Congress intended that result....This requirement
stems from our prudential desire not to needlessly reach constitutional issues and our
assumption that Congress does not casually authorize administrative agencies to interpret
a statute to push the limit of Congressional authority.... This concern is heightened where
the administrative interpretation alerts the federal-state framework by permitting federal
encroachment upon a traditional state power.
531 U.S. at 172-173 (citations omitted).
However, the Court's analysis in Illinois v. Milwaukee and City of Milwaukee makes
clear that Congress has broad authority to create federal law to resolve interstate water pollution
disputes. As discussed above, the Court in Illinois v. Milwaukee, invited further federal
legislation to address interstate water pollution, and in so doing concluded that state law was not
an appropriate basis for addressing interstate water pollution issues. 406 U.S. at 107 n. 9 {citing
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Texas v. Pankey, 441 F.2d 236, 241-242). In City of Milwaukee, the Court indicated that central
to its holding in Illinois v. Milwaukee was its concern "that Illinois did not have any forum to
protect its interests [in the matters involving interstate water pollution]." 451 U.S. 325. As
discussed above, the Court cited with approval the statutory provisions of the CWA regulating
water pollution as an appropriate means to address that concern.
The City of Milwaukee and Illinois v. Milwaukee decisions make clear that assertion of
federal authority to resolve disputes involving interstate waters does not alter "the federal-state
framework by permitting federal encroachment on a traditional state power." 531 U.S. at 173.
"Our decisions concerning interstate waters contain the same theme. Rights in interstate streams,
like questions of boundaries, have been recognized as presenting federal questions." Illinois v.
Milwaukee, 406 U.S. at 105 (internal quotations and citations omitted).
The Supreme Court's analysis in SWANCC and Rapanos materially altered the criteria for
analyzing CWA jurisdictional issues for wholly intrastate waters. However, these decisions by
their terms did not affect the body of case law developed to address interstate waters. The
holdings in the Supreme Court's interstate waters jurisprudence, in particular City of Milwaukee,
apply CWA jurisdiction to interstate waters without regard to, or discussion of, navigability. In
City of Milwaukee, the Court held that the CWA provided a comprehensive statutory scheme for
addressing the consequences of interstate water pollution. Based on this analysis, the Court
expressly overruled its holding in Illinois v. Milwaukee that the federal common law of nuisance
would apply to resolving interstate water pollution disputes. Instead, the Court held that such
disputes would now be resolved through application of the statutory provisions of the CWA
regulating water pollution.
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It would be unreasonable to interpret SWANCC or Rapanos as overruling City of
Milwaukee with respect to CWA jurisdiction over non-navigable interstate waters. Such an
interpretation would result in no law to apply to water pollution disputes with regard to such
waters, unless one were to assume that the Court intended (without discussion or analysis) to
restore the federal common law of nuisance as the law to apply in such matters. Moreover,
SWANCC and Rapanos acknowledge that CWA jurisdiction extends to at least some non-
navigable waters. See, e.g., 547 U.S. at 779 (Kennedy, J.). Neither the SWANCC Court nor the
plurality or Kennedy opinions in Rapanos purports to set out the complete boundaries of CWA
jurisdiction. See, e.g., 547 U.S. at 731 ("[w]e need not decide the precise extent to which the
qualifiers 'navigable' and 'of the United States' restrict the coverage of the Act.") (plurality
opinion).
In addition, as the Supreme Court has repeatedly admonished, if a Supreme Court
precedent has direct application in a case yet appears to rest on a rationale rejected in some other
line of decisions, lower courts should follow the case which directly controls, leaving to the
Supreme Court the prerogative of overruling its precedents. Agostino v. Felton, 521 U.S. 203,
237 (1997); United States v. Hatter, 532 U.S. 557, 566-567(1981). Moreover, when the
Supreme Court overturns established precedent, it is explicit. See, Lawrence v. Texas, 539 U.S.
558, 578 ("Bowers was not correct when it was decided, and it is not correct today. It ought not
to remain binding precedent. Bowers v. Hardwick should be and now is overruled.").
D. The Agencies' Longstanding Interpretation of the Term "Navigable Waters"
to Include "Interstate Waters"
EPA, the agency charged with implementing the CWA, has always interpreted the 1972
Act to cover interstate waters. Final Rules, 38 FR 13528, May 22, 1973 (the term "waters of the
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United States" includes "interstate waters and their tributaries, including adjacent wetlands").
While the Corps of Engineers initially limited the scope of coverage for purposes of section 404
of the CWA to those waters that were subject to the Rivers and Harbors Act of 1899, after a
lawsuit, the Corps amended its regulations to provide for the same definition of "waters of the
United States" that EPA's regulations had always established. In 1975, the Corps' revised
regulations defined "navigable waters" to include "[interstate waters landward to their ordinary
high water mark and up to their headwaters." In their final rules promulgated in 1977, the Corps
adopted EPA's definition and included within the definition of "waters of the United States"
"interstate waters and their tributaries, including adjacent wetlands." The preamble provided an
explanation for the inclusion of interstate waters:
The affects [sic] of water pollution in one state can adversely affect the quality of
the waters in another, particularly if the waters involved are interstate. Prior to
the FWPCA amendments of 1972, most federal statutes pertaining to water
quality were limited to interstate waters. We have, therefore, included this third
category consistent with the Federal government's traditional role to protect these
waters from the standpoint of water quality and the obvious effects on interstate
commerce that will occur through pollution of interstate waters and their
tributaries.
Final Rules, 42 FR 37122, July 19, 1977.
The legislative history similarly provides support for the agencies' interpretation.
Congress in 1972 concluded that the mechanism for controlling discharges and, thereby abating
pollution, under the FWPCA and Refuse Act "has been inadequate in every vital aspect." S.
Rep. No. 414, 92d Cong., 1st Sess. 7 (1972). The Senate Committee on Public Works reported
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that development of water quality standards, assigned to the states under the 1965 FWPCA
Amendments, "is lagging" and the "1948 abatement procedures, and the almost total lack of
enforcement," prompted the search for "more direct avenues of action against water polluters and
water pollution." Id. at 5. The Committee further concluded that although the Refuse Act permit
program created in 1970 "seeks to establish this direct approach," it was too weak because it
applied only to industrial polluters and too unwieldy because the authority over each permit
application was divided between two Federal agencies. See id. at 5; see also id. at 70-72
(discussing inadequacies of Refuse Act program).
In light of the poor success of those programs, the Committee recommended a more
direct and comprehensive approach which, after amendment in conference, was adopted in the
1972 Act. The text, legislative history and purpose of the 1972 Amendments all show an intent -
through the revisions - to broaden, improve and strengthen, not to curtail, the federal water
pollution control program that had existed under the Refuse Act and FWPCA.18 The 1972
FWPCA Amendments were "not merely another law 'touching interstate waters'" but were
"viewed by Congress as a 'total restructuring' and 'complete rewriting' of the existing water
pollution legislation."19
As the legislative history of the 1972 Act confirms, Congress' use of the term "waters of
the United States" was intended to repudiate earlier limits on the reach of federal water pollution
1 R
See id. at 9 ("The scope of the 1899 Refuse Act is broadened; the administrative capability is strengthened.");
id. at 43 ("Much of the Committee's time devoted to this Act centered on an effort to resolve the existing water
quality program and the separate pollution program developing under the 1899 Refuse Act."). Congress made an
effort "to weave" the Refuse Act permit program into the 1972 Amendments, id. at 71, as the statutory text shows.
See 33 U.S.C. § 1342(a) (providing that each application for a permit under 33 U.S.C. § 407, pending on October
18, 1972, shall be deemed an application for a permit under 33 U.S.C. § 1342(a)).
19 City of Milwaukee v. Illinois, 451 U.S. at 317; see also id. at 318 (holding that the CWA precluded federal
common-law claims because "Congress' intent in enacting the [CWA] was clearly to establish an all-encompassing
program of water pollution regulation"); Middlesex County Sewerage Auth. v. National Sea Clammers Ass'n, 453
U.S. I, 22 (1981) (existing statutory scheme "was completely revised" by enactment of the CWA).
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efforts: "The conferees fully intend that the term 'navigable waters' be given the broadest
possible constitutional interpretation unencumbered by agency determinations which have been
made or may be made for administrative purposes." See S. Conf. Rep. No. 1236, 92d Cong., 2d
Sess. 144 (1972). The House and Senate Committee Reports further elucidate the Conference
Committee's rationale for removing the word "navigable" from the definition of "navigable
waters," in 33 U.S.C. § 1362(7). The Senate report stated:
The control strategy of the Act extends to navigable waters. The definition of this term
means the navigable waters of the United States, portions thereof, tributaries thereof, and
includes the territorial seas and the Great Lakes. Through a narrow interpretation of the
definition of interstate waters the implementation of the 1965 Act was severely limited.
Water moves in hydrologic cycles and it is essential that discharge of pollutants be
controlled at the source. Therefore, reference to the control requirements must be made
the navigable waters, portions thereof, and their tributaries.
See S. Rep. 414, 92d Cong., 1st Sess. 77 (1971); see also H.R. Rep. No. 911, 92d Cong., 2d Sess.
131 (1972) ("The Committee fully intends that the term "navigable waters" be given the broadest
possible constitutional interpretation unencumbered by agency determinations which have been
made or may be made for administrative purposes."). These passages strongly suggest that
Congress intended to expand federal protection of waters. There is no evidence that Congress
intended to exclude interstate waters which were protected under federal law if they were not
water that is navigable for purposes of federal regulation under the Commerce Clause or
connected to water that is navigable for purposes of federal regulation under the Commerce
Clause. Such an exclusion would be contrary to all the stated goals of Congress in enacting the
sweeping amendments which became the CWA.
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The CWA was enacted in 1972. EPA's contemporaneous regulatory definition of
"waters of the United States," promulgated in 1973, included interstate waters. The definition
has been EPA's interpretation of the geographic jurisdictional scope of the CWA for
approximately 40 years. Congress has also been aware of and has supported the Agency's
longstanding interpretation of the CWA. "Where 'an agency's statutory construction has been
fully brought to the attention of the public and the Congress, and the latter has not sought to alter
that interpretation although it has amended the statute in other respects, then presumably the
legislative intent has been correctly discerned.'" North Haven Board of Education v. Bell, 102
456 U.S. 512, 535 (1982) (iquoting United States v. Rutherford, 442 U.S. 544 n. 10 (1979)
(internal quotes omitted)).
The 1977 amendments to the CWA were the result of Congress' thorough analysis of the
scope of CWA jurisdiction in light of EPA and Corps regulations. The 1975 interim final
regulations promulgated by the Corps in response to NRDC v. Callaway,20 aroused considerable
congressional interest. Hearings on the subject of section 404 jurisdiction were held in both the
House and the Senate.21 An amendment to limit the geographic reach of section 404 to waters
that are navigable for purposes of federal regulation under the Commerce Clauses and their
adjacent wetlands was passed by the House, 123 Cong. Rec. 10434 (1977), defeated on the floor
of the Senate, 123 Cong. Rec. 26728 (1977), and eliminated by the Conference Committee, H.R.
Conf. Rep. 95-830, 95th Cong., 1st Sess. 97-105 (1977). Congress rejected the proposal to limit
the geographic reach of section 404 because it wanted a permit system with "no gaps" in its
20 40 Fed.Reg. 31320, 31324 (July 25, 1975).
21
Section 404 of the Federal Water Pollution Control Act Amendments of1972: Hearings Before the Senate
Comm. on Public Works, 94th Cong., 2d Sess. (1976); Development of New Regulations by the Corps of Engineers,
Implementing Section 404 of the Federal Water Pollution Control Act Concerning Permits for Disposal of Dredge
or Fill Material: Hearings Before the Subcomm. on Water Resources of the House Comm. on Public Works and
Transportation, 94th Cong., 1st Sess. (1975).
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protective sweep. 123 Cong. Rec. 26707 (1977) (remarks of Sen. Randolph). Rather than alter
the geographic reach of section 404, Congress amended the statute by exempting certain
activities — most notably certain agricultural and silvicultural activities — from the permit
requirements of section 404. See 33 U.S.C. § 1344(f).
Other evidence abounds to support the conclusion that when Congress rejected the
attempt to limit the geographic reach of section 404, it was well aware of the jurisdictional scope
of EPA and the Corps' definition of "waters of the United States." For example, Senator Baker
stated (123 Cong. Rec. 26718 (1977)):
Interim final regulations were promulgated by the [CJorps [on] July 25, 1975. . . .
Together the regulations and [EPA] guidelines established a management
program that focused the decisionmaking process on significant threats to aquatic
areas while avoiding unnecessary regulation of minor activities. On July 19,
1977, the [C]orps revised its regulations to further streamline the program and
correct several misunderstandings. . . .
Continuation of the comprehensive coverage of this program is essential for the
protection of the aquatic environment. The once seemingly separable types of
aquatic systems are, we now know, interrelated and interdependent. We cannot
expect to preserve the remaining qualities of our water resources without
providing appropriate protection for the entire resource.
Earlier jurisdictional approaches under the [Rivers and Harbors Act] established
artificial and often arbitrary boundaries ....
This legislative history leaves no room for doubt that Congress was aware of the
agencies' definition of navigable waters. While there was controversy over the assertion of
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jurisdiction over all adjacent wetlands and some non-adjacent wetlands, the agencies' assertion
of CWA jurisdiction over interstate waters was uncontroversial.
Finally, the constitutional concerns which led the Supreme Court to decline to defer to
agency regulations in SWANCC and Rapanos are not present here where the agency is asserting
jurisdiction over interstate waters. In SWANCC, the Court declined to defer to agency
regulations asserting jurisdiction over non-adjacent, non-navigable, intrastate waters because the
Court felt such an interpretation of the statute invoked the outer limits of Congress' power. The
Court's concern "is heightened where the administrative interpretation alters the federal-state
framework by permitting federal encroachment upon a traditional state power." 531 U.S. at 172-
173 (citations omitted). Authority over interstate waters is squarely within the bounds of
Congress' Commerce Clause powers.22 Further, the federal government is in the best position to
address issues which may arise when waters cross state boundaries, so this interpretation does
not disrupt the federal-state framework in the manner the Supreme Court feared that the assertion
of jurisdiction over a non-adjacent, non-navigable, intrastate body of water based on the presence
of migratory birds did. The Supreme Court's analysis in Illinois v. Milwaukee and City of
Milwaukee makes clear that Congress has broad authority to create federal law to resolve
interstate water pollution disputes. Therefore, as discussed in Section II.B above, it is
appropriate for the agencies to adopt an interpretation of the extent of CWA jurisdiction over
interstate waters that gives full effect to City of Milwaukee unless and until the Supreme Court
elects to revisit its holding in that case.
Some commenters stated that the proposed rule accords new status to interstate waters,
equating them with traditional navigable waters and allowing for features to be jurisdictional
22 In Illinois v. Milwaukee, the Supreme Court noted that "Congress has enacted numerous laws touching interstate
waters." 406 U.S. at 101.
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based on a relationship to interstate waters. Those commenters stated that there is no support for
this interpretation in Riverside Bayview Homes, SWANCC, or Rapanos, because those decisions
did not concern interstate waters and that the significant nexus principles that originated in
SWANCC and Rapanos are tied to traditional navigable waters - not interstate waters. The
agencies disagree that the proposed rule accords new status to interstate waters. The final rule
does not change the existing regulation's provision that defines "waters of the United States" to
include "interstate waters, including interstate wetlands," and also included, for example,
tributaries to interstate waters. The agencies agree that the Supreme Court did not specifically
address the status of interstate waters for purposes of the CWA in Riverside Bayview Homes,
SWANCC, or Rapanos. However, as discussed above, the agencies do conclude that the
Supreme Court provided guidance on the status of interstate waters for purposes of the CWA in
earlier decisions. Some commenters state that reliance on the Supreme Court's earlier decisions
is insufficient because to "discern whether federal law governing interstate water pollution
applies to nonnavigable waters, one must look to Congress and the language of the CWA." That
is exactly what the agencies have done, and in the final rule, based on the language of the statute,
the statutory history, the legislative history, and the caselaw, the agencies' continue their
longstanding interpretation of "navigable waters" to include interstate waters. In addition, since
the Supreme Court's decision in SWANCC identified a significant nexus to the waters clearly
covered by the CWA - in those cases, the traditional navigable waters - as the basis for CWA
jurisdiction, the agencies promulgated a rule that similarly protects the interstate waters that the
agencies concluded were similarly clearly covered by the CWA.
Some commenters expressed concern that a definition had not been provided for
"interstate waters" in the proposed rule. This provision remains unchanged from the existing
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rule which does not contain a definition of interstate waters. As discussed above, the assertion of
jurisdiction over interstate waters is based on the statute and under predecessor statutes
"interstate waters" were defined as all rivers, lakes, and other waters that flow across, or form a
part of, state boundaries. § 10, 62 Stat. 1161 (1948). The agencies will continue to implement
the provision consistent with the intent of Congress.
V. Territorial Seas
The CWA and its existing regulations include "the territorial seas" as a "water of the
United States." The rule makes no changes to that provision of the regulation other than to
change the ordering to earlier in the regulation. The CWA defines "navigable waters" to include
the territorial seas at section 502(7). The CWA goes on to define the "territorial seas" as "the
belt of the seas measured from the line of ordinary low water along that portion of the coast
which is in direct contact with the open sea and the line marking the seaward limit of inland
waters, and extending seaward a distance of three miles." The territorial seas establish the
seaward limit of "waters of the United States." As the territorial seas are clearly covered by the
CWA (they are also traditional navigable waters), it is reasonable to use Justice Kennedy's
significant nexus framework to protect the integrity of the territorial seas. The rule reflects this
by protecting the tributaries and adjacent waters that flow into the territorial seas.
Although some comments addressed the definition of "territorial seas" provided in the
CWA suggesting that the distance thresholds be revised to reflect other resource statutes, the
agencies do not have authority to revise statutory language.
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VI. Impoundments of "Waters of the United States"
The final rule states that all impoundments of waters otherwise identified as "waters of
the United States" are jurisdictional by rule in all cases without need to demonstrate a case-
specific significant nexus. The agencies also note that an impoundment of a water that is not a
"water of the United States" can become jurisdictional if, for example, the impounded waters
become navigable-in-fact and covered under paragraph (a)(1) of the rule.
The existing agency regulations provide that impoundments of "waters of the United
States" remain "waters of the United States" and the agencies do not propose any substantive
revisions to that component of the regulation. Impoundments also may be one of the waters
through which tributaries indirectly contribute flow to a traditional navigable water, interstate
water, or territorial sea. As a matter of law and science, an impoundment does not cut off a
connection between upstream tributaries and a downstream traditional navigable water, interstate
water, or territorial sea, so covered tributaries above the impoundment are still considered
tributary to a downstream traditional navigable waters, interstate waters, or the territorial seas
even where the flow of water might be impeded due to the impoundment. The agencies'
longstanding practice is that the lateral limits of impoundments are delineated by the ordinary
high water mark. The ordinary high water mark sets the lateral limits of jurisdiction over non-
tidal water bodies, including impoundments, in the absence of adjacent wetlands. U.S. Army
Corps of Engineers 2005b.
A. Impoundments Have a Significant Nexus
Scientific literature, as well as the agencies' scientific and technical expertise, and
practical knowledge confirm that impoundments have chemical, physical, and biological effects
on downstream traditional navigable waters, interstate waters, and the territorial seas.
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Impoundments do not sever the effects the impounded "waters of the United States" have on the
chemical, physical, or biological integrity of (a)(1) through (a)(3) waters.
Berms, dikes, and similar features used to create impoundments typically do not block all
water flow. Indeed, even dams, which are specifically designed and constructed to impound large
amounts of water effectively and safely, do not prevent all water flow, but rather allow seepage
under the foundation of the dam and through the dam itself. See, e.g., International Atomic
Energy Agency ("All dams are designed to lose some water through seepage."); U.S. Bureau of
Reclamation ("All dams seep, but the key is to control the seepage through properly designed
and constructed filters and drains."); Federal Energy Regulatory Commission Commission2005)
("Seepage through a dam or through the foundations or abutments of dams is a normal
condition.").
As an agency with expertise and responsibilities in engineering and public works, the
Corps extensively studies water retention structures like berms, levees, and earth and rock-fill
dams. The agency has found that all water retention structures are subject to seepage through
their foundations and abutments. See, e.g., U.S. Army Corps of Engineers 1992 at 1-1; U.S.
Army Corps of Engineers 1993 at 1-1; U.S. Army Corps of Engineers 2004 at 6-1. The Supreme
Court has recognized that a canal and an impoundment area separated by levees were
hydrologically connected (and might even be considered a single water body) because, inter alia,
the "levees continually leak." South Florida Water Mgmt. District v. Miccosukee Tribe of
Indians, 541 U.S. 95, 110 (2004).
The inevitability of seepage is a consequence not of poor design, but of physics: water
will flow downward where it can and thus will seep through small spaces in the structure and in
the ground beneath it. See, e.g., U.S. Army Corps of Engineers 1993 at 4-1 to 4-26; U.S. Army
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Corps of Engineers 2000 at Appendix B. Thus, good engineering practices do not entail the
prevention of all seepage; rather, they assume seepage and entail steps to manage it so that it will
not compromise the integrity of berms, levees, and dams. See, e.g., U.S. Army Corps of
Engineers 1993 at 7-1 to 14-3; U.S. Army Corps of Engineers 2004 at 2-1, 6-1 to 6-7; U.S. Army
Corps of Engineers 2000 at 5-1 to 5-11, Appendix C; U.S. Army Corps of Engineers 1992 at 1-1;
U.S. Army Corps of Engineers 2005a at 1-9; Federal Energy Regulatory Commission 2005 at
14-36 to 14-39.
Many tributary systems in the United States have impoundments located along their
reach. There are more than 80,000 dams in the United States, with over 6,000 exceeding 15
meters in height. Science Report at 2-45 (citing U.S. Army Corps of Engineers 2009). The
purpose of a dam is to impound (store) water for any of several reasons (e.g. flood control,
human water supply, irrigation, livestock water supply, energy generation, containment of mine
tailings, recreation or pollution control). See Association of State Dam Safety Officials; Field
and Lichvar 2007. Many dams fulfill a combination of the above functions. Because the purpose
of a dam is to retain water effectively and safely, the water retention ability of a dam is of prime
importance. Water may pass from the reservoir to the downstream side of a dam by: passing
through the main spillway or outlet works; passing over an auxiliary spillway; overtopping the
dam; seepage through the abutments; and seepage under the dam. Id. All water retention
structures are subject to seepage through their foundations and abutments. U.S. Army Corps of
Engineers 1992. Thus waters behind a dam still maintain a hydrologic connection to downstream
waters, though the presence of the dam can reduce the hydrological connectivity to downstream
(a)(1) through (a)(3) waters.
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Numerous studies have shown that dams impede biotic movements, reducing biological
connectivity between upstream and downstream locations. Science Report at 2-45 (citing
Greathouse et al. 2006; Hall et al. 2011). They also form a discontinuity in the normal stream-
order-related progression in stream ecosystem structure and function. Id. (citing Stanford and
Ward 1984). Dams, however, can have the opposite effect with respect to natural lakes:
increasing their biological connectivity with respect to invasive species by adding impoundments
that decrease average distances between lakes and serving as stepping stone habitat. Id. (citing
Johnson et al. 2008). Dams alter but typically do not sever the hydrologic connection between
upstream and downstream waters. Riparian areas are permanently inundated upstream of large
dams, increasing hydrological connectivity. Downstream, peak flows decrease during normal
high-runoff seasons, while minimum flows increase during normal low-flow seasons—an overall
reduction of stream-flow variability. Id. (citing Poff et al. 2007). Many species that live in or
near rivers are adapted (via life history, behavioral, and morphological characteristics) to the
seasonality of natural flow regimes, so a reduction in flow variability can have harmful effects on
the persistence of such species where dams have been built. Id. (citing Lytle and Poff 2004). This
reduction in high flows also decreases the connectivity of riparian wetlands with the stream by
reducing the potential for overbank lateral flow. Reducing overbank lateral flow can affect
downstream water quality, because overbank flow deposits sediment and nutrients that otherwise
remain entrained in the river. Id. (citing Hupp et al. 2009).
The reservoirs behind dams are very effective at retaining sediment, which can reduce the
amount of sediment delivered downstream and have significant effects in downstream waters.
For instance, the Mississippi River's natural sediment load has been reduced by an estimated
50% through dam construction in the Mississippi Basin. Blum and Roberts 2009. Sediment
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concentrations and suspended loads can be reduced for hundreds of kilometers downstream of
dams, as is especially apparent in the semiarid and arid western U.S. river networks. Id. at 3-14
(citing Williams and Wolman 1984). As described above in section II.D.i., sediment is a
necessary material needed in river networks in certain quantities. Id. at 3-13. Too much sediment
can impact downstream water integrity, but too little sediment can also impact downstream
waters. Sediment helps structure stream and river channels by slowing the flow of water through
channels and providing substrate and habitat for aquatic organisms. Id. at ES-8. At some point in
the lower portions of river networks, sediment deposition becomes the dominant process and
floodplains form. Id. at 2-4. Sediment also helps to build wetlands in coastal areas. Mitsch and
Gosselink 2007. In coastal Louisiana, an estimated 25-38 square miles of wetlands are being lost
each year to open water areas on the coastline due in part to the loss of sediment upstream behind
the levee systems. Mitsch and Gosselink 2007. The river is no longer able to naturally replenish
the sediment that rebuilds the marsh system. The disruption of downstream sediment supply by
dams alters the balance between sediment supply and transport capacity. Science Report at 3-14
(citing Williams and Wolman 1984; Kondolf 1997). In addition, water released from dams lacks
sediment load and thus has excess energy. This energy often downcuts channels downstream of
dams, causing channel incision and streambed coarsening as finer gravels and sands are
transported downstream overtime. Id. (citing Williams and Wolman 1984; Kondolf 1997). The
elimination of floods enables the encroachment of terrestrial vegetation, resulting in channel
narrowing and the conversion of complex, multithreaded channels into simple, single-thread
channels.
Though the man-altered nature of impoundments can change the nature of the chemical,
physical, and biological connections that such waters have downstream, it does not eliminate
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them. Thus, impoundments continue to serve the same important functions as an integral part of
the tributary system, which in turn greatly impact downstream (a)(1) through (a)(3) waters,
particularly when their functional contributions to the chemical, physical, and biological
conditions of downstream waters are combined at a watershed scale and considered in part with
the tributaries that connect them downstream.
By their nature, impoundments of jurisdictional waters would also often meet the
definition of adjacent waters, as they are typically bordering or contiguous. Impoundments of
"waters of the United States" are per ^jurisdictional under (a)(4) of the rule without the need to
determine if they are also adjacent under (a)(6). However, as described in section VHI.b. below,
adjacent waters, as defined, have a significant nexus to traditional navigable waters, interstate
waters, or the territorial seas which bolsters the agencies' determination that impoundments of
"waters of the United States" remain "waters of the United States."
Finally, as previously stated, an impoundment of a water that is not a "water of the
United States" can become jurisdictional if, for example, the impounded waters become
navigable-in-fact and covered as traditional navigable waters. For example, if a stream that is
part of a river network located in a closed basin (e.g., a watershed that does not drain to a
traditional navigable water, interstate water, or the territorial seas), is impounded, and that
impoundment now has the physical characteristics that it can be considered a traditional
navigable water (see, e.g., Traditional Navigable Waters above), that water would become
jurisdictional under (a)(1).
B. Rationale for Conclusion
Impoundments are jurisdictional because as a legal matter an impoundment of a "water of
the United States" remains a "water of the United States" and because scientific literature
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demonstrates that impoundments continue to significantly affect the chemical, physical, or
biological integrity of downstream traditional navigable waters, interstate waters, or the
territorial seas.
The Supreme Court has confirmed that damming or impounding a "water of the United
States" does not make the water non-jurisdictional. See S. D. Warren Co. v. Maine Bd. ofEnvtl.
Prot., 547 U.S. 370, 379 n.5 (2006) ("[N]or can we agree that one can denationalize national
waters by exerting private control over them."). Similarly, when presented with a tributary to the
Snake River which flows only about two months per year because of an irrigation diversion
structure installed upstream, the Ninth Circuit opined "it is doubtful that a mere man-made
diversion would have turned what was part of the waters of the United States into something else
and, thus, eliminated it from national concern." U.S. v. Moses, 496 F.3d 984 (9th Cir. 2007), cert,
denied, 554 U.S. 918 (2008). As a matter of policy and law, impoundments do not denationalize
a water, even where there is no longer flow below the impoundment. The agencies will analyze
the stream network, above and below the impoundment, for connection to downstream
traditional navigable waters, interstate waters, or the territorial seas.
Some commenters stated that "impoundment" is a broad term that should not be per se
regulated. The proposed rule defined "waters of the United States" to include: (4) All
impoundments of waters identified in paragraphs (a)(1) through (3) and (5) of this section; and
(5) All tributaries of waters identified in paragraphs (a)(1) through (4) of this section. In the final
rule the agencies are retaining the language of the existing rule that simply states that "waters of
the United States" includes all impoundments of "waters of the United States." The existing
language is straightforward and can continue to be implemented to ensure that "waters of the
United States" cannot be denationalized by impounding them. As with the existing rule, the key
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is that to be covered under this provision the water must be an impoundment of a "water of the
United States." Examples, therefore, include a lake created by the damming of a water that
would otherwise meet the definition of a tributary and impoundment of a wetland that meets the
definition of adjacent water under the rule.
The agencies have also addressed the confusion of commenters that interpreted the
proposed rule to allow for waters to be jurisdictional based on their relationship to
impoundments without requiring impoundments to have a significant nexus or any meaningful
connection to traditional navigable waters. The final rule defines "waters of the United States"
to include: (5) All tributaries, as defined in paragraph (c)(3) of this section, of waters identified
in paragraphs (a)(1) through (3) of this section. The rule defines tributary to mean: a water that
contributes flow, either directly or through another water (including an impoundment identified
in paragraph (a)(4) of this section), to a water identified in paragraphs (a)(1) through (3) of this
section that is characterized by the presence of the physical indicators of a bed and banks and an
ordinary high water mark. Combined, these provisions make it clear that a tributary is not
jurisdictional simply because it is tributary to an impoundment; rather, the tributary is a tributary
to a traditional navigable water, interstate water, or the territorial seas because just as an
impoundment does not denationalize a "water of the United States," it also does not
denationalize the tributaries (and their adjacent waters) that would flow through to a traditional
navigable water, interstate water, or the territorial seas absent the impoundment. Some
commenters stated that if an impoundment cuts off a physical connection and flow is stopped,
then the upstream waters lack a significant nexus and are not jurisdictional. First, Justice
Kennedy did not indicate that he intended to change longstanding Supreme Court precedent that
waters cannot be denationalized. Second, the science indicates that while impoundments can
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change the functions provided by waters that have been impounded, those impoundments (and
their upstream tributaries and adjacent waters) still provide important functions that significantly
affect the physical, chemical, or biological integrity of the downstream traditional navigable
water, interstate water, or the territorial seas. Third, Justice Kennedy's opinion recognized that
the absence of a hydrologic connection could serve as the basis for a significant nexus. As noted
above, one example in the Science Report was that because dams reduce the amount of sediment
delivered downstream, the reservoirs behind dams are very effective at retaining sediment, which
can have significant effects in downstream waters. Science Report at 3-14. Finally, the judgment
of the agencies based on their experience and the data and information available is that berms,
dikes, dams, and similar features used to create impoundments typically do not block all water
flow, and therefore, impoundments continue to have a significant nexus with downstream
traditional navigable waters, interstate waters, or the territorial seas.
VII. Tributaries
All waters that meet the rule's definition of tributary are "waters of the United States"
because they meet Justice Kennedy's test for jurisdiction under Rapanos. In other words, the
agencies are asserting that all tributaries as defined in the rule have a significant nexus with
traditional navigable waters, interstate waters, and/or the territorial seas. EPA and the Corps'
longstanding definition of "waters of the United States" has included tributaries. That regulation
was based on the agencies' historic view of the scope of the CWA and the general scientific
understanding about the ecological and hydrological relationships between waters.
Tributaries have a substantial impact on the chemical, physical, or biological integrity of
waters into which they eventually flow—including traditional navigable waters, interstate waters,
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and the territorial seas. The great majority of tributaries are headwater streams, and whether they
are perennial, intermittent, or ephemeral, they play an important role in the transport of water,
sediments, organic matter, pollutants, nutrients, and organisms to downstream environments.
Tributaries serve to store water (thereby reducing flooding), provide biogeochemical functions
that help maintain water quality, trap and transport sediments, transport, store and modify
pollutants, provide habitat for plants and animals, and sustain the biological productivity of
downstream rivers, lakes and estuaries. These conclusions are strongly supported in the scientific
literature, as discussed throughout this document.
Headwater streams are the smallest channels where stream flows begin, and often occur
at the outer rims of a watershed. Typically these are first-order streams (i.e., they do not have any
other streams flowing into them). However, headwater streams can include streams with multiple
tributaries flowing into them and can be perennial, intermittent or ephemeral, but are still located
near the channel origins of the tributary system in a watershed.
Protection of tributaries under the CWA is critically important because they serve many
important functions which directly influence the integrity of downstream waters. Discharges of
pollutants into the tributary system adversely affect the chemical, physical, or biological integrity
of traditional navigable waters, interstate waters, and the territorial seas. For example,
destruction or modification of headwater streams has been shown to affect the integrity of
downstream waters, in part through changes in hydrology, chemistry and stream biota. Freeman
et al. 2007; Wipfli 2007. Additionally, activities such as discharging a pollutant into one part of
the tributary system are well-documented to affect, at times, other parts of the system, even when
the point of discharge is far upstream from the navigable water that experiences the effect of the
discharge. See, e.g., National Research Council 1997; Dunnivant and Anders 2006. In order to
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protect traditional navigable waters, interstate waters, and the territorial seas it is also critically
important to protect tributaries as defined that are upstream from those waters.
A. Definition of Tributary
Previous definitions of "waters of the United States" regulated all tributaries without
qualification. The final rule more precisely defines "tributaries" as waters that contribute flow,
either directly or through another water (including an impoundment), to a traditional navigable
water, interstate water, or the territorial seas, and are characterized by the presence of physical
indicators of bed and banks and ordinary high water mark - and concludes that such tributaries
are "waters of the United States." These physical indicators demonstrate there is volume,
frequency, and duration of flow sufficient to create a bed and banks and an ordinary high water
mark, and thus to qualify as a tributary. A tributary can be a natural, man-altered, or man-made
water and includes waters such as rivers, streams, canals, and ditches that are not excluded under
paragraph (b) of the rule. A water that otherwise qualifies as a tributary under this definition does
not lose its status as a tributary if, for any length, there are one or more constructed breaks (such
as bridges, culverts, pipes, or dams), or one or more natural breaks (such as wetlands along the
run of a stream, debris piles, boulder fields, or a stream that flows underground) so long as a bed
and banks and an ordinary high water mark can be identified upstream of the break. A water that
otherwise qualifies as a tributary under this definition does not lost its status as a tributary if it
contributes flow through a "water of the United States" that does not meet the definition of a
tributary (e.g. a lake or a wetland), or through water excluded under paragraph (b) of the rule,
directly or through another water, to a traditional navigable water, interstate water, or the
territorial sea.
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The agencies conclude that covered tributaries with a bed and banks and ordinary high
water mark are similarly situated for purposes of the agencies' significant nexus analysis. The
science demonstrates that covered tributaries provide many common vital functions important to
the chemical, physical, and biological integrity of downstream waters, regardless of the size of
the tributaries (see section Vll.b.vi) or whether they are natural, man-made, or man-altered (see
section Vll.b.v.). Therefore, "tributaries" as defined are jurisdictional by rule.
i. Bed and Banks and Ordinary High Water Mark
The physical indicators of bed and banks and ordinary high water mark (OHWM)
demonstrate that there is sufficient volume, frequency, and flow in tributaries to a traditional
navigable water, interstate water, or the territorial seas to establish a significant nexus. These
physical indicators can be created by perennial, intermittent, and ephemeral flows. See, e.g.,
Lichvar and McColley 2008; Mersel and Lichvar 2014. For purposes of the rule, "bed and
banks" means the substrate and sides of a channel between which flow is confined. The banks
constitute a break in slope between the edge of the bed and the surrounding terrain, and may vary
from steep to gradual. Existing Corps regulations define ordinary high water mark as the line on
the shore established by the fluctuations of water and indicated by physical characteristics such
as a clear, natural line impressed on the banks, shelving, changes in the character of soil,
destruction of terrestrial vegetation, the presence of litter and debris, or other appropriate means
that consider the characteristics of the surrounding areas. 33 CFR 328.3(e). That definition is not
changed by the rule and is added to EPA's regulations. As noted above, the agencies'
longstanding practice is that the ordinary high water mark sets the lateral limits of jurisdiction
over non-tidal water bodies, including tributaries, in the absence of adjacent wetlands. U.S.
Army Corps of Engineers 2005b.
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The Science Report also utilized physical indicators of flow, such as bed and banks, to
identify the components of the river system. See, e.g, Science Report at ES-15, 2-2. The term
river refers to a relatively large volume of flowing water within a visible channel, including
subsurface water moving in the same direction as the surface water and lateral flows exchanged
with associated floodplain and riparian areas. Id. at 2-2 (citing Naiman and Bilby 1998).
Channels are natural or constructed passageways or depressions of perceptible linear extent that
convey water and associated materials downgradient. They are defined by the presence of
continuous bed and bank structures, or uninterrupted (but permeable) bottom and lateral
boundaries. Although bed and bank structures might in places appear to be disrupted (e.g.,
bedrock outcrops, braided channels, flow-through wetlands), the continuation of the bed and
banks downgradient from such disruptions is evidence of the surface connection with the channel
that is upgradient of the perceived disruption. Such disruptions are associated with changes in the
gradient and in the material over and through which the water flows. If a disruption in the bed
and bank structure prevented connection, the area downgradient would lack a bed and banks, be
colonized with terrestrial vegetation, and be indiscernible from the nearby land. The concentrated
longitudinal movement of water and sediment through these channels lowers local elevation,
prevents soil development, selectively transports and stores sediment, and hampers the
colonization and persistence of terrestrial vegetation. Streams are defined in a similar manner as
rivers: a relatively small volume of flowing water within a visible channel, including subsurface
water moving in the same direction as the surface water and lateral flows exchanged with
associated floodplain and riparian areas. Id. (citing Naiman and Bilby 1998).
Current Corps regulations and guidance identify bed and banks as indicators of ordinary
high water mark. The definition of "tributary" in the rule also requires another indicator of
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ordinary high water mark such as staining, debris deposits, or other indicator identified in the
rule or agency guidance. In many tributaries, the bed is that part of the channel below the
ordinary high water mark, and the banks often extend above the ordinary high water mark. For
other tributaries, such as those that are incised, changes in vegetation, changes in sediment
characteristics, staining, or other ordinary high water mark indicators may be found within the
banks. See, e.g., Lichvar and McColley 2008. In concrete-lined channels, the concrete serves as
the bed and banks and can have other ordinary high water mark indicators such as staining and
debris deposits. Indicators of an ordinary high water mark may vary from region to region
across the country. To address the variability, the Corps has released several regional manuals
for areas where identification of ordinary high water mark is technically complex. See, e.g.,
Lichvar and McColley 2008; Mersel and Lichvar 2014.
Other evidence, besides direct field observation, may establish the presence of bed and
banks and another indicator of ordinary high water mark, which are discussed in detail in the
preamble. The agencies currently use many tools in identifying tributaries and will continue to
rely on their experience and technical expertise in identifying the presence of a bed and banks
and ordinary high water mark. Among the types of data and remote sensing or mapping
information that can assist in establishing the presence of a tributary with bed and banks and an
ordinary high water mark are USGS topographic data, the USGS National Hydrography Dataset
(NHD), Natural Resources Conservation Service (NRCS) Soil Surveys, and State or local stream
maps which are mapped independently of the USGS, as well as the analysis of aerial
photographs, and light detection and ranging (also known as LIDAR) data, gage data, flood
predictions, historic records of water flow, and desktop tools that provide for the hydrologic
estimation of a discharge sufficient to create an ordinary high water mark, such as a regional
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regression analysis or hydrologic modeling. See, e.g., U.S. Army Corps of Engineers 2005b; U.S.
Army Corps of Engineers 2007a; Lichvar and McColley 2008; Mersel and Lichvar 2014. These
sources of information can sometimes be used independently to infer the presence of a bed and
banks and another indicator of ordinary high water mark, or where they correlate, can be used to
reasonably conclude the presence of a bed and banks and ordinary high water mark. Both the
USGS topographic data and the NHD data assist to delineate tributaries to traditional navigable
waters, interstate waters, or the territorial seas. Corps of Engineers 2007a. Where one or both of
these sources have indicated a "blue line stream," there is an indication that the tributary could
exhibit a bed and banks and another indicator of ordinary high water mark. Where this
information is combined with stream order,23 more certainty can result. For example, a water that
is a second-order stream will be more likely to exhibit a bed and banks and another indicator of
ordinary high water mark as compared to a first-order stream. Similarly, the indicators gleaned
from aerial photography interpretation, as discussed in more detail in the preamble, can be
correlated with the presence of USGS streams data in reasonably concluding that a bed and
banks and another indicator of ordinary high water mark are present. As discussed in the
preamble, LIDAR-indicated tributaries can be correlated with aerial photography interpretation
and USGS stream data, to reasonably conclude the presence of a bed and banks and another
indicator of an ordinary high water mark in the absence of a field visit. The agencies have been
using such remote sensing and desktop tools to delineate tributaries for many years where data
from the field are unavailable or a field visit is not possible. The agencies' experience and
23 Stream order is a method for stream classification based on relative position within a river network, when streams
lacking upstream tributaries (i.e., headwater streams) are first-order streams and the junction of two streams of the
same order results in an increase in stream order (i.e., two first-order streams join to form a second-order stream, and
so on). When streams of different orders join, the order of the larger stream is retained. See Science Report at 2-2,
A-12 (citing Strahler 1957).
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technical expertise in using such tools to detect the presence of tributaries over the past 30 years
of Clean Water Act implementation provide support that when used in combination, such tools
and data can appropriately demonstrate the presence of a bed and banks and another indicator of
ordinary high water mark.
The term "ordinary high water mark" reflects that the presence of an OHWM is
indicative of regularity of flow. Mersel and Lichvar 2014. For instance, the word "ordinary" can
be interpreted to exclude extremes on either end of the stream flow spectrum (i.e., very low or
very high flows), while the term "high" is in contrast to low or moderate stream flow levels.
Together, "ordinary high water" indicates stream flow levels that are greater than average, but
less than extreme, and that occur with some regularity. Id. A common and reasonable
interpretation of this term is that ordinary high water refers to the ordinary or normal water levels
that occur during the high water season. However, this reasoning is used only to help narrow the
concept of the OHWM, and does not strictly define it. Id. Existing Corps guidance on OHWM
supports that the OHWM forms due to some regularity of flow and does not occur due to
extraordinary events. The guidance states, "[w]hen making OHWM determinations, districts
should be careful to look at characteristics associated with ordinary high water events, which
occur on a regular or frequent basis. Evidence resulting from extraordinary events, including
major flooding and storm surges, is not indicative of the OHWM. For instance, a litter or wrack line
resulting from a 200-year flood event would in most cases not be considered evidence of an
OHWM." U.S. Army Corps of Engineers 2005b.
In 2005, the Corps issued a regulatory guidance letter (RGL 05-05) to Corps districts on
OHWM identification that was designed to ensure more consistent practice. U.S. Army Corps of
Engineers 2005b. As noted above, the Corps has also issued regional manuals to provide
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additional technical assistance for technically complex OHWM delineations. See, e.g., Lichvar
and McColley 2008; Mersel and Lichvar 2014.
This regulation clearly provides that a water that otherwise meets the definition of
tributary remains a jurisdictional tributary even if there are natural or man-made breaks in the
OHWM. The definition of tributary also provides a non-exclusive list of examples of natural or
man-made breaks in the bed and banks or OHWM (e.g. culverts, dams, wetlands) to assist in
clearly and consistently determining what meets the definition of tributary. As described above
and in section VII.B.v., breaks in the bed and banks or OHWM sever neither the connectivity nor
the significant nexus that a tributary has with downstream (a)(1) through (a)(3) waters. While
science does not set a threshold distance that a break in the bed and banks or OHWM must be in
order to maintain connectivity with the upstream portion of the tributary, the Science Report is
clear that the continuation of bed and banks downstream from disruptions is evidence of the
surface connection with the channel that is upstream of the perceived disruption. Science Report
at ES-15. Where breaks in the bed and banks or the OHWM occur due to natural causes, such
disruptions are associated with changes in the gradient and in the material over and through
which the water flows. Id. at 2-2. If a disruption in the bed and banks or the OHWM prevented
connection, the area downstream would lack a bed and banks or OHWM, be colonized with
terrestrial vegetation, and be indiscernible from the nearby land. Id. The concentrated
longitudinal movement of water and sediment through these channels lowers local elevation,
prevents soil development, selectively transports and stores sediment, and hampers the
colonization and persistence of terrestrial vegetation. Id.
The upper limit of the tributary is the point where a bed and banks and another indicator
of ordinary high water mark cease to be identifiable. The ordinary high water mark establishes
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the lateral limits of a water, and its absence generally determines when a tributary's channel or
bed and banks has ended, representing the upper limit of the tributary. However, a natural or
constructed break in bed and banks or other indicator of ordinary high water mark does not
constitute the upper limit of a tributary where bed and banks or other indicator ordinary high
water mark can be found farther upstream. Note that waters, including wetlands, which are
adjacent to a tributary at the upper limit of the channel are jurisdictional as adjacent waters,
ii. Rationale for Conclusion
The identification of tributaries by the presence of physical indicators of flow - bed and
banks and another indicator of high water mark - is supported by the scientific literature which
utilizes the presence of physical channels as a compelling line of evidence for surface-water
connections from tributaries to downstream traditional navigable waters, interstate waters, and
the territorial seas. Science Report at ES-15. In addition, the definition states that a tributary
does not lose its status as a tributary even if there are constructed or natural breaks and that is
again supported by the scientific literature. Physical channels are defined by continuous bed-
and-bank structures, which can include apparent disruptions (such as by bedrock outcrops,
braided channels, flow-through wetlands) associated with changes in the material and gradient
over and through which water flows. Id. at ES-15 and 2-2. The continuation of bed and banks
downgradient from such disruptions is evidence of the surface connection with the channel that
is upgradient of the perceived disruption. Id. The agencies note that the definition of tributary
focuses on the appearance of physical indicators of flow upstream of the break because the
definition is designed to indicate the extent of jurisdiction upstream as a tributary based on the
presence of bed and banks and another indicator of ordinary high water mark. The water is a
tributary until those indicators cease rather than are simply disrupted.
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Justice Kennedy opined that the requirement of a perceptible ordinary high water mark
for tributaries "may well provide a reasonable measure of whether specific minor tributaries bear
a sufficient nexus with other regulated waters to constitute navigable waters under the Act." 547
U.S. at 781, see also id. at 761. The science supports Justice Kennedy's perception.
Some commenters stated that the proposed rule was problematic because it determines
that tributaries regardless of size or significance have a significant nexus. To the contrary, the
rule limits the definition of tributaries that are "waters of the United States" to those that have
two indicators of ordinary high water mark, physical indicators which demonstrate duration and
frequency of flow that excludes some waters because of their lack of size and significance. In
fact, the SAB expressed the view that from a scientific perspective there are tributaries that do
not have an ordinary high water mark but still affect downstream waters. The SAB also advised
EPA to consider changing the wording in the definition to "bed, bank, and other evidence of
flow" SAB 2014b at 2. The agencies have made a determination about which tributaries to
assess in combination and those tributaries have a significant nexus under Justice Kennedy's test.
Further, by defining tributaries for purposes of the rule based on their physical indicators of flow,
the agencies have identified those tributaries to which waters defined as adjacent will also have a
significant nexus to downstream traditional navigable water, interstate waters, or the territorial
seas. The agencies exercised their judgment to conclude that the limitations that they established
in the definition of tributary were reasonable and appropriate to ensure that they were identifying
as categorically jurisdictional those waters that were similarly situated and therefore appropriate
to assess in combination, and that those waters in combination had a significant nexus. This
careful line drawing, and the scientific support for those waters to be included within the
definition of tributary, demonstrate that the agencies' definition is not overbroad or unsupported
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by the science. This definition of tributaries is thus reasonable and based on significance. In
addition, the SAB suggested that EPA reconsider whether flow-through lentic systems should be
included as adjacent waters and wetlands, rather than as tributaries. As discussed in the
preamble, the agencies made this change suggested by the SAB and have not defined tributaries
to include lotic systems such as wetlands.
B. The Agencies Have Concluded that Tributaries, as Defined, Have a
Significant Nexus
The scientific literature documents that tributary streams, including perennial,
intermittent, and ephemeral streams, and certain categories of ditches are integral parts of river
networks because they are directly connected to rivers via permanent surface features (channels
and associated alluvial deposits) that concentrate, mix, transform, and transport water and other
materials, including food resources, downstream. Alluvial deposits, or alluvium, are deposits of
clay, silt, sand, gravel, or other particulate materials that have been deposited by a stream or
other body of running water in a streambed, on a flood plain, on a delta, or at the base of a
mountain. Science Report at A-l. Tributaries transport, and often transform, chemical elements
and compounds, such as nutrients, ions, dissolved and particulate organic matter and
contaminants, influencing water quality, sediment deposition, nutrient availability, and biotic
functions in rivers. Streams also are biologically connected to downstream waters by dispersal
and migration, processes which have critical implications for aquatic populations of organisms
that use both headwater and river or open water habitats to complete their life cycles or maintain
viable populations. The scientific literature clearly demonstrates that cumulatively, streams exert
strong influence on the character and functioning of rivers. In light of these well documented
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connections and functions, the agencies concluded that tributaries, as defined, alone or in
combination with other tributaries in a watershed, significantly affect the chemical, physical, or
biological integrity of a traditional navigable water, interstate water, or the territorial seas. The
scientific literature supports this conclusion for ephemeral tributaries, as well as for intermittent
and perennial tributaries; for tributaries both near to and far from the downstream traditional
navigable water, interstate water, or the territorial seas; and for natural tributaries, man-altered,
or man-made tributaries, which may include certain ditches and canals.
The discussion below summarizes the key points in the literature regarding the chemical,
physical, and biological connections and functions of tributaries that significantly affect
downstream waters. In addition, the evidence regarding man-altered and man-made tributaries
and headwater streams and non-perennial streams, types of tributaries whose important
functional relationships to downstream traditional navigable waters and interstate waters might
not be obvious, is summarized. The scientific literature does not use legal terms like "traditional
navigable water," "interstate water," or "the territorial seas." Rather, the literature assesses
tributaries in terms of their connections to and effects on larger downstream waters in a
watershed. Traditional navigable waters, interstate waters, and the territorial seas are simply a
subset of downstream waters and their distinction is a legal, not scientific, one; the strength of
the connections and effects does not change because a river does not meet the legal standards for
being traditionally navigable. While the rule, consistent with Supreme Court case law, addresses
only those tributaries, as defined, that drain to a traditional navigable water, interstate water, or
the territorial seas, the conclusions of the scientific literature with respect to the effects of
tributaries on downstream waters are applicable to the subset of downstream waters that are
traditional navigable waters, interstate waters, or the territorial seas.
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i. Tributaries as Defined Are "Similarly Situated"
The agencies determine based on their scientific and technical expertise that waters
meeting the definition of "tributary" in a single point of entry watershed are similarly situated
and have a significant nexus because they significantly affect the chemical, physical, and
biological integrity of traditional navigable waters, interstate waters, and the territorial seas. As
such, it is appropriate to conclude covered tributaries as a category are "waters of the United
States." As discussed above, the agencies limited the tributaries that are "waters of the United
States" to those that have both a bed and banks and another indicator of ordinary high water
mark. The agencies reasonably concluded that covered tributaries are similarly situated because
those physical characteristics indicate sufficient flow such that the covered tributaries are
performing similar functions and tributaries located in the single point of entry watershed are
working together in the region to provide those functions to the nearest traditional navigable
water, interstate water, or the territorial seas.
Science demonstrates that tributaries within a single point of entry watershed act together
as a system in affecting downstream waters. Structurally and functionally, tributary networks and
the watersheds they drain are fundamentally cumulative in how they are formed and maintained.
Science Report at ES-13. Downstream traditional navigable waters, interstate waters, or the
territorial seas are the time-integrated result of all tributaries contributing to them. Id. at ES-5.
The incremental effects of individual streams are cumulative across entire watersheds and
therefore must be evaluated in context with other streams in the watershed. Id. Thus, science
supports that tributaries within a point of entry watershed are similarly situated.
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ii. Tributaries Significantly Affect the Physical Integrity of (a)(1)
through (a)(3) Waters
The scientific literature unequivocally demonstrates that tributaries exert a strong
influence on the physical integrity of downstream waters. Tributaries, even when seasonal, are
the dominant source of water in most rivers, rather than direct precipitation or groundwater input
to main stem river segments. See, e.g., Science Report at 3-5 (citing Winter 2007; Bukaveckas
2009). Distant headwaters with stronger connections to groundwater or consistently higher
precipitation levels than downstream reaches contribute more water to downstream rivers. Id. In
the northeastern United States headwater streams contribute greater than 60% of the water
volume in larger tributaries, including navigable rivers. See, e.g., id. (citing Alexander et. al.
2007). The contributions of tributaries to river flows are often readily measured or observed,
especially immediately below confluences, where tributary flows increase the flow volume and
alter physical conditions, such as water temperature, in the main stream. The physical effects of
tributaries are particularly clear after intense rainfall occurs over only the upper tributary reaches
of a river network. For example, a study of ephemeral tributaries to the Rio Grande in New
Mexico found that after a storm event contributions of the stormflow from ephemeral tributaries
accounted for 76% of the flow of the Rio Grande. Id. at 3-7 to 3-8 (citing Vivoni et. al. 2006). A
key effect of tributaries on the hydrologic response of river networks to storm events is
dispersion, or the spreading of water output from a drainage basin over time. Geomorphic
dispersion of connected tributaries influences the timing and volume of water reaching a river
network outlet. See, e.g., id. at 3-10 (citing Saco and Kumar 2002). Tributaries also can reduce
the amount of water that reaches downstream rivers and minimize downstream flooding, often
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through infiltration or seepage through channel beds and banks or through evapotranspiration.
See, e.g., id. at 3-11 (citing Hamilton et al. 2005; Costelloe et.al. 2007).
One of the primary functions of tributaries is transporting sediment to downstream
waters. Tributaries, particularly headwaters, shape and maintain river channels by accumulating
and gradually or episodically releasing sediment and large woody debris into river channels.
Sediment transport is also clearly provided by ephemeral streams. Effects of the releases of
sediment and large woody debris are especially evident at tributary-river confluences, where
discontinuities in flow regime and temperature clearly demonstrate physical alteration of river
structure and function by headwater streams. Science Report at 3-14, 3-16, 3-18, 3-20 to 3-21.
Sediment movement is critical for maintaining the river network, including rivers that are
considered to be traditional navigable waters, as fluvial (produced by the action of a river or
stream) sediments are eroded from some channel segments, and deposited in others downstream
to form channel features, stream and riparian habitat which supports the biological communities
resident downstream, and influence the river hydrodynamics. See, e.g., Florsheim et al. 2008;
Science Report at 3-13 (citing Church 2006). While essential to river systems, too much
sediment can impair ecological integrity by filling interstitial spaces, blocking sunlight
transmission through the water column, and increasing contaminant and nutrient concentrations.
Id. (citing Wood and Armitage 1997). Over-sedimentation thus can reduce photosynthesis and
primary productivity within the stream network and otherwise have harmful effects on
downstream biota, including on the health and abundance of fish, aquatic macrophytes (plants),
and aquatic macroinvertebrates (insects) that inhabit downstream waters. See, e.g., Wood and
Armitage 1997. Headwater streams tend to trap and store sediments behind large structures, such
as boulders and trees, that are transported downstream only during infrequent large storm events
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and that are the dominant means for downstream sediment transport. Science Report at 3-15
(citing Gomi and Sidle 2003; Gooderham et al. 2007). Similarly, large, infrequent disturbance
events are the primary drivers for wood movement from headwater streams to downstream
waters. Id. at 3-17 (citing Benda and Cundy 1990; Benda et al. 2005; Bigelow et al. 2007).
Tributaries can greatly influence water temperatures in tributary networks. This is
important because water temperature is a critical factor governing the distribution and growth of
aquatic life, both directly (through its effects on organisms) and indirectly (through its effects on
other physiochemical properties, such as dissolved oxygen and suspended solids). Id. at 3-19
(citing Allan 1995). For instance, water temperature controls metabolism and level of activity in
cold-blooded species like fish, amphibians, and aquatic invertebrates. See, e.g., Ice 2008.
Temperature can also control the amount of dissolved oxygen in streams, as colder water holds
more dissolved oxygen, which fish and other fauna need to breathe. Connections between
tributaries and downstream rivers can affect water temperature in river networks. See, e.g.,
Science Report at 3-19 (citing Knispel and Castella 2003; Rice et al.2008). In particular,
tributaries provide both cold and warm water refuge habitats that are critical for protecting
aquatic life. Id. at 3-42. Because headwater tributaries often depend on groundwater inputs,
temperatures in these systems tend to be warmer in the winter (when groundwater is warmer than
ambient temperatures) and colder in the summer (when groundwater is colder than ambient
temperatures) relative to downstream waters. Id. (citing Power et al. 1999). Thus tributaries
provide organisms with both warm water and coldwater refuges at different times of the year. Id.
(citing Curry et al. 1997; Baxter and Hauer 2000; Labbe and Fausch 2000; Bradford et al. 2001).
For example, when temperature conditions in downstream waters are adverse, fish can travel
upstream and use tributaries as refuge habitat. Id. (citing Curry et al. 1997; Cairns et al. 2005).
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Tributaries also help buffer temperatures in downstream waters. Id. at 3-19 (citing Caissie 2006).
Temperatures in tributaries affect downstream water temperature many kilometers away. Id. at 3-
20 (citing Gardner and Sullivan 2004; Johnson et al. 2010).
iii. Tributaries Significantly Affect the Chemical Integrity of (a)(1)
through (a)(3) Waters
The scientific literature unequivocally demonstrates that tributaries exert a strong
influence on the chemical integrity of downstream waters. Tributaries transform and export
significant amounts of nutrients and carbon to downstream waters, serving important source
functions that greatly influence the chemical integrity of downstream waters. Organic carbon, in
both dissolved and particulate forms, exported from tributaries is consumed by downstream
organisms. The organic carbon that is exported downstream thus supports biological activity
(including metabolism) throughout the river network. See, e.g., Science Report at 3-30 (citing
Fisher and Likens 1973; Meyer 1994; Wallace et al. 1997; Hall and Meyer 1998; Hall et al.
2000; Augspurger et al. 2008). Much or most of the organic carbon that is exported from
tributaries has been altered either physically or chemically by ecosystem processes within the
tributary streams, particularly by headwater streams. In addition to transformations associated
with microbial and invertebrate activity, organic matter in streams can be transformed through
other processes such as immersion and abrasion; photodegradation also can be important in
ephemeral and intermittent streams where leaves accumulate in dry channels exposed to sunlight.
Id. (citing Paul et al. 2006; Corti et al. 2011; Dieter et al. 2011; Fellman et al. 2013).
Nutrient export from tributaries has a large effect on downstream water quality, as excess
nutrients from surface runoff from lawns and agricultural fields can cause algal blooms that
reduce dissolved oxygen levels and increase turbidity in rivers, lakes, estuaries, and territorial
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seas. Water low in dissolved oxygen cannot support aquatic life; this widely-recognized
phenomenon, known as hypoxia or "dead zones," occurs along coasts throughout the country,
including the northern Gulf of Mexico and the Chesapeake Bay. Committee on Environment and
Natural Resources 2000; Diaz and Rosenberg 2011; Murphy et al. 2011. Hypoxia threatens
valuable commercial and recreational fisheries, including in the northern Gulf of Mexico, and
reduces aquatic habitat quality and quantity. Committee on Environment and Natural Resources
2000; Freeman et al. 2007; Diaz and Rosenberg 2011; O'Connor and Whitall 2007; He and Xu
2015. The amount of nitrogen that is exported downstream varies depending on stream size, and
how much nitrogen is present in the system. Nitrogen loss is greater in smaller, shallow streams,
most likely because denitrification and settling of nitrogen particles occur at slower rates in
deeper channels. Science Report at 3-23 (citing Alexander et al. 2000). At low loading rates, the
biotic removal of dissolved nitrogen from water is high and occurs primarily in small tributaries,
reducing the loading to larger tributaries and rivers downstream. At high nitrogen loading rates,
tributaries become nitrogen saturated and are not effectively able to remove nitrogen, resulting in
high nitrogen export to rivers. Id. at 3-25 to 3-26 (citing Mulholland et al. 2008). The transport
of nitrogen and phosphorus downstream has also been well-documented, particularly in the cases
of the Gulf of Mexico and the Chesapeake Bay. Tributary streams in the uppermost portions of
the Gulf and Bay watersheds transport the majority of nutrients to the downstream waters; an
estimated 85% of nitrogen arriving at the hypoxic zone in the Gulf originates in the upper
Mississippi (north of Cairo, Illinois) and the Ohio River Basins. Goolsby et al. 1999. The export
of nutrients from streams in the Mississippi River Basin has an effect on anoxia, or low oxygen
levels, in the Gulf. Science Report at 3-24 (citing Rabalais etal. 2002). Similarly, nutrient loads
from virtually the entire 64,000 square mile watershed affect water quality in the Chesapeake
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Bay. Simulation tools have been used to determine the nutrient and sediment load reductions that
must be made at many different points throughout the entire watershed in order to achieve
acceptable water quality in the mainstem of the Bay. These reductions included specific annual
nitrogen caps on the upper reaches of the Susquehanna River in New York State, more than 400
miles from the mouth of the Chesapeake Bay. See e.g., U.S. Environmental Protection
Agency 2003; Rabalais etal. 2002.
Although tributaries export nutrients, carbon, and contaminants downstream, they also
transform these substances. Phosphorous and nitrogen arrive at downstream waters having
already been cycled, or taken up and transformed by living organisms, many times in headwater
and smaller tributaries. Science Report at 1-3, 3-26 to 3-27 (citing Webster and Patten 1979;
Newbold etal. 1981; Elwood etal. 1983; Ensign and Doyle 2006). In addition, some of the
nutrients taken up as readily available inorganic forms are released back to the water as organic
forms that are less available for biotic uptake. Id. at 3-27 (citing Mulholland el al. 1988;
Seitzinger et al. 2002). Similarly, nutrients incorporated into particulates are not entirely
regenerated, but accumulate in longitudinally increasing particulate loads (i.e. increases moving
downstream). Id. (citing Merriam et al. 2002; Whiles and Dodds 2002; Hall, et al. 2009).
Headwater streams have seasonal cycles in the concentrations of phosphorous and nitrogen that
are delivered downstream by accumulating nutrient derived from temporarily growing streambed
biomass. Id. (citing Mulholland and Hill 1997; Mulholland 2004). Such variations have been
demonstrated to affect downstream productivity. Id. (citing Mulholland et al. 1995).
Nitrification, the microbial transformation of ammonium to nitrate, affects the form of
downstream nutrient delivery. Nitrification occurs naturally in undisturbed headwater streams,
but increases sharply in response to ammonium inputs, thereby reducing potential ammonium
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toxicity from pollutant inputs. Id. at 3-28 (citing Newbold et al. 1983; Chapra 1996; Bernhardt,
et al. 2002). Denitrification, the removal of nitrate from streamwater through transformation to
atmospheric nitrogen, is widespread among headwater streams; research indicates that small,
tributaries free from agricultural or urban impacts can reduce up to 40% of downstream nitrogen
delivery through denitrification. Id. at 3-28 (citing Mulholland et al. 2008). Small tributaries also
affect the downstream delivery of nutrients through abiotic processes. Streams can reduce
phosphorus concentrations through sorption (i.e., "sticking") to stream sediments. Id. (citing
Meyer and Likens 1979). This is particularly beneficial to downstream chemical integrity where
phosphorus sorbs to contaminants such as metal hydroxide precipitates. Id. (citing Simmons
2010).
Tributaries also store significant amounts of nutrients and carbon, functioning as
important sinksfor river networks so that they do not reach downstream traditional navigable
waters, interstate waters, or the territorial seas. Small tributary streams in particular often have
the greatest effect on downstream water quality, in terms of storage and reducing inputs to
downstream waters. For instance, uptake and transformation of inorganic nitrogen often occurs
most rapidly in the smallest tributaries. See, e.g., id. at 3-25 (citing Peterson et al. 2001). Small
tributaries affect the downstream delivery of nutrients such as phosphorus through abiotic
processes; such streams can reduce phosphorus concentrations by sorption to stream sediments.
Tributaries can also serve as a temporary or permanent source or sink for contaminants
that adversely affect organisms when occurring at excessive or elevated concentrations, reducing
the amounts of such pollutants that reach downstream traditional navigable waters, interstate
waters, or the territorial seas. The transport of contaminants to downstream waters can impact
water quality downstream, if they are not stored in tributaries. See, e.g., id. at 3-34 (citing Wang
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et al. 2007). Tributaries can also serve as at least a temporary sink for contaminants that would
otherwise impair downstream water quality. See, e.g., id. at 3-36 to 3-37 (citing Graf 1994).
The distances and extent of metal contaminant transport was shown in separate studies in
the upper Arkansas River in Colorado, and Clark Fork River in Montana, where past mining
activities impacted the headwater tributaries. River bed sediments showed that metals originating
from the mining and smelting areas in the headwaters were reaching water bodies up to 550 km
downstream. Id. at 3-34 (citing Axtmann and Luoma 1991; Kimball et al. 1995).
Military studies of the distribution, transport, and storage of radionuclides (e.g.,
plutonium, thorium, uranium) have provided convincing evidence for distant chemical
connectivity in river networks because the natural occurrence of radionuclides is extremely rare.
From 1942 to 1952, prior to the full understanding of the risks of radionuclides to human health
and the environment, plutonium dissolved in acid was discharged untreated into several
intermittent headwater streams that flow into the Rio Grande at the Los Alamos National
Laboratory, New Mexico. Id. at 3-36 (citing Graf 1994; Reneau et al. 2004). Also during this
time, nuclear weapons testing occurred west of the upper Rio Grande near Socorro, New Mexico
(Trinity blast site) and in Nevada, where fallout occurred on mountainous areas with thin soils
that are readily transported to headwater streams in the upper Rio Grande basin. The distribution
of plutonium within the Rio Grande illustrates how headwater streams transport and store
contaminated sediment that has entered the basin through fallout and from direct discharge. Los
Alamos Canyon, while only representing 0.4% of the drainage area at its confluence with the Rio
Grande, had a mean annual bedload contribution of plutonium almost seven times that of the
mainstem. Id. (citing Graf 1994). Much of the bedload contribution occurred sporadically during
intense storms that were out of phase with flooding on the upper Rio Grande. Total estimated
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contributions of plutonium between the two sources to the Rio Grande were approximately 90%
from fallout to the landscape and 10% from direct effluent discharge at Los Alamos National
Laboratory. Id. at 3-36 to 3-37 (citing Graf 1994).
iv. Tributaries Significantly Affect the Biological Integrity of (a)(1)
through (a)(3) Waters
Tributaries are biologically linked to downstream waters through the movement of living
organisms or their reproductive propagules, such as eggs or seeds. For organisms that drift with
water flow, biological connections depend on hydrological connections. However, many aquatic
organisms are capable of active movement with or against water flow, and others disperse
actively or passively over land by walking, flying, drifting, or "hitchhiking." All of these
different types of movement form the basis of biological connectivity between headwater
tributaries and downstream waters.
Headwater tributaries increase the amount and quality of habitat available to aquatic
organisms. Under adverse conditions, small tributaries provide safe refuge, allowing organisms
to persist and recolonize downstream areas once adverse conditions have abated. See, e.g.,
Science Report at 3-38 (citing Meyer and Wallace 2001; Meyer et al. 2004; Huryn et al. 2005).
Use of tributaries by salmon and other anadromous fish for spawning is well-documented, but
even non-migratory species can travel great distances within the river and tributary networks.
See, e.g., id. at 3-40 (citing Gorman 1988; Hitt and Angermeier 2008). Tributaries also serve as
an important source of food for biota in downstream rivers. Tributaries export plankton,
vegetation, fish eggs, insects, invertebrates like worms or crayfish, smaller fish that originate in
upstream tributaries and other food sources that drift downstream to be consumed by other
animals. See, e.g., id. at 3-38 (citing Progar and Modenke 2002). For example, many fish feed on
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drifting insects, and numerous studies document the downstream drift of stream invertebrates
that then are eaten by fish in larger rivers. See, e.g., id. at 4-29 to 4-30 (citing Nakano and
Murakami 2001;Wipfli and Gregovich 2002).
Biological connectivity also allows gene flow, or genetic connectivity, among tributary
and river populations. Gene flow is needed to maintain genetic diversity in a species, a basic
requirement for that species to be able to adapt to environmental change. Populations connected
by gene flow have a larger breeding population size, making them less prone to the deleterious
effects of inbreeding and more likely to retain genetic diversity or variation. Id. at 3-43 (citing
Lande and Shannon 1996). Genetic connectivity exists at multiple scales and can extend beyond
one a single river watershed, and for species capable of long distance movement (such as
salmon), reveals complex interactions among spatially distant populations of aquatic organisms
Id. (citing Hughes etal. 2009; Anderson 2010; Bohonak and Jenkins 2003).
Headwater streams provide unique habitat and protection for amphibians, fish, and other
aquatic or semi-aquatic species living in and near the stream that may use the downstream waters
for other portions of their life stages. See, e.g., Report at ES-8; Meyer el al. 2007. They also
serve as migratory corridors for fish. Tributaries can improve or maintain biological integrity and
can control water temperatures in the downstream waters. See, e.g., Report at 3-20 (citing
Ebersole et. al. 2003; Gardner and Sullivan 2004; Johnson etal. 2010). Headwater streams also
provide refuge habitat for riverine organisms seeking protection from temperature extremes, flow
extremes, low dissolved oxygen, high sediment levels, or the presence of predators, parasites,
and competitors. See, e.g., id. at 3-42 (citing Scrivener et al. 1994; Fraser etal. 1995; Curry
1997; Pires et al. 1999; Bradford et al. 2001; Cairns et al. 2005; Wigington et al. 2006;
Woodford and Mcintosh 2010). Headwater streams serve as a source of food materials such as
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insects, larvae, and organic matter to nourish the fish, mammals, amphibians, and other
organisms in downstream streams, rivers, and lakes. See, e.g., id. at 4-22, 3-30, 3-31 (citing
Fisher and Likens 1973; Meyer 1994; Wallace et al. 1997; Hall and Meyer 1998; Hall et al.
2000; Gomi et al. 2002; Augspurger et al. 2008). Disruptions in these biological processes affect
the ecological functions of the entire downstream system. See, e.g., Kaplan et al. 1980; Vannote
et. al. 1980. Headwater streams can help to maintain base flow in the larger rivers downstream,
which is particularly important in times of drought. See, e.g., Science Report at 3-6, B-42, B-48
(citing Brooks and Lemon 2007; Tetzlaff and Soulsby 2008). At the same time, the network of
headwater streams can regulate the flow of water into downstream waters, mitigating low flow
and high flow extremes, reducing local and downstream flooding, and preventing excess erosion
caused by flooding. See, e.g., Levicke^a/. 2008.
v. Man-made or Man-altered Tributaries Significantly Affect the
Physical, Chemical and Biological Integrity of (a)(1) through (a)(3)
Waters
The agencies' rule clarifies that man-made and man-altered tributaries as defined in the
rule are "waters of the United States" because the significant nexus between a tributary and a
traditional navigable water or interstate water is not broken where the tributary flows through a
culvert or other structure. The scientific literature indicates that structures that convey water do
not affect the connectivity between streams and downstream rivers. Indeed, because such
structures can reduce water losses from evapotranspiration and seepage, such structures likely
enhance the extent of connectivity by more completely conveying the water downstream.
Man-made and man-altered tributaries include impoundments, ditches, canals,
channelized streams, piped streams, and the like. Ditches and canals are wide-spread across the
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United States. Where ditches are streams that have been channelized, they are tributaries if the
otherwise meet the definition of "tributary." Preamble, IV. Ditches are also purposely
constructed to allow the hydrologic flow of the tributary to continue downstream. Man-made and
man-altered tributaries, despite human manipulation, usually continue to have chemical,
physical, or biological connections downstream and to serve important functions downstream.
Because these tributaries are hydrologically connected to downstream waters, the chemical and
some biological connections to downstream waters that are supported by this hydrologic
connection are still intact. Often-times man-made tributaries create connections where they did
not previously exist, such as canals that connect two rivers in different watersheds. Science
Report at 1-11.
Tributary ditches and other man-made or man-altered waters that meet the definition of
"tributary" have a significant nexus to (a)(1) through (a)(3) waters due to their impact, either
individually or with other tributaries, on the chemical, physical, or biological integrity of those
downstream waters. Tributary ditches and the like, as with other tributaries, have chemical,
physical, and biological connections with downstream waters that substantially impact those
waters. Tributary ditches and canals can have perennial, intermittent, or ephemeral flow. Due to
the often straightened and channelized nature of ditches, these tributaries quickly move water
downstream to (a)(1) through (a)(3) waters. Ditches and canals, like other tributaries, export
sediment, nutrients, and other materials downstream and are effective at transporting water and
these materials, including nitrogen, downstream. See, e.g., Schmidt el al. 2007; Strock el ai
2007. Ditches provide habitat for fish and other aquatic organisms. See, e.g., Smiley Jr. el al.
2008. Fish and other aquatic organisms utilize canals and ditches to move to different habitats,
sometimes over long distances. Rahel 2007.
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These significant connections and functions continue even where the tributary has a
natural or man-made break in its channel, bed and banks, or OHWM. The presence of a channel,
bed and banks, and OHWM upstream or downstream of the break is an indication that
connections still exist. See, e.g., id. at 2-2 and section VII.A.i. above. The significant nexus
between a tributary and a downstream water is not broken where the tributary flows underground
for a portion of its length, such as in karst topography. The hydrologic connection still exists,
meaning that the chemical and biological connections that are mediated by the hydrologic
connection also still exist. Similarly, flow through boulder fields does not sever the hydrologic
connection. When a tributary flows through a wetland enroute to another or the same tributary,
the significant nexus still exists even though the bed and banks or ordinary high water mark is
broken for the length of the wetland. In-stream adjacent wetlands provide numerous benefits
downstream, and the presence of the wetland in stream can provide additional water quality
benefits to the receiving waters. Flow in flat areas with very low gradients may temporarily
break the tributary's bed and banks or OHWM, but these systems continue to have a significant
nexus downstream. These are just illustrative examples of break in ordinary high water mark;
there are several other types, all of which do not break the significant nexus between a tributary
and the downstream (a)(1) through (a)(3) water.
Man-made or man-altered tributaries continue to have chemical, physical, and biological
connections that significantly affect the integrity of (a)(1) through (a)(3) waters. Though the
man-made or man-altered nature of such tributaries can change the nature of the connections, it
does not eliminate them. Thus, man-made and man-altered tributaries continue to serve the same
important functions as "natural" tributaries, which in turn greatly impact downstream (a)(1)
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through (a)(3) waters, particularly when their functional contributions to the chemical, physical,
and biological conditions of downstream waters are combined at a watershed scale.
vi. Ephemeral and Intermittent Tributaries Significantly Affect the
Chemical, Physical, or Biological Integrity of (a)(1) through (a)(3)
Waters
Tributaries do not need to flow perennially to have a significant nexus to downstream
waters. As described above in section II.A.i., approximately 59% of streams across the United
States (excluding Alaska) flow intermittently or ephemerally; ephemeral and intermittent streams
are particularly prevalent in the arid and semi-arid Southwest, where they account for over 81%
of streams. Levick et al. 2008. Despite their intermittent or ephemeral flow, these streams
nonetheless perform the same important ecological and hydrological functions documented in
the scientific literature as perennial streams, through their movement of water, nutrients, and
sediment to downstream waters. Id. The importance of intermittent and ephemeral streams is
documented in a 2008 peer-reviewed report by EPA's Office of Research and Development and
the U.S. Department of Agriculture's Agricultural Research Service, which addresses the
hydrological and ecological significance of ephemeral and intermittent streams in the arid and
semi-arid Southwestern United States and their connections to downstream waters; the report is a
state-of-the-art synthesis of current knowledge of the ecology and hydrology in these systems.
Id.
Intermittent and ephemeral streams are chemically, physically, and biologically
connected to downstream waters, and these connections have effects downstream. See, e.g., id. In
some areas, stormflows channeled into alluvial floodplain aquifers by intermittent and ephemeral
streams are the major source of annual streamflow in rivers. Perennial flows are not necessary
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for chemical connections. Periodic flows in ephemeral or intermittent tributaries can have a
strong influence on biogeochemistry by connecting the channel and other landscape elements.
See, e.g., Report at 3-22 (citing Valett et. al. 2005). This episodic connection can be very
important for transmitting a substantial amount of material into downstream rivers. See, e.g., id.
(citing Nadeau and Rains 2007). Ephemeral desert streams have been shown to export
particularly high sediment loadings. See, e.g., id. at 3-15 (citing Hassan 1990). Ephemeral
streams can also temporarily and effectively store large amounts of sediment that would
otherwise wash downstream, contributing to the maintenance of downstream water quality and
productive fish habitat. See, e.g., id. at 3-15 to 3-16 (citing Duncan et al. 1987; Trimble 1999;
May and Gresswell 2003). This temporary storage of sediment thus helps maintain the chemical
and biologic integrity of downstream waters.
Tributaries also need not be large rivers to have a significant nexus. As discussed above,
the scientific literature supports the conclusion that tributaries, including headwater streams,
have a significant nexus to downstream waters based on their contribution to the chemical,
physical, or biological integrity of (a)(1) through (a)(3) waters. Headwater tributaries, the small
streams at the uppermost reaches of the tributary network, are the most abundant streams in the
United States. See, e.g., id. at 3-4 (citing Nadeau and Rains 2007). Collectively, they help shape
the chemical, physical, and biological integrity of downstream waters, and provide many of the
same functions as non-headwater streams. See, e.g., id. at ES-2, ES-7 to ES-9, 3-1. For
example, headwater streams reduce the amount of sediment delivered to downstream waters by
trapping sediment from water and runoff. See, e.g., Dieterich and Anderson 1998. Headwater
streams shape river channels by accumulating and gradually or episodically releasing sediment
and large woody debris into river channels. They are also responsible for most nutrient cycling
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and removal, and thus transforming and changing the amount of nutrients delivered to
downstream waters. See, e.g., Science Report at 3-25 (citing Peterson et al. 2001). A close
connection exists between the water quality of these streams and the water quality of traditional
navigable waters, interstate waters, and the territorial seas. See, e.g., id.-, State of Ohio
Environmental Protection Agency 2003. Activities such as discharging a pollutant into one part
of the tributary system are well-documented to affect other parts of the system, even when the
point of discharge is far upstream from the navigable water that experiences the effect of the
discharge. See, e.g., National Research Council 1997; Dunnivant and Anders 2006.
The Science Report provides case studies of prairie streams and Southwest intermittent
and ephemeral streams, two stream types whose jurisdictional status has been called into
question post-Rapanos. These case studies highlight the importance of these streams to
downstream waters, despite their small size and ephemeral or intermittent flow regime.
For example, the Science Report assessed the connectivity of prairie streams that drain
temperate grasslands in the Great Plains physiographic region of the central United States and
Canada. Id. at B-22 to B-37. Eventually, these streams drain into the Mississippi River or flow
directly into the Gulf of Mexico or the Hudson Bay. Id. at 5-6, B-23. Climate in the Great Plains
region ranges from semiarid to moist subhumid and intra- and interannual variation in
precipitation and evapotranspiration is high. Id. at 5-6, B-23 to B-24 (Borchert 1950; Lauenroth
et al. 1999; Boughton et al. 2010). This variation is reflected in the hydrology of prairie streams,
which include ephemeral, intermittent, and perennial streamflows. Id. at 5-6, B-24 (citing
Matthews et al. 1985; Matthews 1988; Brown and Matthews 1995; Sawin et al. 1999; Dodds et
al. 2004; Bergey et al. 2008). Prairie streams are frequently subjected to the extremes of drying
and flooding, and intermittent or flashy hydrology is prevalent in river networks throughout most
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of the Great Plains. Id. at B-24 (citing Matthews 1988; Zale et al. 1989; Poff 1996; Dodds et al.
2004). Prairie streams typically represent a collection of spring-fed, perennial pools and reaches,
embedded within larger, intermittently flowing segments. Id. at B-36 (citing Labbe and Fausch
2000). Row cropping and livestock agriculture are the dominant land uses in the region, resulting
in the withdrawal of water from stream channels and regional aquifers and its storage in
reservoirs to support agriculture. Id. at 5-6, B-27 to B-28 (citing Cross and Moss, 1987;
Ferrington, 1993; Galat etal. 2005; Matthews et al. 2005; Sophocleous 2010; Falke etal. 2011).
Prairie streams typically are connected to downstream waters. Like other types of
streams, prairie streams present strong fluvial geomorphic evidence for connectivity to
downstream waters, in that they have continuous channels (bed and banks) that make them
physically contiguous with downstream waters. Id. at 5-6. Prairie river networks are dendritic
and generally have a high drainage density, so they are particularly efficient at transferring water
and materials to downstream waters. Id. Their pool-riffle morphology, high sinuosity, and
seasonal drying, however, also enhance material storage and transformation. Id. The timing of
connections between prairie streams and downstream waters is seasonal and therefore relatively
predictable. Id. For example, high-magnitude floods tend to occur in late fall into later spring,
although they also occur at other times during the year; this observation indicates that the
magnitude of connections to downstream also varies seasonally. Id. at 5-6 and B-28 (citing
Fausch and Bramblett 1991; Hill et al. 1992; Fritz and Dodds 2005).
The frequent and predictable connections between prairie streams and downstream waters
have multiple physical, chemical, and biological consequences for downstream waters.
Dissolved solids, sediment, and nutrients are exported from the prairie river network to
downstream waters. Id. at 5-6. Ultimately, the expansion of the hypoxic zone in the Gulf of
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Mexico is a downstream consequence of cumulative nutrient loading to the Mississippi River
network. Id. Relative to small streams and large rivers draining the moist eastern parts of the
Mississippi River basin, small to midsized prairie streams deliver less than 25-50% of their
nutrient load to the Gulf of Mexico. Id. at 5-6, B-32 (citing Alexander et al. 2008). Nonetheless,
given the large number and spatial extent of headwater prairie streams connected to the
Mississippi River, their cumulative effect likely contributes substantially to downstream nutrient
loading. Id. at 5-6, B-32.
Organisms inhabiting prairie streams have adapted to their variable hydrologic regimes
and harsh physicochemical conditions via evolutionary strategies that include rapid growth, high
dispersal ability, resistant life stages, fractional reproduction (i.e., spawn multiple times during a
reproductive season), and life cycles timed to avoid predictably harsh periods. Id. at 5-6, B-26
(citing Matthews 1988; Dodds et al. 1996b; Fausch and Bestgen 1997). Alterations in the
frequency, duration, magnitude, and timing of flows —and thus hydrologic connectivity—are
associated with the extinction or extirpation of species in downstream systems. Id. at 5-6, 3-41
(citing Morita and Yamamoto 2002; Letcher et al. 2007). Moreover, many fish species (e.g.,
Arkansas River shiner, speckled chub, flathead chub) in prairie river networks require sufficient
unfragmented (i.e., connected) channel length with adequate discharge to keep their
nonadhesive, semibuoyant eggs in suspension for incubation and early development. Id. at 5-6 to
5-7, B-35 (citing Cross and Moss 1987; Fausch and Bestgen 1997; Platania and Altenbach 1998;
Durham and Wilde 2006; Perkin and Gido 2011). When these conditions are not met, the
biological integrity of downstream waters is impaired. Id. at 5-7.
Human alteration of prairie river networks has affected the physical, chemical, and
biological connectivity to and their consequences for downstream waters. Impoundments and
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water removal, through both surface flow diversions and pumping of ground-water aquifers, are
common in this region. Id. at 5-7, B-27 to B-28 (citing Smith et al. 2002; Galat et al. 2005;
Matthews et al. 2005; Sophocleous 2010). These activities have reduced flood magnitude and
variability, altered timing, and increased predictability of flows to downstream waters. Id. As a
result, physical, chemical, and biological connections to downstream waters have been altered.
Id. at B-28 (citing Cross and Moss 1987; Hadley et al. 1987; Galat and Lipkin, 2000). In addition
to the altered land uses and application of nutrients and pesticides for agriculture, human
alteration of the river network itself, through channelization, levee construction, desnagging,
dredging, and ditching, has enhanced longitudinal connectivity while reducing lateral and
vertical connectivity with the floodplain and hyporheic zone, respectively. Id. at 5-7. Pumping
from streams and ground water has caused historically perennial river segments to regularly dry
during summer months. Id. at 5-7, B-27 to B-28 (citing Cross and Moss 1987; Ferrington 1993;
Falke et al. 2011). Changes to the prairie's grazing (from bison to cattle) and burning regimes
increase nutrient and suspended sediment loading to downstream waters. Id. at 5-7. Introduced
species have extirpated endemic species and altered food web structure and processes in prairie
streams, thereby affecting the biological integrity of downstream waters. Id.
Prairie streams have significant chemical, physical, and biological connections to
downstream waters, despite extensive alteration of historical prairie regions by agriculture, water
impoundment, water withdrawals, and other human activities, and the challenges these
alterations create for assessing connectivity. Id. at B-36 to B-37 (citing Matthews and Robinson
1998; Dodds et al. 2004). The most notable connections are via flood propagation, contaminated
sediment transport, nutrient retention and transformation, the extensive transport and movement
of fish species (including eggs and larvae) throughout these networks, and refuges for prairie
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fishes. Id. at B-37 (citing Matthai 1969; Horowitz etal. 1988; Marron 1989; Dodds etal. 1996a;
Fausch and Bestgen 1997; Platania and Altenbach 1998; Fritz and Dodds 2004; Fritz and Dodds
2005; Franssen et al. 2006; Alexander et al. 2008; Perkin and Gido 2011).
Similarly, southwestern intermittent and ephemeral streams exert strong influences on the
structure and function of downstream waters, and the case study (included in the Science Report)
echoes many of the findings of the functions of intermittent and ephemeral tributaries generally,
which are described above. The case study focuses on the heavily studied San Pedro River,
located in southeast Arizona, in particular, as a representative example of the hydrological
behavior and the connectivity of rivers in the Southwest, but also examines evidence relevant to
other Southwestern streams. See, id. at B-37 to B-60.
Southwestern streams are predominantly ephemeral and intermittent (nonperennial)
systems located in the southwestern United States. Id. at 5-7, B-37. Based on the National
Hydrography Dataset, 94%, 89%, 88%, and 79% of the streams in Arizona, Nevada, New
Mexico, and Utah, respectively, are nonperennial. Id. (citing NHD 2008). Most of these streams
connect to downstream waters, although 66% and 20% of the drainage basins in Nevada and
New Mexico, respectively, are closed and drain into playas (dry lakes). Id. at 5-7. Southwestern
streams generally are steep and can be divided into two main types: (1) mountainous streams that
drain higher portions of basins and receive higher rates of precipitation, often as snow, compared
to lower elevations; and (2) streams located in valley or plateau regions that generally flow in
response to high-intensity thunderstorms. Id. at 5-7, B-39 (citing Blinn and Poff 2005).
Headwater streams are common in both types of southwestern streams.
Nonperennial southwestern streams, excluding those that drain into playas, are
periodically connected to downstream waters by low-duration, high-magnitude flows. Id. at 5-7.
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In contrast to streams in humid regions where discharge is typically supplemented by ground
water as drainage area increases, many southwestern streams lose streamflow to channel
transmission losses as runoff travels downstream. Id. Connection of runoff and associated
materials in ephemeral and intermittent streams to downstream waters is therefore a function of
distance, the relative magnitude of the runoff event, and transmission losses. Id.
Spatial and temporal variation in frequency, duration, and timing of southwestern stream
runoff is largely explained by elevation, climate, channel substrate, geology, and the presence of
shallow groundwater. Id. at 5-8. In nonconstraining substrate, southwestern rivers are dendritic
and their watersheds tend to have a high drainage density. Id. When high flows are present,
southwestern streams are efficient at transferring water, sediment, and nutrients to downstream
reaches. Id. Due to the episodic nature of flow in ephemeral and intermittent channels, sediment
and organic matter can be deposited some distance downstream, and then moved farther
downstream by subsequent precipitation events. Id. Over time, sediment and organic matter
continue to move downstream and affect downstream waters. Id.
The southwestern streams case study describes the substantial connection and important
consequences of runoff, nutrients, and particulate matter originating from ephemeral tributaries
on the integrity and sustainability of downstream perennial streams. Channel transmission losses
can be an important source of ground-water recharge that sustains downstream perennial stream
and riparian systems. Id. For example, isotopic studies indicate that runoff from ephemeral
tributaries like Walnut Gulch, Arizona supplies roughly half the San Pedro River's baseflow
through shallow alluvial aquifer recharge. Id. Important cumulative effects of tributaries - that is
the incremental contributions of individual streams in combination with similarly situated
tributaries - are exemplified by ephemeral stream flows in arid landscapes, which are key
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sources of baseflow for downgradient waters. Science Report at 1-10 (citing Schlesinger and
Jones 1984; Baillie et al. 2007; Izbicki 2007).
Human alterations to southwestern river networks affect the physical, chemical, and
biological connectivity to downstream waters. Impoundments trap water, sediment, and
particulate nutrients and result in downstream impacts on channel morphology and aquatic
function. Id. at 5-8. Diversion of water for consumptive can decrease downstream baseflows but
typically does not affect the magnitude of peak flows. Id. Excessive ground-water pumping can
lower ground-water tables, thereby diminishing or eliminating baseflows. Id. Urbanization
increases runoff volume and flow velocity, resulting in more erosive energy that can cause bank
erosion, streambed down-cutting, and reduced infiltration to ground water. Id.
Flows from ephemeral streams are one of the major drivers of the dynamic hydrology of
Southwest rivers (particularly of floods during monsoon seasons). Id. at B-42, B-49 (citing
Goodrich et al. 1997; Yuan and Miyamoto 2008). Downstream river fishes and invertebrates are
adapted to the variable flow regimes that are influenced strongly by ephemeral tributary systems,
which provide isolated pools as refuges for fish during dry periods. Id. at B-57 to B-58 (citing
John 1964; Meffe 1984; Labbe and Fausch 2000; Rinne and Miller 2006; Lytle et al. 2008).
Ephemeral tributaries in the Southwest also supply water to mainstem river alluvial aquifers,
which aids in the sustaining river baseflows downstream. Id. at B-46 (citing Goodrich et al.
1997; Callegary et al. 2007). Ephemeral tributaries export sediment downstream during major
hydrologic events; the sediment, in turn, influences the character of river floodplains and alluvial
aquifers of downstream waters. Id. at B-47 (citing Nanson and Croke 1992; Shaw and Cooper
2008). The nutrient and biogeochemical integrity of downstream Southwestern rivers, such as the
San Pedro River, is heavily influenced by nutrient export from ephemeral tributaries after storm
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flow events. Id. at 3-25, B-48 (citing Brooks and Lemon 2007; Fisher et al. 2001). Extensive
downstream river riparian communities are supported by water, sediment and nutrients exported
to the river from ephemeral tributaries; these riparian communities have a profound influence on
the river attributes through shading, allochthonous (originating from outside of the channel)
inputs of organic matter, detritus, wood, and invertebrates to the river. Id. at B-47 to B-48 (citing
Gregory et al. 1991; National Research Council 2002; Naiman et al. 2005; Stromberg et al.
2005; Baillie et al. 2007).
As described in section VII.A.i., ephemeral streams can have a bed and banks and an
ordinary high water mark. See, e.g., Lichvar and McColley 2008; Mersel and Lichvar 2014. Even
discontinuous ephemeral streams, or streams characterized by alternating erosional and
depositional reaches (e..g. channelized flow interspersed with channel fans or other depositional
areas) can exhibit OHWMs, and the Corps has developed field indicators to help field staff
identify OHWM in these and other common stream types in the arid West. Lichvar and
McColley 2008. In addition to discontinuous ephemeral streams, the Arid West OHWM manual
also looks at alluvial fans, compound channels (streams characterized by a mosaic of terraces
within a wide, active floodplain and frequently shifting low-flow channel(s)), and single-thread
channels with adjacent floodplains. Lichvar and McColley 2008. These arid West stream types
can exhibit an OHWM. M; Lefebvre et al. 2013. In arid non-perennial streams, the active
floodplain represents a zone that most closely fits the concept of "ordinary" stream flow for use
in delineating the OHWM. Lichvar and McColley 2008; Lichvar et al. 2009. Where ephemeral
streams have a bed and banks and ordinary high water mark and otherwise meet the definition of
tributary in the rule, they are "waters of the United States."
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Intermittent and ephemeral tributaries are distinct erosional features like rills and gullies
that typically lack a bed and banks or an ordinary high water mark. Gullies are small, relatively
deep channels that are ordinarily formed on valley sides and floors where no channel previously
existed. They are commonly found in areas with low-density vegetative cover or with soils that
are highly erodible. See, e.g., Brady and Weil 2002. Rills are very small incisions formed by
overland water flows eroding the soil surface during rain storms. See, e.g., Leopold 1994;
Osterkamp 2008. Rills are less permanent on the landscape than streams and typically lack an
ordinary high water mark, whereas gullies are younger than streams in geologic age, smaller than
streams in size, and also typically lack an ordinary high water mark; time has shaped streams
into geographic features distinct from gullies and rills. See, e.g., American Society of Civil
Engineers 1996; Osterkamp 2008. A rill is it is one of the first and smallest incisions to be
formed as a result of concentrated flow eroding the land surface. Id. The two main processes that
result in the formation of gullies are downcutting and headcutting, which are forms of
longitudinal (incising) erosion. These actions ordinarily result in erosional cuts that are often
deeper than they are wide, with very steep banks, often small beds, and typically only carry
water during precipitation events. The principal erosional processes that modify streams are also
downcutting and headcutting. In streams, however, lateral erosion is also very important. The
result is that streams, except on steep slopes or where soils are highly erodible, are typically
characterized by the presence of bed and banks and an ordinary high water mark as compared to
typical erosional features that are more deeply incised. It should be noted that some ephemeral
streams are called "gullies" or the like when they are not "gullies" in the technical sense; such
streams where they are tributaries under the rule's definition would be considered "waters of the
United States," regardless of the name they are given locally. Similarly, a swale is a shallow
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trough-like depression that carries water mainly during rainstorms or snowmelt. Science Report
at A-12. A swale might or might not be considered a wetland depending on whether it meets the
three-parameter wetland criteria, and only wetlands that meet the definition of "waters of the
United States" are considered jurisdictional. A swale does not have the defined channel,
including bed and banks and an ordinary high water mark that a stream exhibits.
Commenters asserted that the science does not demonstrate that treating ephemeral
waters as "waters of the United States" will have benefits for downstream waters. To the
contrary, the SAB noted that although water bodies differ in degree of connectivity that affects
the extent of influence they exert on downstream waters (i.e., they exist on a "connectivity
gradient"), the available science supports the conclusion that the types of water bodies identified
as "waters of the United States" in the proposed rule exert strong influence on the chemical,
physical, and biological integrity of downstream waters. In particular, the SAB expressed
support for the proposed rule's inclusion of tributaries and adjacent waters as categorical waters
of the United States. Regarding tributaries, the SAB found, "[tjhere is strong scientific evidence
to support the EPA's proposal to include all tributaries within the jurisdiction of the Clean Water
Act. Tributaries, as a group, exert strong influence on the physical, chemical, and biological
integrity of downstream waters, even though the degree of connectivity is a function of variation
in the frequency, duration, magnitude, predictability, and consequences of physical, chemical,
and biological process." SAB 2014b. The SAB advised the agencies to reconsider the definition
of tributaries because not all tributaries have ordinary high water marks (e.g., ephemeral streams
with arid and semi-arid environments or in low gradient landscapes where the flow of water is
unlikely to cause an ordinary high water mark). As noted previously, only those ephemeral
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streams that contribute flow to traditional navigable waters, interstate waters, and the territorial
seas and that have a bed and bank and ordinary high water mark are considered tributaries.
Though the two case studies focus on intermittent and ephemeral prairie streams and arid
Southwestern streams, the science is clear that intermittent and ephemeral streams have
important connections and impacts on downstream waters, regardless of where they are located
geographically. The functions and effects of intermittent and ephemeral streams are discussed
throughout the Science Report and this document. The agencies have concluded that all
tributaries as defined in the rule, including those that are intermittent and ephemeral, when
considered individually or in combination with other tributaries in the same point of entry
watershed, have a significant effect on the chemical, physical, and biological integrity of
downstream traditional navigable waters, interstate waters, and territorial seas.
C. Rationale for Conclusions
In Rapanos, Justice Kennedy reasoned that Riverside Bayview and SWANCC "establish
the framework for" determining whether an assertion of regulatory jurisdiction constitutes a
reasonable interpretation of "navigable waters" - "the connection between a non-navigable water
or wetland and a navigable water may be so close, or potentially so close, that the Corps may
deem the water or wetland a 'navigable water' under the Act;" and "[ajbsent a significant nexus,
jurisdiction under the Act is lacking." 547 U.S. at 767. "The required nexus must be assessed in
terms of the statute's goals and purposes. Congress enacted the law to 'restore and maintain the
chemical, physical, and biological integrity of the Nation's waters,' 33 U.S.C. § 1251(a), and it
pursued that objective by restricting dumping and filling in 'navigable waters,' §§ 1311(a),
1362(12)." Id. at 779. "Justice Kennedy concluded that the term "waters of the United States"
encompasses wetlands and other waters that "possess a 'significant nexus' to waters that are or
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were navigable in fact or that could reasonably be so made." Id. at 759. He further concluded
that wetlands possess the requisite significant nexus: "if the wetlands, either alone or in
combination with similarly situated [wetlands] in the region, significantly affect the chemical,
physical, and biological integrity of other covered waters more readily understood as
'navigable.'" Id. at 780.
While Justice Kennedy's opinion focused on adjacent wetlands in light of the facts of the
cases before him, the agencies determined it was reasonable and appropriate to undertake a
detailed examination of the scientific literature to determine whether tributaries, as a category
and as the agencies propose to define them, significantly affect the chemical, physical, or
biological integrity of downstream navigable waters, interstate waters, or territorial seas into
which they flow. Based on this extensive analysis, the agencies concluded that tributaries with
bed and banks, and ordinary high water marks, alone or in combination with other tributaries, as
defined by the regulation, in the watershed perform these functions and should be considered, as
a category, to be "waters of the United States."
The assertion of jurisdiction over this category of waters is consistent with Justice
Kennedy's opinion in Rapanos. "Justice Kennedy concluded that the term "waters of the United
States" encompasses wetlands and other waters that "possess a 'significant nexus' to waters that
are or were navigable in fact or that could reasonably be so made." Id. at 759. With respect to
tributaries, Justice Kennedy rejected the plurality's approach that only "relatively permanent"
tributaries are within the scope of CW A jurisdiction. He stated that the plurality's requirement
of "permanent standing water or continuous flow, at least for a period of 'some months' . . .
makes little practical sense in a statute concerned with downstream water quality." Id. at 769.
Instead, Justice Kennedy concluded that "Congress could draw a line to exclude irregular
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waterways, but nothing in the statute suggests it has done so;" in fact, he stated that Congress has
done "[qjuite the opposite . . . Id. at 769. Further, Justice Kennedy concluded, based on "a
full reading of the dictionary definition" of "waters," that "the Corps can reasonably interpret
the Act to cover the paths of such impermanent streams." Id. at 770 (emphasis added).
Moreover, Justice Kennedy's opinion did not reject the agencies' existing regulations
governing tributaries. The consolidated cases in Rapanos involved discharges into wetlands
adjacent to non-navigable tributaries and, therefore, Justice Kennedy's analysis focused on the
requisite showing for wetlands. Justice Kennedy described the Corps' standard for asserting
jurisdiction over tributaries: "the Corps deems a water a tributary if it feeds into a traditional
navigable water (or a tributary thereof) and possesses an ordinary high water mark . . . ." Id. at
781, see also id at 761. He acknowledged that this requirement of a perceptible ordinary high
water mark for ephemeral streams, 65 FR 12828, March 9, 2000, "[ajssuming it is subject to
reasonably consistent application, . . . may well provide a reasonable measure of whether
specific minor tributaries bear a sufficient nexus with other regulated waters to constitute
navigable waters under the Act." 547 U.S. at 781, see also id. at 761. With respect to wetlands,
Justice Kennedy concluded that the breadth of this standard for tributaries precluded use of
adjacency to such tributaries as the determinative measure of whether wetlands adjacent to such
tributaries "are likely to play an important role in the integrity of an aquatic system comprising
navigable waters as traditionally understood." Id. at 781. He did not, however, reject the Corps'
use of "ordinary high water mark" to assert regulatory jurisdiction over tributaries themselves.
Id.
In the foregoing passage regarding the existing regulatory standard for ephemeral
streams, Justice Kennedy also provided a "but see" citation to a 2004 U.S. General Accounting
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Office (now the U.S. Government Accountability Office) (GAO) report "noting variation in
results among Corps district offices." Id.
Most fundamentally, the agencies have determined that the scientific literature
demonstrates that tributaries, as a category and as the agencies define them, play a critical role in
the integrity of aquatic systems comprising traditional navigable waters and interstate waters,
and therefore are "waters of the United States" within the meaning of the Clean Water Act. As
summarized above, the agencies analyzed the Science Report and other scientific literature to
determine whether tributaries to traditional navigable waters, interstate waters, or the territorial
seas have a significant nexus to constitute "waters of the United States" under the Act such that it
is reasonable to assert CW A jurisdiction over all such tributaries by rule. Covered tributaries
have a significant impact on the chemical, physical, and biological integrity of waters into which
they eventually flow— for CWA purposes, traditional navigable waters, interstate waters, and
the territorial seas. The great majority of covered tributaries are headwater streams, and whether
they are perennial, intermittent, or ephemeral, they play an important role in the transport of
water, sediments, organic matter, nutrients, and organisms to downstream waters. Covered
tributaries serve to store water, thereby reducing flooding; provide biogeochemical functions that
help maintain water quality; trap and transport sediments; transport, store and modify pollutants;
provide habitat for plants and animals; and sustain the biological productivity of downstream
rivers, lakes, and estuaries. Such waters have these significant effects whether they are natural,
modified, or constructed.
The Science Report concludes, "[although less abundant, the available evidence for
connectivity and downstream effects of ephemeral streams was strong and compelling,
particularly in context with the large body of evidence supporting the physical connectivity and
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cumulative effects of channelized flows that form and maintain stream networks." Science
Report at 6-13. The agencies' conclusions are bolstered not only by the major conclusions of the
Science Report, but also by the specific case studies for southwestern and prairie streams in the
Science Report, as highlighted in section VII.B.vi. above.
VIII. Adjacent Waters
Adjacent waters, including adjacent wetlands, alone or in combination with other
adjacent waters in the watershed, have a significant impact on the chemical, physical, or
biological integrity of traditional navigable waters, interstate waters, and the territorial seas. In
addition, waters adjacent to tributaries serve many important functions that directly influence the
integrity of downstream waters including traditional navigable waters, interstate waters, and the
territorial seas. Adjacent waters store water, which can reduce flooding of downstream waters,
and the loss of adjacent waters has been shown, in some circumstances, to increase downstream
flooding. Adjacent waters maintain water quality and quantity, trap sediments, store and modify
potential pollutants, and provide habitat for plants and animals, thereby sustaining the biological
productivity of downstream rivers, lakes and estuaries, which may be traditional navigable
waters, interstate waters, or the territorial seas. The scientific literature and Science Report
support these conclusions, as discussed in greater detail below.
A. Definition of "Adjacent Waters"
Under the final rule, "adjacent" means bordering, contiguous, or neighboring, including
waters separated from other "waters of the United States" by constructed dikes or barriers,
natural river berms, beach dunes and the like. Further, waters that connect segments of, or are at
the head of, a stream or river are "adjacent" to that stream or river. "Adjacent" waters include
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wetlands, ponds, lakes, oxbows, impoundments, and similar water features. Under the rule,
"adjacent" waters do not include waters in which established, normal farming, silviculture, and
ranching activities under Section 404(f) of the CWA occur. The agencies determined that
"adjacent" waters, as defined in the rule, have a significant nexus to traditional navigable waters,
interstate waters, and the territorial seas based upon their chemical, physical, and biological
connections to, and interactions with, those waters, and the effects of those connections and
interactions. The term adjacent is a policy term and is not one that is used in the scientific
literature. The terms bordering, contiguous, and neighboring are discussed further below.
For purposes of adjacency, including all three provisions of the definition of
"neighboring," the entire water is adjacent if any part of the water is bordering, contiguous or
neighboring. For example, the entire wetland or open water is "adjacent" if any part of it is
within the distance thresholds established in the definition of "neighboring." The agencies'
determination that an entire water is adjacent if any part of the water meets the definition of
adjacent is informed by science and the agencies technical expertise and experience. It would be
artificial to separate a single water body into an adjacent and non-adjacent portion, as the entire
water body is a single functional unit, and the agencies' current practice is to treat an entire
adjacent water as one entity.
Note that there are adjacent waters that meet the definition of "neighboring" that are also
"bordering" or "contiguous" (for example, a wetland that directly abuts a tributary, is in within
the 100-year floodplain, and is well within 1,500 feet of the ordinary high water mark). Such
waters are, of course, adjacent waters under the regulation even if they fall within one, two, or all
three of the "types" of adjacent waters - the fact that a wetland happens to be both bordering and
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meet the definition of neighboring does not change the fact that it is a "water of the United
States" under the regulation.
The ordinary high water mark sets the boundaries of adjacent non-wetland waters (open
waters such as lakes, oxbow lakes, and ponds), while adjacent wetlands have long been
delineated using the 1987 Corps Delineation Manual and its regional supplements. U.S. Army
Corps of Engineers; U.S. Army Corps of Engineers 1987; U.S. Corps of Engineers 2005.
i. Bordering and Contiguous Waters
Within the definition of "adjacent," the terms bordering and contiguous are well
understood, and for continuity and clarity the agencies continue to interpret and implement those
terms consistent with the current policy and practice. Waters that are bordering or contiguous are
often located within the floodplain or riparian area of the waters to which they are adjacent.
Bordering or contiguous waters include those that are directly abutting the water to which they
are adjacent (e.g. the wetland is not separated from the tributary by uplands, a berm, dike, or
similar feature). See, e.g., U.S. Army Corps of Engineers 2007a. Waters that are bordering and
contiguous also typically include in-stream wetlands, lakes, and ponds, as well as wetlands,
lakes, and ponds that are at the head of the tributary network.
As discussed further below, wetlands, ponds, lakes, oxbows, impoundments, and similar
water features that are bordering or contiguous perform a myriad of critical chemical and
biological functions associated with the downstream traditional navigable waters, interstate
waters, or the territorial seas. Such waters are integrally linked with the jurisdictional waters to
which they are adjacent. Because of their close physical proximity to nearby jurisdictional
waters, bordering or contiguous waters readily exchange their waters through the saturated soils
surrounding the (a)(1) through (a)(5) water or through surface exchange. This commingling of
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waters allows bordering or contiguous waters to both provide chemically transformed waters to
streams and to absorb excess stream flow, which in turn can significantly affect downstream
traditional navigable waters, interstate waters, or the territorial seas. The close proximity also
allows for the direct exchange of biological materials, including organic matter that serves as
part of the food web of downstream traditional navigable waters, interstate waters, or the
territorial seas.
As previously discussed, "adjacent" is a policy term and not one found in the scientific
literature. Similarly, "bordering, contiguous, and neighboring" are not terms found readily in the
scientific literature regarding the relationship of a wetland or open water to the tributary system.
However, the agencies' technical expertise and experience support that bordering and contiguous
waters are generally but not always found with the riparian area or floodplain. In addition,
neighboring waters can also be located within the floodplain or a riparian area, as indicated in the
sections below. Though this section addresses how bordering and contiguous waters affect the
chemical, physical, and biological integrity of traditional navigable waters, interstate waters, and
the territorial seas, largely drawing from the scientific literature regarding waters in the
floodplain or riparian area, that same literature on floodplain and riparian waters is used
throughout this document, where appropriate and applicable, to support the agencies' conclusion
regarding neighboring waters.
The science demonstrates that bordering and contiguous waters are physically,
chemically, and biologically integrated with downstream traditional navigable waters, interstate
waters, or the territorial seas and significantly affect their integrity. Bordering and contiguous
waters can include waters in the floodplain or the riparian area, run-of-the-stream wetlands and
open waters, and headwater wetlands and open waters, amongst others.
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As discussed below in section VIII.B., floodplain and riparian waters that meet the
definition of adjacent have a significant nexus to downstream waters, and bordering and
contiguous wetlands are often a subset of such wetlands. The scientific literature supports that
wetlands and open waters in riparian areas and floodplains are physically, chemically, and
biologically connected to downstream traditional navigable waters, interstate waters, or the
territorial seas and significantly affect the integrity of such waters. The Science Report concludes
that wetlands and open waters located in "riparian areas and floodplains are physically,
chemically and biologically integrated with rivers via functions that improve downstream water
quality, including the temporary storage and deposition of channeling-forming sediment and
woody debris, temporary storage of local ground water that supports baseflow in rivers, and
transformation and transport of stored organic matter." Science Report at ES-2 to ES-3. Such
waters act as the most effective buffer to protect downstream waters from nonpoint source
pollution (such as nitrogen and phosphorus), provide habitat for breeding fish and aquatic insects
that also live in streams, and retain floodwaters, sediment, nutrients, and contaminants that could
otherwise negatively impact the condition or function of downstream waters.
Bordering or contiguous waters, including wetlands, that are in the riparian area or
floodplain lie within landscape settings that have bidirectional hydrological exchange with (a)(1)
through (a)(5) waters. Science Report at 2-7. Such waters play an integral role in the chemical,
physical, and biological integrity of the waters to which they are adjacent and to downstream
(a)(1) through (a)(3) waters. Riparian areas and floodplains often describe the same geographic
region. Science Report at 2-5. Therefore, the discussion of the functions of waters, including
wetlands, in riparian areas will typically apply to floodplains unless otherwise noted. Where
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connections arise specifically from the act of inundation of adjacent land during times of higher-
than-normal water, the term "floodplain" is solely used to describe the area.
Riparian areas are transition zones between terrestrial and aquatic ecosystems that are
distinguished by gradients in biophysical conditions, ecological processes, and biota. Id. at 2-4.
Like riparian areas, wetlands are also transitional areas between terrestrial and aquatic
ecosystems. Wetlands are often but not always found in riparian areas, but not all of the riparian
area is a wetland. As noted in section II. A. above and in paragraph (c)(4) of the rule, from a
Clean Water Act regulatory perspective, wetlands are those areas that are inundated or saturated
by surface or groundwater at a frequency and duration sufficient to support, and that under
normal circumstances do support, a prevalence of vegetation typically adapted for life in
saturated soil conditions. Only those wetlands that meet the provisions of paragraphs (a)(1)
through (a)(8) of this rule are considered "waters of the United States." Waters including
wetlands in riparian areas significantly influence exchanges of energy and matter with aquatic
ecosystems. See, e.g., id. (citing National Research Council 2002).
As discussed in section II.A.i., floodplains are low areas bordering streams, rivers, lakes,
and impoundments and are inundated during moderate to high water events. Id. (citing Leopold
1994; Osterkamp 2008). Floodplains are also considered riparian areas, but not all riparian areas
have floodplains. Id. at 2-5. All rivers and streams within river networks have riparian areas, but
small streams in constrained valleys are less likely to have floodplains than larger streams and
rivers in unconstrained valleys. Id. Riparian and floodplain waters take many different forms.
Some may be wetlands, while others may be ponds, oxbow lakes, or other types of open waters.
Waters are considered in-stream or "run-of-the-stream" where they are directly part of the
tributary system. For example, an in-stream wetland or open water can be part of the headwaters
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(e.g., a headwater wetland or pond that is directly connected to the headwater stream) or can be
further downstream where, for example, a tributary flows into a lake that the flows into another
tributary. Under the proposed rule, such waters would have been considered in the definition of
tributary, but after consideration of public comments, in the final rule, the agencies have defined
adjacent waters to include these open waters and wetlands. The SAB also suggested that lotic
systems such as wetlands should not be defined as tributaries but should be included instead in
the adjacent waters category. For bordering and contiguous waters that are run-of-the-stream
wetlands, the fact that such wetlands are in-stream often enhances their ability to filter pollutants
and contaminants that would otherwise make it downstream; in-stream wetlands also attenuate
floodwaters during wet periods and provide important sources of baseflow downstream during
dry periods. See, e.g., id. at 4-21 (citing Morley et al. 2011). Similarly, headwater and run-of-
the-stream lakes and ponds serve many important functions that affect the chemical, physical,
and biological conditions downstream. Such open waters can act as sinks, storing floodwaters,
sediment, and nutrients, as these materials have the opportunity to settle out, at least temporarily,
as water moves through the lake to downstream waters. See, e.g., Phillips et al. 2011. The
attenuation of floodwaters can also maintain stream flows downstream. Id. In-stream lakes, as
with other bordering and contiguous waters, can also act as sources, contributing flow, nutrients,
sediment, and other materials downstream. Total Maximum Daily Loads (TMDLs) for nutrients
have been established for many in-stream lakes across the country in recognition of the ability of
lakes to transport nutrients downstream, contributing to downstream impairments. See, e.g.,
Maine Department of Environmental Protection 2006; U.S. Environmental Protection Agency
2012. In-stream lakes can also serve as habitat for species that then move downstream. For
instance, brook trout that are stocked in headwater lakes in Idaho and Montana are capable of
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invading most downstream habitat, including through very steep channel slopes and waterfalls.
Adams et al. 2001. These non-native species can then affect the biological integrity of
downstream waters by impacting populations of native fish species, such as cutthroat trout,
downstream. See, e.g., Dunham et al. 2002. For example, non-native trout were introduced in
headwater lakes to the Little Kern River in the southern Sierra Nevada and dispersed
downstream, causing the near-extinction of the native Little Kern golden trout. Knapp and
Matthews 2000. These studies demonstrate the ability of organisms to travel from bordering and
contiguous lakes to downstream waters, which is not limited to just non-native species; many
other species can also move downstream and back again.
One type of wetland often located in-stream are wetlands that are connected to the river
network through a channel (e.g., wetlands that serve as stream origins). These are wetlands from
which a stream channel originates. Science Report at 4-2. Where these wetlands directly flow
into jurisdictional waters, they are bordering and contiguous. Because these wetlands are often
located at the headwaters, the stream to which they are bordering or contiguous may not be large
enough to have a floodplain (e.g. they lie at the hillslope or in high gradient areas), and thus they
are generally non-floodplain waters (however, some waters stream-origin wetlands can be
located within the floodplain). They are part of the stream network itself, and along with first-
and second-order streams, form the headwaters of the river network. Such bordering and
contiguous wetlands have a direct hydrologic connection to the tributary network via
unidirectional flow from the wetland to the headwater stream.
Wetlands that serve as stream origins connect via perennial, intermittent, or ephemeral
drainages to river networks. Id. at 4-21 (citing Rains et al. 2006; Rains et al. 2008; Morley et al.
2011; McDonough et al. 2015). Regardless of the permanence of flow, such wetlands have an
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impact on downstream water. Id. at 4-2, 4-40. Wetland seeps, for example, can form where
groundwater discharges from breaks in slope. Id. at 4-20 (citing Hall etal. 2001; O'Driscoll and
DeWalle 2010). They often have perennial connections to the stream, providing important
sources of water downstream, particularly during summer baseflow. Id. at 4-21 (citing Morley el
al. 2011). In Maine, for example, seeps were found to provide 40 to 80% of stream water during
baseflow periods. Id. In other cases, surface connections between channel origin wetlands and
streams are intermittent or ephemeral. In addition to surface water connections, groundwater
flow can hydrologically connect wetlands that serve as stream origins with the stream network.
Id. at 4-22.
Wetlands and open waters at the channel origin generally have important chemical,
physical, and biological effects on (a)(1) through (a)(3) waters, including hydrologic, water
quality, and habitat functions, regardless if the outflow from the wetland or open water to the
stream is perennial, intermittent, or ephemeral. Id. Like other wetlands, wetlands that serve as
stream origins can transport channel-forming sediment and woody debris, transport stored
organic matter, remove and transform pollutants and excess nutrients such as nitrogen and
phosphorus, attenuate and store floodwaters, contribute to stream baseflow through groundwater
recharge, and provide habitat for breeding fish, amphibians, reptiles, birds, and other aquatic and
semi-aquatic species that move from the wetlands to the river network. Id. at 4-40, 4-42. These
overall conclusions also apply to adjacent open waters (e.g., ponds and lakes) because the same
principles govern hydrologic connectivity between these water bodies and downstream waters.
See, e.g., id. at 4-41.
Bordering and contiguous lakes, ponds, and wetlands, including wetlands that serve as
stream origins, have important chemical, physical, and biological connections downstream that
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affect (a)(1) through (a)(3) waters. Their direct hydrologic connection to the stream network
facilitates the significant impact they have downstream. This impact on downstream waters
occurs regardless of whether their connection to the tributary network is perennial, intermittent,
or ephemeral. Thus, bordering and contiguous lakes, ponds, and wetlands serve important
functions, which in turn greatly impact downstream (a)(1) through (a)(3) waters, particularly
when their functional contributions to the chemical, physical, and biological conditions of
downstream waters are combined at a watershed scale.
The agencies determine that waters that are bordering or contiguous to an (a)(1) through
(a)(5) water have a significant nexus with the downstream traditional navigable waters, interstate
waters, or the territorial seas, and these aquatic resources are critical to protect as "waters of the
United States." Based on a review of the scientific literature and the agencies' technical expertise
and experience, the rule continues the longstanding interpretation in prior regulations that waters
that are "bordering" or "contiguous" to (a)(1) through (a)(5) waters meet the definition of
"adjacent" and thus are "waters of the United States" by rule,
ii. Waters Separated by a Berm
As previously mentioned, waters separated from other "waters of the United States" by
constructed dikes or barriers, natural river berms, beach dunes and the like are adjacent. This has
been a longstanding part of the concept of adjacency under the agencies' regulations
implementing the CWA, and the final rule does not change this. Waters separated by constructed
dikes or barriers, natural river berms, beach dunes, and the like are considered bordering,
contiguous, or neighboring, and the presence of the artificial or natural barrier does not affect
their adjacency. The scientific literature demonstrates that waters separated by constructed dikes
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or barriers, natural river berms, beach dunes and the like have a significant effect on the
chemical, physical, and biological integrity of downstream (a)(1) through (a)(3) waters.
The terms earthen dam, dike, berm, and levee are used to describe similar structures
whose primary purpose is to help control flood waters. Such structures vary in scale and size. A
levee is an embankment whose primary purpose is to furnish flood protection from seasonal high
water and which is therefore subject to water loading for periods of only a few days or weeks a
year. Earthen embankments that are subject to water loading for prolonged periods (longer than
normal flood protection requirements) are called earth dams. There are a wide variety of types of
structures and an even wider set of construction methods. These range from a poorly constructed,
low earthen berm pushed up by a backhoe to a well-constructed, impervious core, riprap lined
levee that protects houses and cropland. Generally, levees are built to detach the floodplain from
the channel, decreasing overbank flood events. Franklin et al. 2009. The investigation methods
to determine the presence or absence of the hydrologic connection depend on the type of
structure, the underlying soils, the presence of groundwater, and the depth of the water table.
U.S. Army Corps of Engineers 2000 at 1-1.
Man-made berms and the like are fairly common along streams and rivers across the
United States and often accompany stream channelization. Franklin etal. 2009. One study
conducted in Portland, Oregon found that 42% of surveyed wetlands had dams, dikes, or berms.
Kentula et al. 2004. Likewise, over 90% of the tidal freshwater wetlands of the Sacramento-San
Joaquin Delta have been diked or leveed. Simenstad et al. 1999. At least 40,000 kilometers of
levees, floodwalls, embankments, and dikes are estimated across the United States, with
approximately 17,000 kilometers of levees in the Upper Mississippi Valley alone. Gergel etal.
2002.
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Adjacent waters separated from the tributary network by dikes, levees, berms and the like
continue to have a hydrologic connection to downstream waters. This is because berms and
similar features typically do not block all water flow. Indeed, even dams, which are specifically
designed and constructed to impound large amounts of water effectively and safely, do not
prevent all water flow, but rather allow seepage under the foundation of the dam and through the
dam itself. See, e.g., International Atomic Energy Agency 2003; U.S. Bureau of Reclamation;
Federal Energy Regulatory Commission 2005 at 14-36 to 14-39.
Seepage is the flow of a fluid through the soil pores. Seepage through a dam, through the
embankments, foundations or abutments, or through a berm is a normal condition. Kovacic et al.
2000; Federal Energy Regulatory Commission 2005 at 14-36 to 14-39. This is because water
seeks paths of least resistance through the berm or dam and its foundation. Michigan Department
of Environmental Quality. All earth and rock-fill dams are subject to seepage through the
embankment, foundation, and abutments. U.S. Army Corps of Engineers 1993 at 1-1; U.S. Army
Corps of Engineers 2004 at 6-1 to 6-7. Concrete gravity and arch dams similarly are subject to
seepage through the foundation and abutments. U.S. Army Corps of Engineers 1993 at 1-1.
Levees and the like are subject to breaches and breaks during times of floods. Nilsson et al.
2005. Levees are similarly subject to failure in the case of extreme events, such as the extensive
levee failures caused by Hurricanes Katrina and Rita. Day et al. In designing levees and similar
structures, seepage control is necessary to prevent possible failure caused by excessive uplift
pressures, instability of the downstream slope, piping through the embankment and/or
foundation, and erosion of material by migration into open joints in the foundation and
abutments. M; Kovacic et al. 2000; U.S. Bureau of Reclamation; International Atomic Energy
Agency 2003; California Division of Safety of Dams 1993.
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The rate at which water moves through the embankment depends on the type of soil in
the embankment, how well it is compacted, the foundation and abutment preparation, and the
number and size of cracks and voids within the embankment. All but the smallest earthen dams
are commonly built with internal subsurface drains to intercept water seeping from the reservoir
(i.e., upstream side) to the downstream side. U.S. Army Corps of Engineers 1995 at 1-1. Where
it is not intercepted by a subsurface drain, the seepage will emerge downstream from or at the toe
of the embankment. Michigan Department of Environmental Quality. Seepage may vary in
appearance from a "soft," wet area to a flowing "spring." It may show up first as an area where
the vegetation is lush and darker green. Cattails, reeds, mosses, and other marsh vegetation may
grow in a seepage area. Id.
Engineered berms are typically designed to interfere with the seasonal pattern of water
level (hydroperiod) of the area behind the berm, reducing the frequency and severity of
inundation. Berms are not designed to eliminate all hydrologic connection between the channel
on one side and the area behind the berm on the other. It is almost always impracticable to build
a berm that will not be overtopped by a flood of maximum severity, and most berms are not
designed to withstand severe floods. See, e.g., U.S. Army Corps of Engineers 1993 at 1-1.
Levees are designed to allow seepage and are frequently situated on foundations having natural
covers of relatively fine-grain impervious to semipervious soils overlying pervious sands and
gravels. U.S. Army Corps of Engineers 2005a at 1-9. These surface strata constitute impervious
or semipervious blankets when considered in connection with seepage. Principal seepage control
measures for foundation underseepage are (a) cutoff trenches, (b) riverside impervious blankets,
(c) landslide berms, (d) pervious toe trenches, and (e) pressure relief wells. U.S. Army Corps of
Engineers 2000 at 1-1. Overtopping of an embankment dam is very undesirable because the
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embankment materials may be eroded away. Additionally, only a small number of concrete dams
have been designed to be overtopped. Water normally passes through the main spillway or outlet
works; it should pass over an auxiliary spillway only during periods of high reservoir levels and
high water inflow. All embankment and most concrete dams have some seepage. See, e.g.,
Association of State Dam Safety Officials. However, it is important to control the seepage to
prevent internal erosion and instability. Proper dam construction, and maintenance and
monitoring of seepage provide control.
Berm-like landforms known as natural levees occur naturally and do not isolate adjacent
wetlands from the streams that form them. Hydrologic connections can be bidirectional across
berms or other similar features when integrated over time during and after floods when the
hydraulic or hydrostatic gradient changes direction. Natural levees and the wetlands and waters
behind them are part of the floodplain, including along some small streams and streams in the
Arid West. Johnston etal. 2001. Every flowing watercourse transports not only water, but
sediment—eroding and rebuilding its banks and floodplains continually. Federal Interagency
Stream Restoration Working Group 1998. Different deposition patterns occur under varying
levels of streamflow, with higher flows having the most influence on the resulting shape of
streambanks and floodplains. Id. In relatively flat landscapes drained by low-gradient streams,
this natural process deposits the most sediment on the bank immediately next to the stream
channel while floodplains farther from the channel are usually lower-lying wetlands
("backswamps" or "backwater wetlands") that receive less sediment. See, e.g., Johnston et al.
1997. The somewhat elevated land thus built up at streamside is called a natural levee, and this
entirely natural landform is physically and hydrologically similar to narrow, man-made berms.
See, e.g., Leopold etal. 1964. Natural levees are discontinuous, which allows for a hydrologic
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connection to the stream or river via openings in the levees and thus the periodic mixing of river
water and backwater. Johnston et al. 2001. In addition, streams with natural levees, in settings
with no human interference whatsoever, retain hydrologic connection with their wetlands behind
the levees by periodic flooding during high water and via seepage through and under the levee.
Similarly, man-made berms are typically periodically overtopped with water from the near-by
stream, and as previously mentioned, are connected via seepage.
Waters, including wetlands, separated from a stream by a natural or man-made berm
serve many of the same functions as those discussed above on other adjacent waters.
Furthermore, even in cases where a hydrologic connection may not exist, there are other
important considerations, such as chemical and biological factors, that result in a significant
nexus between the adjacent wetlands or waters and the nearby "waters of the United States," and
(a)(1) through (a)(3) waters.
The movement of surface and subsurface water both over berms and through soils and
berms adjacent to rivers and streams is a hydrologic connection between wetlands and flowing
watercourses. The intermittent connection of surface waters over the top of, or around, natural
and manmade berms further strengthens the evidence of hydrologic connection between
wetlands and flowing watercourses. Both natural and man-made barriers can be topped by
occasional floods or storm events. See, e.g., Turner et al. 2006; Keddy et al. 2007. When berms
are periodically overtopped by water, wetlands and waters behind the barriers are directly
connected to and interacting with the nearby stream and its downstream waters. In addition,
surface waters move to and from adjacent soils (including adjacent wetland soils) continually.
Along their entire length, streams alternate between effluent (water-gaining) and influent (water-
losing) zones as the direction of water exchange with the streambed and banks varies. Federal
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Interagency Stream Restoration Working Group 1998. The adjacent areas involved in this
surface water exchange with a stream or river are known as the hyporheic zone. Hyporheic zone
waters are part of total surface waters temporarily moving through soil or sediment. Like within-
channel waters, these waters are oxygenated and support living communities of organisms in the
hyporheic zone.
Because a hydrologic connection between adjacent wetlands and waters and downstream
waters still exists despite the presence of a berm or the like, the chemical and biological
connections that rely on a hydrologic connection also exist. For instance, adjacent waters behind
berms can still serve important water quality functions, serving to filter pollutants and sediment
before they reach downstream waters. Wetlands behind berms can function to filter pollutants
before they enter the nearby tributary, with the water slowly released to the stream through
seepage or other hydrological connections. See, e.g., Osborne and Kovacic 1993; Kovacic 2000.
Their ability to retain sediment and floodwaters may be enhanced by the presence of the berm.
For instance, some backwater wetlands in floodplain/riparian areas exhibit higher sedimentation
rates than streamside locations. Kuenzler et al. 1980; Johnston etal. 2001. The presence of
manmade levees can actually increase denitrification rates, meaning that the adjacent waters can
more quickly transform nitrogen. Gergel etal. 2005. However, the presence of manmade berms
does limit the ability of the river to connect with its adjacent wetlands through overbank flooding
and thus limits sediment, water and nutrients transported from the river to the adjacent waters.
M; Florsheim and Mount 2003. However, the presence of a berm does not completely eliminate
the transport of sediments and water from the river to the nearby adjacent wetland, as suspended
sediments and water can overflow both natural and man-made levees, though the transport is
usually more pronounced in settings with natural levees. See, e.g., Turner etal. 2006; Keddy et
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al. 2007. Sediment deposition over levees is particularly enhanced by extreme events like
hurricanes. M; Reed el al. 2006. Wetlands behind berms, where the system is extensive, can
help reduce the impacts of storm surges caused by hurricanes. Day et al. 2007.
Adjacent waters, including wetlands, separated from water bodies by berms and the like
maintain ecological connection with those water bodies. Though a berm may reduce habitat
functional value and may prevent some species from moving back and forth from the wetland to
the river, many major species that prefer habitats at the interface of wetland and stream
ecosystems remain able to utilize both habitats despite the presence of such a berm. Additional
species that are physically isolated in either stream or wetlands habitat still interact ecologically
with species from the other component. Thus, adjacent wetlands with or without small berms can
retain numerous similarities in ecological function. For example: wetland bird species such as
wading birds are able to utilize both wetland and adjacent stream/ditch habitats; wetland
amphibians would be able to bypass the berm in their adult stage; aquatic invertebrates and fish
would still interact with terrestrial/wetland predators and prey in common food web relationships
despite the presence of a berm. See, e.g., Butcher and Zimpel 1991; Willson and Halupka 1995;
Cederholm et al. 1999; Schwartz and Jenkins 2000; Bilton et al. 2001.
One example of adjacent waters behind berms and the like are interdunal wetlands
located in coastal areas, including some areas of the Great Lakes and along barrier islands.
Interdunal wetlands form in swales or depressions within open dunes or between beach ridges
along the coast and experience a fluctuating water table seasonally and yearly in synchrony with
sea or lake level changes. Odum 1988; Albert 2000; Albert 2003; Albert 2007. For those along
the ocean coast, they are typically formed as a result of oceanic processes where the wetlands
establish behind relict dune ridges (dunes that were formed along a previously existing coast
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line). Wetlands in the interdunal system are in close proximity to each other and to the
surrounding (a)(1) through (a)(3) waters. Their proximity to one another and to the (a)(1)
through (a)(3) waters indicates a close physical relationship between interdunal wetland systems
and the traditional navigable waters, interstate waters, or the territorial seas. Despite the presence
of the beach dunes, interdunal wetlands have chemical, physical, or biological connections that
greatly influence the integrity of the nearby (a)(1) through (a)(3) waters. The wetlands are
hydrologically connected to these (a)(1) through (a)(3) waters through unconfined, directional
flow and shallow subsurface flow during normal precipitation events and extreme events. As
previously noted, they are linked to the rise and fall of the surrounding tides—the water-level
fluctuations of the nearby a)(l) through (a)(3) waters are important for the dynamics of the
wetlands. Albert 2003. The wetlands provide floodwater storage and attenuation, retaining and
slowly releasing floodwaters before they reach the nearby (a)(1) through (a)(3) waters. Like
other adjacent wetlands, interdunal wetlands also have important chemical connections to the
nearby (a)(1) through (a)(3) waters, as they serve important water quality benefits. The wetlands
store sediment and pollutants that would otherwise reach the surrounding (a)(1) through (a)(3)
waters. The wetlands are biologically connected to the surrounding (a)(1) through (a)(3) waters.
For instance, they provide critical habitats for species that utilize both the wetlands and the
nearby (a)(1) through (a)(3) waters, supporting high diversity and structure. Habitat uses include
basic food, shelter, and reproductive requirements. Aquatic insects, amphibians, and resident and
migratory birds all use interdunal wetlands as critical habitat, and the wetlands provide better
shelter than the nearby exposed beach. Albert 2000; Smith et al. 2008. In marine coastal areas,
the wetlands are often the only freshwater system in the immediate landscape, thus providing
critical drinking water for the species that utilize both the wetlands and the nearby (a)(1) through
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(a)(3) waters, although some interdunal wetlands are brackish in nature. See, e.g., Heckscher and
Bartlett 2004.
Wetlands behind the extensive levee system in the Yazoo Basin are an example of
adjacent waters behind man-made barriers. A regional hydrogeomorphic approach guidebook for
the Yazoo Basin of the Lower Mississippi River Alluvial Valley assesses the functions of these
wetlands. Smith and Klimas 2002. An extensive levee system was built along the river system to
prevent flooding of the Mississippi River, resulting in drastic effects to the hydrology of the
basin. Id. Despite the alteration of hydrology in the basin, extensive wetlands systems still exist
behind the man-made and natural levees and maintain a hydrologic connection to the river
system. These wetlands detain floodwater, detain precipitation, cycle nutrients, export organic
carbon, remove elements and compounds, maintain plant communities, and provide fish and
wildlife habitat. Id. The functions in turn provide numerous and substantial benefits to the nearby
river.
iii. Neighboring Waters
The rule establishes a definition of "neighboring" for purposes of determining adjacency.
In the rule, the agencies identify three circumstances, which are discussed in detail below, under
which waters would be "neighboring" and therefore "waters of the United States":
(1) Waters located in whole or in part within 100 feet of the ordinary high water mark
of a traditional navigable water, interstate water, the territorial seas, an impoundment, or a
tributary (discussed in section VIII.A.iii.l. below).
(2) Waters located in whole or in part in the 100-year floodplain that are within 1,500
feet of the ordinary high water mark of a traditional navigable water, interstate water, the
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territorial seas, an impoundment, or a tributary ("floodplain waters") (discussed in section
VIII.A.iii.2. below).
(3) Waters located in whole or in part within 1,500 feet of the high tide line of a
traditional navigable water or the territorial seas and waters located within 1,500 feet of the
ordinary high water mark of the Great Lakes (discussed in section VIII.A.iii.3. below).
As noted above, the rule provides that with respect to the boundaries for adjacent waters
the entire water is jurisdictional as long as the water is at least partially located within the
distance threshold, and the agencies interpret the rule to apply to any single water body or
wetland that may straddle a distance threshold. Low-centered polygonal tundra and patterned
ground bogs (also called strangmoor, string bogs, or patterned ground fens) are considered a
single water for purposes of the rule because their small, intermingled wetland and non-wetland
components are physically and functionally integrated. See, e.g., U.S. Army Corps of Engineers
2007b. These areas, like other wetland/non-wetland mosaics often have complex micro-
topography with repeated small changes in elevation occurring over short distances. Barrett
1979; U.S. Army Corps of Engineers 2007b; Michigan Natural Features Inventory 2010;
Liljedahl et al. 2012; Lara el al. 2015. Science demonstrates that these wetlands function as a
single wetland matrix and ecological unit having clearly hydrophytic vegetation, hydric soils,
and wetland hydrology. Corps regional wetland delineation manuals address how to address
wetland/non-wetland mosaics, that is a landscape where wetland and non-wetland components
are too closely associated to be easily delineated or mapped separately. U.S. Army Corps of
Engineers 2007b; U.S. Army Corps of Engineers 2012. For example, at Klatt Bog, one of the
prominent patterned ground bogs in Anchorage, Alaska, the plant communities (and thus the
wetland and non-wetland areas) intersperse more than can be mapped. Hogan and Tande 1983.
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Ridges and hummocks are often non-wetland but are interspersed throughout a wetland matrix
having clearly hydrophytic vegetation, hydric soils, and wetland hydrology. Id. Longstanding
practice is that wetlands in the mosaic are not individually delineated, but that the Corps
considered the entire mosaic and estimates percent wetland in the mosaic. See, e.g., id.. As a
result, the agencies will continue to evaluate these wetlands as a single water under the rule.
1. Waters within 100 Feet of the Ordinary High Water Mark
Waters located in whole or in part within 100 feet of the ordinary high water mark of a
traditional navigable water, interstate water, the territorial seas, an impoundment of a
jurisdictional water, or a tributary are considered neighboring waters under the rule and are thus
adjacent and "waters of the United States." Based on a review of the scientific literature and the
agencies' expertise and experience, the agencies determined that such neighboring waters are
integrally linked to the chemical, physical, or biological functions of waters to which they are
adjacent and downstream to the traditional navigable waters, interstate waters or the territorial
seas.
All wetlands, ponds, lakes, oxbows, impoundments, and similar water features that are
located in whole or in part within 100 feet of the ordinary high water mark of a jurisdictional
water perform a myriad of critical chemical, physical, and biological functions associated with
the downstream traditional navigable water, interstate water or the territorial seas and therefore
the agencies have determined that they are "neighboring" and thus "waters of the United States."
Waters within 100 feet of a jurisdictional water are often located within the riparian area or
floodplain and are often connected via surface and shallow subsurface hydrology to the water to
which they are adjacent. While the SAB was clear that distance is not the only factor that
influences connections and their effects downstream, due to their close proximity to
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jurisdictional waters, waters within 100 feet are often located within a landscape position that
allows for them to receive and process surface and shallow subsurface flows before they reach
streams and rivers. These waters individually and collectively affect the integrity of downstream
waters by acting primarily as sinks that retain floodwaters, sediments, nutrients, and
contaminants that could otherwise negatively impact the condition or function of downstream
waters. Wetlands and open waters within close proximity of jurisdictional waters improve water
quality through assimilation, transformation, or sequestration of nutrients, sediment, and other
pollutants that can affect the integrity of downstream traditional navigable waters, interstate
waters, or the territorial seas. These waters, including wetlands, also provide important habitat
for aquatic-associated species to forage, breed, and rest.
As noted above, waters within 100 feet may be within the riparian area even if the
floodplain is limited. Riparian waters within and outside of floodplains are an important part of
the overall riverine landscape. Science Report at 4-7 (citing Ward 1998). Waters within riparian
areas are also connected to streams and rivers by a diverse set of hydrologic inputs and outputs.
Id. (citing Junk et al. 1989; Winter and Rosenberry 1998; Benke et al. 2000; Tockner et al. 2000;
Bunn et al. 2006). Waters in stream and river channels can readily reach wetlands and open
waters in riparian areas via overbank flow, which occurs when floodwaters flow over stream and
river channels. Id. at 2-12 (citing Mertes 1997).
Riparian areas can have a diverse array of hydrologic inputs and outputs, which, in turn
influence riparian wetlands. Id. at 2-14. Riparian areas receive water from precipitation; overland
flow from upland areas; local, intermediate, regional ground water; and hyporheic flows. Id.
(citing National Research Council 2002; Richardson et al. 2005; Vidon et al. 2010). Water
flowing over the land surface in many situations can infiltrate soils in riparian areas. If low
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permeability subsoils or impervious clay layers are present, water contact with the plant root
zone is increased and the water is subject to ecological functions such as denitrification before it
reaches the stream channel. Id. (citing National Research Council 2002; Naiman et al. 2005;
Vidon et al. 2010). Riparian wetlands can have bidirectional, lateral hydrologic connections to
the river network, either through overbank flooding (i.e., lateral expansion of the network) or
hyporheic flow, in addition to unidirectional flows from upland and ground-water sources. Id. at
2-20.
In order to provide greater clarity and consistency and based on a review of the science
and the agencies' expertise and experience, the agencies identified a 100-foot threshold for
neighboring waters to a traditional navigable water, interstate water, territorial sea, tributary or
impoundment. Further, the agencies determined that there is a significant nexus with the
downstream traditional navigable waters, interstate waters, or the territorial seas, and these
adjacent waters are "waters of the United States."
All factors being equal, wetlands closer to the tributary network will have greater
hydrologic and biological connectivity than wetlands located farther from the same network. Id.
at 2-40. Distance is a factor that is well known to have various effects on physical and biological
processes within and between system components. Id. at 4-44. Sometimes this is due to the direct
effect of distance. In some cases there is an indirect effect due to distance controlling how long
transport of a material will take. This fact is embedded in the time of concentration concept in
hydrology, whereby under similar slope and velocities, water traveling from more distant points
and with a longer flowpath will - because of the length of time in transit - have greater potential
for evapotranspiration and soil infiltration losses before reaching a stream. Id. at 2-39; Blanco-
Canqui and Lai 2008. There are many examples in the scientific literature of distance effects
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from various factors with respect to physical, chemical, and biological processes. Graf 1984;
Marron 1989; Leigh 1997; King etal. 2005; Alexander et al. 2007; Attum etal. 2007;
Subalusky, 2007; Van Sickle and Johnson, 2008; Colvin et al. 2009; Flitcroft et al. 2012;
Greathouse et al. 2014. While these distance effects occur as a continuous function, it is a
common scientific practice to use such variables to define discrete bins, which can then serve as
a basis for a boundary. See, e.g., Dent and Grimm 1999; Johnson et al. 2010.
With respect to provision of water quality benefits downstream, non-floodplain waters
within close proximity of the stream network often are able to have more water quality benefits
than those located at a distance from the stream. Many studies indicate that the primary water
quality and habitat benefits will generally occur within a several hundred foot zone of a water.
See, e.g., Peteijohn and Correll 1984; Hawes and Smith 2005. In addition, the scientific literature
indicates that to be effective, contaminant removal needs to occur at a reasonable distance prior
to entry into the downstream traditional navigable waters, interstate waters, or the territorial seas.
Some studies also indicate that fish, amphibians (e.g., frogs, toads), reptiles (e.g., turtles), and
small mammals (e.g., otters, beavers, etc.) will use at least a 100-foot zone for foraging,
breeding, nesting, and other life cycle needs. Dole 1965; Smith and Green 2005; Semlitsch 2008;
Steen etal. 2012.
Based on a review of the scientific literature and the agencies' expertise and experience,
there is clear evidence that the identified waters within 100 feet of the ordinary high water mark
of a jurisdictional water, even when located outside the floodplain, perform critical processes and
functions discussed in section III above. All waters within 100 feet of a jurisdictional water
significantly affect the chemical, physical, or biological integrity of the waters to which they are
adjacent, and those waters in turn significantly affect the chemical, physical, or biological
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integrity of the downstream traditional navigable waters, interstate waters, or the territorial seas.
The agencies established a 100-foot threshold from the water's lateral limit in the definition of
neighboring because, based on the agencies' expertise and experience implementing the CWA
and in light of the science, the agencies concluded this was a reasonable and practical boundary
within which to conclude the waters clearly significantly affecting the integrity of the (a)(1)
through (a)(5) waters, and these adjacent waters are "waters of the United States."
2. Waters in the Floodplain within 1,500 Feet of the Ordinary High
Water Mark
Waters located in whole or in part in the 100-year floodplain (i.e., the area with a one
percent annual chance of flooding) that are within 1,500 feet of the ordinary high water mark of a
traditional navigable water, interstate water, the territorial seas, an impoundment, or a tributary
("floodplain waters") are considered neighboring waters under the rule. Such neighboring
wetlands and open waters perform a myriad of critical chemical and biological functions
associated with the downstream traditional navigable waters, interstate waters, or the territorial
seas. As stated in section VII. A.i. above, the scientific literature, including the Science Report,
supports that wetlands and open waters in floodplains are physically, chemically, and
biologically connected to downstream traditional navigable waters, interstate waters, or the
territorial seas and significantly affect the integrity of such waters. Unlike bordering or
contiguous waters, neighboring waters within the floodplain are typically not directly abutting
(a)(1) through (a)(5) waters, but science still demonstrates that they individually or cumulatively
have a significant impact on the chemical, physical, and biological integrity of traditional
navigable waters, interstate waters, and the territorial seas due to their location within the
floodplain. They perform the same important functions that improve downstream water quality
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as bordering or contiguous floodplain waters, including the temporary storage and deposition of
channeling-forming sediment and woody debris, temporary storage of local ground water that
supports baseflow in rivers, and transformation and transport of stored organic matter. Science
Report at ES-2 to ES-3. Floodplain waters improve water quality through the assimilation,
transformation, or sequestration of pollutants, including excess nutrients and chemical
contaminants such as pesticides and metals, that can degrade downstream water integrity. Id. at
ES-3. In addition to providing effective buffers to protect downstream waters from point source
and nonpoint source pollution, these systems form integral components of river food webs,
providing nursery habitat for breeding fish and amphibians, colonization opportunities for stream
invertebrates, and maturation habitat for stream insects. Id. Lateral expansion and contraction of
the river in its floodplain result in an exchange of organic matter and organisms, including fish
populations that are adapted to use floodplain habitats for feeding and spawning during high
water, that are critical to river ecosystem function. Id. Floodplain wetlands and open waters also
affect the integrity of downstream waters by subsequently releasing (desynchronizing)
floodwaters and retaining large volumes of stormwater, sediment, and contaminants in runoff
that could otherwise negatively affect the condition or function of downstream waters. Id.
Due to their location within the 100-year floodplain, neighboring waters, including
wetlands, that are in the 100-year floodplain and within 1,500 feet of the ordinary high water
mark lie within landscape settings that have bidirectional hydrological exchange with (a)(1)
through (a)(5) waters. See, e.g., Science Report at 2-7. As described earlier, the "100-year
floodplain" is the area with a one percent annual chance of flooding.
In order to add the clarity and predictability that some commenters requested, the
agencies have decide that 100-year floodplain is the appropriate floodplain for determining the
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adjacency limits of (c)(2)(B) neighboring waters. Flood insurance rate maps are based on the
probability of a flood event occurring (e.g., 100-year floods have a 1% probability of occurring
in a given year or 500 year-floods have a 0.2% probability of occurring in a particular year).
Federal Emergency Management Agency. Flood insurance rate maps are developed by applying
models and other information to identify areas that would be inundated by a flood event of a
particular probability of recurring. See, e.g., Federal Emergency Management Agency 1995.
Oxbow lakes and ponds (hereafter referred to as oxbow lakes), commonly found in
floodplains of large rivers, are formed when river meanders (curves) are cutoff from the rest of
the river, and are an example of neighboring floodplain waters where they are located within the
100-year floodplain and within 1,500 feet of the OHWM. Id. at 5-3. The Science Report
presents a case study of these floodplain waters, and concludes that the scientific evidence
supports that oxbow lakes periodically connect to the active river channel and the connection
between oxbow lakes and the active river channel provides for several ecological effects on the
river ecosystem. Id. at B-8.
For waters in the 100-year floodplain within 1,500 feet of the ordinary high water mark
of an (a)(1) through (a)(5) water, the agencies determine there is a significant nexus with the
downstream traditional navigable waters, interstate waters, or the territorial seas and these areas
are critical to protect "waters of the United States." Based on a review of the scientific literature,
the agencies' technical expertise and experience, and the implementation value of drawing clear
lines, the rule establishes a distance limit for floodplain waters to meet the definition of
"neighboring" and thus to be "waters of the United States" by rule. This distance limitation was
established in order to protect vitally important waters within a watershed while at the same time
providing a practical and implementable rule. The agencies are not determining that waters in
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the floodplain farther than 1,500 feet from the ordinary high water mark never have a significant
nexus. Rather, the agencies are using their technical expertise to promulgate a practical rule that
draws reasonable boundaries in order to protect the waters that clearly have a significant nexus
while minimizing uncertainty about the scope of "waters of the United States." Because waters
beyond these limits may have a significant nexus, the rule also establishes areas in which a case-
specific significant nexus determination must be made (see section IX.B.).
3. Waters within 1,500 Feet of the High Tide Line
Waters located in whole or in part within 1,500 feet of the high tide line of a tidally-
influenced traditional navigable water or territorial sea or within 1,500 feet of the ordinary high
water mark of the Great Lakes, are considered neighboring under the rule. Many tidally-
influenced waters do not have floodplains, so the agencies include a separate provision within
the definition of "neighboring" to protect the adjacent waters that have a significant nexus to
tidally-influenced traditional navigable waters, the Great Lakes, or the territorial seas. Under
Riverside Bayview and Justice Kennedy's opinion in Rapanos, waters adjacent to traditional
navigable waters, including the territorial seas, are "waters of the United States." Because the
connection to a tidally-influenced traditional navigable water or a Great Lake is so close, the
100-year floodplain is not as relevant to identifying connections to those traditional navigable
waters, so the rule defines "neighboring" to include waters within 1,500 feet of the high tide line
of a tidal (a)(1) water or an (a)(3) or the ordinary high water mark of a Great Lake. Wetlands,
ponds, lakes, oxbows, impoundments, and similar water features within 1,500 feet of a tidal
(a)(1) or (a)(3) water or a Great Lake are physically-connected to such waters by surface and
shallow subsurface connections. These waters perform a myriad of critical chemical and
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biological functions associated with the nearby (a)(1) and (a)(3) waters to which they are
adjacent.
These neighboring waters in combination with other adjacent waters significantly affect
the integrity of the connected (a)(1) and (a)(3) waters (for example, the Great Lakes or territorial
seas, respectively) by acting primarily as sinks that retain floodwaters, sediments, nutrients, and
contaminants that could otherwise negatively impact the condition or function of those waters.
Like floodplain waters, the scientific literature supports that wetlands and other similar waters
within close proximity to tidal waters or the Great Lakes improve water quality through
assimilation, transformation, or sequestration of nutrients, sediment, and other pollutants that can
affect downstream water quality. These waters also provide important habitat for aquatic-
associated species to forage, breed, and rest in.
For example, wetlands dominated by grass-like vegetation that occur in depressional
areas between sand dunes or beach ridges along the territorial seas and other waters such as the
Great Lakes are dependent upon these waters for their water source (intradunal and interdunal
wetlands). The waters, including wetlands, generally form when water levels of the territorial
seas fall or the Great Lakes drop, creating swales that support a diverse mix of wetland
vegetation and many endangered and threatened species. Odum 1988; Albert 2000; Albert 2003;
Tiner 2003c; Albert 2007. Many studies demonstrate that these waters have been shown to act in
concert with the rising and lowering of the tide or water levels in the case of the Great Lakes and
that the critical functions provided by these waters are similar and play an important role in
maintaining the chemical, physical, or biological integrity of the nearby traditional navigable
waters or the territorial seas because of the hydrological and ecological connections to and
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interactions with those waters. See, e.g., id. (See also VIII. A.ii. for additional information about
this wetland type.).
Science demonstrates that distance is a factor in the connectivity and the strength of
connectivity of wetlands and open waters to downstream waters. Science Report at ES-4, 4-2. 5-
6-5. Thus, waters that are more distant generally have less opportunity to be connected to
downstream waters. Wetlands and open waters closer to the stream network or coastline
generally will have greater hydrologic and biological connectivity than waters located farther
from the same network. See, e.g., id. at 2-38. For instance, waters that are more closely
proximate have a greater opportunity to contribute flow, as water is likely to be lost from the
channel through evaporation or transpiration. Id. Via their hydrologic connectivity, proximate
wetlands and open waters also have chemical connectivity to and effects on downstream (a)(1)
and (a)(3) waters and are more likely to impact water quality due to their close distance. Waters
more closely located to (a)(1) and (a)(3) waters are also more likely to be biologically connected
to such waters more frequently and by more species, including amphibians and other aquatic
animals. To protect tidal traditional navigable waters, the territorial seas, and the Great Lakes,
the 1,500-foot threshold is a reasonable distance to capture most wetlands and open waters that
are so closely linked to the (a)(1) and (a)(3) waters that they can properly be considered adjacent
as neighboring waters.
Based on a review of the scientific literature and the agencies' expertise and experience,
there is clear evidence these waters, even when located outside the floodplain, perform critical
processes and functions discussed in section III above. The agencies established a 1,500-foot
threshold from the water's lateral limit, which would be either the high tide line (for tidally-
influenced (a)(1) waters or the territorial seas) or the ordinary high water mark (for the Great
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Lakes), in the definition of neighboring because, based on the agencies' expertise and experience
implementing the CWA and in light of the science, the agencies concluded this was a reasonable
and practical boundary within which to conclude the waters clearly significantly affected the
integrity of the (a)(1) or (a)(3) waters, and these adjacent waters are "waters of the United
States." Waters located within the 100-year floodplain of a traditional navigable water, interstate
water, or the territorial seas and waters located more than 1,500 feet and less than 4,000 feet
from the lateral limit of an (a)(1) or (a)(3) water may still be determined to have a significant
nexus on a case-specific basis under paragraph (a)(8) of the rule and, thus, be a "water of the
United States" (see section IX).
B. Adjacent Waters, As Defined, Have a Significant Nexus
The discussion below summarizes the key points made in the Science Report and
explains the technical basis for supporting a conclusion that adjacent waters, as defined in this
rule, have a significant nexus to waters identified in paragraphs (a)(1) through (a)(3) of the rule.
The geographic position of an "adjacent" water relative to the (a)(1) through (a)(5) water in to
which it is adjacent is indicative of the relationship they share, with many of its defining
characteristics resulting from the movement of materials and energy between the two. A review
and analysis of the scientific literature supports the conclusion that individually or in
combination with similarly situated waters in a watershed, adjacent waters have a significant
effect on the chemical, physical, and biological integrity of downstream traditionally navigable
waters, interstate waters, and the territorial seas.
i. Adjacent Waters as Defined are "Similarly Situated"
The agencies conclude that all waters meeting the definition of "adjacent" in the rule are
similarly situated for purposes of analyzing whether they have a significant nexus to a traditional
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navigable water, interstate water, or the territorial sea. Based on a review of the scientific
literature, the agencies conclude that these bordering, contiguous, or neighboring waters provide
similar functions and work together to significantly affect the chemical, physical, or biological
integrity of traditional navigable waters, interstate waters, or the territorial seas. Further, because
the definition of "adjacent" focuses on the proximity of the waters (i.e., those that are located
near traditional navigable waters, interstate waters, the territorial seas, impoundments, and
covered tributaries), interpreting the term "similarly situated" to include all covered adjacent
waters, as defined in the rule, is reasonable and consistent with the science. The geographic
proximity of an "adjacent" water relative to the traditional navigable waters, interstate waters,
the territorial seas, impoundments, and covered tributaries is indicative of the relationship to it,
with many of its defining characteristics resulting from the movement of materials and energy
between the categories of waters. The scientific literature supports that waters, including
wetlands, ponds, lakes, oxbow lakes, and similar waters, that are "adjacent," as defined in the
rule, to traditional navigable waters, interstate waters, the territorial seas, impoundments, and
covered tributaries, are integral parts of stream networks because of their ecological functions
and how they interact with each other, and with downstream traditional navigable waters,
interstate waters, or the territorial seas.
ii. Adjacent Waters Significantly Affect the Physical Integrity of (a)(1)
through (a)(3) Waters
Scientific research shows waters and wetlands in riparian areas and floodplains to be
important in protecting the physical integrity of aquatic resources. Because riparian and
floodplain waters exhibit bidirectional exchange of water with the waters to which they are
adjacent, they play an important role in determining the volume and duration of stream flow.
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Riparian and floodplain waters also have an essential role in regulating and stabilizing sediment
transport to downstream waters. These characteristics are fundamental to the physical integrity of
streams as well as downstream traditional navigable waters, interstate waters, and the territorial
seas.
Riparian and floodplain wetlands are important for the reduction or delay of floods. Mat
2-21, 4-7 (citing Mertes et al. 1995; Walton et al. 1996; Bullock and Acreman 2003; Poole et al.
2006; Rassam et al. 2006). Waters in riparian areas control flooding during times of high
precipitation or snowmelt by capturing water from overbank flow and storing excess stream
water. Id. at 4-7. One study found that peak flows in the Cache River in Arkansas decreased by
10-20% mainly because of floodplain water storage. Id. (citing Walton et al. 1996). Research
has shown that floodplain wetlands in Ohio store about 40% of the flow of small streams. Id.
(citing Gamble et al. 2007). These and similar findings point to the close hydrological influence
that waters in riparian and floodplain areas have on streams.
Some adjacent waters are bordering or contiguous with (a)(1) through (a)(5) waters.
Because of their close physical proximity to nearby water bodies, they readily exchange their
waters through the saturated soils surrounding the stream or through surface exchange. This
commingling of waters allows bordering or contiguous waters to both provide chemically
transformed waters to streams and to absorb excess stream flow.
Flow between neighboring waters and streams is more longitudinal (downslope) at
headwaters and more lateral further downstream. Id. at 4-40, Table 4-3. These connections in
part determine stream flow volume and duration. Waters, including wetlands, in riparian areas
connect to nearby water bodies through various surface and subsurface connections. See, e.g., id.
at 2-4 (citing National Research Council 2002). Floodplains, similarly, are closely associated
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with the groundwater found beneath and beside river channels (which are considered shallow
aquifers), and waters in floodplains readily exchange water with such aquifers. Id. at 2-12 (citing
Stanford and Ward 1993; Amoros and Bornette 2002; Poole etal. 2006). Riparian and
floodplain waters are frequently contiguous with streams and other water bodies and
significantly influence the physical form, hydrology, chemistry, and biology of such water
bodies. Id. at 4-6 (citing Junk et al. 1989; Abbott et al. 2000; Tockner et al. 2000; Woessner
2000; Amoros and Bornette 2002; Ward et al. 2002; King et al. 2003; Naiman et al. 2005;
Church 2006; Kondolf et al. 2006; Poole et al. 2006; Poole 2010; Tockner et al. 2010; Vidon et
al. 2010; Helton et al. 2011; McLaughlin et al. 2011; Humphries et al. 2015). Floodplain
wetlands are important for the reduction or delay of floods by capturing water from overbank
flow and by storing excess water from the streams to which they are adjacent. Id. at 4-7 (citing
Bullock and Acreman 2003). Oxbow lakes also retain flood waters. Id. at B-10. Adjacent ponds
generally function similarly to oxbow lakes.
Waters in riparian areas and floodplains filter sediment washed down from uplands and
collect sediment from overbank flow as the river or stream floods. Id. at 4-8 (citing Boto and
Patrick 1979; Whigham et al. 1988). For example, riparian areas were observed to collect 80-
90% of the sediment from farmlands in a study in North Carolina. Id. (citing Cooper et al. 1987;
Daniels and Gilliam 1996; Naiman and Decamps 1997). Maintaining the equilibrium between
sediment deposition and sediment transport is important to maintain the physical shape and
structure of stream channels. Significant changes to upstream channels can affect the chemical,
physical, and biological condition of downstream (a)(1) through (a)(3) waters.
The physical effects of excess sediment can impair chemical and ecological integrity in a
variety of ways. Id. at 5-9 (citing Wood and Armitage 1997). Excess sediment is linked to
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increasing contaminant and nutrient concentrations, all of which tributaries can transmit
downstream, affecting water quality. Excess sediment may block and absorb sunlight
transmission through the water column, inhibiting plant photosynthesis and warming the water in
the stream. Sediment may fill the interstitial spaces between rocks in a streambed, which many
fish and aquatic species use for mating, reproduction, and shelter from predators. This kind of
physical degradation of tributary streambeds results in less suitable habitat available for animals
and fish that move between upstream and downstream waters. Riparian waters that retain
sediments thus protect downstream waters from the effects of excess sediment.
Oxbow lakes play similar roles in the floodplain as they are an integral part of alluvial
floodplains of meandering rivers. Id. at B-8 (citing Winemiller et al. 2000; Glinska-Lewczuk
2009). They connect to rivers by periodic overland flow, typically from the river during flooding
events, and bidirectional shallow subsurface flow through fine river soils (bidirectional means
flow occurs both from the river to oxbow lake when the river has a high water stage and from the
oxbow lake to the river at low water stage). Id. at B-9 to B-10. Oxbow lakes generally have an
important influence on the chemical, physical, and biological condition and function of rivers. Id.
at B-13 to B-14. That influence can vary with the distance from the river and the age of the
oxbow, reflecting the frequency and nature of the exchange of materials that takes place between
the two water bodies.
Because adjacent waters support riparian vegetation, they affect the capacity of riparian
vegetation to influence stream flow, morphology, and habitat provided in the nearby water body.
Vegetation in riparian waters influences the amount of water in the stream by capturing and
transpiring stream flow and intercepting groundwater and overland flow. Id. at 2-21, 4-8 (citing
Meyboom 1964). Riparian vegetation in adjacent waters also reduces stream bank erosion,
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serving to maintain the physical integrity of the channel. See, e.g., id. at 4-8 to 4-9 (citing Beeson
and Doyle 1995; Naiman and Decamps 1997; Burt et al. 2002; Zaimes et al. 2004). In addition,
inputs of woody debris from aquatic vegetation or logs into waters make important contributions
to the channel's geomorphology and the stream's aquatic habitat value. Id. at 4-9 (citing
Anderson and Sedell 1979; Harmon et al. 1986; Nakamura and Swanson 1993; Abbe and
Montgomery 1996; Naiman and Decamps 1997; Gurnell etal. 2002; Brummer etal. 2006; Sear
et al. 2010; Collins etal. 2012). Also, the riparian vegetation that overhangs streams provides
shade, providing a critically important function of reducing fluctuations in water temperature
helping to reduce excessive algal production and to maintain life-supporting oxygen levels in
streams and other waters. Id. at 4-9 to 4-10 (citing Gregory et al. 1991; Volkmar and Dahlgren
2006). Even small changes in water temperature can have significant impacts on the type and
number of species present in waters, with higher temperatures generally associated with
degraded habitat which supports only those species that can tolerate higher temperatures and
reduced levels of dissolved oxygen. Higher water temperatures are associated with streams and
rivers with less valuable recreational and commercial fisheries. As discussed below, these
physical characteristics of headwater streams influence what types of organisms live in the
region.
Headwaters and nearby wetlands supply downstream waters with dissolved organic
carbon as a result of decomposition processes from dead organic matter such as plants. Both
production and consumption of organic and inorganic carbon occur in adjacent wetlands. Id. at 4-
13. Adjacent waters are an important sources of dissolved organic carbon (DOC) to downstream
waters. Allochthonous inputs from adjacent wetlands to streams are important to aquatic food
webs, particular in headwaters. Id. (citing Tank et al. 2010). Allochthonous inputs are terrestrial
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organic materials that enter the stream through vegetation litter (i.e., woody debris, leaves, and
partially decomposed plant parts), erosion, and hydrologic flows. Id. (citing Wetzel 1992). These
inputs of organic matter are the primary source of energy flow into the food webs of streams. Id.
Organic matter inputs are important because they affect food availability to aquatic organisms by
releasing organic carbon and nitrogen into streams. Id. (citing Wetzel and Manny 1972;
Mulholland and Hill 1997). This organic carbon contributes to the downstream foodweb and
ultimately supports downstream fisheries. See, e.g., id. at 4-16. Export of DOC to downstream
waters supports primary productivity, effects pH and buffering capacity, and can protect aquatic
organisms from the harmful effects of UV-B radiation. Id. at 4-28 (citing Eshelman and Hemond
1985; Hobbie and Wetzel 1992; Hedin et al. 1995; Schindler and Curtis 1997; Nuff and Asner
2001; Reddy and DeLaune 2008). However, too much organic matter downstream can have
negative effects because contaminants, such as methylmercury and other trace metals, can be
adsorbed to it. Id. (citing Thurman 1985; Driscoll et al. 1995).
iii. Adjacent Waters Significantly Affect the Chemical Integrity of (a)(1)
through (a)(3) Waters
As stated above in the section on tributaries, pollutants such as petroleum waste products
and other harmful pollutants dumped into any part of the tributary system are likely to flow
downstream, or to be washed downstream, and thereby pollute traditional navigable waters,
interstate waters, and the territorial seas from which American citizens take their drinking water,
shellfish, fin fish, water-based recreation, and many other uses. Some wetlands perform the
valuable function of trapping or filtering out some pollutants (such as fertilizers, silt, and some
pesticides), thereby reducing the likelihood that those pollutants will reach and pollute the
tributaries of the downstream navigable or interstate waters (and eventually pollute those
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downstream waters themselves). However, many other pollutants (such as petroleum wastes and
toxic chemical wastes), if dumped into wetlands or other waters that are adjacent to tributary
streams, may reach those tributaries themselves, and thereafter flow downstream to pollute the
nation's drinking water supply, fisheries, and recreation areas.
Riparian and floodplain waters play a critical role in controlling the chemicals that enter
streams and other "waters of the United States" and as a result are vital in protecting the
chemical, physical, and biological integrity of downstream (a)(1) through (a)(3) waters. Runoff
(the water that has not evaporated or infiltrated into the groundwater) from uplands is a large
source of pollution, but research has shown that wetlands and other riparian waters trap and
chemically transform a substantial amount of the nutrients, pesticides, and other pollutants before
they enter streams, river, lakes and other waters.
Chemicals and other pollutants enter waters from point sources such as outfalls and pipes,
non-point sources (e.g., runoff from agricultural and urban fields and lawns), dry and wet (e.g.,
rain, snow) atmospheric deposition, upstream reaches, and through the hyporheic zone, a region
beneath and alongside a stream bed where surface water and shallow groundwater mix. Id. at 4-
10 (citing Nixon and Lee 1986; Tiner 2003c; Whigham and Jordan 2003; Comer et al. 2005;
Whitmire and Hamilton 2008). Throughout the stream network, but especially in headwater
streams and their adjacent wetlands, chemicals are sequestered via sorption (adsorption and
absorption) or sedimentation processes, assimilated into the flora and fauna, transformed into
other compounds, or lost to the atmosphere through transformational processes performed by
microbes, fungi, algae, and macrophytes present in riparian waters and soils. Id. (citing Nixon
and Lee 1986; Johnston 1991; Boon 2006; Mitsch and Gosselink 2007; Reddy and DeLaune
2008). These chemical processes reduce or eliminate pollution that would otherwise enter
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streams, rivers, lakes and other waters and subsequently downstream traditional navigable
waters, interstate waters, or the territorial seas.
The removal of the nutrients nitrogen and phosphorus is a particularly important role for
riparian and floodplain waters. As described previously, nutrients are necessary to support
aquatic life, but the presence of excess nutrients can lead to eutrophication and the depletion of
oxygen (hypoxia) in nearby waters and in waters far downstream. See, e.g., id. at ES-8.
Eutrophi cation is a large problem in waters across the United States including such important
ecosystems as the Chesapeake Bay and Lake Spokane in Washington. Kemp etal 2005; Moore
and Ross 2010; Murphy et al. 2011. Eutrophi cation is the natural or artificial enrichment of a
water body by nutrients, typically phosphates and nitrates. Science Report at A-4. It can occur
when plants and algae grow in waters to such an extent that the abundance of vegetation
monopolizes the available oxygen, detrimentally affecting other aquatic organisms. Oxbow lakes
also have high mineralization rates, suggesting that similar to adjacent wetlands they process and
trap nutrients in runoff before the runoff reaches the river channel. Science Report at B-l 1 (citing
Winemiller etal. 2000). Protection of these waters therefore helps maintain the chemical
integrity of the nation's waters.
The removal of nitrogen is an important function of all waters, including wetlands, in the
riparian areas. Riparian areas regularly remove more than half of dissolved nitrogen found in
surface and subsurface water by plant uptake and microbial transformation. Id. at 4-11 (citing
Vidon etal. 2010). Denitrification potential in surface and subsurface flows is highest where
there is high organic matter and/or anoxic conditions. Id. at 4-12 (citing McClain et al. 2003;
Orr et al. 2014). The highest denitrification potentials occur in floodplain and riparian waters
where high organic matter, denitrifying microbes, and saturated soil conditions are present, and
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rates increase with proximity to streams. Id. (citing Gregory et al. 1991; Vidon et al. 2010).
Riparian waters are therefore important in maintaining the conditions important for
denitrification, which in turn protects streams, rivers, lakes and other waters from nitrogen
pollution.
Plant uptake of dissolved nitrogen in subsurface flows through riparian areas also
accounts for large quantities of nitrogen removal. Id. (citing Vidon et al. 2010). Riparian forests
have been found to remove 75% of dissolved nitrate transported from agricultural fields to a
Maryland river. Id. (citing Vidon et al. 2010). Likewise, riparian forests in Georgia remove 65%
of nitrogen and 30% of phosphorus from agricultural sources. Id. (citing Vidon, et al. 2010). A
Pennsylvania forested riparian area removed 26% of the total nitrate input from the subsurface.
Id. (citing Newbold et al. 2010). The vegetation associated with riparian waters also removes
nitrogen from subsurface flows. Therefore, the conservation of riparian waters helps protect
downstream waters from influxes of dissolved nitrogen.
Phosphorus is another potentially harmful nutrient that is captured and processed in
riparian waters. Id. at 4-12 to 4-13 (citing Dillaha and Inamdar 1997; Sharpley and Rekolainen
1997; Carlyle and Hill 2001). Biogeochemical processes, sedimentation, and plant uptake
account for high rates of removal of particulate phosphorus in riparian areas. Id. at 4-12 (citing
Hoffmann et al. 2009). The amount of contact the water has with nearby soils and the
characteristics of that soil determine the ability of the riparian area to remove phosphorus. Id.
Riparian areas are phosphorus sinks in oxic soils (containing oxygen), while riparian soils
generally can serve as sources of phosphorus when soils are anoxic (lacking oxygen) or when
mineral dissolution releases phosphorus. Id. at 4-12 (citing Baldwin and Mitchell 2000; Carlyle
and Hill 2001; Chacon et al. 2008). Portions of riparian areas where agricultural sediments are
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deposited are phosphorus sources to streams if the phosphorus is desorbed and leached but can
be sinks by adsorbing dissolved phosphorus if sediment phosphorus concentrations are low. Id.
at 4-12 to 4-13 (citing Dillaha and Inamdar 1997; Sharpley and Rekolainen 1997). Riparian areas
also serve as phosphorus sinks when upland surface runoff travels through the riparian area or
when fine-grained sediment containing phosphorus is deposited overbank onto the riparian area.
Id at 4-13 (citing Dillaha and Inamdar 1997). These sediments, however, can become sources of
phosphorus if they are later saturated with water and iron and manganese are reductively
dissolved during anoxic conditions, thus causing them to desorb phosphorus. Id. (citing Reddy
and DeLaune 2008). The function of riparian waters to move and uptake phosphorus is crucial
for maintaining the chemical and biological integrity of the waters to which they are adjacent,
and for preventing eutrophication in downstream traditional navigable waters, interstate waters,
and the territorial seas. In the case where riparian waters are acting as a source of phosphorus for
(a)(1) through (a)(3) waters, this also can significantly affect the chemical and biological
integrity of these downstream waters.
iv. Adjacent Waters Significantly Affect the Biological Integrity of (a)(1)
through (a)(3) Waters
Adjacent waters support the biological integrity of downstream (a)(1) through (a)(3)
waters in a variety of ways. They provide habitat for aquatic and water-tolerant plants,
invertebrates (aquatic insects), and vertebrates, and provide feeding, refuge, and breeding areas
for invertebrates and fish. Seeds, plants, and animals move between adjacent waters and the
nearby streams, and from there colonize or utilize downstream waters, including traditional
navigable waters, interstate waters, and the territorial seas.
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Organic matter from adjacent wetlands is critical to aquatic food webs, particularly in
headwaters, where it is the primary source of energy flow due to low light conditions that inhibit
photosynthesis. See, e.g., id. at 4-13 (citing Tank el al. 2010). Headwater streams tend to be
located in heavily vegetated areas compared to larger waters, so they are more likely to contain
leaf litter, dead and decaying plants, and other organic matter that forms the basis of headwater
food webs. The organic matter is processed by microbes and insects that make the energy
available to higher levels of stream life such as amphibians and fish. Studies have shown that
aquatic insects rely on leaf inputs in headwater streams and that excluding organic litter from a
stream resulted in significant changes to the food web at multiple levels. Id. (citing Minshall
1967; Wallace and Webster 1996; Wallace et al. 1997; Meyer et al. 1998). Fish and amphibian
species found in headwaters travel downstream and in turn become part of the food web for
larger aquatic organisms in rivers and other waters. Organic material provided by riparian waters
to small, headwater streams is therefore important not only to the small streams that directly
utilize this source of energy to support their biological populations but also to the overall
biological integrity of downstream waters that benefit from the movement of fish and other
species that contribute to the food web of larger streams and rivers.
Floodplain waters, including oxbow lakes, accumulate organic carbon and nitrogen, an
important function influenced by the size and frequency of floods from rivers to which they are
adjacent. See, e.g., id. at B-l 1 (citing Cabezas et al. 2009). These stored chemicals are available
for exchange with river water when hydrological connections are present. Organic materials are
the basis for the food web in stream reaches where photosynthetic production of energy is absent
or limited, particularly in headwater systems where vegetative litter alone makes up the base of
the aquatic food web. The maintenance of floodplain waters is therefore an important component
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of protecting the biological integrity of downstream (a)(1), (a)(2), and (a)(3) waters into which
the headwaters flow.
The waters, including wetlands, in the riparian area play an important role in the removal
of pesticides. Id. at 4-14 (citing Vidon et al. 2010). Microbes near plant roots break down these
pesticides. See, e.g., id. (citing Voos and Groffman 1996). Uptake by aquatic plants has also been
shown to be an important mechanism of removal of the pesticides alachlor and atrazine. Id.
(citing Paterson and Schnoor 1992). Riparian waters also trap and hold pesticide contaminated
runoff preventing it from harming neighboring waters.
Riparian areas and floodplains are dynamic places that support a diversity of aquatic,
amphibious, and terrestrial species adapted to the unique habitat created by periodic or episodic
flooding or inundation events. Id. at 4-15 (citing Power et al. 1995a; Power et al. 1995b; Galat et
al. 1998; Robinson et al. 2002; Toth and van der Valk 2012; Rooney et al. 2013; Granado and
Henry 2014). Plants, aquatic insects, and vertebrates use waters, including wetlands, in riparian
areas and floodplains for habitat, nutrients, and breeding. As a result, the waters, including
wetlands, in riparian areas and floodplains act as sources of organisms, particularly during
inundation events, replenishing neighboring waters with organisms, seeds, and organic matter.
Inundation and hydrological connectivity of riparian areas and floodplains to the tributary
network greatly increase the area of aquatic habitats and species diversity. Id. at 4-15, 4-16
(citing Junk et al. 1989; Tockner et al. 2000; Jansson et al. 2005; Brooks and Serfass 2013).
Aquatic animals, including amphibians and fish, take advantage of the riparian and floodplain
waters, either inhabiting them or moving between the riparian or floodplain water and
neighboring waters. Id. at 4-15, 4-17 through 4-19 (citing Copp 1989; Smock et al. 1992; Smock
1994; Robinson et al. 2002; Richardson et al. 2005; Ilg et al. 2008; Shoup and Wahl 2009).
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Likewise, seeds, plant fragments, and whole plants move between riparian and floodplain waters
and the river network. Id. at 4-15 (citing Schneider and Sharitz 1988; Middleton 2000; Nilsson et
al. 2010).
Hydrological connections are often drivers of biological connections, and flooding events
enhance the existing connections between riparian and floodplain waters and the river network.
As a result, waters within floodplains have important functions for aquatic health. Many species
have cycles timed to flooding events, particularly in circumstances where flooding is associated
with annual spring snowmelt or high precipitation. Id. at 4-15 to 4-16, 4-19 (citing Thomas et al.
2006; Tronstad et al. 2007; Gurnell et al. 2008). Waters within floodplains act as sinks of seeds,
plant fragments, and invertebrate eggs and as sources of such biological material during times of
periodic flooding, allowing for cross-breeding and resulting gene flow across time. Id. at 4-16, 4-
19 to 4-20 (citing Middleton, 2000; Jenkins and Boulton 2003; Frisch and Threlkeld 2005;
Gurnell et al. 2008; Vanschoenwinkel etal. 2009). Stream macroinvertebrates (e.g., insects,
crayfish, and mollusks) and microinvertebrates (e.g. zooplankton such as cladocerans, copepods,
rotifers, and gastropods) colonize nutrient rich waters within riparian areas and floodplains in
large numbers during periods of seasonal or episodic inundation, facilitating an increase in
population and sustaining them though times of limited resources and population decline. Id. at
4-19 to 4-20 (citing Fisher and Willis 2000; Frisch and Threlkeld 2005; Junk et al. 1989;
Malmqvist 2002; Ilg etal. 2008). Such animals are adapted to high floods, desiccation (drying
out), or other stresses that come with these regular, systemic fluctuations. Id. at 4-19. Riparian
and floodplain waters therefore maintain various biological populations, which periodically
replenish jurisdictional waters to which they adjacent and the downstream (a)(1) through (a)(3)
waters they flow into, serving to maintain their biological integrity.
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Plants and animals use waters, including wetlands, in riparian areas and floodplains for
habitat, food, and breeding. Oxbow lakes in the floodplain provide critical fish habitat needed
for feeding and rearing, leading researchers to conclude that the entire floodplain should be
considered a single functional unit, essential to the river's biological integrity. Id. at 4-17 (citing
Shoup and Wahl 2009). Since adjacent ponds are structurally and biologically similar to oxbow
lakes they serve similar functions relative to the nearby river or stream. Waters, including
wetlands, in the riparian areas also provide food sources for stream invertebrates, which colonize
during inundation events. Id. at 4-19 (citing Junk et al. 1989; Ilg et al. 2008). Riparian and
floodplain waters also form an integral part of the river food web, linking primary producers and
plants to higher animals. Id. (citing Malmqvist 2002; Woodward and Hildrew 2002; Stead et al.
2005; Woodford and Mcintosh 2010). Likewise, floodplains are important foraging, hunting, and
breeding sites for fish, amphibians, and aquatic macroinvertebrates. Id. at 4-15 (citing Copp
1989; Smock et al. 1992; Smock, 1994; Bestgen et al. 2000; Richardson et al. 2005; Schramm
and Eggleton 2006; Sullivan and Watzin 2009; Alford and Walker 2013; Magana 2013).
Plants and animals move back and forth between adjacent waters and the river network.
This movement is assisted in some cases when flooding events create hydrological connections.
For instance, these floodplain and riparian wetlands provide refuge, feeding, and rearing habitat
for many fish species. Id. at 4-17 (citing Wharton et al. 1982; Boltz and Stauffer 1989; Matheney
and 1995; Pease et al. 2006; Henning et al. 2007; Jeffres etal. 2008). Seeds of aquatic and
riparian plants ingested by animals such as carp are dispersed in stream channels and associated
waters. See, e.g., id. at 4-16 (citing King etal. 2003; Pollux etal. 2007). Also, phytoplankton
move between floodplain wetlands and the river network. Id. at 4-16 (citing Angeler et al. 2010).
In turn, the primary productivity conditions in the floodplain results in large populations of
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phytoplankton that enrich river networks when hydrological connections form. Id. at 4-16 to 4-
17 (citing Lehman etal. 2008). This influx of carbon into the river system nourishes the aquatic
food webs of downstream waters, for example, supporting fisheries.
However, even when hydrological connections are absent, some organisms can move
between adjacent waters and their nearby tributaries by overland movement in order to complete
their life cycle. River-dwelling mammals, such as river otters, move from the river to
riparian/floodplain wetlands. Id. at 4-17 (citing Newman and Griffin 1994). In addition, both
river otters and beavers have a strong preference for riparian areas that are pond- and lake-
dominated (Swimley etal. 1999). Several species of amphibians and reptiles including frogs,
snakes and turtles use both streams and neighboring waters. Id. at ES-10, 3-47 (Table 3-1), 4-15
(citing Richardson et al. 2005). Movement between wetlands and the river network also occurs
by the dispersal of seed and plant fragments and the wind dispersal of invertebrates. Id. at 4-15 to
4-16, 4-20 (citing Schneider and Sharitz 1988; Middleton 2000; Gurnell 2007; Gurnell et al.
2008; Nilsson et al. 2010; Tronstad et al. 2007; Vanschoenwinkel et al. 2009). Animals,
particularly migratory fish, can thus move between adjacent waters and (a)(1) through (a)(3)
waters. And even when some species do not traverse the entire distance from adjacent waters to
downstream waters, the downstream waters still benefit from the ecological integrity that persists
because of the close relationship that adjacent waters have with nearby waters. This is because
the chemical and biological properties that arise from interactions between adjacent waters and
tributaries move downstream and support the integrity of (a)(1) through (a)(3) waters.
Biological connections between adjacent waters and river systems do not always increase
with hydrologic connections. In some cases, the lack of connection improves the biological
contribution provided by riparian waters towards nearby streams, rivers, and lakes. For instance,
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the periodic hydrologic disconnectedness of oxbow lakes is necessary for the accumulation of
plankton, an important source of carbon more easily assimilated by the aquatic food chain than
terrestrial forms of carbon. Id. at B-l 1 to B-12 (citing Baranyi et al. 2002; Keckeis et al. 2003).
Similarly, some degree of hydrological disconnectedness is important in increasing the number
of mollusk species and macroinvertebrate diversity in oxbow lakes, which in turn support the
diversity of mollusks throughout the aquatic system. Id. at B-12 (citing Reckendorfer et al. 2006;
Obolewski et al. 2009).
C. Rationale for Conclusions
The scientific literature supports that waters which are adjacent to (a)(1) through (a)(5)
waters, including wetlands, lakes, oxbow lakes, and adjacent ponds, are integral parts of tributary
networks to (a)(1) through (a)(3) waters because they are directly connected to streams via
surface and shallow subsurface connections that concentrate, mix, transform, and transport water
and other materials, including food resources, downstream to larger rivers. Adjacent wetlands
and other adjacent waters filter pollutants before they enter the tributary system, they attenuate
flow during flood events, they regulate flow rate and timing, they trap sediment, and they input
organic material into rivers and streams, providing the basic building blocks for their healthy
functioning. These waters also are biologically connected to downstream waters by providing
habitat and refuge to many species, and storing and releasing food sources. The scientific
literature demonstrates that adjacent waters in a watershed together exert a strong influence on
the character and functioning of rivers, streams and lakes. Note that non-jurisdictional surface
(e.g. non-wetland swales) and shallow subsurface connections that serve as a hydrologic
connection between an adjacent water and the jurisdictional water to which it is adjacent, or are a
consideration for a case-specific significant nexus determination, do not become "waters of the
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United States" themselves. As stated throughout the preamble of the rule, only waters that meet
the provisions in (a)(1) through (a)(8) are considered "waters of the United States." Groundwater
is explicitly excluded from the definition of "waters of the United States" under paragraph (b)(5).
Adjacent waters, as defined, alone or in combination with other adjacent waters in a point
of entry watershed, significantly affect the chemical, physical, or biological integrity of
traditional navigable waters, interstate waters, and the territorial seas. Based on studies of waters
the agencies identify as bordering, contiguous, or neighboring, including floodplain wetlands,
and their hydrologic connections through the tributary system there is sufficient scientific
evidence regarding the important functions of these adjacent wetlands to demonstrate that, alone
or in combination with similarly situated waters in the region, wetlands and open waters adjacent
to any tributary have a significant effect on the chemical, physical, or biological integrity of
traditional navigable waters, interstate waters, or the territorial seas. The reviewed scientific
literature supports the conclusion that adjacent waters generally play a larger role in the
ecological condition of smaller tributary systems, which, in turn, determines the effects on the
chemical, physical, and biological health of larger downstream waters. See, e.g., Science Report
at 1-14.
The CWA explicitly establishes authority over adjacent wetlands. Under section 404(g),
states are authorized to assume responsibility for administration of the section 404 permitting
program with respect to "navigable waters (other than those waters which are presently used, or
are susceptible to use in their natural condition or by reasonable improvement as a means to
transport interstate or foreign commerce shoreward to their ordinary high water mark, including
all waters which are subject to the ebb and flow of the tide shoreward to their mean high water
mark, or mean higher high water mark on the west coast, including wetlands adjacent thereto)."
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33 U.S.C. § 1344(g)(1) (emphasis added). While this provision mainly serves as a limitation on
the scope of waters for which states may be authorized to issue permits, it also shows that
Congress was concerned with the protection of adjacent wetlands and recognized their important
role in protecting downstream traditional navigable waters. Indeed, the existing definition of
adjacency was developed in recognition of the integral role wetlands play in broader aquatic
ecosystems:
The regulation of activities that cause water pollution cannot rely on . . . artificial lines . . .
but must focus on all waters that together form the entire aquatic system. Water moves in
hydrologic cycles, and the pollution of this part of the aquatic system, regardless of
whether it is above or below an ordinary high water mark, or mean high tide line, will
affect the water quality of the other waters within that aquatic system. For this reason, the
landward limit of Federal jurisdiction under Section 404 must include any adjacent
wetlands that form the border of or are in reasonable proximity to other waters of the
United States, as these wetlands are part of this aquatic system.
42 FR 37128, July 19, 1977.
As the Supreme Court found in United States v. Riverside Bayview Homes, Inc., "the
evident breadth of congressional concern for protection of water quality and aquatic ecosystems
suggests that it is reasonable for the Corps to interpret the term 'waters' to encompass wetlands
adjacent to waters as more conventionally defined." 474 U.S. at 133.
In upholding the Corps' judgment about the relationship between waters and their
adjacent wetlands, the Supreme Court in Riverside Bayview acknowledged that the agencies'
regulations take into account functions provided by wetlands in support of this relationship.
"[AJdjacent wetlands may 'serve significant natural biological functions, including food chain
production, general habitat, and nesting, spawning, rearing and resting sites for aquatic . . .
species.'" Id. at 133 (citing § 320.4(b)(2)(i)). The Court further stated that the Corps had
reasonably concluded that "wetlands adjacent to lakes, rivers, streams, and other bodies of water
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may function as integral parts of the aquatic environment even when the moisture creating the
wetlands does not find its source in the adjacent bodies of water." 474 U.S. at 135.
Two decades later, in Rapanos Justice Kennedy stated:
As the Court noted in Riverside Bay view, 'the Corps has concluded that wetlands may
serve to filter and purify water draining into adjacent bodies of water, 33 CFR
§320.4(b)(2)(vii)(1985), and to slow the flow of surface runoff into lakes, rivers, and
streams and thus prevent flooding and erosion, see §§320.4(b)(2)(iv) and (v).' Where
wetlands perform these filtering and runoff-control functions, filling them may increase
downstream pollution, much as a discharge of toxic pollutants would. ... In many cases,
moreover, filling in wetlands separated from another water by a berm can mean that flood
water, impurities, or runoff that would have been stored or contained in the wetlands will
instead flow out to major waterways. With these concerns in mind, the Corps' definition
of adjacency is a reasonable one, for it may be the absence of an interchange of waters
prior to the dredge and fill activity that makes protection of the wetlands critical to the
statutory scheme.
547 U.S. at 775 (citations omitted).
The four dissenting justices in Rapanos similarly concluded:
The Army Corps has determined that wetlands adjacent to tributaries of traditionally
navigable waters preserve the quality of our Nation's waters by, among other things,
providing habitat for aquatic animals, keeping excessive sediment and toxic pollutants
out of adjacent waters, and reducing downstream flooding by absorbing water at times of
high flow. The Corps' resulting decision to treat these wetlands as encompassed within
the term 'waters of the United States' is a quintessential example of the Executive's
reasonable interpretation of a statutory provision.
Id. at 778 {citing Chevron U.S.A. Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837,
842-845 (1984)).
For those wetlands adjacent to traditional navigable waters, Justice Kennedy concluded in
Rapanos that the agencies' existing regulation "rests upon a reasonable inference of ecologic
interconnection, and the assertion of jurisdiction for those wetlands is sustainable under the Act
by showing adjacency alone." 547 U.S. at 780. For other adjacent waters, including adjacent
wetlands, Justice Kennedy's significant nexus standard provides a framework for establishing
categories of waters which are per se "waters of the United States." First, he provided that
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wetlands are jurisdictional if they "either alone or in combination with similarly situated lands in
the region, significantly affect the chemical, physical, and biological integrity of other covered
waters more readily understood as 'navigable.'" Id. at 780. Next, Justice Kennedy stated that
"[t]hrough regulation or adjudication, the Corps may choose to identify categories of tributaries
that, due to their volume of flow (either annually or on average), their proximity to navigable
waters, or other relevant considerations, are significant enough that wetlands adjacent to them
are likely, in the majority of cases, to perform important functions for an aquatic system
incorporating navigable waters." Id. at 780-81.
With this regulation, the agencies have identified those tributaries that are significant
enough that wetlands adjacent to them are likely in the majority of cases to perform important
functions for an aquatic system incorporating navigable waters. Tributaries are defined as waters
"that contribute^] flow, either directly or through another water (including an impoundment
identified in paragraph (a)(4) of this section), to a water identified in paragraphs (a)(1) through
(3) of this section that is characterized by the presence of the physical indicators of a bed and
banks and an ordinary high water mark. These physical indicators demonstrate there is volume,
frequency and duration of flow sufficient to create a bed and banks and an ordinary high water
mark, and thus to qualify as a tributary." As discussed above in section VII, the scientific
literature unequivocally demonstrates that streams, individually or cumulatively, exert a strong
influence on the integrity of downstream waters.
While the issue was not before the Supreme Court, it is reasonable to also assess whether
non-wetland waters have a significant nexus, as Justice Kennedy's opinion makes clear that a
significant nexus is a touchstone for CW A jurisdiction. The agencies have determined that
adjacent waters as defined in today's rule, alone or in combination with other adjacent waters in
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the region that drains to a traditional navigable water, interstate water or the territorial seas,
significantly affect the chemical, physical, and biological integrity of those waters. The science
supports the agencies' inclusion of adjacent open waters - like ponds, oxbow lakes, and other
lakes - as waters that have a significant nexus. As mentioned in section II.B., open waters
perform many of the same important functions as wetlands that impact downstream waters,
including contribution of flow, water retention, and nutrient processing and retention.
The agencies have concluded that all waters that meet the definition of "adjacent" are
similarly situated for purposes of analyzing whether they, in the majority of cases, have a
significant nexus to an (a)(1) through (a)(3) water. Based on the agencies' review of the
scientific literature, we have concluded that these waters provide many similar functions that
significantly affect the chemical, physical, or biological integrity of traditional navigable waters,
interstate waters, or the territorial seas. The scientific literature documents that waters that are
adjacent to (a)(1) through (a)(5) waters, including wetlands, oxbow lakes and adjacent ponds, are
integral parts of stream networks because of their ecological functions and how they interact with
each other, and with downstream traditional navigable waters, interstate waters, or the territorial
seas. In other words, tributaries and their adjacent waters, and the downstream traditional
navigable waters, interstate waters, and territorial seas into which those waters flow, are an
integrated ecological system, and discharges of pollutants, including discharges of dredged or fill
material, into any component of that ecological system, must be regulated under the CWA to
restore and maintain the chemical, physical, or biological integrity of these waters.
Based on the science, the agencies have concluded that waters, including wetlands,
adjacent to all (a)(1) through (a)(5) waters provide vital functions for downstream traditional
navigable waters, interstate waters, or the territorial seas and therefore have a significant nexus.
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IX. Case-Specific Significant Nexus Determinations
The rule establishes two exclusive circumstances under which case-specific
determinations will be made for whether the water has a "significant nexus" and is therefore a
"water of the United States." First, the rule identifies at paragraph (a)(7) five subcategories of
waters (prairie potholes, Carolina and Delmarva bays, pocosins, western vernal pools in
California, and Texas coastal prairie wetlands) that the agencies have determined are "similarly
situated" for purposes of the significant nexus determination. Second, the rule identifies at
paragraph (a)(8) circumstances under which waters will be subject to a case-specific significant
nexus determination but for which the agencies have not made a "similarly situated"
determination: waters within the 100-year floodplain of a traditional navigable water, interstate
water, or the territorial seas, and waters within 4,000 feet of the high tide line or the ordinary
high water mark of a traditional navigable water, interstate water, the territorial seas,
impoundments, or tributaries, as defined.
When selecting the circumstances under which a case-specific significant nexus
determination could be made, the agencies considered their expertise and experience and
available scientific literature and data. For example, the Science Report includes a focused
evaluation of the connections and effects to downstream waters for several regional types of
wetlands, including Carolina and Delmarva bays, prairie potholes, and vernal pools. Science
Report at Appendix B. These regional types were chosen for evaluation in the Science Report
because they represent a broad geographic area as well as a diversity of water types based on
their origin, landscape setting, hydrology, and other factors. Individual Carolina and Delmarva
bays, prairie potholes, and Western vernal pools in California may or may not be considered
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adjacent to (a)(1) through (a)(5) waters. Similarly, though not specifically analyzed in a case
study in the Science Report, individual pocosins and Texas coastal prairie wetlands may or may
not be considered adjacent to (a)(1) through (a)(5) waters. Where such waters do not meet the
regulatory requirements under (a)(1) through (a)(6) to be considered a "water of the United
States," these five subcategories of waters must be evaluated to determine whether they have a
significant nexus under (a)(7) in combination with other waters of the same type in the same
point of entry watershed.
Case-specific determinations are made under (a)(7) and (a)(8) for waters that cannot be
considered "waters of the United States" under (a)(1) through (a)(6) and that meet the criteria set
out in (a)(7) and (a)(8). Case-specific determinations must be made for waters that are either in
the five subcategories specified in (a)(7), or are located within the 100-year floodplain of a
traditional navigable water, interstate water, or the territorial seas or located within 4,000 feet of
the high tide line or the OHWM of an (a)(1) through (a)(5) water, as specified at (a)(8). Waters
located within the 100-year floodplain of a traditional navigable water, interstate water, or the
territorial seas beyond the 1,500 boundary for "neighboring" individually span the gradient of
connectivity identified in the Science Report; they are in the floodplain of the foundational
waters of the CWA, but may also may be fairly distant, and a case-specific significant nexus
analysis will enable the agencies to properly consider the strength of connectivity for these
particular waters. Waters within the 4,000 foot boundary are typically located outside of the
floodplain, but can be connected to downstream (a)(1) through (a)(3) waters via confined surface
connections, unconfined surface connections, shallow subsurface connections, deeper
groundwater connections, biological connections, spillage, or by providing additional functions
such as storage and mitigating peak flows. The degree of connectivity of such wetlands will vary
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depending on landscape features such as distance from downstream waters and proximity to
other wetlands of similar nature that as a group connect to jurisdictional downstream waters.
Science Report at ES-4, 4-2, 6-5.
These waters, primarily depressional wetlands, small open waters, and peatlands, are
known to have important hydrologic, water quality, and habitat functions which vary as a result
of the diverse settings in which they exist across the country. For example, a report that reviewed
the results of multiple scientific studies concluded that depressional wetlands lacking a surface
outlet functioned together to significantly reduce or attenuate flooding. Science Report at 4-25
(citing Bullock and Acreman 2003). Some of the important factors which influence the
variability of their functions and connectivity include the wetland type, topography, geology, soil
features, antecedent moisture conditions, available storage capacity, and seasonal position of the
water table relative to the wetland. Id. at 4-23 and 4-25.
If a water is a great distance from a group of case-specific waters in the same point of
entry watershed, it may be performing some of the same functions as those in the group, but their
distance from each other or from downstream (a)(1) through (a)(3) waters will decrease the
probability that it has some kind of chemical, physical, or biological connectivity to the
downstream water, assuming that conditions governing the type and quantity of flows (e.g. slope,
soil, and aquifer permeability, etc.) are similar. Id. at ES-4, 4-2, 6-5.
Assessing whether a particular water is a "water of the United States" because it, alone or
in combination with other similarly situated waters, has a significant nexus to an (a)(1) through
(a)(3) water will be determined on a case-specific basis. The science supports the agencies'
determination that waters that do not otherwise meet the definition of "waters of the United
States" under paragraphs (a)(1) through (a)(6) of the rule can on a case-specific basis have a
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significant nexus to downstream traditional navigable waters, interstate waters, or the territorial
seas. For instance, the SAB in its review of the technical basis of the rule concluded, "[t]he
scientific literature has established that 'other waters' can influence downstream waters,
particularly when considered in aggregate. Thus, it is appropriate to define 'other waters' as
waters of the United States on a case-by-case basis, either alone or in combination with similarly
situated waters in the same region." SAB 2014b at 3. In the final rule, the agencies have
amended the "other waters" category into the two case-specific categories at (a)(7) and (a)(8).
As with other non-tidal open waters (e.g. ponds and lakes), case-specific waters that have
a significant nexus are delineated using the ordinary high water mark, while such case-specific
waters that are wetlands are delineated using the 1987 Corps Delineation Manual and its ten
regional supplements.
A. Five Subcategories of Waters are "Similarly Situated"
The agencies have determined by rule that prairie potholes, Carolina and Delmarva bays,
pocosins, Texas coastal prairie wetlands, and western vernal pools in California are similarly
situated. See, e.g., Tiner 2003c; Forbes et al. 2012. These waters, where they do not meet the
provisions of other parts of the rule, are to be evaluated in combination with other waters of the
same subcategory located in the same watershed that drains to the nearest traditional navigable
water, interstate water, or the territorial seas (point of entry watershed) for a case-specific
significant nexus analysis.
The agencies' determination that the five subcategories of waters specified in (a)(7) are
similarly situated is informed by science and the agencies' experience and technical expertise.
Specifically, the SAB stated there is "also adequate scientific evidence to support a
determination that certain subcategories and types of 'other waters' in particular regions of the
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United States (e.g., Carolina and Delmarva Bays, Texas coastal prairie wetlands, prairie
potholes, pocosins, western vernal pools) are similarly situated (i.e., they have a similar influence
on the physical, chemical, and biological integrity of downstream waters and are similarly
situated on the landscape) and thus could be considered waters of the United States." SAB
2014b. In addition, as described in more detail in sections IX.A.i. through IX.A.v. below, the
agencies have determined that waters in each of the five subcategories function alike and are
sufficiently close to function together in affecting downstream waters when in the same point of
entry watershed.
The agencies at this time are not able to determine that the available science supports that
the five subcategories of waters as a class have a significant nexus to traditional navigable
waters, interstate waters, or the territorial seas. This is because individual waters of the class vary
in the level of connectivity and the effects of that connectivity to downstream waters. However,
the agencies conclude that the science supports that such waters, particularly when considered in
combination with similarly situated waters, can on a case-specific basis have a significant nexus
to (a)(1) through (a)(3) waters in light of their numerous functions that can impact downstream
water integrity of (a)(1) through (a)(3) waters. The Science Report concludes, "current science
does not support evaluations of the degree of connectivity for specific groups or classes of
wetlands (e.g., prairie potholes or vernal pools). Evaluations of individual wetlands or groups of
wetlands, however, could be possible through case-by-case analysis." Science Report at ES-4.
The specific subcategories of similarly situated waters under (a)(7) - prairie potholes,
Carolina and Delmarva bays, pocosins, western vernal pools in California, and Texas coastal
prairie potholes - are discussed below.
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i. Prairie Potholes
Prairie potholes are a complex of glacially formed wetlands, usually occurring in
depressions that lack permanent natural outlets, found in the central United States and Canada.
Science Report at B-14; Tiner 2003c. In the United States, they are found from central Iowa
through western Minnesota, eastern South Dakota, and North Dakota, van der Valk and Pederson
2003. The vast area they occupy is variable in many aspects, including climatically,
topographically, geologically, and in terms of land use and alteration, which imparts variation on
the prairie potholes themselves. Science Report at B-14 to B-15 (citing van der Valk and
Pederson 2003; Kahara et al. 2009). Prairie potholes demonstrate a wide range of hydrologic
permanence; some hold permanent standing water and others are wet only in years with high
precipitation. This in turn influences the diversity and structure of their biological communities.
Id. at B-14.
Prairie potholes generally accumulate and retain water effectively due to the low
permeability of their underlying soil, which can modulate flow characteristics of nearby streams
and rivers and reduce flooding downstream. Id. One of the most noted hydrologic functions of
prairie potholes is water storage. Because most of the water outflow in prairie potholes is via
evapotranspiration, prairie potholes can become water sinks, preventing flow to downstream
waters. Id. at B-15 (citing Carroll et al. 2005; van der Kamp and Hayashi 2009); Tiner 2003c.
When considered in combination with other prairie potholes in the watershed, these wetlands
provide considerable surface-water capacity. Tiner 2003c. For example, in various subbasins
across the Prairie Pothole Region, including those that feed Devils Lake and the Red River of the
North, both of which have a long history of flooding, potholes have consistently been estimated
to hold tens of millions of cubic meters of water. Science Report at B-17 (citing Hubbard and
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Linder 1986; Vining 2002; Gleason et al. 2007). Prairie potholes in North Dakota's Devils Lake
Basin can store as much as 72% of the total runoff from a two-year frequency storm and about
41% from a 100-year storm. Tiner 2003c. This water storage controls seasonal flooding. Id.
Another study involving prairie potholes draining to Devils Lake indicated that streamflow
declines substantially with increased wetland storage capacity. Science Report at 6-6. Increasing
the volume of pothole storage across the subbasin by approximately 60% caused simulated total
annual streamflow to decrease by 50% during a series of dry years and by 20% during wet years.
Id. Similarly, studies of the Red River of the North in North Dakota and Minnesota suggest the
ability of prairie potholes to control streamflow could be widespread across eastern portions of
the Prairie Pothole Region. Id. Reducing water storage capacity of wetlands by connecting
formerly isolated potholes through ditching or drainage to the Devils Lake and Red River basins
could increase stormflow and contribute to downstream flooding. Id. The impacts of changing
streamflow are numerous, including altered flow regime, stream geomorphology, habitat, and
ecology.
Prairie potholes also can accumulate and transform various pollutants, including nutrients
and chemicals in overland flow, thereby reducing chemical loading and pollution to other bodies
of water. Id. at B-14; 6-6. Denitrification that takes place in the anaerobic zone of these wetlands
can make them effective nitrogen sinks. Id. at B-16 (citing van der Valk 2006).When prairie
potholes are artificially connected to streams and lakes through drainage, they become sources of
water and chemicals to downstream waters. Id.
Prairie potholes also support a community of highly mobile organisms, from plants to
invertebrates that move among prairie potholes and that can biologically connect the entire
complex to the river network. Id. at B-14. These mobile organisms can move from prairie
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potholes to the river network and vice versa via wind, water, or land, by either self-propelling or
hitchhiking on other mobile organisms, similar to the ability of organisms to move to and from
adjacent waters and throughout the tributary network. Id. at B-20 (citing Keiper el al. 2002;
Soons 2006). Plants and invertebrates can also travel by becoming attached to or consumed and
excreted by waterfowl. Id. (citing Amezaga et al. 2002). Dispersal via waterfowl can occur over
long distances. Id. (citing Mueller and van der Valk 2002). Perhaps the best-known and most
well-studied attribute of prairie potholes is their role as productive feeding and nesting habitat for
waterfowl. Id. at B-17. Waterfowl often move between prairie wetlands during the breeding
season in search of food and cover, and some species also use habitats within the river network
as wetlands dry or freeze. Id (citing Pattenden and Boag 1989; Murkin and Caldwell 2000). In
addition, a diverse assemblage of microorganisms, invertebrates, amphibians, reptiles, and
sometimes fish, use potholes to feed or reproduce. Id. at B-14 (citing Hentges and Stewart 2010).
Fish and other organisms that can be suspended in water (e.g., floating insect larvae or seeds)
and can also move through manmade waterways that connect prairie potholes to stream
networks. Id. at B-20 (citing Zimmer et al. 2001; van der Valk and Pederson 2003; Hanson et al.
2005; Hentges and Stewart 2010; Herwig et al. 2010). Overland movement of amphibians and
mammals can connect potholes to each other and to lakes and streams, and some species can
disperse over long distances to feed and breed. Id. at B-21 (citing Clark 2000; Lehtinen and
Galatowitsch 2001; Winter and LaBaugh 2003).
Prairie potholes can be highly connected to other prairie potholes or to the stream
network via surface hydrologic connections during the wet season. Temporary hydrologic
connectivity between prairie potholes and from prairie potholes to the tributary system can
periodically occur via "fill-and-spill" events. Id. at B-12 (citing Winter and Rosenberry 1998;
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Leibowitz and Vining 2003). "Fill-and-spill" describes situations where wetlands or open waters
fill to capacity during intense precipitation events or high cumulative precipitation over time and
then spill to another water, such as another wetland in the same wetland complex or to a
downstream stream or lake. See, e.g., id.] Tromp-van Meerveld and McDonnell 2006. In essence,
water fills in one aquatic research and spills downstream to another. Water connected through
such flows originates from the wetland or open water, travels to the downstream water, and is
connected to the downstream water or waters by swales or other directional flowpaths on the
surface. A directional flowpath is a path where water flows repeatedly from the wetland or open
water to another water, and that at times contains water originating in the wetland or open water
as opposed to just directly from precipitation. Factors such as climate, local topography, and
stream density can impact the likelihood and frequency surface hydrologic connections. Science
Report at B-18. For instance, the relatively wet and topographically low Red River Valley zone
of the prairie pothole region should display greater surface-water connectivity of prairie potholes
than either the Draft Prairie or Missouri Coteau zones, while the higher stream density in the Red
River Valley or Drift Prairie should increase the chance that prairie pothole spillage connects to
the larger river network. Id. (citing Leibowitz and Vining 2003).
Shallow subsurface connections and deeper regional groundwater flows can also highly
connect prairie potholes to other prairie potholes and to the river network. A high water table and
soil pocketed with root pores or fractures from wet-dry cycles promote water movement between
wetlands via shallow groundwater aquifers. Id. In these cases, water moves most often from
topographically high, recharge wetlands to low, discharge wetlands, although a single wetland
can shift from recharge to discharge in years where the water table is high. Id. (citing Carroll et
al. 2005; van der Kamp and Hayashi 2009). Other wetlands shift multiple times from recharge to
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discharge conditions during a single year, which can either facilitate or prevent ground-water
connections to nearby wetlands. Id. at B-18 to B-19 (citing Rosenberry and Winter 1997). Prairie
potholes can also connect to the river network via groundwater if both are located within the
zone of shallow local aquifer flows. Id. at B-19. For instance, prairie pothole wetlands and lakes
can serve as waters sources to the downstream James River via shallow subsurface connections.
Id. (citing Swanson etal. 1988).
Prairie pothole density across the landscape varies from region to region as the result of
several factors, including patterns of glacial movement, topography, and climate. Id. at B-14 to
B-15 (citing van der Valk and Pederson 2003; Kahara et al. 2009). In some parts of the region,
prairie pothole density is very high. Though their density varies across the landscape, prairie
potholes often act as a complex. Id. at B-14. They have similar functions that can collectively
impact downstream waters.
Prairie potholes have been determined to be similarly situated based on the characteristics
of this resource type, including their density on the landscape, their interaction and formation as
a complex of wetlands and open waters, their connections to each other and the tributary
network, and their similar functions. In addition, their chemical, physical, and biological
connections to downstream waters and the strength of their effects on the chemical, physical, or
biological integrity of a traditional navigable water, interstate water, or the territorial seas
support this determination that prairie potholes are similarly situated by rule,
ii. Carolina and Delmarva Bays
Carolina and Delmarva bays are elliptical, ponded, depressional wetlands that occur
along the Atlantic coastal plain from northern Florida to New Jersey. Id. at 5-2, B-l (citing
Prouty 1952; Williams 1996; Hunsinger and Lannoo 2005; Tiner 2003c. They typically are
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oriented in a northwest-southwest direction, with a sand rim to the southeast. Sharitz 2003.
Though Carolina and Delmarva bays are from the same category of wetland and perform similar
functions, they are located in different parts of the Atlantic coastal plain and thus have unique
names. Carolina bays are most abundant in North Carolina and South Carolina, while Carolina
bays found in the Delmarva Peninsula are commonly referred to as Delmarva bays or Delmarva
potholes. Science Report at 5-2, B-l (citing Sharitz and Gibbons 1982; Sharitz 2003); Tiner
2003c. Delmarva bays frequently have the same elliptical shape and orientation as other Carolina
bays, but some lack the shape or rim. Id. at B-l (citing Stolt and Rabenhorst 1987a; Sharitz
2003).
Most bays receive water through precipitation, lose water through evapotranspiration, and
lack natural surface outlets. Id. at B-l, B-3 (citing Sharitz 2003). Though the name "bay"
suggests the presence of water, these shallow basin wetlands in fact range from permanently
inundated to frequently dry. Id. at B-l (citing (Sharitz 2003). The water levels of bays fluctuate
in response to seasonal rainfall, snowmelt, and temperature, and bays are often wetter in winiter
and early spring and tend to dry down in the summer. Id. at B-3. Both mineral-based and peat-
based bays have shown connections to shallow groundwater, via both nearly continuous shallow
groundwater recharge and periodic shallow groundwater discharge. Id. at 5-2, B-l. Some
recharge water eventually discharges into local streams and contributes to their base flows. Tiner
2003c. Due to their abundance on the landscape, they can provide temporary storage of surface
water during storm events and periods of heavy rainfall, helping to reduce local flooding. Sharitz
2003; Tiner 2003c. Bays typically are in proximity to each other or to streams, providing for
hydrologic connections to each other and to downstream waters in large rain events via overland
flow or shallow subsurface connections. Science Report at B-3. Some Delmarva bays are
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intersected by natural stream channels and thus have surface water connections to the
Chesapeake Bay. Id. at B-3 (citing Lang et al. 2012). Some Carolina bays are directly connected
to flatwood wetlands that drain into coastal streams and rivers, while others have small creeks
flowing into them or form the headwaters of perennial streams. Sharitz 2003; Tiner 2003c. In
addition, human channeling and ditching of the bays are widespread and create surface
connections to other waters, including the tributary system and estuaries. These ditches
commonly connect the surface water of bays to other bays that are lower on the landscape, and
ultimately, to streams. Some bays, particularly those along the coast, can be flooded by high
tides and thus are connected to coastal waters. Science Report at B-3 (citing Bliley and Pettry
1979; Sharitz 2003).
Where they occur, hydrologic connections are likely to result in effects on downstream
waters. Id. at 5-2. The hydrology in bays (periodic wetting and drying) allows for denitrification,
which can reduce the amount of nitrate in both groundwater and downstream surface waters. Id.
A study of a Carolina bay used long-term for agriculture suggests that the wetlands can be
effective at retaining excess nutrients and heavy metals. Ewing et al. 2012. Seasonal connections
of Delmarva bays to stream networks export accumulated organic matter from wetlands into
tributaries of Chesapeake Bay. Id. Because bays are frequently connected chemically to
downstream waters through ditches, they can be sources of sediment and nutrients to
downstream waters. Where they are not connected via confined surface connections, bays can act
as sediment and nutrient sinks.
Carolina and Delmarva bays provide valuable habitat and food web support for numerous
plant and animal species that can move between bays and other water bodies. Id. at 5-2. Fish are
reported in bays that are known to dry out, indirectly demonstrating surficial connections through
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either overland flow during periods of high water or via ditches. Id. at B-l; Sharitz 2003.
Amphibians and reptiles use bays extensively for breeding and for rearing young. Science Report
at B-l. In bays that lack fish, the absence of predators allows abundant amphibian populations to
thrive. Id. at 5-2. These animals can then disperse many feet on the landscape and can colonize,
or serve as a food source to, downstream waters. Id. at B-l. Similarly, bays foster abundant
aquatic insects that have the potential to become part of the downstream food chain. Id. at B-l.
As mentioned above, humans have ditched and channelized a high percentage of bays for
agricultural or logging purposes, creating new surface connections to downstream waters and
allowing transfer of nutrients, sediment, and other pollutants such as methylmercury. Id. ab B-l
(citing Bennett and Nelson 1991; Sharitz 2003).
Carolina and Delmarva bays are densely concentrated in many areas and can act as a
wetlands complex. See, e.g., Science Report at 5-2. Bays have similar functions to other bays and
cumulatively these functions can impact downstream waters.
The agencies conclude that Carolina and Delmarva bays are similarly situated based on
their close proximity to each other and the tributary network, their hydrologic connections to
each other and the tributary network, their density on the landscape, and their similar functions,
iii. Pocosins
The word pocosin comes from the Algonquin Native American word for "swamp on a
hill," and these evergreen shrub and tree-dominated wetlands are found from Virginia to northern
Florida, but mainly in North Carolina. Richardson 2003; Tiner 2003c. Bay, bayland, bayhead,
xeric shrub bog, and evergreen shrub bog are common synonyms for pocosin, but generally only
bays in the lower Coastal Plain have vegetation similar to pocosins. Id. In addition, pocosin and
Carolina bays differ in size and geologic origin. Id. Their hydrogeomorphic classification would
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be "wet flats" on organic soils. Id.; Rheinhardt el al. 2002. They range in size from less than an
acre to several thousand acres.
Pocosins are generally located on interfluves, or the area of higher land between ancient
rivers and coastal sounds on the South Atlantic Coastal Plain. Richardson 2003; Tiner 2003c;
Osterkamp 2008. They are found on flat, clay-based soils, in shallow basins and have water poor
in nutrients (oligotrophic). Richardson 2003. The pocosins landscape undergoes a succession that
is hypothesized to be from marsh to swamp forest to bay forest to tall pocosin to short pocosins.
Id. Tall pocosins typically occur over shallower peat deposits, have higher soil nutrient content,
and have taller and more trees and shrubs than short pocosins.
Pocosins receive most or all of their water from precipitation. Richardson 1983; Tiner
2003c. These wetlands have long hydroperiods, temporary surface water, periodic burning, and
soils of sandy humus, muck, or peat. Richardson 2003. Usually, there is no standing water
present in these peat-accumulating wetlands, but a shallow water table leaves the soil saturated
for much of the year. Tiner 2003 c. High evapotranspiration during the summer can lower the
water table and gives pocosins extensive capacity to store stormwater. Richardson 1983.
Pocosins temporarily hold water and then slowly release it to downstream waters. Tiner 2003c.
The slow movement of water through the dense organic matter in pocosins removes excess
nutrients deposited by rainwater. The same organic matter also acidifies the water. This pocosin-
purified water is slowly released to downstream waters and estuaries, where it helps to maintain
the proper salinity, nutrients, and acidity. Richardson 2003. Given their proximity to estuaries,
the ability to retain floodwaters is particularly important because it gives estuaries time to absorb
and process the freshwater runoff without rapid and drastic fluxes in water quality. Tiner 2003 c.
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Because pocosins are the topographic high areas on the regional landscape, they serve as
the source of water for downstream waters. Rheinhardt et al. 2002; Richardson 2003. They often
are hydrologically connected to the stream network via confined surface flow, sheetflow, or
shallow subsurface flows. Richardson 2003. For example, some pocosins are located at the
headwaters, while other pocosins occur in swales and in seasonally saturated interfluves.
Rheinhardt et al. 2002; Tiner 2003c. Pocosins often have seasonal connections to drainageways
leading to estuaries or are adjoining other wetlands draining into perennial streams or estuaries.
Tiner 2003c. Other pocosins have been ditched and are directly connected to streams. Id.
Pocosins are the main sources of fresh water on the coastal landscape where the cover a large
expanse. Richardson 2003. The amount and timing of the runoff from these wetlands is critical to
downstream flows and water quality, particularly in the estuaries. M; Richardson 1983;
Richardson 2012.
The largest area of the wetland complex is the short pocosin, which has the deepest peat.
Richardson 2003; Richardson 2012. Runoff drains slowly from short pocosins to shallow
dystrophic lakes (brown- or tea-colored lakes that are colored as the result of high concentrations
of humic substances and organic acids suspended in the water) or the surrounding tall pocosins.
Id. Water flows laterally into either shallow lakes or into small streams, and then flows into the
bay forest communities at the downstream end of the pocosin systesm. Id. The components of
the pocosin complex are also likely connected by shallow subsurface connections. Id.
Pocosins provide habitat for many species that utilize both the wetlands and nearby
streams for different life cycle needs. This includes the pine barrens tree frog and the American
alligator. Richardson 2003.
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Ditching and conversion of pocosins can have major detrimental effects on the quality of
coastal waters. When pocosins are artificially drained via ditches, the value of their buffering
capacity is lost, and the ditched pocosins may contribute possibly enriched water downstream via
their direct hydrologic connection. Id. Many pocosins have been converted for forestry and
agricultural purposes. Conversion of pocosins to agriculture has lowered salinity in nearby
estuaries, particularly during periods of heavy precipitation due to introduction of more fresh
water from cropland drainage, increased peak flow rates (up to three to four times that of
undrained pocosins, increased turbidity, and increased concentration of nutrients such as
phosphate, nitrate, and ammonia in streams and nearby estuaries. Id. The draining of pocosins
and decreased the associated salinity in estuaries may be having a negative effect on brown
shrimp in North Carolina. Id.
The agencies conclude that pocosins are similarly situated based on their close proximity
to each other and the tributary network, their hydrologic connections to each other and the
tributary network, their density on the landscape, and their similar functions. Based on these
connections and the strength of their effects, in combination with other pocosins in the
watershed, on the chemical, physical, or biological integrity of an (a)(1) through (a)(3) water, the
agencies will determine on a case-specific basis if such waters have a significant nexus and are
jurisdictional.
iv. Western Vernal Pools in California
Vernal pools are shallow, seasonal wetlands that accumulate water during colder, wetter
months and gradually dry up during warmer, drier months. Science Report at B-60; Tiner 2003c.
Western vernal pools are seasonal wetlands in western North America from Washington and
Oregon to northern Baja California, Mexico associated with topographic depressions, soils with
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poor drainage, mild, wet winters and hot, dry summers. Science Report at B-60 (citing Bauder
and McMillan 1998); Tiner 2003c. For purposes of this rule, the agencies have determined that
western vernal pools in California are "similarly situated."
Western vernal pools in California have formed in mound and swale topography and
located primarily in parts of the California steppe (Central Valley) and coastal terraces and level
terraces of California's coastal mountains. Zedler 1987; Tiner 2003c. Western vernal pools in
California occur on impermeable or slowly permeable soils or bedrock that limit percolation and
thus produce surficial aquifers that perch above regional ground-water aquifers. Id. at B-61
(citing Smith and Verrill 1998). Pool-forming soil layers in this region include clay-rich soils,
silica-cemented hardpans (duripans), volcanic mudflows, or bedrock. Id. (citing Weitkamp el al.
1996; Hobson and Dahlgren 1998; Smith and Verrill 1998; Rains et al. 2006). Clay-rich and
hardpan vernal pool complexes are particularly common in California's Central Valley. Id. at B-
63 (citing Smith and Verrill 1998).
Western vernal pools are cyclical wetlands with very different seasonal vegetative cover
and water levels. Tiner 2003c. Western vernal complexes saturate and begin to pool during
winter rains, reach maximum depth by early spring, and lose all standing water by late spring.
Science Report at B-62 (citing Zedler 1987). Zedler (1987) described western vernal pools as
generally having four distinct phases or stages in the annual hydrologic cycle that highlight their
cyclic seasonality:
• Wetting or newly flooded phase: The first fall rains stimulate the germination of
dormant seeds and the growth of perennial plants. Typically seedlings and resprouts
densely develop before the pools hold water for any prolonged period. Rainwater,
snow, runoff, or snowmelt infiltrate upper layers of permeable soil and, when topsoils
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are saturated, collect in pool basins formed by impervious rock, clay, or till layers
(aquitards or aquicludes). Science Report at B-61; Zedler 1987; Rains el al. 2008.
• Aquatic phase: Soils are saturated when the cumulative rainfall is sufficient and pools
hold standing water, in many locations filled to capacity. In some western vernal
pools, surface and subsurface flows from upland pools through swales feed
downgradient pools, connecting pools at a site and extending the aquatic phase of the
pool complex. Science Report at B-61 to B-52 (citing Weitkamp et al. 1996; Hanes
and Stromberg 1998); Zedler 1987. Pools are colonized by dispersing aquatic insects
and breeding amphibians.
• Drying phase: Evapotranspiration rates increase and pool water recedes, although
soils remain saturated. Plant growth continues after the standing water disappears due
to high soil moisture. Aquatic plants flower and seed. Aquatic animals disperse or
become dormant. Terrestrial plant communities persist. Science Report at B-52;
Zedler 1987.
• Drought phase: Pools and soils dry out, and many plants dry out or die. Some plants
able to access deeper moisture may continue to grow and flower even into early fall.
Drying cracks materialize. Even if summer rains occur, generally no new ponding or
plant growth occurs. Science Report at B-52; Zedler 1987.
As suggested above, the wetlands are primarily precipitation fed. Science Report at B-62.
Though they typically lack permanent inflows from or outflows to streams and other water
bodies, western vernal pools, they can be connected temporarily to such waters via surface or
shallow subsurface flow (flow through) or groundwater exchange (recharge). Hydrologic
connectivity is typically limited to flow through in western vernal pools formed by perching
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layers; groundwater exchange can occur in western vernal pool systems without perching layers
(Brooks 2005).
Because their hydrology and ecology are so tightly coupled with the local and regional
geological processes that formed them, western vernal pools typically occur within "vernal pool
landscapes," or complexes of pools in which swales connect pools to each other and to seasonal
streams. Id. at B-61 (citing Weitkamp et al. 1996; Smith and Verrill 1998; Rains et al. 2006;
Rains et al. 2008). Weitkamp et al. 1996; Brooks 2005; Rains et al. 2008). The winter rains
characteristic of the region's Mediterranean climate fill the depressional wetlands and swales,
and they may remain flooded for weeks or months in certain years. Tiner 2003. Temporary
storage of heavy rainfall and snowmelt in individually small vernal pool systems (pools plus
soils) can attenuate flooding that would otherwise reach downstream waters. Science Report 5-9.
Some common findings about the hydrologic connectivity of western vernal pools include
evidence for temporary or permanent outlets, frequent filling and spilling of higher pools into
lower elevation pools, swales, and stream channels, and conditions supporting subsurface flows
through pools without perched aquifers to nearby streams. Id. at 5-9, B-63 (citing Hanes and
Stromberg 1998; Pyke 2004; Bauder 2005; Rains et al. 2006; Rains et al. 2008). For example,
California vernal pools spill water a great number of days during the years via channels,
providing water downstream. Id. at 4-21 (citing Rains et al. 2006; Rains et al. 2008). Western
vernal pool basins, swales, and seasonal streams were shown to be part of a single surface-water
and shallow subsurface system connected to the river network when precipitation exceeds
storage capacity of the wetland system. Id. at B-63 (citing Rains et al. 2006; Rains etal. 2008).
In extremely wet years, individual vernal pools coalesce to form large inundated complexes that
can drain to the tributary system. Zedler 1987; Tiner 2003. Other studies showed that direct
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precipitation could fill pools to or beyond capacity in most years, creating conditions under
which water flows from pools into swales and stream channels. Science Report at B-63, B-66
(citing Hanes and Stromberg 1998; Pyke 2004). Collectively, these findings suggest that filling
and overflow of western vernal pools are not rare phenomena. Id.
The timing of seasonal inundation and lack of permanent surface connections make
vernal pools important biological refuges, which has consequences on the biological health of
downstream waters. Id. at 5-9. Western vernal pools support large breeding populations of
amphibians, aquatic invertebrates, and aquatic or semi-aquatic plants, including many that are
rare or endemic. Id. at B-62. Non-glaciated vernal pools in western states are reservoirs of
biodiversity and can be connected genetically to other locations and aquatic habitats through
wind- and animal-mediated dispersal. The annual four phases play an important role in
structuring biological communities in western vernal pools. The wetting phase prevents
establishment of upland plant species in vernal pool basins, while the drought phase limits
colonization by aquatic and semiaquatic plant and animal species that occur in permanent
wetlands, ponds, or streams. Id. (citing Keeley and Zedler 1998; Bauder 2000). Despite their
cyclical nature, western vernal pool habitats are species rich and highly productive, in part
because they provide relatively predator-free breeding habitat for aquatic invertebrates and
amphibians. Id. (citing Keeley and Zedler 1998; Calhoun etal. 2003). Many resident species are
locally adapted to the timing and duration of inundation, soil properties, and spatial distribution
of western vernal pools in a specific geographic subregion. Id. Other species that are widespread
across regions and aquatic habitat types (including streams or lakes) use inundated pools
periodically for refuge, reproduction, or feeding. Id. (citing King et al. 1996; Williams 1996;
Colburn 2004). Western vernal pools can play an important role in the food web and other
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lifecycle needs of species that utilize both the vernal pools and waters in the tributary network. In
addition, aquatic and semi-aquatic animals and other organisms, like the Pacific tree frog and the
western spadefoot toad, can move between western vernal pool complexes and streams. Insects
and zooplankton can be flushed from vernal pools into streams and other water bodies during
periods of overflow, carried by animal vectors (including humans), or dispersed by wind. Plant
seeds and invertebrate eggs and larvae can also disperse into streams and other water bodies via
birds, and this dispersal can be critical to maintaining the species diversity of both western vernal
pools and streams and other waters in the tributary network. Zedler 1987. The effects of
dispersal on community structure and diversity—including metapopulation effects of wetland-to-
wetland connectivity—have been well documented, especially for amphibians. Science Report at
4-31 (citing, e.g., Wellborn et al. 1996; Snodgrass et al. 2000; Julian et al. 2013).
As mentioned previously, western vernal pools provide an example of cumulative effects
over time. Id. at 1-11. They typically occur as complexes in which the hydrology and ecology are
tightly coupled with the local and regional geological processes that formed them. When
seasonal precipitation exceeds wetland storage capacity and wetlands overflow into the river
network and generate stream discharge, the vernal pool basins, swales, and seasonal streams
function as a single surface-water and shallow ground-water system connected to the river
network.
The agencies conclude that western vernal pools are similarly situated based on their
close proximity to each other and the tributary network, their interaction and arrangement as a
complex of wetlands, their hydrologic connections to each other and the tributary network, their
density on the landscape, and their similar functions.
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v. Texas Coastal Prairie Wetlands
Along the Gulf of Mexico from western Louisiana to south Texas, freshwater wetlands
occur as a mosaic of depressions, ridges, swales, intermound flats, and mima mounds. Comer et
al. 2008 (Appendix HI); Forbes et al. 2012. These coastal prairie wetlands were formed
thousands of years ago by ancient rivers and bayous and once occupied almost a third of the
landscape around Galveston Bay, Texas. The mosaic of Texas coastal prairie wetlands typically
are located on a flat landscape with microtopography that gently slopes toward the Gulf of
Mexico. Enwright et al. 2011. The term Texas coastal prairie wetlands is not used uniformly in
the scientific literature but encompasses Texas prairie pothole (freshwater depressional wetlands)
and marsh wetlands that are described in some studies that occur on the Lissie and Beaumont
Geological Formations, and the Ingleside Sand. Enwright et al. 2011; Moulton and Jacob 2000.
The extensive coverage and distribution of this wetland type through the Gulf coastal plain
demonstrates that they form an integral component of the regional landscape. Enwright et al.
2011.
Texas coastal prairie wetlands are locally abundant and in close proximity to other
coastal prairie wetlands and function together cumulatively. See, e.g., Enwright et al. 2011.
Collectively as a complex, Texas coastal prairie wetlands can be geographically and
hydrologically connected to each other via swales and connected to downstream waters,
contributing flow to those downstream waters. Wilcox et al. 2011. Even where not connected by
swales, during some rainfall events, individual wetlands can fill and spill into down-gradient
wetlands. Sipocz 2002; Sipocz 2005; Enwright et al. 2011; Wilcox et al. 2011. One study found
that in a study area near Galveston Bay, over one-third of the precipitation that fell within the
study area was captured within Texas coastal prairie wetland drainage basins and thus have the
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potential for the wetlands to provide floodwater storage and water quality benefits to
downstream waters. Enwright et al. 2011. In other study, during a study period of almost four
years, nearly 20% of the precipitation that fell on a Texas coastal prairie wetland complex flowed
as surface runoff through an intermittent stream to the nearby Armand Bayou, a traditional
navigable water. Science Report at 4-22 (citing Wilcox et al. 2011). Intermittent drawdown due
to evapotranspiration is a natural feature of this wetland type that increases their flood storage
capacity. Id. Another study found that Texas coastal prairie wetlands intercept runoff before it
enters large water bodies and thus have the opportunity to filter pollutants before they reach
downstream (a)(1) through (a)(3) waters, such as Galveston Bay. Sipocz 2002; Sipocz 2005.
Cumulatively, these wetlands can control nutrient release levels and rates to downstream waters,
as they capture, store, transform and pulse releases of nutrients to those waters. Enwright et al.
2011; Forbes et al. 2012.
The agencies conclude that Texas coastal prairie wetlands are similarly situated based on
their close proximity to each other and the tributary network, their hydrologic connections to
each other and the tributary network, their interaction and formation as a complex of wetlands,
their density on the landscape, and their similar functions.
B. Waters within the 100-Year Floodplain of a Traditional Navigable Water,
Interstate Water, or the Territorial Sea and Waters within 4,000 Feet of the
High Tide Line or Ordinary High Water Mark
Paragraph (a)(8) in the rule specifies that a water that does not otherwise meet the
definition of adjacency is evaluated on a case-specific basis for significant nexus where it is
located within the 100-year floodplain of a traditional navigable water, interstate water, or the
territorial seas or located within 4,000 feet of the high tide line or the ordinary high water mark
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of a traditional navigable water, interstate water, the territorial seas, impoundment, or covered
tributary. Although these waters are not considered similarly situated by rule, waters under this
paragraph can be determined on a case-specific basis to be similarly situated. If a portion of the
water is located within the 100-year floodplain of a traditional navigable water, interstate water,
or the territorial seas or 4,000 feet of the high tide-line or ordinary high water mark of a
traditional navigable water, interstate water, the territorial seas, impoundment, or covered
tributary, the entire water will be considered to be within the boundaries for (a)(8) and will
undergo a case-specific significant nexus determination.
i. Waters within the 100-Year Floodplain of a Traditional Navigable Water,
Interstate Water, or the Territorial Sea
The agencies have determined that on a case-specific basis, waters located within the
100-year floodplain of a traditional navigable water, interstate water, or the territorial sea can
have significant nexus with that (a)(1) through (a)(3) water, when considered individually or in
combination with similarly situated waters. As discussed in sections III and VIII of this
document, the scientific literature, including the Science Report, supports that wetlands and open
waters in floodplains are physically, chemically, and biologically connected to downstream
traditional navigable waters, interstate waters, or the territorial seas and significantly affect the
integrity of such waters. As noted above, the Science Report concludes that wetlands and open
waters located in "floodplains are physically, chemically and biologically integrated with rivers
via functions that improve downstream water quality, including the temporary storage and
deposition of channel-forming sediment and woody debris, temporary storage of local ground
water that supports baseflow in rivers, and transformation and transport of stored organic
matter." Science Report at ES-2 to ES-3. Such waters act as the most effective buffer to protect
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downstream waters from nonpoint source pollution (such as nitrogen and phosphorus), provide
habitat for breeding fish and aquatic insects that also live in streams, and retain floodwaters,
sediment, nutrients, and contaminants that could otherwise negatively impact the condition or
function of downstream waters. As discussed above and in the preamble, in defining waters as
adjacent, and therefore categorically jurisdictional, the agencies established a 1,500 foot
boundary for waters located within the 100-year floodplain of an (a)(1) through (a)(5) water in
order to protect vitally important waters while at the same time providing a practical and
implementable rule. In light of the science on the functions provided by floodplain waters and
wetlands, open waters and wetlands within the 100-year floodplain of traditional navigable
waters, interstate waters, or the territorial seas are likely to provide those functions for traditional
navigable waters, interstate waters, or the territorial seas. Moreover, because of the unique status
under the CWA of traditional navigable waters, interstate waters, and the territorial seas, the 100-
year floodplain boundary for these waters provides a means of identifying on a case-specific
basis those waters that significantly affect traditional navigable waters, interstate waters or the
territorial seas. However, because the 100-year floodplain of a traditional navigable water can, in
some case be quite large, the agencies concluded it was reasonable to subject waters and
wetlands in the 100-year floodplain that are beyond 1,500 feet of the ordinary high water mark,
and therefore do not meet the definition of "neighboring," to a case-specific significant nexus
analysis rather than concluding that such waters are categorically jurisdictional.
This inclusion of a case-specific analysis for such floodplain waters is supported by the
SAB. The SAB concluded that "distance should not be the sole indicator used to evaluate the
connection of 'other waters' to jurisdictional waters." SAB 2014b at 3. In allowing the case-
specific evaluation of waters within the 100-year floodplain of (a)(1) through (a)(3) waters that
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do not meet the definition of adjacency, the agencies are allowing for the functional relationship
of those floodplain waters to be considered regardless of distance. The SAB also supported the
Science Report's conclusion that "the scientific literature strongly supports the conclusions that
streams and 'bidirectional' floodplain wetlands are physically, chemically, and/or biologically
connected to downstream navigable waters; however, these connections should be considered in
terms of a connectivity gradient." SAB 2014a at 1. In addition, the SAB noted, "the literature
review does substantiate the conclusion that floodplains and waters and wetlands in floodplain
settings support the physical, chemical, and biological integrity of downstream waters." Id. at 3.
By allowing for waters, including wetlands, that are outside the distance limitations set under
neighboring but still within the 100-year floodplain of an (a)(1) through (a)(3) water, the
agencies are recognizing the science supporting the important effects that floodplain waters have
on the chemical, physical, and biological integrity of traditional navigable waters, interstate
waters, and the territorial seas.
The agencies do not anticipate that there will be numerous circumstances in which this
provision will be utilized because relatively few traditional navigable waters will have
floodplains that span more than 4,000 feet from the high tide line or the ordinary high water
mark (the other threshold in (a)(8) for waters regardless of floodplain). Further, the agencies
recognize that extensive areas of the nation's floodplains have been affected by levees and dikes
which reduce the scope of flooding. In these circumstances, the scope of the 100-year floodplain
is also reduced and is reflected in FEMA mapping. In circumstances where there is little or no
alteration of the floodplain of an (a)(1) through (a)(3) water and it remains relatively broad, the
agencies will explicitly consider distance between the water being evaluated and the TNW,
interstate water, or territorial seas when making a case-specific significant nexus determination.
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Based on the science concerning the important functions provided by floodplain waters and
wetlands, the agencies established this provision to ensure that truly important waters may still
be protected on a case-specific basis. By using the 100-year floodplain and limiting the
provision to traditional navigable waters, interstate waters, or the territorial seas, the agencies are
reasonably balancing the protection of waters that may have a significant nexus with the goal of
providing additional certainty.
ii. Waters within 4,000 Foot of the High Tide Line or Ordinary High Water
Mark of a Traditional Navigable Water, Interstate Water, the Territorial
Sea, Impoundment, or Covered Tributary
For the other category of case-specific waters under (a)(8), waters within 4,000 feet of the
OHWM of a traditional navigable water, interstate water, the territorial sea, impoundment, or
covered tributary, the science available today does not establish that waters as a group should be
determined to be jurisdictional by rule under the CWA, but the agencies' experience and
expertise indicate that there are individual waters out to 4,000 feet where the science
demonstrates that they, either alone or in combination with similarly situated waters, often have a
significant effect on downstream waters. As stated above, the agencies establish a provision in
the rule for case-specific significant nexus determinations because the agencies concluded that
some waters located beyond the distance limitations established for "adjacent waters" can have
significant chemical, physical, and biological connections to and effects on traditional navigable
waters, interstate waters, or the territorial seas. The agencies reasonably identified the 4,000 foot
boundary for these case-specific significant nexus determinations by balancing consideration of
the science and the agencies' technical expertise and experience in making significant nexus
determinations with the goal of providing clarity to the public while protecting the environment
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and public health. The agencies' experience has shown that the vast majority of waters where a
significant nexus has been found, and which are therefore important to protect to achieve the
goals of the Act, are located within the 4,000 foot boundary. The agencies' balancing of these
considerations is consistent with the statute and the Supreme Court opinions. The agencies
decided that it is important to promulgate a rule that not only protects the most vital of our
Nation's waters, but one that is practical and provides sufficient boundaries so that the public
reasonably understands where CW A jurisdiction ends.
In circumstances where waters within 4,000 feet of the high tide line or ordinary high
water mark are subject to a case-specific significant nexus analysis and such waters may be
evaluated as "similarly situated," it must be first demonstrated that these waters perform similar
functions and are located sufficiently close to each other to function together in affecting the
integrity of the downstream waters. The significant nexus analysis must then be conducted
based on consideration of the functions provided by those waters in combination in the point of
entry watershed. A "similarly situated" analysis is conducted where it is determined that there is
a likelihood that there are waters that function as a system to affect downstream water integrity.
To provide greater clarity and transparency in determining what functions will be considered in
determining what constitutes a significant nexus, the final rule lists specific functions that the
agencies will consider.
The agencies recognize that in establishing the 4,000-foot "bright line" threshold for
these case-specific significant nexus determinations in the rule, the agencies are carefully
applying the available science. The science itself does not establish bright lines for establishing
where waters do not have a significant nexus to downstream (a)(1) through (a)(3) waters. For
instance, as noted above, the SAB concluded that distance should not be a sole factor used to
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evaluate the connection of waters to jurisdictional waters. SAB 2014b at 3. In setting a limit of
4,000 feet for case-specific determinations under (a)(8), the agencies have made a decision based
on public input for clarity regarding other waters, as well as based on expertise and experience
with implementing the significant nexus standard in light of the SWANCC and Rapanos
decisions.
The agencies establish a provision in the rule for case-specific significant nexus
determinations because the agencies concluded that waters located within 4,000 feet of the
ordinary high water mark of a traditional navigable water, an interstate water, the territorial seas,
an impoundment, or a covered tributary can have significant chemical, physical, and biological
connections to and effects on traditional navigable waters, interstate waters, or the territorial
seas, either alone or in combination with similarly situated waters. The agencies establish a
distance limit on case-specific significant nexus determinations because the Supreme Court has
been clear that CW A jurisdiction is not without limit. Based on the agencies' extensive
experience, and applying the best available science, the agencies conclude that the 4,000 foot
distance limit reasonably identifies the areas in which waters have been determined to have a
significant nexus (outside of those that are within the 100-year floodplain of an (a)(1) through
(a)(3) water) and appropriately establishes the limits of CW A jurisdiction under this case-
specific provision. This approach also supports the goal of providing greater clarity to the public.
The agencies decided that it is important to promulgate a rule that not only protects the most vital
of our Nation's waters, but one that is practical and provides sufficient limits so that the public
reasonably understands where CW A jurisdiction ends.
The agencies emphasize that they fully support efforts by states and tribes to protect
under their own laws any additional waters, including locally important waters that may not be
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within the federal interests of the CWA as the agencies have interpreted its scope in this rule.
Indeed, the promulgation of this 4,000-foot limit for purposes of a case-specific analysis of
significant nexus does not foreclose states from acting consistent with their state authorities to
establish protection for waters that fall outside of the protection of the CWA. In promulgating
the 4,000-foot limit, the agencies have balanced protection and clarity, scientific uncertainties
and regulatory experience, and established a line that is, in their judgment, reasonable and
consistent with the statute and its goals and objectives.
As noted above in section II.D., since the Rapanos decision, the agencies have developed
extensive experience making significant nexus determinations, and that experience and expertise
has informed the judgment of the agencies in establishing the 4,000 foot boundary. The agencies
have made determinations in every state in the country, for a wide range of waters in a wide
range of conditions. The vast majority of the waters that the Corps has determined have a
significant nexus are located within 4,000 feet of a jurisdictional tributary, traditional navigable
or interstate water, or the territorial seas. Based on this experience, and informed by the science
that acknowledges the connectivity of waters lies on a continuum, the agencies have concluded
that the 4,000-foot limitation will protect the types of waters that have in practice been
determined to have a significant nexus on a case-specific basis. Based on this experience, the
agencies have concluded that the 4,000 foot limitation will enable the agencies to make case-
specific significant nexus determinations for waters located within a zone that represents a key
section of the watershed in terms of influence on downstream waters. While the science does not
provide for a precise line in the landscape, it is important to note that this provision is not
purporting to draw a categorical line between waters that meet the definition of "water of the
United States" and those that do not. Rather, the provision reflects the agencies'
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acknowledgment that there are waters for which an absolute, precise categorization is not
possible based on the available science and that it is therefore reasonable to establish an area
within which case-specific analysis will occur. Faced with this lack of precision in the science,
the agencies proposed a rule that set no limitations on where case-specific significant nexus
analyses could occur and sought comment from the public on this approach and a combination of
other approaches that could provide more certainty. In response to the many concerns raised by
the uncertainty of an unconstrained approach to case-specific significant nexus analysis, the
agencies have responded by establishing this 4,000 foot limit. Therefore, the agencies conclude
that the 4,000 foot boundary in the rule, along with the 100-year floodplain boundary discussed
above, will sufficiently capture for analysis those waters that are important to protect to achieve
the goals of the Clean Water Act.
The agencies decision to establish a provision that authorizes a case-specific significant
nexus analysis for waters within 4,000 feet is based on a number of factors. These waters may
be located within the floodplain of a traditional navigable water, interstate water, the territorial
seas, impoundment, or covered tributary. This Technical Support Document and the Science
Report have demonstrated the importance of floodplain waters on the chemical, physical, and
biological integrity of downstream traditional navigable waters, interstate waters, or the
territorial seas. For purposes of clarity and to provide regulatory certainty, the agencies decided
to use distance boundaries within the 100-year floodplain to define adjacency for floodplain
waters. Under the rule, the only floodplain waters that are specifically identified as being
jurisdictional as adjacent are those located in whole or in part within the 100-year floodplain and
not more than 1,500 feet of the ordinary high water mark of jurisdictional waters. In addition, as
described above, waters within the 100-year floodplain of an (a)(1) through (a)(3) water that do
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not meet the definition of adjacent are to be considered under a case-specific analysis under the
other provision of (a)(8). However, there may be some waters located in the floodplains of
jurisdictional impoundments or jurisdictional tributaries that fall outside of the 1,500-foot
limitation for adjacency. Due to the many functions that floodplain wetlands and open waters
provide to downstream water integrity, and based on the scientific literature, agency expertise
and experience, and applicable case law, the rule calls for waters to be considered on a case-
specific basis, either alone or in combination with other waters, where they are located within
4,000 feet of the high tide line or the ordinary high water mark of a water jurisdictional under
(a)(1) through (a)(5), in part because such waters may be located within the floodplain.
Similarly, due to the many functions that waters located within 4,000 feet of the high tide
line of a traditional navigable water or the territorial seas provide and their often close
connections to the surrounding navigable in fact waters, science supports the agencies'
determination that such waters are rightfully evaluated on a case-specific basis for significant
nexus to a traditional navigable water or the territorial seas. Waters within 4,000 feet of the
ordinary high water mark of a traditional navigable water, interstate water, the territorial seas,
impoundment, or covered tributary may fall within the riparian areas of such waters. These
waters may not have a 100-year floodplain associated with them, as described in section
VIII. A.vi. above, so the other provision of (a)(8) may or may not apply to such waters. As
discussed in the preamble, in response to comments regarding the uncertainty of the term
"riparian area," the agencies removed the term from the definition of neighboring. However, the
agencies continue to recognize that science is clear that wetlands and open waters in riparian
areas individually and cumulatively can have a significant effect on the chemical, physical, and
biological integrity of downstream waters. See, e.g., ES-2 to ES-3. Thus, the rule allows for a
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case-specific determination of significant nexus for waters located within 4,000 feet of the high
tide line or the ordinary high water mark of a traditional navigable water, interstate water, the
territorial seas, impoundment, or covered tributary.
The agencies have always recognized that adjacency is bounded by proximity, and the
rule adds additional clarity to adjacency by bounding what can be considered neighboring. The
science is clear that a water's proximity to downstream waters influences its impact on those
waters. The Science Report states, "[sjpatial proximity is one important determinant of the
magnitude, frequency and duration of connections between wetlands and streams that will
ultimately influence the fluxes of water, materials and biota between wetlands and downstream
waters." Science Report at ES-11. Generally, waters that are closer to a jurisdictional water are
more likely to be connected to that water than waters that are farther away. A case-specific
analysis for waters located within 4,000 feet of the high tide line or the ordinary high water mark
of a traditional navigable water, interstate water, the territorial seas, impoundment, or covered
tributary allows such waters to be considered jurisdictional only where they meet the significant
nexus requirements. Even where not within a 100-year floodplain, waters within 4,000 feet of the
high tide line or the ordinary high water mark of a traditional navigable water, interstate water,
the territorial seas, impoundment, or covered tributary can have significant chemical, physical,
and biological connections with traditional navigable waters, interstate waters, or the territorial
seas.
As noted previously, in response to comments concerned that there were no bounds in the
proposed rule on how far a surface hydrologic connection could be for purposes of adjacency,
the agencies did not include surface hydrologic connections as its own factor for determining
adjacency in the final rule. Such connections, however, are relevant in a case-specific significant
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nexus determination under (a)(8). For example, waters located within 4,000 feet of the high tide
line or the ordinary high water mark of a traditional navigable water, interstate water, the
territorial seas, impoundment, or covered tributary that contribute confined surface flow to a
downstream water can have important hydrologic connections to and effects on that downstream
water such as the attenuation and cycling of nutrients that would otherwise effect downstream
water quality.
The agencies' decision to establish the case-specific provision at (a)(8), including the
distance limitation, was also informed by the knowledge that waters located within 4,000 feet of
the high tide line or the ordinary high water mark of a traditional navigable water, interstate
water, the territorial seas, impoundment, or covered tributary can have a confined surface or
shallow subsurface connection to such a water. In order to provide the clarity and certainty that
many commenters requested regarding adjacent waters, the rule does not define "neighboring" to
include all waters with confined surface or shallow subsurface connections.
However, the agencies recognize that the science demonstrates that waters with a
confined surface or shallow subsurface connection to jurisdictional waters can have important
effects on downstream waters. For purposes of a case-specific significant nexus analysis under
the rule, a shallow subsurface hydrologic connection is lateral water flow over a restricting layer
in the top soil horizons, or a shallow water table which fluctuates within the soil profile,
sometimes rising to or near the ground surface. In addition, water can move within confined
man-made subsurface conveyance systems such as drain tiles and storm sewers, and in karst
typography. O'Driscoll and Parizek 2003. Confined subsurface systems can move water, and
potential contaminants, directly to surface waters rapidly without the opportunity for nutrient or
sediment reduction along the pathway. Science Report at 3-28; 4-24 (citing Royer et al. 2004).
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The proposed rule did not set a distance threshold for case-specific waters to be evaluated
for a significant nexus. Some commenters argued that there should be a limitation on areas
subject to case-specific analysis while others contended that the agencies lack discretion to set
regulatory limits that would exclude from jurisdiction any water meeting the significant nexus
test. The agencies disagree that the agencies lack the authority to establish reasonable
boundaries to determine what areas are subject to case-specific significant nexus analysis.
Nothing in the CWA or case law mandates that the agencies require every water feature in the
nation be subject to analysis for significant nexus. The Supreme Court has made clear that the
agencies have the authority and responsibility to determine the limits of CWA jurisdiction, and
establishing boundaries based on agency judgment, expertise and experience in administering the
statute is at the core of the agencies authority and discretion.
Wetlands and open waters, including those outside the riparian zone and floodplain, can
be connected downstream through unidirectional flow from the wetland or open water to a
nearby tributary. Such connections can occur through a surface or a shallow subsurface
hydrologic connection. Science Report at 2-7, 4-1 to 4-2, 4-22. Outside of the riparian zone and
floodplain, surface hydrologic connections between adjacent waters and jurisdictional waters can
occur via confined flows (e.g. a swale, gully, ditch, or other discrete feature). In some cases,
these connections will be a result of "fill and spill" hydrology. A directional flowpath is a path
where water flows repeatedly from the wetland or open water to the nearby jurisdictional water
that at times contains water originating in the wetland or open water as opposed to just directly
from precipitation. Id. at B-12 (citing Winter and Rosenberry 1998; Leibowitz and Vining
2003). Water connected through such flows originate from the adjacent wetland or open water,
travel to the downstream jurisdictional water, and are connected to those downstream waters by
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swales or other directional flowpaths on the surface. Surface connections can also be unconfined
(non-channelized flow), such as overland flow. Id. at 2-14.
A confined surface hydrologic connection, which may be perennial, intermittent or
ephemeral, supports periodic flows between the adjacent water and the jurisdictional water. For
example, wetland seeps are likely to have perennial connections to streams that provide
important sources of baseflow, particularly during summer. Id. at 4-21 (citing Morley el al.
2011). Other wetlands are connected to streams via intermittent or ephemeral conveyances and
can contribute flow to downstream waters via their surface hydrologic connection. Id. (citing
Rains etal. 2006; Rains el al. 2008; McDonough el al. 2015). The surface hydrologic connection
of the neighboring water to the jurisdictional water and the close proximity of the waters enhance
the neighboring waters substantial effects the waters have on downstream (a)(1) through (a)(3)
waters. Wetlands and open waters that are connected to (a)(1) through (a)(5) waters through a
confined surface hydrologic connection will have an impact on downstream (a)(1) through (a)(3)
waters, regardless of whether the outflow is permanent, intermittent, or ephemeral. See, e.g., id.
at 4-40.
Wetlands and open waters with confined surface connections can affect the physical
integrity of waters to which they connect. Such waters can provide an important source of
baseflow to the streams to which they are adjacent, helping to sustain the water levels in the
nearby streams. Id. at 4-21 to 4-22 (citing Morley et al. 2011; Rains et al. 2006; Rains et al.
2008; Wilcox et al. 2011; McDonough et al. 2015); Lee et al. 2010. Waters with a confined
surface connection to downstream jurisdictional waters can affect streamflow by altering
baseflow or stormflow through several mechanisms, including surface storage and groundwater
recharge. Science Report at 4-24. Wetlands and open waters with confined surface connections
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can affect water quality of jurisdictional waters through source and sink functions, often
mediated by transformation of chemical constituents. The surface hydrologic connections to
nearby jurisdictional waters provide pathways for materials transformed in the wetlands and
open waters (such as methylmercury or degraded organic matter) to reach and affect the nearby
waters and the downstream (a)(1) through (a)(3). Id. at 4-26 to 4-27. Wetlands and open waters
with confined surface connections also can affect the biological integrity of waters to which they
connect. Movement of organisms between these adjacent waters and the nearby jurisdictional
water is governed by many of the same factors that affect movement of organisms between
riparian/floodplain waters and the river network. Id. at 4-30. Because such waters are at least
periodically hydrologically connected to the nearby jurisdictional tributary network on the
surface, dispersal of organisms can occur actively through the surface connection or via wind
dispersal, hitchhiking, walking, crawling, or flying. See, e.g., id. at 4-30 to 4-31.
Shallow subsurface connections move quickly through the soil and impact surface water
directly within hours or days rather than the years it may take long pathways to reach surface
waters. The Science Report refers to local groundwater flow or shallow groundwater flow, which
is a type of shallow subsurface connections. Id. at 2-11. Such shallow subsurface connections
flow from the highest elevations of the water tables to nearby lowlands or surface waters. Id.
(citing Winter and LaBaugh 2003). These are dynamic hydrologic connections that have the
greatest interchange with surface waters. Id. The presence of a confining layer near the surface
also leads to shallow subsurface flows through the soil. Id. at 2-34.
Tools to assess shallow subsurface flow include reviewing the soils information from the
Natural Resources Conservation Service Soil Survey, which is available for nearly every county
in the United States. See Natural Resources Conservation Service. The soil survey will have
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information on hydric soils, the hydrologic class of the soil, and the occurrence of a high or
seasonal water table. Other indicators of a shallow subsurface connection include slope soil
permeability, saturated hydraulic conductivity, the presence of an aquitard (confining layer), and
permafrost. See, e.g., Science Report at 2-34. Direct visual observations on the ground, such as
noting a change in vegetation or evidence of hillslope springs or seeps can be indicators, as can
direct measurements of the water table. Location with a floodplain or riparian area is also an
indicator of shallow subsurface connection, as wetlands and open waters located within a
floodplain or riparian area of a water often have shallow subsurface flows to that water that
contribute to connectivity and function. Science Report at ES-9.
When assessing whether a water within 4,000 foot boundary performs any of the
functions identified in the rule's definition of significant nexus, the significant nexus
determination can consider whether shallow subsurface connections contribute to the type and
strength of functions provided by a water or similarly situated waters. The SAB as noted the
importance of shallow subsurface connections and stated, "[t]he available science... shows that
groundwater connections, particularly vial shallow flow paths in unconfined aquifers, can be
critical in support the hydrology and biogeochemical functions of wetlands and other waters."
SAB 2014b. However, neither shallow subsurface connections nor any type of groundwater,
shallow or deep, are themselves "waters of the United States."
Waters within 4,000 feet of the ordinary high water mark or the high tide line would
include non-floodplain wetlands and open waters. Non-floodplain waters perform many of the
same functions as floodplain waters, but as discussed above, their connectivity to downstream
waters varies. Generalizations about their effects on downstream waters are difficult to ascertain
from the available scientific literature. Therefore, the agencies have determined it is appropriate
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to consider such waters within 4,000 feet of the ordinary high water mark or high tide line on a
case-specific basis. A significant nexus evaluation would evaluate waters within the 4,000 feet of
the ordinary high water mark or high tide line of an (a)(1) through (a)(5) water, either alone or in
combination with any similarly situated water, and would consider the functions performed by
the water or waters. The functions of non-floodplain waters are discussed below.
Non-floodplain waters can affect streamflow by altering baseflow or storm flow through
several mechanisms, including surface storage and groundwater recharge. Science Report at 4-
24. Studies at the larger scale have shown that wetlands, by storing water, reduce peak
streamflows and, thus, downstream flooding. Id. at 4-25 (citing Jacques and Lorenz 1988; Vining
2002; McEachern el ai 2006; Gleason etal. 2007). In some cases, however, where wetlands that
serve as stream origins are already saturated prior to rainfall, they can convey stormwater
quickly downstream and thus actually increase flood peaks. Id. (citing Bullock and Acreman
2003). This is because the wetland soil, if completely saturated, cannot store any additional
water, making the wetland unable to store floodwater. Id.
Non-floodplain waters wetlands contain diverse microbial populations that perform
various chemical transformations, acting as source of compounds and potentially influencing the
water quality downstream. Id. at 4-27 (citing Reddy and DeLaune 2008). Sulfate-reducing
bacteria found in some non-floodplain wetlands produce methylated mercury, which is then
transported downstream by surface flows. Id. (citing Linqvist etal. 1991; Mierle and Ingram
1991; Driscoll et al. 1995; Branfireun et al. 1999). Wetlands, including those that are non-
floodplain, are the principle sources of dissolved organic carbon (DOC) in forests to downstream
waters. Id. at 4-28 (citing Mulholland and Kuenzler 1979; Urban et al. 1989; Eckhardt and
Moore 1990; Koprivnjak and Moore 1992; Kortelainen 1993; Clair et al. 1994; Hope et al. 1994;
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Dillon and Molot 1997; Gergel et al. 1999). Export of DOC to downstream waters from non-
floodplain wetlands can support primary productivity, affect pH and buffering capacity, and
regulate exposure to UV-B radiation. Id. (citing Eshelman and Hemond 1985; Hedin et al. 1995;
Schindler and Curtis 1997; Nuff and Asner 2001).
Non-floodplain wetlands also act as sinks and transformers for pollutants, including
excess nutrients, through such processes as denitrification, ammonia volatilization, microbial and
plant biomass assimilation, sedimentation, sorption and precipitation, biological uptake, and
long-term storage of plant detritus. Id. at 4-29 (citing Ewel and Odum 1984; Nixon and Lee
1986; Johnston 1991; Detenbeck et al. 1993; Reddy et al. 1999; Mitsch and Gosselink 2007;
Reddy and DeLaune 2008; Kadlec and Wallace 2009). Specifically, non-floodplian waters can
reduce phosphorus, nitrate, and ammonium by large percentages. Id. (citing Dierberg and
Brezonik 1984; Dunne et al. 2006; Jordan et al. 2007; Cheesman et al. 2010). Wetland microbial
processes reduce other pollutants, such as pesticides, hydrocarbons, heavy metals, and
chlorinated solvents. Id. at 4-30 (citing Brooks et al. 1977; Kao et al. 2002; Boon 2006).
Non-floodplain waters can have biological connections downstream that have the
potential to impact the integrity of (a)(1) through (a)(3) waters. Emergent and aquatic vegetation
found in non-floodplain wetlands disperse downstream by water, wind, and hitchhiking on
migratory animals. Id. at 4-31 (citing Soons and Heil 2002; Soons 2006; Nilsson et al. 2010).
Similarly, fish move between the river network and non-floodplain wetlands during times of
surface water connections. Id. at 4-34 (citing Snodgrass et al. 1996; Zimmer et al. 2001; Baber et
al. 2002; Hanson et al. 2005; Herwig et al. 2010). Mammals that can disperse overland can also
contribute to connectivity. Id. (citing Shanks and Arthur 1952; Roscher 1967; Serfass et al. 1999;
Clark 2000; Spinola et al. 2008). Insects also hitchhike on birds and mammals from non-
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floodplain wetlands to the stream network, which can then serve as a food source for
downstream waters. Id. at 4-31 (citing Figuerola and Green 2002; Figuerola et al. 2005). Insects
that are flight-capable also use both the stream and non-floodplain wetlands, moving from the
stream to the wetland to find suitable habitat for overwintering, refuge from adverse conditions,
hunting, foraging, or breeding. Id. at 4-34 (citing Williams 1996; Bohonak and Jenkins 2003).
Amphibians and reptiles, including frogs, toads, and newts, also move between streams or rivers
and non-floodplain wetlands to satisfy part of their life history requirements, feed on aquatic
insects, and avoid predators. Id. at 4-34 to 4-35 (citing Lamoureux and Madison 1999; Babbitt et
al. 2003; Adams et al. 2005; Green 2005; Hunsinger and Lannoo 2005; Petranka and Holbrook
2006; Attum et al. 2007; Subalusky et al. 2009a; Subalusky et al. 2009).
The proposed rule did not set a distance threshold for case-specific waters to be evaluated
for a significant nexus. Some commenters argued that there should be a limitation on areas
subject to case-specific analysis while others contended that the agencies lack discretion to set
regulatory limits that would exclude from jurisdiction any water meeting the significant nexus
test. The agencies disagree that the agencies lack the authority to establish reasonable
boundaries to determine what areas are subject to case-specific significant nexus analysis.
Nothing in the CWA or case law mandates that the agencies require every water feature in the
nation be subject to analysis for significant nexus. The Supreme Court has made clear that the
agencies have the authority and responsibility to determine the limits of CWA jurisdiction, and
establishing boundaries based on agency judgment, expertise, and experience in administering
the statute is at the core of the agencies' authority and discretion.
After weighing the scientific information about these waters' connectivity and
importance to protecting downstream waters, the agencies' considerable experience making
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jurisdictional determinations, the objective of enhancing regulatory clarity and consistent with
the statute and the caselaw, the agencies decided to set a boundary of 4,000 feet for case-specific
significant nexus analysis for waters that do not otherwise meet the requirements of (a)(1)
through (a)(7). Tying this provision for case-specific significant nexus analysis to distance
informed by the science and the agencies' experience and expertise, as spatial proximity is a key
contributor to connectivity among waters. Id. at ES-11. Distance is by no means the sole factor,
and aquatic functions will play a prominent role in determining whether specific waters covered
under this aspect of paragraph (a)(8) have a significant nexus. In light of the role spatial
proximity plays in connectivity and the objective of enhancing regulatory clarity, predictability,
and consistency, the agencies conclude that establishing a boundary for this aspect of waters
subject to case-specific significant nexus analysis based on distance is reasonable.
While, for purposes of this national rule, distance is a reasonable and appropriate measure
for identifying where this case-specific significant nexus analysis will be conducted, the science
does not point to any particular bright line delineating waters that have a significant nexus from
those that do not. The Science Report concluded that connectivity of streams and wetlands to
downstream waters occurs along a gradient. Id. at ES-4. The evidence unequivocally
demonstrates that the stream channels and floodplain wetlands or open waters that together form
river networks are clearly connected to downstream waters in ways that profoundly influence
downstream water integrity. Id. at ES-5. The connectivity and effects of non-floodplain wetlands
and open waters are more variable and thus more difficult to address solely from evidence
available in peer-reviewed studies. Id.. Because of this variability, with respect to waters that
are not covered by (a)(1) through (a)(7) of the rule, the science does not provide a precise point
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along the continuum at which waters provide only speculative or insubstantial functions to
downstream waters.
Like connectivity itself, there is also a continuum of outcomes associated with picking a
distance threshold. A smaller threshold increases the likelihood that waters that could have a
significant nexus will not be analyzed and therefore not subject to the Act; a larger threshold
reduces that possibility, but also means that agency and the public's resources are expended
conducting significant nexus analyses on waters that have a lower likelihood of meriting the
Act's protection.
For these reasons, the agencies decided to allow case-specific determinations of
significant nexus for waters located within 4,000 feet of the high tide line or the ordinary high
water mark of a traditional navigable water, an interstate water, the territorial seas, an
impoundment, or a covered tributary.
C. Rationale for Conclusions
The scientific literature regarding the two categories of waters for which case-specific
determinations will be made documents their functions, including the chemical, physical, and
biological impact they can have downstream. Available literature indicates that case-specific
waters have important hydrologic, water quality, and habitat functions that have the ability to
affect downstream waters if and when a connection exists between the water and downstream
waters. Science Report at 6-5. Connectivity of case-specific waters to downstream waters will
vary within a watershed and over time, which is why a case-specific significant nexus
determination is necessary under (a)(7) and (a)(8). See, e.g., id. The types of chemical, physical,
and biological connections between case-specific waters and downstream waters are described
below for illustrative purposes. As described in the rule's preamble, when the agencies are
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conducting a case-specific determination for significant nexus under (a)(7) or (a)(8), they
examine the connections between the water (including any similarly situated waters in the
region) and downstream waters and determine if those connections significantly affect the
chemical, physical, or biological integrity of the downstream (a)(1) through (a)(3) water, using
any available site-information and field observations where available, relevant scientific studies
or data, or other relevant jurisdictional determinations that have been made on similar resources
in the region.
The hydrologic connectivity of case-specific waters to downstream waters occurs on a
gradient and can include waters in the floodplain, waters that have groundwater or occasional
surface water connections (through overland flow) to the tributary network, and waters that have
no hydrologic connection to the tributary network. Id. at 4-2. The connectivity of case-specific
waters to downstream waters will vary within a watershed as a function of local factors (e.g.
position, topography, and soil characteristics). Id. at 4-41. Connectivity also varies over time, as
the tributary network and water table expand and contract in response to local climate. Id. Lack
of connection does not necessarily translate to lack of impact; even when lacking connectivity,
waters can still impact chemical, physical, and biological conditions downstream. Id. at 4-42 to
4-43.
The physical effect that case-specific waters have downstream is less obvious than the
physical connections of waters that are adjacent or waters that are tributary, due to the physical
distance of (a)(7) and (a)(8) waters from the stream network. Despite this physical distance, they
are frequently connected in some degree through either surface water or groundwater systems;
over time, impacts in one part of the hydrologic system will be felt in other parts. Winter and
LaBaugh 2003. For example, case-specific waters that overspill into downstream water bodies
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during times of abundant precipitation are connected over the long term. Id. Wetlands that lack
surface connectivity in a particular season or year can, nonetheless, be highly connected in wetter
seasons or years. Science Report at 4-24. Floodplain waters beyond the 1,500 foot boundary are
connected to the nearby traditional navigable water, interstate water, or the territorial seas via
both surface and subsurface hydrologic flowpaths and can reduce flood peaks by storing
floodwaters. Id. at ES-9. Many case-specific waters interact with groundwater, either by
receiving groundwater discharge (flow of groundwater to the case-specific water), contributing
to groundwater recharge (flow of water from the case-specific water to groundwater), or both. Id.
at 4-22 (citing Lide etal. 1995; Devito etal. 1996; Matheney and Gerla 1996; Rosenberry and
Winter 1997; Pyzoha et al. 2008). Factors that determine whether a water recharges groundwater
or is a site of groundwater discharge include topography, geology, soil features, and seasonal
position of the water table relative to the water. Id. at 4-23 (citing Phillips and Shedlock 1993;
Shedlock et al. 1993; Lide et al. 1995; Sun et al. 1995; Rosenberry and Winter 1997; Pyzoha et
al. 2008; McLaughlin et al. 2014). Similarly, the magnitude and transit time of groundwater flow
from an "other water" to downstream waters depend on several factors, including the intervening
distance and the properties of the rock or unconsolidated sediments between the water bodies
(i.e., the hydraulic conductivity of the material). Id. at 4-23. Surface and groundwater
hydrological connections are those generating the capacity for case-specific waters to affect
downstream waters, as water from the case-specific water may contribute to baseflow or
stormflow through groundwater recharge. Id. at 4-24. Contributions to baseflow are important
for maintaining conditions that support aquatic life in downstream waters. As discussed further
below, even in cases where waters lack a connection to downstream waters, they can influence
downstream water through water storage and mitigation of peak flows. Id. at 4-2, 4-42, 4-43.
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The chemical effects that case-specific waters have on downstream waters are linked to
their hydrologic connection downstream, though a surface connection is not needed for a water
to influence the chemical integrity of the downstream water. Because the majority of case-
specific waters are hydrologically connected to downstream waters via surface or groundwater
connections, most case-specific waters can affect water quality downstream (although these
connections do not meet the definition of adjacency). Whigham and Jordan 2003. Case-specific
waters can act as sinks and transformers for nitrogen and phosphorus, metals, pesticides, and
other contaminants that could otherwise negatively impact downstream waters. Science Report at
4-29 to 4-30 (citing Brooks etal. 1977; Hemond 1980; Davis et al. 1981; Hemond 1983; Ewel
and Odum 1984; Moraghan 1993; Craft and Chiang 2002; Kao et al. 2002; Boon 2006; Dunne et
al. 2006; Cohen et al. 2007; Jordan et al. 2007; Whitmire and Hamilton 2008; Bhadha et al.
2011; Marton et al. 2014). Also see, e.g., Isenhart 1992. The body of published scientific
literature and the Science Report indicate that sink removal of nutrients and other pollutants by
case-specific waters is significant and geographically widespread. Science Report at 4-30.
Floodplain waters beyond the 1,500 foot boundary provide water quality benefits for the nearby
traditional navigable waters, interstate waters, and territorial seas, including retention of
sediment and organic matter and retention, cycling, and transformation of pollutants like
nutrients. Id. at ES-9. Water quality characteristics of case-specific waters are highly variable,
depending primarily on the sources of water, characteristics of the substrate, and land uses within
the watershed. Whigham and Jordan 2003. These variables inform whether a case-specific water
has a significant nexus to an (a)(1) through (a)(3) water. For instance, some prairie potholes may
improve water quality and may efficiently retain nutrients that might otherwise cause water
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quality problems downstream; in such systems it may be their lack of a direct hydrologic
connection that enables the prairie potholes to more effectively retain nutrients. Id.
Case-specific waters can be biologically connected to each other and to downstream
waters through the movement of seeds, macroinvertebrates, amphibians, reptiles, birds, and
mammals. Science Report at 4-30 to 4-35; Leibowitz 2003. The movement of organisms
between case-specific waters and downstream waters is governed by many of the same factors
that affect movement of organisms between adjacent wetlands and downstream waters (See
section VIII). Science Report at 4-30. For example, like other floodplain waters, floodplain
waters beyond the 1,500 foot boundary are hydrologically connected to the traditional navigable
water, interstate water, or the territorial seas by lateral expansion and contraction of the (a)(1)
through (a)(3) water in its floodplain, resulting in an exchange of matter and organisms,
including fish populations that are adapted to use floodplain wetlands and open waters for
feeding and spawning during high water. Id. at ES-9 to ES-10. Generally, case-specific waters
are further away from stream channels than adjacent waters, making hydrologic connectivity less
frequent, and increasing the number and variety of landscape barriers over which organisms must
disperse. Id. Plants, though non-mobile, have evolved many adaptations to achieve dispersal over
a variety of distances, including water-borne dispersal during periodic hydrologic connections,
"hitchhiking" on or inside highly mobile animals, and more typically via wind dispersal of seeds
and/or pollen. Id. at 4-31 (citing Galatowitsch and van der Valk 1996; Murkin and Caldwell
2000; Amezaga 2002; Figuerola and Green 2002; Soons and Heil 2002; Soons 2006; Haukos et
al. 2006 and references therein; Nilsson et al. 2010). Mammals that disperse overland can also
contribute to connectivity and can act as transport vectors for hitchhikers such as algae. Id. at 4-
34 (citing Shanks and Arthur 1952; Roscher 1967; Serfass et al. 1999; Clark 2000; Spinola et al.
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2008). Invertebrates also utilize birds and mamals to hitchhike, and these hitchhikers can be an
important factor structuring invertebrate metapopulations in case-specific waters and in aquatic
habitats separated by hundreds of kilometers. Id. at 4-31 through 4-32 (Figuerola and Green
2002; Figuerola et al. 2005; Allen 2007; Frisch 2007). Numerous flight-capable insects use both
"other waters" and downstream waters; these insects move outside the tributary network to find
suitable habitat for overwintering, refuge from adverse conditions, hunting, foraging, or
breeding, and then can return back to the tributary network for other lifecycle needs. Id. at 4-34
(citing Williams 1996; Bohonak and Jenkins 2003). Amphibians and reptiles also move between
case-specific waters and downstream waters to satisfy part of their life history requirements. Id.
at 4-34. Alligators in the Southeast, for instance, can move from tributaries to shallow, seasonal
limesink wetlands for nesting, and also use these wetlands as nurseries for juveniles; sub-adults
then shift back to the tributary network through overland movements. Id. (citing Subalusky et al.
2009a; Subalusky et al. 2009b). Similarly, amphibians and small reptile species, such as frogs,
toads, and newts, commonly use both tributaries and "other waters," during one or more stages
of their life cycle, and can at times disperse over long distances. Id. at 4-34 to 4-35 (citing
Knutson et al. 1999; Lamoureux and Madison 1999; Babbitt et al. 2003; Adams et al. 2005;
Green 2005; Hunsinger and Lannoo 2005; Petranka and Holbrook 2006; Attum et al. 2007).
Even when a surface or groundwater hydrologic connection between a water and a
downstream water is visibly absent, many waters still have the ability to substantially influence
the integrity of downstream waters. However, such circumstances would be uncommon, but can
occur, for instance, where a wetland recharges a deep groundwater aquifer that does not feed
surface waters, or it is located in a basin where evapotranspiration is the dominant form of water
loss. Id. at 4-21 to 4-24. Aquatic systems that may seem disconnected hydrologically are often
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connected but at irregular timeframes or through subsurface flow, and perform important
functions that can be vital to the chemical, physical, or biological integrity of downstream
waters. Some wetlands that may be hydrologically disconnected most of the time but connected
to the stream network during rare high-flow events or during wetter seasons or years. Although
the Science Report focuses primarily on the benefits that connectivity can have on downstream
systems, isolation also can have important positive effects on the condition and function of
downstream waters. Id. at 2-28. For instance, the lack of a hydrologic connection allows for
water storage in such waters, attenuating peak streamflows, and, thus, downstream flooding, and
also reducing nutrient and soil pollution in downstream waters. Id. at 2-28 to 2-29, 4-2, 4-38.
Prairie potholes a great distance from any tributary, for example, are thought to store significant
amounts of runoff. Id. at 4-38 (citing Novitzki 1979; Hubbard and Linder 1986; Vining 2002;
Bullock and Acreman 2003; McEachern et al. 2006; Gleason et al. 2007). Filling wetlands
reduces water storage capacity in the landscape and causes runoff from rainstorms to overwhelm
the remaining available water conveyance system. See, e.g., Johnston et al. 1990; Moscrip and
Montgomery 1997; Detenbeck et al. 1999; Detenbeck et al. 2005. Wetlands, even when lacking
a hydrologic connection downstream, improve downstream water quality by accumulating
nutrients, trapping sediments, and transforming a variety of substances. See, e.g., National
Research Council 1995.
The structure and function of a river are highly dependent on the constituent materials
that are stored in, or transported through the river. Most of the materials found in rivers originate
outside of them. Thus, the fundamental way that "other waters" are able to affect river structure
and function is by providing or altering the materials delivered to the river. Science Report at 1-
13. Since the alteration of material fluxes depends on the functions within these waters and the
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degree of connectivity, it is appropriate to consider both these factors for purposes of significant
nexus under this provision
Under the rule, on a case-specific basis, waters that have a significant nexus to an (a)(1)
through (a)(3) water are "waters of the United States" under (a)(7) or (a)(8) where the meet the
requirements set out in those paragraphs of the rule. The scientific literature and data in the
Science Report and elsewhere support that some waters (including some of those in the case
studies), along with other similarly situated waters in the region, do greatly affect the chemical,
physical, or biological integrity of (a)(1) through (a)(3) waters, and thus would be jurisdictional
under (a)(7) or (a)(8).
Though much of the literature cited in the Science Report relates to case-specific waters
that are wetlands, the Science Report indicates that non-wetland waters that are not (a)(1)
through (a)(6) waters also can have chemical, physical, or biological connections that
significantly impact downstream waters. For instance, non-adjacent ponds or lakes that are not
part of the tributary network can still be connected to downstream waters through chemical,
physical, and biological connections. Lake storage has been found to attenuate peak streamflows
in Minnesota. Id. at 4-25 (citing Jacques and Lorenz 1988; Lorenz et al. 2010). Similar to
wetlands, ponds are often used by invertebrate, reptile, and amphibian species that also utilized
downstream waters for various life history requirements, particularly because many ponds,
particularly temporary ponds, are free of predators, such as fish, that prey on larvae. The
American toad and Eastern newt are widespread habitat generalists that can move among
streams, wetlands, and ponds to take advantage of each aquatic habitat, feeding on aquatic
invertebrate prey, and avoiding predators. See, e.g., Id. at 4-35 (citing Babbitt etal. 2003; Green
2005; Hunsinger and Lannoo 2005; Petranka and Holbrook 2006). Additionally, stream networks
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that are not part of the tributary system (e.g., streams in closed basins without an (a)(1) through
(a)(3) water or losing streams and other streams that cease to flow before reaching downstream
(a)(1) through (a)(3) waters) may likewise have a significant impact on the chemical, physical, or
biological integrity of downstream waters. Non-tributary streams may be connected via
groundwater to downstream waters. Such streams may also provide habitat to insect, amphibian,
and reptile species that also use the tributary network.
In Rapanos, Justice Kennedy provides an approach for determining what constitutes a
"significant nexus" that can serve as a basis for defining "waters of the United States" through
regulation. Justice Kennedy concluded that "to constitute 'navigable waters' under the Act, a
water or wetland must possess a 'significant nexus' to waters that are or were navigable in fact or
that could reasonably be so made." Id. at 759 (citingSWANCC, 531 U.S. at 167, 172). Again, the
four justices who signed on to Justice Stevens' opinion would have upheld jurisdiction under the
agencies' existing regulations and stated that they would uphold jurisdiction under either the
plurality or Justice Kennedy's opinion. Justice Kennedy stated that wetlands should be
considered to possess the requisite nexus in the context of assessing whether wetlands are
jurisdictional: "if the wetlands, either alone or in combination with similarly situated [wetlands]
in the region, significantly affect the chemical, physical, and biological integrity of other covered
waters more readily understood as 'navigable.'" Id. at 780. In light of Rapanos and SWANCC,
the "significant nexus" standard for CWA jurisdiction that Justice Kennedy's opinion applied to
adjacent wetlands also can reasonably be applied to other waters such as ponds, lakes, and non-
adjacent wetlands that may have a significant nexus to a traditional navigable water, an interstate
water, or the territorial seas.
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The rule includes a definition of significant nexus that is consistent with Justice
Kennedy's significant nexus standard. In characterizing the significant nexus standard, Justice
Kennedy stated: "The required nexus must be assessed in terms of the statute's goals and
purposes. Congress enacted the [CWA] to 'restore and maintain the chemical, physical, and
biological integrity of the Nation's waters' . . . ." 547 U.S. at 779. It clear that Congress intended
the CWA to "restore and maintain" all three forms of "integrity," 33 U.S.C. § 1251(a), so if any
one form is compromised then that is contrary to the statute's stated objective. It would subvert
the intent if the CWA only protected waters upon a showing that they had effects on every
attribute of a traditional navigable water, interstate water, or territorial sea. Therefore, a showing
of a significant chemical, physical, or biological affect should satisfy the significant nexus
standard.
Justice Kennedy's opinion provides guidance pointing to many functions of waters that
might demonstrate a significant nexus, such as sediment trapping, nutrient recycling, pollutant
trapping and filtering, retention or attenuation of flood waters, and runoff storage. See 547 U.S.
at 775, 779-80. Furthermore, Justice Kennedy recognized that a hydrologic connection is not
necessary to establish a significant nexus, because in some cases the absence of a hydrologic
connection would show the significance of a water to the aquatic system, such as retention of
flood waters or pollutants that would otherwise flow downstream to the traditional navigable
water or interstate water. Id. at 775. Finally, Justice Kennedy was clear that the requisite nexus
must be more than "speculative or insubstantial" in order to be significant. Id. at 780. Justice
Kennedy's standard is consistent with basic scientific principles about how to restore and
maintain the integrity of aquatic ecosystems and the final rule is consistent with both.
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Recognizing that there is no optimal line for setting a distance threshold, in selecting both
the 100-year floodplain for traditional navigable waters, interstate waters, and the territorial seas
and the 4,000 foot boundaries the agencies looked principally to the extensive experience the
Corps has gained in making significant nexus determinations since the Rapanos decision. As
noted in section II.D. above, since the Rapanos decision, the agencies have developed extensive
experience making significant nexus determinations, and that experience and expertise informed
the judgment of the agencies in establishing both the 100-year floodplain boundary and the 4,000
foot boundary. The agencies have made determinations in every state in the country, for a wide
range of waters in a wide range of conditions. The vast majority of the waters that the Corps has
determined have a significant nexus are located within 4,000 feet of a jurisdictional tributary,
traditional navigable or interstate water, or the territorial seas. In addition, the science supports
that floodplain waters influence downstream water integrity. Therefore, the agencies conclude
that the 100-year floodplain and 4,000 foot boundaries in the rule will sufficiently capture for
analysis those waters that are important to protect to achieve the goals of the Clean Water Act.
The agencies acknowledge that, as with any meaningful boundary, some waters that
could be found jurisdictional lie beyond the 4,000 foot boundary and will not be analyzed for
significant nexus. The agencies minimize that risk by also establishing a provision in (a)(8) for
case-specific significant nexus analysis of waters located within the 100-year floodplain of a
traditional navigable water, interstate water, or the territorial seas. While in the agencies'
experience the vast majority of wetlands with a significant nexus are located within the 4,000
foot boundary, it is the agencies' experience that there are a few waters that have been
determined to be jurisdictional that are located beyond this boundary, typically due to a surface
or shallow subsurface hydrologic connections. Nonetheless, the agencies have weighed these
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considerations and concluded that the value of enhancing regulatory clarity, predictability and
consistency through a distance limit outweigh the likelihood that a distinct minority of waters
that might be shown to meet the significant nexus test will not be subject to analysis. In the
agencies' experience, requiring an evaluation of significant nexus for waters covered by
paragraph (a)(8) should capture the vast majority of waters having a significant nexus to the
downstream waters. The agencies therefore conclude that that adoption of the 4,000 foot
boundary is reasonable when coupled with the 100-year floodplain provision in paragraph (a)(8).
The rule's requirements for these waters, coupled with those for "adjacent waters," create
an integrated approach that tailors the regulatory regime based on the science and the agencies'
policy objectives. Determining by rule that covered adjacent waters have a significant nexus
follows the science, achieves regulatory clarity and predictability, and avoids expenditure of
agency and public resources on case-specific significant nexus analysis. Similarly, providing for
case-specific significant nexus analysis for waters that are not adjacent but within the 4,000 foot
distance limit, as well as those within the 100-year floodplain of a traditional navigable water,
interstate water, or the territorial seas, is consistent with science and agency experience, will
ensure protection of the important waters whose protection will advance the goals of the Clean
Water Act, and will greatly enhance regulatory clarity for agency staff, regulated parties, and the
public.
For these reasons, the agencies decided to allow case-specific determinations of
significant nexus for waters located within the 100-year floodplain of a traditional navigable
water, interstate water, or the territorial seas and for waters located within 4,000 feet of the high
tide line or the ordinary high water mark of a traditional navigable water, an interstate water, the
territorial seas, an impoundment, or a covered tributary. Under the rule, these waters are
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jurisdictional only where they individually or cumulatively (if it is determined that there are
other similarly situated waters) have a significant nexus to traditional navigable waters, interstate
waters, or the territorial seas.
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Appendix 1: References
Note that the below references are only those that were cited in this technical support document.
In addition, EPA's Office of Research and Development considered additional peer-reviewed
literature for the completion of the Science Report. The references for the Science Report are
available in that Report, which is available in the Docket for the rule and on EPA's website at
http://cfpub.epa. gov/ncea/cfm/recordisplav.cfm?deid=296414.
Abbe, T.E., and D.R. Montgomery. 1996. "Large Woody Debris Jams, Channel Hydraulics and
Habitat Formation in Large Rivers." Regulated Rivers: Research & Management 12:201-
221.
Abbott, M.D., etal. 2000. "180, D, and 3H Measurements Constrain Groundwater Recharge
Patterns in an Upland Fractured Bedrock Aquifer, Vermont, USA." Journal of Hydrology
228:101-112.
Adams, S.B., etal. 2001. "Geography of Invasion in Mountain Streams: Consequences of
Headwater Lake Fish Introductions." Ecosystems 4(4): 296-307.
Adams, S.B., etal. 2005. "Instream Movements by Boreal Toads (Bufo boreas boreas)."
Herpetological Review 3 6:27-3 3.
Albert, D.A. 2000. Borne of the Wind: An Introduction to the Ecology of Michigan Sand Dunes.
Michigan Natural Features Inventory, Lansing, MI.
Albert, D.A. 2003. Between Land and Lake: Michigan's Great Lakes Coastal Wetlands. Bulletin
E-2902. Michigan Natural Features Inventory, Michigan State University Extension, East
Lansing, MI.
Albert, D.A. 2007. Natural Community Abstract for Inter dunal Wetland. Michigan Natural
Features Inventory, Lansing, MI.
Alexander, R., et al. 2009. "Dynamic Modeling of Nitrogen Losses in River Networks Unravels
the Coupled Effects of Hydrological and Biogeochemical Processes." Biogeochemistry
93:91-116.
Alexander, R.B., etal. 2007. "The Role of Headwater Streams in Downstream Water Quality"
Journal of the American Water Resources Association 43:41-59.
Alexander, R.B., et al. 2008. "Differences in Phosphorus and Nitrogen Delivery to the Gulf of
Mexico from the Mississippi River Basin." Environmental Science & Technology 42:822-
830.
Alexander, R.G., etal. 2000. "Effect of Stream Channel Size on the Delivery of Nitrogen to the
Gulf of Mexico." Nature 403:758-761.
Alford, J.D., and M.R. Walker. 2013. "Managing the Flood Pulse for Optimal Fisheries
Production in the Atchafalaya River Basin, Louisiana (USA)." River Research and
Applications 29:279-296.
Allan, J.D. 1995. Ecology - Structure and Function of Running Waters. Chapman & Hall, New
York, NY.
Allan, J.D. 2004. "Landscapes and Riverscapes: The Influence of Land Use on Stream
Ecosystems." Annual Review of Ecology Evolution and Systematics 35: 257-284.
Allen, M.R. 2007. "Measuring and Modeling Dispersal of Adult Zooplankton." Oecologia
153:135-143.
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May 2015
American Society of Civil Engineers. 1996. Hydrology Handbook. 2nd Edition. ASCE Manuals
and Reports on Engineering Practice No. 28. Task Committee on Hydrology Handbook.
ASCE Publications, New York, NY.
Amezaga, J.M., et al. 2002. "Biotic Wetland Connectivity - Supporting a New Approach for
Wetland Policy." Acta Oecologica-International Journal of Ecology 23:213-222.
Amoros, C., and G. Bornette. 2002. "Connectivity and Biocomplexity in Waterbodies of
Riverine Floodplains." Freshwater Biology 47:761 -776.
Anderson, C.D. 2010. "Considering Spatial and Temporal Scale in Landscape-Genetic Studies of
Gene Flow." Molecular Ecology 19:3565-3575.
Anderson, N.H., and J.R. Sedell. 1979. "Detritus Processing by Macroinvertebrates in Stream
Ecosystems." Annual Review of Entomology 24:351-377.
Angeler, D.G., et al. 2010. "Phytoplankton Community Similarity in a Semiarid Floodplain
under Contrasting Hydrological Connectivity Regimes." Ecological Research 25:513-520.
Association of State Dam Safety Officials. "Introduction to Dams."
http://www.damsafetv.om/news/?p=e4cda 171 -b510-4a91 -aa30-067140346bb2.
Attum, O., el al. 2007. "Upland-wetland Linkages: Relationship of Upland and Wetland
Characteristics with Watersnake Abundance." Journal of Zoology 271:134-139.
Augspurger, C., el al. 2008. "Tracking Carbon Flow in a 2-Week-Old and 6-Week-Old Stream
Biofilm Food Web." Limnology and Oceanography 53:642-650.
Axtmann, E.V., and S.N. Luoma. 1991. "Large-scale Distribution of Metal Contamination in the
Fine-grained Sediments of the Clark Fork River, Montana, USA," Applied Geochemistry
6:75-88.
Babbitt, K.J., and G.W. Tanner. 2000. "Use of Temporary Wetlands by Anurans in a
Hydrologically Modified Landscape." Wetlands 20:313-322.
Babbitt, K.J., et al. 2003. "Patterns of Larval Amphibian Distribution along a Wetland
Hydroperiod Gradient." Canadian Journal of Zoology-Revue Canadienne De Zoologie
81:1539-1552.
Baber, M.J., et al. 2002. "Controls on Fish Distribution and Abundance in Temporary
Wetlands." Canadian Journal of Fisheries and Aquatic Sciences 59:1441-1450.
Baillie, M., el al. 2007. "Quantifying Water Sources to a Semiarid Riparian Ecosystem, San
Pedro River, Arizona." Journal of Geophysical Research 112:G03S02.
Baldwin, D.S., and A.M. Mitchell. 2000. "The Effects of Drying and Re-flooding on the
Sediment and Soil Nutrient Dynamics of Lowland River-Floodplain Systems: A Synthesis."
Regulated Rivers: Research & Management 16:457-467.
Baranyi, C., el al. 2002. "Zooplankton Biomass and Community Structure in a Danube River
Floodplain System: Effects of Hydrology." Freshwater Biology 47:473-482.
Baron, J.S., et al. 2002. "Meeting Ecological and Societal Needs for Freshwater." Ecological
Applications 12: 1247-1260.
Barrett, P. 1979. "Interaction of Bryophytes and Thermal Cracking in the Genesis of Hummock
and String-like Microtopography in High Arctic Tundra Meadows." Polarforschung 49
(l):70-79.
Battin, T.J., et al. 2009. "Biophysical Controls on Organic Carbon Fluxes in Fluvial Networks."
Nature Geoscience 1:95-100.
Bauder, E.T. 2000. "Inundation Effects on Small-Scale Plant Distributions in San Diego,
California Vernal Pools." Aquatic Ecology 34:43-61.
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May 2015
Bauder, E.T. 2005. "The Effects of an Unpredictable Precipitation Regime on Vernal Pool
Hydrology." Freshwater Biology 50:2129-2135.
Bauder, E.T., and S. McMillan. 1998. "Current Distribution and Historical Extent of Vernal
Pools in Southern California and Northern Baja California, Mexico—Proceedings from a
1996 Conference." Pages 56-70 in Ecology, Conservation, and Management. C.W. Witham,
et al., editors. California Native Plant Society, Sacramento, CA.
Baxter, C.V., and F.R. Hauer. 2000 "Geomorphology, Hyporheic Exchange and Selection of
Spawning Habitat by Bull Trout {Salvelinus confluentus)." Canadian Journal of Fisheries
and Aquatic Sciences 57: 1470-1481.
Beeson, C.E., and P.F. Doyle. 1995. "Comparison of Bank Erosion at Vegetated and Non-
Vegetated Channel Bends." Journal of the American Water Resources Association 31:983-
990.
Bencala, K.E. 1993. "A Perspective on Stream-Catchment Connections." Journal of the North
American Benthological Society 12:44-47.
Bencala, K.E. 2005. "Hyporheic Exchange Flows." Pages 1733-1740 in Encyclopedia of
Hydrological Sciences. M.G. Anderson, editor. John Wiley and Son, Ltd., New York, NY.
Bencala, K.E. 2011. "Stream-Groundwater Interactions." Pages 537-546 in Treatise on Water
Science. P. Wilderer, editor. Academic Press, Oxford, UK.
Bencala, K.E., et al. 2011. "Rethinking Hyporheic Flow and Transient Storage to Advance
Understanding of Stream-Catchment Connections." Water Resources Research 47:W00H03.
Benda, L. 2008. "Confluence Environments at the Scale of River Networks." Pages 271-300 in
River Confluences, Tributaries and the Fluvial Network. S.P. Rice, et al., editors. John Wiley
& Sons, Chichester, UK.
Benda, L., el al. 2004. "The Network Dynamics Hypothesis: How Channel Networks Structure
Riverine Habitats." Bioscience 54:413-427.
Benda, L.E., and T. W. Cundy. 1990. "Predicting Deposition of Debris Flows in Mountain
Channels." Canadian Geotechnical Journal 27:409-417.
Benda, L.E., et al. 2005. "Geomorphology of Steepland Headwaters: The Transition from
Hillslopes to Channels." Journal of the American Water Resources Association 41:83 5-851.
Benke, A.C., et al., 2000. "Flood Pulse Dynamics of an Unregulated River Floodplain in the
Southeastern US Coastal Plain." Ecology 81:2730-2741.
Bennett, S.H., and J.B. Nelson. 1991. Distribution and Status of Carolina Bays in South
Carolina. Nongame and Heritage Trust Publication No. 1. South Carolina Wildlife and
Marine Resources Department, Columbia, SC.
Bergey, E.A., et al. 2008. "Springs in Time: Fish Fauna and Habitat Changes in Springs over a
20-Year Interval " Aquatic Conservation: Marine and Freshwater Ecosystems 18:829-83 8.
Bernhardt, E.S., et al. 2002. "Whole-system Estimates of Nitrification and Nitrate Uptake in
Streams of the Hubbard Brook Experimental Forest." Ecosystems 5:419-430.
Bestgen, A.C., et al. 2000. "Flood Pulse Dynamics of an Unregulated River floodplain in the
Southeastern U.S. Coastal Plain." Ecology 81:2730-2741.
Beven, K., and P. Germann. 1982. "Macropores and Water Flow in Soils." Water Resources
Research 18:1311-1325.
Bhadha, J., etal. 2011. "Phosphorus Mass Balance and Internal Load in an Impacted Subtropical
Isolated Wetland." Water, Air, & Soil Pollution 218:619-632.
Bigelow, P.E., etal. 2007. "On Debris Flows, River Networks, and the Spatial Structure of
Channel Morphology." Forest Science 53:220-238.
Page 384 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Bilton, D.T., el al. 2001. "Dispersal in Freshwater Invertebrates" Annual Review of Ecology and
Systematics 32:159-81.
Black, P.E. 1997. "Watershed Functions." Journal of the American Water Resources Association
33.1:1-11.
Blanco-Canqui, H. and R. Lai. 2008. Principles of Soil Conservation and Management. Springer,
Netherlands.
Blann, K.L., et al. 2009. "Effects of Agricultural Drainage on Aquatic Ecosystems: A Review."
Critical Reviews in Environmental Science and Technology 39:909-1001.
Bliley, D.J., and D.E. Pettry. 1979. "Carolina Bays on the Eastern Shore of Virginia." Soil
Science Society of America Journal 43:558-564.
Blinn, D.W., and N.L. Poff 2005. "Colorado River Basin." Pages 483-526 in Rivers of North
America. A.C. Benke and C. E. Cushing, editors. Elseviar Academic Press, Amsterdam, The
Netherlands.
Blum, M.D., and H. H. Roberts. 2009. "Drowning of the Mississippi Delta Due to Insufficient
Sediment Supply and Global Sea-Level Rise." Nature Geoscience 2(7): 488-491.
Bodamer, B.L., and J.M. Bossenbroek. 2008. "Wetlands as Barriers: Effects of Vegetated
Waterways on Downstream Dispersal of Zebra Mussels." Freshwater Biology 53:2051-2060.
Bohonak, A. J., and D.G. Jenkins. 2003. "Ecological and Evolutionary Significance of Dispersal
by Freshwater Invertebrates." Ecology Letters 6:783-796.
Bohlke, J., el al. 2009. "Multi-Scale Measurements and Modeling of Denitrification in Streams
with Varying Flow and Nitrate Concentration in the Upper Mississippi River Basin, USA."
Biogeochemistry 93:117-141.
Boltz, J.M., and R.R.J. Stauffer. 1989. "Fish Assemblages of Pennsylvania Wetlands." Pages
158-170 in Wetland Ecology and Conservation: Emphasis in Pennsylvania. S.K. Majumdar,
editor. The Pennslyvania Academy of Sciences, Lafayette College, Easton, PA.
Boon, P.I. 2006. "Biogeochemistry and Bacterial Ecology of Hydrologically Dynamic
Wetlands." Pages 115-176 in Ecology of Freshwater and Estuarine Wetlands. D.P. Batzer
and R.R. Sharitz, ed. University of California Press, Berkeley, CA.
Booth, D.B., et al. 2002. "Forest Cover, Impervious-Surface Area, and the Mitigation of
Stormwater Impacts." Journal of the American Water Resources Association 38:835-845.
Borchert, J.R. 1950. "The Climate of the Central North American Grassland." Annals of the
Association of American Geographers 40:1-39.
Boto, K.G., and W.H. Patrick. 1979. "Role of Wetlands in the Removal of Suspended
Sediments." Pages 479-489 in Wetland Functions and Values: The State of Our
Understanding. Proceedings of National Symposium on Wetlands. P.E. Greeson, et al,
editors. American Water Resources Association, Minneapolis, MN.
Boughton, E.H., et al. 2010. "Land-use and Isolation Interact to Affect Wetland Plant
Assemblages." Ecography 33:461-470.
Boulton, A. J., et al. 1998. "The Functional Significance of the Hyporheric Zone in Streams and
Rivers." Annual Review of Ecology and Systematics 29:59-81.
Bracken, L.J., and J. Croke. 2007. "The Concept of Hydrological Connectivity and Its
Contribution to Understanding Runoff-Dominated Geomorphic Systems." Hydrological
Processes 21:1749-1763.
Bradford, M.J., etal. 2001. "Ecology of Juvenile Chinook Salmon in a Small Non-natal Stream
of the Yukon River Drainage and the Role of Ice Conditions on Their Distribution and
Survival." Canadian Journal of Zoology-Revue Canadienne De Zoologie 79:2043-2054.
Page 385 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Brady, N.C., and R.R. Weil. 2002. The Nature and Properties of Soils. 13th Edition. Prentice
Hall, Upper Saddle River, NJ.
Branfireun, B.A., et al. 1999. "In situ Sulphate Stimulation of Mercury Methylation in a Boreal
Peatland: Toward a Link Between Acid Rain and Methylmercury Contamination in Remote
Environments." GlobalBiogeochemical Cycles 13:743-750.
Brinson, M.M. 1993. A Hydrogeomorphic Classification for Wetlands. Washington, D.C.: U.S.
Army Corps of Engineers.
Brittain, J.E., and T.J. Eikeland. 1988. "Invertebrate Drift: A Review." Hydrobiologia 166:77-
93.
Brooks, P.D., and M.M. Lemon. 2007. "Spatial Variability in Dissolved Organic Matter and
Inorganic Nitrogen Concentrations in a Semiarid Stream, San Pedro River, Arizona." Journal
of Geophysical Research-Biogeosciences 112:G03S05.
Brooks, R.J., et al. 2012. "Willamette River Basin Surface Water Isoscape (S180 and S2H):
Temporal Changes of Source Water within the River." Ecosphere 3:39.
Brooks, R.P., and T.L. Serfass. 2013. "Wetland-riparian wildlife of the Mid-Atlantic Region: An
overview. Pages 259-268 in Mid-Atlantic freshwater wetlands: Advances in wetlands
science, management, policy, and practice. R. P. Brooks and D. H. Wardrop, editors.
Springer, New York, NY.
Brooks, R.R., et al. 1977. "Cobalt and Nickel Uptake by the Nyssaceae." Taxon 26:197-201.
Brooks, R.T. 2005. "A Review of Basin Morphology and Pool Hydrology of Isolated Ponded
Wetlands: Implications for Seasonal Forest Pools of the Northeastern United States.
Wetlands Ecology and Management 13:335-348.
Brown, A.V., and W.J. Matthews. 1995. "Stream Ecosystems of the Central United States."
Pages 89-116 in River and Stream Ecosystems. C. E. Cushing, et al., editors. Elsevier
Science, Amsterdam, The Netherlands.
Brummer, C.J., et al. 2006. "Influence of Vertical Channel Change Associated with Wood
Accumulations on Delineating Channel Migration Zones, Washington, USA."
Geomorphology 80:295-309.
Bukaveckas, P. A. 2009. "Rivers." Pages 721-732 in Encyclopedia of Inland Waters. G.E.
Likens, ed. Elsevier, Oxford, UK.
Bull, W.B. 1997. "Discontinuous Ephemeral Streams." Geomorphology 19: 227-276.
Bullock, A., and M. Acreman. 2003. "The Role of Wetlands in the Hydrological Cycle."
Hydrology and Earth System Sciences 7:358-389.
Bunn, S.E., and A.H. Arthington. 2002. "Basic Principles and Ecological Consequences of
Altered Flow Regimes for Aquatic Biodiversity." Environmental Management 30:492-507.
Bunn, S.E., et al., 2006. "Flow Variability in Dryland Rivers: Boom, Bust and the Bits in
Between." River Research and Applications 22:179-186.
Burkart, M. R., et al. 1999. "Tributary Stream Infiltration as a Source of Herbicides in an
Alluvial Aquifer." Journal of Environmental Quality 28:69-74.
Burt, T.P., et al. 2002. "Water Table Fluctuations in the Riparian Zone: Comparative Results
from a Pan-European Experiment." Journal of Hydrology 265:129-148.
Butcher, G.S., and B. Zimpel. 1991. "Habitat Value of Isolated Waters to Migratory Birds."
Prepared by Cornell Laboratory of Ornithology and The Cadmus Group, Inc. for U.S.
Environmental Protection Agency Office of Wetlands Protection. Cornell and Cadmus,
Washington, D.C.
Page 386 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Cabezas, A. etal. 2009. "Changing Patterns of Organic Carbon and Nitrogen Accretion on the
Middle Ebro Floodplain (NE Spain)." Ecological Engineering 35:1547-1558.
Cairns, M.A., et al. 2005. "Influence of Summer Stream Temperatures on Black Spot Infestation
of Juvenile Coho Salmon in the Oregon Coast Range." Transactions of the American
Fisheries Society 134:1471-1479.
Caissie, D. 2006. "The Thermal Regime of Rivers: A Review Freshwater Biology 51:1389-
1406.
California Division of Safety of Dams. 1993. Guidelines for the Design and Construction of
Small Embankment Dams. Department of Water Resources, Sacramento, CA.
http://www.water.ca.gov/damsafetv/docs/GuidelinesSmallDams.pdf.
Callegary, J.B., et al. 2007. "Rapid Estimation of Recharge Potential in Ephemeral-Stream
Channels using Electromagnetic Methods, and Measurements of Channel and Vegetation
Characteristics." Journal of Hydrology 344:17-31.
Carlyle, G.C., and A.R. Hill. 2001. "Groundwater Phosphate Dynamics in a River Riparian
Zone: Effects of Hydrologic Flowpaths, Lithology, and Redox Chemistry." Journal of
Hydrology 247:151-168.
Carroll, R., et al. 2005. "Simulation of a Semipermanent Wetland Basin in the Cottonwood Lake
Area, East-Central North Dakota." Journal of Hydrologic Engineering 10:70-84.
Cayan, D.R., and D.H. Peterson. 1989. "The Influence of North Pacific Atmospheric Circulation
on Streamflow in the West." Geophysical Monographs 55:375-397.
Cederholm, C.J., etal. 1999. "Pacific Salmon Carcasses: Essential Contributions of Nutrients
and Energy for Aquatic and Terrestrial Ecosystems." Fisheries 24(10):6-15.
Chacon, N., et al. 2008. "Seasonal Changes in Soil Phosphorus Dynamics and Root Mass along a
Flooded Tropical Forest Gradient in the Lower Orinoco River, Venezuela." Biogeochemistry
87:157-168.
Chapra, S.C. 1996. Surface Water Quality Modeling. McGraw-Hill, New York, NY.
Cheesman, A.W., etal. 2010. "Soil Phosphorus Forms in Hydrologically Isolated Wetlands and
Surrounding Pasture Uplands." Journal of Environmental Quality 39:1517-1525.
Chen, X., and X. Chen. 2003. "Stream Water Infiltration, Bank Storage, and Storage Zone
Changes Due to Stream-Stage Fluctuations." Journal of Hydrology 280:246-264.
Church, M. 2002. "Geomorphic Thresholds in Riverine Landscapes." Freshwater Biology
47:541-557.
Church, M. 2006. "Bed Material Transport and the Morphology of Alluvial River Channels."
Annual Review of Earth and Planetary Sciences: 325-354.
Clair, T.A., et al. 1994. "Exports of Carbon and Nitrogen from River Basins in Canada's Atlantic
Provinces." Global Biogeochemical Cycles 8:441-450.
Clark, W.R. 2000. "Ecology of Muskrats in Prairie Wetlands." Pages 287-313 in Prairie Wetland
Ecology: The Contribution of the Marsh Ecology Research Program. H. R. Murkin, etal.,
editors. Iowa State University Press, Ames, IA.
Colburn, E.A. 2004. Vernal Pools: Natural History and Conservation. McDonald and
Woodward Publishing Company, Blacksburg, VA.
Collins, B.D., et al. 2012. "The Floodplain Large-Wood Cycle Hypothesis: A Mechanism for the
Physical and Biotic Structuring of Temperature Forested Alluvial Valleys in the North
Pacific Coastal Ecoregion. Geomorphology 139-140:460-470.
Page 387 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Colvin, R., et al. 2009. "Fish Use of Intermittent Watercourses Draining Agricultural Lands in
the Upper Willamette River Valley, Oregon." Transactions of the American Fisheries Society
138:1302-1313.
Comer, P., et al. 2005. Biodiversity Values of Geographically Isolated Wetlands in the United
States. NatureServe, Arlington, VA.
Committee on Environment and Natural Resources. 2000. Integrated Assessment of Hypoxia in
the Northern Gulf of Mexico. National Science and Technology Council, Washington, D.C.
Cooper, A., et al. 1987. "Riparian Areas as Filters for Agricultural Sediment." Soil Science
Society of America Proceedings 51:416-420.
Copp, G.H. 1989. "The Habitat Diversity and Fish Reproductive Function of Floodplain
Ecosystems." Environmental Biology of Fishes 26:1-27.
Corti, R., et al. 2011. "Natural Variation in Immersion and Emersion Affects Breakdown and
Invertebrate Colonization of Leaf Litter in a Temporary River. Aquatic Sciences 73:537-550.
Costelloe, J.F., et.al. 2007. "Determining Loss Characteristics of Arid Zone River Waterbodies."
River Research and Applications 23:715-731.
Cowardin, L.M., et al. 1979. Classification of Wetlands and Deepwater Habitats of the United
States. U.S. Department of the Interior, U.S. Fish and Wildlife Service, Office of Biological
Services, Washington, D.C.
Craft, C.B., and C. Chiang. 2002. "Forms and Amounts of Soil Nitrogen and Phosphorus across
a Longleaf Pine-Depressional Wetland Landscape." Soil Science Society of America Journal
66:1713-1721.
Cross, F.B., and R.E. Moss. 1987. "Historic Changes in Fish Communities and Aquatic Habitats
in Plains Streams of Kansas." Pages 155-165 in Community and Evolutionary Ecology of
North American Stream Fishes. W.J. Matthews and D.C. Heins, editors. University of
Oklahoma Press, Norman, OK.
Curry, R.A., et al. 1997. "Use of Small Streams by Young Brook Trout Spawned in a Lake."
Transactions of the American Fisheries Society 126:77-83.
Dahl, T.E. 1990. Wetlands Losses in the United States 1780's to 1980's. U.S. Department of the
Interior, U.S. Fish and Wildlife Service, Washington, D.C.
Daniels, R.B., and J.G. Gilliam. 1996. "Sediment and Chemical Load Reduction by Grass and
Riparian Filters." Soil Science Society of America Journal 60:246-251.
Davis, C.B., et al. 1981. "Prairie Pothole Marshes as Traps for Nitrogen and Phosphorus in
Agricultural Runoff," in B. Richardson, ed., Selected Proceedings of the Midwest Conference
on Wetland Values and Management, June 17-19, 1981, St. Paul, MN, (St. Paul, MN: The
Freshwater Society), pp. 153-163.
Day, D.G. 1978. "Drainage Density Changes during Rainfall." Earth Surface Processes and
Landforms 3:319-326.
Day, J.W., et al. 2007. "Restoration of the Mississippi Delta: Lessons from Hurricanes Katrina
and Rita." Science 315(5819): 1679-1684.
Dent, C.L., and N.B. Grimm. 1999. "Spatial Heterogeneity of Stream Water Nutrient
Concentrations over Successional Time." Ecology 80:2283-2298.
Detenbeck, N. E., et al. 1993. "Wetland Effects on Lake Water Quality in the Minneapolis/St.
Paul Metropolitan Area." Landscape Ecology 8:39-61.
Detenbeck, N.E., et al. 1999. "Evaluating Perturbations and Developing Restoration Strategies
for Inland Wetlands in the Great Lakes Basin" Wetlands 19(4): 789-820.
Page 388 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Detenbeck, N.E., et al. 2005. "Relationship of Stream Flow Regime in the Western Lake
Superior Basin to Watershed Type Characteristics." Journal of Hydrology 309(1-4): 258-276.
Devito, K., etal. 2005. "A Framework for Broad-Scale Classification of Hydrologic Response
Units on the Boreal Plain: Is Topography the Last Thing to Consider?" Hydrological
Processes 19:1705-1714.
Devito, K.J., et al. 1996. "Groundwater Surface-Water Interactions in Headwater Forested
Wetlands of the Canadian Shield." Journal of Hydrology 181:127-147.
Diaz, R.J., and R. Rosenberg. 2011. "Introduction to Environmental and Economic
Consequences of Hypoxia." International Journal of Water Resources Development 27
(l):71-82.
Dierberg, F.E., and P.L. Brezonik. "Nitrogen and Phosphorus Mass Balances in a Cypress Dome
Receiving Wastewater." Pages 112-118 in Cypress Swamps. K.C. Ewel and H.T. Odum, ed.,
University Presses of Florida, Gainesville, FL.
Dieter, etal. 2011. "Preconditioning Effects of Intermittent Stream Flow on Leaf Litter
Decomposition." Aquatic Sciences 73:599-609.
Dieterich, M., and N.H. Anderson. 1998. "Dynamics of Abiotic Parameters, Solute Removal and
Sediment Retention in Summer-Dry Headwater Stream of Western Oregon." Hydrobiologia
379: 1-15.
Dietrich, W.E., and T. Dunne. 1993. "The Channel Head." Pages 175-219 in Channel Network
Hydrology. K. Beven and M. J. Kirby, editors. John Wiley & Sons, New York, NY.
Dillaha, T.A., and S.P. Inamdar. 1997. "Buffer Zones as Sediment Traps or Sources." Pages 33-
42 in Buffer Zones: Their Processess and Potential in Water Protection. N.E. Haycock, et
al., ed., Proceedings of the International Conference on Buffer Zones, September 1996.
Quest Environmental, Hertfordshire, UK.
Dillon, P.J., and L.A. Molot. 1997. "Effects of Landscape Form on Export of Dissolved Organic
Carbon, Iron, and Phosphorus from Forested Stream Catchments." Water Resources
Research 33:2591-2600.
Dodds, W.K., et al. 1996a. "Nitrogen Transport from Tallgrass Prairie Watersheds." Journal of
Environmental Quality 25:973-981.
Dodds, W.K., et al. 1996b. "The Relationship of Floods, Drying, Flow and Light to Primary
Production and Producer Biomass in a Prairie Stream." Hydrobiologia 333:151-159.
Dodds, W.K., et al. 2004. "Life on the Edge: The Ecology of Great Plains Prairie Streams,"
Bioscience 54:205-216.
Dole, J.W. 1965. "Summer Movements of Adult Leopard Frogs, Rana Pipiens Schreber, in
Northern Michigan." Ecology 46 (3):236-255.
Driscoll, C.T., et al. 1995. "The Role of Dissolved Organic Carbon in the Chemistry and
Bioavailability of Mercury in Remote Adirondack Lakes." Water Air and Soil Pollution
80:499-508.
Duncan, S.H., etal. 1987. "Transport of Road-Surface Sediment through Ephemeral Stream
Channels." Water Resources Bulletin 23(1): 113-119.
Dunham, J.B., et al. 2002. "Alien Invasions in Aquatic Ecosystems: Toward an Understanding of
Brook Trout Invasions and Potential Impacts on Inland Cutthroat Trout in Western North
America " Reviews in Fish Biology and Fisheries 12(4): 373-391.
Dunne, E.J., etal. 2006. "Phosphorus Release and Retention by Soils of Natural Isolated
Wetlands." International Journal of Environment and Pollution 28:496-516.
Page 389 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Dunne, T., and R.D. Black. 1970. "Partial Area Contributions to Storm Runoff in a Small New
England Watershed." Water Resources Research 6:1296-1311.
Dunne, T., and L.B. Leopold. 1978. Water in Environmental Planning. W.H. Freeman and Co.,
San Francisco, CA.
Dunnivant, F.M., and E. Anders. 2006. A Basic Introduction to Pollutant Fate and Transport: An
Integrated Approach with Chemistry, Modeling, Risk Assessment, and Environmental
Legislation. John Wiley & Sons, Inc., Hoboken, NJ.
Durham, B.W., and G.R. Wilde. 2008. "Composition and Abundance of Drifting Fish Larvae in
the Canadian River, Texas." Journal of Freshwater Ecology 23:273-280.
Ebersole, J.L., et. al. 2003. "Cold Water Patches in Warm Streams: Physicochemical
Characteristics and the Influence of Shading." Journal of the American Water Resources
Association 39:355-368.
Eckhardt, B.W., and T.R. Moore. 1990. "Controls on Dissolved Organic Carbon Concentrations
in Streams of Southern Quebec." Canadian Journal of Fisheries and Aquatic Sciences
47:1537-1544.
Elliott, J.M. 1971. "Distances Travelled by Drifting Invertebrates in a Lake District Stream."
Oecologia 6:350-379.
Elliott, J.M. 2003. "A Comparative Study of the Dispersal of 10 Species of Stream
Invertebrates." Freshwater Biology 48:1652-1668.
Elwood, J., et al. 1983. "Resource Spiraling: An Operational Paradigm for Analyzing Lotic
Ecosystems." Pages 3-23 in Dynamics of Lotic Ecosystems. T.D. Fontaine and S.M. Bartell,
ed. Ann Arbor Science, Ann Arbor, MI.
Ensign, S.H., and M.W. Doyle. 2006. "Nutrient Spiraling in Streams and River Networks."
Journal of Geophysical Research-Biogeosciences 111 :G04009.
Enwright, N., et al. 2011. "Using Geographic Information Systems (GIS) to Inventory Coastal
Prairie Wetlands Along the Upper Gulf Coast, Texas." Wetlands 31:687-697.
Erman, D.C., and V.M. Hawthorne. 1976. "The Quantitative Importance of an Intermittent
Stream in the Spawning of Rainbow Trout." Transactions of the American Fisheries Society
105:675-681.
Eshelman, K.N., and H.F. Hemond. 1985. "The Role of Organic Acids in the Acid-base Status of
Surface Waters at Bickford Watershed, Massachusetts." Water Resources Research 21:1503-
1510.
Ewel, K.C., and H.T. Odum, ed. 1984. Cypress Swamps. (Gainesville, Florida: University of
Florida Press).
Ewing, J. M., et al. 2012. "Changes in Wetland Soil Morphological and Chemical Properties
after 15, 20, and 30 Years of Agricultural Production." Geoderma 179-180 (0):73-80.
Falke, J. A., et al. 2011. "The Role of Groundwater Pumping and Drought in Shaping Ecological
Futures for Stream Fishes in a Dryland River Basin of the Western Great Plains, USA."
Ecohydrology 4:682-697.
Fausch, K.D., and K.R. Bestgen. 1997. "Ecology of Fishes Indigenous to the Central and
Southwestern Great Plains." Pages 131-166 in F.L. Knopf and F.B. Samson, ed. Ecology and
Conservation of Great Plains Vertebrates. Springer-Verlag, New York, NY.
Fausch, K.D., and R.G. Bramblett. 1991. "Disturbance and Fish Communities in Intermittent
Tributaries of a Western Great Plains River." Copeia 1991:659-674.
Fausch, K.D., et al. 2002. "Landscapes to Riverscapes: Bridging the Gap between Research and
Conservation of Stream Fishes." Bioscience 52:483-498.
Page 390 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Federal Emergency Management Agency. "Flood Zones." Last updated April 26, 2015.
https://www.fema.gov/flood-zones.
Federal Emergency Management Agency. 1995. The Zone A Manual: ManagingFloodplain
Development in Approximate Zone A Areas - A Guide for Obtaining and Developing Base
(100-Year) Flood Elevations. FEMA 265.
Federal Energy Regulatory Commission. 2005. "Chapter 14: Dam Safety Performance
Monitoring Program." Engineering Guidelines for the Evaluation of Hydropower Projects.
http://www.ferc.gov/industries/hvdropower/safetv/guidelines/eng-guide/chapl4.pdf.
Federal Interagency Stream Restoration Working Group. 1998. Stream Corridor Restoration:
Principles, Processes and Practices. GPO Item No. 0120-A; SuDocs No. A 57.6/2:EN
3/PT.653, USDA National Engineering Handbook Part 653.
http://vvvvvv.nrcs.usda.gov/lnternet/FSE DOCUMENTS/stelprdb 1044574.pdf.
Fellman, J.B., etal. 2013. "Leaf Litter Age, Chemical Quality, and Photodegradation Control the
Fate of Leachate Dissolved Organic Matter in a Dryland River." Journal of Arid
Environments 89:30-37.
Fernald, A.F., etal. 2001. "Transient Storage and Hyporheic Flow along the Willamette River,
Oregon: Field Measurements and Model Estimates. Water Resources Research 37:1681-
1694.
Ferrington, L.C. 1993. "Endangered Rivers: A Case History of the Arkansas River in the Central
Plains." Aquatic Conservation: Marine and Freshwater Ecosystems 3:305-316.
Field, J. J., and R.W. Lichvar. 2007. Review and Synopsis of Natural and Human Controls on
Fluvial Channel Processes in the Arid West. ERDC/CRREL TR-07-16. U.S. Army Engineer
Research and Development Center, Cold Regions Research and Engineering Laboratory,
Hanover, NH.
Figuerola, J., and A.J. Green. 2002. "Dispersal of Aquatic Organisms by Waterbirds: A Review
of Past Research and Priorities for Future Studies." Freshwater Biology 47:483-494.
Figuerola, J., etal. 2005. "Invertebrate Eggs Can Fly: Evidence of Waterfowl-Mediated Gene
Flow in Aquatic Invertebrates." American Naturalist 165:274-280.
Finkelstein, P.L., and L.E. Truppi. 1991. "Spatial Distribution of Precipitation Seasonality in the
United States. Journal of Climate 4:373-385.
Fisher, S.G. and G.E. Likens. 1973. "Energy Flow in Bear Brook, New Hampshire: An
Integrative Approach to Stream Ecosystem Metabolism." Ecological Monographs 43: 421-
439.
Fisher, S.G., etal. 2001. "Landscape Challenges to Ecosystem Thinking: Creative Flood and
Drought in the American Southwest." ScientiaMarina 65:181-192.
Fisher, S.J., and D.W. Willis. 2000. "Seasonal Dynamics of Aquatic Fauna and Habitat
Parameters in a Perched Upper Missouri River Wetland." Wetlands 20:470-478.
Fleming, S.W., etal. 2007. "Regime-Dependent Streamflow Sensitivities to Pacific Climate
Modes Cross the Georgia-Puget Transboundary Ecoregion. HydrologicalProcesses 21:3264-
3287.
Flitcroft, R.L., el al. 2012. "Do Network Relationships Matter? Comparing Network and
Instream Habitat Variables to Explain Densities of Juvenile Coho Salmon (iOncorhynchus
Kisutch) in Mid-Coastal Oregon, USA." Aquatic Conservation: Marine and Freshwater
Ecosystems 22:288-302.
Page 391 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Florsheim, J.L., and J.F. Mount. 2003. "Changes in Lowland Floodplain Sedimentation
Processes: Pre-disturbance to Post-rehabilitation, Cosumnes River, CA." Geomorphology
56(3-4):305-323.
Florsheim, J.L., etal. 2008. "Bank Erosion as a Desirable Attribute of Rivers." Bioscience 58:
519-529.
Forbes, M.G., etal. 2012. "Nutrient Transformation and Retention by Coastal Prairie Wetlands,
Upper Gulf Coast, Texas." Wetlands 32(4): 705-715.
Franklin, S.B., etal. 2009. "Complex Effects of Channelization and Levee Construction on
Western Tennessee Floodplain Forest Function." Wetlands 29(2): 451-464.
Franssen, N.R., et al. 2006. "Effects of Floods on Fish Assemblages in an Intermittent Prairie
Stream." Freshwater Biology 51:2072-2086.
Fraser, D.F., etal. 1995. "Predation As an Agent of Population Fragmentation in a Tropical
Watershed." Ecology 76:1461-1472.
Fraser, D.J., etal. 2011. "Extent and Scale of Local Adaptation in Salmonid Fishes: Review and
Mmeta-Analysis." Heredity 106:404-420.
Freeman, M.C., etal. 2007. "Hydrologic Connectivity and the Contribution of Stream
Headwaters to Ecological Integrity at Regional Scales." Journal of the American Water
Resources Association 43:5-14.
Frisch, D., and S.T. Threlkeld. 2005. "Flood-Mediated Dispersal Versus Hatching: Early
Recolonisation Strategies of Copepods in Floodplain Ponds." Freshwater Biology 50:323-
330.
Frisch, D., etal. 2007. "High Dispersal Capacity of a Broad Spectrum of Aquatic Invertebrates
Via Waterbirds." Aquatic Sciences 69:568-574.
Frissell, C.A., etal. 1986. "A Hierarchical Framework for Stream Habitat Classification:
Viewing Streams in a Watershed Context." Environmental Management 10:199-214.
Fritz, K.M., and W.K. Dodds. 2004. "Resistance and Resilience of Macroinvertebrate
Assemblages to Drying and Flood in a Tallgrass Prairie Stream System." Hydrobiologia
527:99-112.
Fritz, K.M., and W.K. Dodds. 2005. "Harshness: Characterization of Intermittent Stream Habitat
over Space and Time." Marine and Freshwater Research 56:13-23.
Fritz, K.M., et al. 2006b. Field Operations Manual for Assessing the Hydrologic Permanence
and Ecological Condition of Headwater Streams. EPA/600/R-06/126, U.S. Environmental
Protection Agency, Office of Research and Development, National Exposure Research
Laboratory, Washington, D.C.
Fullerton, A.H., etal. 2010. "Hydrological Connectivity for Riverine Fish: Measurement
Challenges and Research Opportunities." Freshwater Biology 55:2215-2237.
Galat, D.L., and R. Lipkin. 2000. "Restoring Ecological Integrity of Great Rivers: Historical
Hydrographs Aid in Defining Reference Conditions for the Missouri River." Hydrobiologia
422/423:29-48.
Galat, D.L., etal. 1998. "Flooding to restore connectivity of regulated, large-river wetlands."
BioScience 48:721-733.
Galat, D.L., et al. 2005. "Missouri River Basin." Pages 427-480 in Rivers of North America. A.
C. Benke and C. E. Cushing, editors. Elsevier Academic Press, Burlington, MA.
Galatowitsch, S.M., and A.G. van der Valk. 1996. "The Vegetation of Restored and Natural
Prairie Wetlands,"Ecological Applications 6:102-112.
Page 392 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States May 2015
Gamble, D., et al. 2007. An Ecological and Functional Assessment of Urban Wetlands in Central
Ohio. Columbus, Ohio. Ohio EPA Technical Report WET/2007-3B, Ohio Environmental
Protection Agency, Wetland Ecology Group, Division of Surface Water, Columbus, OH.
Gardner, B., and P.J. Sullivan. 2004. "Spatial and Temporal Stream Temperature Prediction:
Modeling Nonstationary Temporal Covariance Structures." Water Resources Research
40(1):W01102.
Gergel, S.E. 2005. "Spatial and Non-spatial Factors: When Do They Affect Landscape Indicators
of Watershed Loading?" Landscape Ecology 20:177-189.
Gergel, S.E., et al. 1999. "Dissolved Organic Carbon as an Indicator of the Scale of Watershed
Influence on Lakes and Rivers." Ecological Applications 9:1377-1390.
Gergel, S.E., et al. 2002. "Consequences of Human-altered Floods: Levees, Floods, and
Floodplain Forests along the Wisconsin River." Ecological Applications 12(6): 1755-1770.
Gergel, S.E., et al. 2005. "Do Dams and Levees Impact Nitrogen Cycling? Simulating the
Effects of Flood Alterations on Floodplain Denitrification." Global Change Biology 11(8):
1352-1367.
Gibbons, J.W., et al. 2006. "Remarkable Amphibian Biomass and Abundance in an Isolated
Wetland: Implications for Wetland Conservation." Conservation Biology 20:1457-1465.
Glinska-Lewczuk, K. 2009. "Water Quality Dynamics of Oxbow Lakes in Young Glacial
Landscape of NE Poland in Relation to Their Hydrological Connectivity." Ecological
Engineering 35:25-37.
Gleason, R. A., et al. 2007. Estimating Water Storage Capacity of Existing and Potentially
Restorable Wetland Depressions in a Subbasin of the Red River of the North, U.S.
Geological Survey Open-File Report 2007-1159 (Reston, VA: U.S. Geological Survey).
Gleeson, T., et al. 2011. "Classifying the Water Table at Regional to Continental Scales."
Geophysical Research Letters 38:L05401.
Golden, H.E., et al. 2013. "Climate Change and Watershed Mercury Export: A Multiple
Projection and Model Analysis." Environmental Toxicology and Chemistry 32:2165-2174.
Gomi, T., and R.C. Sidle. 2003. "Bed Load Transport in Managed Steep-gradient Headwater
Streams of Southeastern Alaska." Water Resources Research 39:1336.
Gomi, T., et al. 2002. "Understanding Processes and Downstream Linkages of Headwater
Systems." Bioscience 52:905-916.
Gooderham, J.P.R., etal. 2007. "Upstream Heterogeneous Zones: Small Stream Systems
Structured by a Lack of Competence?" Journal of the North American Benthological Society
26:365-374.
Goodrich, D.C., et al. 1997. "Linearity of Basin Response as a Function of Scale in a Semiarid
Watershed." Water Resources Research 33:2951-2965.
Goolsby, D., et al. 1999. Topic Report 3, Flux and Sources of Nutrients in the Mississippi-
Atchafalaya River Basin. National Science and Technology Council Committee on
Environment and Natural Resources, Washington, D.C.
Gooseff, M.N., etal. 2008. "Solute Transport along Stream and River Networks." Pages 395-417
in River Confluences, Tributaries, and the Fluvial Network. S.P. Rice, et al., editors. John
Wiley & Sons, Chichester, UK.
Gorman, O.T. 1986. "Assemblage Organization of Stream Fishes: The Effects of Rivers on
Adventitious Streams " American Naturalist 128(4): 611-616.
Graf, W. L. 1984. "A Probabilistic Approach to the Spatial Assessment of River Channel
Instability." Water Resources Research 20(7):953-962.
Page 393 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Graf, W.L. 1994. Plutonium and the Rio Grande: Environmental Change and Contamination in
the Nuclear Age. Oxford University Press, New York, NY.
Granado, D.C., and R. Henry. 2014. "Phytoplankton Community to Hydrologic Variations in
Oxbow Lakes with Different Levels of Connection to a Tropical River." Hydrobiologia
721:223-238.
Grant, E.H.C., et al. 2007. "Living in the Branches: Population Dynamics and Ecological
Processes in Dendritic Networks." Ecology Letters 10:165-175.
Greathouse, E.A., et al. 2006. "Indirect Upstream Effects Of Dams: Consequences Of Migratory
Consumer Extirpation In Puerto Rico." Ecological Applications 16: 339-352.
Greathouse, E.A., et al. 2014. "Linking Landscape Characteristics and High Stream Nitrogen in
the Oregon Coast Range: Red Alder Complicates Use of Nutrient Criteria." Journal of the
American Water Resources Association 50:1383-1400.
Green, D.M. 2005. "Bufo americanus, American Toad." Pages 692-704 in Amphibian Declines:
The Conservation Status of United States Species. M. Lannoo, ed. University of California
Press, Berkeley, CA.
Gregory, K. J., and D.E. Walling. 1968. "The Variation of Drainage Density within a
Catchment." Bulletin of the International Association of Scientific Hydrology 13:61-68.
Gregory, S.V., et al. 1991. "An Ecosystem Perspective of Riparian Zones: Focus on Links
between Land and Water." Bioscience 41:540-551.
Gurnell, A., et al. 2008. "Propagule Deposition along River Margins: Linking Hydrology and
Ecology." Journal of Ecology 96:553-565.
Gurnell, A.M. 2007. "Analogies Between Mineral Sediment and Vegetative Particle Dynamics
in Fluvial Systems." Geomorphology 89:9-22.
Gurnell, A.M et al. 1995. "The Role of Coarse Woody Debris in Forest Aquatic Habitats:
Implications for Management." Aquatic Conservation: Marine and Freshwater Ecosystems
5:143-166.
Gurnell, A.M., et al. 2002. "Large Wood and Fluvial Processes." Freshwater Biology 47:601-
619.
Hadley, R.F., et al. 1987. "Water Development and Associated Hydrologic Changes in the Platte
River, Nebraska, U.S.A." Regulated Rivers: Research & Management 1:331-341.
Hall, B.R., et al. 2001. "Environmental Influences on Plant Species Composition in Ground-
water Seeps in the Catskill Mountains of New York." Wetlands 21:125-134.
Hall, C.J., et al. 2011. "The Historic Influence of Dams on Diadromous Fish Habitat with a
Focus on River Herring and Hydrologic Longitudinal Connectivity." Landscape Ecology 26:
95-107.
Hall, R.O., and J.L. Meyer. 1998. "The Trophic Significance of Bacteria in a Detritus-Based
Stream Food Web." Ecology 79:1995-2012.
Hall, R.O., et al. 2000. "Organic Matter Flow in Stream Food Webs with Reduced Detrital
Resource Base." Ecology 81:3445-3463.
Hall, R.O., et al. 2009. "Hydrologic Control of Nitrogen Removal, Storage, and Export in a
Mountain Stream," Limnology and Oceanography 54:2128-2142.
Hamilton, S.K., et al. 2005. "Persistence of Aquatic Refugia between Flow Pulses in a Dryland
River System (Cooper Creek, Australia)" Limnology and Oceanography 50:743-754.
Hammersmark, C.T., et al. 2008. "Quantifying the Hydrological Effects of Stream Restoration in
a Montane Meadow Environment." River Research and Applications 24:735-753.
Page 394 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Hanes, T., and L. Stromberg. 1998. "Hydrology of Vernal Pools on Non-Volcanic Soils in the
Sacramento Valley." Pages 38-49 in Ecology, Conservation, and Management of Vernal
Pool Ecosystems—Proceedings from a 1996 Conference. C. W. Witham, et al., editors.
California Native Plant Society, Sacramento, CA.
Hanson, M.A., et al. 2005. "Biotic Interactions as Determinants of Ecosystem Structure in
Prairie Wetlands: An Example Using Fish." Wetlands 25:764-775.
Harmon, M.E., et a\. 1986. "Ecology of Coarse Woody Debris in Temperature Ecosystems."
Advances in Ecological Research 15:13 3 -3 02.
Hawes, E., and M. Smith. 2005. Riparian Buffer Zones: Functions and Recommended Widths.
Prepared for the Eightmile River Wild and Scenic Study Committee.
He, S., and Y.J. Xu. 2015. "Three Decadal Inputs of Total Organic Carbon from Four Major
Coastal River Basins to the Summer Hypoxic Zone of the Northern Gulf of Mexico."
Marine Pollution Bulletin 90 (1-2): 121-128.
Heckscher C.M., and C.R. Bartlett. 2004. "Rediscovery and Habitat Associations of Photuris
Bethaniensis McDermott (Coleoptera: Lampyridae)." The Coleopterists Bulletin 58(3): 349-
353.
Hedin, L.O., et al. 1995. "Patterns of Nutrient Loss from Unpolluted Old-growth Temperate
Forests: Evaluation of Biogeochemical Theory." Ecology 76:493-509.
Hedman, E.R., and W.R. Osterkamp. 1982. Streamflow Characteristics Related to Channel
Geometry of Streams in Western United States. United States Geological Survey Water-
Supply Paper 2193. United States Government Printing Office, Washington D.C.
Heine, R.A., et al. 2004. "Development and Comparison of Approaches for Automated Mapping
of Stream Channel Networks." Annals of the Association of American Geographers 94:477-
490.
Hemond, H.F. 1980. "Biogeochemistry of Thoreau's Bog, Concord, Massachusetts." Ecological
Monographs 50:507-526.
Hemond, H.F. 1983. "The Nitrogen Budget of Thoreau's Bog." Ecology 64:99-109.
Henning, J. A., et al. 2007. "Use of Seasonal Freshwater Wetlands by Fishes in a Temperate
River Floodplain." Journal of Fish Biology 71:476-492.
Hentges, V.A., and T.W. Stewart. 2010. "Macroinvertebrate Assemblages in Iowa Prairie
Pothole Wetlands and Relation to Environmental Features." Wetlands 30:501-511.
Helton, A.M., etal. 2011. "Thinking Outside the Channel: Modeling Nitrogen Cycling in
Networked River Ecosystems." Frontiers in Ecology and the Environment 9:229-238.
Herwig, B.R., etal. 2010. "Factors Influencing Fish Distributions in Shallow Lakes in Prairie
and Prairie-parkland Regions of Minnesota, USA." Wetlands 30:609-619.
Hess, G.R. 1996. "Linking Extinction to Connectivity and Habitat Destruction in Metapopulation
Models." The American Naturalist 148:226-236.
Hewlett, J.D. 1982. Principles of Forest Hydrology. University of Georgia Press, Athens, GA.
Hewlett, J.D., and A.R. Hibbert. 1967. "Factors Affecting the Response of Small Watersheds to
Precipitation in Humid Areas. Pages 275-290 in International Symposium on Forest
Hydrology. W.S. Sopper and H.W. Hull, editors. Pergamon Press, New York, NY.
Hewlett, J.D., et al. 1977. "Predicting Stormflow and Peakflow from Small Basin in Humid
Areas by the R-Index Method." Water Resources Bulletin 13:231 -253.
Hill, B.H., et al. 1992. "Predicatability of Streamflow and Particulate Organic Matter
Concentration as Indicators of Stability in Prairie Streams." Hydrobiologia 242:7-18.
Page 395 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Hitt, N.P., and P.L. Angermeier. 2008. "Evidence for Fish Dispersal from Spatial Analysis of
Stream Network Topology." Journal of the North American Benthological Society 27:304-
320.
Hobbie, J.E., and R.G. Wetzel. 1992. "Microbial Control of Dissolved Organic Carbon in Lakes:
Research for the Future." Hydrobiologia 229:169-180.
Hobson, W.A., and R.A. Dahlgren. 1998. "Soil Forming Processes in Vernal Pools of Northern
California, Chico Area." Pages 24-37 in Ecology, Cconservation, and Management of Vernal
Pool Ecosystems—Proceedings from a 1996 Conference. C.W. Witham, et a/, editors.
California Native Plant Society, Sacramento, CA.
Hoffmann, C.C., et al. 2009. "Phosphorus Retention in Riparian Buffers: Review of Their
Efficiency." Journal of Environmental Quality 38:1942-1955.
Hogan, M.E., and G.F. Tande. 1983. Anchorage Wetlands Study: Special Report on Connors
Bog and Klatt Bog: U.S. Fish and Wildlife Service, Special Studies.
Hope, D., et al. 1994. "A Review of the Export of Carbon in River Water: Fluxes and
Processes." Environmental Pollution 84:301-324.
Horton, R.E. 1945. "Erosional Development of Streams and Their Drainage Basins:
Hydrophysical Approach to Quantitative Morphology." Bulletin of the Geological Society of
America 56:275-370
Hubbard, D.E., and R.L. Linder. 1986. "Spring Runoff Retention in Prairie Pothole Wetlands."
Journal of Soil and Water Conservation 41(2): 122-125.
Hughes, J.M., et al. 2009. "Genes in Streams: Using DNA to Understand the Movement of
Freshwater Fauna and Their Riverine Habitat." BioScience 59:573-583.
Humphries, P., et al. 2015. "The River Wave Concept: Integrating River Ecosystem Models."
BioScience: doi: 10.1093/biosci/biul 130.
Hunsinger, T.W., and M.J. Lannoo. 2005. "Notophthalmus viridescens, Eastern Newt." Pages
912-914 in Amphibian Declines: The Conservation Status of United States Species. M.
Lannoo, ed. University of California Press, Berkeley, CA.
Hunter, M.A., et al. 2005. "Low Flow Spatial Characteristics in Forested Headwater Channels of
Southwest Washington." Journal of the American Water Resources Association 41:503-516.
Hupp, C. R., etal. 2009. "Floodplain Geomorphic Processes and Environmental Impacts of
Human Alteration along Coastal Plain Rivers, USA." Wetlands 29:413-429.
Huryn, A.D., and K.E. Gibbs. 1999. "Riparian Sedge Meadows in Maine. A Macroinvertebrate
Community Structured by River-Floodplain Interaction." Pages 363-382 in Invertebrates in
Freshwater Wetlands of North America: Ecology and Management. D. P. Batzer, etal,
editors. John Wiley & Sons, New York, NY.
Huryn, A.D., etal. 2005. "Landscape Heterogeneity and the Biodiversity of Arctic Stream
Communities: A Habitat Template Analysis. Canadian Journal of Fisheries and Aquatic
Sciences 62:1905-1919.
Ice, G.G. 2008. "Chapter 3: Stream Temperature and Dissolved Oxygen." Pages 37-54 in
Hydrologic and Biological Responses to Forest Practices. J.D. Stednick, ed. Springer, New
York, NY.
Ilg, C., et al. 2008. "Long-term Reactions of Plants and Macroinvertebrates to Extreme Floods in
Floodplain Grasslands." Ecology 89:2392-2398.
International Atomic Energy Agency. 2003. "Investigating Leaks in Dams & Reservoirs." INIS-
XA-616. Vienna, Austria.
http ://www. i aea. oru/i ni s/col 1 ecti on/N C LCol 1 ecti on Store/ Public/34/028/34028298.pdf.
Page 396 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Isenhart, T.M. 1992. Transformation and Fate of Nitrate in Northern Prairie Wetlands, Ph.D.
Dissertation. Iowa State University, Ames, Iowa.
Izbicki, J. A. 2007. "Physical and Temporal Isolation of Mountain Headwater Streams in the
Western Mojave Desert, Southern California." Journal of the American Water Resources
Association 43:26-40.
Jacques, J., and D.L. Lorenz. 1988. Techniques for Estimating the Magnitude and Frequency of
Floods ofUngauged Streams in Minnesota. USGS Water-Resources Investigations Report
84-4170. U.S. Geological Survey, Washington, D.C.
Jansson, A., et al. 1998. "Quantifying the Nitrogen Retention Capacity of Natural Wetlands in
the Large-Scale Drainage Basin of the Baltic Sea." Landscape Ecology 13:249-262.
Jansson, R., et al. 2005. "Hydrochory Increases Riparian Plant Species Richness: A Comparison
between a Free-Flowing and a Regulated River." Journal of Ecology 93:1094-1103.
Jeffres, C.A., el al. 2008. "Ephemeral Floodplain Habitats Provide Best Growth Conditions for
Juvenile Chinook Salmon in a California River." Environmental Biology of Fishes 83:449-
458.
Jencso, K.G., and B.L. McGlynn. 2011. "Hierarchical Controls on Runoff Generation:
Topographically Driven Hydrologic Connectivity, Geology, and Vegetation." Water
Resources Research 47: W11527.
Jenkins, K.M., and A.J. Boulton. 2003. "Connectivity in a Dryland River: Short-term Aquatic
Microinvertebrate Recruitment following Floodplain Inundation." Ecology 84:2708-2723.
John, K.R. 1964. "Survival of Fish in Intermittent Streams of the Chirichua Mountains,
Arizona." Ecology 45:112-119.
Johnson, B.R., et al. 2010. "Use of Spatially Explicit Physicochemical Data to Measure
Downstream Impacts of Headwater Stream Disturbance." Water Resources Research
46:W09526.
Johnson, P.T.J., et al. 2008. "Dam Invaders: Impoundments Facilitate Biological Invasions into
Freshwaters." Frontiers in Ecology and the Environment 6:357-363.
Johnston, C. 1991. "Sediment and Nutrient Retention by Freshwater Wetlands: Effects on
Surface Water Quality." Critical Reviews in Environmental Control 21:491-565.
Johnston, C.A., et al. 1990. "The Cumulative Effect of Wetlands on Stream Water Quality and
Quantity." Biogeochemistry 10:105-141.
Johnston, C.A., et al., 1997. "The Potential Role of Riverine Wetlands as Buffer Zones." Pages
155-170 in Buffer Zones Their Processes and Potential in Water Protection. N.E. Haycock,
et al., ed. Quest International, Harpenden, UK.
Johnston, C.A., et al. 2001. "Nutrient Dynamics in Relation to Geomorphology of Riverine
Wetlands." Soil Science Society of America Journal 65(2):557-577.
Jordan, T.E., et al. 2007. "Comparing Functional Assessments of Wetlands to Measurements of
Soil Characteristics and Nitrogen Processing." Wetlands 27:479-497.
Julian, J.T., et al. 2013. "Assessing Wetland-Riparian Amphibian and Reptile Communities of
the Mid-Atlantic Region." Pages 313-337 in Mid-Atlantic Freshwater Wetlands: Advances in
Wetlands Science, Management, Policy, and Practice. R.P. Brooks and D.H. Wardrop,
editors. Springer, New York, NY.
Junk, W.J., et al. 1989. "The Flood Pulse Concept in River-Floodplain Systems." Pages 110-127
in Proceedings of the International Large River Symposium Ottawa. D.P. Dodge, ed.
Canadian Special Publication of Fisheries and Aquatic Sciences 106, Ottawa, Canada.
Page 397 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States May 2015
Kadlec, R.H., and S.D. Wallace. 2009. Treatment Wetlands. 2nd edition. CRC Press, Boca
Raton, FL.
Kahara, S.N., et al. 2009. "Spatiotemporal Patterns of Wetland Occurrence in the Prairie Pothole
Region of Eastern South Dakota." Wetlands 29:678-689.
Kao, C.M., et al. 2002. "Non-point Source Pesticide Removal by a Mountainous Wetland."
Water Science and Technology 46:199-206.
Kaplan, L.A., et al. 1980. "Patterns of Dissolved Organic Carbon in Transport." Limnology and
Oceanography 25: 1034-1043.
Keckeis, S., et al. 2003. "The Significance of Zooplankton Grazing in a Floodplain System of the
River Danube." Journal of Plankton Research 25:243-253.
Keddy, P. A., et al. 2007. "The Wetlands of Lakes Pontchartrain and Maurepas: Past, Present and
Future." Environmental Reviews 15: 43-77.
Keeley, J.E., and P. H. Zedler. 1998. "Characterization and Global Distribution of Vernal Pools."
Pages 1-14 in Ecology, Conservation, and Management of Vernal Pool Ecosystems—
Proceedings from a 1996 Conference. C.W. Witham, et al., editors. California Native Plant
Society, Sacramento, CA.
Keiper, J.B., et al. 2002. "Biology and Ecology of Higher Diptera from Freshwater Wetlands."
Annual Review of Entomology 47:207-232.
Kemp, W.M., et al. 2005. "Eutrophication of Chesapeake Bay: Historical Trends and Ecological
Interactions." Marine Ecology Progress Series 303(21): 1-29.
Kentula, M., et al. 2004. "Tracking Changes in Wetlands with Urbanization: Sixteen Years of
Experience in Portland, Oregon, USA." Wetlands 24(4):734-743.
Kimball, B.A., et al. 1995. "Effects of Colloids on Metal Transport in a River Receiving Acid
Mine Drainage, Upper Arkansas River, Colorado, USA." Applied Geochemistry 10:285-306.
King, A.J., et al. 2003. "Fish Recruitment on Floodplains: The roles of Patterns of Flooding and
Life History Characteristics." Canadian Journal of Fisheries and Aquatic Sciences 60:773-
786.
King, J.L., et al. 1996. "Species Richness, Endemism and Ecology of Crustacean Assemblages in
Northern California Vernal Pools." Hydrobiologia 328:85-116.
King, R.S., et al. 2005. "Spatial Considerations for Linking Watershed Land Cover to Ecological
Indicators in Streams." Ecological Applications 15:137-153.
Knapp, R.A., and K.R. Matthews. 2000. "Effects on Nonnative Fishes on Wilderness Lake
Ecosystems in the Sierra Nevada and Recommendations for Reducing Impacts." Pages 312-
317 in Wilderness Science in a Time of Change Conference, Volume 5: Wilderness
Ecosystems, Threats, and Management, Missoula, Montana, May 23-27, 1999.
Knispel, S., and E. Castella. 2003. "Disruption of a Longitudinal Pattern in Environmental
Factors and Benthic Fauna by a Glacial Tributary." Freshwater Biology 48:604-618.
Knutson, M.G., et al. 1999. "Effects of Landscape Composition and Wetland Fragmentation on
Frog and Toad Abundance and Species Richness in Iowa and Wisconsin, U.S.A."
Conservation Biology 13:1437-1446.
Kondolf, G. M. 1997. "Hungry Water: Effects of Dams and Gravel Mining on River Channels."
Environmental Management 21:533-551.
Kondolf, G.M., et al. 2006. "Process-Based Ecological River Restoration: Visualizing Three-
Dimensional Connectivity and Dynamic Vectors to Recover Lost Linkages. Ecology and
Society 11:5.
Page 398 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Koprivnjak, J.-F., and T.R. Moore. 1992. "Sources, Sinks, and Fluxes of Dissolved Organic
Carbon in Subarctic Fen Catchments." Arctic and Alpine Research 24:204-210.
Kortelainen, P. 1993. "Content of Total Organic Carbon in Finnish Lakes and Its Relationship to
Catchment Characteristics." Canadian Journal of Fisheries and Aquatic Sciences 50:1477-
1483.
Kovacic, D.A., etal. 2000. "Effectiveness of Constructed Wetlands in Reducing Nitrogen and
Phosphorus Export from Agricultural Tile Drainage." Journal of Environmental Quality
29(4): 1262-1274.
Kuenzler, E.J., etal. 1980. Distributions and Budgets of Carbon, Phosphorus, Iron and
Manganese in a Floodplain Swamp Ecosystem. Water Resources Research Institute Report
157. University of North Carolina, Chapel Hill, NC.
Labbe, T.R., and K.D. Fausch. 2000. "Dynamics of Intermittent Stream Habitat Regulate
Persistence of a Threatened Fish at Multiple Scales." Ecological Applications 10:1774-1791.
Lamoureux, V.S. and D.M. Madison. 1999. "Overwintering Habitats of Radio-Implanted Green
Frogs, Rana clamitans." Journal of Herpetology 33:430-435.
Lande, R., and S. Shannon. 1996. "The Role of Genetic Variation in Adaptation and Population
Persistence in a Changing Environment." Evolution 50:434-437.
Lane, C.R. and E. D'Amico. 2010. "Calculating the Ecosystem Service of Water Storage in
Isolated Wetlands using LiDAR in North Central Florida, USA." Wetlands 30:967-977.
Lang, M., etal. 2012. "Enhanced Detection of Wetland-Stream Connectivity using LiDAR."
Wetlands 32:461-473.
Langston, M.A., and D.M. Kent. 1997. Fish recruitment to a constructed wetland. Journal of
Freshwater Ecology 12:123-129.
Lara, M.J., etal. 2015. "Polygonal Tundra Geomorphological Change in Response to warming
Alters Future CO2 and CH4 flux on the Barrow Peninsula." Global Change Biology 21:1634—
1651.
Larned, S.T., et al 2010. "A Framework of Analyzing Longitudinal and Temporal Variation in
River Flow and Developing Flow-Ecology Relationships." Journal of the American Water
Resources Association 46:541-553.
Lauenroth, W.K., etal. 1999. "The Structure and Function of Ecosystems in the Central North
American Grassland Region. Great Plains Research 9:223-259.
Lefebvre, L., et al. 2013. Channel Classification across Arid West Landscapes in Support of
OHW Delineation. ERDC/CRREL TR-13-3. U.S. Army Corps of Engineers, Hanover, NH.
Lee, T.M., et al. 2010. Effect of Groundwater Levels and Headwater Wetlands on Streamflow in
the Charlie Creek Basin, Peace River Watershed, West-Central Florida. U.S. Geological
Survey Scientific Investigations Report 2010-5189. U.S. Department of the Interior, U.S.
Geological Survey, Reston, VA.
Lehman, P.W., et al. 2008. "The Influence of Floodplain Habitat on the Quantity and Quality of
Riverine Phytoplankton Carbon Produced During the Flood Season in San Francisco
Estuary." Aquatic Ecology 42:363-378.
Lehtinen, R.M., and S.M. Galatowitsch. 2001. "Colonization of Restored Wetlands by
Amphibians in Minnesota." American Midland Naturalist 145:388-396.
Leibowitz, S.G. 2003. "Isolated Wetlands and Their Functions: An Ecological Perspective."
Wetlands 23:517-531.
Leibowitz, S.G., andK.C. Vining. 2003. "Temporal Connectivity in a Prairie Pothole Complex."
Wetlands 23:13-25.
Page 399 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States May 2015
Leibowitz, S.G., etal. 2008. "Non-Navigable Streams and Adjacent Wetlands: Addressing
Science Needs Following the Supreme Court's Rapanos Decision." Frontiers in Ecology and
the Environment 6:3 64-3 71.
Leigh, D. S. 1997. "Mercury-Tainted Overbank Sediment from Past Gold Mining in North
Georgia, USA." Environmental Geology 30:244-251.
Leopold, L.B. 1994. A View of the River. Harvard University Press, Cambridge, MA.
Leopold, L.B., et al. 1964. Fluvial Processes in GeomorphologyGeneml Publishing Co. Ltd.,
Toronto, Canada.
Letcher, B.H., et al. 2007. "Population Response to Habitat Fragmentation in a Stream-Dwelling
Brook Trout Population." PLOS ONE 2:el 139.
Levick, L., etal. 2008. The Ecological and Hydrological Significance of Ephemeral and
Intermittent Streams in the Arid and Semi-arid American Southwest. EPA/600/R-08/134 and
ARS/233046. U.S. Environmental Protection Agency, Office of Research and Development
and U.S. Department of Agriculture/Agricultural Research Service. Southwest Watershed
Research Center, Washington, D.C.
Lichvar, R.W., and S.M. McColley. 2008. A Field Guide to the Identification of the Ordinary
High Water Mark (OHWM) in the Arid West Region of the Western United States: A
Delineation Manual. ERDC/CRREL TR-08-12. U.S. Army Corps of Engineers, Hanover,
NH.
Lichvar, R.W., et al. 2009. Vegetation and Channel Morphology Responses to Ordinary High
Water Discharge Events in Arid West Stream Channels. ERDC/CRREL TR-09-5. U.S. Army
Corps of Engineers, Hanover, NH.
Lide, R.F., et al. 1995. "Hydrology of a Carolina Bay Located on the Upper Coastal Plain of
Western South Carolina." Wetlands 15:47-57.
Liljedahl, A.K., etal. 2012. "Ice-Wedge Polygon Type Controls Low-Gradient Watershed-Scale
Hydrology." Tenth International Conference on Permafrost, Salekhard, Russia, June 25-29,
2012.
Linqvist, O.K., etal. 1991. "Mercury in the Swedish Environment - Recent Research on Causes,
Consequences, and Remedial Measures." Water Air and Soil Pollution 55:xi-xiii.
Lloyd, O.B., and W.L. Lyke. 1995. Ground Water Atlas of the United States, Segment 10,
Illinois, Indiana, Kentucky, Ohio, Tennessee. USGS Hydrologic Investigations Atlas 730-K.
U.S. Department of the Interior, U.S. Geological Survey, Reston, VA.
Lorenz, D.L., etal. 2010. Techniques for Estimating the Magnitude and Frequency of Peak
Flows on Small Streams in Minnesota Based on Data through Water Year 2005. U.S.
Geological Survey Scientific Investigations Report 2009-5250. U.S. Geological Survey,
Reston, VA.
Lytle, D. A., and N. L. Poff 2004. "Adaptation to Natural Flow Regimes." Trends in Ecology
and Evolution 19:94-100.
Lytle, D.A., etal. 2008. "Evolution of Aquatic Insect Behaviors across a Gradient of Disturbance
Predictability." Proceedings of the Royal Society - Series B 275:453-462.
Maine Department of Environmental Protection. 2006. Phosphorus Control Action Plan and
Total Maximum Daily (Annual Phosphorous) Load Report, Daigle Pond, New Canada,
Aroostook County, Maine, Daigle Pond PCAP - TMDL Report, Maine DEPLW - 0789.
Magana, H.A. 2013. "Flood Pulse Trophic Dynamics of Larval Fishes in a Restored Arid-Land
River Floodplain, Middle Rio Grande, Los Lunas, New Mexico." Reviews in Fish Biology
and Fisheries 23:507-521.
Page 400 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Malard, F., etal. 2002. "A Landscape Perspective on Surface-Subsurface Hydrological
Exchanges in River Corridors." Freshwater Biology 47:621-640.
Malard, F., el al. 1999. "Shifting Dominance of Subcatchment Water Sources and Flow Paths in
a Glacial Floodplain, Val Roseg, Switzerland." Arctic, Antarctic, and Alpine Research
31:135-150.
Malard, F., et al. 2006. "Flood-Pulse and Riverscape Dynamics in a Braided Glacier River."
Ecology 87:704-716.
Malmqvist, B. 2002. "Aquatic Invertebrates in Riverine Landscapes." Freshwater Biology
47:679-694.
Marron, D.C. 1989. "The Transport of Mine Tailings as Suspended Sediment in the Belle
Fourche River, West-central South Dakota, USA." International Association of Hydrologic
Sciences 184:19-26.
Marton, J.M., etal. 2014. "USDA Conservation Practices Increase Carbon Storage and Water
Quality Improvement Functions: An Example from Ohio." Restoration Ecology 22:117-124.
Matheney, R.K., and P.J. Gerla. 1996. "Environmental Isotopic Evidence for the Origins of
Ground and Surface Water in a Prairie Discharge Wetland." Wetlands 16:109-120.
Matthai, H.F. 1969. Floods of June 1965 in South Platte River Basin, Colorado. Water Supply
Paper 1850-B. U.S. Geological Survey, Washington, D.C.
Matheney, M.P., and C.F. Rabeni. 1995. "Patterns of Movement and Habitat use by Northern
Hogsuckers in an Ozark Stream. Transactions of the American Fisheries Society 124:886-
897.
Matthews, W.J. 1988. "North American Prairie Streams as Systems for Ecological Study."
Journal of the North American Benthological Society 7:387-409.
Matthews, W.J., and H.W. Robinson. 1998. "Influence of Drainage Connectivity, Drainage Area
and Regional Species Richness on Fishes of the Interior Highlands in Arkansas." American
Midland Naturalist 139:1-19.
Matthews, W.J., et al. 1985. "Fishes of Oklahoma springs." Southwestern Naturalist 30:23-32.
Matthews, W.J., et al. 2005. "Southern Plains Rivers." Pages 283-325 in Rivers of North
America. A.C. Benke and C.E. Cushing, editors. Elsevier Academic Press, Burlington, MA.
May, C.L., and R.E. Gresswell. 2003. "Processes and Rates of Sediment and Wood
Accumulation in Headwater Streams of the Oregon Coast Range, USA." Earth Surface
Processes andLandforms 28:409-424.
May, C.L., and D.C. Lee. 2004. "The Relationship among In-Channel Sediment Storage, Pool
Depth, and Summer Survival of Juvenile Salmonids in Oregon Coast Range Streams." North
American Journal of Fisheries Management 24:761-774.
McClain, M.E., et al. 2003. "Biogeochemical Hot Spots and Hot Moments at the interface of
Terrestrial and Aquatic Ecosystems." Ecosystems 6:301-312.
McDonough, O. T., etal. 2015. "Surface Hydrologic Connectivity between Delmarva Bay
Wetlands and Nearby Streams Along a Gradient of Agricultural Alteration." Wetlands
35(l):41-53.
McEachern, P., etal. 2006. "Landscape Control of Water Chemistry in Northern Boreal Streams
of Alberta." Journal of Hydrology 323:303-324.
McGlynn, B.L., and J J. McDonnell. 2003. "Quantifying the Relative Contributions of Riparian
and Hillslope Zones to Catchment Runoff." Water Resources Research 39:1310.
McGlynn, B.L., etal. 2004. "Scale Effects on Headwater Catchment Runoff Timing, Flow
Sources, and Groundwater-Streamflow Relations." Water Resources Research. 40:W07504.
Page 401 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States May 2015
McGuire, K.J., el al. 2005. "The Role of Topography on Catchment-Scale Water Residence
Time." Water Resources Research 41:W05002.
McLaughlin, D.L., et al. 2014. "A Significant Nexus: Geographically Isolated Wetlands
Influence Landscape Hydrology." Water Resources Research 50:7153-7166.
McLaughlin, J.W., etal. 2011. "Biogeochemical Cycling and Chemical Fluxes in a Managed
Northern Forested Wetland, Michigan, USA." Forest Ecology and Management 261:649-
661.
Meffe, G.K. 1984. "Effects of Abiotic Disturbance on Coexistence of Predator-Prey Fish
Species." Ecology 65:1525-1534.
Merriam, J.L, et al. 2002. "Characterizing Nitrogen Dynamics, Retention and Transport in a
Tropical Rainforest Stream Using an in situ N-15 Addition." Freshwater Biology 47:143-
160.
Mersel, M.K., and R.W. Lichvar. 2014. A Guide to Ordinary High Water Mark (OHWM)
Delineation for Non-perennial Streams in the Western Mountains, Valleys, and Coast Region
of the United States. ERDC/CRREL TR-14-13. U.S. Army Corps of Engineers, Hanover,
NH.
Mertes, L.A.K., et al. 1995. "Spatial Patterns of Hydrology, Geomorphology, and Vegetation on
the Floodplain of the Amazon River in Brazil from a Remote Sensing Perspective."
Geomorphology 13:215-232.
Mertes, L.A.K. 1997. "Documentation and Significance of the Perirheic Zone." Water Resources
Research 33:1749-1762.
Meyboom, P. 1964. "Three Observations on Streamflow Depletion by Phreatophytes." Journal
of Hydrology 2:248-261.
Meyer, A., et al. 2004. "The Effect of Low Flow and Stream Drying on the Distribution and
Relative Abundance of the Alien Amphipod, Echinogammarus berilloni (Catta, 1878) in a
Karstic Stream System (Westphalia, Germany)." Crustaceana 77:909-922.
Meyer, J.L. 1994. "The Microbial Loop in Flowing Waters." Microbial Ecology 28:195-199.
Meyer, J.L., and G.E. Likens. 1979. "Transport and Transformation of Phosphorus in a Forest
Stream Ecosystem." Ecology 60:1255-1269.
Meyer, J.L., and J.B. Wallace. 2001. "Lost Linkages and Lotic Ecology: Rediscovering Small
Streams." Pages 295-317 in Ecology: Achievement and Challenge. M. C. Press, N. J. Huntly,
and S. Levin, editors. Blackwell Science, Oxford, UK.
Meyer, J.L., et al. 1998. "Leaf Litter as a Source of Dissolved Organic Carbon in Streams."
Ecosystems 1:240-249.
Meyer, J.L., et al. 2007. "The Contribution of Headwater Streams to Biodiversity in River
Networks." Journal of the American Water Resources Association 43(1): 86-103.
Michigan Department of Environmental Quality. "Seepage Through Earth Dams." Last updated
September 10, 2013. https://www.michigan.gOv/deq/0.4561.7-135-3313 3684 3723-9536—
.00. html.
Michigan Natural Features Inventory. 2010. Patterned Fen: Community Abstract. Michigan
State University Extension, Lansing, MI.
Middleton, B. 2000. "Hydrochory, Seed Banks, and Regeneration Dynamics along the
Landscape Boundaries of aForested Wetland." Plant Ecology 146:169-184.
Mierle, G., and R. Ingram. 1991. "The Role of Humic Substances in the Mobilization of Mercury
from Watersheds." Water Air and Soil Pollution 56:349-357.
Page 402 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Miller, E.L., et al. 1988. "Forest Harvest and Site Preparation Effects on Stormflow and
Peakflow of Ephemeral Streams in the Ouachita Mountains." Journal of Environmental
Quality 17:212-218.
Minshall, G.W. 1967. "Role of Allochthonous Detritus in the Tropic Structure of a Woodland
Springbrook Community." Ecology 48:139-149.
Mitsch, W.J., et al. 1995. "Phosphorus Retention in Constructed Freshwater Riparian Marshes."
Ecological Applications 5:830-845.
Mitsch, W.J., et al. 2001. "Reducing Nitrogen Loading to the Gulf of Mexico from the
Mississippi River Basin: Strategies to Counter a Persistent Ecological Problem." Bioscience
51(5): 373-388.
Mitsch, W.J., et al. 2009. Wetland Ecosystems. 1st edition. John Wiley & Sons, Hoboken, NJ.
Mitsch, W.J., and J.G. Gosselink. 2007. Wetlands, 4th edition. John Wiley & Sons Inc.,
Hoboken, NJ.
Mock, S.J. 1971. "A Classification Channel Links in Stream Networks." Water Resources
Research 7:1558-1566.
Moll, D. 1990. "Population Sizes and Foraging Ecology in a Tropical Freshwater Stream Turtle
Community." Journal of Herpetology 24:48-53.
Montgomery, D.R. 1999. "Process Domains and the River Continuum." Journal of the American
Water Resources Association 35:397-410.
Moore, D. J., and J. Ross. 2010. Spokane River and Lake Spokane Dissolved Oxygen Total
Maximum Daily Load: Water Quality Improvement Report. Publication No. 07-10-073.
Washington State Department of Ecology, Spokane, WA,
Moraghan, J.T. 1993. "Loss and Assimilation of 15N-nitrate Added to a North Dakota Cattail
Marsh," Aquatic Botany 46:225-234.
Moreno-Mateos, D., el al. 2008. "Relationships between Landscape Pattern, Wetland
Characteristics, and Water Quality in Agricultural Catchments." Journal of Environmental
Quality 37:2170-2180.
Morita, K., and S. Yamamoto. 2002. "Effects of Habitat Fragmentation by Damming on the
Persistence of Stream-dwelling Charr Populations." Conservation Biology 16:1318-1323.
Morley, T.R., et al. 2011. "The Role of Headwater Wetlands in Altering Streamflow and
Chemistry in a Maine, USA Catchment." Journal of the American Water Resources
Association 47:337-349.
Moscrip, A.L., and D.R. Montgomery. 1997. "Urbanization, Flood Frequency, and Salmon
Abundance in Puget Lowland Streams." Journal of the American Water Resources
Association 33:1289-1297 (1997).
Moulton, D.W., and J.S. Jacob.200. Texas Coastal Wetlands Guidebook. TAMU-SG-00-605.
Texas Sea Grant College Program, College Station, TX. 66 pp.
Mueller, M.H., and A.G. van der Valk. 2002. "The Potential Role of Ducks in Wetland Seed
Dispersal." Wetlands 22:170-178.
Mulholland, P.J. 2004. "The Importance of In-stream Uptake for Regulating Stream
Concentrations and Outputs of N and P from a Forested Watershed: Evidence from Long-
Term Chemistry Records for Walker Branch Watershed." Biogeochemistry 70:403-426.
Mulholland, P.J., and E.J. Kuenzler. 1979. "Organic Carbon Export from Upland and Forested
Wetland Watersheds." Limnology and Oceanography 24:960-966.
Page 403 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States May 2015
Mulholland, P.J., and W.R. Hill. 1997. "Seasonal Patterns in Stream water Nutrient and
Dissolved Organic Carbon Concentrations: Separating Catchment Flow Path and In-Stream
Effects." Water Resources Research 33:1297-1306.
Mulholland, P.J., et al. 1988. "Production of Soluble, High Molecular Weight Phosphorus and Its
Subsequent Uptake by Stream Detritus." Verhandlungen des Internationalen Verein
Limnologie 23:1190-1197.
Mulholland, P.J., et al. 1995. "Longitudinal Patterns of Nutrient Cycling and Periphyton
Characteristics in Streams: a Test of Upstream-Downstream Linkage." Journal of the North
American Benthological Society 14:357-370.
Mulholland, P.J., et al. 2008. "Stream Denitrification across Biomes and Its Response to
Anthropogenic Nitrate Loading." Nature 452:202-205.
Mulhouse, J.M., and S.M. Galatowitsch. 2003. "Revegetation of Prairie Pothole Wetlands in the
Midcontinental US: Twelve Years Post-Reflooding." Plant Ecology 169:143-159.
Miiller, K. 1982. "The Colonization Cycle of Insects." Oecologia 53:202-207.
Murkin, H.R., and P.J. Caldwell. 2000. "Avian Use of Prairie Wetlands." Pages. 249-286 in
Prairie Wetland Ecology: The Contribution of the Marsh Ecology Research Program. H.R.
Murkin, et al., ed. Iowa State University Press, Ames, IA.
Murphy, R.R., et al. 2011. "Long-Term Trends in Chesapeake Bay Seasonal Hypoxia,
Stratification, and Nutrient Loading." Estuaries and Coasts 34(6): 1293-1309.
Nadeau, T.L., and M.C. Rains. 2007. "Hydrological Connectivity Between Headwater Streams
and Downstream Waters: How Science Can Inform Policy." Journal of the American Water
Resources Association 43:118-133.
Naiman, R.J., and R.E. Bilby. 1998. River Ecology and Management: Lessons from the Pacific
Coastal Ecoregion. Springer-Verlag, New York, NY.
Naiman, R.J., and H. Decamps. 1997. "The Ecology of Interfaces: Riparian Zones." Annual
Review of Ecology and Systematics 28:621-658.
Naiman, R.J., et al. 2005. Riparia: Ecology, Conservation, and Management of Streamside
Communities. Elsevier, Inc., Burlington, MA.
Nakamura, F., and F.J. Swanson. 1993. "Effects of Coarse Woody Debris on Morphology and
Sediment Storage of a Mountain Stream System in Western Oregon." Earth Surface
Processes and Landforms 18:43-61.
Nakano, S., and M. Murakami. 2001. "Reciprocal Subsidies: Dynamic Interdependence between
Terrestrial and Aquatic Food Webs." Proceedings of the National Academy of Sciences USA
98:166-170.
Nanson, G.C., and J.C. Croke. 1992. "A Genetic Classification of Floodplains." Geomorphology
4:459-486.
National Research Council. 1995. Wetlands: Characteristics and Boundaries. National Academy
Press, Washington, D.C.
National Research Council. 1997. Watershed Research in the U.S. Geological Survey. National
Academy Press, Washington, D.C.
National Research Council. 2002. Riparian Areas: Functions and Strategies for Management.
National Academy Press, Washington, D.C.
Natural Resources Conservation Service. "Web Soil Survey." U.S. Department of Agriculture.
http://websoilsurvev.sc.egov.usda.gov/App/HomePage.htm. Last updated December 6, 2013.
Newbold, J.D., et al. 1981. "Measuring Nutrient Spiraling in Streams." Canadian Journal of
Fisheries and Aquatic Sciences 38:860-863.
Page 404 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Newbold, J.D., etal. 1982a. "Organic Carbon Spiralling in Stream Ecosystems." Oikos 38:266-
272.
Newbold, J.D., etal. 1982b. "Nutrient Spiraling in Streams: Implications for Nutrient Limitation
and Invertebrate Activity." The American Naturalist 120:628-665.
Newbold, J.D., et al. 1983. "Phosphorus Dynamics in a Woodland Stream Ecosystem: a Study
of Nutrient Spiraling." Ecology 64:1249-1265.
Newbold, J.D., et al. 2010. "Water Quality Functions of a 15-Year-Old Riparian Forest Buffer
System." Journal of the American Water Resources Association 46:299-310.
Newman, D.G., and C.R. Griffin. 1994. "Wetland Use by River Otters in Massachusetts."
Journal of Wildlife Management 58:18-23.
NHD. 2008. National Hydrography Dataset. U.S. Geological Survey.
Nilsson, C., et al. 2005. "Fragmentation and Flow Regulation of the World's Large River
Systems." Science 308(5720):405-408.
Nilsson, C., et al. 2010. "The Role of Hydrochory in Structuring Riparian and Wetland
Vegetation." Biological Reviews 85:837-858.
Nixon, S.J., and V.J. Lee. 1986. Wetlands and Water Quality: A Regional Review of Recent
Research in the United States on the Role of Freshwater and Saltwater Wetlands as Sources,
Sinks, and Transformers of Nitrogen, Phosphorus, and Various Heavy Metals, Technical
Report Y-86-2. U.S. Army Corp of Engineers, Waterways Experiment Station, Vicksburg,
MS.
Novitzki, R.P. 1979. "Hydrologic Characteristics of Wisconsin's Wetlands and Their Influence
on Floods," in P. Greeson, et al., ed., Wetland Functions and Values: The State of Our
Understanding, Proceedings of the National Symposium on Wetlands (Minneapolis, MN:
American Water Resources Association), pp. 377-388.
Nuff, J.C., and G.P. Asner. 2001. "Dissolved Organic Carbon in Terrestrial Ecosystems:
Synthesis and a Model." Ecosystems 4:29-48.
O'Connor, T., and D. Whitall. 2007. "Linking Hypoxia to Shrimp Catch in the Northern Gulf of
Mexico." Marine Pollution Bulletin 54 (4):460-463.
O'Driscoll, M.A., and D.R. DeWalle. 2010. "Seeps Regulate Stream Nitrate Concentration in a
Forested Appalachian Catchment." Journal of Environmental Quality 39:420-431.
O'Driscoll, M.A., and R.R. Parizek, "The Hydrologic Catchment Area of a Chain of Karst
Wetlands in Central Pennsylvania, USA." Wetlands 23:171-79 (2003).
Obolewski, K., et al. 2009. "Effect of Hydrological Connectivity on the Molluscan Community
Structure in Oxbow Lakes of the Lyna River." Oceanological and Hydrobiological Studies
38:75-88.
Odum, W.E. 1988. "Non-Tidal Freshwater Wetlands in Virginia." Virginia Journal of Natural
Resources Law 7: 421-434.
Omernik, J.M., and R.G. Bailey. 1997. "Distinguishing Between Watersheds and Ecoregions."
Journal of the American Water Resources Association 33.5: 939-40.
Orr, C.H., etal. 2014. "Spatial Autocorrelation of Denitrification in a Restored and a Natural
Floodplain." Wetlands 34:89-100.
Osborne, L.L., and D.A. Kovacic. 1993. "Riparian Vegetated Buffer Strips in Water-Quality
Restoration and Stream Management." Freshwater Biology 29(2): 243-258.
Osterkamp, W.R. 2008. Annotated Definitions of Selected Geomorphic Terms and Related Terms
of Hydrology, Sedimentology, Soil Science and Ecology. USGS Open File Report 2008-1217.
U.S. Department of the Interior, U.S. Geological Survey, Reston, VA.
Page 405 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Paterson, KG., and J.L. Schnoor. 1992. "Fate of Alachlor and Atrazine in a Riparian Zone Field
Site." Water Environment Research 64:274-283.
Patten, D.T., etal. 2008. "Isolated Spring Wetlands in the Great Basin and Mojave Deserts,
USA: Potential Response of Vegetation to Groundwater Withdrawal." Environmental
Management 41:398-413.
Pattenden, R.K., and D.A. Boag. 1989. "Skewed Sex Ratio in a Northern Wintering Population
of Mallards." Canadian Journal of Zoology 67:1084-1087.
Paul, M. J., et al. 2006. "Leaf Breakdown in Streams Differing in Catchment Land Use."
Freshwater Biology 51:1684-1695.
Pease, A.A., et al. 2006. "Habitat and Resource Use by Larval and Juvenile Fishes in an Arid-
land River (Rio Grande, New Mexico)." Freshwater Biology 51:475-486.
Perkin, J.S., and K.B. Gido. 2011. "Stream Fragmentation Thresholds for a Reproductive Guild
of Great Plains Fishes." Fisheries 36:371-383.
Peterson, B.J., et al. 2001. "Control of Nitrogen Export from Watersheds by Headwater
Streams." Science 292: 86-90.
Peterson, E.E., et al. 2007. "Geostatistical Modelling on Stream Networks: Developing Valid
Covariance Matrices Based on Hydrologic Distance and Stream Flow." Freshwater Biology
52:267-279.
Petranka, J.W., and C.T. Holbrook. 2006. "Wetland Restoration for Amphibians: Should Local
Sites Be Designed to Support Metapopulations or Patchy Populations?" Restoration Ecology
14:404-411.
Phillips, P.J., and R.J. Shedlock. 1993. "Hydrology and Chemistry of Groundwater and Seasonal
Ponds in the Atlantic Coastal-Plain in Delaware, USA." Journal of Hydrology 141:157-178.
Phillips, R.W., et al. 2011. "Connectivity and Runoff Dynamics in Heterogeneous Basins."
HydrologicalProcesses 25(19): 3061-3075.
Pires, A.M., etal. 1999. "Seasonal Changes in Fish Community Structure of Intermittent
Streams in the Middle Reaches of the Guadiana Basin, Portugal." Journal of Fish Biology
54:235-249.
Platania, S.P., and C.S. Altenbach. 1998. "Reproductive Strategies and Egg Types of Seven Rio
Grande Basin Cyprinids." Copeia 1998:559-569.
Poff, N.L. 1996. "A Hydrogeography of Unregulated Streams in the United States and an
Examination of Scale Dependence in Some Hydrological Descriptors." Freshwater Biology
36:71-91.
Poff, N.L., et al. 2007. "Homogenization of Regional River Dynamics by Dams and Global
Biodiversity Implications." Proceedings of the National Academy of Sciences of the United
States of America 104: 5732-5737.
Pollux, B.J.A., etal. 2007. "Consequences of Intraspecific Seed-Size Variation in Sparganium
emersum for Dispersal by Fish." Functional Ecology 21:1084-1091.
Poole, G.C. 2010. "Stream Hydrogeomorphology as a Physical Science Basis for Advances in
Stream Ecology." Journal of the North American Benthological Society 29:12-25.
Poole, G.C., etal. 2006. "Multiscale Geomorphic Drivers of Groundwater Flow Paths:
Subsurface Hydrologic Dynamics and Hyporheic Diversity." Journal of the North American
Benthological Society 25:288-303.
Power, G., et al. 1999. "Groundwater and Fish: Insights from Northern North America."
Hydrological Processes 13:401 -422
Page 406 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Power, M.E., and W.E. Dietrich. 2002. "Food Webs in River Networks." Ecological Research
17:451-471.
Power, M.E., etal. 1995a. "How does floodplain width affect floodplain river ecology? A
preliminary exploration using simulations." Geomorphology 13:301-317.
Power, M.E., etal. 1995b. "Hydraulic food-chain models." BioScience 45:159-167.
Powers, S.M., etal. 2012. "Nutrient Retention and the Problem of Hydrologic Disconnection in
Streams and Wetlands." Ecosystems 15:435-449.
Pringle, C.M. 2001. "Hydrologic Connectivity and the Management of Biological Reserves: A
Global Perspective." Ecological Applications 11:981-998.
Progar, D. J., and A.R. Modenke. 2002. "Insect Production from Temporary and Perennially
Flowing Headwater Streams in Western Oregon." Journal of Freshwater Ecology 17:391-
407.
Prouty, W.F. 1952. "Carolina Bays and Their Origin." Bulletin of the Geological Society of
America 63:167-224.
Pyke, C.R. 2004. "Simulating Vernal Pool Hydrologic Regimes for Two Locations in California,
USA." Ecological Modelling 173:109-127.
Pyzoha, J.E., et al. 2008. "A Conceptual Hydrologic Model for a Forested Carolina Bay
Depressional Wetland on the Coastal Plain of South Carolina, USA." Hydrological
Processes 22:2689-2698.
Rabalais, N.N., et al. 2002. "Gulf of Mexico Hypoxia, a.k.a. 'the Dead Zone." Annual Review of
Ecology and Systematics 33:235-263.
Rahel, F.J. 2007. "Biogeographic Barriers, Connectivity and Homogenization of Freshwater
Faunas: It's a Small World after All." Freshwater Biology 52(4): 696-710.
Rains, M.C., et al. 2006. "The Role of Perched Aquifers in Hydrological Connectivity and
Biogeochemical Processes in Vernal Pool Landscapes, Central Valley, California."
Hydrological Processes 20:1157-1175.
Rains, M.C., et al. 2008. "Geological Control of Physical and Chemical Hydrology in California
Vernal Pools." Wetlands 28:347-362.
Rassam, D.W., et al. 2006. "The Hydrology of Riparian Buffer Zones; Two Case Studies in an
Ephemeral and a Perennial Stream." Journal of Hydrology 325:308-324.
Reckendorfer, W., etal. 2006. "Floodplain Restoration by Reinforcing Hydrological
Connectivity: Expected Effects on Aquatic Mollusc Communities." Journal of Applied
Ecology 43:474-484.
Reddy, K.R. and R.D. DeLaune. 2008. Biogeochemistry of Wetlands: Science and Applications.
774 p. CRC Press, Boca Raton, FL.
Reddy, K.R., et al. 1999. "Phosphorus Retention in Streams and Wetlands: A Review." Critical
Reviews in Environmental Science and Technology 29:83-146 (1999).
Reed, D.J., etal. 2006. "Reducing the Effects of Dredged Material Levees on Coastal Marsh
Function: Sediment Deposition and Nekton Utilization." Environmental Management
37(5):671-685.
Reneau, S.L., et al. 2004. "Geomorphic Controls on Contaminant Distribution along an
Ephemeral Stream." Earth Surface Processes andLandforms 29:1209-1223.
Rheinhardt, R.D., et al. 2002. A Regional Guidebook for Applying the Hydrogeomorphic
Approach to Assessing Wetland Functions of Wet Pine Flats on Mineral Soils in the Atlantic
and Gulf Coastal Plains. ERDC/EL TR-02-9, U.S. Army Corps of Engineers, Vicksburg,
MS.
Page 407 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Rhoads, B.L. 1987. "Changes in Stream Channel Characteristics at Tributary Junctions."
Physical Geography 8:346-367.
Richardson, C.J. 1983. "Pocosins: Vanishing Wastelands or Valuable Wetlands? Bioscience
33:626-633.
Richardson, C.J. 2003. "Pocosins: Hydrologically Isolated or Integrated Wetlands on the
Landscape?" Wetlands 23(3):563-576.
Richardson, C.J. 2012. "Pocosins." Pages 189-202 in A.H. Baldwin and D. Batzer, editors.
Wetland Habitats of North America: Ecology and Conservation Concerns. University of
Califonia Press, Berkley, CA.
Richardson, J.S., et al. 2005. "Riparian Communities Associated with Pacific Northwest
Headwater Streams: Assemblages, Processes, and Uniqueness." Journal of the American
Water Resources Association 41:935-947.
Rice, S.P., et al. 2008. "The Ecological Importance of Tributaries and Confluences." Pages 209-
242 in River Confluences, Tributaries and the Fluvial Network. S.P. Rice, et al., ed. John
Wiley & Sons, Chichester, UK.
Rinne, J.N., andD. Miller. 2006. "Hydrology, Geomorphology and Management: Implications
for Sustainability of Native Southwestern Fishes." Reviews in Fisheries Science 14:91-110.
Robinson, C.T., et al. 2002. "The Fauna of Dynamic Riverine Landscapes." Freshwater Biology
47:661-677.
Rodriguez-Iturbe, I.R., et al. 2009. "River Networks as Ecological Corridors: A Complex
Systems Perspective for Integrating Hydrologic, Geomorphologic, and Ecologic Dynamics."
Water Resources Research 45:W01413.
Rooney, R.C., et al. 2013. "River connectivity affects submerged and floating aquatic vegetation
in floodplain wetlands." Wetlands 33:1165-1177.
Roscher, J.P. 1967. "Alga Dispersal by Muskrat Intestinal Contents." Transactions of the
American Microscopical Society 86:497-498.
Rosenberry, D.O. and T.C. Winter. 1997. "Dynamics of Water-Table Fluctuations in an Upland
between Two Prairie-Pothole Wetlands in North Dakota," Journal of Hydrology 191:266-
289.
Roy, A.G., and M.J. Woldenberg. 1986. "A Model for Changes in Channel Form at a River
Confluence." Journal of Geology 94:402-411.
Royer, T.V., et al. 2004. "Transport and Fate of Nitrate in Headwater Agricultural Streams in
Illinois. Journal of Environmental Quality 33:1296-1304.
Saco, P. M., and P. Kumar. 2002. "Kinematic dispersion in stream networks coupling hydraulics
and network geometry." Water Resources Research 38:1244.
Sawin, R.S., et al. 1999. "Flint Hills Springs." Transactions of the Kansas Academy of Science
102:1-31.
Schalk, C.M., and T.M. Luhring. 2010. "Vagility of Aquatic Salamanders: Implications for
Wetland Connectivity." Journal of Herpetology 44:104-109.
Schindler, D.E., etal. 2005. "Marine-Derived Nutrients, Commercial Fisheries, and Production
of Salmon and Lake Algae in Alaska." Ecology 86:3225-3231.
Schindler, D.W., and P.J. Curtis. "The Role of DOC in Protecting Freshwaters Subjected to
Climate Warming and Acidification from UV Exposure." Biogeochemistry 36:1-8.
Schlesinger, W.H., and C.S. Jones. 1984. "The Comparative Importance of Overland Runoff and
Mean Annual Rainfall to Shrub Communities of the Mojave Desert." Botanical Gazette
145:116-124.
Page 408 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Schlosser, I.J. 1991. "Stream Fish Ecology: A Landscape Perspective." Bioscience 41(10):704-
712.
Schmidt, J.P., etal. 2007. "Nitrogen Export from Coastal Plain Field Ditches." Journal of Soil
and Water Conservation 62(4):23 5-243.
Schneider, R.L., and R.R. Sharitz. 1988. "Hydrochory and Regeneration in a Bald Cypress Water
Tupelo Swamp Forest." Ecology 69:1055-1063.
Schramm, H.L., and M. A. Eggleton. 2006. "Applicability of the Flood-Pulse Concept in a
Temporal Floodplain River Ecosystem: Thermal and Temporal Components." River
Research and Applications 22:543-553.
Schroder, B. 2006. "Pattern, Process, and Function in Landscape Ecology and Catchment
Hydrology— How Can Quantitative Landscape Ecology Support Predictions in Ungauged
Basins? Hydrology and Earth System Sciences 10:967-979.
Schwalb, A.N., et al. 2010. "Dispersion of Freshwater Mussel Larvae in a Lowland River."
Limnology and Oceanography 55:628-638.
Schwartz, S.S., and D.G. Jenkins. 2000. "Temporary Aquatic Habitats: Constraints and
Opportunities." Aquatic Ecology 34:3-8.
Scrivener, J.C., etal. 1994. "Juvenile Chinook salmon (Oncorhynchus tshawytscha) utilization
of Hawks Creek, a small and nonnatal tributary of the Upper Fraser River." Canadian
Journal of Fisheries and Aquatic Sciences 51:1139-1146.
Sear, D.A., et al. 2010. "Log Jam Controls on Channel: Floodplain Interactions in Wooded
Catchments and Their Role in the Formation of Multi-Channel Patterns. Geomorphology
116:305-319.
Seitzinger, S.P., etal. 2002. "Bioavailability of DON from Natural and Anthropogenic Sources
to Estuarine Plankton." Limnology and Oceanography 47:353-366.
Semlitsch, R.D. 2008. "Differentiating Migration and Dispersal Processes for Pond-Breeding
Amphibians." The Journal of Wildlife Management 72:260-267.
Semlitsch, R.D., and J.R. Bodie. 2003. "Biological Criteria for Buffer Zones around Wetlands
and Riparian Habitats for Amphibians and Reptiles." Conservation Biology 17:1219-1228.
Serfass, T. L., etal. 1999. "Status and Distribution of River Otters in Pennsylvania following a
Reintroduction Project." Journal of the Pennsylvania Academy of Science 73:10-14.
Shanks, C.E., and G.C. Arthur. 1952. "Muskrat Movements and Population Dynamics in
Missouri Farm Ponds and Streams." Journal of Wildlife Management 16:138-148.
Sharitz, R.R. 2003. "Carolina Bay Wetlands: Unique Habitats of the Southeastern United
States." Wetlands 23:550-562.
Sharitz, R.R., and J.W. Gibbons. 1982. The Ecology of Southeastern Shrub Bogs (Pocosins) and
Carolina Bays: A Community Profile. FWS/OBS-82/04, U.S. Department of the Interior,
U.S. Fish and Wildlife Services Program, Washington, DC.
Sharpley, A.N., and S. Rekolainen. 1997. "Phosphorus in Agriculture and Its Environmental
Implications." Pages 1-54 in Phosphorus Losses from Soil to Water. H. Tunney, et al., ed.
CAB International, Cambridge, UK.
Shaw, J.R., and D.J. Cooper. 2008. "Linkages among Watersheds, Stream Reaches, and Riparian
Vegetation in Dryland Ephemeral Stream Networks." Journal of Hydrology 350:68-82.
Shedlock, R.J., etal. 1993. "Interactions between Ground-Water and Wetlands, Southern Shore
of Lake-Michigan, USA," Journal of Hydrology 141:127-55.
Sheldon, A. L. 1988. "Conservation of Stream Fishes: Patterns of Diversity, Rarity, and Risk."
Conservation Biology 2:149-156.
Page 409 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States May 2015
Shook, K.R., and J.W. Pomeroy. 2011. "Memory Effects of Depressional Storage in Northern
Prairie Hydrology." HydrologicalProcesses 25:3890-3898.
Shoup, D.E., and D. H. Wahl. 2009. "Fish diversity and abundance in relation to interannual and
lakespecific variation in abiotic characteristics of floodplain lakes of the lower Kaskaskia
River, Illinois." Transactions of the American Fisheries Society 138:1076-1092.
Simenstad, C., etal. 1999. "Preliminary Results from the Sacramento-San Joaquin Delta
Breached Levee Wetland Study." Interagency Ecological Program for the Sacramento-San
Joaquin Estuary Newsletter 12(4): 15 -21.
Simmons, J. A. 2010. "Phosphorus Removal by Sediment in Streams Contaminated with Acid
Mine Drainage." Water Air and Soil Pollution 209:123-132.
Sipocz A. 2002. "Southeast Texas Isolated Wetlands and Their Role in Maintaining Estuarine
Water Quality." Paper presented at "The Coastal Society 2002 Conference: Converging
Currents: Science, Culture, and Policy at the Coast," Galveston, Texas.
Sipocz A. 2005. "The Galveston Bay Wetland Crisis." National Wetlands Newsletter 27: 1,17—
18.
Sjodin, A., et al. 2001. "Analysis of Groundwater Exchange for a Large Plains River in Colorado
(USA)." Hydrological Processes 15:609-620.
Smiley, P.C., Jr., etal. 2008. "Contribution of Habitat and Water Quality to the Integrity of Fish
Communities in Agricultural Drainage Ditchesn" Journal of Soil and Water Conservation
63(6):218A-219A.
Smith, D.W., and W.L. Verrill. 1998. "Vernal Pool-Soil-Landform Relationships in the Central
Valley, California." Pages 15-23 in Ecology, Conservation, and Management of Vernal Pool
Ecosystems - Proceedings from a 1996 Conference. C.W. Witham, etal., editors. California
Native Plant Society, Sacramento, CA.
Smith, M.A., and D.M. Green. 2005. "Dispersal and the Metapopulation Paradigm in Amphibian
Ecology and Conservation: Are All Amphibian Populations Metapopulations?" Ecography
28 (1): 110-128.
Smith, R.D., and C.V. Klimas. 2002. A Regional Guidebook for Applying the Hydrogeomorphic
Approach to Assessing Wetland Functions of Selected Regional Wetland Subclasses, Yazoo
Basin, Lower Mississippi River Alluvial Valley. ERDC/EL TR-02-4. U.S. Army Corps of
Engineers, Vicksburg, MS.
Smith, R.D., etal. 1995. An Approach for Assessing Wetland Functions Using Hydrogeomorphic
Classification, Reference Wetlands, and Functional Indices. Wetlands Research Program
Technical Report WRP-DE-9. U.S. Army Corps of Engineers, Waterways Experiment
Station, Wetlands Research Program, Vicksburg, MS.
Smith, S.M., etal. 2008. "Development of Vegetation in Dune Slack Wetlands of Cape Cod
National Seashore (Massachusetts, USA)." Plant Ecology 194(2): 243-256.
Smith, S. V., et al. 2002. "Distribution and Significance of Small, Artificial Water Bodies Across
the United States Landscape." The Science of the Total Environment 299:21-36.
Smock, L.A. 1994. "Movements of invertebrates between stream channels and forested
Floodplains." Journal of the North American Benthological Society 13:524-531.
Smock, L.A., etal. 1992. "Lotic Macroinvertebrate Production in Three Dimensions: Channel
Surface, Hyporheic, and Floodplain Environments." Ecology 73:876-886.
Snodgrass, J.W., etal. 1996. "Factors Affecting the Occurrence and Structure of Fish
Assemblages in Isolated Wetlands of the Upper Coastal Plain, USA." Canadian Journal of
Fisheries and Aquatic Sciences 53:443-454 (1996).
Page 410 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States May 2015
Snodgrass, J.W., etal. 2000. "Relationships among Isolated Wetland Size, Hydroperiod, and
Amphibian Species Richness: Implications for Wetland Regulations." Conservation Biology
14:414-419.
Soons, M.B. 2006. "Wind Dispersal in Freshwater Wetlands: Knowledge for Conservation and
Restoration." Applied Vegetation Science 9:271-278.
Soons, M.B., and G.W. Heil. 2002. "Reduced Colonization Capacity in Fragmented Populations
of Wind-Dispersed Grassland Forbs." Journal of Ecology 90:1033-1043.
Sophocleous, M. 2010. "Review: Groundwater Management Practices, Challenges, and
Innovations in the High Plains Aquifer, USA—Lessons and Recommended Actions.
Hydrogeology Journal 18:559-575.
Spinola, R. M., et. al. 2008. "Survival and Post-Release Movements of River Otters Translocated
to Western New York. Northeastern Naturalist 15:13-24.
Stanford, J. A., and J.V. Ward. 1984. "The Effects of Regulation on the Limnology of the
Gunnison River: A North American Case History." Pages 467-480 in Regulated Rivers.
Proceedings of the Second International Symposium on Regulated Streams, Oslo, August
1982. A. Lillehammer and S. J. Salveit, ed. Universitetsforlaget AS, Oslo, Norway.
Stanford, J.A., and J.V. Ward. 1993. "An Ecosystem Perspective of Alluvial Rivers:
Connectivity and the Hyporheic Corridor." Journal of the North American Benthological
Society 12:48-60.
Stanley, E.H., etal. 1997. "Ecosystem Expansion and Contraction in Streams." BioScience
47:427-435.
State of Ohio Environmental Protection Agency. 2003. Nonpoint Source Impacts on Primary
Headwater Streams. Ohio Environmental Protection Agency, Columbus, OH.
http://www.epa.state.oh.us/portals/35/wcis/headwaters/HWH nonpoint ian2003.pdf.
Stead, T.K., etal. 2005. "Secondary Production of a Stream Metazoan Community: Does the
Meiofauna Make a Difference?," Limnology and Oceanography 50:398-403.
Steen, D.A., et al. 2012. "Terrestrial Habitat Requirements of Nesting Freshwater Turtles."
Biological Conservation 150 (1): 121-128.
Stevenson, R.J. and F.R. Hauer. 2002. "Integrating Hydrogeomorphic and Index of Biotic
Integrity Approaches for Environmental Assessment of Wetlands," Journal of the North
American Benthological Society 21(3): 502-513.
Steward, A.L., et al. 2012. "When the River Runs Dry: Human and Ecological Values of Dry
Riverbeds." Frontiers in Ecology and the Environment 10:202-209.
Stolt, M.H., and M.C. Rabenhorst. 1987a. "Carolina Bays on the Eastern Shore of Maryland: 1.
Soil Characterization and Classification." Soil Science Society of America Journal 57:394-
398.
Strahler, A.N. 1957. "Quantitative Analysis of Watershed Geomorphology." American
Geophysical Union Transactions 38:913-920.
Strock, J.S. et al. 2007. "Managing Natural Processes in Drainage Ditches for Nonpoint Source
Nitrogen Control." Journal of Soil and Water Conservation 62(4): 188-196.
Stromberg, J.C., et al. 2005. "Effects of Stream Flow Intermittency on Riparian Vegetation of a
Semiarid Region River (San Pedro River, Arizona) " River Research and Applications
21:925-938.
Subalusky, A.L. 2007. The Role of Seasonal Wetlands in the Ecology of the American Alligator.
Texas A&M University, College Station, TX.
Page 411 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Subalusky, A.L., et al. 2009a. "Ontogenetic Niche Shifts in the American Alligator Establish
Functional Connectivity between Aquatic Systems," Biological Conservation 142:1507-
1514.
Subalusky, A.L. et al. 2009b. "Detection of American Alligators in Isolated, Seasonal
Wetlands," AppliedHerpetology 6:199-210.
Sullivan, S.M.P., and M.C. Watzin. 2009. "Stream-Floodplain Connectivity and Fish
Assemblage Diversity in the Champlain Valley, Vermont, U.S.A." Journal of Fish Biology
74:1394-1418.
Sun, G.W., et al. 1995. "Shallow Groundwater Table Dynamics of Cypress Wetland Pine Upland
Systems in Florida Flatwoods." Soil and Crop Science Society of Florida Proceedings 54:66-
71.
Suter, G.W., and S.M. Cormier. 2011. "Why and How to Combine Evidence in Environmental
Assessments: Weighing Evidence and Building Cases." Science of The Total Environment
409:1406-1417.
Suter, G.W., et al. 2002. "A Methodology for Inferring the Causes of Observed Impairments in
Aquatic Ecosystems." Environmental Toxicology and Chemistry 21:1101-1111.
Swanson, G.A., et al. 1988. Chemical Characteristics of Prairie Lakes in South-Central North
Dakota—Their Potential for Impacting Fish and Wildlife. U.S. Fish and Wildlife Technical
Report 18, U.S. Department of the Interior, U.S. Fish and Wildlife Service, Washington, DC.
Swimley, T.J., et al. 1999. "Otter and Beaver Interactions in the Delaware Water Gap National
Recreation Area." Journal of the Pennsylvania Academy of Science 72:97-101.
Tank, J.L., et al. 2010. "A Review of Allochthonous Organic Matter Dynamics and Metabolism
in Streams." Journal of the North American Benthological Society 29:118-146.
Tetzlaff, D., and C. Soulsby. 2008. "Sources of Baseflow in Larger Catchments - Using Tracers
to Develop a Holistic Understanding of Runoff Generation." Journal of Hydrology 359:287-
302.
Thomas, J.R., et al. 2006. "A Landscape Perspective of the Stream Corridor Invasion and Habitat
Characteristics of an Exotic (Dioscorea oppositifolia) in a Pristine Watershed in Illinois."
Biological Invasions 8:1103-1113.
Thorp, J.H., et al. 2006. "The Riverine Ecosystem Synthesis: Biocomplexity in River Networks
across Space and Time." River Research and Applications 22:123-147.
Thurman, E.M. 1985. Organic Geochemistry of Natural Waters. Martinus Nijhoff/Dr. W. Junk
Publishers, Boston, MA.
Tihansky, A.B. 1999. "Sinkholes, West-Central Florida." Pages 121-140 in Land Subsidence in
the United States. USGS Circular 1182. D. Galloway, et al., editors. U.S. Department of the
Interior, U.S. Geological Survey, Reston, VA.
Tiner, R.W. 2003 a. Dichotomous Keys and Mapping Codes for Wetland Landscape Position,
Landform, Water Flow Path, and Waterbody Type Descriptors. U.S Fish and Wildlife
Service, National Wetlands Inventory Program, Northeast Region, Hadley, MA.
Tiner, R.W. 2003b. "Estimated Extent of Geographically Isolated Wetlands in Selected Areas of
the United States." Wetlands 23:636-652.
Tiner, R.W. 2003c. "Geographically Isolated Wetlands of the United States." Wetlands
23(3):494-516.
Tiner, R.W. 2011. Dichotomous Keys and Mapping Codes for Wetland Landscape Position,
Landform, Water Flow Path, and Waterbody Type Descriptors: Version 2.0. U.S. Fish and
Wildlife Service, National Wetlands Inventory Program, Northeast Region, Hadley, MA.
Page 412 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Tockner, K., et al. 2000. "An Extension of the Flood Pulse Concept." Hydrological Processes
14:2861-2883.
Tockner, K., et al. 2010. "Multiple Stressors in Coupled Riverfloodplain Ecosystems."
Freshwater Biology 55 (Suppl. 1): 135-151.
Toth, L.A., and A. van der Valk. 2012. "Predictability of Flood Pulse Driven Assembly Rules for
Restoration of a Floodplain Plan Community." Wetlands Ecology and Management 20:59-
75.
Trimble, S.W. 1999. "Decreased Rates of Alluvial Sediment Storage in the Coon Creek Basin,
Wisconsin, 1975-93." Science 285:1244-1246.
Tromp-van Meerveld, H.J., and J.J. McDonnell. 2006. "Threshold Relations in Subsurface
Stormflow: 2. The Fill and Spill Hypothesis." Water Resources Research 42:W02411.
Tronstad, L.M., et al. 2007. "Aerial Colonization and Growth: Rapid Invertebrate Responses to
Temporary Aquatic Habitats in a River Floodplain." Journal of the North American
Benthological Society 26:460-471.
Turner, R.E., et al. 2006. "Wetland Sedimentation from Hurricanes Katrina and Rita." Science
314(5798): 449-452.
Turton, D.J., et al. 1992. "Subsurface Flow Responses of a Small Forested Catchment in the
Ouachita Mountains." HydrologicalProcesses 6:111-125.
Urban, N.R., et al. 1989. "Export of Dissolved Organic Carbon and Acidity from Peatlands."
Water Resources Research 25:1619-1628.
U.S. Army Corps of Engineers. "Regional Supplements to Corps Delineation Manual."
http://www.usace.armv.mil/Missions/CivilWorks/ReeulatoryProgramandPermits/reg supp.as
px.
U.S. Army Corps of Engineers. 1987. Corps of Engineers Wetlands Delineation Manual.
Wetlands Research Program Technical Report Y-87-1. Department of the Army, Vicksburg,
VA.
U.S. Army Corps of Engineers. 1992. Engineering and Design: Design, Construction, and
Maintenance of Relief Wells. EM 1110-2-1914. Department of the Army, Washington, D.C.
http://vvvvvv.publications.usace.annv.mil/Portals/76/Publications/EngineerManuals/EM 1110
-2-1914.pdf.
U.S. Army Corps of Engineers. 1993. Engineering and Design: Seepage Analysis and Control
for Dams. Engineer Manual 1110-2-1901. Original 1986 - Revised 1993. Department of the
Army, Washington, D.C.
http://vvvvvv.publications.usace.annv.mil/Portals/76/Publications/EngineerManuals/EM 1110
-2-1901.pdf.
U.S. Army Corps of Engineers. 1995. Construction Control for Earth and Rock-filled Dams. EM
1110-2-1911. Department of the Army, Washington, D.C.
http://vvvvvv.publications.usace.annv.mil/Portals/76/Publications/EngineerManuals/EM 1110
-2-1911.pdf.
U.S. Army Corps of Engineers. 2000. Engineering and Design: Design and Construction of
Levees. EM 1110-2-1913. Department of the Army, Washington, D.C.
http://vvvvvv.publications.usace.annv.mil/Portals/76/Publications/EngineerManuals/EM 1110
-2-1913.pdf.
U.S. Army Corps of Engineers. 2004. Engineering and Design: General Design and
Construction Considerations for Earth and Rock-Fill Dams. EM 1110-2-2300. Department
of the Army, Washington, D.C.
Page 413 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States May 2015
http://www.publications.usace.army.mil/Portals/76/Publications/EngineerManuals/EM 1110
-2-2300.pdf.
U.S. Army Corps of Engineers. 2005a. Engineering and Design: Design Guidance for Levee
Underseepage. ETL 1110-2-569. Department of the Army, Washington, D.C.
http://www.usace.army.mil/usace-docs/eng-tech-ltrs/etllll0-2-569/entire.pdf.
U.S. Army Corps of Engineers. 2005b. Regulatory Guidance Letter, Subject: Ordinary High
Water Mark. RGL 05-05. Department of the Army, Washington, D.C.
http://www.usace.armv.mi1/Portals/2/docs/civilworks/RGLS/rgl05-05.pdf.
U.S. Army Corps of Engineers. 2007a. Jurisdictional Determination Form Instructional
Guidebook. Department of the Army, Washington, D.C.
U.S. Army Corps of Engineers. 2007b. Regional Supplement to the Corps of Engineers Wetland
Delineation Manual: Alaska Region (Version 2.0). Department of the Army, Vicksburg, MS.
U.S. Army Corps of Engineers. 2009. National Inventory of Dams. U.S. Army Corps of
Engineers.
U.S. Army Corps of Engineers. 2012. Regional Supplement to the Corps of Engineers Wetland
Delineation Manual: Northcentral and Northeast Region (Version 2.0). Department of the
Army, Vicksburg, MS.
U.S. Bureau of Reclamation. "Safety of Dams." Provo Area Office. Last updated July 1, 2014.
http://www.usbr.gov/uc/provo/progact/damsafetv.html.
U.S. Environmental Protection Agency. 1996. Why Watersheds? EPA 800-F-96-001.
U.S. Environmental Protection Agency. 2003. Setting and Allocating the Chesapeake Bay Basin
Nutrient and Sediment Loads: The Collaborative Process, Technical Tools and Innovative
Approaches. EPA 903-R-03-007. Region III, Chesapeake Bay Program Office, Washington,
D.C.
U.S. Environmental Protection Agency. 2008. Handbook for Developing Watershed Plans to
Restore and Protect Our Waters: Planning & Implementation Steps. EPA 841-B-08-002.
U.S. EPA, Washington D.C.
U.S. Environmental Protection Agency. 2010. FY2011-2015 Strategic Plan: Achieving Our
Vision.
U.S. Environmental Protection Agency. 2012. "Section 6 Echo Park Lake TMDLs." Los Angeles
Area Lakes TMDLs. March 2012.
U.S. Environmental Protection Agency. 2014. FY2014-2018 EPA Strategic Plan: Achieving Our
Vision.
U.S. Environmental Protection Agency. 2014. SAB review of the draft EPA report Connectivity
of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific
Evidence. EPA-SAB-15-001, U.S. Environmental Protection Agency, Washington, D.C.
("SAB 2014a.")
U.S. Environmental Protection Agency. 2014. SAB Consideration of the Adequacy of the
Scientific and Technical Basis of the EPA's Proposed Rule titled "Definition of Waters of the
United States under the Clean Water Act." EPA-SAB-14-007, U.S. Environmental Protection
Agency, Washington, D.C. ("SAB 2014b")
U.S. Environmental Protection Agency. 2014. Memorandum from Dr. Amanda Rodewald to Dr.
David Allen. Comments to the chartered SAB on the Adequacy of the Scientific and
Technical Basis of the EPA's Proposed Rule titled "Definition of 'Waters of the United
States' under the Clean Water Act." ("SAB 2014c.")
Page 414 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
U.S. Environmental Protection Agency. 2015. Connectivity of Streams and Wetlands to
Downstream Waters: A Review and Synthesis of the Scientific Evidence (Final Report).
EPA/600/R-14/475F. U.S. Environmental Protection Agency, Washington, D.C.
U.S. Geological Survey. "Floods: Recurrence Intervals and 100-Year Floods (USGS)." Last
updated November 12, 2014. https://water.usgs.gov/edu/100vearflood.html.
Valett, H.M., et. al. 2005. "Biogeochemical and Metabolic Responses to the Flood Pulse in a
Semiarid Floodplain." Ecology 86(1): 220-234.
van der Kamp, G., and M. Hayashi. 1998. "The Groundwater Recharge Function of Small
Wetlands in the Semi-Arid Northern Prairies." Great Plains Research 8:39-56.
van der Valk, A.G. 2006. The Biology of Freshwater Wetlands. Oxford University Press, New
York, NY.
van der Valk, A.G., and R.L. Pederson. 2003. "The SWANCC Decision and Its Implications for
Prairie Potholes." Wetlands 23:590-596.
Van Meter, K.J., and N.B. Basu. 2015. "Signatures of Human Impact: Size Distributions and
Spatial Organization of Wetlands in the Prairie Pothole Landscape." Ecological Applications:
25:451-465.
Vannote, R.L., et. al. 1980. "The River Continuum Concept." Canadian Journal of Fisheries and
Aquatic Sciences 37: 130-137.
Vanschoenwinkel, B., et al. 2009. "Wind Mediated Dispersal of Freshwater Invertebrates in a
Rock Pool Metacommunity: Differences in Dispersal Capacities and Modes." Hydrobiologia
635:363-372.
Van Sickle, J. and C.B. Johnson. 2008. "Parametric Distance Weighting of Landscape Influence
on Streams." Landscape Ecology 23:427-438.
Ver Hoef, J.M., and E.E. Peterson. 2010. "A Moving Average Approach for Spatial Statistical
Models of Stream Networks." Journal of the American Statistical Association 105:6-18.
Ver Hoef, J.M., et al. 2006. "Spatial Statistical Models that Use Flow and Stream Distance."
Environmental and Ecological Statistics 13:449-464.
Vidon, P., et al. 2010. "Hot Spots and Hot Moments in Riparian Zones: Potential for Improved
Water Quality Management." Journal of the American Water Resources Association 46:278-
298.
Vining, K.C. 2002. Simulation of Streamflow and Wetland Storage, Starkweather Coulee
Subbasin, North Dakota, Water Years 1981-98. Water-Resources Investigations Report 02-
4113 U.S. Geological Survey, Bismarck, North Dakota.
Vivoni, E.R., et al. 2006. "Analysis of a Monsoon Flood Event in an Ephemeral Tributary and Its
Downstream Hydrologic Effects." Water Resources Research 42:W03404.
Volkmar, E.C., and R.A. Dahlgren. 2006. Biological Oxygen Demand Dynamics in the Lower
San Joaquin River, California." Environmental Science & Technology 40:5653-5660.
Voos, G., and P.M. Groffman. 1996. "Relationships between Microbial Biomass and Dissipation
of 2,4-D and Dicamba in Soil." Biology and Fertility of Soils 24:106-110.
Wagener, T., et al. 2007. "Catchment Classification and Hydrologic Similarity." Geography
Compass 1:901-931.
Wallace, J.B., and J.R. Webster. 1996. "The Role of Macroinvertebrates in Stream Ecosystem
Function." Annual Review of Entomology 41:115-139.
Wallace, J.B., et al. 1997. "Multiple Trophic Levels of a Forest Stream Linked to Terrestrial
Litter Inputs," Science 277:102-104.
Page 415 of 423
-------
Technical Support Document for the Clean Water Rule: Definition of Waters of the United States
May 2015
Walton, R., etal. 1996. "Hydrology of the Black Swamp Wetlands on the Cache River,
Arkansas." Wetlands 16:279-287.
Wang, X., et al. 2007. "Water Quality Changes as a Result of Coalbed Methane Development in
a Rocky Mountain Watershed." Journal of the American Water Resources Association
43:1383-1399.
Ward, J.V. 1989. "The Four-Dimensional Nature of Lotic Ecosystems." Journal of the North
American Benthological Society 8:2-8.
Ward, J.V. 1998. "Riverine Landscapes: Biodiversity Patterns, Disturbance Regimes, and
Aquatic Conservation." Biological Conservation 83:269-278.
Ward, J.V., and J.A. Stanford. 1983. "The Serial Discontinuity Concept of Lotic Ecosystems."
Pages 29-42 in Dynamics of Lotic Ecosystems. T.D. Fontaine and S.M. Bartell, editors. Ann
Arbor Science, Ann Arbor, MI.
Ward, J. V., et al. 2002. "Applicability of Ecological Theory to Riverine Ecosystems."
Verhandlungen der Internationale Vereinigungfur Theoretische und Angewandte Limnologie
28:443-450.
Webster, J.R., and B.C. Patten. 1979. "Effects of Watershed Perturbation on Stream Potassium
and Calcium Dynamics." Ecological Monographs 49:51-72.
Weitkamp, W. A., et al. 1996. "Pedogenesis of a Vernal Pool Entisol-Alfisol-Vertisol Catena in
Southern California." Soil Science Society of America Journal 60:316-323.
Wellborn, G.A., et al. 1996. "Mechanisms Creating Community Structure across a Freshwater
Habitat Gradient." Annual Review of Ecology and Systematics 27:337-363.
Wetzel, R.G. 1992. "Gradient-Dominated Ecosystems: Sources and Regulatory Functions of
Dissolved Organic Matter in Freshwater Ecosystems. Hydrobiologia 229:181-198.
Wetzel, R G., and B.A. Manny. 1972. "Decomposition of Dissolved Organic Carbon and
Nitrogen Compounds from Leaves in an Experimental Hard-Water Stream." Limnology and
Oceanography 17:927-931.
Wharton, C.H., et al. 1982. The Ecology of Bottomland Hardwood Sswamps of the Southeast: A
Community Profile. FWS/OBS-81/37, U.S. Department of the Interior, U.S. Fish and
Wildlife Service, Biological Services Program, Washington, DC.
Whigham, D.F., and T.E. Jordan. 2003. "Isolated Wetlands and Water Quality." Wetlands
23:541-549.
Whigham, D.F., et al. 1988. "Impacts of Fresh-Water Wetlands on Water-Quality: A Landscape
Perspective. Environmental Management 12:663-671.
Whiles, M.R., and W.K. Dodds. 2002. "Relationships between Stream Size, Suspended Particles,
and Filter-Feeding Macroinvertebrates in a Great Plains Drainage Network." Journal of
Environmental Quality 31:1589-1600.
Whiting, P.J., and M. Pomeranets. 1997. "A Numerical Study of Bank Storage and Its
Contribution to Streamflow " Journal of Hydrology 202:121-136.
Whitmire, S.L., and S.K. Hamilton. 2008. "Rates of Anaerobic Microbial Metabolism in
Wetlands of Divergent Hydrology on a Glacial Landscape." Wetlands 28:703-714.
Wiens, J.A. 2002. "Riverine Landscapes: Taking Landscape Ecology into the Water."
Freshwater Biology 47:501 -515.
Wigington, P.J., etal. 2003. "Nitrate Removal Effectiveness of a Riparian Buffer along a Small
Agricultural Stream in Western Oregon." Journal of Environmental Quality 32:162-170.
Wigington, P.J., et al. 2005. "Stream Network Expansion: A Riparian Water Quality Factor."
Hydrological Processes 19:1715-1721.
Page 416 of 423
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May 2015
Wigington, P.J., etal. 2006. "Coho Salmon Dependence on Intermittent Streams." Frontiers in
Ecology and the Environment 4:513-518.
Wigington, P.J., etal. 2013. "Oregon Hydrologic Landscapes: A Classification Framework."
Journal of the American Water Resources Association 49.1:163-182.
Wilcox, B.P., et al. 2011. "Evidence of Surface Connectivity for Texas Gulf Coast Depressional
Wetlands." Wetlands 31(3):451-458.
Williams, D.D. 1996. "Environmental Constraints in Temporary Fresh Waters and Their
Consequences for the Insect Fauna." Journal of the North American Benthological Society
15:634-650.
Williams, G.P., and M.G. Wolman. 1984. Downstream Effects of Dams on Alluvial Rivers.
USGS Professional Paper 1286, U.S. Department of the Interior, U.S. Geological Survey,
Washington, DC.
Willson M.F., and K.C. Halupka. 1995. "Anadromous Fish as Keystone Species in Vertebrate
Communities." Conservation Biology 9(3):489-497.
Winemiller, K.O., et al. "Fish Assemblage Structure in Relation to Environmental Variation
among Brazos River Oxbow Lakes." Transactions of the American Fisheries Society
129:451-468.
Winter, T.C. 2001. "The Concept of Hydrologic Landscapes." Journal of the American Water
Resources Association 37: 335-349.
Winter, T.C. 2007. "The Role of Groundwater in Generating Streamflow in Headwater areas and
in Maintaining Base Flow." Journal of the American Water Resources Association 43:15-25.
Winter, T.C., and J.W. LaBaugh. 2003. "Hydrologic Considerations in Defining Isolated
Wetlands." Wetlands 23:532-540.
Winter, T.C., and D.O. Rosenberry. 1998. "Hydrology of Prairie Pothole Wetlands during
Drought and Deluge: A 17-Year Study of the Cottonwood Lake Wetland Complex in North
Dakota in the Perspective of Longer Term Measured and Proxy Hydrological Records."
Climatic Change 40:189-209.
Winter, T.C., et al. 1998. Ground Water and Surface Water: A Single Resource. USGS Circular
1139, U.S. Department of the Interior, U.S. Geological Survey, Denver, CO.
Wipfli, M.S., and D.P. Gregovich. 2002. "Export of Invertebrates and Detritus from Fishless
Headwater Streams in Southeastern Alaska: Implications for Downstream Salmonid
Production." Freshwater Biology 47:957-969.
Wipfli, M.S., etal. 2007. "Ecological Linkages between Headwaters and Downstream
Ecosystems: Transport of Organic Matter, Invertebrates, and Wood Down Headwater
Channels." Journal of the American Water Resources Association 43:72-85.
Wiskow, E., and R.R. van der Ploeg. 2003. "Calculation of drain Spacings for Optimal
Rainstorm Flood Control." Journal of Hydrology 272:163-174.
Woessner, W.W. 2000. "Stream and Fluvial Plain Ground Water Interactions: Rescaling
Hydrogeologic Thought." Ground Water 38:423-429.
Wolman, M.G., and J.P. Miller. 1960. "Magnitude and Frequency of Forces in Geomorphic
Processes." Journal of Geology 68:54-74.
Wolock, D.M., et al. 2004. "Delineation and Evaluation of Hydrologic-Landscape Regions in the
United States Using Geographic Information System Tools and Multivariate Statistical
Analysis." Environmental Management 34:S71-S88.
Wood, P. J., and P.D. Armitage.1997. "Biological Effects of Fine Sediment in the Lotic
Environment." Environmental Management 21:203 -217.
Page 417 of 423
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Woodford, D.J., and A.R. Mcintosh. 2010. "Evidence of Source-Sink Metapopulations in a
Vulnerable Native Galaxiid Fish Driven by Introduced Trout." Ecological Applications
20:967-977.
Woodward, G.U.Y., and A.G. Hildrew. 2002. "Food Web Structure in Riverine Landscapes."
Freshwater Biology 47:777-798.
Yuan, F., and S. Miyamoto. 2008. "Characteristics of Oxygen-18 and Deuterium Composition in
Waters from the Pecos River in American Southwest." Chemical Geology 255:220-230.
Zaimes, G.N., et al. 2004. "Stream Bank Erosion Adjacent to Riparian Forest Buffers, Row-Crop
Fields, and Continuously-Grazed Pastures along Bear Creek in Central Iowa." Journal of Soil
and Water Conservation 59:19-27.
Zale, A. V., etal. 1989. "The Physicochemistry, Flora, and Fauna of Intermittent Prairie Streams:
A Review of the Literature." United States Fish and Wildlife Service Biological Report 89:1 -
44.
Zedler, P.H. 1987. The Ecology of Southern California Vernal Pools: A Community Profile.
United States Department of the Interior, United States Fish and Wildlife Service,
Washington, D.C.
Zhang, T., et al. 2012. "Evaluating the Effects of Upstream Lakes and Wetlands on Lake
Phosphorus Concentrations using a Spatially-Explicit Model." Landscape Ecology 27
(7): 1015-1030.
Zimmer, K.D., et al. 2001. "Effects of Fathead Minnow Colonization and Removal on a Prairie
Wetland Ecosystem." Ecosystems 4:346-357.
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Appendix 2: Traditional Navigable Waters ("Appendix D")
Legal Definition of "Traditional Navigable Waters"
(Appendix D from the Corps Jurisdictional Determination Form
Instructional Guidebook, available at
httD://www.usace.arniv.niil/Portals/2/docs/civilworks/regulatorv/cwa
guide/app d traditional navigable waters.pdD
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Waters that Qualify as Waters of the United States
Under Section (a)(1) of the Agencies' Regulations
The Environmental Protection Agency (EPA) and United States Army Corps of
Engineers (Corps) "Clean Water Act Jurisdiction Following the U.S. Supreme Court's
Decision in Rapanos v. United States and Carabell v. United States" guidance
(Rapanos guidance) affirms that EPA and the Corps will continue to assert jurisdiction
over "[a]ll waters which are currently used, or were used in the past, or may be
susceptible to use in interstate or foreign commerce, including all waters which are
subject to the ebb and flow of the tide." 33 C.F.R. § 328.3(a)(1); 40 C.F.R. §
230.3(s)(1). The guidance also states that, for purposes of the guidance, these "(a)(1)
waters" are the "traditional navigable waters." These (a)(1) waters include all of the
"navigable waters of the United States," defined in 33 C.F.R. Part 329 and by numerous
decisions of the federal courts, plus all other waters that are navigable-in-fact (e.g., the
Great Salt Lake, UT and Lake Minnetonka, MN).
EPA and the Corps are providing this guidance on determining whether a water
is a "traditional navigable water" for purposes of the Rapanos guidance, the Clean
Water Act (CWA), and the agencies' CWA implementing regulations. This guidance is
not intended to be used for any other purpose. To determine whether a water body
constitutes an (a)(1) water under the regulations, relevant considerations include Corps
regulations, prior determinations by the Corps and by the federal courts, and case law.
Corps districts and EPA regions should determine whether a particular waterbody is a
traditional navigable water based on application of those considerations to the specific
facts in each case.
As noted above, the (a)(1) waters include, but are not limited to, the "navigable
waters of the United States." A water body qualifies as a "navigable water of the United
States" if it meets any of the tests set forth in 33 C.F.R. Part 329 (e.g., the water body is
(a) subject to the ebb and flow of the tide, and/or (b) the water body is presently used,
or has been used in the past, or may be susceptible for use (with or without reasonable
improvements) to transport interstate or foreign commerce). The Corps districts have
made determinations in the past regarding whether particular water bodies qualify as
"navigable waters of the United States" for purposes of asserting jurisdiction under
Sections 9 and 10 of the Rivers and Harbors Act of 1899 (33 USC Sections 401 and
403). Pursuant to 33 C.F.R. § 329.16, the Corps should maintain lists of final
determinations of navigability for purposes of Corps jurisdiction under the Rivers and
Harbors Act of 1899. While absence from the list should not be taken as an indication
that the water is not navigable (329.16(b)), Corps districts and EPA regions should rely
on any final Corps determination that a water body is a navigable water of the United
States.
If the federal courts have determined that a water body is navigable-in-fact under
federal law for any purpose, that water body qualifies as a "traditional navigable water"
subject to CWA jurisdiction under 33 C.F.R. § 328.3(a)(1) and 40 C.F.R. § 230.3(s)(1).
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Corps districts and EPA regions should be guided by the relevant opinions of the federal
courts in determining whether waterbodies are "currently used, or were used in the past,
or may be susceptible to use in interstate or foreign commerce" (33 C.F.R. §
328.3(a)(1); 40 C.F.R. § 230.3(s)(1)) or "navigable-in-fact."
This definition of "navigable-in-fact" comes from a long line of cases originating
with The Daniel Ball, 77 U.S. 557 (1870). The Supreme Court stated:
Those rivers must be regarded as public navigable rivers in law which are
navigable in fact. And they are navigable in fact when they are used, or are
susceptible of being used, in their ordinary condition, as highways for commerce,
over which trade and travel are or may be conducted in the customary modes of
trade and travel on water.
The Daniel Ball. 77 U.S. at 563.
In The Montello, the Supreme Court clarified that "customary modes of trade and
travel on water" encompasses more than just navigation by larger vessels:
The capability of use by the public for purposes of transportation and commerce
affords the true criterion of the navigability of a river, rather than the extent and
manner of that use. If it be capable in its natural state of being used for purposes
of commerce, no matter in what mode the commerce may be conducted, it is
navigable in fact, and becomes in law a public river or highway.
The Montello, 87 U.S. 430, 441-42 (1874). In that case, the Court held that early
fur trading using canoes sufficiently showed that the Fox River was a navigable water of
the United States. The Court was careful to note that the bare fact of a water's capacity
for navigation alone is not sufficient; that capacity must be indicative of the water's being
"generally and commonly useful to some purpose of trade or agriculture." ]d. at 442.
In Economy Light & Power, the Supreme Court held that a waterway need not be
continuously navigable; it is navigable even if it has "occasional natural obstructions or
portages" and even if it is not navigable "at all seasons ... or at all stages of the water."
Economy Light & Power Co. v. U.S.. 256 U.S. 113, 122 (1921).
In United States v. Holt State Bank, 270 U.S. 49 (1926), the Supreme Court
summarized the law on navigability as of 1926 as follows:
The rule long since approved by this court in applying the Constitution and laws of
the United States is that streams or lakes which are navigable in fact must be
regarded as navigable in law; that they are navigable in fact when they are used,
or are susceptible of being used, in their natural and ordinary condition, as
highways for commerce, over which trade and travel are or may be conducted in
the customary modes of trade and travel on water; and further that navigability
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does not depend on the particular mode in which such use is or may be had -
whether by steamboats, sailing vessels or flatboats- nor on an absence of
occasional difficulties in navigation, but on the fact, if it be a fact, that the stream
in its natural and ordinary condition affords a channel for useful commerce.
Holt State Bank, 270 U.S. at 56.
In U. S. v. Utah, 283 U.S. 64, (1931) and U.S. v. Appalachian Elec. Power Co,
311 U.S. 377 (1940), the Supreme Court held that so long as a water is susceptible to
use as a highway of commerce, it is navigable-in-fact, even if the water has never been
used for any commercial purpose. U.S. v. Utah, at 81-83 ("The question of that
susceptibility in the ordinary condition of the rivers, rather than of the mere manner or
extent of actual use, is the crucial question."); U.S. v. Appalachian Elec. Power Co., 311
U.S. 377, 416 (1940) ("Nor is lack of commercial traffic a bar to a conclusion of
navigability where personal or private use by boats demonstrates the availability of the
stream for the simpler types of commercial navigation.").
In 1971, in Utah v. United States, 403 U.S. 9 (1971), the Supreme Court held that
the Great Salt Lake, an intrastate water body, was navigable under federal law even
though it "is not part of a navigable interstate or international commercial highway." ]d
at 10. In doing so, the Supreme Court stated that the fact that the Lake was used for
hauling of animals by ranchers rather than for the transportation of "water-borne freight"
was an "irrelevant detail." ]d at 11. "The lake was used as a highway and that is the
gist of the federal test." Ibid. 1
1Also of note are two decisions from the courts of appeals. In FPL Energy
Marine Hydro, a case involving the Federal Power Act, the D.C. Circuit reiterated the
fact that"actual use is not necessary for a navigability determination" and repeated
earlier Supreme Court holdings that navigability and capacity of a water to carry
commerce could be shown through "physical characteristics and experimentation." FPL
Energy Marine Hydro LLC v. FERC, 287 F.3d 1151, 1157 (D.C. Cir. 2002). In that case,
the D.C. Circuit upheld a FERC navigability determination that was based upon three
experimental canoe trips taken specifically to demonstrate the river's navigability. ]d at
1158-59.
The 9th Circuit has also implemented the Supreme Court's holding that a water need
only be susceptible to being used for waterborne commerce to be navigable-in-fact.
Alaska v. Ahtna, Inc., 891 F.2d 1404 (9th Cir. 1989). In Ahtna, the 9th Circuit held that
current use of an Alaskan river for commercial recreational boating is sufficient evidence
of the water's capacity to carry waterborne commerce at the time that Alaska became a
state. ]cL at 1405. It was found to be irrelevant whether or not the river was actually
being navigated or being used for commerce at the time, because current navigation
showed that the river always had the capacity to support such navigation. ]cL at 1404.
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In summary, when determining whether a water body qualifies as a "traditional
navigable water" (i.e., an (a)(1) water), relevant considerations include whether a
Corps District has determined that the water body is a navigable water of the United
States pursuant to 33 C.F.R § 329.14, or the water body qualifies as a navigable water
of the United States under any of the tests set forth in 33 C.F.R. § 329, or a federal
court has determined that the water body is navigable-in-fact under federal law for any
purpose, or the water body is "navigable-in-fact" under the standards that have been
used by the federal courts.
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