October 2024
EPA-843-B2-24001

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Environmental Protection
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Streamflow Duration Assessment
Method for the Great Plains
of the United States

ENGINEER RESEARCH & DEVELOPMENT CENTER

US Army Corps
of Engineers®


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Streamflow Duration Assessment Method for
the Great Plains of the United States

Version 2.0
October 2024

Prepared by Amy James1, Ken M. Fritz2, Brian Topping3, Tracie-Lynn Nadeau4, Rachel Fertik Edgerton3,
Kristina Nicholas5, and Raphael Mazor6.

1	Ecosystem Planning and Restoration. Raleigh, NC

2	U.S. Environmental Protection Agency—Office of Research and Development. Cincinnati, OH

3	U.S. Environmental Protection Agency—Office of Wetlands, Oceans, and Watersheds. Washington,
D.C.

4	U.S. Environmental Protection Agency—Region 10. Portland, OR

5	Oak Ridge Institute of Science and Education (ORISE) Fellow at U.S. Environmental Protection
Agency—Office of Wetlands, Oceans, and Watersheds. Washington, D.C.

6Southern California Coastal Water Research Project. Costa Mesa, CA

The following members of the National Steering Committee, and the Regional Steering Committee for
the Great Plains, provided input and technical review:

National

Tunis McElwain

U.S. Army Corps of Engineers

Headquarters, Regulatory Program

Washington, DC

Gabrielle David

U.S. Army Corps of Engineers

Engineer Research and Development Center

Hanover, NH

Matt Wilson

U.S. Army Corps of Engineers
Headquarters, Regulatory Program
Washington, DC

Rose Kwok

U.S. Environmental Protection Agency
Office of Wetlands, Oceans and Watersheds
Washington, DC

Regional

Micah Bennett, Kerryann Weaver,
and Ed Hammer

U.S. Environmental Protection Agency
Region 5

Loribeth Tanner and Chelsey Sherwood
U.S. Environmental Protection Agency
Region 6
Dallas, TX


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Gabriel DuPree and Shawn Henderson
U.S. Environmental Protection Agency
Region 7
Lenexa, KS

Kristen Brown

U.S. Army Corps of Engineers
Regulatory Branch
Rock Island District

Faye Healy and April Marcangeli
U.S. Army Corps of Engineers
Regulatory Branch
St. Paul District

Rob Hoffmann

U.S. Army Corps of Engineers
Regulatory Branch
Tulsa District

Sabrina Miller

U.S. Army Corps of Engineers
Regulatory Branch
Detroit District

Billy Bunch and Rachel Harrington
U.S. Environmental Protection Agency
Region 8
Denver, CO

Wayne Fitzpatrick and Elizabeth Shelton
U.S. Army Corps of Engineers
Regulatory Branch
Galveston District

Jeremy Grauf

U.S. Army Corps of Engineers
Regulatory Branch
Omaha District

Andrew Blackburn
U.S. Army Corps of Engineers
Regulatory Branch
Chicago District

Suggested citation:

James, A., Fritz, K.M., Topping, B., Nadeau, T.-L., Fertik Edgerton, R., Nicholas, K., and Mazor, R. 2024.
Streamflow Duration Assessment Method for the Great Plains of the United States. Version 2.0.
Document No. EPA-843-B-24001.

Photographs courtesy of the U.S. Environmental Protection Agency unless otherwise noted.


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Acknowledgments

We thank Abel Santana, Robert Butler, Duy Nguyen, Kristine Gesulga, Kenneth McCune, Adriana
LeCompte Santiago, and Anne Holt for assistance with data management, and Kort Kirkeby, Abe
Margo, Alex Swain, Addison Ochs, Morgan Proko, Alec Lambert, Zak Erickson, Alex Berryman, Jack
Poole, Joe Kiel, Joe Klein, Jackson Bates, Buck Meyer, Margaret O'Brien, Elliot Broder, Jason Glover, and
James Treacy for assistance with data collection.

Numerous researchers and land managers with local expertise assisted with the selection of study
reaches to calibrate the method: Tim Bonner, Jeffrey Brenkenridge, Taylor Dorn, Tim Fallon, John
Genet, Linda Hansen, Garret Hecker, Stephanie Kampf, Julie Kelso, Kort Kirkeby, Ji Yeow Law, John
Lyons, Kyle McLean, Miranda Meehan, Steve Robinson, Mateo Scoggins, Patrick Trier, Linda Vance,

Ross Vander Vorste, and Jason Zhang.

This work was funded through EPA contract 68HERC21D0008 to Ecosystem Planning and Restoration
and EPA contracts EP-C-16-006 and 68HERC22D0002 to ESS Group.

Disclaimers

This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and
approved for publication. Any mention of trade names, manufacturers or products does not imply an
endorsement by the United States (U.S.) Government or the U.S. Environmental Protection Agency.
The EPA and its employees do not endorse any commercial products, services, or enterprises.

The contents of this report are not to be used for advertising, publication, or promotional purposes.
Citation of trade names does not constitute an official endorsement or approval of the use of such
commercial products. All product names and trademarks cited are the property of their respective
owners. The findings of this report are not to be construed as an official Department of the Army or
the U.S. Environmental Protection Agency position unless so designated by other authorized
documents. Destroy this report when no longer needed. Do not return it to the originator.

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Table of Contents

Section 1: Introduction and Background	1

1.1	The SDAM for the Great Plains	4

1.2	Intended use and limitations	5

1.3	Development of the GP SDAM	6

Section 2: Overview of the GP SDAM and the Assessment Process	9

2.1 Considerations for assessing streamflow duration and interpreting indicators	9

2.1.1	Clean Water Act jurisdiction	9

2.1.2	Scales of assessment	9

2.1.3	Spatial variability	9

2.1.4	Temporal variability	10

2.1.5	Ditches and modified natural streams	10

2.1.6	Other disturbances	10

2.1.7	Multi-threaded systems	11

Section 3: Data Collection	12

3.1	Conduct desktop reconnaissance	12

3.2	Prepare sampling gear	13

3.3	Order of operations for completing the GP SDAM field assessment	14

3.4	Timing of sampling	15

3.5	Assessment reach considerations	16

3.5.1	Reach placement	16

3.5.2	Reach length	17

3.5.3	How many assessment reaches are needed?	17

3.6	Photo-documentation	17

3.7	Conducting assessments and completing the field form	18

3.7.1	General reach information	18

3.7.2	Assessment reach sketch	23

3.8	How to measure indicators of streamflow duration	24

3.8.1	Bankfull channel width	24

3.8.2	Total aquatic macroinvertebrate abundance	25

3.8.3	Number of hydro phytic plant species	28

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3.8.4	Presence/absence of rooted upland plants in streambed	34

3.8.5	Differences in vegetation	34

3.8.6	Riffle-pool sequence	36

3.8.7	Particle size or stream substrate sorting	38

3.8.8	Sediment on plants or debris	40

3.9 Additional notes and photographs	41

Section 4: Data Interpretation and Using the Web Application	42

4.1	Outcomes of GP SDAM classification	42

4.2	Applications of the GP SDAM outside the intended area	43

4.3	What to do when a more specific classification is needed	43

4.3.1	Review historical aerial imagery	43

4.3.2	Conduct additional assessments at the same reach	45

4.3.3	Conduct assessments at nearby reaches	45

4.3.4	Conduct reach revisits during regionally appropriate wet and dry seasons	46

4.3.5	Collect hydrologic data	46

Section 5: References	47

Appendix A. Glossary of Terms	51

Appendix B. Field Form

Table of Figures

Figure 1. Streams of different flow classes	2

Figure 2. Map of flow duration study regions	3

Figure 3. Locations of ephemeral, intermittent, and perennial stream reaches used to calibrate the GP

SDAM	6

Figure 4. Bankfull measurement and photo point locations	19

Figure 5. Measuring bankfull width	20

Figure 6. Examples of difficult conditions that may interfere with the observation or interpretation of

indicators	22

Figure 7. Examples of estimating surface and subsurface flow, and isolated pools	23

Figure 8. Examples of evidence of aquatic macroinvertebrates in dry channels	27

Figure 9. Examples of terrestrial macroinvertebrates you may find in a dry channel	28

Figure 10. National Wetland Plant List (NWPL) regions that overlap with the GP SDAM region	29

Figure 11. Local conditions that support growth of hydrophytes	30

Figure 12. Long-lived species only represented by young specimens	31

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Figure 13. Water-stressed riparian trees near Oro Grande on the Mojave River	31

Figure 14. Examples of plants determined to be hydrophytes based on context	32

Figure 15. Example of an ephemeral stream with rooted upland vegetation growing in the channel.34

Figure 16. Examples illustrating scoring levels for the Differences in Vegetation indicator	36

Figure 17. Examples illustrating scoring levels for the Riffle-Pool Sequence indicator	38

Figure 18. Examples illustrating scoring levels for the Particle Size/Stream Substrate Sorting indicator.

	40

Figure 19. Examples of using aerial imagery to support streamflow duration classification	45

Table of Tables

Table 1. Examples of online resources for generating local flora lists	13

Table 2. Scoring guidance for the Differences in Vegetation indicator	35

Table 3. Scoring guidance for the Riffle-Pool Sequence indicator	37

Table 4. Scoring guidance for Particle Size/Streambed Sorting indicator	39

Table 5. Scoring guidance for the Sediment on Plants or Debris indicator	41

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Section 1: Introduction and Background

Section 1: Introduction and Background

Streams exhibit a diverse range of hydrologic regimes, and the hydrologic regime strongly influences
the physical, chemical, and biological characteristics of active stream channels and adjacent riparian
areas. Thus, information describing a stream's hydrologic regime is useful to support resource
management decisions, including Clean Water Act Section 404 decisions. One important aspect of the
hydrologic regime is streamflow duration—the length of time that a stream sustains surface flow.
However, hydrologic data to determine flow duration has not been collected for most stream reaches
nationwide. Although maps, hydrologic models, and other data resources exist (e.g., the National
Hydrography Dataset, McKay et al. 2014), these may exclude small headwater streams and unnamed
second- or third-order tributaries, and limitations on accuracy and spatial or temporal resolution may
reduce their utility for many management applications (Hall et al. 1998, Nadeau and Rains 2007, Fritz
et al. 2013). Therefore, rapid, field-based methods are needed to determine flow duration class at the
reach scale (defined in Section 2: Overview of the GP SPAM and the Assessment Process) in the
absence of long-term hydrologic data (Fritz et al. 2020).

This method is intended to classify stream reaches into one of three streamflow duration classes1:

Ephemeral reaches are channels that flow only in direct response to precipitation. Water typically
flows only during and/or shortly after large precipitation events, the streambed is always above the
water table, and stormwater runoff is the primary water source.

Intermittent reaches are channels that contain sustained flowing water for only part of the year,
typically during the wet season, where the streambed may be below the water table and/or where
the snowmelt from surrounding uplands provides sustained flow. The flow may vary greatly with
stormwater runoff.

Perennial reaches are channels that contain flowing water continuously during a year of normal
rainfall, often with the streambed located below the water table for most of the year. Groundwater
typically supplies the baseflow for perennial reaches, but the baseflow may also be supplemented
by stormwater runoff and/or snowmelt.

Example photographs and hydrographs of stream reaches in each class are shown in Figure 1.

1 The definitions used for development of this manual are consistent with the definitions used to develop the SDAMs for
the Pacific Northwest, Arid West, Western Mountains, Northeast, and Southeast.

1


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Section 1: Introduction and Background

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Ephemeral stream reach
Tributary to North Fork Solomon River (at Kirwin Reservoir), Kirwin National Wildlife Refuge,

KS

Figure 1. Streams of different flow classes. Photos of stream reaches in each streamflow duration class are shown at left,
with corresponding visualizations of daily flowing vs dry periods of these reaches on the right, Including flow classification.
Daily flowing vs dry observations are derived from Stream Temperature, Intermittency, and Conductivity (STIC) loggers
deployed in the channel thalweg in erosional or riffle habitat in each study reach (Chapin et al. 2014, Kelso et al. 2023). For
these loggers, the presence of flowing surface water is inferred from raw intensity values that are higher than logger-
specific intensity values calibrated to distilled water (yellow lines). Blue areas above the yellow lines denote flowing periods
and black bars denote field visits when logger data was downloaded, and indicator data was collected.

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Section 1: Introduction and Background

These classes describe the typical patterns exhibited by a stream reach over multiple years, although
observed patterns in a single year may vary due to extreme and transient climatic events (e.g., severe
droughts). Although flow duration classes are not strictly defined by their sources of flow (e.g., storm
runoff, groundwater, snowmelt), the duration is often related to the relative importance of different
flow sources to stream reaches and the stability of their contributions. Perennial reaches have year-
round surface flow in the absence of drought conditions. Intermittent reaches have one or more
periods of extended surface flow in most years, where the flow is sustained by sources other than
surface runoff in direct response to precipitation, such as groundwater, melting snowpack, irrigation,
reservoir operations, or wastewater discharges. Ephemeral reaches have a surface flow for short
periods and only in direct response to precipitation.

This manual describes the final Streamflow Duration Assessment Method (SDAM) intended to
distinguish flow duration classes of stream reaches in the Great Plains (GP) region of the United States
as defined in Synthesizing the Scientific Foundation for Ordinary High-Water Mark Delineation in Fluvial
Systems (Wohl et al, 2016), which is based largely on vegetation type and precipitation levels (Figure
2). However the western boundary of GP is more precisely defined in the Arid West and Western
Mountains, Valleys and Coast regional supplements to the U.S. Army Corps of Engineers wetland
delineation manual (U.S. Army Corps of Engineers 2008, 2010).

Pacific
Northwest

Great
Plains

Arid
West

Northeast

Western
Mountains

Figure 2. Map of flow duration study regions.

The GP SDAM is based on biological and geomorphological indicators. Biological indicators, known to
respond to gradients of streamflow duration (Fritz et al. 2020), have notable advantages for assessing

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Section 1: Introduction and Background

natural resources. The primary advantage of these indicators is the ability to reflect long-term
environmental conditions (e.g., Karr et al. 1986, Rosenberg and Resh 1993) making them well suited
for assessing streamflow duration, because some species reflect the aggregate hydrologic conditions
that a stream has experienced over multiple years. As a result, relatively rapid field observations of
biological indicators made at a single point in time can provide long-term insights into streamflow
duration and other hydrological characteristics of a stream reach. Geomorphological indicators can
also be rapidly measured and provide information about the hydrologic drivers of streamflow duration.
For example, wide channels in areas with low precipitation are associated with shorter durations of
streamflow; in wetter areas, narrow channels are typically associated with headwaters, where the
contributing catchments may be too small to generate long-duration flows.

1.1 The SDAM for the Great Plains

This manual describes a method that uses a small number of indicators to predict the streamflow
duration class of stream reaches in the GP. All indicators are measured during a single field visit. A beta
SDAM for the GP was released in September 2022 (James et al. 2022a). After additional data collection,
analysis, and user feedback, this final SDAM was developed, reflecting somewhat different indicators
from the beta method. For more information on the development of the GP SDAM or SDAMs for other
U.S. regions, please refer to the U.S. Environmental
Protection Agency's (EPA's) SDAM website.

The GP SDAM assigns reaches to one of six possible
classifications: ephemeral, intermittent, perennial, at least
intermittent, less than perennial, and needs more
information. An at least intermittent classification occurs
when an intermittent or perennial classification cannot be
made with high confidence, but an ephemeral
classification can be ruled out. A less than perennial
classification is the opposite; an ephemeral or intermittent
classification cannot be made with high confidence, but a
perennial classification can be ruled out. If no class can be
determined with confidence, the stream is classified as
needs more information.

The method was developed using a machine learning
model known as a random forest. Random forest models
are increasingly common in the environmental sciences
because of their superior performance in handling complex relationships among indicators used to
predict classifications (Cutler et al. 2007). In some cases, a random forest model can be simplified into
a decision tree or table (e.g., Nadeau et al. 2015, Mazor et al. 2021); however, that was not possible for
the GP model. To obtain a flow classification for an individual assessment reach, there is an open-
access, user-friendly web application for entering indicator data and running the region-specific

Indicators of the GP SDAM

Biological indicators

•	Total aquatic
macroinvertebrate abundance

•	Number of hydrophytic plant
species

•	Presence/absence of rooted
upland plants in the streambed

•	Differences in vegetation

Geomorphological indicators

•	Bankfull channel width

•	Riffle-pool sequence

•	Particle size or stream
substrate sorting

•	Sediment on plants or debris

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Section 1: Introduction and Background

random forest model. No data entered into the web application are visible to or stored by the EPA or
any other agency.

1.2 Intended use and limitations

The GP SDAM is intended to support field classification of streamflow duration at the reach scale in
streams with defined channels (having a bed and banks) in the GP region. 3.5 Assessment reach
considerations discusses when more than one reach should be assessed to classify streamflow duration
for a stream segment longer than the assessment reach. Use of the GP SDAM may inform a range of
activities where information on streamflow duration is useful, including jurisdictional determinations
under the Clean Water Act; however, the classification resulting from use of an SDAM is not in itself a
jurisdictional determination. SDAMs are not mandatory for completing a Clean Water Act jurisdictional
determination, nor are they intended to supersede more direct measures of streamflow duration (e.g.,
long-term records from stream gages). Other sources of information, such as aerial imagery, reach
photographs, traditional ecological knowledge, and local expertise, can supplement the GP SDAM
when classifying streamflow duration (Fritz et al. 2020).

Although the GP SDAM is intended for use in both natural and altered stream systems, some
alterations may complicate the interpretation of field-measured indicators or potentially lead to
incorrect conclusions. For example, streams managed as flood control channels may undergo frequent
maintenance to remove some or all vegetation in the channel and along the banks of the assessment
reach. Although some biological indicators recover quickly from these disturbances, the results from
assessments conducted shortly after such disturbances may be misleading. In addition, these types of
channels may not display channel features that result from natural geomorphic processes, such as a
typical riffle-pool sequence.

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Section 1: Introduction and Background

1.3 Development of the GP SDAM

This method resulted from a multi-year study conducted in 287 locations across the Great Plains. Of
these, data from 268 sites (or reaches) where flow class could be determined from direct hydrologic
data were used to develop the GP SDAM (Figure 3). Of these 268 reaches, 72 were ephemeral, 103
were intermittent, and 93 were perennial. Streamflow duration class was directly determined from
continuous (hourly interval) data loggers deployed at the study reaches (170) or from active U.S.
Geological Survey (USGS) stream gages (28). Multiple sources of hydrologic data (e.g., inactive USGS
stream gage data, published studies, consultation with local experts) were used to classify the
remaining reaches (70), that did not have continuous data loggers deployed for this study.

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Section 1: Introduction and Background

Development of the GP SDAM followed the process steps below (Fritz et al. 2020):

Preparation

•	Conducted a literature review (James et al. 2022b):

o Identified existing SDAMs, focusing on those originating in the Great Plains or developed
using a similar approach (see Nadeau 2015; NMED 2020).

o Identified 27 potential field biological, hydrological, and geomorphological characteristics
related to streamflow duration for evaluation in the Great Plains.

•	Identified candidate study reaches with known streamflow duration class, representing
diverse environmental settings throughout the region.

Data Collection: Beta Method Development

•	Collected field data at 287 study reaches, visited up to 4 times.

Data Analysis

•	Evaluated 95 candidate metrics from the field data and GIS metrics for their ability to
discriminate among streamflow duration classes. GIS metrics included climatic measures that
characterize hydrologic drivers of streamflow duration (e.g., long-term precipitation and
temperature) and are straightforward to calculate.

•Calibrated a classification model using a machine learning algorithm (i.e., random forest).

•Refined and simplified the beta method for rapid and consistent application.

Evaluation / Beta Implementation

•	Published a beta method, data analysis report, and data used to develop the method.

•Trained the EPA and Corps staff on the beta method.

•Collected public comment and agency experience using the beta method for more than a year.

	'Collected additional data at study reaches for a maximum of 6 visits.	

Re-Analysis and Evaluation

•	Evaluated 97 candidate metrics from the field data and GIS metrics for their ability to
discriminate among streamflow duration classes. GIS metrics included climatic measures that
characterize hydrologic drivers of streamflow duration (e.g., long-term precipitation and
temperature) and are straightforward to calculate.

•Calibrated a classification model using a machine learning algorithm (i.e., random forest).

•Refined and simplified the final method for rapid and consistent application in light of the
agency experience and public comments received on the beta method.

Implementation

•Publish User Manual, data analysis report, and data used to develop the method.

•Publish web application and code.

•Publish training materials to support implementation.

	'Train the the EPA and Corps staff on the method and how to train others.	

The final method correctly classified 68% of study reaches among three classes (perennial vs.
intermittent vs. ephemeral), while 93% of study reaches were classified correctly between ephemeral
and at least intermittent and 75% between perennial and less than perennial. Generally,
misclassifications among intermittent and perennial reaches were more common than
misclassifications among ephemeral and intermittent reaches. The ability of the GP SDAM to
discriminate ephemeral more accurately and consistently from at least intermittent reaches is

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Section 1: Introduction and Background

consistent with previous studies evaluating streamflow duration indicators and assessment methods
(Fritz et al. 2008, 2013, Nadeau et al. 2015).

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Section 2: Overview of the GP SDAM and the Assessment Process

Section 2: Overview of the GP SDAM and the Assessment Process
2.1 Considerations for assessing streamflow duration and interpreting indicators

2.1.1	Clean Water Act jurisdiction

Regulatory agencies evaluate aquatic resources for jurisdiction based on applicable regulations,
guidance, and policy. The GP SDAM does not incorporate that broad scope of analysis. Rather, the GP
SDAM provides information that may be used to inform jurisdictional decisions because it helps
determine streamflow duration as ephemeral, intermittent, or perennial in the absence of a hydrologic
record.

2.1.2	Scales of assessment

The GP SDAM applies to an assessment reach, the length of which scales with the mean bankfull
channel width. Regardless of channel width, reaches must be a minimum of 40 m and no longer than
200 m. The minimum reach-length of 40 m ensures that a sufficient area has been assessed to evaluate
indicators. Quantification and observations of indicators are restricted to the bankfull channel and
within one-half bankfull channel width from the top of each bank. However, ancillary information from
outside the assessment reach (such as surrounding land use) is also recorded.

2.1.3	Spatial variability

Indicators of streamflow duration (and other biological, hydrologic, and geomorphic characteristics of
streams) vary in their strength of expression within and among reaches in a stream system. The main
natural drivers of spatial variation are generally the physiographic province (e.g., geology and soils) and
climate (e.g., seasonal patterns of precipitation, snowmelt, and evapotranspiration). For example,
certain indicators, such as riparian vegetation, may be more strongly expressed in a floodplain with
deep alluvial soils than they would be in a reach underlain by shallow bedrock, even if both reaches
have a similar duration of flow. Therefore, understanding the sources of spatial variability in
streamflow indicators will help ensure that assessments are conducted within relatively homogenous
reaches.

Common sources of variation within a stream system that may affect the expression of indicators
include:

•	Natural longitudinal changes in channel gradient and size, and valley width (e.g., going from a
confined canyon to an alluvial fan, or going from wide to narrow valley).

•	Other natural sources of variation, such as bedrock material (limestones, sandstones, shales,
conglomerates, and lignite) or water source (runoff, springs, summer rains, and groundwater).

•	Drought or unusually high precipitation.

•	Transitions in land use with different water use patterns (e.g., from commercial forest to
pasture, from pasture to cultivated farmland, or cultivated farmland to an urban setting), or
changes in management practices (e.g., intensification of grazing).

•	Stream management and manipulation, such as diversions, water importation, dam operations,
and habitat modification (e.g., streambed armoring).

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Section 2: Overview of the GP SDAM and the Assessment Process

2.1.4	Temporal variability

Temporal variability in indicators may affect streamflow duration assessment in two ways: interannual
(e.g., year-to-year) variability and intra-annual (e.g., seasonal) variability. This method was developed
to be robust to both types of temporal variability and is intended to classify streams based on their
long-term patterns in either flowing or dry conditions. However, both long-term sources of temporal
variability (such as El Nino-related climatic cycles) and short-term sources (such as scouring storms
before sampling) may influence the ability to measure or interpret indicators at the time of
assessment. Timing of management practices, such as dam operations, channel clearing, or
groundwater pumping, may also affect the flow duration assessment.

Some indicators are highly responsive to temporal variability. For example, the GP is known to
experience high intensity, short-lived flood events. After these scouring events, aquatic
macroinvertebrates may be displaced from a stream reach. In contrast, rooted hydrophytic plants, if
present, will likely remain. Similarly, greater numbers of aquatic macroinvertebrates may be able to
colonize an ephemeral to intermittent reach during wet years, depending on the presence of upstream
or downstream refugia; however, changes in flow regimes may take several years to result in changes
to vegetation in the riparian corridor. For example, willows with well-established root systems are
likely to survive in an intermittent reach experiencing severe drought, even when flow in a single year
is insufficient to support aquatic macroinvertebrates in greater numbers or at all.

2.1.5	Ditches and modified natural streams

Assessment of streamflow duration is sometimes needed in canals, ditches, and modified natural
streams that are primarily used to convey water. These systems tend to have altered flow regimes
compared to natural systems with similar drainage areas (Carlson et al. 2019), and the GP SDAM may
determine if these flow regimes support indicators consistent with different streamflow duration
classes. Thus, the GP SDAM may be applied to these systems when streamflow duration information is
needed.

Geomorphological indicators (specifically, bankfull channel width and riffle-pool sequence) may be
difficult to assess in straightened or heavily modified systems. Indicator measurements should be
based on present-day conditions, not historic conditions. Assessors should note if the channel
geomorphology reflects natural processes or if it reflects the effects of management activities.

2.1.6	Other disturbances

Assessors should be alert for natural or human-induced disturbances that either alter streamflow
duration directly or modify the ability to measure indicators. Streamflow duration can be directly
affected by groundwater withdrawals, flow diversions, urbanization and stormwater management,
septic inflows, agricultural and irrigation practices, effluent dominance, or other activities. In the
method development data set, disturbed reaches were identified as those in urban or agricultural
settings or those with notable impacts from grazing, mining, or other human activities; the GP SDAM
classified disturbed reaches with similar accuracy as undisturbed reaches.

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Section 2: Overview of the GP SDAM and the Assessment Process

Streamflow duration indicators can also be affected by disturbances that may not substantially affect
streamflow duration (for instance, grading, grazing, recent fire, riparian vegetation management, and
bank stabilization); in extreme cases, these disturbances may eliminate specific indicators (e.g.,
absence of aquatic macroinvertebrates in channels that have undergone recent grading activity).
Groundwater pumping, impoundments, and diversions can affect both vegetation and
geomorphological indicators (e.g., Friedman et al. 1997). Some long-term alterations or disturbances
(e.g., impoundments) can make streamflow duration class more predictable by reducing year-to-year
variation in flow duration and/or indicators. Discussion of how specific indicators are affected by
disturbance is provided below in Section 3: Data Collection. Assessors should describe disturbances in
the "Notes on disturbances or difficult assessment reach conditions" section of the field form.

2.1.7 Multi-threaded systems

Assessors should identify the lateral extent of the active channel, based on the outer limits of ordinary
high-water mark (OHWM). and apply the method to that area. That is, do not perform separate
assessments on each of the main and secondary channels within a multi-threaded system. Some
indicators may be more apparent in the main channel versus the secondary channels; note these
differences on the field form. Upland islands within the OHWM should not be included in the
assessment.

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Section 3: Data Collection

Section 3: Data Collection
3.1 Conduct desktop reconnaissance

Before an assessment, desktop reconnaissance helps ensure a successful assessment of a stream.
During desktop reconnaissance, assessors evaluate reach
accessibility and set expectations for conditions that may
affect field sampling. In addition, assessors can begin to
compile additional data that may inform determination of
streamflow duration, such as location of nearby stream
gages.

This stage of the evaluation is crucial for determining reach
access. The reach or project area should be plotted on a map to determine access routes and whether
landowner permissions are required. Safety concerns or hazards that may affect sampling should be
identified, such as road closures, controlled burns, or hunting seasons. These access constraints are
sometimes the most challenging aspect of environmental field activities, and desktop reconnaissance
can reduce these difficulties. Also, assessors can determine if inaccessible portions of the reach (e.g.,
those on adjacent private property) have consistent geomorphology or other attributes, compared
with accessible portions.

Desktop reconnaissance can also help identify features that may affect assessment reach placement or
determine the number of assessment reaches required for a project. Look for natural and artificial
features that may affect streamflow duration at the reach—particularly those that may not be evident
during the field visit, or that are on inaccessible land outside the assessment area. These features
include sharp transitions in geomorphology, upstream dams or reservoirs, springs, storm drains and
major tributaries. It may be possible to see bedrock outcrops or other features that modify streamflow
duration in sparsely vegetated areas.

A preliminary assessment of adjacent landuse may be ascertained during desktop reconnaissance. This
preliminary assessment should be verified during the field visit.

Evaluating watershed characteristics during desktop reconnaissance can produce useful information
that will help assessors anticipate field conditions or provide contextual data to help interpret results.
The USGS StreamStats tool, as well as the EPA's WATERS GeoViewer. provide convenient online access
to watershed information for most assessment reaches in the United States, such as drainage area,
soils, land use or impervious cover in the catchment, or modeled bankfull channel dimensions and
discharge.

Assessors should consider consulting local experts and agencies to gain further insights about reach
conditions and request additional available data. For example, state agencies may have records on
water quality sampling indicating times when the reach was sampled and when it was dry. Local
experts may have information about changes in the reach's streamflow.

Desktop Reconnaissance for:

•	Access, permissions and permits;

•	Reach placement;

•	Watershed and site context; and

•	Flora and fauna lists.

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Local or regional flora lists of species known to grow in the vicinity of an assessment reach may be
available to assist with plant identification and helpful for determining a plant's hydrophytic status.
Nearby public land managers (such as U.S. Forest Service or the National Park Service) should be
consulted to see if they have lists of common riparian plants in the vicinity of the assessment reach.
Several online databases can generate regionally appropriate flora lists and/or assist with identification
(Table 1), check the SPAM website for updates to the list of references. Note that there are multiple
National Wetland Plant List (NWPL) regions that overlap with the region covered by the GP SDAM;
consult the appropriate list for your location (see further discussion under 3.8.3 Number of
hydrophytic plant species).

Table 1. Examples of online resources for generating local flora lists.

| Resource

Geographic coverage |

National Wetland Plant List

United States and territories

The Biota of North America Program (BONAP)
Vascular Flora Taxonomic Data Center

United States and territories

USDA Plants Database

United States and territories

Consortium of Midwest Herbaria

Illinois, Michigan, Minnesota, and Wisconsin

Lady Bird Johnson Wildflower Center

Continental U.S. (native species only)

Kansas Wildflowers and Grasses

Kansas

Rocky Mountain Herbarium

Montana, Wyoming, Colorado, Utah,
Arizona and New Mexico

Minnesota Wildflowers

Minnesota

Desktop reconnaissance also helps determine if permits are required to collect aquatic
macroinvertebrates. Threatened and endangered species may be expected in the area, and stream
assessment activities may require additional permits from appropriate federal, Tribal, and state
agencies. Additional information on threatened or endangered species may be found on the U.S. Fish
and Wildlife Service's Environmental Conservation Online System, as well as at state resource agencies
and natural heritage programs.

3.2 Prepare sampling gear

The following gear is suggested for completion of the GP SDAM. Ensure that all equipment is functional
before each assessment visit and has been cleaned off-site between assessment visits to prevent the
spread of invasive species.

•	This manual and field forms (paper or digital).

•	Clipboard, pencils, permanent markers, field notebook.

•	Flagging tape.

•	Maps and aerial photographs (1:250 scale if possible).

•	Global Positioning System (GPS) - used to identify the downstream boundary of the reach
assessed. A smartphone that includes a GPS may be a suitable substitute.

•	Tape measures - for measuring bankfull channel width and reach length.

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•	Kick-net or small net and tray - used to sample aquatic macroinvertebrates.

•	Hand lens - to assist with plant and aquatic macroinvertebrate identification.

•	Digital camera (or smartphone with camera), plus charger. Ideally, use a camera that
automatically records metadata, such as time, date, directionality, and location, as part of the
EXIF data associated with the photograph.

•	Shovel, soil auger, rock hammer, hand trowel, pick or other digging tools to facilitate
hydrological observations of subsurface flow.

•	Aquatic macroinvertebrate field guides (e.g., Guide to Aquatic Invertebrates of the Upper
Midwest, Bouchard et al. 2004).

•	Vials filled with 70% ethanol and sealable plastic bags for collection of biological specimens,
with sample labels printed on waterproof paper.

•	Bags or plant press for collecting plant vouchers.

•	Hydrophytic plant identification guides (e.g., Wetland and Aquatic Plants of the Northern Great
Plains, Chadde 2019).

•	The U.S. Army Corps of Engineers List of wetland plants for sites to be visited.

•	Boots or waders.

•	First-aid kit, sunscreen, insect repellant, and appropriate clothing.

Sampling gear that comes into contact with the water (such as nets and boots or waders) should be
properly decontaminated to prevent the spread of aquatic invasive species. Stop Aquatic Hitchhikers.
an initiative of Aquatic Nuisance Species Task Force sponsored by USFWS provides resources and links.

3.3 Order of operations for completing the GP SDAM field assessment

After completing the in-office activities described above, the following general workflow is
recommended for efficiency in the field:

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1. Walk Assessment Reach (avoid walking in channel)

•Confirm assessment reach placement in the field (3.5.1).

•Measure the bankfull channel width at 3 locations and calculate average to determine
assessment reach length and identify reach boundaries (3.5.2). Record average bankfull
channel width in Step 2.

•Record coordinates of downstream reach boundary from center of channel and
photograph reach.

•Begin to note expression and strength of indicators (except bankfull width and aquatic
macroinvertebrate indicators).

•Take photographs at middle and upstream end of reach.

•Start sketching assessment reach on field form.

2. Record General Reach Site Information on Field Form (3.7.1)

3. Evaluate Indicators (3.8)

•Collect aquatic macroinvertebrates from reach, starting from downstream end.

•Identify hydrophytic vegetation taxa and determine presence/absence of upland plants
in the channel.

•Assess the degree to which the riparian corridor has different or more vigorous
vegetation than surrounding uplands.

•Assess the expression and degree of a riffle-pool sequence.

•Assess the degree of substrate sorting and/or difference of channel substrate material
from surrounding uplands.

•Assess the expression and degree of fine sediment on plants and/or debris.

•Complete sketch of the assessment reach on the field form.



4. Review Field Form for Completeness











5. Enter Data into Web Application (in office)







3.4 Timing of sampling

Ideally, application of the GP SDAM should occur during the growing season when many aquatic
macroinvertebrates are most active, hydrophytes are readily identifiable, and differences in vegetation
or growth vigor in the riparian corridor are easier to discern. Assessments may be made during other
times of the year, but there is an increased likelihood of specific indicators being dormant or difficult to
observe at the time of assessment, especially in northern parts of the GP, where the presence of snow
and channel ice during the colder months may also be a factor. However, most of the indicators
included in the method persist well beyond a single growing season (e.g., hydrophytic vegetation) or
are not dependent on it (e.g., geomorphological indicators), reducing the sensitivity of the method to
the timing of sampling.

The protocol may be used in flowing streams as well as in dry or drying streams. However, care should
be taken to avoid sampling during flooding conditions and assessors should wait at least one week
after large storm events that impact vegetation and sediment in the active stream channel before
collecting data to allow aquatic macroinvertebrates and other biological indicators to recover (Grimm
and Fisher 1989; Hax and Golladay 1998; Fritz and Dodds 2004). In general, aquatic macroinvertebrate

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abundance is suppressed during and shortly after major channel-scouring events, potentially leading to
inaccurate assessments. Recent rainfall can interfere with measurements (e.g., by washing away
aquatic macroinvertebrates). Assessors should note recent rainfall events on the field form and
consider the timing of field evaluations to assess each indicator's applicability. Field evaluations should
not be completed within one week of significant rainfall that results in surface runoff. Local weather
data and drought information should be reviewed before assessing a reach or interpreting indicators.
Evaluating antecedent precipitation data from nearby weather stations after each sampling event
helps to determine if storms may have affected data collection and informs interpretation of GP SDAM
data. The Antecedent Precipitation Tool (APT; U.S. Army Corps of Engineers 2023) can also be helpful
for evaluating recent precipitation conditions at a site relative to the 30-year average.

3.5 Assessment reach considerations

3.5.1 Reach placement

Stream assessments should begin by first walking the channel's length, to the extent feasible, from the
target downstream end to the top of the assessment reach. This initial review of the reach allows the
assessor to examine the channel's overall form, landscape, parent material, and variation within these
attributes as they develop or disappear upstream and downstream. This helps determine whether
adjustments to assessment reach boundaries are needed, or whether multiple assessment reaches are
needed to adequately characterize streamflow duration throughout the project area where
information is needed. Walking alongside, rather than in, the channel is recommended for the initial
review to avoid unnecessary disturbance to the stream. Walking alongside the channel also allows the
assessor to observe the surrounding landscape's characteristics, such as land use and sources of flow
(e.g., stormwater pipes, springs, seeps, and upstream tributaries).

The assessor should document the areas along the stream channel where various sources (e.g.,
stormflow, tributaries, or groundwater) or sinks of water (alluvial fans, abrupt changes in bed slope,
etc.) may cause abrupt changes in flow duration. When practical, assessment reaches should have
relatively uniform channel morphology. When evaluating the reach's homogeneity, focus on
permanent features that control streamflow duration (such as valley gradient and width), rather than
on the presence or absence of surface water. Project areas that include confluences with large
tributaries, significant changes in geologic confinement, or other features that may affect flow duration
may require separate assessments above and below the feature.

For some applications, reach placement is dictated by project requirements. For example, a small
project area may be fully covered by a single assessment reach. In these cases, assessment reaches
may contain diverse segments with different streamflow duration classes (e.g., a primarily perennial
reach with a short intermittent portion where the flow goes subsurface). In these cases, the portions of
the reach with long-duration flows will likely have a greater influence on the outcome than the
portions with short-duration flows, depending on each portion's relative size.

Natural features, such as bedrock outcrops or valley confinements, and non-natural features like
culverts or road crossings may alter hydrologic characteristics in their immediate vicinity. For example,

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culverts may create plunge pools, and drainage from roadways is often directed to roadside ditches
that enter the stream near crossings, leading to a potential increase in indicators of long streamflow
duration. Specific applications may require that these areas be included in the assessment, even
though they are atypical of the larger assessment reach. For other applications, the area of influence
may be avoided by moving the reach at least 10 m up- or downstream.

3.5.2	Reach length

An assessment reach should have a length equal to 40 bankfull channel-widths, with a minimum
length of 40 m and a maximum of 200 m. An assessment reach should not be less than 40 m in length
to ensure that sufficient area is assessed to observe and appropriately measure indicators.
Assessments based on reaches shorter than 40 m may not detect all indicators and could provide
inaccurate classifications.

Bankfull channel width is averaged from measurements at three locations: at the bottom of the reach,
15 m upstream, and 30 m upstream from the bottom of the reach, or at three locations that are
representative of the reach as a whole. See 3.7.1 General reach information and 3.8.1 Bankfull channel
width for more guidance on measuring bankfull channel width. Width measurements are made at
bankfull elevation, perpendicular to the thalweg (i.e., the deepest point within the channel that
generally has the greatest portion of flow); how to find bankfull elevation is discussed in 3.7.1 General
reach information. In multi-thread systems, the bankfull width is measured for the entire active
channel, based on the outer limits of the OHWM. Reach length is measured along the thalweg (Figure
4). If access constraints require a shorter assessment reach than needed, the actual assessed reach-
length should be noted on the field form along with an explanation for why a shortened reach was
necessary.

Note that bankfull channel width is also an indicator of streamflow duration, as described below in
3.8.1 Bankfull channel width.

3.5.3	How many assessment reaches are needed?

The outcome of an assessment applies to the assessed reach and may also apply to adjacent reaches
some distance upstream or downstream if the same conditions are present. The factors affecting
spatial variability of streamflow duration indicators (described above) dictate how far from an
assessment reach a classification applies. More than one assessment may be necessary for a large or
heterogenous project area and multiple assessments are usually preferable to a single assessment. In
areas that include the confluence of large tributaries, road crossings, or other features that may alter
the hydrology, multiple assessment reaches may be required (e.g., one above and one below the
feature).

3.6 Photo-documentation

Photographs can provide strong evidence to support conclusions resulting from application of the GP
SDAM, and extensive photo-documentation is recommended. Taking several photos of the reach
condition and any disturbances or modifications relevant to making a final streamflow duration

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classification is strongly recommended. Specifically, the following photos should be taken as part of
every assessment:

•	A photograph from the top (upstream) end of the reach, looking downstream.

•	Two photographs from the middle of the reach, one looking upstream and one looking
downstream.

•	A photograph from the bottom (downstream) end of the reach, looking upstream.

Photographs that illustrate the following are also strongly recommended:

•	Hydrophytic plant identifications, showing diagnostic features and extent within the reach.

•	Extent of rooted upland plants in channel.

•	Typical riffle-pool sequence, if present

•	Particle size and/or stream substrate sorting.

•	Disturbed or unusual conditions that may affect the measurement or interpretation of
indicators.

3.7 Conducting assessments and completing the field form

3.7.1 General reach information

After walking the reach and determining the appropriate boundaries for the assessment area, record
on the field form the project name, reach code or identifier, waterway name, assessor(s) name(s), and
the date of the assessment visit. These data provide essential context for understanding the
assessment but are not indicators for determining streamflow duration class.

Coordinates

Record the coordinates of the downstream end of the reach from the center of the channel.

Weather conditions

Note current weather conditions (e.g., rain and intensity, sun, clouds, snow). If known, note
precipitation within the previous week on the datasheet, and consider delaying sampling, if possible. If
rescheduling is not possible, note whether the streambed is recently scoured, and if turbidity is likely
to affect the measurement of indicators.

Surrounding land use

A preliminary assessment of surrounding land use should be conducted during desktop reconnaissance
(see 3.1 Conduct desktop reconnaissance). Once at the site, verify whether the preliminary assessment
is correct, making sure to note evidence of human activities that may not be evident in aerial imagery.

Indicate the dominant land-use around the reach within a 100-m buffer. Check up to two of the
following:

•	Urban/industrial/residential (buildings, pavement, or other anthropogenically hardened
surfaces).

•	Agricultural (e.g., farmland, crops, vineyard, pasture).

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•	Developed open space (e.g., golf course, sports fields).

•	Forested.

•	Other natural.

•	Other (describe).

Bankfull channel width

Measure bankfull channel width values (to nearest 0.1 m) at 0, 15, and 30 m above the downstream
end of the reach or at three locations spread out over approximately one-third of the expected reach
length and record values on the field form (Figure 5 and Figure 5). Note, this approach replicates how
the data used to develop this SDAM was collected at study reaches across the GP. Widths should be
measured perpendicular to the thalweg. In multi-threaded systems, width measurements should span
all channels within the OHWM. Calculate the average width.

Flow

# Photopoint location
	 Bankfull width measurement

Figure 4. Bankfull measurement and photo point locations.Bankfull is represented by the yellow area and the
blue line represents the thalweg of the channel. It is suggested that bankfull width be measured from the
downstream end of the reach, but it is not required, as long as the three locations are spread out over one-third
of the expected reach length.

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Section 3: Data Collection

Figure 5. Measuring bankfull width, image credit: james Treacy

The bankfull width2, is the portion of the channel that contains the bankfull discharge, which is a flow
event that occurs frequently (typically every 1.01 to 5 years; David and Hamill 2024), but that does not
include larger flood events. The bankfuli discharge has an important role in forming the physical
dimensions of the channel. For many stream channels, the bankfull elevation (from where bankfull
width is measured) can be identified in the field by an obvious slope break that differentiates the
channel from a relatively flat floodplain terrace higher than the channel, or a transition from exposed
stream sediments or more water and scour tolerant vegetation (e.g., willows) to terrestrial and
intolerant vegetation (David et al, 2022). In locations without vegetation, moss growth on rocks along
the banks can be an indicator of bankfull height as can breaks in bank slope or changes in substrate
composition.

Certain indicators of bankfull height may be more or less evident in different stream types, so assessors
should evaluate multiple bankfull indicators when measuring bankfull channel width. The bankfull
width should be measured in a straight section of the stream (e.g., riffle, run, or glide if present) that is
representative of the study reach. Pools and bends in the stream or areas where the stream width is
affected by the deposition of rocks, debris, fallen trees, or other unusual constrictions or expansions
should be avoided. In the field, it may often be possible to determine the bankfull channel width using
bankfull indicators on only one bank of the stream. This point can be used as a reference to determine
the bankfull elevation on the opposite bank by creating a level line across the stream from the
identified bankfull elevation perpendicular to the stream flow.

2 Resources for bankfull identification are found on the SPAM training materials site.

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In larger systems (e.g., drainage area > 0.5 square miles), it may be helpful to compare field
measurements to bankfull channel dimensions derived from regional curves relating bankfull
dimensions to watershed characteristics. These models may be derived at a national or regional scale
(e.g., StreamStats; U.S. Geological Survey 2024) or a local scale (e.g., Texas: Asquith et al. 2020;
Wyoming: Foster (2012)). Bieger et al. (2015) provides regional curves for several regions of the
continental United States. If observed bankfull dimensions are substantially different from estimated
bankfull dimensions derived from regional curves (e.g., more than twice the maximum or less than half
the minimum estimates), it may be helpful to re-evaluate bankfull indicators that were used to
establish bankfull channel height. Regional curve estimates for bankfull dimensions of small channels
(small drainage areas) may be extrapolated outside the range used to develop relationships so such
estimates have unknown errors (bias) associated with them and should be used with caution if at all.

Note that bankfull channel width is also an indicator of streamflow duration, as described below in
3.8.1 Bankfull channel width-

Describe reach length and boundaries

Record the reach length in meters as described in 3.5.2 Reach length. Record observations about the
reach on the field form, such as changes in land use, disturbances, or natural changes in stream
characteristics that occur immediately up or downstream. If the reach is less than 200 m and shorter
than 40 times the average bankfull channel width, explain why a shorter reach length was appropriate.
For example: "The downstream end is 30 m upstream of a culvert under a road. The upstream end is
close to a conspicuous dead tree just past a large meander, near a fence marking a private property
boundary. The reach length was shortened to 150 m to avoid private property."

Photo-documentation of reach

Record the photo ID or number, or check the designated part of the field form for required
photographs taken from the bottom (facing upstream), middle (facing upstream and downstream) and
top (facing downstream) of the reach (see Figure 4).

Disturbed or difficult conditions

Note any disturbances or unusual conditions that may create challenges for assessing flow duration.
Common situations include practices that alter hydrologic regimes, such as diversions, culverts,
discharges of effluent or runoff, and drought. Note circumstances that may limit the growth of
hydrophytes and/or affect stream geomorphology, such as channelization, or vegetation removal that
may affect the measurement or interpretation of several indicators (Figure 6). Also note if the stream
appears recently restored, for example, stream armoring with large substrate or wood additions and
recently planted vegetation in the riparian zone.

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Figure 6. Examples of difficult conditions that may interfere with the observation or interpretation of indicators. Left: As the
San Marcos River progresses through the city of San Marcos in Texas, its banks have been hardened and the natural riparian
vegetation has been removed (though there is still aquatic vegetation apparent in the channel itself). The removal of in-
stream and riparian zone habitat and addition of urban non-point source discharges may also impact the abundance of
aquatic macroinvertebrates and hardened banks may obscure identification of bankfull elevation. Right: Keenan Creek in
Wisconsin has been straightened and channelized, affecting naturally occurring stream pattern (e.g., riffle-pool sequence).
Image credits: James Treacy.

Observed hydrology

Surface flow

Visually estimate or use a tape measure to determine the percentage of the reach length that has
flowing surface water or subsurface flow. The reach sketch should indicate where surface flow is
evident and where dry portions occur.

Subsurface flow

If the reach has discontinuous surface flow, investigate the dry portions to see if subsurface flow is
evident. Examine below the streambed by turning over cobbles and digging with a trowel. Resurfacing
flow downstream may be considered evidence of subsurface flow (Figure 7). Other evidence of
subsurface flow includes:

•	Flowing surface water disappears into alluvial deposits and reappears downstream. This
scenario is common when a large, recent alluvium deposit created by a downed log or other
grade-control structure creates a sharp transition in the channel gradient or in valley
confinement.

•	Water flows out of the streambed (alluvium) and into isolated pools.

•	Water flows below the streambed and may be observed by moving streambed rocks or digging
a small hole in the streambed.

•	Shallow subsurface water can be heard moving in the channel, particularly in steep channels
with coarse substrates.

Record the percent of the reach length with subsurface and surface flow (combined). That is, the
percent of reach length with subsurface flow should be greater than or equal to the percent of reach
length with surface flow (Figure 7).

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The reach sketch should indicate where subsurface flow is evident.

Number of isolated pools

If the reach is dry or has discontinuous surface flow, look for isolated pools within the channel that
provide aquatic habitat. If there is continuous surface flow throughout the reach, enter 0 (zero)
isolated pools. The reach sketch should indicate the location of pools in the channel or on the
floodplain (Figure 7). However, only isolated pools within the channel are counted, including isolated
pools within secondary channels that are part of the active channel and within the OHWM. Pools
connected to flowing surface water and isolated pools on the floodplain do not count. Dry pools (i.e.,
pools that contain no standing water at the time of assessment) do not count.

100% surface flow
100% surface +
subsurface flow
0 isolated pools

B

/

70% surface flow
70% surface +
subsurface flow
0 isolated pools

/

r

80% surface flow
100% surface +
subsurface flow
0 isolated pools

/
/

70% surface flow
70% surface +
subsurface flow
1 isolated pool

Figure 7. Examples of estimating surface and subsurface flow, and isolated pools. Orange represents the dry channel and
blue represents surface water in the channels. White represents the floodplain outside the channel. The pool in A does not
count because it is outside the channel, whereas the pools in B and C do not count because they are connected to flowing
surface water. In contrast, the lower pool in D counts because it is isolated from any flowing surface water and is within the
channel.

3.7.2 Assessment reach sketch

Sketch the assessment reach on the field form, indicating important features, such as access points,
important geomorphological features, the extent of dry or aquatic habitats, riffles, pools, etc. Note
locations where photographs are taken and where channel measurements are made.

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3.8 How to measure indicators of streamflow duration

Assessments are based on the measurement of eight indicators of streamflow duration. All must be
evaluated to determine a flow classification.

Biological indicators

•	Total aquatic macroinvertebrate abundance

•	Number of hydrophytic plant species

•	Presence/absence of rooted upland plants in the streambed

•	Differences in vegetation

Geomorphological indicators

•	Bankfull channel width

•	Riffle-pool sequence

•	Particle size or stream substrate sorting

•	Sediment on plants or debris

Total aquatic macroinvertebrate abundance, number of hydrophytic plant species, differences in
vegetation, riffle-pool sequence, particle size/stream substrate sorting, and sediment on plants or
debris are positive indicators of streamflow duration. A greater abundance or strength of these
indicators is generally associated with longer duration flows (e.g., Dodds et al. 2004, Burk and Kennedy
2013, Bigelow et al. 2020). For example, hydrophytic riparian corridor vegetation and a stronger riffle-
pool sequence are both associated with perennial reaches. The relationship between streamflow
duration and bankfull channel width is less straightforward. In general, wider channels are more likely
to be perennial and positioned lower in the watershed than narrower non-perennial channels (Lenhart
et al. 2023). Rooted upland plants and abundance of ephemeral indicator taxa are negative indicators
of streamflow duration. Greater abundance or expression of rooted upland plants in the assessment
reach is associated with shorter flow duration classes, as are the presence of taxa determined to be
tolerant of ephemeral flow.

These indicators are based on what is observed at the time of assessment, not on what would be
predicted to occur if the channel were wet, or in the absence of disturbances or modifications.
Disturbances and modifications (e.g., vegetation management, channel hardening, diversions) should
be described in the "Notes" section of the datasheet and are considered when drawing conclusions.
Common ways that disturbances can interfere with indicator measurement are described within each
indicator description, where applicable. The indicators are presented in the order they appear on the
field forms, reflecting the recommended order of operations for efficiency in the field.

3.8.1 Bankfull channel width

Bankfull channel width is generally associated with streamflow duration, as wider channels tend to
reflect longer-lasting flows. However, this pattern is sometimes reversed in more arid regions and in
regions overlying alluvial geology. While this reversed pattern is more common in a region like the Arid
West, it may also occur within the GP, particularly near its boundary with the Arid West (parts of New
Mexico, Texas, and Wyoming). Bankfull channel width is measured (to the nearest 0.1 m) at three

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locations during the initial layout of the assessment reach and then averaged, as described in 3.5
Assessment reach considerations. In multi-threaded channels, the width of the entire active channel is
measured, based on the outer limits of the OHWM. Wohl et al. (2016) describe the active channel as
the portion of the valley bottom distinguished by one or more of the following characteristics:

•	Channels defined by erosional and depositional features created by river processes (as opposed
to upland processes, such as sheet flow or debris flow).

•	The upper elevation limit at which water is contained within a channel.

•	Portions of a channel generally without trunks of mature woody vegetation.

3.8.2 Total aquatic macroinvertebrate abundance

This indicator scores the total abundance of aquatic macroinvertebrates in the reach, including insects
and non-insects. It does not require identification of aquatic macroinvertebrates; however, counted
individuals must only represent aquatic stages (or instars). Both living material (e.g., live larvae) and
non-living material (e.g., caddisfly cases, shed exuviae) are equally considered during enumeration.

A user will choose between three categories for this indicator. Counting of individuals is only required
up to ten.

•	Total abundance of aquatic macroinvertebrates is zero;

•	Total abundance is >1 and <10; or

•	Total abundance is >10.

Sample Collection Instructions

Aquatic macroinvertebrates are assessed within the defined reach. A kick-net or D-frame net is used to
collect specimens. Assessors begin sampling at the most downstream point in the assessment reach
and proceed to sample the upstream direction. Where there is rapidly flowing water, the net is placed
perpendicular against the streambed while the substrate is disturbed upstream of the net for a
minimum of one minute. This disturbance will dislodge and suspend aquatic macroinvertebrates such
that they are carried by the stream flow into the net. For slower flowing or standing water areas, jab
the net under banks, overhanging terrestrial and aquatic vegetation, leaf packs, and in log jams or
other woody material to dislodge and capture aquatic macroinvertebrates and the leaves or other light
materials they may be clinging to. Samples should be collected from at least six distinct locations
representing the different habitats occurring in the reach. Without releasing aquatic
macroinvertebrates, strain the net contents to remove fine sediments that would interfere with
observing them. Empty contents of the net into a white tray with fresh stream water for determining
abundance of individuals present.

Searching is complete when:

•	At least six different locations within the reach have been sampled across the range of habitat
types and a minimum of 15 minutes of effort expended (not including sample sorting to
facilitate enumeration), or

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• All available habitat in the assessment reach has been completely searched in less than 15
minutes. A search in dry stream channels with little bed or bank development and low habitat
diversity may be completed in less than 15 minutes.

During the 15-minute sampling period, search the full range of habitats present, including: water under
overhanging banks or roots, in pools and riffles, accumulations of leaf packs, woody debris, and coarse
inorganic particles (i.e., pick up rocks and loose gravel). If a reach contains both dry and wet areas,
focus on searching the wet habitats, as these are the most likely places to encounter aquatic
macroinvertebrates, but do not ignore dry areas.

Dry channels: Focus the search on areas serving as refuge such as any remaining pools or areas of
moist substrate for living aquatic macroinvertebrates, and under cobbles and other larger bed
materials for evidence such as caddisfly casings (Figure 8) and snail shells. Exuviae of emergent
mayflies or stoneflies may be observed on dry cobbles or stream-side vegetation (Figure 8). In
summary, sampling methodology consistent with the Xerces Society's recommendations on using
aquatic macroinvertebrates as indicators of streamflow duration (Blackburn and Mazzacano 2012), as
developed for the Pacific Northwest SDAM (Nadeau 2015) is recommended. Take care, especially in dry
channels, to only collect aquatic species and life stages. Field guides (e.g., Voshell 2002) and
identification keys (e.g., Merritt et al. 2019) are recommended, especially if users are unfamiliar with
common types of aquatic macroinvertebrates.

When searching dry channels (or dry portions of partially wet channels), be sure to avoid counting
terrestrial macroinvertebrates in the streambed. Figure 9 depicts some taxa (especially snails) that may
be found near stream channels in the GP, though this list is certainly not exhaustive. If you are unsure
whether the invertebrates you encounter are aquatic or terrestrial, collecting a voucher specimen and
identifying it in a lab setting or consulting an entomologist is recommended.

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Section 3: Data Collection

Figure 8, Examples of evidence of aquatic macroinvertebrates in dry channels. Left: Caddisfly cases may persist under large
cobbles or boulders well after the cessation of flow. Right: Stonefly (Plecoptera) exuvia. Exuviae are left behind when
aquatic nymphs or pupae emerge from the stream and go through a final molt to metamorphose to winged adults. Image
credits: Raphael Mazor.

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Section 3: Data Collection

Figure 9. Examples of terrestrial macroirivertebrates you may find in a dry channel, Top left: larvae of soldier flies
(Stratiomyidae); Top right: garden snail (Cornu aspersum) (Image credits: Raphael Mazor); Middle left: Prairie rabdotus
(Rabdotus mooreanus) (Image credit: David G, Barker CC-BY-NC); Middle right: Decollate snail (Rumina decollata) (Image
credit: Nicholas Cowev CC-BY-NC); Bottom left: White-lipped globe snail (Mesodon thyroidus) (Image credit: Meghan
Cassidv CC-BY-SA); Bottom right: White-washed rabdotus (Rabdotus deaibatus) (Image credit: Sam Kieschnick CC-BY).

3.8.3 Number of hydrophytic plant species

For the GP SDAM, hydrophytes are defined as those with a Facultative Wetland (FACW) or Obligate
(OBL) wetland indicator status in the National Wetland Plant List (U.S. Army Corps of Engineers 2020).

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The GP region encompasses multiple NWPL regions, including all or large parts of the Great Plains,
Midwest (MW), and Northcentral Northeast (NCNE) (Figure 10). Indicator status for certain species
may differ between regions; therefore, it is important to consult the correct list when determining
indicator status. For example, stinging nettle (Urtica dioica), a common, widespread herb often found
growing in riparian zones, is FACW in the MW but only Facultative (FAC) in the GP and NCNE.

Coastal Plain (AGCP)

Figure 10. National Wetland Plant List (NWPL) regions that overlap with the GP SDAM region.

Hydrophytic plant species that exhibit an odd or unusual distribution pattern in the assessment reach
should not be considered among the number of hydrophytic plant species present. Examples of odd or
unusual distribution patterns are described below; all Figures are from the Arid West and are strictly
for illustrative purposes.

•	Isolated individuals, or small patches covering only a small portion of the total assessment area
(e.g., < 2%) and only found in one location (as opposed to plants sparsely distributed
throughout the reach). Hyperlocal hydrologic conditions may support the growth of
hydrophytes in otherwise unsuitable stream reachs. In more arid regions, this can occur at road
crossings, where road runoff increases water availability to vegetation (Figure 11).

•	Long-lived species exclusively represented by seedlings or plants less than one-year old. A large
flood may promote the growth of hydrophytes in streams that are normally too dry to sustain
them (Figure 12).

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Section 3: Data Collection

• Old specimens clearly in decline. This scenario may be a sign of major long-term reductions in
water availability due to changes in water use practices or to extreme and/or persistent
drought (Figure 13).

These species may be recorded on the field form, along with notes explaining the unusual distribution
patterns observed, but should not be among the number of hydrophyte species entered for this GP
SDAM indicator.

Figure 11, Local conditions that support growth of hydrophytes. In Ridgecrest, California, a culvert at an ephemeral stream
crossing disrupts the movement of water, sustaining the growth of hydrophytes in the immediate vicinity. Photo credit:
Cara Clark.

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Section 3: Data Collection

Figure 12, Long-lived species only
represented by young specimens. Red
alders (Alnus rubra), while abundant at
Mission Creek in the Mojave Desert, were
only observed as seedlings. Photo credit:
Raphael Mazor,

Figure 13. Water-stressed riparian trees near Oro Grande on the Mojave River. Reproduced from Lines (1999).

For this indicator, identify hydrophytic plant species growing within the channel or up to one half-
channel width from the channel of the assessment reach that do not have unusual or odd distribution
patterns. Hydrophytes growing at greater distances from the channel may be supported by local water

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sources not related to streamflow in the assessment reach, A user wili choose between two categories
for this indicator, as shown below. Once three taxa are identified, counting can stop; however, where
the user may not be confident in all identifications, more species should be assessed, if possible.

In general, focusing on the most dominant species in the reach is efficient. Take photos of each plant
species, focusing on diagnostic features and photos that illustrate the abundance and environmental
context where the species grows. Where practical, voucher material (e.g., flowers, leaves, etc.) may be
collected and preserved (e.g., in a plant press) for later identification.

If the site is devoid of vegetation, check the box marked "No vegetation within reach."

Figure 14. Examples of plants determined to be hydrophytes based on context. Left: An emergent macrophyte growing
within the channel. Right: Sedges and cattails growing exclusively in the streamside zone absent from adjacent uplands.

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Common questions about identifying hydrophytes

Are FACW and OBL plants equally important?

Yes. For this method, OBL and FACW plants are equally important indicators of streamflow duration.
Do Facultative (FAC) or Facultative Upland (FACU) status plants count?

No. Although some applications of the N WPL treat FAC or FACU plants as hydrophytes, they do not
count towards this indicator for the GP SDAM. For instance, some important, high-profile riparian
species are FAC in some or all of the NWPL regions applicable to the Great Plains, such as American
sycamore (Platanus occidentalis; GP NWPL region), Eastern cottonwood (Populus deltoides; all
applicable NWPL regions), green ash (Fraxinus pennsylvanica; GP NWPL region), and box elder (Acer
negundo; all applicable NWPL regions). This exclusion in no way lessens the ecological importance or
conservation value of these plants, but rather indicates their relative tolerance for drier conditions
than FACW or OBL species.

What if a species is not included in the NWPL?

If a plant is not included in the NWPL, assume that it is not a hydrophyte unless environmental
context strongly indicates otherwise. (See "What if I can't confidently identify a dominant plant?"
below.)

Is genus-level identification sufficient?

It depends on the genus. Consult the NWPL. Some genera contain high levels of diversity (e.g.,

Carex), while others are dominated by wetland species (e.g., Ludwigia). For instance, across the GP,
nearly all willow (Salix) species are hydrophytes (although there are a few exceptions), so genus-
level identifications of willows are usually acceptable. Post-sampling confirmation based on photos
or collected specimens is recommended.

What if I can't confidently identify a dominant plant?

It may be acceptable to use environmental context and cues to determine that a plant is a
hydrophyte, even if taxonomic identifications cannot be made. Examples include submerged or
emergent macrophytes, or plants observed to grow exclusively in saturated soil and absent from
adjacent uplands (Figure 14). Post-sampling confirmation based on photos or collected specimens is
strongly recommended. Photo documentation should convey this context. Photo confirmation is
particularly important if the only hydrophytes observed in an assessment cannot be identified on-
site. Photos can also be used when consulting plant identification applications that use image
recognition (e.g., Seek, iNaturalist).

What if a hydrophytic plant species covers <2% of the assessment area (channel width plus 1A channel
width on both sides of the channel x reach length) and is represented only by seedlings and/or
dead/dying individuals?

Do not consider the species among the number of hydrophyte plant species present in the reach.
The species with such distributions can be photographed and noted for additional information on
the reach.

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3.8.4 Presence/absence of rooted upland plants in streamhed

Few plants can tolerate the conditions they would experience on the streambed of a reach with
relatively long flow duration. Prolonged inundation, soil saturation, and shear stress create an
inhospitable environment for most upland plants, preventing their establishment or perseverance.
Thus, the presence of upland plants in the streambed indicates that flows have insufficient frequency,
duration, or severity to limit these species. For the GP SDAM, upland plants in the context of this
indicator are those with FAC, Facultative Upland (FACU) and Upland (UPL) indicators on the most
recent NWPL. Species not listed in the NWPL (No Indicator; Nl) are also considered upland plants.

When assessing this indicator, the focus should be on plants rooted in the streambed (Figure 15);
plants growing on any part of the bank or on upland islands within the OHWM should not be
considered. A user will indicate whether upland plants are present or absent from the reach and
identify them on the field form.

Figure 15. Example of an ephemeral stream with rooted upland vegetation growing in the channel. Where
vegetation is growing within the streambed of Safe Dolan Creek in Texas, it is dominated by Texas sotol
(Dasylirion texanum) and Ashe juniper (Juniperus ashei), both of which have no indicator (Nl) on the National
Wetland Plant List for the Great Plains region,

3.8.5 Differences in vegetation

Streams with longer streamflow durations tend to support a distinct riparian vegetation community
that includes more hydrophytic species compared to surrounding uplands. Even streams of shorter
duration may allow upland species found in the riparian corridor to grow more vigorously in and or
near the channel than in surrounding uplands. It is important to note in the context of this indicator, an
'upland' species does not have the same definition as in 3.8.3 Number of hydrophytic plant species and

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3.8.4 Presence/absence of upland plants in streambed indicators. For this indicator, an 'upland' species
is not defined by its NWPL indicator status but rather by its location relative to the channel. For
example, cottonwoods (Populus deltoides, which are FAC and would be considered 'upland' plants for
other indicators) found only in the riparian corridor along the length of the assessment reach, but not
in the uplands outside of the riparian corridor, would receive a strong score for this indicator (see Table
2).

When assessing this indicator, consider the entire length of the reach, and choose the score from Table
2 that best characterizes the predominant condition; photos that demonstrate the scoring guidance
are shown in Figure 16. High levels of distinctness in either composition or vigor results in a higher
score. In settings where upland vegetation cannot be assessed due to development in the surrounding
area, consider the upland vegetation growing in comparable areas outside the reach. In settings where
the riparian corridor has been eliminated due to wildfire or management activities (e.g., channel
clearing, mowing), the preferred option is to conduct the assessment after the vegetation has
recovered. When a delay is not an option and the riparian corridor is devoid of vegetation, a score of
zero is appropriate.

This indicator is derived from the New Mexico Hydrology Protocol (NMED 2020). As with other
indicators derived from the New Mexico Hydrology Protocol, "moderate" scores (i.e., 2) are intended
as an approximate midpoint between the extremes of "poor" and "strong". Half scores (i.e., 0.5, 1.5,
and 2.5) midway between the scores shown in Table 2 are appropriate to allow the assessor flexibility
to characterize this indicator more continuously.

Table 2. Scoring guidance for the Differences in Vegetation indicator.

Evidence of



Score perennial

Guidance

flows



No compositional or density differences in vegetation are present between
the streambanks and adjacent uplands.

1

Weak

Vegetation growing along the reach may occur in greater densities or grow
more vigorously than vegetation in the adjacent uplands, but there are no
dramatic compositional differences between the two.

2

Moderate

A distinct riparian vegetation corridor exists along part of the reach.
Riparian vegetation is interspersed with upland vegetation along the length
of the reach.

3

Strong

Dramatic compositional differences in vegetation are present between the
stream banks and adjacent uplands. A distinct riparian corridor exists along
the entire reach. Riparian, aquatic, or wetland species dominate the length
of the reach.

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Section 3: Data Collection

Figure 16. Examples illustrating scoring levels for the Differences in Vegetation indicator. (0): The vegetation along the
reach is similar in composition and vigor to surrounding uplands; (1) While the plant community composition is similar,
the riparian vegetation is growing with more vigor; (2) The riparian corridor is a mix of upland (e.g., Phegopteris
connectilis) and hydrophytic (e.g., Alnus spp.) vegetation while hydrophytic vegetation is absent from the surrounding
uplands (3) The streambanks are dominated by hydrophytes (e.g., Eleocharis palustris, Schoenoplectus pungens) that are
absent in adjacent uplands.

3.8.6 Riffle-pool sequence

A riffle is a zone with a relatively high channel slope gradient, shallow water, and high flow velocity and
turbulence. In smaller streams, riffles are defined as areas of a distinct change in gradient where
flowing water can be observed. The bottom substrate material in riffles contains the largest particles
that are moved by bankfull flow (bedload). A pool is a zone with relatively low channel slope gradient
and deep water that moves at a low velocity and with minimal turbulence. Fine textured sediments
generally dominate the bottom substrate material in pools. A repeating sequence of riffles and pools
can be readily observed in most perennial systems, though the form of this sequence can differ based
on gradient and bed material (riffle-run or ripple-pool in low gradient and sand bed systems, or step-
pool in higher gradient systems). Riffle-run (or ripple-run) sequences in low gradient systems are often
created by in-channel woody structures such as roots and woody debris. No matter the form, these
features can be observed even in dry channels by closely examining their local profile and patterns of

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Section 3: Data Collection

sediment deposition (at least for streams with coarser bed material). Score the indicator using the
guidance in Table 3. Scoring guidance for the Riffle-Pool Sequence indicator.

This indicator is derived from the New Mexico Hydrology Protocol (NMED 2020). As with other
indicators derived from the New Mexico Hydrology Protocol, "moderate" scores (i.e., 2) are intended
as an approximate midpoint between the extremes of "poor" and "strong". Photos that demonstrate
the scoring guidance are shown in Figure 17. Half scores (i.e., 0.5,1.5, and 2.5), midway between the
scores shown in Table 3 are appropriate to allow the assessor flexibility to characterize this indicator
more continuously.

Table 3. Scoring guidance for the Riffle-Pool Sequence indicator.



Evidence of



Score

perennial
flows

Guidance

0

Poor

No riffle-pool sequences observed.

1

Weak

Mostly has areas of pools or of riffles.

¦y

Moderate

Represented by a less frequent number of riffles and pools. Distinguishing

£.

the transition between riffles and pools is difficult to observe.





Demonstrated by a frequent number of structural transitions (e.g., riffles

3

Strong

followed by pools) along the entire reach. There is an obvious transition
between riffles and pools.

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Section 3: Data Collection

Figure 17. Examples illustrating scoring levels for the Riffle-Pool Sequence indicator, (0): No structural definition is apparent
throughout the reach; (1) The reach is largely comprised of pools and transitions to other structures infrequent or not
distinct; (2) More structural definition is apparent, but distinctions are subtle, (3) A sequence of structures is present
throughout the reach and transitions between them are obvious.

3.8.7 Particle size or stream substrate sorting

Well-developed streams that have eroded through the soil profile often have substrate materials
dominated by larger sediment sizes, such as coarse sand, gravel, and cobble, relative to floodplain
sediments and adjacent soils. Finding similar sediment sizes in the stream bed and the adjacent stream
side area may indicate that stream channel-forming processes have not been consistent enough to cut
into the soil profile as typically seen in intermittent and perennial streams. The bed in ephemeral
channels is often soil, having the same or similar texture as areas adjacent to the channel, and often
having differentiated soil horizons.

This indicator can be evaluated in two ways:

1) In channel versus outside channel: Determine if the sediment texture on the bed of the channel
is similar to sediment texture adjacent to the channel (e.g., on banks or adjacent floodplain). If
this is the case, then there is evidence that erosive forces have not been active enough to down

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Section 3: Data Collection

cut the channel and support an intermittent or perennial system. Stormflow runoff resulting
from human development can form incised ephemeral or intermittent channels; however,
these channels often show little to no coarsening of the substrate.

2) Substrate sorting: Look at the particle size distribution on the channel bed, are there substrate
differences between the bedforms identified in Section 3.8.6 Riffle-pool sequence? For lower
gradient channels dominated by sand substrate, the user may need to identify sorting across
coarse versus fine sand.

Regardless of the approach used to assess channel sediments (e.g., pebble count, sand-gauge
reference card), evaluate an area adjacent to but not in the channel for comparison purposes. Avoid
adjacent areas with dense vegetation or recent soil disturbance.

Score the indicator using the guidance in Table 4. Photos that demonstrate the scoring guidance are
shown in Figure 18.

This indicator is derived from the New Mexico Hydrology Protocol (NMED 2020). As with other
indicators derived from the New Mexico Hydrology Protocol, "moderate" scores (i.e., 1.5) are intended
as an approximate midpoint between the extremes of "poor" and "strong". Half scores (i.e., 0.75,
2.25), midway between the scores shown in Table 4 are appropriate to allow the assessor flexibility to
characterize this indicator more continuously.

Table 4. Scoring guidance for Particle Size/Streambed Sorting indicator.

Score

Evidence of
perennial
flows

Guidance

0.0

Poor

Particle sizes in the channel are similar or comparable to particle sizes in
areas close to but not in the channel. Substrate sorting is not readily
observed in the channel.

1.5

Moderate

Particle sizes in the channel are moderately similar to particle sizes in
areas close to but not in the channel. Various sized substrates are
present in the channel and are represented by a higher ratio of larger
particles (gravel/cobble).

3.0

Strong

Particle sizes in the channel are noticeably different from particle sizes
in areas close to but not in the channel. There is a clear distribution of
various sized substrates in the channel with finer particles accumulating
in the pools and larger particles accumulating in the riffles/runs.

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Section 3: Data Collection

Figure 18. Examples illustrating scoring levels for the
Particle Size/Stream Substrate Sorting indicator. Top left
photo: Dry channel in Texas where the in channel particle
size of material is similar to surrounding uplands (score of
0); Top right photo: This Montana stream shows signs of
increased sorting in the middle of the channel, with slightly
larger particles than low flow channels or surrounding
uplands (score of 1.5); Left photo: Particle sizes in this North
Dakota channel are much larger compared to surrounding
uplands and a high level of sorting can be seen in the riffle in
the middle of the photo (score of 3).

3.8.8 Sediment on plants or debris

The transportation and processing of sediment is a main function of streams. Therefore, evidence of
fine sediment on plants or other debris in the channel, streambank, and/or floodplain may be an
important indicator of persistent flow. Note that sediment production in stable, vegetated watersheds
is considerably less than in disturbed watersheds. For this indicator, look for silt/sand accumulating in
thin layers on debris or rooted aquatic vegetation in the runs and pools, as well as along the channel
fringes, banks, and adjacent floodplain. Be aware of upstream land-disturbing construction activities,
which may contribute greater amounts of sediments to the channel and can confound this indicator.
Note these activities on the field form if these confounding factors are present. Score the indicator
using the guidance in Table 5,

This indicator is derived from the New Mexico Hydrology Protocol (NMED 2020). As with other
indicators derived from the New Mexico Hydrology Protocol, "moderate" scores (i.e., 1) are intended
as an approximate midpoint between the extremes of "poor" and "strong". Half scores (i.e., 0.25, 0.75,

. m

40


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Section 3: Data Collection

and 1.25), midway between the scores shown in Table 5 are appropriate to allow the assessor
flexibility to characterize this indicator more continuously.

Table 5. Scoring guidance for the Sediment on Plants or Debris indicator.

Score

Evidence of
perennial
flows

Guidance

0.0

Poor

No fine sediment is present on plants or debris.

0.5

Weak

Fine sediment is isolated in small amounts along the stream.

1.0

Moderate

Fine sediment found on plants or debris within the stream channel,
although it is not prevalent along the stream. Mostly accumulating in pools.

1.5

Strong

Fine sediment found readily on plants and debris within the stream
channel, on the streambank, and within the floodplain throughout the
length of the stream.

3.9 Additional notes and photographs

After assessing and recording all the indicators described above, provide any additional notes about
the assessment, and include photographs in the photo log.

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Section 4: Data Interpretation

Section 4: Data Interpretation and Using the Web Application

The GP SDAM relies on a random forest model to make classifications; therefore, the EPA has
developed a free, open-access web application that runs the model for each assessment reach and is
required to return a flow classification. This application allows assessors to input data from
assessments, including ordinal scores and non-ordinal information like number of aquatic
macroinvertebrates. In addition, users have the option to produce a PDF report, which may be
included as documentation of SDAM results.

The web application walks users through three steps in analyzing data from an SDAM. First, the user
selects the desired regional SDAM (either by entering coordinates, clicking on a map, or selecting from
a drop-down list). The coordinates field of the web application uses decimal degrees format of the
World Geodetic System of 1984 (WGS84) datum. Then the user enters field data on each indicator
required for the selected SDAM. At this point, the user can run the model and obtain the resulting
classification. The third step, report production is optional. Users may enter additional information
about the assessment (such as date of the site visit, notes, and photos of indicators) and produce a PDF
report. No data entered into the web application is stored or submitted to the EPA or other agencies. A
link at the top of the web application goes to Supporting Materials including User Manuals. Field
Forms. Training Videos and more.

4.1 Outcomes of GP SDAM classification

As described in 1.1 The SDAM for the Great Plains, application of the SDAM can result in one of six
possible classifications:

•	Ephemeral

•	Intermittent

•	Perennial

•	At least intermittent

•	Less than perennial

•	Needs more information

The first three streamflow duration classifications correspond to the three classes of streams used to
calibrate the GP SDAM. These outcomes occur when the pattern of observed indicators closely
matches patterns in the calibration data, and thus a classification can be assigned with high
confidence. Single indicators of flow duration were tested for the GP SDAM, but data analysis did not
suggest that their use would improve classification accuracy.

In some cases, the pattern of indicators is associated with multiple classes, and the GP SDAM model
cannot assign a single classification with high confidence. However, the GP SDAM model may be able
to rule out an ephemeral classification with high confidence or a perennial classification with high
confidence. In the former case, the outcome is at least intermittent, meaning that there is a high
likelihood that the stream is either perennial or intermittent, but not ephemeral. In the latter case, the
outcome is less than perennial, meaning that there is a high likelihood that the stream is either

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Section 4: Data Interpretation

intermittent or ephemeral, but not perennial. In both cases the two classes (i.e., perennial vs.
intermittent and intermittent vs. ephemeral) cannot be distinguished with confidence. In some
instances, this information may be sufficient for management decisions, although additional
assessment may be warranted. Two outcomes, at least intermittent and less than perennial, were rare
in the GP SDAM development data set; less than 2% of the time for both classifications. The needs
more information outcome is possible and generally occurs when no classification can be made with
confidence, but this did not occur in the GP SDAM development data set.

4.2	Applications of the GP SDAM outside the intended area

The GP SDAM is intended only for application to the GP region shown in Figure 2. The online web
application allows the user to apply the protocol to reaches outside the GP; however, classifications
resulting from these applications are for informational purposes only. For example, it may be helpful to
assess reaches with more than one regional SDAM near regional boundaries. Reports generated from
such applications are accompanied by warnings.

4.3	What to do when a more specific
classification is needed

If the application of the GP SDAM results in need
more information, it means that no classification
can be made with confidence. If an assessment's
outcome is ambiguous about the specific flow
duration class (i.e., less than perennial or at least
intermittent), it may help to examine other lines of
evidence or conduct additional assessments, as
described below in approximate order of
increasing effort.

4.3.1 Review historical aerial imagery

In many parts of the GP, sequences of aerial imagery can
provide information about streamflow duration. Google
Earth's time slider and USGS Earth Explorer offer a
convenient method of reviewing historical imagery,
particularly for areas where trees do not obscure channels
(however, Google Earth time slider may not have accurate
image dates). If surface water is observed in all interpretable
images across multiple years (especially during dry seasons),
this may provide evidence that the reach is likely perennial. If
surface water is never observed, even when other nearby
intermittent streams show water, the consistent absence of surface water may provide evidence that
the reach is likely ephemeral (particularly if images are captured during the wet season or after major
storm events). If surface water is present in some images and dry in others, the stream may be
intermittent. The evidence for perennial flow is strong if the images with surface water occur in the dry

When a more specific classification is needed:

•

Review historical aerial imagery

•

Conduct additional assessments at the



same reach

•

Conduct assessment at similar nearby



reaches

•

Conduct reach revisits during regionally



appropriate wet or dry seasons

•

Collect hydrologic data

Considerations for aerial imagery

•	Accurate dates of images

•	Changes in reach or watershed
conditions since image was
taken

•	Seasonal and recent climatic
conditions for each image

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Section 4: Data Interpretation

season and do not coincide with recent storm events. It is also important that users consider whether
conditions as reflected by historical imagery are congruent with current conditions. For example, due
to groundwater withdrawals, a stream that once flowed perennially may now have ephemeral flow;
therefore, images from 15-20+ years ago might not be indicative of current flow conditions.

Any time that discrete observations of flow or no flow are used to inform a determination of flow
duration class, such observations should be evaluated in the context of relatively normal climatic
conditions. Doing so ensures that flow duration class is not determined based on observations of flow
or no flow during abnormally wet or abnormally dry periods. The Antecedent Precipitation Tool (U.S.
Army Corps of Engineers 2023) is a useful tool to determine if climate conditions are 'normal' for a
locale (see 3.4 Timing of sampling). However, aerial images may not have high enough temporal
resolution to confidently classify streams as ephemeral or perennial without additional data. See
examples in Figure 19.

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Section 4: Data Interpretation
Perennial reach: South Loup River at Arnold, Nebraska

7/2006: Flowing	5/2012: Flowing	4/2017: Flowing

intermittent reach: Tributary to North Fork Grand River, Dakota Prairie Grasslands, South Dakota

9/1997: Pools only

10/2014: Discontinuous flow

12/2003: Pools only

Ephemeral reach: Tributary to East Carrizo Creek, Pike and San Isabel National Forests, Colorado

m	—i mm

6/2005: Dry

10/2016: Dry

10/2011: Dry

Figure 19. Examples of using aerial imagery to support streamflow duration classification. Images were taken from Google
Earth using the time slider.

4.3.2	Conduct additional assessments at the same reach

Some indicators may be difficult to detect or interpret due to short-term disturbances, floods, severe
drought, or other conditions that affect the sampling event's validity. A repeat application of the GP
SDAM, even a few weeks later when effects from the disturbance have abated, may be sufficient to
provide a determination. Similarly, conducting an additional evaluation during a different season may
improve the ability to identify vegetation and collect aquatic macroinvertebrates, leading to a more
conclusive assessment.

4.3.3	Conduct assessments at nearby reaches

Indicators may provide more conclusive results at reaches upstream from the assessment reach or
downstream from the assessment reach, and if those locations represent similar conditions may be

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useful for interpreting ambiguous results. For example, there should be no significant discharges,
diversions, or confluences between the new and original assessment locations, and they should have
similar geomorphology. See 3.5 Assessment reach considerations for additional information.

4.3.4	Conduct reach revisits during regionally appropriate wet and dry seasons

A single, well-timed assessment may provide sufficient hydrologic evidence about streamflow duration.
As with observations from aerial imagery, any time onsite observations of flow or absence of flow are
used to inform a determination of flow duration class, such observations should be evaluated in the
context of normal climatic conditions. Doing so ensures that flow duration class is not determined
based on hydrologic observations of flow that occurred during abnormally wet or abnormally dry
periods. The previously mentioned APT can provide this information.

4.3.5	Collect hydrologic data

Properly deployed loggers, stream gauges, or wildlife cameras can provide direct evidence about
streamflow duration at ambiguous assessment reaches. It may be possible to distinguish intermittent
from ephemeral streams in just a single season with these tools, assuming typical precipitation.

46


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Section 5: References

Section 5: References

Asquith, W. H., J. D. Gordon, and D. S. Wallace. 2020. Regional Regression Equations for Estimation of
Four Hydraulic Properties of Streams at Approximate Bankfull Conditions for Different
Ecoregions in Texas: U.S. Geological Survey Scientific Investigations Report 2020-5086.
(Available from: https://pubs.usgs.gov/sir/2020/5086/sir20205086.pdf)

Bieger, K., H. Rathjens, P. M. Allen, and J. G. Arnold. 2015. Development and evaluation of bankfull

hydraulic geometry relationships for the physiographic regions of the United States. Journal of
the American Water Resources Association 51: 842-858.

Bigelow, S.G., E.J. Hillman, B. Hills, G.M. Samuelson, and S.B. Rood. 2020. Flows for floodplain forests:
conversion from an intermittent to a continuous flow regime enabled riparian woodland
development along a prairie river. River Research and Applications 36(10): 2051-2062.

Blackburn, M. and C. Mazzacano. 2012. Using Aquatic Macroinvertebrates as Indicators of Streamflow
Duration: Washington and Idaho Indicators. The Xerces Society, Portland, OR.

Bouchard, R.W., Jr., L.C. Ferrington, Jr., and M.L. Karius. 2004. Guide to Aquatic Invertebrates of the
Upper Midwest. University of Minnesota Press. 183 pp.

Burk, R. A. and J. H. Kennedy. 2013. Invertebrate communities of groundwater-dependent refugia with
varying hydrology and riparian cover during a supraseasonal drought. Journal of Freshwater
Ecology 28:251-270.

Carlson, E.A., D.J. Cooper, D.M. Merritt, B.C. Kondratieff, and R.M. Waskom. 2019. Irrigation canals are
newly created streams of semi-arid agricultural regions. Science of the Total Environment 646:
770-781.

Chadde, S. 2019. Wetland and Aquatic Plants of the Northern Great Plains: A Field Guide for North and
South Dakota, Nebraska, eastern Montana and eastern Wyoming. Orchard Innovations. 342 pp.

Chapin, T. P., A. S. Todd, and M. P. Zeigler. 2014. Robust, low-cost data loggers for stream

temperature, flow intermittency, and relative conductivity monitoring. Water Resources
Research 50: 6542-6548.

Cutler, D. R., T. C. Edwards, K. H. Beard, A. Cutler, K. T. Hess, J. Gibson, and J. J. Lawler. 2007. Random
forests for classification in ecology. Ecology 88: 2783-2792.

David, G. C. L., K. M. Fritz, T.-L. Nadeau, B. J. Topping, A. O. Allen, P. H. Trier, S. L. Kichefski, L. A. James,
E. Wohl, and D. Hamill. 2022. National Ordinary High Water Marks Field Delineation Manual for
Rivers and Streams: Interim Version. Wetlands Regulatory Assistance Program (WRAP)
ERDC/CCRREL TR-22-26, US Army Corps of Engineers - Engineer Research and Development
Center, Vicksburg, MS.

David, G.C. L. and D. Hamill. 2024. Is the ordinary high water mark ordinarily at bankfull? Applying a
weight-of-evidence approach to stream delineation. Journal of the American Water Resources
Association 00(0): 1-29.

Dodds, W. K., K. Gido, M. R. Whiles, K. M. Fritz, and W. J. Matthews. 2004. Life on the edge: the
ecology of Great Plains prairie streams. Bioscience 54: 205-216.

47


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Section 5: References

Foster, K. 2012. Bankfull-Channel Geometry and Discharge Curves for the Rocky Mountains Hydrologic
Region in Wyoming: U.S. Geological Survey Scientific Investigations Report 2012-5178
(Available from: https://pubs.usgs.gov/sir/2012/5178/sir2012-5178.pdf).

Friedman, J.M., M.L. Scott, and G.T. Auble. 1997. Water management and cottonwood forest dynamics
along prairie streams. Pages 49-71 in F.L. Knopf and F.B. Samson (eds), Ecology and
Conservation of Great Plains Vertebrates. Springer-Verlag, NY.

Fritz, K.M. and W.K. Dodds. 2004. Resistance and resilience of macroinvertebrates to drying and flood
in a tallgrass prairie stream system. Hydrobiologia 527: 99-112.

Fritz, K. M., B. R. Johnson, and D. M. Walters. 2008. Physical indicators of hydrologic permanence in

forested headwater streams. Journal of the North American Benthological Society 27: 690-704.

Fritz, K. M., W. R. Wenerick, and M. S. Kostich. 2013. A validation study of a rapid field-based rating
system for discriminating among flow permanence classes of headwater streams in South
Carolina. Environmental Management 52: 1286-1298.

Fritz, K. M., T.-L. Nadeau, J. E. Kelso, W. S. Beck, R. D. Mazor, R. A. Harrington, and B. J. Topping. 2020.
Classifying streamflow duration: the scientific basis and an operational framework for method
development. Water 12: 2545.

Grimm, N.B. and S.G. Fisher. 1989. Stability of periphyton and macroinvertebrates to disturbance by

flash floods in a desert stream. Journal of the North American Benthological Society 8: 293-307.

Hall, R. K., P. Husby, G. Wolinsky, O. Hansen, and M. Mares. 1998. Site access and sample frame issues
for R-EMAP Central Valley, California, stream assessment. Environmental Monitoring and
Assessment 51: 357-367.

Hax, C.L. and S.W. Golladay. 1998. Flow disturbance of macroinvertebrates inhabiting sediments and
woody debris in a prairie stream. American Midland Naturalist 139: 210-223.

James, A., T.-L. Nadeau, K.M. Fritz, B.J. Topping, R. Fertik Edgerton, J. Kelso, and R. Mazor. 2022a. User
Manual for a Beta Streamflow Duration Assessment Method for the Great Plains of the United
States. Version 1.0. Document No. EPA-840-B-22009.

James, A., K. McCune, and R. Mazor. 2022b. Review of Flow Duration Methods and Indicators of Flow
Duration in the Scientific Literature, Great Plains of the United States. Document No. EPA-840-
B-22006 (Available from: https://www.epa.gov/system/files/documents/2022-
09/FlowDurationLitReview-gp.pdf).

Karr, J. R., K. D. Fausch, P. R. Angermeier, and I. J. Schlosser. 1986. Assessment of Biological Integrity in
Running Waters: A Method and Its Rationale. Special Publication 5, Illinois Natural History
Survey.

Kelso, J.E., W. Saulnier, K.M. Fritz, T-L. Nadeau, and B. Topping. 2023. The stream intermittency

visualization dashboard: a Shiny web application to evaluate high-frequency logger data and
daily flow observations. Hydrological Processes 37(2): el4809.

Lenhart, C., K. Blann, and K. Ehlert. 2023. Intermittent prairie streams in the northern Great Plains: A
case of an undervalued ecosystem. Case Studies in the Environment 7(1): 20066981.

Lines, G.C. 1999. Health of Native Riparian Vegetation and its Relation to Hydrologic Conditions Along
the Mojave River, Southern California: U.S. Geological Survey Water-Resources Investigations
Report 99-4112.

48


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Section 5: References

Mazor, R. D., B. J. Topping, T.-L. Nadeau, K. M. Fritz, J. E. Kelso, R. A. Harrington, W. S. Beck, K. S.

McCune, A. 0. Allen, R. Leidy, J. T. Robb, and G. C. L. David. 2021. Implementing an operational
framework to develop a streamflow duration assessment method: A case study from the Arid
West United States. Water 13: 3310.

McKay, L., T. Bondelid, T. Dewald, J. Johnson, R. Moore, and A. Rea. 2014. NHDPIus Version 2: User
Guide. U.S. Environmental Protection Agency (Available from:

https://nctc.fws.gov/courses/references/tutorials/geospatial/CSP7306/Readings/NHDPIusV2_U
ser_Guide.pdf).

Merritt, R. W., K. W. Cummins, and M. B. Berg (Eds.). 2019. An Introduction to the Aquatic Insects of
North America.

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.

Nadeau, T.-L. 2015. Streamflow Duration Assessment Method for the Pacific Northwest. Document No.
EPA-910-K-14-001, U.S. Environmental Protection Agency, Region 10, Seattle, WA.

Nadeau, T.-L., S. G. Leibowitz, P. J. Wigington, J. L. Ebersole, K. M. Fritz, R. A. Coulombe, R. L. Comeleo,
and K. A. Blocksom. 2015. Validation of rapid assessment methods to determine streamflow
duration classes in the Pacific Northwest, USA. Environmental Management 56: 34-53.

New Mexico Environment Department (NMED). 2020 (revised). Water Quality Management Plan and
Continuing Planning Process Appendix C: Hydrology Protocol for the Determination of Uses
Supported by Ephemeral, Intermittent, and Perennial Waters. Surface Water Quality Bureau,
New Mexico Environment Department, Albuquerque, NM (Available from:
https://www.env.nm.gov/surface-water-quality/wp-

content/uploads/sites/25/2019/ll/WQMP-CPP-Appendix-C-Hydrology-Protocol-20201023-
APPROVED.pdf).

Rosenberg, D. M., and V. H. Resh (Eds.). 1993. Freshwater Biomonitoring and Benthic
Macroinvertebrates. Chapman & Hall, New York.

U.S. Army Corps of Engineers. 2008. Regional Supplement to the Corps of Engineers Wetland

Delineation Manual: Arid West Region (Version 2.0). Page 135. ed. J. S. Wakeley, R. W. Lichvar,
and C. V. Noble. ERDC/EL TR-08-28, U.S. Army Engineer Research and Development Center,
Vicksburg, MS: U.S. Army Engineer Research and Development Center.

U.S. Army Corps of Engineers. 2010. Regional Supplement to the Corps of Engineers Wetland

Delineation Manual: Western Mountains, Valleys, and Coast Region (Version 2.0). Page 153. ed.
J. S. Wakeley, R. W. Lichvar, and C. V. Noble. ERDC/EL TR-10-3, U.S. Army Engineer Research
and Development Center, Vicksburg, MS: U.S. Army Engineer Research and Development
Center.

U.S. Army Corps of Engineers. 2020. National Wetland Plant List, version 3.5. Engineer Research and
Development Center Cold Regions Research and Engineering Laboratory. Hanover, NH.

U.S. Army Corps of Engineers. 2023. Antecedent Precipitation Tool (APT) (Available from:
https://github.com/erdc/Antecedent-Precipitation-Tool).

49


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Section 5: References

U.S. Geological Survey. 2024. The StreamStats program (Available from:
https://streamstats.usgs.gov/ss/).

Voshell, Jr., J. R. 2002. A Guide to Common Freshwater Invertebrates of North America. McDonald &
Woodward Publishers, Blacksburg, VA.

Wohl, E., M. K. Mersel, A. 0. Allen, K. M. Fritz, S. L. Kichefski, R. W. Lichvar, T.-L. Nadeau, B. J. Topping,
P. H. Tier, and F. B. Vanderbilt. 2016. Synthesizing the Scientific Foundation for Ordinary High
Water Mark Delineation in Fluvial Systems. Wetlands Regulatory Assistance Program
ERDC/CCREL SR-16-5, U.S. Army Corps of Engineers Engineer Research and Development Center
(Available from: https://apps.dtic.mil/sti/pdfs/AD1025116.pdf).

50


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Appendix A: Glossary of Terms

Appendix A. Glossary of Terms

Term Definition

Active channel

A portion of the valley bottom that can be distinguished based on the three
primary criteria of (i) channels defined by erosional and depositional forms
created by river processes, (ii) the upper elevation limit at which water is
contained within a channel, and (iii) portions of a channel without mature
woody vegetation. Braided systems have multiple threads and channel bars
that are all part of the active channel.

Alluvial

Refers to natural, channelized runoff from terrestrial terrain, and the material
borne or deposited by such runoff.

Assessment reach

The length of reach, ranging from 40 m to 200 m, where GP SDAM indicators
are measured.

Aquatic

macroinvertebrates

Invertebrate organisms that require aquatic environments for parts or all of
their life cycle and are visible without the use of a microscope (i.e., > 0.5 mm
body length). Includes bottom dwelling or benthic macroinvertebrates.

Bank

The side of an active channel, typically associated with a steeper side gradient
than the adjacent channel bed, floodplain, or valley bottom.

Bankfull elevation

The elevation associated with a shift in the hydraulic geometry of the channel
and the transition point between the channel and the floodplain. In
unconstrained settings this is the height of the water in the channel just when
it begins to flow onto the floodplain.

Bankfull width

Width of the stream channel at bankfull elevation.

Braided system

A stream with a wide, relatively horizontal channel bed over which during low
flows, water forms an interlacing pattern of splitting into numerous small
conveyances that coalesce a short system downstream. Same as multi-
threaded system.

Canal

An artificial or formerly natural waterway used to convey water between
locations, possibly in both directions. Same as ditch.

Catchment

An area of land, bounded by a drainage divide, which drains to a channel or
waterbody. Synonymous with watershed.

Channel

A feature in fluvial systems consisting of a bed and its opposing banks which
confines and conveys surface water flow. A braided system consists of multiple
channels, including inactive or abandoned channels.

Confinement

The degree to which levees, terraces, hillsides, or canyon walls prevent the
lateral migration of a fluvial channel.

Culvert

A drain or covered channel that crosses under a road, pathway, or railway.

Ditch

An artificial or formerly natural waterway used to convey water between
locations, possibly in both directions. Same as canal.

Ephemeral

Channels that flow only in direct response to precipitation. Water typically
flows at the surface only during and/or shortly after large precipitation events,
the streambed is always above the water table, and stormwater runoff is the
primary water source.

51


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Appendix A: Glossary of Terms

Exuviae

The shed exoskeletons of arthropods typically left behind when an aquatic
larva or nymph becomes a winged adult. Singular: exuvium.

FAC

Facultative plants. They are equally likely to occur in wetlands and non-
wetlands.

FACU

Facultative upland plants. They usually occur in non-wetlands but are
occasionally found in wetlands.

FACW

Facultative wetland plants. They usually occur in wetlands but may occur in
non-wetlands.

Floodplain

The bench or broad flat area of a fluvial channel that corresponds to the height
of bankfull flow. It is a relatively flat depositional area that is periodically
flooded (as evidenced by deposits of fine sediment, wrack lines, vertical
zonation of plant communities, etc.).

Groundwater

Water found underground in soil, pores, or crevices in rocks.

Hydrophyte

Plants that are adapted to inundated conditions found in wetlands and riparian
areas.

Hyporheic

The saturated zone under a river or stream, including the substrate and water-
filled spaces between the particles.

Indicator

For the SDAM GP, indicators are rapid, generally field-based measurements
that are used to predict streamflow duration class.

Instar

A phase between two periods of molting in arthropods (i.e., insects).

Intermittent

Channels that contain sustained flowing surface water for only part of the year,
typically during the wet season, where the streambed may be below the water
table and/or where the snowmelt from surrounding uplands provides
sustained flow. The flow may vary greatly with stormwater runoff.

Larva

An immature stage of an insect or other invertebrates. Several insects have
aquatic larval stages, such as mayflies, stoneflies, and caddisflies. Immature
salamanders are sometimes also described as larvae. Plural: larvae.

Low-flow channel

In braided systems, the main channel with the lowest thalweg elevation. In
intermittent or ephemeral reaches, the low-flow channel typically retains flow
longer than other channels.

Macrophyte

Aquatic plants.

Multi-threaded
system

A stream with a wide, relatively horizontal channel bed over which during low
flows, water forms an interlacing pattern of splitting into numerous small
conveyances that coalesce a short system downstream. Same as braided
system.

Nl

Plants that have no assigned wetland indicator (e.g., FACW, FACU) in a specific
National Wetland Plant List region.

OBL

Obligate wetland plants. They almost always occur in wetlands.

52


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Appendix A: Glossary of Terms

Ordinary high-
water mark
(OHWM)

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 bank,
shelving, changes in the character of the soil, destruction of terrestrial
vegetation, the presence of litter and debris, or other appropriate means that
consider the characteristics of the surrounding areas. See 33 CFR 328.3. An
OHWM is required to establish lateral extent of U.S. Army Corps of Engineers
jurisdiction in non-tidal streams. See 33 CFR 328.4.

Perennial

Channels that contain flowing surface water continuously during a year of
normal rainfall, often with the streambed located below the water table for
most of the year. Groundwater typically supplies the baseflow for perennial
reaches, but the baseflow may also be supplemented by stormwater runoff
and/or snowmelt.

Pool

A depression in a channel where water velocity is slow and suspended particles
tend to deposit. Pools typically retain surface water longer than other portions
of intermittent or ephemeral streams.

Reach

A length of stream that generally has consistent geomorphological and
biological characteristics.

Riffle

A shallow portion of a channel where water velocity and turbulence is high,
typically with coarse substrate (cobble and gravels). Riffles typically dry out
earlier than other portions of intermittent or ephemeral streams, and harbor
higher abundance and diversity of aquatic invertebrates.

Riparian

A transitional area between the channel and adjacent upland ecosystems.

Rooted upland
plants

Plants rooted in the streambed that have wetland indicator statuses of FAC,
FACU, UPL, and Nl

Runoff

Surface flow of water caused by precipitation or irrigation over saturated or
impervious surfaces.

SAV

Submerged aquatic vegetation. This class is treated the same as OBL in current
versions of the National Wetland Plant List.

Scour

Concentrated erosive action of flowing water in streams that removes and
carries material away from the bed or banks. Algal and invertebrate abundance
is typically depressed after scouring events.

Secondary channel

A subsidiary channel that branches from the main channel and trend parallel or
subparallel to the main channel before rejoining it downstream.

Streambed

The bottom of a stream channel between the banks that is inundated during
baseflow conditions.

Thalweg

The line along the deepest flowpath within the channel.

Tributary

A stream that conveys water and sediment to a larger waterbody downstream.

UPL

Upland plants. They almost always occur in non-wetlands.

Uplands

Any portion of a drainage basin outside the river corridor.

Valley width

The portion of the valley within which the fluvial channel is able to migrate
without cutting into hill slopes, terraces, or artificial structures.

Watershed

An area of land, bounded by a drainage divide, which drains to a channel or
waterbody. Synonymous with catchment.

53


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Appendix B. Field Form


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Great Plains SDAM Field Form
October 2024

Page 1 of 6

Great Plains Streamflow Duration Assessment Method

General site information

Project name or number:

Site code or identifier:

Assessor( s):

Waterway name:

Visit date:

Current weather conditions (check one): Notes on current or recent

~	Storm/heavy rain weather conditions (e.g.,

~	Steady rain precipitation in prior week):

~	Intermittent rain

~	Snowing

~	Cloudv ( % cover)

~	Clear/sunny

Coordinates at downstream end
(decimal degrees):

Lat (N):

Long (E):

Datum:

Surrounding land-use within 100 m (check one or two):

~	Urban/industrial/residential

~	Agricultural (farmland, crops, vineyards, pasture)

~	Developed open-space (e.g., golf course)

~	Forested

~	Other natural

~	Other:

Describe reach boundaries:

Mean bankfull channel
width (m):

(Indicator 1)

Reach length (m):

40x width
min 40 m
max 200 m

Site photographs:

Enter photo ID or check if completed.
Tod down: Mid down:
Mid up: Bottom up:

Disturbed or difficult conditions (check all that apply):

~	Recent flood or debris flow ~ Drought

~	Stream modifications (e.g., channelization) ~ Vegetation removal/limitations

~	Diversions ~ Other (explain in notes)

~	Discharges ~ None
Notes on disturbances or difficult site conditions:

Observed hydrology: Comments on observed hydrology:
% of reach with surface flow
% of reach with sub-surface or surface flow
# of isolated pools


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Great Plains SDAM Field Form
October 2024

Site sketch:

Page 2 of 6

1. Mean bankfull channel width (m) (nearest 0.1 m, copy from first page of field form)

Notes about mean bankfull channel width:

2. Total aquatic macroinvertebrate abundance

Collect aquatic macroinvertebrates from at least 6 locations in the assessment reach and determine total abundance using
the following categories:

Mark the appropriate box for the total number of aquatic macroinvertebrates observed.

~	Total abundance of aquatic macroinvertebrates is zero.

~	Total abundance is >1 and <10.

~	Total abundance is >10.

Notes on total aquatic macroinvertebrate abundance:


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Great Plains SDAM Field Form
October 2024

Page 3 of 6

3. Number of hydrophytic plant species

Record up to 3 hydrophytic plant species (FACW or OBL in the appropriate regional wetland plant list, depending on
location) within the assessment area: within the channel or up to one half-channel width outside the channel. Explain in
notes if species has an odd distribution (e.g., one individual or small patch, long-lived species solely represented by
seedlings, or long-lived species solely represented by specimens in decline), or if there is uncertainty about the
identification. Enter photo ID or check if photo is taken.

	Number of hydrophytic plant species identified from the assessment reach without odd distribution. Enter zero if

none were found.

Check if applicable: ~ No vegetation in assessment area

Notes on hydrophytic vegetation:

4. Presence/absence of rooted upland plants in streambed

Evaluate the reach for rooted upland plants (i.e., plants rated as FAC, FACU, UPL, Nl, or not listed in regionally appropriate
regional National Wetland Plant List) in the streambed.

Mark the appropriate box for rooted upland plants.

~	Rooted upland plant individuals are present in the streambed.

~	Rooted upland plant individuals are absent in the streambed.

Notes on presence/absence of rooted upland plants in streambed:


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Great Plains SDAM Field Form
October 2024

Page 4 of 6

5. Differences in vegetation

(0-3)

Half scores (0.5,
1.5, 2.5) are
allowed.

Compare the composition and density of plants growing on the banks and riparian areas to plants
in the adjacent uplands. For this indicator, upland vegetation is not defined by its wetland
indicator status but by its location relative to the channel.

0	(Poor) No compositional or density differences in vegetation are present between the
streambanks and adjacent uplands.

1	(Weak) Vegetation growing along the reach may occur in greater densities or grow more
vigorously than vegetation in the adjacent uplands, but there are no dramatic compositional
differences between the two.

2	(Moderate) A distinct riparian vegetation corridor exists along part of the reach. Riparian
vegetation is interspersed with upland vegetation along the length of the reach.

3	(Strong) Dramatic compositional differences in vegetation are present between the stream
banks and adjacent uplands. A distinct riparian corridor exists along the entire reach.
Riparian, aquatic, or wetland species dominate the length of the reach.

Notes on differences in vegetation:

6. Riffle-pool sequence

Evaluate the prevalence of riffles, pools, and other microhabitats in the streambed.

(0-3)

Half scores (0.5,1.5,
2.5) are allowed.

0	(Poor) No riffle-pool sequences observed.

1	(Weak) Mostly has areas of pools or riffles.

2	(Moderate) Represented by a less frequent number of riffles and pools. Distinguishing the
transition between riffles and pools is difficult to observe.

3	(Strong) Demonstrated by a frequent number of structural transitions (e.g., riffles followed
by pools) along the entire reach. There is an obvious transition between riffles and pools.

Notes about riffle-pool sequence:


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Great Plains SDAM Field Form
October 2024

Page 5 of 6

7. Particle size or stream substrate sorting

(0-3)

Half-scores (0.75,
2.25) are allowed.

Evaluate the extent of substrate sorting. Compare substrate on the channel bed to the banks and
adjacent floodplain. Look for sorting within the channel bed (e.g., along bars and islands).

0 (Poor) Particle sizes in the channel are similar or comparable to particle sizes in areas close to

but not in the channel. Substrate sorting is not readily observed in the channel.
1.5 (Moderate) Particle sizes in the channel are moderately similar to particle sizes in areas close
to but not in the channel. Various sized substrates are present in the channel and are
represented by a higher ratio of larger particles (gravel/cobble).

3 (Strong) Particle sizes in the channel are noticeably different from particle sizes in areas close
to but not in the channel. There is a clear distribution of various sized substrates in the
channel with finer particles accumulating in the pools, and larger particles accumulating in
the riffles/runs.

Notes about substrate sorting:

8. Sediment on plants or debris

(0-1.5)

Half scores (0.25,
0.75,1.25) are
allowed.

Evaluate the extent of fine sediment on plants or debris within the stream channel, streambank,
and floodplain.

0	(Poor) No fine sediment is present on plants or debris.

0.5 (Weak) Fine sediment is isolated in small amounts along the stream.

1	(Moderate) Fine sediment found on plants or debris within the stream channel, although it is
not prevalent along the stream. Mostly accumulating in pools.

1.5 (Strong) Fine sediment found readily on plants and debris within the stream channel, on the
streambank, and within the floodplain throughout the length of the stream.

Notes about sediment on plants or debris:


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Great Plains SDAM Field Form
October 2024

Page 6 of 6

Photo log

Indicate if any other photographs taken during the assessment:

Photo ID

Description





















Additional notes about the assessment:

Model classification:

~	Ephemeral

~	At least intermittent

~	Intermittent

~	Less than perennial

~	Perennial

~	Needs more information


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