Oregon Streamflow Duration Assessment Method 

Interim Version – March 2009 

U.S. Environmental Protection Agency, Oregon Operations Office Region 

10, and Office of Wetlands, Oceans and Watersheds 

U.S. Army Corps of Engineers, Portland District 
 

Table of Contents 

PURPOSE ................................................................................................................................................3

ACKNOWLEDGEMENTS.........................................................................................................................3

SECTION 1: INTRODUCTION .....................................................................................................................4

BACKGROUND.............................................................................................................................................5

DEFINITIONS ...............................................................................................................................................6

CONSIDERATIONS WHEN USING THE METHOD ..............................................................................................7

Spatial Variability..................................................................................................................................7

The Concept of Scale...........................................................................................................................8

Reach Selection ...................................................................................................................................8

Recent Precipitation .............................................................................................................................9

Ditches and Modified Natural Streams.................................................................................................9

Disturbed or Altered Streams .............................................................................................................10

CONDUCTING FIELD ASSESSMENTS AND COMPLETING THE ASSESSMENT FORM...........................................10

Suggested Field Equipment ...............................................................................................................10

General Guidance for Completing the Field Assessment Form.........................................................10

Scoring ...............................................................................................................................................11

SECTION 2: INDICATORS OF STREAMFLOW DURATION ...................................................................13

A. GEOMORPHIC INDICATORS ....................................................................................................................13

1. Continuous Bed and Bank..............................................................................................................13

2. In-channel Structure – Coherent, Organized Sequences ..............................................................15

3. Soil Texture or Stream Substrate Sorting ......................................................................................15

4. Erosional Features .........................................................................................................................19

5. Depositional Features ....................................................................................................................20

6. Sinuosity.........................................................................................................................................22

7. Headcuts And Grade Controls .......................................................................................................23

B. HYDROLOGIC INDICATORS.....................................................................................................................25

8. Groundwater (Wet Channel) / Hyporheic Saturation (Dry Channel)..............................................25

9. Springs and Seeps .........................................................................................................................26

10. Evenly Dispersed Leaf Litter and Loose Debris...........................................................................27

11. Debris Piles and Wrack Lines ......................................................................................................29

12. Redoximorphic Features in the Toe of Bank................................................................................30

C. BIOLOGICAL INDICATORS.......................................................................................................................32

13. Wetland Plants In or Near Streambed .........................................................................................32

14. Fibrous Roots and Rooted Plants in Thalweg (Upland Plants)....................................................33

15. Streamer Mosses or Algal Mats ...................................................................................................34

16. Iron-Oxidizing Bacteria, Fungi, or Flocculent Material .................................................................35

17. Macroinvertebrates.......................................................................................................................36

18. Amphibians and Snakes...............................................................................................................39

19. Fish...............................................................................................................................................42

20. Lichen Line (Used Only in Arid Regions and Alpine Areas).........................................................43

21. Distinct Riparian Vegetation Corridor (Used Only in Arid Regions).............................................44

SECTION 3: DRAWING CONCLUSIONS..................................................................................................45

APPENDIX A: REFERENCES CONSULTED............................................................................................46

APPENDIX B: STREAMFLOW DURATION FIELD ASSESSMENT FORM.............................................52

APPENDIX C: A FIELD GUIDE TO ACCOMPANY THE MACROINVERTEBRATE SCORING PORTION 

OF THE OREGON STREAMFLOW DURATION ASSESSMENT METHOD ............................................55

 
 

PURPOSE 

The purpose of this manual and accompanying field assessment form is to guide natural 

resource professionals in the identification of the geomorphic, hydrological and biological 

indicators of stream flow to help distinguish between ephemeral, intermittent and perennial 

streams. Section 1 contains an introduction to the method, including definitions of key terms, 

method development, scoring, sources of variability, and suggested field equipment. Section 2 

describes the indicators assessed by the method and provides guidance for scoring. Section 3 

discusses drawing conclusions based on the assessed indicators of flow. 

This method and assessment form can be used to distinguish between perennial, intermittent, 

and ephemeral streams, but is primarily designed to distinguish ephemeral streams from 

intermittent and perennial streams in a single site visit. This method is an assessment tool for 

natural resource professionals and should support, but not replace, best professional judgment. 

ACKNOWLEDGEMENTS 

This manual has come together with the hard work of many people, and was particularly 

improved by the critical review and continuing input from participants in the September 2007 

field verification workshop: Scott Hoffman Black, The Xerces Society for Invertebrate 

Conservation (Xerces Society); Kyle Blasch, United States Geological Survey (USGS) Arizona 

Water Science Center; Ken Fritz, United States Environmental Protection Agency (EPA) Office 

of Research and Development (ORD); Jim Goudzwaard, United States Army Corps of 

Engineers (USACE) Portland District; Sarina Jepsen, Xerces Society; Jess Jordan, Oregon 

Department of State Lands (ODSL); Periann Russell, North Carolina Division of Water Quality; 

Yvonne Vallette, EPA Oregon Operations Office; Jim Wigington, EPA ORD; and Molly Wood, 

USGS Idaho Water Science Center. 

Many others have contributed important review and insight: Scott Leibowitz, Joe Ebersole, and 

Randy Cameleo, EPA ORD; Rob Coulombe, Lindsey Webb, Blake Hatteberg, and Shawn 

Majors, Dynamac Corporation; Stephen Lancaster, Oregon State University (OSU), Dept. of 

Geosciences; Judith Li, OSU, Dept. of Fisheries and Wildlife; Celeste Mazacanno, Xerces 

Society; Mark Rains, University of South Florida, Dept. of Geology; Chris Rombough, 

Rombough Biological; Nicole Navas, Russ Klassen, and Peter Ryan, ODSL.

Photographs were provided by the following contributors: Rob Coulombe, Lindsey Webb, Blake 

Hatteberg, and Shawn Majors (Dynamac Corporation), Jim Wigington and Ken Fritz (EPA 

ORD), Jess Jordan and Peter Ryan (ODSL), and Dana Eckard (Bureau of Land Management). 

Figures are credited in the document following the title with full citation information in Appendix 

A. 

To cite this document: 

Oregon Streamflow Duration Assessment Method Interim Version. Brian J.D. Topping, TracieLynn Nadeau, Michael R. Turaski. Public Notice release date, 6 March 2009. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 3
 

Section 1: Introduction 

A stream* can be described as a channel containing flowing surface water including: 

• Stormflow – increased stream flow resulting from the relatively rapid runoff of 

precipitation from the land as interflow (rapid, unsaturated, subsurface flow), overland 

flow, or saturated flow from surface water tables close to the stream, or; 

• Baseflow – flow resulting from ground water entering the stream or sustained melt water 

from glaciers and snowmelt (observed during long gaps between rainfall events), or; 

• A combination of both stormflow and baseflow, and; 

• Contributions of discharge from upstream tributaries as stormflow or baseflow, if present. 

*Note: For the purposes of this method the descriptor ‘stream’ is attached to the 

channel, and applies regardless of whether flow dries up seasonally or otherwise. 

As a stream flows from its origin, water may be derived primarily from stormflow, baseflow, or 

some combination of the two. Streams typically continue to accumulate water from stormflow, 

baseflow and other tributaries as they flow downstream. As streams accumulate flow they 

commonly transition along a gradient from ephemeral to intermittent and perennial; but 

sometimes quickly transition from ephemeral to perennial in high gradient systems, or transition 

from perennial to ephemeral to total cessation of flow on the surface. Often these changes are 

gradual and may not be obvious to the casual observer. There are, however, several indicators 

of stream flow that collectively can be used to characterize the flow duration of a stream along a 

particular reach as ephemeral, intermittent or perennial. In this manual duration is used to 

encompass the concept of the cumulative time period of flow in a year, which may vary 

interannually with climate, groundwater withdrawal or streamflow diversion, and other patterns. 

This manual describes these indicators and presents a method for assessing and drawing 

conclusions from these indicators in the state of Oregon. 

Stream systems can be characterized by interactions among hydrologic, geomorphic (physical) 

and biological processes. Variations in these attributes along the length of a stream are used as 

indicators of the dominant processes related to flow duration (Figure 1). To identify the 

indicators and distinguish ephemeral streams from intermittent streams or intermittent streams 

from perennial streams using the information presented in this manual, the field evaluator 

should have experience making geomorphic, hydrologic and biologic observations in streams. 

Figure 1. Hydrologic and geomorphic 

characteristics in relation to drainage area 

(FISRWG 1998). 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 4
 

This method and assessment form are designed to help the USACE Portland District Regulatory 

Program and EPA Region 10, and Oregon Department of State Lands distinguish between 

ephemeral, intermittent and perennial streams. This method is designed to be used throughout 

Oregon; however, the climatic and hydro-geomorphic variation across Oregon requires that 

local conditions and the potential strength of an indicator be considered when assessing 

indicator strength. For example, the arid regions of eastern Oregon will not produce thick wrack 

lines as will the deciduous forests of western Oregon in fall, but both systems can produce 

“strong” wrack lines. In addition, one indicator - presence of a clear riparian vegetated corridor - 

is used only in arid regions of Oregon (defined for this method as those areas that occur within 

the Arid West Region described in the Regional Supplement to the 1987 USACE Wetland 

Delineation Manual). Another indicator, presence of a lichen line on stream bed rocks or on the 

bank, is used only in arid regions and alpine areas. 

Background 

This method has been developed, in part, based on the experiences and progress of the North 

Carolina Division of Water Quality on their Identification Methods for the Origins of Intermittent 

and Perennial Streams.1

 The North Carolina Stream Identification Method (NC Method) was 

developed and tested based on documented scientific principles in hydrology, geomorphology 

and biology. Version 1 of the method was implemented in 1998 after extensive review from the 

academic and regulatory community. Since 1998, several major revisions have been made as 

experience and science advanced. The NC Method is viewed as an evolving document, and will 

continue to change over time. Since the NC Method is a regulatory tool used to guide rapid 

assessment of intermittent and perennial streams, it is used as a guide only and does not 

replace best professional judgment. As a regulatory tool, the NC Method facilitates consistent 

stream identification across many scientific disciplines, and evaluators must be certified by 

passing a state-legislated four-day training course. 

Starting from that base, experts in relevant academic and professional fields have been 

consulted in the development of the Oregon Streamflow Duration Assessment Method (Oregon 

Method). A team of experts from the USACE Portland District, USEPA Region 10 Oregon 

Operations Office and Office of Research and Development, USGS Idaho and Arizona Water 

Science Centers, Oregon Department of State Lands, and North Carolina Division of Water 

Quality conducted a one week field assessment of the method in the five major physiographic 

and climatic regions of Oregon. The field assessment compared the Oregon Method to known 

flow durations for headwater streams in the Coast Range, Willamette Valley Lowlands, 

Cascades Range, Great Basin, and the High Desert Plateau. In addition, several other efforts 

have informed selection of appropriate indicators, identification of potential problems in the field, 

and development of meaningful indicator descriptions and scoring, including: review of the 

scientific literature; beta-testing by the USACE Portland District, USEPA Oregon Operations 

Office, and Oregon Department of State Lands; development of a Xerces Society report “Using 

Aquatic Macroinvertebrates as Indicators of Streamflow Duration;” external peer-review; and 

results of the first phase of a USEPA field verification study of the OR Method including more 

than 170 streams from both sides of the Cascade Range. This interim version of the 

streamflow duration assessment method will be used, evaluated, and refined as experience and 

scientific understanding advances. 

Application of this method requires that users receive training in the identification and 

rating of these indicators to ensure accuracy and consistency in results. 

 

1 http://h2o.enr.state.nc.us/ncwetlands/documents/NC_Stream_ID_Manual.pdf

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 5
 

Definitions 

As used by this method: 

Channel forming flow is the discharge that maintains the channel form and transports the 

greatest quantity of sediment over time (commonly referred to as bankfull flow). For streams 

with active floodplains, the channel forming flow can be defined as the point at which the flow 

just begins to enter the floodplain. Thus there are a variety of indicators that can be used to 

identify this point. For example, on some streams without active floodplains the distance 

between the lower limit of rooted terrestrial vegetation on each bank can be used (Dunne & 

Leopold, 1978). 

Channel is an area that contains flowing water (continuously or not) that is confined by banks 

and a bed. 

Dry Channel is an area confined by banks and a bed that at times contains flowing 

water, but at the time of assessment does not contain flowing water (it may contain 

disconnected pools with no sign of connecting flow). 

Wet Channel is an area confined by banks and a bed that contains flowing water at the 

time of assessment (flow may be interstitial). 

Ephemeral Stream flows only in direct response to precipitation. Water typically flows only 

during and shortly after large precipitation events.,. An ephemeral stream may or may not have 

a well-defined channel, the stream bed is always above the water table, and stormwater runoff 

is the primary source of water. An ephemeral stream typically lacks biological, hydrological, and 

physical characteristics commonly associated with the continuous or intermittent conveyance of 

water. 

Groundwater occurs at the subsurface under saturated conditions and contains water that is 

free to move under the influence of gravity, often horizontally to stream channels when a 

confining layer blocks downward percolation. 

Hyporheic Zone is the zone under and adjacent to the channel where stream water infiltrates, 

mixes with local and/or regional groundwater, and returns to the stream. The dimensions of the 

hyporheic zone are controlled by the distribution and characteristics of alluvial deposits and by 

hydraulic gradients between streams and local groundwater. It may be up to two to three feet 

deep in small streams, and is the site of both biological and chemical activity associated with 

stream function. 

Intermittent Stream is a channel that contains water for only part of the year, typically during 

winter and spring when the stream bed may be below the water table and/or when snowmelt 

from surrounding uplands provides sustained flow. The channel may or may not be well-defined. 

The flow may vary greatly with stormwater runoff. An intermittent stream may lack the biological 

and hydrological characteristics commonly associated with the continuous conveyance of water. 

Normal Precipitation is defined as the 30-year average, provided by NOAA National Climatic 

Data Center, computed at the end of each decade. These data are available as annual and 

monthly means. 

Perennial Stream contains water continuously during a year of normal rainfall, often with the 

stream bed located below the water table for most of the year. Groundwater supplies the 

baseflow for perennial streams, but flow is also supplemented by stormwater runoff and 

snowmelt. A perennial stream exhibits the typical biological, hydrological, and physical 

characteristics commonly associated with the continuous conveyance of water. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 6
 

Stream Origin is the point where flow first appears on the land surface with enough force to 

disturb the substrate creating a lasting sign of flow. Stream origins are often wetlands, springs, 

seeps or headcuts. 

Swales can be wetlands or uplands (when assessed under the USACE 1987 Wetlands 

Delineation Manual or appropriate regional supplements) and primarily serve as a vegetated 

flow path occurring in a slight depression in the landscape but lacking differentiation between 

bed and bank. Swales often connect uplands to wetlands or streams, connect wetlands 

together, or connect upstream and downstream reaches of small streams that flow through a 

colluvial fan or an abrupt change in grade. 

Thalweg is the deepest part of a stream channel and the last part of the stream to contain 

flowing water as a stream dries up. As used in this method, the thalweg comprises the “lowest 

flow” pathway and typically spans approximately 5 to 20% of the channel width. 

Water Table is the surface elevation of the saturated zone below which all interconnected voids 

are filled with water and at which the pressure is atmospheric, commonly identified as the top of 

the local (i.e., floodplain) or regional groundwater aquifer. 

Considerations When Using the Method 

Spatial Variability 

Spatial variations in stream indicators occur within and among stream systems. Sources of 

variation between stream systems in Oregon are due primarily to physiographic province 

(geology and soils) and climate (seasonal patterns of precipitation and evapotranspiration). For 

example, riffles and pools result from in-channel structures and these structures can vary 

between rocks and boulders in the mountains and roots and wood debris in the alluvial valleys. 

The method was designed to apply to all stream systems within the diverse physiographic and 

climatic regions of Oregon. 

A substantial amount of variability can also occur along the length of a given stream system. 

Common sources of variation within a stream system include: 

• Longitudinal changes in stream indicators related to increasing duration and volume of 

flow. As streams gain or lose streamflow, the strength of indicators changes. 

• Longitudinal changes due to variables such as channel gradient and valley width, which 

affect physical processes and thus directly or indirectly affect many indicators. 

• Temporal variation of flow related to precipitation and evapotranspiration seasonality. 

For instance, in western Oregon the strong seasonal rainfall pattern - several months of 

wet weather followed by several months of dry weather - supports the establishment of 

intermittent streams. Due to these long periods of rain many of the intermittent streams 

in Oregon carry 80 - 90 percent of the yearly discharge associated with a perennial 

stream of the same size. This large yearly discharge results in very strong 

geomorphological development of the stream channel relative to the flow duration when 

compared with intermittent streams in other parts of the country. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 7
 

The Concept of Scale 

For the purposes of applying this method perhaps the most important type of variation between 

streams, however, is simply the size of the stream. Streams develop different channel 

dimensions due to differences in flow magnitude, landscape position, land use history, and other 

factors. When assessing a stream, it is of paramount importance to consider scale when 

determining the strength of indicators. For instance, depositional features or channel 

structures of a given size may be insignificant (i.e., “weak”) in a large stream, while features of 

the same size in a small stream may be a clear expression of physical processes and thus merit 

a score of “strong.” Section 2 provides specific guidance for considering the scale of features 

when assessing individual indicators; some indicators are scale-independent, in which case no 

additional commentary on scale is provided. 

Reach Selection 

This manual lays out a method for assessing geomorphic, hydrologic, and biologic indicators of 

stream flow duration. However, flow characteristics often vary along the length of a stream, 

resulting in gradual transitions in flow duration. Recognizing that in many streams flow duration 

exists on a continuum, choosing the reach on which to conduct an assessment can influence 

the resulting conclusion about flow duration. 

Assessments should be made for a representative reach, rather than at one point of a stream. 

A representative reach for stream assessments is equivalent to 35 - 40 channel widths of 

the stream. For narrow streams, the length of the assessment reach should be a minimum of 

30 meters. 

Assessments should begin by first walking up and down the channel, from the stream origin to 

the downstream confluence with a larger stream (to the extent feasible). This initial review of 

the site allows the evaluator to examine the overall form of the channel, landscape, and parent 

material, and variation within these attributes as the channel develops or disappears upstream 

and downstream. Walking the channel also allows the assessor to observe characteristics of 

the watershed such as land use and sources of flow (e.g. stormwater pipes, springs, seeps, and 

upstream tributaries). Once these observations are made, the assessor can identify the areas 

along the stream channel where these various sources (stormflow, tributaries or groundwater) or 

sinks (alluvial fans, abrupt change in bed slope, etc.) of water may cause abrupt changes in flow 

duration. Similarly, the assessor can identify if the stream segment in question is generally 

uniform or should be assessed as two or more distinct reaches. 

For regulatory purposes the reach in question will often be predetermined by property 

ownership or proposed activities; the above process for assessing the stream should be 

followed to the extent possible, and if the reach in question is generally uniform one assessment 

is appropriate. If the reach in question is not uniform, two or more assessments are 

recommended to fully describe the changes along the reach. Regardless of the number of 

reaches assessed, decisions should be made in conjunction with “best professional judgment” 

to reach a conclusion on flow duration as ephemeral, intermittent, or perennial. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 8
 

Recent Precipitation 

The rate and duration of flow in stream channels is influenced by climate and by recent weather. 

Recent (within 48 hours) rainfall can influence scoring; therefore it is strongly 

recommended that field evaluations be conducted at least 48 hours after the last 

significant rainfall. 

However, note that this assessment method has been designed with redundancy to allow for 

reasonably accurate ratings even after a recent rainfall. Evaluators should note recent rainfall 

events on the assessment form and take them into consideration when drawing conclusions and 

assessing the applicability of individual indicators. 

Ditches and Modified Natural Streams 

This method can be used, in combination with best professional judgment, to assess the flow 

duration of natural streams, modified natural streams, and ditches dug in wetlands or uplands. 

When assessing a reach that is a ditch or modified natural stream, it is important to walk the 

entire reach and locate the inflow point or origin as well as the downstream terminus of flow 

(most often a confluence with another channel). Similarly, any disturbance or modifications to 

the stream channel should be noted on the assessment form – especially if it means one or 

more indicators are not applicable (Figure 2). For highly modified streams, and many ditches, it 

may be necessary to use an alternative method to identify flow duration based on the presence 

of one or two key indicators that were not affected by the modifications; it may also be 

appropriate to visit the site multiple times or conduct hydrologic monitoring. For all 

assessments, disturbances or modifications to the stream or its catchment that may 

affect the presence and/or strength of the stream indicators should be noted. 

Figure 2. Example of a 

modified stream. Several 

indicators are apparent in this 

reach, but assessor should note 

the strength of indicators in 

upstream or downstream 

segments that are not directly 

affected by the road. Such field 

notes will more fully describe 

the site and may be useful in 

determining flow duration. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 9
 

Disturbed or Altered Streams 

Assessors should be alert for natural or human-induced disturbances that affect streamflow 

duration and/or the strength of indicators. Streamflow duration can be directly affected by flow 

diversions, urbanization and stormwater management, septic inflows, agricultural and irrigation 

practices, vegetation management, or other activities. The strength of indicators can be affected 

by changes in streamflow, and can also be affected by disturbances that may not substantially 

affect streamflow (for instance, a channel could be graded, thus removing many indicators even 

without changing the flow duration; other examples include grazing, logging, recent fire, beaver 

activity, riparian management, culvert installation, bank stabilization). Such disturbances 

should be described in the “Notes” section of the field assessment form. Similarly, 

natural sources of variation should also be noted such as fractured bedrock, volcanic parent 

material, recent or large relic colluvial activity (landslides or debris flows), and drought or 

unusually high precipitation. 

Conducting Field Assessments and Completing the Assessment 

Form 

Suggested Field Equipment 

• This guidebook. 

• Amphibian and macroinvertebrate field guides: (e.g. Amphibians of Oregon, Washington 

and British Columbia, Corkran and Thomas, 1996, Lone Pine Publishing, Redmond, WA; 

Macroinvertebrates of the Pacific Northwest, Adams and Vaughan, 2003, The Xerces 

Society, Portland, OR) 

• Plant identification guide and current wetland indicator status list 2

• Global Positioning System (GPS) – used to identify the boundaries of the reach 

assessed. 

• Camera – used to photograph and document site features. 

• Clinometer – used to measure channel slope.3

• Tape measure 

• Calculator 

• Kicknet or small net and tray – used to sample aquatic insects and amphibians. 

• Hand lens 

• Munsell Soil Color Chart – used to classify the color of various soils and distinguish 

redoximorphic features. 

• Polarized sun glasses – for eliminating surface glare when looking for fish, amphibians, 

and macroinvertebrates. 

• Soil auger and/or soil probe – used to examine soils in the toe of the bank and determine 

if the hyporheic zone is saturated. 

• Rock hammer or equivalent – useful for digging into the hyporheic zone. 

General Guidance for Completing the Field Assessment Form 

The Oregon Streamflow Duration Assessment Method relies upon the assessment of up to 21 

indicators of flow duration and on the assessor’s understanding of the site. As described in the 

 

2

 The 1988 plant list and 1993 Region 9 supplement are the currently applicable lists for use in Oregon. 3 Channel slope can also be determined from topographic maps or surveys.

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 10
 

Ditches and Modified Natural Streams section above, modifications to the site or areas 

upstream of the site may affect the presence or strength of the indicators. Similarly, natural 

variation such as interannual variation in precipitation can affect the year to year depth to 

groundwater, stream discharge, and the presence of the indicators used in this method. 

Therefore, it is important to accurately complete the field assessment form, including 

information for date, project, evaluator, waterway name and location, recent 

precipitation, observed hydrologic status, and channel gradient and width. Furthermore, 

the evaluator should indicate whether she has participated in a classroom “orientation” to the 

method, a field-based training class, or both. 

If the stream does not have defined a channel (i.e., bed and banks are not apparent), estimate 

the width of the flow path and describe in the “Notes” section. Any other relevant observations 

should also be recorded in the “Notes” section of the form. These may include the local geology, 

runoff rates, hydrologic unit codes, evidence of stream modifications or hydrologic alterations 

upstream of the assessment area (e.g. dams, diversions, stormwater discharge), and recent 

land clearing activities upstream. All pertinent observations should be recorded on the form, 

including a clear and repeatable way of identifying the boundaries of the reach being assessed 

and the reasons for choosing those boundaries. 

Scoring 

Identification of stream type is accomplished by evaluating up to 21 different indicators of 

streamflow duration and assigning a score to each. The scoring sheet is used to tally the scores 

for each indicator and determine the total numeric score for the stream. The total score reflects 

the persistence of flow, with higher scores indicating intermittent and perennial streams. 

Thresholds for total scores separate perennial, intermittent and ephemeral streams, but local 

conditions including disturbances and modifications made to the stream should be taken into 

account when using best professional judgment to reach a flow duration conclusion for a 

stream. If a quick or comprehensive assessment leads to an overall score within a point or two 

of the threshold for flow duration category, the assessor should carefully review the indicators 

and the potential disturbances and modifications made to the stream before reaching a final 

conclusion on flow duration category, carefully documenting rationale for the conclusion on the 

assessment form or supporting documents. 

A four-tiered scheme is used for scoring each indicator or attribute while accounting for the 

variability of streams. The scores, “Absent”, “Weak”, “Moderate”, and “Strong” are applied to 

sets of geomorphic, hydrologic and biological indicators.4

 Each score reflects the evaluator’s 

judgment of the average degree of an indicator’s development along the stream reach being 

evaluated. 

The range of scores is intended to allow the evaluator flexibility in assessing indicators that exist 

along a continuum, instead of relying simply on presence/absence of an attribute. The small 

increments in scoring between gradations also will help reduce the range in scores between 

different evaluators. 

It is important to note that “Moderate” scores are intended as an approximate qualitative 

midpoint between the two extremes of “Absent” and “Strong.” The remaining 

description, “Weak”, represents gradations between “Absent” and “Moderate” that will 

often be observed in the field. 

 

4 The scoring system includes both primary and secondary indicators: the secondary indicators are 

weighted less than the primary indicators.

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 11
 

Natural disturbances such as recent landslides and wildfires could mask the presence of some 

indicators. Similarly, human modifications to streams, such as toxic pollution or cement lined 

channels, could also preclude some indicators from forming. These situations should be 

explained in the “Notes” section of the assessment form. 

General definitions of “strong”, “moderate”, “weak”, and “absent” are provided in Table 1. These 

definitions are intended as overall guidelines. The evaluator must select the most 

appropriate score for each indicator based primarily upon specific guidance (see Section 

2) and secondarily upon experience and professional judgment, observations of the 

stream, and characteristics of the watershed and physiographic region.5

Scoring of the indicators is based on observations and should not include predictions of what 

could or should be present. Disturbances and modifications to the stream should be described 

in the notes section of the assessment form and taken into consideration when drawing 

conclusions from the information collected. It is also important to explain the rationale behind 

conclusions reached, and when necessary that rationale should be supported with photos and 

other documentation of the reach condition and any disturbances or modifications that were 

taken into consideration. 

Table 1. General Guide to Scoring Categories 

Category Description 

Absent The indicator is not observed

Weak The indicator is present but not common 

Moderate The indicator is common but not ubiquitous

Strong The indicator is present throughout the reach

 

5 Physiographic region is an important consideration when assessing the presence of certain indicators. 

For example, assessment of the strength of indicators 10 - Leaf litter / loose debris and 11 - Debris piles 

or wrack lines in the arid eastern half of Oregon should reflect the vegetation present and the potential for 

accumulation. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 12
 

Section 2: Indicators of Streamflow Duration 

A. Geomorphic Indicators 

1. Continuous Bed and Bank. 

Throughout the length of the stream reach, is the channel clearly defined by having a 

discernable bank and streambed? (Figures 3, 4, 5, and 6) 

The bed of a stream is the physical confine of the baseflow; it often also confines stormflow, but 

it will always confine the baseflow. The lateral constraints (channel margins) during all but flood 

stage are known as the stream banks. In fact, a flood occurs when a stream overflows its banks 

and partly or completely fills its flood plain. 

As a general rule, the bed is that part of the channel below the "normal" water line, and the 

banks are that part above the water line; however, because water flow varies, this differentiation 

is subject to local interpretation. In perennial and intermittent streams the bed is usually kept 

clear of terrestrial vegetation, whereas the banks are subjected to water flow only during 

infrequent high water stages, and therefore can support vegetation much of the time. 

This indicator will lessen and may diminish or become fragmented upstream as the stream 

becomes ephemeral. This feature may also be weak or absent when a stream passes over 

waterfalls, long stretches of exposed bedrock, or when it enters a water control or conveyance 

structure – in such cases those confounding factors should be noted on the assessment form, 

as should the presence of a bed and bank where they had the potential to form (immediately 

upstream or downstream). Artificially created bed and banks should still be assessed for their 

presence and degree of confinement along the reach. For heavily incised channels, assess the 

active channel’s bed and banks, not the relic incision. 

Note: If the aquatic feature does not have a bed and banks it may be more appropriate to 

consider the feature as a swale or a wetland (if it meets hydrology, soils, and vegetation 

criteria). 

Strong – There is a continuous bed and bank present throughout the length of the stream 

reach. 

Moderate – The majority of the stream has a continuous bed and bank. However, there are 

obvious interruptions. 

Weak – The majority of the stream has obvious interruptions in the continuity of bed and bank. 

However, there is still some representation of the bed and bank sequence. 

Absent – There is little or no ability to distinguish between the bed and bank. 

 

 

 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 13
 

Figure 3. “Weak” discontinuous bed and 

bank (western Cascades, channel width 

0.7 m) 

Figure 4. “Weak” poorly defined bed and 

bank (Blue Mountains, flow path width 0.5 m)

Figure 5. “Moderate” bed and bank (Blue 

Mountains, channel width 0.7 m) 

Figure 6. “Strong” bed and bank (western 

Cascades, channel width 0.6 m)

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 14
 

2. In-channel Structure – Coherent, Organized Sequences 

Is there a regular sequence of coherent, organized fluvial erosion/deposition structural 

features in the channel indicative of recurring high flows? (Figures 7, 8, 9, and 10) 

A repeating sequence of riffle/pool (riffle/run in lower-gradient streams, riffle/pool in sand bed 

streams, or step/pool in higher gradient streams) can be readily observed in many but not all 

perennial streams. This morphological feature is almost always present to some degree in 

higher gradient mountain streams. Riffle-run (or ripple-run) sequences in low gradient streams 

are often created by in-channel woody structure such as roots and woody debris. When present, 

these characteristics can be observed even in a dry stream bed or in small streams by closely 

examining the local profile of the channel. Streams with particularly course beds may lack inchannel structure. 

A riffle is a zone with relatively high channel gradient, shallow water, and turbulence. In smaller 

streams, areas of a distinct change in gradient where flowing water can be observed are often 

identified as riffles. The substrate material in riffles contains the largest sediment particles that 

are moved by bankfull flow (bedload). A pool is a zone with relatively low channel gradient, deep 

water, and low turbulence during low flow periods. Fine textured sediments may dominate the 

substrate material in pools where a fine sediment supply exists. Along the stream reach, take 

notice of the spacing and frequency of the riffles and pools or other types of in-stream 

structures. This feature may also be absent or not well defined when a stream passes over long 

stretches of exposed bedrock, or when it enters a water control or conveyance structure. In 

such cases those confounding factors should be noted, as should the presence of an in-stream 

structure where it had the potential to form (i.e. immediately upstream or downstream). 

Strong – Stream has a coherent and organized sequence of fluvial erosion/deposition structural 

features along the entire reach. There is an obvious transition between structural features. 

Moderate – Stream has a sequence of fluvial erosion/deposition structural features along the 

reach but distinguishing between the features is difficult or they do not occur over the entire 

reach. 

Weak – Stream has some fluvial erosion/deposition structural features but not a coherent 

sequence, mostly one structural form. 

Absent – There are no fluvial erosion/deposition structural features in the stream. 

3. Soil Texture or Stream Substrate Sorting 

Has channel downcutting penetrated through the soil profile, such that the texture of the 

stream substrate different (i.e. much coarser) than that of the soil in the adjacent 

floodplain? Is there evidence of sorting of the stream substrate materials, indicative of 

frequent high flows? (Figures 11, 12, 13, and 14) 

This feature can be examined in two ways. The first is to determine if the soil texture in the bed 

of the stream channel is similar to the soil texture outside the channel. If the soil texture is 

similar, then there is evidence that erosive forces have not been active enough to down cut 

through the soil profile as expected in an intermittent or perennial stream. Soils in the bed of 

ephemeral channels typically have the same or similar texture as the soils adjacent to the 

channel (Figure 11). Accelerated stormflow resulting from development, for example, may 

produce deep, well-developed ephemeral or intermittent channels but which have little or no 

coarse bottom materials indicative of upstream erosion and downstream transport (i.e., 

alluvium). The substrate of intermittent or perennial streams often has accumulations of coarse 

sediment, 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 15
 

Figure 7. “Weak” geomorphic sequences; 

channel is dominated by a single structural 

form (Blue Mountains, channel width 2.6 m)

Figure 8. “Weak” development of riffle/pool 

structure (Crooked River basin, channel 

width 1.7 m)

Figure 9. “Moderate” frequency of riffle/run 

sequences (Blue Mountains, channel width 

2.2 m)

Figure 10. “Strong” set of step-pool 

sequences (foothills of western Cascades; 

channel width 2.0 m)

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 16
 

either from deposition or winnowing away of fines leaving behind the coarse sediments. 

Bedrock streams may lack any sediment on the bed for significant reaches. 

The second way this feature can be examined is to look at the distribution of sediment in the 

substrate in the stream channel. Is there an even distribution of various sized particles 

throughout the reach, or is the sediment sorted into discrete patches of different grain sizes 

(Table 2; Figures 12 and 14)? In the arid area of eastern Oregon one may need to look for size 

variations among sand grains – for instance, coarse versus fine sand. The occurrence of 

depositional features may be infrequent in intermittent streams. Perennial streams, on the other 

hand, tend to exhibit larger depositional features, with cobble/gravel/boulders being localized in 

riffles and runs, and may have accumulations of fine sediments settling out in slow water areas. 

Notes: The usefulness of this attribute may vary among physiographic provinces. For instance, 

in parts of eastern Oregon dominated by fine-textured parent materials (such as volcanic ash) 

the variability in the size of soil particles may be less than in the mountains and valleys. 

Assessors should also note if the deposits are potentially colluvial (i.e. from rock slides and 

other terrestrial movements outside of stream flows) and therefore not indicative of flow 

duration. 

Table 2. Standard USDA Particle Sizes 

Diameter

Description millimeters inches 

fine sand 0.1-0.25 .004-.01 

medium sand 0.25-0.5 .01-.02 

coarse/very coarse sand 0.5-2.0 .02-.08 

pebbles (gravel) 2-75 .08-3.0 

cobbles 75-250 3.0-9.8 

stones 250-600 9.8-23.6 

boulders > 600 > 23.6 

Strong – There is a well-developed channel through the soil profile with relatively coarsetextured substrate compared to riparian zone soils; for instance, course sand, gravel, or 

cobbles on the coast or in the valleys; gravel, cobbles, stones, or boulders in the mountain 

regions. OR - There is clear evidence of sediment sorting, soil texture differs between the 

stream substrate and adjacent land. 

Moderate – There is a well-developed channel but it has not incised through the soil profile. Soil 

texture differs somewhat between the stream substrate and adjacent land. Some coarse 

sediments are present. OR - There is relatively little sorting of fine material from coarser 

materials. 

Weak – The channel is poorly developed through the soil profile. Soil texture differs little 

between the stream substrate and adjacent land. OR - Some coarse sediments are present, but 

substrate sorting is not readily observed. There may be some small depositional features 

present on the downstream side of obstructions (large rocks, etc.). 

Absent – The channel is poorly developed, very little to no coarse sediments are present, and 

substrate sorting is absent. No difference between soil texture in the stream substrate and 

adjacent land is observed. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 17
 

Figure 11. Both substrate sorting and soil 

texture differentiation are “weak” (Willamette

Valley, channel width 0.7 m)

Figure 12. “Strong” sorting of particle sizes 

amongst stream substrate (Willamette 

Valley, channel width 1.2 m)

Figure 13. “Weak” substrate sorting (Blue 

Mountains, channel width 0.9 m) 

Figure 14. Example of different patches of 

sorted particles (pine needles are approx. 

10 cm long).

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 18
 

4. Erosional Features 

Is there evidence of fluvial erosion? Does the channel show evidence of fluvial erosion in 

the form of undercut banks, scour marks, channel downcutting, or other features of 

channel incision? (Secondary Indicator) (Figures 15 and 16) 

Undercut banks and scour marks are the most common signs of fluvial erosion for streams in a 

floodplain system. In steeper landscapes, channel downcutting and incision may occur. Other 

weaker signs of erosion include the scour marks on the downstream side of boulders and other 

obstructions. 

Assess the erosional features within the active channel; relic channel incision that is not part of 

the active channel should not be assessed. Human modifications to armor or stabilize the bed 

or banks of the stream (e.g. root wads and riprap) should be considered an indicator of fluvial 

erosion. Note that bank sloughing is not directly caused by fluvial processes and should not be 

considered an erosional feature. 

Note: Erosion and deposition processes differ between bedrock and alluvial channels. The 

field assessment form includes a check box to denote if the streambed consists of more than 

50% exposed bedrock. This information is used to interpret indicator scores and document best 

professional judgment. 

Strong – Fluvial erosion is obvious throughout the reach, or there are some substantial 

erosional features present. 

Moderate – Fluvial erosion is present throughout most of the reach, or there are some 

moderate erosional features present. 

Weak – Fluvial erosion is infrequent along sampling reach and the features are weak. 

Absent – Fluvial erosion is completely lacking. 

Figure 15. “Weak” lateral erosion is not 

continuous along length of reach, and banks 

are relatively stable (Northern Basin and 

Range, approximate channel width 1.8 m) 

Figure 16. “Strong” erosional feature is 

continuous along length of reach, and bank 

is actively undercutting (Blue Mountains, 

channel width 2.4 m) 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 19
 

5. Depositional Features 

Are there depositional features such as bars or fresh deposits of alluvial materials in the 

stream channel or on the floodplain? Is there an active floodplain at the bankfull 

elevation? (Figures 17, 18, and 19) 

When a stream channel conveys perennial flow, the forces of channel scouring and deposition 

create distinct erosional and depositional features. Alluvium may be deposited as sand, silt, 

gravel and cobble. There are several different types of depositional features, all of which are 

assessed with this one indicator and should be scored based on the presence of depositional 

features along the reach of stream being assessed. Observing depositional feature(s) along 

only a third of the reach would be weak, but depositional feature(s) along the entire length of the 

reach would be strong. 

Bars are accumulations of sand or silt in a stream channel which may or may not be covered 

with vegetation. These include point bars, lateral bars and mid-channel bars. The presence of 

depositional bars suggests that the channel transports sediment and is in or near dynamic 

equilibrium with the shaping forces of its water/sediment load. Depositional bars also indicate a 

relatively continuous hydrologic regime. 

Floodplains are relatively flat areas that accumulate organic matter and inorganic alluvium 

deposited during flooding, and are usually located outside of and adjacent to the stream 

channel. An active floodplain (at current bankfull elevation, such that it is inundated on an 

approximate 2-year recurrence interval) shows characteristics such as drift lines, sediment 

deposits on the surface or surrounding plants, or flattening of vegetation. The floodplain of 

incised streams may be restricted to within the channel itself and the previous floodplain (now a 

terrace) may be inundated rarely or infrequently. In these instances, look for indicators along the 

sides and within the incised channel. Floodplains on smaller order, incised streams may not be 

continuous but rather may be present in some locations and absent in others. In many cases 

there should be evidence of a floodplain if the stream has perennial flow. 

Depositional features are often absent in very small channels. Sometimes there may be 

depositional features along the side of the channel or on the lee side of obstructions in the 

channel (e.g. in the hydraulic shadow of logs, boulders, etc.), the tops of which are below 

bankfull elevation. These features should not score as highly as well-developed bankfull 

depositional features, but are nonetheless evidence of deposition. 

Strong – Depositional features are obvious throughout the reach, or there are some substantial 

depositional features present. 

Moderate – Depositional features are present throughout most of the reach, or there are some 

moderate depositional features present. 

Weak – Depositional features are infrequent along sampling reach, and the features are weak. 

Absent – Indications of depositional bar, floodplain connection, or other depositional features 

are lacking. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 20
 

Figure 17. Example of depositional feature 

in small stream (channel width 0.5 m) 

Figure 18. Point bar (Willamette Valley, 

approximate channel width 3 m). Also note 

seep areas (on right), indicated by oxidized 

iron. 

Figure 19. “Strong” depositional features in 

a small headwater stream (western 

Cascades, channel width 0.9 m) 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 21
 

6. Sinuosity 

Measure the stream’s sinuosity. (Figure 20)

Sinuosity is a measure of a stream’s “crookedness.” Specifically, it is the total stream length 

measured along the stream thalweg divided by the straight line valley length (Figure 20). Higher 

ratios indicate more and/or larger curves in the stream. Sinuosity is related to the gradient, but 

can also be influenced by parent material and obstructions (natural or otherwise). Typically 

higher gradient streams are less sinuous than lower gradient streams, and perennial streams 

are more sinuous than intermittent or ephemeral streams. Sinuosity is the natural result of the 

stream dissipating the force of its flow. 

Note: Sinuosity may not be an applicable indicator for highly modified or managed streams, but 

even so, sinuosity is sometimes evident in the path of the thalweg in the bottom of a cement 

lined canal. Any modifications or artificial restrictions on a stream’s sinuosity should be noted 

on the assessment form and taken into consideration when drawing conclusions from the total 

score for the reach. 

Strong – Ratio > 1.2. (i.e., stream has numerous, closely-spaced bends, very few straight 

sections) 

Moderate – 1.1 < Ratio ≤ 1.2. (i.e.., stream is a combination of sinuous and straight sections) 

Weak – 1.03 < Ratio ≤ 1.1. (i.e.,., stream has very few bends and mostly straight sections) 

Absent – Ratio ≤ 1.03. (i.e., the stream is essentially straight) 

Figure 20. Varying degrees of sinuosity, from left to right: “absent” (sinuosity of 

1.01), “weak” (1.07), “moderate” (1.14), “strong” (1.27), and “strong” (2.18) 

(Upper Klamath Lake basin). (These pictures are used for illustrative purposes; 

alterations to streams should be noted on the assessment form.) 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 22
 

7. Headcuts And Grade Controls 

Is there a headcut at the upstream end of the reach being evaluated? Are there one or 

more headcuts within the reach being evaluated? Are there grade controls within the 

reach being evaluated? (Secondary Indicator) (Figures 21, 22, 23, 24, and 25)

A headcut is an active erosion feature expressed as an abrupt vertical drop in the bed of a 

stream. It often resembles a small intermittent waterfall (or a miniature cliff) and may have a 

deep pool at the base resulting from the turbulent scour produced during high flows. Head cuts 

are transient structures of the stream and often exhibit relatively rapid upstream movement 

during periods of high flow. Intermittent or perennial streams sometimes begin at a head cut, 

particularly common in the drier east side and in the mountains. Groundwater seepage may also 

be present from the face or base of a headcut. 

A grade control is a structural feature in the channel that separates an abrupt change in grade 

of the stream bed or a point where a headcut has been stopped by an obstruction. Grade 

controls may consist of bedrock outcrops, large stones or large roots which extend across the 

channel, or accumulations of large woody debris (Figures 21 and 23). Sediment typically 

accumulates immediately upstream of grade controls. Pipes and hard bottomed culverts can 

also serve as grade control – and should be counted when they are functioning as grade 

control. These structures separate an abrupt change in grade of the stream bed. 

The strength of this indicator is based on the number and relative size of the features compared 

to the channel size and bed slope. Assess these features by comparing the dimensions of the 

headcut/grade control to the dimensions of the channel, and by determining if the feature affects 

the direction of the thalweg flow path. 

Note: To be considered as “grade control,” sediment particles should be larger than the vast 

majority of other sediment particles in the channel, such that they are not mobilized during 

channel-forming flows (i.e., boulders may provide grade control in a sand-bed stream, but are 

unlikely to provide a similar function in a high-energy cobble-bed stream). Structural features 

comprised of coarse sediment organized fluvially in repeating sequences should be evaluated 

using Indicator 2 (In-channel Structure). 

Strong – One or more large headcuts or grade 

control features are present within the reach. 

Moderate – One or more medium or several 

small headcuts or grade control features are 

present within the reach. 

Weak – One or two small headcuts or grade 

control features are present within the reach. 

Absent – No headcuts or grade control features 

are present within the reach. 

Figure 21. Grade control comprised of very 

large sediment particles (channel width 2.8 

m). This is a medium-sized feature, given 

the channel dimensions. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 23
 

Figure 22. Stream channel with headcuts 

and grade controls “absent” (Blue 

Mountains, channel width 2.4 m) 

Figure 23. Grade control of woody debris 

and roots (western Cascades, channel width 

0.7 m). This is a medium-sized feature, 

given the channel dimensions. 

Figure 24. Headcut, viewed from 

downstream (Blue Mountains, approximate 

channel width outside of the scour zone is 

0.5 m). This is a large feature, given the 

channel dimensions. 

Figure 25. Headcut, viewed from upstream 

(Upper Klamath Basin, approximate channel 

width outside of the scour zone is 0.8 m). 

This is a medium-sized feature, given the 

channel dimensions. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 24
 

B. Hydrologic Indicators 

8. Groundwater (Wet Channel) / Hyporheic Saturation (Dry Channel) 

Groundwater discharge to a stream indicates longer flow durations and more sustained 

baseflow between precipitation events. Observing flow in a channel does not conclusively 

indicate groundwater discharge to the channel within the reach being observed. Similarly, 

observing a dry stream bed does not conclusively indicate that the channel does not receive 

groundwater discharge. So separate assessment measures are used for this indicator when the 

channel is wet, versus when the channel is dry. When assessing this indicator, choose the 

location along the reach that will be most likely to show the presence of groundwater or 

hyporheic saturation (e.g., tails of riffles, deep pools). This assessment strategy indicates 

whether there are groundwater inputs anywhere along the reach, not whether groundwater is 

entering the stream throughout the entire reach. 

When the channel is wet: Are there signs of groundwater discharge to the stream along 

the reach, or is there a seasonal high water table? 

Groundwater Table: the presence of a seasonal high water table or groundwater discharge (i.e. 

seeps or springs) from the bank indicates a relatively reliable source of baseflow to a stream. 

The presence of pools or standing water are indicators of the height of the water table. A water 

table can also be inferred by the presence of wetlands in close proximity to the stream (i.e., 

within 2 channel widths) above the elevation of the streambed. The height of the water table 

can also be observed by digging a hole in the adjacent floodplain approximately one channel 

width away from the streambed (to avoid intercepting bank storage). The presence of water 

standing in the hole above the elevation of the channel bottom after waiting for at least 30 

minutes (longer for clayey soils) indicates the presence of the water table. This hole can be dug 

with a shovel, auger, or probe. If soil conditions prevent digging an adequately deep hole, 

assess this indicator as best you can and note the depth of refusal in the “Notes” section. 

Strong – Groundwater table higher than stream height is readily observable adjacent to the 

reach, or pools or standing water are apparent along the reach. 

Moderate – Groundwater table present, but nearly equal to the stream height. 

Weak – Groundwater table present, but well below the stream height or indicators of 

groundwater discharge are present, but require considerable time to locate. 

Absent – No indication of groundwater table in close proximity to stream bed elevation (within 

30 cm of streambed surface). 

When the channel is dry: Is the streambed / hyporheic zone saturated? 

Hyporheic Saturation: even when there is no visible flow above the channel bed, there may be 

flow in, or groundwater discharge into, the hyporheic zone (Figure 26). 

The hyporheic zone is the site of groundwater discharge to the stream, downstream flow, and 

biological and chemical activity associated with aquatic functions of the stream. The presence of 

hyporheic saturation can be assessed by making a hole in the thalweg (where possible) and 

seeing whether the hole fills with water (similar to the method for observing water table height 

described above). The hole may be dug with a shovel, but using an auger, probe, or pounding 

in a steel bar are recommended to minimize disturbance to the channel. If soil conditions 

prevent digging an adequately deep hole, assess this indicator as best you can and note the 

depth of refusal in the “Notes” section. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 25
 

Strong – Hyporheic zone is saturated (i.e., standing water visible in excavated hole) to 

streambed surface. 

Moderate – Hyporheic zone is saturated in close proximity to stream bed elevation (within 10 

cm of channel bottom for channels < 1 meter wide; within 20 cm for channels with width 

between 1 and 5 meters; within 30 cm for channels > 5 meter wide). 

Weak – Hyporheic zone is saturated well below streambed surface. 

Absent – No saturation of the hyporheic zone within 50 cm of the streambed surface. 

9. Springs and Seeps 

Are springs or seeps observed or mapped in the reach being evaluated or in an upstream 

reach? (Figure 27) 

Springs and seeps often are present at toeslopes of adjacent hillslopes but may also be present 

at the heads of secondary channels, at the toe of stream banks, and at grade controls and 

headcuts. The presence of springs and seeps suggest that the stream is supported at least 

partly by groundwater except during droughts. Score this category based on the abundance of 

these features observed within the reach. USGS and other maps often identify springs; however 

the accuracy with which these features are identified is often greater in arid and semi-arid areas, 

and less so in forested areas and wetter climates. 

Figure 26. Idealized depiction of hyporheic zone and groundwater 

aquifer (from FISRWG, 1998). 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 26
 

Note: If a spring or seep exists within the assessment reach, indicate the location of that feature 

on the assessment form. If a spring within or upstream from the reach is mapped, check USGS 

and state or local records for any discharge data and attach that to the field assessment form. 

Strong – A spring or seeps occur within the stream reach or a mapped spring occurs within the 

reach. If a spring is mapped in the reach but is not observed in the reach, this indicator should 

be rated moderate. 

Moderate – A spring or seeps are observed immediately upstream of the reach or a mapped 

spring occurs within a mile upstream of the assessment reach. 

Weak – A spring or seeps are observed upstream of the reach, or a mapped spring occurs 

more than a mile upstream of the assessment reach 

Absent – No springs or seeps are mapped or observed within, or upstream of, the reach. 

10. Evenly Dispersed Leaf Litter and Loose Debris 

Are leaves (freshly fallen or older leaves that may be “blackish” in color and/or partially 

decomposed) or other available aerially deposited debris accumulating in the thalweg? 

(Secondary Indicator) (Figures 28, 29, and 30) 

Perennial streams (with deciduous riparian vegetation) should continuously transport plant 

material through the channel. Leaves and other aerially deposited debris will occur throughout 

the length of non-perennial stream channels, whereas there will be little to no leaves or debris 

present in the stronger flowing areas (riffles) with small accumulations on the upstream side of 

obstructions. Assessing this indicator may be more difficult during autumn in deciduous forests 

when sampling between rain events. In areas where vegetation is non-deciduous, or is sparse 

or absent, the presence of other forms of light debris that could be aerially deposited uniformly 

on the landscape should be assessed (Figure 30). 

Dry channels: The distribution of aerially deposited debris should be assessed for the thalweg, 

comparing the distribution of debris in the thalweg to the surrounding channel and uplands. 

Figure 27. Seep discharging from 

fractured bedrock on channel margins. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 27
 

Note: The scoring range is reversed for this indicator. “Strong” indicates less flow and receives 

fewer points than “Absent”.

Strong – Leaf or other aerially deposited litter is present and abundant throughout the length of 

the stream. 

Moderate – Leaf litter or other aerially deposited debris is present throughout most of the 

stream’s reach with some accumulation on the upstream side of obstructions and in pools. 

Weak – Leaf litter or other aerially deposited debris is present, mostly located in small packs 

along the upstream side of obstructions and in pools. 

Absent – Leaf litter or other aerially deposited debris is not present in the fast moving areas of 

the reach, but there may be some present in the pools.

Figure 28. “Weak” distribution of leaf litter, 

with accumulations at discrete locations 

(western Cascades, channel width 1.7 m) 

Figure 29. “Strong” abundance and 

distribution of leaf litter (Klamath Mountains, 

approximate channel width 1.5 m) 

Figure 30. “Strong” distribution of light 

organic debris (Blue Mountains, channel 

width 0.8)

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 28
 

11. Debris Piles and Wrack Lines 

Are there accumulations of debris in piles or lines in the channel or on the active 

floodplain? (Secondary Indicator) (Figures 31, 32, and 33) 

Debris piles are defined as twigs, sticks, logs, leaves, trash, plastics, and any other floating 

materials piled up on the upstream side of obstructions in the stream, on the stream bank, in 

overhanging branches, and/or in the floodplain that indicate high stream flows. Wrack lines are 

twigs, sticks, logs, leaves, trash, plastics, and any other floating materials piled up / deposited in 

lines parallel to the channel’s direction of flow. Ephemeral streams usually exhibit fewer or no 

drift lines within their channels unless downstream of a storm drain or extensive urban runoff. 

The magnitude of the accumulation of drift may be influenced by watershed characteristics and 

sources of debris. For example, streams in watersheds dominated by herbaceous vegetation 

may not exhibit large drift piles. When assessing the strength of coverage by debris piles look 

at all the obstructions in the reach that could support a debris pile and assess strength based on 

the percentage of obstructions that actually have a debris pile. 

Dry channels: Focus the assessment of debris piles on the thalweg. 

Strong – Debris piles are prevalent along the upstream side of most obstructions within the 

channel and / or wrack lines are prevalent in the floodplain along the length of the reach. 

Moderate – Debris piles are on the upstream side of many obstructions and dispersed 

throughout the reach or wrack lines are present along parts of the reach. 

Weak – Small debris piles are present on the upstream side of one or two of the obstructions or 

one wrack line exists along the reach. 

Absent – No debris piles or wrack lines are present.

 

 

Figure 31. “Weak” abundance of debris 

piles; most debris is distributed rather than 

aggregated (Blue Mountains, channel width 

0.8 m) 

Figure 32. “Weak” abundance of debris 

piles (foothills of the western Cascades; 

channel width 0.5 m) 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 29
 

12. Redoximorphic Features in the Toe of Bank 

Are there redoximorphic features present in soils at the toe of the bank, at the base of 

head cuts above the streambed, or in the hyporheic zone? (Secondary Indicator) (Figures 

34 and 35) 

Soils with sufficient periods of inundation or saturation that contain iron (Fe) and manganese 

(Mn) may develop distinctive color features. Such redoximorphic (“redox”) features form by the 

processes of reduction, translocation, and/or oxidation of iron and manganese oxides. Thus, the 

presence of redox features in soils in the stream bed or bank provides evidence of extended 

annual periods of base flow. Types of redox features include: 

• Redox concentrations: Bodies of apparent accumulation of Fe-Mn oxides. Includes soft 

masses and pore linings, but does not include nodules and concretions. 

• Redox depletions: Bodies of low soil chroma (≤ 2) having values of 4 or more where FeMn oxides have been stripped or where both Fe-Mn oxides and clay have been 

stripped. Redox depletions contrast contrast distinctly or prominently with the soil 

matrix6

. 

• Reduced matrix: A soil matrix that has low chroma and high value, but in which the color 

changes in hue or chroma when the soil is exposed to air. 

• Gleyed matrix: A soil matrix that has bluish, greenish, or grayish colors, and high 

values and low chroma. While technically not a “redoximorphic feature,” the presence of 

gleyed soils is a strong indicator of saturated soil conditions.

Soils immediately adjacent to the stream bed along the stream bank may have redoximorphic 

features. Use an auger, soil probe or spade to obtain at least a 30- to 35-cm (12- to 14-inch) 

deep core and examine the soil pedon for redoximorphic features. The soil sample should be 

representative of the major streambed/bank soil type observed throughout the assessment 

 

6

 The soil matrix is the dominant soil volume that is continuous in appearance. When three colors occur, 

such as when a matrix, depletions, and concentrations are present, the matrix may represent less than 50 

percent of the total soil volume.

Figure 33. Example of debris pile. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 30
 

reach. Look for redoximorphic features in the surface and in the subsoil. Note that in cumulic 

(alluvial) soils with thick surfaces, redoximorphic features may only be found much deeper in the 

profile. Also, redoximorphic features can be masked by the presence of high organic matter 

concentrations (i.e. N 2.5/, 2.5Y 2.5/1 colors in the Munsell Soil Color Charts). 

Saturated soils, such as those found in the streambeds of perennial streams, have limited or no 

contact with oxygen and will remain reduced, thereby producing low chroma or gleyed soils. 

Soils subject to repeated periods of alternating aerobic and anaerobic conditions, such as those 

found along the banks of perennial streams, often have a dark colored matrix with brightly 

colored redoximorphic features. 

Note: While this indicator does not assess the presence or absence of hydric soils, the 

definition and discussion of redoximorphic features in the guide Field Indicators of Hydric Soils 

in the United States is nonetheless a useful reference.7

 

7 http://www.usace.army.mil/cw/cecwo/reg/techbio.htm under the Plants and Soils heading 

Figure 34. Masses of oxidized iron in a 

sandy soil (from NRCS, 2006). 

Figure 35. Soil matrix that has been 

depleted of iron and manganese oxides 

(scale in inches). Concentrations of 

oxidized iron are also present (from NRCS, 

2006). 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 31
 

C. Biological Indicators 

13. Wetland Plants In or Near Streambed 

What is the wetland indicator status of hydrophytic plants found in the streambed or 

within one-half channel width of the streambank? 

The USACE wetland delineation procedure uses a plant species classification system which 

identifies hydrophytic plants. This same system can be used as an indicator of the duration of 

soil saturation in stream channels. Small, low gradient, low velocity intermittent and perennial 

streams with adequate sunlight will often have Obligate (OBL) and Facultative Wetland (FACW) 

plants or Submerged Aquatic Vegetation (SAV) growing in the stream bed. SAV grows 

completely underwater (Figure 36). 

Wetland plant designations can be found in the National List of Plant Species that Occur in 

Wetlands: Northwest R9 (1988) and the 1993 Northwest Region 9 Supplement. The score for 

this indicator is based on the most hydrophytic wetland plant found in the assessed reach (e.g., 

if both FACW and OBL species are found, the score for this indicator would be 1.5). 

Note: Abundance and prevalence throughout the reach is not a factor in scoring this indicator, 

but if the reach is covered with wetland species and the stream scores very low overall the site 

may be more appropriately considered as a wetland than a stream. 

 Figure 36. Example of 

submerged aquatic vegetation. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 32
 

14. Fibrous Roots and Rooted Plants in Thalweg (Upland Plants) 

Are fibrous roots of woody upland plants present in the thalweg of the stream? Are 

rooted herbaceous upland plants growing in the thalweg of the stream? (Figure 37) 

Fibrous roots are small diameter (<1 cm or < 0.25 in), shallow, wide spreading roots without 

bark that often form dense masses in the top few inches of the soil. Fibrous roots of perennial, 

woody plants (i.e., trees and shrubs) are those which provide for water and nutrient uptake. 

Because oxygen is needed for respiration, fibrous roots are intolerant of saturation, unless they 

are roots of water tolerant plants. Thus, in substrates where water is persistent, or frequent high 

energy flows disturb the bottom substrate, fibrous roots may be infrequent or absent. 

Because streamflow often deters upland plant establishment by removing seeds, scouring 

plants, and preventing aeration of roots, herbaceous upland plants are also generally absent in 

the thalweg of perennial streams. 

Observe the bottom of the stream and determine if very small (fibrous) roots are present. Focus 

on the presence of rooted plants in the thalweg of the stream. Fibrous roots or plants growing 

on any part of the bank of the stream should not be considered. Note that during dry periods 

and in the growing season, fast growing fibrous roots may grow across the bottom of a dry 

stream that would not be present or survive during normal flow. 

Note: The scoring range is reversed for this indicator. A higher score is given for the absence 

of upland fibrous roots and rooted plants. 

Strong – Fibrous roots or rooted upland plants are present in many places along the reach. 

Moderate – Fibrous roots or rooted upland plants are present in approximately half of the reach. 

Weak – Fibrous roots or rooted upland plants are present in one or two places along the reach. 

Absent – Fibrous roots or rooted upland plants are not present in the reach. 

Figure 37. Example of an 

upland plant’s fibrous roots 

growing in a stream channel. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 33
 

15. Streamer Mosses or Algal Mats 

Are there streamer mosses present in the streambed? Are algal mats present in the 

reach? (Secondary Indicator) (Figures 38, 39, 40, and 41) 

Bryophytes (mosses and liverworts) are long-lived, non-vascular (without lignin) plants which 

inhabit a wide range of habitats. Some bryophytes have growth forms that trap moisture for 

survival; however some growth forms do not efficiently trap moisture and require a sustained (or 

recurring) presence of water in order to survive. Mosses of the streamer morphology – with 

long flowing stems – indicate a sustained or recurring presence of water (Figures 38 and 39). 

Algal matting is another indicator of duration of inundation. Look for clumps of filamentous algae 

attached to the streambed or substrate (Figure 40). Algal mats are also evident in dry channels 

(especially dry pools), and appear as a crust-like layer on top of the streambed. The crust-like 

layer often appears to be salts or other minerals left behind when the last remaining water 

evaporated out of the pool, but upon closer inspection may reveal a dried mat of filamentous 

algae rather than a crystalline/mineral residue. Algal matting often occurs in association with 

prismatic cracking of the streambed, which indicates high clay content in the streambed and is 

another sign of water loss through evaporation (Figure 41). The presence of algal matting 

indicates that the stream held water long to support algal growth sufficient to form a mat. 

Note: Only the presence of streamer mosses and attached or matted filamentous algae are 

being assessed – growth of other mosses (cushion, turfs, etc.) or algae (non-filamentous, 

floating, etc.) should not be considered for this indicator. 

Strong – Streamer mosses are present throughout the reach. 

Moderate – Streamer mosses are present in approximately half of the reach, and / or attached 

filamentous algae are present throughout the reach. 

Weak – Streamer mosses and / or attached filamentous algae are present in the reach. 

Absent –Streamer mosses and / or attached filamentous algae are not present. 

 

 

Figure 38. Example of desiccated streamer 

mosses (Blue Mountains). 

Figure 39. “Strong” abundance of streamer 

mosses (Northern Basin and Range, 

channel width 0.8 m). 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 34
 

16. Iron-Oxidizing Bacteria, Fungi, or Flocculent Material 

In slow moving or stagnant areas of the stream, are there clumps of “fluffy” rust-red 

material in the water? Are orange-red flocculent materials or stained rocks present in the 

stream? Are there red or rust colored stains (usually an “oily sheen” or “oily scum” will 

accompany these areas) on the bank or in the streambed? (Figures 42 and 43) 

Iron-oxidizing bacteria and fungi, and associated flocculent material, are often associated with 

groundwater. Iron-oxidizing bacteria/fungus in streams derive energy by oxidizing iron, 

originating from groundwater, from the ferrous form (Fe2+) to the ferric form (Fe3+). In large 

amounts, iron-oxidizing bacteria and fungi discolor the stream substrate, giving it an orange-red 

appearance. In small amounts, it can be observed as an oily sheen on the water’s surface. This 

indicates that the stream is being recharged by groundwater, and these features are most 

commonly seen at seeps or springs. 

Filmy deposits on the surface or banks of a stream are often associated with the greasy 

"rainbow" appearance of iron-oxidizing bacteria. This is a naturally occurring phenomenon 

where there is iron in the groundwater, but can also be caused by organic acids associated with 

leaf litter and septic tanks. A sudden or unusual occurrence may indicate a petroleum product 

release or septic tank problem. One way to differentiate iron-oxidizing bacteria from petroleum 

releases is to trail a small stick or leaf through the film. If the film breaks up into small islands or 

clusters, it is most likely bacterial in origin; if the film swirls together, it is most likely a petroleum 

product.

Note: Springs or seeps with iron-oxidizing bacteria, fungus or flocculent materials present 

should be assessed for both Indicator 9 (Springs and Seeps) and Indicator 16 – (Iron-Oxidizing 

Bacteria, Fungi, Flocculent Material). 

Figure 40. Example of dried attached 

filamentous algae. 

Figure 41. Example of algal mat on top of 

fine-textured streambed. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 35
 

Strong – Iron-oxidizing bacteria, fungi or flocculent materials are present in many places in the 

reach. 

Moderate – Iron-oxidizing bacteria, fungi or flocculent materials are present in a few places in 

the reach. 

Weak – Iron-oxidizing bacteria, fungi or flocculent materials are present in one or two small 

places in the reach. 

Absent – There are no iron-oxidizing bacteria, fungi or flocculent materials present in the reach. 

 

17. Macroinvertebrates 

Is there evidence of aquatic macroinvertebrates within the reach? (Figures 44 and 45; 

Also see Appendix C) 

Many macroinvertebrates require the presence of water, and in many cases flowing water, for 

their growth and development. Such macroinvertebrates are good indicators of streamflow 

duration because they require aquatic habitat to complete specific life stages. For example, 

clams cannot survive outside of water, in contrast to some stoneflies or alderflies that resist 

desiccation in some seasons of the year by burrowing into the hyporheic zone. Some 

macroinvertebrates can survive short periods of drying in damp soils below the surface, or in 

egg or larval stages resistant to drying. Others are quick to colonize temporary water and 

complete the aquatic portion of their life cycle during the wettest part of the year when sustained 

flows are most likely. 

This indicator includes the range of macroinvertebrates typically associated with stream habitats 

including: Coleoptera (aquatic beetles), Diptera (true flies), Ephemeroptera (mayflies), 

Megaloptera (dobsonflies and alderflies), Mollusca (snails and clams), Odonata (dragonflies and 

damselflies), Plecoptera (stoneflies), Trichoptera (caddisflies), and Astacoidea (crayfish). 

Figure 42. Example of iron-oxidizing 

microorganisms. 

Figure 43. “Strong” abundance of ironoxidizing microorganisms. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 36
 

Macroinvertebrates of the Pacific Northwest (Adams and Vaughan, 2003)8 provides a useful, 

compact and inexpensive field guide for general identification of several aquatic 

macroinvertebrate families found in Oregon streams. A condensed field guide for use with this 

method is included in Appendix C. 

The scoring system for this indicator was informed by a literature review and synthesis 

completed by the Xerces Society for Invertebrate Conservation (Mazzacano and Black, 2008).9

Several taxa and lifestages have been identified as either “Perennial Indicators” or “Intermittent 

Indicators” (Table 3); there is a high level of confidence that these indicator taxa are associated 

with the prolonged presence of water. (These taxa are also “Single Indicators”; see Section 3.) 

Table 3. Indicator status of various macroinvertebrate taxa 

Perennial Indicator Taxa / Lifestage

• Juga spp. (pluerocerid snail)

• Freshwater mussels (Margaritiferidae, Unionidae); less likely in small high-gradient 

streams

Larvae/pupae of: 

• Philopotamidae (finger-net caddisfly) 

• Hydropsychidae (net-spinning caddisfly) 

• Rhyacophilidae (freeliving caddisfly) 

• Glossosomatidae (saddle case-maker caddisfly), esp. in forested headwater streams

Nymphs of: 

• Pteronarcyidae (giant stonefly) 

• Perlidae (golden stonefly)

Larvae of: 

• Elmidae (riffle beetle) 

• Psephenidae (water penny), esp. in eastern regions

Larvae/nymphs of: 

• Gomphidae (clubtail dragonfly) 

• Cordulegastridae (biddies) esp. in larger streams in eastern Oregon

• Calopterygidae (broadwinged damselfly) 

Intermittent Indicator Taxa / Lifestage

Larvae/pupae of: 

• Limnephilidae (Northern caddisfly) 

Nymphs of: 

• Capniidae (small winter stonefly) 

• Nemouridae (forestfly) 

Larvae/adults of: 

• Dytiscidae (predaceous diving beetle) 

• Hydrophilidae (water scavenger beetle) 

Larvae/nymphs of: 

• Lestidae (spread-winged damselfly) 

Ephemeral Indicator Taxa / Lifestage

Larvae/pupae of: 

• Culicidae (mosquito) 

 

8 Published by The Xerces Society. Portland, OR (www.xerces.org)

9

 Available at http://www.xerces.org/aquatic-invertebrates/

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 37
 

This indicator is assessed using a minimum 20-minute search time to sample the range of 

habitats present, including water under overhanging banks or roots, accumulations of organic 

debris (e.g. leaves), woody debris, and the substrate (pick up rocks and loose gravel, also look 

for empty clam shells washed up on the bank in the coarse sand). A kicknet or D-frame net 

and a hand lens are required to collect and identify specimens. Place the kicknet 

perpendicular against the streambed and stir the substrate upstream of the net for a minimum of 

one minute, empty contents of the net into a white tray with fresh water for counting and 

identification. Many individuals will appear the same until seen against a contrasted color 

background, and some bivalves and other macroinvertebrates can be pea-sized or smaller. 

Sweeping grass and shrubs in the riparian zone immediately adjacent to the active channel with 

a funnel-shaped insect net may collect emergent aquatic insects such as stoneflies or 

caddisflies. 

Dry channels: Focus the search on the sandy channel margins for mussel and aquatic snail 

shells, any remaining pools for macroinvertebrates, and under cobbles and other larger bed 

materials for caddisfly casings. Casings of emergent mayflies or stoneflies may be observed on 

dry cobbles or on stream-side vegetation. 

Notes: 

• Time estimates for scoring do not reflect time spent on identifying individuals, rather they are 

wholly focused on searching / gathering effort. 

• This indicator does not differentiate between live organisms and shells, casings, and 

exuviae (i.e., the external coverings of the larvae and nymphs). In other words, mussel 

shells are treated the same as live mussels, and caddisfly cases are treated the same as 

live caddisflies (Figure 45) 

• The assessment is based only on what is observed, not on what would be predicted to occur 

if the channel were wet, or in the absence of disturbances or modifications. Disturbances 

and modifications should be described in the notes section and taken into account when 

drawing conclusions. 

• For greatest efficiency macroinvertebrates should be searched concurrently with the 

amphibian search (Indicator 18). 

 

Strong – At least one of the Perennial Indicator taxa is present, or at least 5 families within the 

orders of Ephemeroptera, Plecoptera, or Trichoptera (EPT) are present. 

Moderate – At least one of the Intermittent Indicator taxa is present, or at least 2 families within 

the EPT orders are present, or at least 5 taxa of aquatic macroinvertebrates are present.

Weak – At least one aquatic macrovinvertebrate is present.

Absent – No aquatic macroinvertebrates are found. 

 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 38
 

18. Amphibians and Snakes 

Are amphibians and snakes that require aquatic habitats present in the reach? 

(Secondary Indicator) (Figures 46 and 47) 

Amphibians by definition are associated with aquatic habitats, and some amphibians require 

aquatic habitat for much or all of their lives. In Oregon, there are likewise three snake species 

that require aquatic habitat for significant portions of their life history. This indicator focuses on 

the life history stages of salamanders, frogs, toads, and snake species, which require aquatic 

habitat by indicating life history stages for these species as FAC, FACW, or OBL (see Table 4). 

This indicator is assessed using a minimum 20-minute search time to sample the range of 

habitats present and can be searched concurrently with the macroinvertebrate search 

(Indicator 17) for greatest efficiency. Various life stages of frogs, salamanders, and tadpoles 

can be found under rocks, on stream banks and on the bottom of the stream channel. They may 

also appear in benthic samples. Using kicknets or smaller nets and tubs for specimen 

collection and identification is recommended. Frogs will alert you of their presence by 

jumping into the water for cover, usually following an audible “squeak”. Certain frogs and 

tadpoles, as well as adult and larval salamanders typically inhabit the shallow, slower moving 

waters of stream pools and near the sides of the bank. Amphibians of Oregon, Washington and 

British Columbia (Corkran and Thomas, 2002)10 is a useful field guide for identifying amphibians 

of the Pacific Northwest. 

 

10 Amphibians of Oregon, Washington and British Columbia (1996). C. Corkran and C. Thomas, Lone 

Pine Publishing, Redmond, WA. 

Figure 44. Example of caddisfly casings of 

the Limnephilidae family. Note that presence 

of these casings would meet the “single 

indicator” criteria for macroinvertebrates. 

Figure 45. Abundant caddisfly casings from 

in the Blue Mountains. Note that presence 

of these casings would meet the “single 

indicator” criteria for macroinvertebrates. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 39
 

Many of the obligate frog (tadpole-adult) and salamander species such as the Tailed frog 

(Figure 46), the Torrent salamanders, and the two Giant Salamander species will be found in 

the fast flowing portions of a stream. The three snake species listed in the table below will 

usually be found along the streambank, within the wetted margin of the stream, or on exposed 

rocks within the stream channel11. 

Amphibian eggs, also included for this indicator, can be located on the bottom of rocks, attached 

to vegetation in backwaters or along the stream margin, and in or on other submerged debris 

(Figure 47). They are usually observed in gelatinous clumps or strings of eggs, unlike snail and 

insect eggs, which are also often found on the bottom of rocks or attached to debris. 

Table 4 lists amphibians and snakes likely to be found in Oregon and the water-dependent life 

history stages for each. All egg masses, tadpoles, or salamander larvae count as OBL for a 

water-dependent life stage. Please note amphibian breeding adults require water, therefore 

adult FACW and FAC species found breeding should be scored as OBL. For instance, the adult 

Western Toad is listed as FAC, but would be scored as OBL if found breeding. 

Table 4. Water-dependent Life Stages of Amphibians and Snakes of the Pacific 

Northwest (Note: OBL: Obligate, requires surface or hyporheic water; FACW: Facultative Wet, 

strong preference for surface or hyporheic water; FAC: Facultative, uses but does not depend 

on surface or hyporheic water.)

Water-Dependent Life Stages

Species Common Name

Eggs Larva / 

Tadpole Juve. Adult

Aquatic Salamanders

Ambystoma gracile Northwest Salamander OBL OBL FACW FACW 

Ambystoma 

macrodactylum Long-toed Salamander OBL OBL FACW FACW 

Ambystoma tigrinum Tiger Salamander (rare) OBL OBL FACW FACW 

Taricha granulosa Roughskin Newt OBL OBL FAC FAC 

Dicamptodon copei Cope’s Giant Salamander OBL OBL OBL OBL 

Dicamptodon tenebrosus Pacific Giant Salamander OBL OBL OBL FACW 

Rhyacotriton spp.

Torrent Salamanders 

(rare) OBL OBL OBL OBL 

Frogs and Toads 

Ascaphus truei Tailed Frog OBL OBL OBL OBL 

Spea intermontana Great Basin Spadefoot 

(Eastern Oregon) OBL OBL FAC FAC 

 

11 Reptiles of the Northwest: California to Alaska; Rockies to the Coast (2002), A. St. John, Lone Pine 

Publishing, Redmond, WA. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 40
 

Water-Dependent Life Stages

Species Common Name

Eggs Larva / 

Tadpole Juve. Adult

Bufo boreas Western Toad OBL OBL FAC FAC 

Bufo woodhousii Woodhouse’s Toad 

(Eastern Oregon) OBL OBL FAC FAC 

Pseudacris regilla Pacific Treefrog OBL OBL FACW FAC 

Rana aurora Red-Legged Frog OBL OBL FACW FACW 

Rana boylii Foothill Yellow-Legged 

Frog OBL OBL OBL OBL 

Rana cascadae Cascades Frog OBL OBL FACW FACW 

Rana catesbeiana Bullfrog OBL OBL FACW FACW 

Rana pretiosa Oregon Spotted Frog OBL OBL OBL OBL 

Rana luteiventris Columbia Spotted Frog OBL OBL OBL OBL 

Snakes 

Thamnophis atratus Western Aquatic Garter 

Snake (SW Oregon) OBL OBL OBL 

Thamnophis elegans Wandering Garter Snake FACW FACW FACW 

Thamnophis sirtalis Common Garter Snake FACW FACW FACW 

Notes: 

• Time estimates do not reflect time spent identifying individuals, rather they are wholly 

focused on searching / gathering effort. 

• The assessment is based only on what is observed, not on what would be predicted to 

occur in the absence of disturbances or modifications. Disturbances and modifications to 

the stream should be described in the notes section and taken into account when 

drawing conclusions. 

• For greatest efficiency, the amphibian/ snake search should be done concurrently with 

the macroinvertebrate search (Indicator 17). 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 41
 

Strong – At least one individual, egg or egg mass of an OBL water-dependent life stage or two 

or more individuals, eggs or egg masses of at least two species listed as FACW for any waterdependent life stage is present. 

Moderate – At least one individual, egg or egg mass of a FACW water-dependent life stage or 

two or more individuals, eggs or egg masses of one or more species listed as FAC for any 

water-dependent life stage is present. 

Weak – At least one individual, egg or egg mass of a water-dependent life stage is present.

Absent – No water-dependent amphibian or snake life stages are found. 

19. Fish 

Are there fish in the stream? 

Fish are an obvious indicator of flow presence and duration. Fluctuating water levels of 

intermittent and ephemeral streams provide unstable and stressful habitat conditions for some 

fish communities. However, the strongly seasonal precipitation pattern in Oregon means 

intermittent streams may flow continuously for several months; thus, some native fish species 

have evolved to use intermittent streams for significant portions of their lifespan. 

When looking for fish, all available habitats should be searched, including pools, riffles, root 

clumps, and other obstructions (polarized sunglasses are helpful to reduce surface glare). In 

small streams, the majority of species usually inhabit pools and runs. Also, fish will seek cover 

once aware of your presence, so be sure to look for them slightly ahead of where you are 

walking along the stream. Check several areas along the stream sampling reach, especially 

underneath undercut banks. 

Figure 46. Tailed frog (Ascaphus truei), an 

“obligate” species whose presence would 

meet the “single indicator” criteria for 

amphibians. 

Figure 47. Amphibian egg mass found on 

the underside of a rock. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 42
 

Strong – Several fish or a few different species of fish are found in the reach. 

Moderate – A few fish or two different species are found in the reach. 

Weak – One or two fish are found in the reach.

Absent – No fish are found in the reach. 

20. Lichen Line (Used Only in Arid Regions and Alpine Areas) 

Is there a line on the rocks in the stream bed, or on the banks, below which no lichen 

grows? (Secondary Indicator) (Figures 48 and 49) 

Lichens are a symbiotic association of fungi and algae growing together. Generally, they are 

tolerant of dry conditions and temperature extremes and can colonize bare rock and survive in 

arctic and alpine conditions. However, they grow very slowly and are not very tolerant of 

physical abrasion or inundation. Lichens may occur on rocks, large woody debris, live trees and 

other hard surfaces extending out of the streambed. If lichens are present, identify whether 

there is a distinct horizontal line below which the substrate does not change but no lichens grow 

(Figure 49). This indicator applies only in arid regions and alpine areas. 

Note: As used below, “height” means elevation above the streambed at a cross-sectional point 

along the reach. The “height” of the lichen line may vary between locations along the length of 

the reach. 

Strong – Lichens are present along the length of the reach and form a line at approximately the 

same height. 

Moderate – A few lichens are present in the reach and most stop at the same height above the 

streambed. 

Weak – Lichens are present, but they do not form a clear height line along the reach. 

Absent – Lichens are not present in or near the channel, or if present are found throughout the 

reach, including in the thalweg. 

Figure 48. Example of lichen line. Figure 49. “Strong” distribution of lichen 

lines (Columbia Plateau, approximate 

channel width 4 m). 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 43
 

21. Distinct Riparian Vegetation Corridor (Used Only in Arid Regions) 

Is there a distinct change in vegetation between the surrounding uplands and the 

riparian corridor along the stream channel? 

Especially in arid regions, intermittent and perennial streams often support riparian areas that 

contrast markedly with adjacent plant communities. A distinct change in vegetation between the 

surrounding lands and the riparian area (top of bank and immediately adjacent areas within a 

channel width) may indicate the presence of seasonal moisture. Such changes may be 

evidenced by the occurrence of less drought tolerant species, vegetation types, or plant 

communities.12 For instance, upland grasses and shrubs may transition abruptly or gradually to 

riparian vegetation (e.g. willows, cottonwood, sedges, etc.). 

Note: This indicator applies only in the Arid West Region. Also note on the assessment form 

any reasons why this indicator would not be present, for example livestock grazing. 

Strong – A distinct riparian vegetation corridor exists along the entire stream reach. 

Moderate – A distinct riparian vegetation corridor exists along part of the stream reach or there 

is some change in vegetation towards less drought tolerant species along the entire stream 

reach. 

Weak – There is some change in vegetation towards less drought tolerant species along parts 

of the stream reach. 

Absent – There is no change in vegetation towards less drought tolerant species along the 

stream reach. 

 

12 Wetland Plants of Specialized Habitats in the Arid West (Lichvar and Dixon, 2007) lists wetland and 

upland plants (and their wetland indicator status) in the arid west, grouped by habitat. 

(http://www.crrel.usace.army.mil/library/technicalpublications-2007.html)

Figure 50. Riparian corridor is “absent” 

along this drainageway (Northern Basin and 

Range). 

Figure 51. “Strong” riparian corridor, as 

indicated by distinct transition from upland 

to riparian species and continuity of riparian 

vegetation along entire stream reach. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 44
 

SECTION 3: Drawing Conclusions 

The results of the field assessment are used to make a finding as to whether the weight of the 

observations indicates perennial, intermittent, or ephemeral streamflow. 

The method indicates the stream is perennial when the following criteria is met: 

1. A numerical value of at least 25 points. 

If the stream segment being evaluated does not meet the above criteria, the method 

indicates the stream is intermittent when any of the following criteria are met: 

2. A numerical value of at least 13 points. 

Or 

3. One or more fish are found in the segment. 

Or 

4. One or more individuals of an amphibian or snake life stage identified as Obligate or 

Facultative Wet (Table 4) are present. 

Or 

5. Two or more individuals classified as “Perennial Indicator” or “Intermittent Indicator” (Table 3) 

are present; or, two or more caddisfly cases, mussel shells, or aquatic invertebrate exuviae (i.e., 

the external coverings of the larvae and nymphs) associated with the sustained presence of 

water are present. 

If the stream has a bed and banks but does not meet any of the above criteria, the 

method indicates the stream is ephemeral. If the stream does not have a bed and banks 

and does not meet any of the above criteria, it may be more appropriate to consider the 

stream as a swale, wetland, or upland. 

As discussed in the introductory sections on Ditches and Modified Natural Streams and Scoring, 

if the channel does not meet any of the above criteria and the practitioner believes the channel 

to be perennial or intermittent s/he must clearly describe on the assessment form the evidence 

supporting this assertion. This may occur in highly polluted or recently manipulated streams. In 

those cases the actual observed indicators should be scored as usual, and the indicators that 

could potentially be there were it not for the pollution/manipulation should be described and the 

“Notes” section of the datasheet. 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 45
 

Appendix A: References Consulted 

Adams, Jeff and Vaughan, Mace. 2003. Macroinvertebrates of the Pacific Northwest: A Field Guide. The Xerces 

Society, Portland, OR. 

Adams, Jeff; Vaughan, Mace; Black, Scott Hoffman. 2004. Stream Bugs as Biomonitors: Guide to Pacific Northwest 

Macroinvertebrate Monitoring. The Xerces Society, Portland, OR. 

Adams, M.J. and R.B. Bury. 2002. The endemic headwater stream amphibians of the American Northwest: 

associations with environmental gradients in a large forested preserve. Global Ecology & Biogeography 

11:169-178. 

Anderson, Russel J.; Bledsoe, Brian P.; Hession, W. Cully. 2004. Width of streams and rivers in response to 

vegetation, bank material, and other factors. Journal of American Water Resources Association. 1159-1172. 

Arp, Christopher D.; Gooseff, Michael N.; Baker, Michelle A.; Wurtsbaugh, Wayne. Surface-water hydrodynamics and 

regimes of a small mountain stream-lake ecosystem. Journal of Hydrology. 329:500– 513. 

Barbour, M.T., J. Gerritsen, B.D. Snyder, and J.B. Stribling. 1999. Rapid Bioassessment Protocols for Use in Streams 

and Wadeable Rivers: Periphyton, Benthic Macroinvertebrates and Fish, Second Edition. EPA 841-B-99-

002. U.S. Environmental Protection Agency; Office of Water; Washington, D.C. 

Bencala, K.E. 2005. Hyporheic exchange flows. In: Anderson, M. and J.J. McDonnell (Eds). Encyclopedia of 

Hydrological Sciences, Volume 3. John Wiley and Sons, New York. 

Benda, Lee; Hassan, Marwan A.; Church, Michael; May, Christine, L.; 2005. Geomorphology of steepland 

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Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 51
 

Appendix B: Streamflow Duration Field Assessment Form 

The Field Assessment Form is provided on the following two pages 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 52
Oregon Streamflow Duration Field Assessment Form (Interim Version – March 2009)

Evaluator Project # / Name Attended Orientation Field Training 

Address Date 

Waterway Name Lat. N

Reach Boundaries 

Coordinates at 

downstream end 

(ddd.mm.ss) Long. W

Precipitation w/in 48 hours (cm) Channel Gradient (%) Channel Width 

(m) 

“Dry Channel” “Wet Channel” 

Observed 

Hydrology: Water 

Absent 

 No surface flow but at 

least one pool present 

 Surface flow present but 

not spatially continuous 

 Continuous 

surface flow 

Disturbed Site / Difficult Situation (Describe in “Notes”) Absent Weak Moderate Strong 

1. Continuous Bed and Bank 0 1 2 3 

2. In-channel Structure / Organized Sequences 0 1 2 3 

3. Soil texture or stream substrate sorting 0 1 2 3 

4. Erosional Features 0 0.5 1 1.5 

5. Depositional Features 0 1 2 3 

6. Sinuosity 0 1 2 3 

7. Headcuts And Grade Controls 0 0.5 1 1.5 

Geomorphology 

GEOMORPHOLOGY SUBTOTAL: ____________ 

8. Groundwater (Wet) / Hyporheic (Dry) 0 1 2 3 

9. Springs And Seeps (Note Locations) 0 1 2 3 

10. Evenly Disbursed Leaf Litter / Loose Debris ▼ 1.5 1 0.5 0 

11. Debris Piles And Wrack Lines 0 0.5 1 1.5 

12. Redoximorphic Features In Toe Of Bank Absent = 0 Present = 1.5 

 Hydrology 

HYDROLOGY SUBTOTAL: ____________ 

13. Wetland Plants In / Near Streambed FAC 0.5 FACW 0.75 OBL 1.5 SAV 2 None 

14. Fibrous Roots / Rooted Plants In Thalweg ▼ 3 2 1 0 

15. Streamer Mosses And Algal Mats 0 0.5 1 1.5 

16. Iron Oxidizing Bacteria, Fungus, Flocculent 0 1 2 3 

17. Macroinvertebrates 0 1 2 3 

18. Amphibians 0 0.5 1 1.5 

19. Fish 0 1 2 3 

20. Lichen Line (Arid Regions and Alpine Areas Only) 0 0.5 1 1.5 

21. Riparian Corridor (Arid Regions Only) 0 1 2 3 

Biology 

BIOLOGY SUBTOTAL: ____________ 

TOTAL SCORE: ____________

Flow Duration (select only one)

Ephemeral Total Score < 13 

Single 

Indicators: 

 Fish 

 Amphibians 

 Macroinvertebrates 

Intermittent Total Score ≥ 13 or Single Indicator Note: Scoring scale is reversed 

for indicators marked with ▼. Perennial Total Score ≥ 25 

□ Check this box if >50% 

of the streambed consists 

of exposed bedrock

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 53
Notes (explanation of any single indicator conclusions, description of disturbances or modifications that may 

interfere with indicators, etc.)

Difficult Situation: 

 Prolonged Abnormal Rainfall / Snowpack 

 Below Average 

 Above Average 

 Natural or Anthropogenic Disturbance 

 Other: ___________________________ 

Describe situation. For disturbed streams, note extent, 

type, and history of disturbance. 

Describe and Explain any Indicators of Questionable Applicability: 

Other Notes (sketch of site, description of photos, depth of observed groundwater, etc.)

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 54
 

Appendix C: A field guide to accompany the 

macroinvertebrate scoring portion of the Oregon Streamflow 

Duration Assessment Method 

The Field Guide is provided on the following four pages 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 55
 

This page intentionally blank 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 56
Macroinvertebrate Indicators of 

Streamflow Duration 

A Field Guide to Accompany the Macroinvertebrate Scoring Portion 

of the Oregon Streamflow Duration Assessment Method

Prepared for the U.S. Army Corps of Engineers & U.S. Environmental Protection Agency by 

The Xerces Society for Invertebrate Conservation 

 www.xerces.org 

Celeste A. Mazzacano, Ph.D., Aquatic Conservation Coordinator 

celeste@xerces.org 

EPHEMEROPTERA: MAYFLIES 

Larvae (nymphs): elongated body, may be cylindrical or flattened, 3-20 mm (0.1-0.8 in.); tip of abdomen with three (sometimes two) long 

slender cerci (“tails”); developing forewing pads visible; plate-like, feathery, or fringed gills at sides of abdomen; some types have larger 

fore-gills that form a shield like cover over other gills; conspicuous eyes; slender antennae 

Caenidae 

(little squaregill mayfly) Isonychiidae

(brush-legged mayfly) 

Heptageniidae 

(flathead mayfly) 

Baetidae 

(small minnow mayfly) 

Ephemerellidae 

(spiny crawler mayfly) 

Ephemeridae 

(common burrower 

mayfly) 

Leptophlebiidae

(prong gill mayfly) 

Oregon Streamflow Duration Assessment Method - Interim Version (March 2009) 57
MOLLUSCA: MUSSELS & SNAILS 

Freshwater mussels, Margaritiferidae (Margaritifera spp), Unionidae 

(Anodonta & Gonidea spp.): bivalved shell with two oblong halves; can reach 

>15 cm (6 in.) ; more common in larger rivers with softer substrate 

Anodonta nuttalliana 

(winged floater)

Margaritifera falcata 

(western pearlshell)

Gonidea angulata 

(western ridged mussel)

Juga snails: dark reddish-brown to black shell, 

smooth or ridged; pale lines may spiral with 

coils; 10-30 mm (0.4-1.2 in.) 

PLECOPTERA: STONEFLIES 

Pteronarcyidae 

(giant stonefly) 

Perlidae (golden stonefly) 

Capniidae (snowfly) 

Nemouridae 

(forestfly) 

Larvae (nymphs): elongate, slightly flattened body with “roachlike” appearance; 5-35 mm (0.2-1.4 in.); long slender antennae; two pairs of 

wing pads visible on older larvae; tip of abdomen has two “tails” (cerci); fingerlike or filamentous gills may be visible on bases of the 

legs, thorax, or underside of abdomen 

TRICHOPTERA: CADDISFLIES 

Peltoperlidae 

(roachfly) 

Larvae: elongate, caterpillar-like body; antennae reduced & inconspicuous; no wing pads; tip of abdomen has pair of short, clawed, anal 

prolegs, but no “tails” (cerci); 2-40 mm (0.08-1.6 in.); filamentous gills may be present in some types; some are free-living & spin silken nets, 

others build elongated, cylindrical, coiled, or saddle-shaped portable cases from stones, twigs, leaves, & other organic material; cases may 

persist in dry channels 

Philopotamidae 

(finger-net caddisfly) 

Hydropsychidae 

(net-spinning caddisfly) 

Rhyacophilidae 

(green rockworm) 

Glossosomatidae 

(saddle case-maker) 

Limnephilidae 

(Northern caddisfly) Helicopsychidae 

(snail case-maker) 

Leptoceriade 

(longhorned case-maker) 

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ODONATA: DRAGONFLIES & DAMSELFLIES 

Gomphidae 

(clubtail dragonfly) Calopterygidae 

(broadwinged damselfly) 

Larvae (nymphs): dragonflies = stout, cylindrical to flattened body; abdomen ends in 3 short stiff points; damselflies = slender elongated 

body with 3 flattened leaf-like gills at tip of abdomen; both have large eyes, wing pads, long extendable “lower lip” (labium) that masks the 

lower part of head when not in use 

Aeshnidae 

(darner dragonfly) 

Coenagrionidae 

(narrowwinged damselfly) 

Libellulidae 

(skimmer dragonfly) 

Macromiidae 

(river skimmer dragonfly) 

Larvae: body shapes vary; most types elongated, cylindrical, some dome-shaped; may have long filaments at the sides or tip of 

abdomen; well-developed, tough head and mouthparts; no wing pads; 2-70 mm (0.08-2.8 in.) 

Adults: body shapes vary; often oval and slightly flattened, some types cylindrical; forewings form hard smooth shiny covers 

(elytra) when folded, meet in straight line down the back, covering membranous hindwings and most of abdomen; legs may be 

flattened or fringed with swimming hairs; 1-40 mm (0.04-1.6 in.) 

Elmidae (riffle beetle, larva and 

adults) Psephenidae (water penny, 

larvae) 

Dytiscidae (predaceous 

diving beetle, adult (top) 

& larva) 

Hydrophilidae (water 

scavenger beetle, adult) 

Gyrinidae 

(whirligig beetle, 

larva (left) & 

adult) 

Haliplidae (crawling water 

Beetle, adult) 

COLEOPTERA: AQUATIC BEETLES 

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HEMIPTERA: AQUATIC TRUE BUGS 

Notonectidae 

(backswimmer, adult) 

Larvae (nymphs) & adults: body slender, oval to elongate, may be flattened; 1-65 mm (0.04-2.6 in.); cone– or needle-like beak arises 

from front of head, folded under body when not in use; have developing wing pads (nymphs) or wings (adults); adult forewings thickened 

& leathery at the base, membranous at the tips, cross at tips when folded; legs may be flattened like oars or fringed with swimming hairs 

Nepidae (water scorpion, adult) 

Corixidae 

(water boatman, adult) 

Belostomatidae 

(giant water bug, nymph) 

Gerridae (water strider, nymph) 

Chironomidae (nonbiting midge, pupa & 

larvae) 

ADDITIONAL GROUPS OF AQUATIC INVERTEBRATES 

Order Amphipoda (scud, side 

swimmer) 

Class Oligochaeta

(aquatic earthworm) 

DIPTERA: AQUATIC & SEMI-AQUATIC TRUE FLIES 

Culicidae (mosquito, 

larva Tipulidae (crane fly, larvae) 

Dixidae (dixid midge, larva) 

Ceratopogonidae (biting midge, larva) 

Athericidae (watersnipe fly, larva) Blepharicidae (netwinged 

midge, larva) 

Subclass Hirudinea

(leeches) 

Class Turbellaria

(flatworms) 

Order Isopoda (aquatic sowbug) 

Order Decapoda (crayfish) 

Order Megaloptera, Family Corydalidae 

(dobsonfly/fishfly larva, left) & Family 

Sialidae (alderfly larvae, right) Phylum Nematomorpha 

(horsehair worm) 

To read the complete report, “Macroinvertebrates as Indicators of Stream Duration”, visit www.xerces.org/aquatic-invertebrates/

All photos copyrighted by The Xerces Society, unless otherwise noted. 

The Xerces Society for Invertebrate Conservation, 4828 SE Hawthorne Blvd., Portland OR 97215, 503-232-6639 

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