Compensation Ratios for Wetland Mitigation
Guidelines and Tables for Applying the Methodology
described in
"Wetland Mitigation: A Framework for Determining
Compensation Ratios"
Dennis M. King, Ph.D.
and
Curtis C.Bohlen, Ph.D. '
"University of Maryland,
Center for Environmental and Estuarine Studies,
Chesapeake Biological Laboratory
P.O. Box 38, Solomons, Maryland 20688
April 1, 1994
University of Maryland, .C'EES Working Paper UMCEES-CBL-94-10, March
1994. Prepared under Cooperative Agreement Number CR818-227 with the
U.S. EPA, Office of Policy Analysis with support from EPA Region IV
(Atlanta) and Region IX (San Francisco).
EPA -230-R-94-022
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I. BACKGROUND
A modern industrial society cannot function without causing some
harm to wetlands. Thus,, despite concerted efforts to conserve remaining wet-
lands, some development projects that cannot be designed to completely
avoid wetlands will occur. In such cases, those seeking permits from federal
or state regulatory agencies charged with protecting wetlands will usually be
required to mitigate wetland impacts by undertaking or funding wetland cre-
ation, restoration, or enhancement projects. To the .regulators responsible for
implementing wetland permitting programs, determining what constitutes
appropriate mitigation for wetland losses is a central challenge. If compen:
satory mitigation requirements are set too low/they will fail to achieve the
"no net loss" goal that the nation has established for wetlands. If compensa-
tion requirements are set too high, the associated economic costs and social
disruptions will be excessive and will lead to frequent legal and political chal-
lenges, poor regulatory compliance, and an undermining of public support
for wetland protection.
Some regulatory programs, including those in Maine, Florida, and
Maryland, address the problem of determining what constitutes appropriate
mitigation by using standard compensation ratios . These ratios establish the
number of acres of created or restored wetlands required to offset each acre of
damaged wetland (Want 1993). Typically, ratios vary by state and according to
the type of wetland harmed and the type of mitigation proposed. The federal
wetlands program administered under ง404 of the Clean Water Act, on the
other hand, does not use standard ratios but instead relies on guidance
contained in a 1990 U.S. Army Corps of Engineers/U.S. EPA Memorandum of
Agreement (MOA) about what constitutes appropriate compensation. That
MOA specifically requires that mitigation requirements should be based
"solely on the values and functions of the aquatic resources impacted" and
not on economic or other considerations. Compensation requirements under
the federal program therefore, at least in principle, should be established on
the basis of a comparison of the wetland functions and values expected from
the compensation wetland and those lost with the destruction of the original
wetland.
The relatively simple idea of comparing the wetland functions and
values at the lost and replacement wetlands has proven to be complex in
practice. Wetlands are important as forms of natural capital because they
provide essential life support functions and generate streams of ecological
and economic functions, products, and services. However, all wetlands are
not equally valuable in ecological or economic terms. The value of each
wetland depends on the level and characteristics of the' many different
biological and geophysical functions it provides, the its proximity to other
-------
features of the watershed, and its accessibility, to animal and human
populations. ,
Assessing the adequacy of compensatory mitigation, therefore, in-
. volves comparing streams of wetland functions and values that would accrue
if the original wetland were not disturbed with streams of functions and val-
ues expected from the proposed mitigation. This comparison depends on
three key factors: - . . '
(1) The sustained levels of wetland function provided by the original and
the replacement wetland, which depends only in part on their relative
size (the compensation ratio);
(2) The speed with which the created or restored wetland reaches the sus-
tained level of function that it is expected to provide; and
(3) The risk of mitigation failure, or more generally, uncertainty about the
level of wetland function that the mitigation project will provide.
II. FOCUS
In a previous paper (King , Bohlen, and Adler 1993), the authors de-
scribed a method for estimating compensation ratios'based on these three fac-
tors. The method assesses whether trade-offs between wetland guality and
wetland area that result from wetland mitigation result in an overall loss of
wetland value. The method described, in the previous-report, does not deal
explicitly with multiple sources of wetland value, and therefore is most use-
ful when a single source of wetland value is of overriding management in-
terest. However, as long as mitigation priorities and regional environmental
goals have been established (e.g., through watershed planning), it can be ap-
plied in situations where multiple1 wetland values are of concern.
This paper responds to the many requests the authors have received
for a set of simple instructions and look-up tables that will allow regulators,
permit seekers, and others to estimate "appropriate" compensation ratios
based on estimates or negotiated values of a few key parameters.
III. THE BASIC FRAMFWDKK
The conceptual basis for the compensation ratio formula is depicted in
Figure 1. Destruction of the original wetland (at time labeled T0 in the figure)
leads to a loss of 100% of it's value. A replacement'wetland is created, en--
hanced, or restored to compensate for the loss of wetland functions. The re-
placement value-of the mitigation site climbs gradually over a period of C
years from level Athe value provided by the mitigation site in the absence
of .the mitigation projectto some maximum levellevel B, Both A and B
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are expressed as a percent of the per acre value of the original wetland. While
B, the maximum level of (per acre) wetland value reached at the mitigation
site, will typically be less'than 100% of the value of the original wetland, that
need not be the case, especially if the original wetland was seriously degraded.
Compensation Model
Framework
100%
2 -a
o j=
< .2
4-1
i_ 0
>
'5 0), and often, that full value is not as great as was
-------
found at the lost wetland (B<0). As a practical matter, therefore, the portion of
the original wetland loss that would be offset by mitigation if mitigation is
provided on an,acre-for-acre basis is .depicted by the cross-hatched area and the
white area above the cross-hatched area depicts lost values associated with the
failure of the mitigation to be fully and immediately successful. The shaded
area below the line at A depicts values already'provided by the mitigation site
that are not attributable to the mitigation effort. Thus, the percentage loss of
value with acre-for-acre mitigation depends on the values of A, B and C,
which are determined by the characteristics of the mitigation project.
IV. THE COMPENSATION FORMULA
Since the cross-hatched area depicts the value provided by an acre of
mitigation and the entire rectangle from T0 to Tmax depicts the values lost with
each acre of the lost wetland, dividing the cross-hatched area by the total area
gives the percentage loss of v'alue with one-for-one mitigation, The inverse of
this percentage gives a crude estimate of the "appropriate" compensation ra-
tiothe number of acres of mitigation required per acre of lost wetland to
achieve no net loss in wetland value..
This simple formula, however, misses a few important considerations.
Regulators, acting in the public interest, cannot be indifferent to issues in-
volving the timing and risk of compensatory mitigation. A more thorough
version takes account of three additional factors, including ,
(1) time discountingto account for the fact that wetland functions re-
placed in future years do not. provide the same in value, measured in
present value terms, as wetland functions lost today;
(2) riskthat a wetland creation or restoration project will not perform as
well as expected; and
(3) advanced or delayed compensationthe possibility that a mitigation
project may be completed and begin providing replacement wetland
value either before or after the loss of the original wetland.
These refinements can be made by introducing a few new parameters
that characterize .when the mitigation is provided and the risk that the
mitigation will fail and developing a compensation formula. The formula is
not very complicated, but calculating compensation ratios directly from the
formula can be time consuming. We have, therefore, developed a set .of look-
up tables, included as Attachment A, which provide the user ,with estimates
of compensation ratios for various combinations of parameter values that
characterize the proposed mitigation. To use the tables, the user needs to
estimate or somehow settle upon acceptable values of the following
parameters:
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A: The level of wetland function provided per acre at the mitigation site
prior to the mitigation project, expressed as a percentage of the value of
the original wetland;
B: The maximum level of wetland function each acre of successful
mitigation is expected to attain, if it is successful, expressed as a percent
of the per acre value of the original wetland;
C: The number of years after construction that the mitigation project is
expected to achieve maximum function;
D: The number of years before destruction of the original wetland that the
mitigation project begins to generate mitigation values (negative
values represent delayed compensation);
E: The percent likelihood that the mitigation project will fail and provide
none of the anticipated'benefits (with mitigation failure, wetland
values at the mitigation site return to level A)
r : The discount rate used for comparing values that accrue at different
times at their present value (Tables provide estimates based on
discount rates of 0%, 5%, and 10%).
Tmax- The time horizon used in the analysis (Using the OMB recommended
discount rate of r=7% comparisons of value beyond about t=75 years are
of negligible significance)
V. SOME ILLUSTRATIONS
Table 1 shows some calculated compensation ratios based on the com-
pensation formula. The first three cases show the effects on the resulting
compensation ratio of delaying or advancing the compensatory mitigation
project. The next three examples illustrate how pre-existing wetland values or
compensation for the loss of a degraded wetland affect compensation re-
quirements. The final set of examples illustrate how the assessment of failure
risk can affect estimated compensation ratio.
The characteristics of the mitigation project itself, as reflected in the
values of A, B, and C are of obvious importance. The last example shown,
however, illustrates why advanced mitigation should provide a significant
advantage over concurrent mitigation in terms .of compensation
requirements. Since many mitigation failures can (1) be detected, and (2) be
corrected within a year or so of project construction, advanced compensation
allows a permittee or a mitigation banker to manage many controllable risk
factors and significantly lower the risk of failure. At the same time, advanced
mitigation provides replacement wetland values sooner than concurrent
-------
mitigation so there is less discounting of replacement values and more
resulting mitigation credit per acre. Combined, these factors., result in a
substantial advantage for advanced as compared to concurrent mitigation in
terms of the number of mitigation acres required. Lower compensation ratios
for advanced mitigation mean lower mitigation costs, which in many cases
could more than offset the cost of committing funds for advanced mitigation
or investing in, a mitigation bank. . ,
Table 1. Calculated compensation ratios for a variety of hypothetical compen-
sation scenarios, based on a time horizon (TmflJ of 100 years.
COMPENSATION
. ' ' ' RATIOS
, Parameters
Discount
.'"'" Rate .
Concurrent Creation
Advanced Creation
Delayed Creation
Concurrent Restoration
Original Wetland Degraded
Concurrent Enhancement
Difficult Creation
Very Difficult Creation
Same, Advanced and Risk
Adjusted
A
0
0
0
.0.1
0
0.5
b ,
0
0 '
B
. 0.7
0.7
0.7
0.7
1.4
0.7
0.7
0.7
0.7
C
10
10
10
10
10
10
10
10
10
D
0
5
-5
0 '
'0
0 ,
0
" 0' ,
5
E '
0
0
0
0
0
0.2
0.5
0.75
. 0.2
0%
1.5
. 1.4
' ~ 1.6
1.8
- -0.8
6.6
3.0
6.0
1.8
5%
1.9
1.5
2.4
2.2 .
0.9 ,
8.1
3.7
7.4
1.8
.. 10%
2.3
, 1.4'
, 3.7
2.7
1.2
10.2
.4.7
',9.3
1.8
20%
3.4
1.4
8.5
4.
1.70
15.0
6.8
13.6
1.7
.6
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ATTACHMENT A
WETLAND COMPENSATION RATIOS IN FIVE EASY STEPS
I. The Approach
A report entitled Watershed Planning and Wetland Mitigation: A Framework for Determining Wetland
Compensation Ratios by Dennis M. King and Curtis C. Bohlen of the University of Maryland, Center for
Environmental and Estuarine Studies describes what the authors believe is a technically and legally
defensible method for estimating compensation ratios for wetland mitigation (acres of created, restored or
enhanced wetland required to compensate for an acre of lost natural wetland).
The method requires that users estimate or at least agree to values of five parameters that characterize
the wetland functions and values to be gained and lost over time with acre for acre replacement. The
parameters are then used in a modified present value formula to estimate the compensation ratio that would be
required to achieve no net loss of wetland value over time. The authors have developed the enclosed look:up
tables that contain estimated compensation ratios for a full range of parameter values.
II. The Key Parameters
i < *
A: The level of per acre wetland function at the compensation site prior to the compensation project,
expressed as a proportion of the value of the original wetland;
B: The maximum a,cre by acre level of wetland function the compensation project will reach,
expressed as a proportion of the per acre value of the original wetland;
C The year after construction of the compensation project that -it achieves maximum function;
D: The number of years before destruction of the original wetland.(at time t=0) that construction of
the compensation project occurs (negative values represent delayed mitigation, positive values,
advanced mitigation);
E: The percent likelihood that the project will fail and wetland values at the mitigation site will
remain at A
E: The estimated chance that the mitigation project will fail and provide substantially fewer
environmental benefits than anticipated
n The discount rate used to arrive at the present Value of wetland values that accrue in the future.
HI. The Five Easy Steps
STEP 1 Estimate or negotiate acceptable values of A, B, C, D, E, and r.
STEP 2 Calculate the expected value of B, the value of B adjusted to account for the risk of project failure,
using the following equation:
B = B(1-E) + AE
adj ' ...
STEP 3: Calculate V, the expected increase in wetland values at the mitigation site due to the mitigation
project., where:
Increase = B A
adj
STEP 4 Go to the Table that corresponds to the selected value of D. In the tables provided D can range
from +5 (mitigation initiated five years in advance of wetland loss) to -5( mitigation initiated five
' years after wetland loss).
STEP 5 Locate the frame that correspond to the calculated value of V and C. and pick the Compensation '
Ratio that corresponds to the selected discount rate of 0% (top), 5% (middle) or 10% (bottom)
For further information contact Dennis King or Curtis Bohlen at:
.: .-,.. ..r ป,_._.,_..., ,-...,_.. r_.. T-----:-.nmentai an& -Estuarine
20688 (410-326-7212)
University of Maryland , Center for Environmental and Estuarine Studies,,
P.O. Box 38, Solomons, Man/land 2C
-------
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