United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

General Technical

Report RMRS-GTR-131

July 2004

Sediment Transport Data and 

Related Information for Selected 

Coarse-Bed Streams and Rivers 

in Idaho

John G. King, William W. Emmett

Peter J. Whiting, Robert P. Kenworthy, Jeffrey J. Barry
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E-mail rschneider@fs.fed.us

Web site http://www.fs.fed.us/rm

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Rocky Mountain Research Station

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Fort Collins, CO 80526

Rocky Mountain Research Station

Natural Resources Research Center

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Fort Collins, CO 80526

King, John G.; Emmett, William W.; Whiting, Peter J.; Kenworthy, Robert P.; Barry, Jeffrey J. 2004. Sediment 

transport data and related information for selected coarse-bed streams and rivers in Idaho. Gen. Tech. 

Rep. RMRS-GTR-131. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain 

Research Station. 26 p.

Abstract

This report and associated web site files provide sediment transport and related data for coarse-bed streams 

and rivers to potential users. Information on bedload and suspended sediment transport, streamflow, channel 

geometry, channel bed material, floodplain material, and large particle transport is provided for 33 study reaches 

in Idaho that represent a wide range of drainage areas, average annual streamflows, channel gradients, and 

substrate sizes. All the study reaches have a coarser layer of surface bed material overlaying finer subsurface 

material.

Both bedload and suspended sediment transport increase with discharge and the relationship can be reasonably 

represented using a log-log model. At most sites, the suspended load makes up the majority of the total sediment 

load. The size of the largest bedload particle in transport and usually the median size of the bedload increase with 

discharge. However, the median size of the bedload is much smaller than the channel surface material and sand 

is the primary or a large component of the bedload material.

A large proportion of the annual sediment production occurs at the higher streamflows during snowmelt. On average, discharges equal to or larger than bankfull occur 3.3 percent of the time and transport 61.5 percent of the 

annual bedload sediment. Discharges less than the average annual discharge, on average, occur 75.0 percent 

of the time and transport about 3.8 percent of the annual bedload sediment.

Key words: channel bed material, channel geometry, sediment transport, stream discharge

Authors

John G. King, Research Hydrologist, USDA Forest Service, Forestry Sciences Laboratory, Boise, ID.

William W. Emmett, Consulting Hydrologist, Littleton, CO.

Peter J. Whiting, Associate Professor of Geological Sciences, Case Western Reserve University, 

 Cleveland, OH.

Robert P. Kenworthy, Hydrologist, USDA Forest Service, Boise Adjudication Team, Boise, ID.

Jeffrey J. Barry, Hydrologist, Boise Cascade Corporation, Boise, ID.

Cover photo: Selway River near Lowell, Idaho, looking upstream of the 

U.S. Geological Survey gaging station.
Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Study Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Methods and Data Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Stream Reach Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

“At-a-Station” Channel Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Channel Bed Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Streamflow Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Bedload Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Suspended Sediment Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Sediment Transport-Discharge Relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Other Sediment Transport Related Information. . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Stream Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Channel Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Channel Bed Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Sediment Transport–Discharge Relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Acknowledgments

We thank the many individuals from several agencies who provided assistance in collecting and collating these 

data. The following individuals provided information for selected sites: Elizabeth Rieffenberger and Robert 

Rose from the Salmon-Challis National Forest provided information for Hawley Creek and Squaw Creek; Gayle 

Howard and Nick Gerhardt from the Nez Perce National Forest provided information on Lolo Creek, Main Fork 

Red River, South Fork Red River, Trapper Creek, Johns Creek, Little Slate Creek, and Rapid River; Robert 

Kasun from the Idaho Panhandle National Forests provided information on Cat Spur Creek; Dr. Thomas Hardy 

and his staff from Utah State University provided information for the Salmon River near Shoup, ID, the Salmon 

River below Yankee Fork, the Salmon River near Obsidian, ID, the Middle Fork Salmon River near the Middle 

Fork Lodge, and the Big Wood River near Ketchum, ID. Idaho District personnel from the Twin Falls, Boise, and 

Sandpoint, ID, field offices of the U.S. Geological Survey collected bedload and suspended sediment transport 

information for the North Fork Clearwater River, Selway River, Lochsa River, South Fork Salmon River, Johnson 

Creek, South Fork Payette River, Valley Creek, Boise River, and the Salmon River below Yankee Fork. We thank 

Charles Berenbrock of the U.S. Geological Survey for conducting the flow frequency analysis for selected sites 

and Robert Thomas for his statistical assistance and collaboration in extending streamflow records. We extend 

our thanks to Dr. M. Gordon (Reds) Wolman for his thoughtful insights on sediment transport and other channel 

processes. Lastly, we acknowledge the photographic skills of Karen Wattenmaker, who provided many of the site 

photographs contained in the web site files.

USDA Forest Service RMRS-GTR-131. 2004 1

Introduction

The United States Forest Service is a participant in 

the adjudication of water rights within the Snake River 

Basin of Idaho. Partly for purposes of the adjudication, 

the Forest Service desired to gain a better understanding of the nature of sediment transport in Idaho gravelbed streams and rivers. Thus, the agency explored the 

availability of existing sources of suspended and bedload sediment transport information for streams and 

rivers within the National Forests of Idaho. In 1994, 

the agency also initiated a program to measure bedload and suspended sediment transport and collect supporting site information for selected streams and rivers. 

This program, which involved collection of data during water years 1994 to 2000, included agreements 

with the United States Geological Survey (USGS), 

Case Western Reserve University (CWRU), and Utah 

State University (USU) to collect information for selected sites. This program also involved collaboration 

with National Forest personnel to provide existing sediment transport and streamflow data and modify existing 

sediment transport measurement programs for selected 

sites.

This report and the associated web site files (http:

//www.fs.fed.us/rm/boise/teams/soils/Bat%20WWW/

index.htm) present the sediment transport data and related information collected and summarized as part of this 

effort. Sediment transport and related data are provided 

for 33 coarse-bed streams and rivers within Idaho. The 

related information includes streamflow, channel geometry, and bed material data for all of the sites, and information on floodplain material, painted rock movement, 

particles in bedload traps, and the largest particles recently moved for selected study sites.

Measuring sediment transport in gravel-bed streams 

and rivers, especially bedload transport, is difficult 

(Ryan and Emmett 2002), time consuming, and expensive (Edwards and Glysson 1998). Due to the high spatial and temporal variability associated with sediment 

transport (Ryan and Emmett 2002; Wohl 2000), a large 

number of measurements that span a large range of 

streamflows are often needed to adequately understand 

and describe the transport processes. Short-term sediment sampling programs often fail to measure transport 

over a representative range of flows, especially higher flows, in part due to the less frequent occurrence of 

higher flows. As a result, there are relatively few data 

sets of sediment transport that span a wide range of 

streamflow. We were fortunate in that the streamflow 

associated with sediment transport measurements exceeded bankfull discharge for 29 of the sites and exceeded twice bankfull discharge for nine of the sites. 

Additionally, very few good sets of sediment transport, 

especially bedload (Wohl 2000), exist for mountain 

streams and rivers and a regional set of sediment transport data for an array of streams is rare. These Idaho 

data sets represent one of the largest and most intensive 

regional concentrations of sediment transport and related information.

Some of the study sites are long-term monitoring 

sites on various Idaho National Forests. Streamflow and 

sediment transport measurements have continued beyond the dates shown in this report and in the web site 

files. We anticipate updating information for these sites 

as new data become available and as resources allow 

for quality assurance and quality control of the data.

Our primary purpose for this report and the associated web site files is to provide sediment transport 

data and supporting site information to potential users. 

These data are useful for improving our understanding of the sediment transport processes in gravel-bed 

mountain streams and rivers, developing and testing 

sediment transport models, estimating sediment production, and quantifying instream flow requirements 

for various purposes. We have received many requests 

for all or portions of these data. Our hope is that making 

this information available on a web site in an organized 

fashion will provide for continued use of the data for a 

variety of purposes.

In this report, we provide a brief overview of the 

study site characteristics and details of the methods 

used to measure and/or collect the various types of data. 

The results section of the report contains some relationships and observations about the nature of streamflow 

Sediment Transport Data and Related Information for 

Selected Coarse-Bed Streams and Rivers in Idaho

John G. King, William W. Emmett, Peter J. Whiting, Robert P. Kenworthy, Jeffrey J. Barry
2 USDA Forest Service RMRS-GTR-131. 2004 

and sediment transport for these sites. The associated 

web site is structured by study site. For each study site, 

we provide data files in a spreadsheet format, with one 

worksheet for each type of data and a site map of the 

study reach. The web site also includes a brief narrative 

report for each study site. This report contains general 

information about the study site, one or two photographs 

of the study reach, and sections on channel profile and 

cross-section, channel geometry, channel bed material, 

and sediment transport.

Study Sites

The study sites include 33 stream and river reaches in 

Idaho (figure 1). All of the study sites, except Cat Spur 

Creek, are within the Snake River Basin. Cat Spur Creek, 

in the Panhandle National Forest of northern Idaho, is 

part of the Spokane River Basin. The headwaters of Cat 

Spur Creek abut the topographic divide that defines the 

Snake River Basin. All but one of the study watersheds 

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Hawley Cr.

(Note: In the site names, nr stands for near and bl stands for below.)

Figure 1. Location of the study 

streams and rivers.
USDA Forest Service RMRS-GTR-131. 2004 3

are within the Northern Rocky Mountain Physiographic 

province (Fenneman 1931). The exception is Rapid 

River, which is in the Columbia Intermontane Province.

The study sites span a wide range of site characteristics (table 1). All of the streams have coarse-bed composed primarily of gravel and cobbles. The median 

diameter of the surface bed material ranges from about 

23 to 207 mm. Although several of the study reaches 

have small areas of exposed bedrock, all the sites have 

sufficient alluvial material to be considered self-forming 

channels. The drainage area ranges from 0.5 to 6,240 

mi2, the average reach gradient ranges from 0.0005 to 

0.0718, and the stream gage elevation ranges from 1,453 

to 7,300 feet above sea level.

There is a variety of rock types represented in the 

study watersheds (table 1). One of the most notable 

geologic features is the Idaho batholith, a large igneous intrusion in central Idaho that extends about 250 

miles in a north-south direction and 90 miles in an 

east-west direction (Bennett 1974). Twenty-one of the 

study watersheds have a large portion of their area on 

the batholith. Many of these areas are characterized 

by rock that weathers deeply to produce coarse sandy 

soils with high erosion rates if disturbed. Other lithologies at the study sites include metamorphic formations 

usually associated with the border of the batholith, 

mixed extrusive volcanics in watersheds in the upper 

portion of the Salmon River basin, and sedimentary 

rocks associated with the Seven Devils formations, the 

upper portion of the Salmon River basin, and in the 

vicinity of the Lemhi River basin. General information 

on predominant geology for each watershed was extracted from the “Geologic Map of Idaho” (Bond and 

Wood 1978). Some of the study watersheds contain a 

number of types of lithology and readers are referred 

to the map for more specific information.

Table 1. Summary of selected characteristics of the study sites.

Gage Average 

Drainageb Predominantc elevation reach Surfaced 

Sitea area mi2 geology ft gradient D50 mm

Big Wood River 137 mixed volcanics 6,240 0.0091 119

Blackmare Creek 17.8 igneous intrusions 4,180 0.0299 95

Boise River 832 igneous intrusions 3,256 0.0038 76

Dollar Creek 16.5 igneous intrusions 4,900 0.0146 74

Johnson Creek 216 igneous intrusions 4,656 0.0040 190

Little Buckhorn Creek 5.99 igneous intrusions 4,150 0.0509 28

Lochsa River 1,180 igneous intrusions, metamorphic 1,453 0.0023 126

Middle Fork Salmon River 1,040 igneous intrusions, mixed volcanics 4,350 0.0041 146

North Fork Clearwater River 1,290 igneous intrusions, metamorphic 1,660 0.0005 95

Salmon River nr Obsidian 93.9 igneous intrusions, sedimentary, glacial deposits 6,950 0.0066 61

Salmon River nr Shoup 6,240 sedimentary, mixed volcanics 3,154 0.0019 96

Salmon River bl Yankee Fork 811 igneous intrusions, mixed volcanics, glacial deposits 5,900 0.0034 104

Selway River 1,910 igneous intrusions, metamorphic 1,540 0.0021 173

South Fork Payette River 449 igneous intrusions 3,790 0.0040 110

South Fork Salmon River 329 igneous intrusions 3,750 0.0025 38

Squaw Creek (USGS) 71.6 sedimentary, mixed volcanics 5,710 0.0100 43

Thompson Creek 21.8 mixed volcanics, sedimentary 5,700 0.0153 66

Valley Creek 149 igneous intrusions, glacial deposits 6,222 0.0040 40

West Fork Buckhorn Creek 22.6 igneous intrusions 4,140 0.0320 180

Cat Spur Creek 10.8 metamorphic 2,930 0.0105 27

Eggers Creek 0.497 igneous intrusions 4,750 0.0718 23

Hawley Creek 42.2 sedimentary 6,630 0.0233 40

Johns Creek 113 igneous intrusions, metamorphic 2,410 0.0207 207

Little Slate Creek 62.6 igneous intrusions, metamorphic 3,500 0.0268 102

Lolo Creek 41.0 igneous intrusions 3,040 0.0097 68

Main Fork Red River 49.7 metamorphic 4,350 0.0059 50

Rapid River 108 sedimentary 2,200 0.0108 63

South Fork Red River 38.2 metamorphic 4,350 0.0146 106

Squaw Creek (USFS) 14.3 metamorphic 3,940 0.0240 27

Trapper Creek 8.00 metamorphic 4,880 0.0414 85

Fourth of July Creek 17.1 igneous intrusions, sedimentary, mixed volcanics 7,300 0.0202 51

Herd Creek 110 mixed volcanics 5,900 0.0077 67

Marsh Creek 79.7 igneous intrusions 6,540 0.0060 56

a In the site names, nr stands for near and bl stands for below.

b Drainage areas for USGS gaged sites are from either Hortness and Berenbrock (2001) or O’Dell and others (2002). Drainage areas from 

other sites are from Forest Service records or were measured from topographic maps. All drainage areas are expressed to three significant 

figures. c Geology information extracted from Bond and Wood (1978).

d The median diameter of the surface bed material from measurements within the reach. Due to multiple measurements over time at some sites, 

other data may apply and are presented in subsequent tables in this report.
4 USDA Forest Service RMRS-GTR-131. 2004 

Higher mountains throughout central Idaho and the 

Seven Devils mountain range were glaciated during the 

Pleistocene by alpine glaciers (USDA Forest Service 

Draft Upper Columbia River Basin EIS 1997; Ross and 

Savage 1967). Many of the high elevation study reaches 

in the upper Salmon River basin—Herd Creek, Marsh 

Creek, Valley Creek, Fourth of July Creek, Salmon 

River near Obsidian, ID, and the Big Wood River—flow 

through valley deposits associated with glaciation (Bond 

and Wood 1978).

Frontal systems moving eastward from the Pacific 

Ocean are the source of most precipitation for these 

study sites. As these systems are lifted over the Idaho 

mountains, they cool and release their moisture. Thus, it 

is common to see increasing precipitation with increasing elevation throughout the state. Average annual precipitation in these basins ranges from about 10 inches to 

over 70 inches (University of Idaho 1995). In most areas, 

winters are wet and summers are relatively dry. At higher elevations, snow accumulates from fall through spring 

and the accumulated spring snowpack may account for 

over half the annual precipitation. Rainstorm activity 

in the summer months is generally in the form of thunderstorms associated with unstable air masses. Summer 

rainfall is generally of short duration and may be of high 

intensity.

Methods and Data Display

This section describes the methods used in collection 

of sediment transport and related data for the study sites. 

It also provides examples of how the data are displayed 

in the narrative reports for each study site available on 

the web. One consistent set of methods does not necessarily apply to all of the study sites or to all of the data for 

a given study site. This is due to reliance on previously 

collected information by different agencies for a variety of purposes and differences in the purposes for the 

collection of additional data between study sites. We describe the methods and indicate, either in this report or in 

the web site data files, to which study reaches they apply. 

Users of the data are encouraged to contact the appropriate agency or agency representatives (see acknowledgments) that collected the different data sets if additional 

information on methods and accuracy is desired.

Stream Reach Surveys

Standard surveying equipment and techniques were 

used to measure the water surface elevations and bed elevations in the center of the channel at about one-channel width intervals within the study reach. The length 

of the study reaches was about 20 channel widths, except for some of the larger rivers where the length was 

about 10 channel widths. Floodplains were identified 

and the elevations associated with streamflow just 

overtopping the floodplain were surveyed. This elevation, extrapolated to the stream gage location, represents the stage of bankfull discharge. Elevations were 

also surveyed at frequent intervals across at least one 

representative channel cross-section, perpendicular 

to the streamflow. All the elevations were surveyed 

with respect to a fixed datum elevation, often one of 

the reference datums associated with the gaging station. Longitudinal profiles and planimetric maps of the 

reaches were prepared for most sites. Both hand-drawn 

plots and computer-generated plots of the data were 

made, depending on the individual site. At sites where 

computer data files were prepared, the data and plots 

of the longitudinal profiles are included in the web site 

files. The longitudinal profile displays the water surface, channel bottom and floodplain elevations, and 

locations of the surveyed cross-sections and the gaging station (figure 2). In this example, cross-section 1 

(XS1) is at the cableway where discharge and sediment 

transport measurement were typically made. The gaging station is several feet upstream of the cableway.

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Figure 2. Example of a longitudinal profile 

of the study reach for Little Slate Creek.
USDA Forest Service RMRS-GTR-131. 2004 5

The distance and elevation data for all the surveyed 

cross-sections in a given study reach are provided in the 

web site data files. In the narrative for each site, we display one cross-section graph (figure 3), which is usually the cross-section associated with sediment transport 

measurements. In 1998, many of the previously surveyed 

cross-sections at selected study sites were resurveyed to 

extend survey information laterally on each side of the 

channel. We include data collected from both surveys in 

the web-page data files. Typically, we also display the 

approximate elevations of the average annual discharge 

(Qa) and bankfull discharge (Qb) to give perspective to the 

cross-section.

Gradient was usually calculated as an average over 

the entire study reach. If a large shift occurred within the 

reach, gradient was calculated for that portion that typically included the gage location and sediment measurement location. The gradients associated with channel 

bed elevations, floodplain elevations, and water surface 

elevations were all used in determining the average gradient for the study reach.

“At-a-Station” Channel Geometry

Instantaneous discharge measurements made by 

the agencies operating the gaging stations were used 

to develop a relationship between stage and discharge. 

Information available from the field notes taken during 

instantaneous discharge measurements typically includes discharge, width, and depth and velocity at intervals across the channel. We used this information 

to develop power relationships between discharge and 

width, discharge and average depth, and discharge and 

average velocity (figure 4). Average depth was determined as cross-section area divided by width. Average 

velocity was determined as discharge divided by 

cross-section area. In developing these power relationships, we generally only used data collected during the 

water years of sediment transport measurements and 

within the range of discharges associated with the sediment transport measurements. However, additional data 

not meeting these criteria are often provided in the web 

site files. To the extent possible, only data collected at or 

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Figure 3. Example of a cross-section in the Little Slate Creek 

study reach.

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Figure 4. Example of channel geometry relationships for the Little Slate Creek study site.
6 USDA Forest Service RMRS-GTR-131. 2004 

very near the cross-section(s) where sediment transport 

measurements were made were used in developing these 

relationships. Also, geometry data associated with noted 

“ice” influences were not used. Measurements of channel 

geometry are useful for estimating the shear stress and 

stream power associated with individual sediment transport measurements.

The power relationships were used to estimate width, 

average depth, and average velocity at bankfull discharge or for the 1.5 year return interval discharge. We 

then developed regional power relationships relating estimates of average velocity, width, and average depth to 

both drainage area and bankfull discharge.

Channel Bed Material

Three different methods were used to characterize 

the particle size distribution of the bed material in the 

study reaches (table 2). These include: Method (1) pebble counts of the surface material often at a single crosssection that is either representative of the reach or is the 

Table 2. Channel material collection method and date of sampling for the study sites.

Bed material

Study site Method 1 Method 2 Method 3 Floodplain

Big Wood River 7/13/2000

Blackmare Creek 7/27/1994 9/15/2000

Boise River 9/9/1994 10/19/1995 10/30/1997

Dollar Creek 7/25/1994 7/21/2000

Johnson Creek 10/11/1994

Little Buckhorn Creek 7/29/1994 9/16/2000

Lochsa River 9/12/1994 9/27/1995 11/7/1997

Middle Fork Salmon River 7/27/2000

North Fork Clearwater River 9/13/1994 9/28/1995 11/5/1997

Salmon River nr Obsidian 7/10/2000

Salmon River nr Shoup 8/12/2000

Salmon River bl Yankee Fork 7/14/2000

Selway River 9/11/1994 9/27/1995 11/8/1997

South Fork Payette River 8/19/1994 10/23/1995 10/31/1997

South Fork Salmon River 10/10/1994, 4/6/1999, 9/13/1999 11/1/1997

Squaw Creek (USGS) 6/29/1994 7/12/2000

Thompson Creek 6/27/1994 7/11/2000

Valley Creeka 6/22/1994 , 8/17/1994 11/15/1995 8/8/1998

West Fork Buckhorn Creek 7/28/1994

Cat Spur Creek 10/7/1994

Eggers Creekb 1975,77-84,10/23/1994

Hawley Creek 7/7/1994

Johns Creek 9/13/1995 9/26/1995

Little Slate Creek 1 10/19/1994 10/4/1995 11/3/1997

Lolo Creek 10/9/1994, 7/21/1995 8/24/1995 11/6/1997

Main Fork Red River 7/11/1994 8/23/1995 11/4/1997

Rapid River 7/17/1994 10/3/1995 11/2/1997

South Fork Red River 7/12/1994 8/23/1995 11/4/1997

Squaw Creek (USFS) 7/5/1994

Trapper Creek 7/22/1994 8/22/1995

Fourth of July Creek 6/17/1994

Herd Creek 7/1/1994

Marsh Creek 6/13/1994

a

 Valley Creek pebble counts were made at three cross-sections on the 8/17/1994 sampling date.

b

 Eggers Creek pebble counts in 1975 and 1977-1984 were made at five cross-sections.

location of sediment transport measurements; Method (2) 

pebble counts of the surface material and core samples 

of the subsurface material at several locations within the 

reach; or Method (3) pebble counts of the surface material and core samples of both the surface and subsurface 

material at several locations within the reach. At many 

of the study sites, more than one method was used to 

characterize the bed material. For example, at many sites 

during the first field season Method 1 was used to characterize surface material at or near the sediment transport 

cross-section. In the following field season, Method 2 

was used to characterize both surface and subsurface 

substrate within the entire study reach.

For all three methods, the particle size distributions 

of the bed surface grains were measured using a pebble 

count procedure (Wolman 1954). The intermediate axis 

(b-axis) of surface particles was measured at fixed intervals along transects perpendicular to the streamflow. 

The sampling interval along a transect was several grain 

diameters (of the larger grains) apart to discourage 

serial correlation (Church and others 1987) and to 
USDA Forest Service RMRS-GTR-131. 2004 7

avoid consecutive hits on all but an unusually large 

particle. Typically, particles smaller than 2 mm in diameter were not measured, but coded as “<2 mm” 

(Harrelson and others 1994). Hits on bedrock, vegetation, and woody debris were so noted. At a sampling 

cross-section, typically at least 100 particles were measured (Wolman 1954; Harrelson and others 1994). In 

narrow streams, sampling 100 particles often required 

sampling at additional transects. These transects were 

spaced at about 1 m intervals from the original transect. Once sampling began along a transect, the entire 

transect was sampled. At some sites, pebble counts of 

the surface grains were done on more than one sampling date.

In 1995 and 2000, Forest Service personnel walked 

many of the study stream reaches and took notes and 

made sketches concerning the sizes and distribution of 

the surface material and the location of pools. Major 

differences in the general size characteristics of the 

substrate over an appreciable area of the reaches were 

observed in Valley Creek, South Fork Salmon River, 

Main Fork Red River, Thompson Creek and Rapid 

River. For these sites, channel units of two different 

substrate classes were mapped and two locations were 

sampled (Methods 2 or 3) within each mapped channel 

unit. Three locations were sampled at the remainder of 

the study sites. Sampling locations were chosen at approximately equally spaced distances within a mapped 

substrate unit throughout the length of the study reach. 

The length of reach represented by pools was omitted because of difficulty in sampling in pools. At each 

sampling location along the reach, the location of the 

core sample was either 1⁄4, 1⁄2, or 3⁄4 of the distance 

across the channel for mapping units in reaches with 

three sampling areas or 1/3 or 2/3 across the channel 

for mapping units in reaches with two sampling areas. On the larger rivers, if depth of water prohibited 

sampling, the field crew was given some latitude to 

move upstream and/or downstream, within the same 

substrate mapping unit, to an area where sampling 

was feasible. If this option did not allow for sampling, 

the crew moved shoreward to the first location where 

sampling was possible.

The particle size distributions of the subsurface bed 

material were measured at many of the sites. Surface 

material was removed to a depth of approximately one 

diameter of the larger particles adjacent to the sampling site (Church and others 1987). A 33 gallon drum 

(cut in half) was placed on the sample site and worked 

into the substrate to reduce the loss of fines by streamflow. Subsurface material was removed to at least two 

diameters in depth or until sufficient material was removed such that the largest particle in the sample represented less than 5 percent of the total sample. Samples 

were wet-sieved in the field (Platts and others 1983) into 

the following size classes: >64 mm, 32-64 mm, and 16-

32 mm and <16 mm. The b-axis of all particles greater than 64 mm was measured individually. The volume 

of each of the other three size classes was determined 

by measuring water displacement in a bucket. Sample 

particles of typical mineralogy on the streambed were 

saved for later particle density determination. Particle 

density was determined in the laboratory by weighing 

the particle(s) and then determining the volume, using a 

water displacement technique. In order to determine the 

weight associated with the three larger size classes, both 

particle density information and a correction for water 

retention in the sample was used (Shirazi and Seim 1979 

in Platts and others 1983). Material less than 16 mm diameter was bagged for later sieve analysis. In the laboratory, a mechanical shaker and sieves were used to 

separate material into the following size classes: 8-16 

mm, 4-8 mm, 2-4 mm, 1-2 mm, 0.5-1 mm, 0.25-0.5 mm, 

and <0.25 mm.

Core sampling was done in 1995 to characterize the 

subsurface material while pebble counts were used to 

characterize the surface material. For the core sampling 

done in 2000, the surface material was retained and particle size distributions were determined for both surface 

and subsurface material using methods described in the 

previous paragraph. In 2000, pebble counts were also 

done at transects across the channel at the core locations.

Samples of floodplain material were collected at 12 

study sites in 1997 and 1998. At one to four floodplain 

locations, identified in the 1994 field surveys, small pits 

were excavated to at least 30 cm to expose a vertical wall 

of the floodplain sediment. Samples were collected of all 

visually apparent strata with different textural composition. Typically, one to three strata were identified and sampled. Samples were dried in the laboratory and the particle 

size distribution of each sample was determined using 

a mechanical shaker and the following sieve sizes: 256 

mm, 128 mm, 64 mm, 32 mm, 16 mm, 8 mm, 4 mm, 2 mm, 

1 mm, 0.5 mm, 0.25 mm, 0.125 mm, and 0.0625 mm.

The web site files include the locations, sampling 

dates, and particle size distributions for all of the individual pebble counts and core samples along with the 

sampling dates and particle size distributions for the 

individual floodplain strata at each study site. The narrative report for each site includes the graphical display of 

these data (figure 5).
8 USDA Forest Service RMRS-GTR-131. 2004 

Streamflow Records

Most of the study sites are associated with a currently 

operational or discontinued gaging station operated by 

either the U.S. Geological Survey or the U.S. Forest 

Service (table 3). In most instances, the gage is located 

within the study reach. The exceptions are Thompson 

Creek, the Salmon River near Shoup, ID, and the 

Middle Fork Salmon River. The brief narrative reports 

on the web site describe the location of these study sites 

with respect to the gage location. Three study sites were 

not associated with a USGS or USFS gaging station: 

Marsh Creek, Fourth of July Creek, and Herd Creek. 

At these sites, temporary gaging stations using pressure 

transducer technology were installed and operated by 

Case Western Reserve University (CWRU) personnel 

in water years 1994 and 1995. The CWRU gages and 

many of the USFS gages operated seasonally, typically 

from near the initiation of spring snowmelt to freeze up 

in the fall.

Streamflow records are often used to estimate total 

water yields and integrated with sediment transport relationships to estimate sediment yields. Estimates of 

long-term average water and sediment yields are dependent upon completeness of the existing streamflow 

record and the representativeness of the period of record. The representativeness of the existing record is a 

potential concern at study sites where a relatively shortterm flow record may not represent the distribution of 

flows associated with climatic variation over the long 

term. Thus, for study sites with seasonally operated 

gages and/or with relatively few years of record (17 

sites), missing daily mean flows were estimated and 

streamflow records were extended to estimate distributions of streamflow over the long term. The streamflow extension procedure relates daily mean flows at 

short-term gages with a nearby continuously operated 

USGS “base station” having a longer discharge record. 

Often there was more than one long-term station that 

could serve as the base station. In choosing a base station, 

consideration was given to similarity of basin size, 

proximity, and mean elevation in the expectation that 

hydrological responses would be similar. Emphasis was 

also given to the goodness-of-fit between the two stations. A relationship was developed using pairs of daily 

mean flows from the concurrent period, the period during which data were available from both stations. This 

relationship was used to estimate missing values and 

extend the records using base-station daily mean flows. 

The technique (Moog and others 1999) is derived from 

a method outlined by Hirsch (1982), Maintenance Of 

Variance Extension (MOVE.1). Although each daily 

mean discharge at the short-term station is estimated as 

a function of the corresponding base-station discharge, 

the focus is not to match each daily mean discharge, but 

to accurately reproduce the distribution of discharges 

over the period of extended record. Extended discharge 

data were then used to estimate long-term average 

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Figure 5. Particle size distributions of surface and 

subsurface bed material and floodplain material in the Little Slate Creek study reach.
USDA Forest Service RMRS-GTR-131. 2004 9

annual discharge for the study sites. Extended discharge 

data was also used in conjunction with sediment-discharge relationships to estimate the long-term average 

annual distribution of sediment production with streamflow and time at some sites. These sites include those 

where the base-station analysis period of record extended up to water year 1999 (table 3). For sites not extended up to water year 1999, we relied on average annual 

discharge estimates previously reported by Whiting 

(1998).

Records of daily mean discharge for sites gaged by 

the USGS are available from annual USGS publications 

of water-resources data Water Resources Data - Idaho, 

from commercial production and sales of CD-ROMs 

(updated annually), and from electronic listings on the 

World Wide Web (http://nwis.waterdata.usgs.gov/id/

nwis/discharge). Therefore, these records are not included in our web site files. However, records of daily mean 

discharge for sites gaged by the USFS or Case Western 

Reserve University (table 3) for the period of record are 

included in the web site files. For the five study sites 

where the base-station analysis period of record extended up to water year 1999, the extended daily mean discharge records are also provided. We again emphasize 

that the extension procedure estimates a distribution of 

mean daily discharges. Thus, estimates should not be 

viewed as the best prediction of streamflow for any particular day.

A flow frequency analysis was performed on the annual maximum series to estimate the return interval of 

bankfull discharge and to estimate the discharge associated with the 1.5 year return interval event. The flow 

frequencies were estimated using the Log Pearson Type 

III analysis (U.S. Interagency Advisory Committee on 

Water Data 1982). For several sites with short term records, the two-station comparison procedure was used 

Table 3. A summary of stream discharge record information for the study sites.

Total 

USGS Gage period years of Base station Base station 

station of recorda discharge for record analysis period 

Site number Agency (complete WY) recordb extensionc of record

Big Wood River 13135500 USGS 1949-71 23 not extended

Blackmare Creek 13310565 USGS 1990-94 5 (23) 13310700 1967-82, 86, 90-95

Boise River 13185000 USGS 1912-P 90 not extended

Dollar Creek 13310520 USGS 1990-94 5 (23) 13310700 1967-82, 86, 90-95

Johnson Creek 13313000 USGS 1928-P 74 not extended

Little Buckhorn Creek 13310660 USGS 1990-94 5 (23) 13310700 1967-82, 86, 90-95

Lochsa River 13337000 USGS 1911-12, 30-P 73 not extended

Middle Fork Salmon River 13309220 USGS 1973-81, 00-P 10 not extended

North Fork Clearwater River 13340600 USGS 1968-P 34 not extended

Salmon River nr Obsidian 13292500 USGS 1942-52 11 not extended

Salmon River nr Shoup 13307000 USGS 1944-81 38 not extended

Salmon River bl Yankee Fork 13296500 USGS 1922-91 70 not extended

Selway River 13336500 USGS 1930-P 71 not extended

South Fork Payette River 13235000 USGS 1942-P 60 not extended

South Fork Salmon River 13310700 USGS 1967-82, 86, 90-02 29 not extended

Squaw Creek (USGS) 13297355 USGS 1971-P 31 not extended

Thompson Creek 13297330 USGS 1973-P 25 not extended

Valley Creek 13295000 USGS 1912-13, 22-71, 93-P 61 not extended

West Fork Buckhorn Creek 13310670 USGS 1990-94 5 (23) 13310700 1967-82, 86, 90-95

Cat Spur Creek USFS 1987-97 11 (32) 12414900 1966-97

Eggers Creek USFS 1965-96 32 not extended

Hawley Creeka USFS 1989-95 6 (23) 13297355 1973-95

Johns Creek USFS 1986-97 12 (31) 13338500 1965-95

Little Slate Creeka USFS 1986-99 14 (46) 13316500 1952-54, 57-99

Lolo Creeka USFS 1986-99 14 (35) 13338500 1965-99

Main Fork Red Rivera USFS 1986-99 14 (35) 13338500 1965-99

Rapid River USFS 1986-99 14 (87) 13317000 1911-17, 20-99

South Fork Red Rivera USFS 1986-99 14 (35) 13338500 1965-99

Squaw Creek (USFS)a USFS 1990, 1992-95 5 (23) 13297355 1973-95

Trapper Creeka USFS 1986-97 12 (33) 13338500 1965-97

Fourth of July Creeka CWRU 1994-95 2 (55) 13295000 1921-72, 92-95

Herd Creeka CWRU 1994-95 2 (55) 13295000 1921-72, 92-95

Marsh Creeka CWRU 1994-95 2(55) 13295000 1921-72, 92-95

a

 Gage operated seasonally, usually started before spring runoff and stopped in the fall before freeze-up.

b Numbers in parenthesis represent the actual plus extended period of record.

c

 13310700 South Fork Salmon River near Krassel Ranger Station; 13338500 South Fork Clearwater River at Stites, ID; 13316500 Little Salmon 

River at Riggins, ID; 13317000 Salmon River at Whitebird, ID; 12414900 St. Maries River near Santa, ID; 13295000 Valley Creek at Stanley, 

ID; 13297355 Squaw Creek near Clayton, ID.
10 USDA Forest Service RMRS-GTR-131. 2004 

to adjust frequency estimates. The generalized skew coefficients for Idaho and the standard errors of the generalized skew coefficients used in this analysis are from 

Kjelstrom and Moffatt (1981). For some sites we relied on earlier reported estimates of the return period of 

bankfull discharge (Whiting 1998).

For most USFS gaged study sites, we participated 

with personnel from the various National Forests in review of historical field measurements of discharge and 

stage-discharge relationships. Stage-discharge relationships were occasionally adjusted to ensure accurate estimates of daily mean discharges and peak flows. There 

was no additional review or modification of daily mean 

discharge records from USGS and CWRU gage sites, 

from a USFS research watershed, Eggers Creek, or from 

a USFS gage site, Cat Spur Creek.

Bedload Transport

Bedload transport rates were measured with the pressure-difference Helley-Smith bedload sampler (Helley 

and Smith 1971) at all of the study sites. The standard 

nozzle has a 3-in (76.2 mm) square entrance and was 

used in most instances. At a few sites, the 6-in (152 

mm) square entrance model was used during higher 

flows. The catch bag on the samplers had a 0.25 mm 

mesh. A sediment-trapping efficiency of 100 percent 

was assumed for all particle sizes. Emmett (1980) suggests that the Helley-Smith sampler not be used for particles smaller than 0.25 mm and for sediment of particle 

sizes that are also transported in suspension. However, 

since we want to display and make all of the data available, we define bedload sediment as all of the material 

collected in the sampler, even though smaller particles 

may be transported in suspension. Users of this data 

may wish to redefine bedload sediment to meet their 

specific needs.

The sampling procedures employed in the collection of bedload data were based upon the Single Equal 

Width Increment method (Edwards and Glysson 1988; 

Williams and others 1988). Multiple samples at equal 

width intervals across the channel were collected and 

composited. Following recommendations of Emmett 

(1980), bedload sampling after 1993 typically was done 

using two traverses of the stream at about 20 verticals. 

The material collected on each traverse was considered 

as one sample. There were, however, some exceptions 

to this guideline, and the number of verticals, sample 

time per vertical, and stream width for each sample are 

detailed in the data files. In several instances the entire 

stream width was not sampled. Portions of the unsampled width were usually associated with shallow stream 

margins, often during overbank flow. In these instances, 

the portion of the width that was not sampled was not 

included in calculating bedload transport and the “comment” column in the bedload data table reflects a width 

adjustment.

Bedload transport measurements at many of the sites 

were confined to the period of the snowmelt hydrograph 

in the spring and early summer. Agencies responsible for 

the measurements included the U.S. Geological Survey, 

U.S. Forest Service, Case Western Reserve University, 

and Utah State University (table 4). Due to logistics specific to a site, sampling was not always done at the same 

cross-section in the study reach. For example, during 

high streamflow sampling may be done from a cableway 

and during lower flows sampling may be done by wading the stream directly below the cableway or at some 

other wadeable cross-section, usually reasonably close 

to the cableway. Occasionally, a considerable distance 

separated measurement locations. The locations of each 

of the sediment transport measurement cross-sections 

are provided in the web site data files.

Bedload samples were dried and standard procedures 

were used for particle size analysis. Typically full phiinterval sieves (64 mm, 32 mm, 16 mm, 8 mm, 4 mm, 

2 mm, 1 mm, 0.5 mm, 0.25 mm) were used for samples 

collected in water year 1994 and later, although Case 

Western Reserve University personnel used 0.5 phi-interval sieves.

All bedload transport data were reviewed for accuracy. For most sites this consisted of a review of field 

and laboratory procedures, field and laboratory notes, 

and subsequent calculations. For most sites, the discharge associated with a bedload sample was based on 

the stage(s) during sampling and the current stage-discharge rating. Any shifts in the rating were also taken 

into account. Exceptions to the level of data review and 

exceptions to the procedure for determining the associated discharge are noted in the web site bedload files.

The following information is included for each bedload sample: sample date, stream discharge, total bedload transport rate, percent of the total bedload rate by 

size fraction, length of the b-axis of the largest particle in the sample, median diameter of the sample, total weight of the sample, sample location, sample type, 

number of verticals, time per vertical, stream width, and 

any comments.

 Suspended Sediment Transport

Suspended sediment samples were collected using 

either a wading version (USDH-48 or USDH-81) or 

a suspension version (USDH-59, USD-49, USD-74, 
USDA Forest Service RMRS-GTR-131. 2004 11

or USD-77) of a depth integrating sampler. For suspended load, sampling from about 10 cross-channel 

locations is adequate to obtain a mean rate of transport through the cross-section. The vertical transit rate 

of lowering and raising the suspended-sediment sampler was everywhere an Equal Transit Rate to maintain 

the equal-discharge weighting (Edwards and Glysson 

1988). Suspended-sediment samples were analyzed using standard laboratory procedures. Suspended sediment concentration is expressed in milligrams per liter. 

The percent of suspended sediment in the sand size 

class (>0.063 mm) was determined by weight for many 

of the samples.

All suspended sediment transport data were reviewed 

for accuracy. For most sites this consisted of a review 

of field and laboratory procedures, field and laboratory 

notes, and subsequent calculations. The discharge associated with a suspended sediment sample was based on the 

stage(s) during sampling and the current stage-discharge 

rating. Shifts in the rating were also taken into account. 

Exceptions to the level of data review and exceptions to 

the procedure for determining the associated discharge 

are noted in the web site suspended sediment files.

The suspended sediment sampling information 

provided includes sample date, stream discharge, suspended sediment concentration, suspended sediment 

transport rate, percent sand or larger in the sample, sample location, sample type, number of verticals, and any 

comments.

Sediment Transport-Discharge Relationships

Relationships (sediment ratings) were developed 

between sediment transport and water discharge pairs 

of data. Scatterplots of logarithms of these data tend 

to plot as linear patterns with approximately constant 

variance across the range of discharge. Therefore, relationships were developed using least squares regression 

Table 4. A summary of sediment transport sampling for the study sites.

Agencya Water years Number of Range of discharge for bedload

measuring of sediment Number of suspended samplingb

sediment transport bedload sediment 

 Site transport collection samples samples ft3/sec Q/Qb or Q/Q1.5

Big Wood River USU 1999-2000 100 26 213-1,090 0.28-1.41

Blackmare Creek USFS 1990-94 88 83 12.0-166 0.07-0.99

Boise River USGS 1994-97 82 40 1,190-10,400 0.20-1.76

Dollar Creek USFS 1990-94 85 76 14.0-239 0.06-1.05

Johnson Creek USGS 1994-95, 97 70 35 224-2,870 0.16-2.05

Little Buckhorn Creek USFS 1990-94 78 73 2.40-26.0 No Qb est

Lochsa River USGS 1994-97 72 36 3,910-26,800 0.25-1.70

Middle Fork Salmon River USU 1997 64 31 2,950-15,300 0.39-2.03

North Fork Clearwater River USGS 1994-97 72 36 3,560-34,400 0.22-2.15

Salmon River nr Obsidian USU 1999 51 23 264-739 0.59-1.64

Salmon River nr Shoup USU 1997 61 21 3,830-19,100 0.33-1.66

Salmon River bl Yankee Fork USGS 1999-2000 60 30 1,360-5,070 0.33-1.22

Selway River USGS 1994-97 72 36 4,760-37,700 0.21-1.64

South Fork Payette River USGS 1994-97 72 37 721-6,390 0.24-2.10

South Fork Salmon River USGS 1985-86, 94-97 130 92 137-5,260 0.05-2.10

Squaw Creek (USGS) CWRU 1994-95 92 32 4.93-267 0.03-1.48

Thompson Creek CWRU 1994-95 84 24 8.15-124 0.09-1.42

Valley Creek USGS/CWRU 1994–97 116 71 139-1,420 0.16-1.67

WF Buckhorn Creek USFS 1990-94 85 68 12.0-242 0.06-1.20

Cat Spur Creek USFS 1988-93, 95 35 32 6.70-67.0 0.08-0.80

Eggers Creek USFS 1975-76, 78-84 137 130 0.426-8.75 0.25-5.18

Hawley Creek USFS 1990-95 85 82 9.83-94.6 0.21-2.02

Johns Creek USFS 1994-95 115 21.1-1,210 0.01-0.70

Little Slate Creek USFS 1986-99 157 80 18.7-647 0.04-1.50

Lolo Creek USFS 1982-83, 86, 88-90, 92-95, 97 112 136 26.8-809 0.06-1.95

Main Fork Red River USFS 1986-99 200 136 9.88-646 0.03-1.96

Rapid River USFS 1986-99 191 85 32.3-1,300 0.05-2.08

South Fork Red River USFS 1986-99 204 136 5.93-458 0.02-1.79

Squaw Creek (USFS) USFS 1991, 93-96 42 90 0.76-53.6 0.03-2.44

Trapper Creek USFS 1987-97 166 143 1.69-135 0.02-1.49

Fourth of July Creek CWRU 1994-95 78 25 5.46-137 0.04-1.00

Herd Creek CWRU 1994-95 72 23 10.2-287 0.05-1.49

Marsh Creek CWRU 1994-95 98 27 30.0-796 0.04-1.08

a

 USGS (United States Geological Survey); USFS (United States Forest Service); CWRU (Case Western Reserve University, Department of 

Geological Sciences); USU (Utah State University). b

 The range of discharge expressed as a ratio of bankfull discharge (Q/Qb) or as a ratio of the 1.5 return interval discharge (bold), for sites with no 

field identification of bankfull stage.
12 USDA Forest Service RMRS-GTR-131. 2004 

analysis on log transformed data using the following 

model,

logG logQ ∧ ∧ ∧= + α α 0 1 (equation 1)

where log Gbiased

ˆ is the predicted logarithm of sediment 

transport, log Q is the logarithm of the corresponding 

water discharge, and 0 αˆ and 1 αˆ are regression estimates of unknown parameters computed from the collected data. The log-log model was the only model used 

to develop sediment ratings for these data sets. However, 

other models may also perform well for some of the individual data sets.

Sediment ratings (equation 1) were developed for total 

bedload, bedload by selected size classes, and suspended 

sediment. At a few sites, the collecting agency reported a 

bedload transport rate of zero on selected sampling dates. 

Since the log of zero is undefined, these data were not 

used in developing the sediment ratings. However, all of 

the bedload data (total and by size fraction) and suspended data are provided in the web site files.

The back transformation of the log-log relationships 

expresses the sediment transport rate (either bedload or 

suspended load), G , as a power function of water discharge, Q. If log( ˆ ) ˆ

β 0 α 0 = anti and 1 1 ˆ β

ˆ = α , backtransformation gives the power function:

1

ˆ

0

ˆ ˆ β Gbiased = β Q (equation 2)

where Gbiased

ˆ denotes a biased estimate of the mean 

transport rate due to back-transformation. Several 

techniques are available to correct for this back-transformation bias (Cohn and Gilroy 1992). We used the 

“smearing” method described by Duan (1983). If the 

n regression residuals in log space are denoted by 

ri , and b is the base of logarithms used (usually base 

10 or base e ), the smearing correction factor (or bias 

correction factor), BCF, for the logarithmic transformation is given by:

∑=

=

n

i

ri b

n

BCF

1

1

. (equation 3)

Multiplying the right side of equation 2 by equation 

3 approximately removes the bias so that a bias corrected estimate of the sediment transport rate, G ˆ , can be 

written:

1

ˆ

0

ˆ ˆ β G = BCF β Q . (equation 4)

In the web site narrative report for each study site, 

we present and briefly discuss three graphs of relationships between sediment transport and discharge. The 

first graph displays the total bedload and suspended load 

transport rate versus stream discharge (figure 6) and 

provides the model for equation 2, the coefficient of 

determination (r2), and the bias correction factor (BCF). 

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Figure 6. Suspended and bedload sediment transport versus stream discharge for the Little Slate Creek study 

site.
USDA Forest Service RMRS-GTR-131. 2004 13

We also provide the value of the average annual discharge (Qa

) and either the bankfull discharge (Qb) or the 

1.5 year return interval discharge (Q1.5) to visually give 

perspective to the range of discharges associated with 

the sediment transport measurements.

The second graph displays the bedload transport rate 

versus discharge and model information for selected 

bedload size classes (figure 7). To reduce the number 

of size classes for clearer display, we typically display 

data for grouped size classes of <0.5 mm, 0.5-2 mm, 

2-8 mm, 8-32 mm, and greater than 32 mm. However, 

the web site files provide data for individual size classes. 

In this example, bedload transport data collected prior to 

1994 used different size classes and are not displayed. 

However, pre-1994 size class transport data are provided in the web site file. These graphs provide information 

on the range of discharges during which the different size classes are represented in the sample and the 

relative magnitudes of transport rates for the different 

size classes of particles.

The third graph displays the median diameter of the 

bedload samples and the diameter (b-axis) of the largest particle in the sample versus stream discharge (figure 

8). Power curve trend lines and their respective coefficients of determination (r2

) are displayed and discussed 

for each site. Typically, the largest particle in each bedload sample is only available for samples collected in 

1995 and later. The display of median diameter may also 

be limited to the later years of sampling (1994 and later 

in this example) depending on the sieve sizes used in the 

particle size analysis. Also displayed are the average annual discharge (Qa

), either the bankfull discharge (Qb) 

or the 1.5 year return interval discharge (Q1.5), and the 

median diameter (D50) of the surface pebble counts and 

subsurface core samples collected in the study reach. 

When available, we also plot any additional data related 

to transport of large particles from painted rock studies, 

bedload trap studies, or site observations.

Other Sediment Transport Related Information

The movement of painted rocks, the observations of 

large particles recently moved, and the capture of large 

particles in bedload traps provide information on the 

sizes of material the stream is capable of moving at certain discharges. These techniques were used at selected 

sites to examine the movement of bed surface particles, 

usually for particles too large to fit into the bedload 

sampler. In general these techniques provide some indication of the size bed material that moves during the 

higher flows at the respective sites.

Painted rocks. Painted rocks, as the name implies, 

are painted and/or otherwise identified (Leopold and 

others1966; Leopold and Emmett 1981; Emmett and 

others 1996). The movement of painted rocks was 

measured during 1995 spring snowmelt discharges at 

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Figure 7. Bedload sediment transport by 

size class versus stream discharge 

for the Little Slate Creek study site.
14 USDA Forest Service RMRS-GTR-131. 2004 

the following sites: Rapid River, Valley Creek, Main 

Fork Red River, South Fork Red River, South Fork 

Salmon River, Johnson Creek, Herd Creek, Fourth 

of July Creek, Squaw Creek (USGS), and Thompson 

Creek.

Prior to the 1995 high snowmelt flows, painted rocks 

were placed on the channel bed and their subsequent 

movements were monitored. Twenty painted rocks were 

placed at approximately equal increments of distance 

across each of two transects. Transects were located 

in straight riffle or glide reaches. Stakes or rebar were 

used to mark the end of transects. At a subset of these 

study sites, the painted rocks were usually of two particle size classes to represent about the D50 and D84 of 

the surface size distribution as determined in 1994. At 

another subset of sites, particles spanned the range of 

sizes from about D25 to D90. Rocks were placed in a stable configuration in pockets of the bed with their shortest dimension (c-axis) pointing upward. For each rock, 

the location of placement and length of the b-axis were 

measured and recorded. At some sites, rocks were monitored for displacement during the snowmelt flows. The 

painted rocks were retrieved during lower flows following the snowmelt runoff period. Downstream and lateral 

displacement were measured for those rocks that could 

be located. Recovery rates varied from 20 to 100 percent. Data tables and graphs in the web site files provide 

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Figure 8. Median diameter of the bedload 

sample and largest particle in sample 

versus stream discharge for the Little 

Slate Creek study site.

information on the size, location, and movement of each 

painted rock (figure 9).

The web site report for each site includes a graph that 

displays the largest particle in the bedload sample and 

the median size of bedload sample versus discharge, 

similar to the example provided in figure 8. For painted 

rock study sites, the largest painted rock moved and the 

associated instantaneous peak discharge during the sampling time interval are also displayed. It should be noted 

that the largest painted rock might have been moved by 

discharges less than the instantaneous peak discharge in 

the sampling time interval. However, the discharge at 

the time of movement(s) is not known.

Coarsest particles observed to have recently 

moved. At some sites, measurements were made of the 

size (b-axis) of the coarsest particle(s) that appeared to 

have been recently moved during the preceding spring 

snowmelt high flows. Particles were interpreted to have 

been moved recently if they were loose, perched precariously atop other grains, found atop vegetation, or lacked 

staining or other coatings found on other grains. The web 

site report for each site includes a graph that displays the 

largest particle in the bedload sample and the median size 

of bedload sample versus discharge, similar to the example provided in figure 8. For selected study sites, the 

largest rock observed to have moved and the associated 

instantaneous peak discharge during the previous spring 
USDA Forest Service RMRS-GTR-131. 2004 15

with spring snowmelt runoff (figure 10). Even those watersheds with relatively low gage elevations (Selway 

River, Lochsa River, North Fork Clearwater River, and 

Rapid River) have most of their drainage area at higher elevations and snowmelt is the dominant annual hydrologic event. High flows occasionally occur in fall 

and winter in association with cyclonic storms or rainon-snow events. Rain-on-snow events are more common at lower elevations. Generally, streamflows drop 

rapidly over the summer following the disappearance 

of the snowpack, but on occasion increase for short 

periods in response to rain events. Low flows are reached 

in September or October and flows typically remain relatively low during winter months.

Average annual discharge (Qa) for the study sites 

ranges from 0.604 to 3,730 ft3/s (table 5). This large 

range of Qa is influenced by large differences between 

sites in both the size of the drainage area and the average annual precipitation. Expressing Qa

 as an equivalent 

depth of water over the contributing watershed removes 

some of the effects of drainage area. However, there is 

still a wide range due to large differences in annual precipitation with equivalent depths of Qa

 ranging from 3.7 

to 36.3 inches. Average annual discharge ranges from 

0.11Qb to 0.40Qb, for the 27 sites where bankfull discharge (Qb

) was determined, and averages 0.21Qb. The 

two basins with the largest Qa/Qb ratios, Hawley Creek 

and Eggers Creek, are both spring-fed streams. These 

results are consistent with earlier analyses by Whiting 

and others (1999) for 21 of these sites plus two additional sites. They also report that the mean annual discharge 

to bankfull discharge ratio averages 0.21. In Emmett’s 

(1975) analyses of streamflow data for five streams in 

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Figure 9. Travel distance of painted rocks 

along transect 1 of the Main Fork Red 

River study reach during spring snowmelt flows in 1995.

snowmelt period are also displayed. It should be noted 

that the largest rock might have been moved by discharges 

less than the instantaneous peak discharge. However, the 

discharge at the time of movement(s) is not known.

Bedload traps. At two sites, the Main Fork Red 

River and South Fork Red River, bedload traps were 

placed on the streambed during the spring snowmelt 

of 1997. These traps consisted of 1 inch wire mesh 

baskets anchored to the streambed. The upstream opening of the baskets was 1.5 feet wide by 0.5 feet high. 

Three baskets were placed along a transect roughly 1⁄4, 

1⁄2, and 3⁄4 the distance across the channel. The baskets 

remained in place for several days at a time. On several 

occasions the traps were removed and the b-axis of all 

the collected particles was measured. The web site reports include a graph that displays the largest particle in 

the bedload sample and the median size of bedload sample versus discharge, similar to the example provided in 

figure 8. For the Main Fork and South Fork Red River 

study sites, the largest particle captured in a trap and the 

associated instantaneous peak discharge during the sampling time interval are also displayed. It should be noted 

that the largest particle might have been moved by discharges less than the instantaneous peak discharge in the 

sampling time interval. However, the discharge at the 

time of movement is not known.

Results

Stream Discharge

These snowmelt-dominated streams and rivers typically reach peak flows in April, May, or June in association 
16 USDA Forest Service RMRS-GTR-131. 2004 

Table 5. A summary of stream discharge information for the study sites.

1.5 year Return

Range Average Average return period

daily mean annual annual interval Bankfull bankfullc 

discharge dischargea discharge discharge dischargeb discharge

 Site ft3/sec ft3/sec area-inches ft3/sec ft3/sec yrs Qa/Qb

Big Wood River 18-1,510 167 16.5 765 nm

Blackmare Creek 4.88-430 39.2 29.9 167 1.1 0.23

Boise River 123-15,400 1,200 19.6 5,330 5,900 1.7 0.20

Dollar Creek 4.0-391 34.9 28.7 227 1.1 0.15

Johnson Creek 28.0-5,440 344 21.6 2410 1,400 0.9 0.25

Little Buckhorn Creek 1.0-46.1 6.64 15.1 n

Lochsa River 110-31,900 2,840 32.7 15,900 15,750 1.5 0.18

Middle Fork Salmon River 240-20,700 1,395 18.4 7,660 nm

North Fork Clearwater River 253-34,200 3,460 36.3 15,800 16,000 1.5 0.22

Salmon River nr Obsidian 2-663 81.1 11.7 442 nm

Salmon River nr Shoup 720-25,400 3,040 6.6 11,300 nm

Salmon River bl Yankee Fork 160-10,300 983 16.5 4,170 nm

Selway River 150-45,300 3,730 26.5 21,700 23,000 1.7 0.16

South Fork Payette River 130-8,900 862 26.1 3,490 3,050 1.2 0.28

South Fork Salmon River 58.0-6,200 540 22.3 2,730 2,500 1.3 0.22

Squaw Creek (USGS) 3.80-640 34.3 6.51 175 181 1.6 0.18

Thompson Creek 0.861-357 16.6 10.3 77 87.6 1.6 0.19

Valley Creek 34.0-1,900 205 18.3 818 850 1.6 0.24

West Fork Buckhorn Creek 1.78-341 36.4 21.9 202 1.2 0.18

Cat Spur Creek 1.07 14.0 83.3 1.4 0.17

Eggers Creek 0.179-9.26 0.604 16.5 2.50 1.69 1.2 0.36

Hawley Creek 10.6-68.2 18.9 6.1 46.9 2.1 0.40

Johns Creek 15.5-2,919 158 19.0 1,730 3.4 0.09

Little Slate Creek 12.5-974 109 23.7 466 430 1.4 0.25

Lolo Creek 6.77-904 93.1 30.8 415 1.2 0.22

Main Fork Red River 73.0 407 330 1.1 0.22

Rapid River 19.1-2,130 162 20.4 687 626 1.4 0.26

South Fork Red River 4.51-972 48.5 17.2 258 256 1.5 0.19

Squaw Creek (USFS) 0.666 3.89 3.7 22.0 4.2 0.18

Trapper Creek 1.05-171 12.7 21.6 90.4 1.9 0.14

Fourth of July Creek 1.9-181 15.0 11.9 137 1.5 0.11

Herd Creek 5.67-505 46.4 5.73 193 1.4 0.24

Marsh Creek 25.3-3207 133 22.7 734 1.6 0.18

a

 Bolded estimates of average annual discharge from Whiting (1998) and based on extended discharge records.

b

 nm = the stage and discharge of bankfull discharge was not measured. n = no floodplains were present. c

 Bolded estimates of the return period for bankfull discharge from Whiting (1998).

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Figure 10. Example hydrographs for two mid-size 

study watersheds, Valley 

Creek and the South Fork 

Salmon River.
USDA Forest Service RMRS-GTR-131. 2004 17

the upper Salmon River basin, he reports an average Qa/

Qb ratio of 0.25 and a range of 0.20 to 0.27.

The bankfull discharge for most of these sites is a 

relatively frequent event. The average return period for 

bankfull discharge is 1.6 years (range 0.9 to 4.2 years). 

The average return period of bankfull discharge for 

long-term USGS gaged sites and USFS gaged sites with 

flood frequency analysis done on data up to 2001 is 1.4 

years (range 0.9-1.7 years). Thus, the 1.5 year event is 

a reasonable approximation of bankfull discharge for 

these snow-dominated systems. This is in agreement 

with Emmett’s (1975) determination of about a 1.5 year 

recurrence interval for bankfull discharge for watersheds in the upper Salmon River basin and with Ryan 

and Emmett’s (2002) conclusion that 1.5 year recurrence discharge approximates the bankfull discharge for 

Little Granite Creek, a 21.1 mi2 watershed in the headwaters of the Snake River Basin in Wyoming.

Since a significant snowpack can develop in all of 

these study watersheds, a large proportion of the annual runoff occurs during a relatively short period of time 

during the spring and early summer months. For example, flows equaled or exceeded 1, 5, and 10 percent of the 

time account for, on average, 7.8, 27.2, and 43.0 percent 

of the annual streamflow (table 6, figure 11). Discharges 

equal to or larger than the bankfull discharge, Qb, on 

average occur 3.3 percent of the time (12.1 days/year) 

and account for 19.7 percent of the annual streamflow. 

Discharges less than the average annual discharge, Qa, 

on average occur 75.0 percent of the time (273.9 days per 

year) and account for 31.6 percent of the annual streamflow. The remaining 48.7 percent of the annual streamflow is associated with discharges between Qa

 and Qb that 

occur 21.7 percent of the time (79.3 days per year).

Bankfull discharge increases with increasing drainage area. This relationship is displayed in figure 12A 

for the 27 study sites where floodplains were identified and the bankfull discharges were estimated. There 

is considerable variation around the power curve fit of 

the data (Equation A) and some of this variation is due 

to the wide range in precipitation regimes and resulting 

runoff across the large area that encompasses the study 

sites. The data points presented in figure 12A are coded 

by categories of average annual runoff (QA), expressed 

as a depth of water. The study sites with greater than 30 

inches of average annual runoff all plot above the power 

curve (solid line) and those sites with less than 10 inches 

of runoff all plot substantially below the power curve. 

Including average annual runoff in the prediction equation (equation B) significantly improves that coefficient 

of determination (r2). Figure 12B displays the actual 

(field determined) versus predicted values of bankfull 

discharge using both drainage area and average annual 

runoff (equation B).

Table 6. Flow duration information for selected study sites.

Percent of time equaled or exceeded

0.50 1 5 10 25 50 75 Qa Qb or Q1.5

c

 Study site ---------------------------------------%Qb--------------------------------------- %Timea %Qb %Timea %Qb

Big Wood River 4.0 7.5 27.2 43.8 69.7 84.2 93.3 24.3 69.0 3.3 19.9

Boise River 3.6 6.5 24.7 40.7 68.3 84.7 93.7 27.1 70.6 2.0 11.9

Johnson Creek 5.4 9.6 33.8 53.4 78.2 89.1 95.5 21.3 75.0 7.0 42.8

Lochsa River 4.2 7.5 27.0 44.0 72.3 88.8 96.0 27.0 74.3 1.8 12.1

Middle Fork Salmon River 5.5 9.1 28.9 45.5 68.4 82.9 92.7 21.5 65.2 2.0 15.0

North Fork Clearwater River 3.7 6.6 23.3 38.1 65.5 84.9 94.3 30.0 71.1 2.0 11.4

Salmon River nr Obsidian 3.7 7.5 27.9 45. 1 72.5 86.2 95.0 22.7 70.5 2.4 15.6

Salmon River nr Shoup 3.3 5.9 21.4 34.8 55.9 74.0 88.4 22.7 53.8 3.0 14.6

Salmon River bl Yankee Fork 3.8 6.9 24.6 39.6 63.7 79.8 91.2 23.8 62.5 3.2 17.7

Selway River 4.2 7.7 27.9 45.5 73.7 89.1 96.0 26.0 74.7 1.3 9.5

South Fork Payette River 3.6 6.5 23.5 38.9 64.3 81.3 92.0 26.3 65.6 5.1 23.9

South Fork Salmon River 4.5 8.1 28.9 46.2 72.1 86.8 94.7 24.6 71.7 4.0 24.6

Squaw Creek (USGS) 6.0 10.8 35.4 52.3 73.9 86.7 94.7 21.5 70.9 3.8 29.5

Thompson Creek 6.9 12.0 35.9 52.8 76.0 88.5 95.5 22.1 73.4 3.5 28.6

Valley Creek 3.3 6.1 23.3 38.7 64.5 80.7 91.6 25.2 64.7 2.9 14.9

Eggers Creek 4.9 8.6 26.3 38.4 57.0 75.4 89.4 21.9 54.0 6.1 29.6

Little Slate Creek 2.9 5.3 20.6 34.9 62.1 81.9 92.6 29.9 67.6 2.5 11.5

Lolo Creek 3.6 6.5 24.4 40.0 67.9 87.1 95.3 30.3 73.8 2.9 16.0

Main Fork Red River 4.8 8.5 28.9 45.0 71.0 87.4 95.1 27.0 73.1 3.8 23.9

South Fork Red River 5.7 9.86 31.1 47.1 71.7 87.5 95.0 25.8 72.5 2.8 20.8

Rapid River 4.0 7.3 25.8 40.8 63.3 79.3 90.9 23.2 62.0 3.5 20.0

Average 4.4 7.8 27.2 43.0 68.2 84.1 93.5 25.0 68.4 3.3 19.7

a

 Percent of time equaled or exceeded.

b

 Percent of streamflow volume.

c

 Bolded values are for the 1.5 year recurrence discharge, used as an estimate for bankfull discharge.
18 USDA Forest Service RMRS-GTR-131. 2004 

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� Figure 12B. Actual (field determined) versus predicted bankfull discharge.

Figure 12A. Bankfull discharge versus drainage area.

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Figure 11. Percent streamflow versus percent of 

the time streamflow is equaled or exceeded. 

(Open circles represent the various exceedance flows presented in table 6.)
USDA Forest Service RMRS-GTR-131. 2004 19

and the D90 ranged from 74 mm to 1,008 mm (table 7). 

The D50 of the subsurface material ranged from 15 mm 

to 43 mm and the D90 of the subsurface material ranged 

from 81 mm to 305 mm. The data presented in table 7 

reflect combined samples for different methods of data 

collection that involved sampling throughout the reach 

(Methods 2 and 3). At all sites, the D50 and D90 of the surface material was larger than the subsurface material, indicating the presence of a coarser surface (armor) layer. 

The ratio of the D50 for the surface and subsurface material gives an indication of the degree of armoring. Based 

on comparison of surface pebble count and subsurface 

core information, this ratio ranges from 1.9 to 7.2 and 

averages 4.0. Armoring has been linked to sediment supply being less than the ability of the stream to transport 

that load (Dietrich and others 1989).

Sediment Transport–Discharge Relationships

At all of the study sites, both bedload and suspended 

sediment transport increases with stream discharge. The 

relationships between sediment transport and discharge 

using the log-log model (equation 1) resulted in statistically significant (alpha = 0.01) models for all sites for 

both total bedload and suspended sediment transport. 

The coefficients of determination, r2, ranged from 0.27 

to 0.89 for bedload sediment and 0.35 to 0.95 for suspended sediment. Expressed as power relationships 

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Figure 13. Bankfull width, average depth, and average velocity as a function of bankfull discharge. 

(Open symbols are width, average depth and 

average velocity at the 1.5 year return interval 

discharge, used as an approximation of bankfull 

discharge, for sites without estimates of bankfull 

discharge. Data represented by the open symbols were not used in developing the power relationships.)

Channel Geometry

The “At-a-Station” channel geometry relationships 

for each study site were used to estimate the width, 

average depth, and average velocity at bankfull discharge for the sites where bankfull was identified in 

the field. As shown in the following power curve relationships incorporating data from the individual study 

sites, width (W), average depth (D), average velocity 

(V), and gradient (G) at bankfull discharge are strongly related to both bankfull discharge (Qb

) and drainage 

area (DA). The bankfull discharge is the better predictor for the variables of width, average depth, and average velocity, probably since it incorporates differences 

in precipitation inputs not reflected in drainage area 

(figure 13).

W = 3.934*DA0.582 r2 = 0.92 W = 2.005*Qb

0.515 r2

 = 0.97

 D = 0.504*DA0.353 r2 = 0.75 D = 0.300*Qb

0.330 r2

 = 0.89

 V = 2.135*DA0.169 r2 = 0.62 V = 1.704*Qb

0.155 r2

 = 0.70

 G = 8.738*DA-0.526 r2 = 0.75 G = 13.589*Qb

-0.438 r2

 = 0.70

Channel Bed Material

The channel beds at the study sites are typically armored, having a coarser layer of surface material overlaying finer subsurface material. The D50 of the surface 

material ranged between sites from 23 mm to 207 mm 
20 USDA Forest Service RMRS-GTR-131. 2004 

(equation 2), the exponents range from 1.489 to 5.749 

(average 2.711) for total bedload transport and 1.362 to 

3.997 (average 2.289) for suspended sediment transport 

(table 8). Using the average exponent values, doubling 

stream discharge results in a more than sixfold increase 

in bedload transport and almost a fivefold increase in 

suspended sediment transport. These ranges of exponent values are much larger than the range reported by 

Leopold (1994), who suggests that most sediment transport data sets have exponents between 2.0 and 3.0. We 

found a high correlation between the exponents for bedload and suspended load (r = 0.76), indicating sites with 

high bedload exponents will generally also have high 

suspended exponents.

The bias correction factor ranges from 1.203 to 3.460 

for the bedload relationships and 1.081 to 3.200 for the 

suspended sediment relationships. Thus, for most sites, 

correcting for bias is important for accurate estimation 

of sediment transport rates and sediment yields.

At most sites, the suspended sediment transport is 

larger than the bedload transport over the entire range of 

discharges when sediment transport was measured. At 

bankfull discharge, suspended sediment transport makes 

up the majority of the total sediment load for all but five 

study sites (table 8). We define the total sediment load 

as the suspended load plus bedload. In general, as watershed size increases, suspended sediment accounts for 

an increasing percentage of the total sediment in transport. For the four largest basins, Salmon River near 

Shoup, Selway River, Lochsa River, and the North Fork 

Clearwater River, bedload accounts for less than 4 percent of the total load at bankfull discharge. Bedload 

accounts for 62 percent of the total load at bankfull discharge for the smallest basin, Eggers Creek.

Table 7. Surface and subsurface bed material information for the study sites.

Ratio:surface to

Surface Subsurface Subsurface Surface Subsurface 

D50 D50 D50 D90 D90 Sample 

 Site mma mm mmb mma mm year

Big Wood River 119/155 25 4.8/6.2 353/210 152 00

Blackmare Creek 95/104/149 -/21 -/5.0/7.1 252/315/210 -/128 94/00

Boise River 71/76 -/23 -/3.3 160/174 -/121 94/95

Dollar Creek 77/87/100 -/-/22 -/4.1/4.5 174/224/164 -/-/94 94/00

Johnson Creek 190 430 94

Little Buckhorn Creek 28/81/119 -/15 -/5.4/7.9 450/285/191 -/108 94/00

Lochsa River 148/126 -/26 -/4.8 320/339 -/177 94/95

Middle Fork Salmon River 146/128 36 3.7/2.9 370/221 174 00

North Fork Clearwater River 60/95 -/23 -/4.1 334/282 -/135 94/95

Salmon River nr Obsidian 61/64 26 2.3/2.5 148/127 97 00

Salmon River nr Shoup 96/150 28 3.4/5.4 203/207 164 00

Salmon River bl Yankee Fork 104/138 25 4.2/5.5 396/182 133 00

Selway River 200/173 -/24 -/7.2 315/310 -/131 94/95

South Fork Payette River 55/110 -/20 -/5.8 175/258 -/102 94/95

South Fork Salmon River 38/2/2 113/87/168 94/A99/S99d

Squaw Creek (USGS) 43/46/83 -/-/29 -/1.6/2.9 82/116/151 -/-/124 94/00

Thompson Creek 66/59/135 -/-/43 -/1.4/3.1 130/140/228 -/-/164 94/00

Valley Creek 48/70/40 -/-/21 -/-/1.9 107/230/132 -/-/81 94/94/95

West Fork Buckhorn Creek 180 750 94

Cat Spur Creek 27 80 94

Eggers Creekc 23/4 164/8 75,77-84,94

Hawley Creek 40 140 94

Johns Creek 180/207 -/35 -/5.9 400/1,008 -/305 94/95

Little Slate Creek 207/102 -/24 -/4.2 450/355 -/169 94/95

Lolo Creek 90/84/68 -/-/20 -/-/3.4 150/127/172 -/-/93 94/95/95

Main Fork Red River 68/50 -/18 -/2.8 110/160 -/86 94/95

Rapid River 94/63 -/16 -/3.9 181/220 -/113 94/95

South Fork Red River 86/106 -/25 -/4.2 165/258 -/145 94/95

Squaw Creek (USFS) 27 74 94

Trapper Creek 67/85 -/17 -/5.0 136/300 -/89 94/95

Fourth of July Creek 51 137 94

Herd Creek 67 122 94

Marsh Creek 56 162 94

a

 Bolded values represent information from surface core samples; unbolded values represent information from pebble counts. In 2000 both 

pebble counts and surface core information are available. b

 Bolded values are ratios of surface and subsurface core information; unbolded values are ratios of surface pebble counts and subsurface core 

information. c

 Eggers Creek pebble counts in 1994 are influenced by annual flushing of a sediment retention pond.

d

 Sampling occurred twice in 1999; once in April (A99) and again in September (S99).
USDA Forest Service RMRS-GTR-131. 2004 21

Table 8. Bedload and suspended sediment transport model information.

Bedload sediment Suspended sediment

 Rate at Qb % of total Rate at Qb 

 Site Exponent r2 BCFa tons/day at Qb Exponent r2 BCFa tons/day

Big Wood River 3.540 0.87 1.300 33.3 13.7 2.982 0.82 1.102 209

Blackmare Creek 1.986 0.61 1.607 3.70 35.8 1.367 0.49 1.534 6.63

Boise River 2.552 0.85 1.203 339 11.3 3.337 0.93 1.257 2,668

Dollar Creek 2.304 0.72 1.509 9.48 38.9 1.378 0.62 1.413 14.9

Johnson Creek 2.819 0.87 1.326 2.53 6.3 1.767 0.81 1.187 37.7

Little Buckhorn Creek 2.271 0.50 1.844 1.362 0.41 1.962

Lochsa River 3.891 0.78 1.428 84.2 2.7 3.696 0.85 1.373 3,062

Middle Fork Salmon River 5.749 0.82 1.886 93.6 10.8 3.997 0.89 1.143 771

North Fork Clearwater River 3.862 0.88 1.272 98.7 2.6 3.707 0.92 1.241 3,679

Salmon River nr Obsidian 3.388 0.61 1.246 14.0 16.1 1.803 0.35 1.218 72.9

Salmon River nr Shoup 3.884 0.71 1.350 206 2.8 3.088 0.46 1.59 7,064

Salmon River bl Yankee Fork 3.851 0.72 1.549 56.9 8.2 3.315 0.84 1.25 637

Selway River 4.426 0.84 1.291 246 3.9 3.598 0.76 1.883 5,998

South Fork Payette River 2.020 0.70 1.353 186 15.1 3.174 0.90 1.238 1,044

South Fork Salmon River 3.007 0.74 2.088 166 42.0 2.066 0.91 1.174 229

Squaw Creek (USGS) 2.516 0.79 1.846 12.1 28.9 2.198 0.95 1.103 29.7

Thompson Creek 3.275 0.89 1.522 7.30 28.7 2.478 0.83 1.081 18.2

Valley Creek 2.808 0.59 1.823 75.5 68.0 1.875 0.75 1.32 35.5

West Fork Buckhorn Creek 1.871 0.43 2.083 7.50 23.1 1.618 0.40 3.2 24.9

Cat Spur Creek 2.726 0.63 2.203 3.70 50.3 1.790 0.72 1.229 3.66

Eggers Creek 1.645 0.67 1.341 0.101 62.0 1.912 0.79 1.236 0.062

Hawley Creek 1.589 0.27 1.767 1.41 24.2 1.998 0.76 1.17 4.41

Johns Creek 2.142 0.55 4.507 3.59

Little Slate Creek 1.643 0.53 2.081 2.74 11.3 1.823 0.75 1.435 21.6

Lolo Creek 1.489 0.37 2.086 4.16 20.2 1.436 0.72 1.538 16.5

Main Fork Red River 2.164 0.70 2.122 17.0 44.2 1.790 0.82 1.363 21.5

Rapid River 2.233 0.59 2.594 15.1 16.9 2.533 0.89 1.34 74.5

South Fork Red River 1.683 0.47 3.460 9.28 35.7 1.613 0.63 1.73 16.7

Squaw Creek (USFS) 2.300 0.49 1.898 0.748 46.8 1.658 0.70 1.521 0.852

Trapper Creek 1.704 0.57 2.548 6.64 53.7 1.492 0.66 1.954 5.73

Fourth of July Creek 2.733 0.78 2.347 13.8 36.2 2.305 0.90 1.277 24.3

Herd Creek 2.458 0.83 1.596 26.1 23.6 2.397 0.95 1.149 84.4

Marsh Creek 2.931 0.74 1.721 79.9 82.0 1.700 0.83 1.176 17.5

a

 BCF = bias correction factor (Duan 1983).

The value of the exponent in the sediment transport 

power equations exerts much control over the range of 

flows most responsible for sediment transport. As the exponent increases, a larger proportion of the sediment load 

is associated with higher discharges that occur a smaller 

portion of the time. Table 9 provides bedload sediment 

transport duration information for 21 of the study sites 

and figure 14 displays this information graphically. These 

sites represent long-term USGS gaged sites and USFS 

gaged sites with extended streamflow records through 

water year 1999. In figure 14, the bedload sediment duration curves for each site are coded by a category for a 

range of exponent values to illustrate the influence of the 

value of the exponent. The site with the largest exponent 

for bedload transport, Middle Fork of the Salmon River, 

transports 93.7 percent of the bedload at high flows that 

occur less than 1 percent of the time. On the other extreme, Lolo Creek, with the smallest bedload exponent, 

only transports about 11.4 percent of the bedload at high 

flows that occur less than 1 percent of the time.

While differences in the exponent indicate large variation between sites, on average, discharges equal to or 

larger than bankfull discharge, which occur 3.3 percent 

of the time (range 1.3-7.0 percent), account for about 

19.7 percent of the total streamflow (range 9.5-42.8 

percent) and transport 61.5 percent (range 21.1-96.8 

percent) of the bedload sediment. Discharges between 

average annual discharge and bankfull discharge occur 21.7 percent of the time (range 14.3-28.0 percent), account for 48.8 percent of the total streamflow 

(range 24.4-65.2 percent), and transport 34.7 percent 

of the bedload (range 10.4-64.5 percent). Discharges 

less than average annual discharge occur 75.0 percent 

of the time (range 69.7-78.7 percent) and account for 

about 31.6 percent of the total streamflow (range 25.0-

46.2 percent) but only transport about 3.8 percent of the 

bedload sediment (range ~0.0 to 21.6 percent). Given 

that the power relationships (equation 2) predict some 

amount of bedload transport even for small discharges, 

our findings should be considered in general agreement 
22 USDA Forest Service RMRS-GTR-131. 2004 

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Figure 14. Bedload sediment duration curves for 

selected study sites.

Table 9. Bedload transport duration information for selected study sites.

Percent of time equaled or exceededa

0.50 1 5 10 25 50 75 Qa Qb or Q1.5

 Study Site -------------------------------% bedload------------------------------- %Time %Beda %Timeb %Bedb

Big Wood River 27.0 42.3 82.8 94.9 99.8 100 100 24.3 99.8 3.3 73.0

Boise River 14.9 24.3 62.4 81.9 97.5 99.5 99.8 27.1 98.0 2.0 38.1

Johnson Creek 25.3 38.2 79.1 94.2 99.8 100 100 21.3 99.6 7.0 87.5

Lochsa River 35.0 48.6 85.0 95.5 99.9 100 100 27.0 99.9 1.8 61.8

Middle Fork Salmon River 89.1 93.7 99.2 99.9 100 100 100 21.5 100.0 2.0 96.8

North Fork Clearwater River 37.8 50.7 83.5 93.7 99.6 100 100 30.0 99.8 2.0 64.8

Salmon River nr Obsidian 18.1 31.8 77.6 92.8 99.8 100 100 22.7 99.8 2.4 57.4

Salmon River nr Shoup 35.1 48.9 85.5 96.0 99.5 99.8 99.9 22.7 99.4 3.0 74.8

Salmon River bl Yankee Fork 34.9 50.1 86.7 96.3 99.8 100 100 23.8 99.8 3.2 77.8

Selway River 40.2 55.0 89.4 97.6 100 100 100 26.0 100.0 1.3 60.8

South Fork Payette River 11.4 19.0 51.2 72.0 91.8 97.0 98.9 26.3 92.4 5.1 51.9

South Fork Salmon River 25.6 38.2 78.3 92.9 99.5 99.9 100 24.6 99.5 4.0 72.6

Squaw Creek (USGS) 26.9 41.8 83.5 94.7 99.3 99.8 99.9 21.5 99.1 3.8 77.1

Thompson Creek 50.2 66.5 93.6 98.4 99.9 100 100 22.1 99.9 3.5 89.5

Valley Creek 16.3 26.5 65.8 85.1 98.1 99.4 99.8 25.2 98.1 2.9 49.8

Eggers Creek 13.7 22.4 52.5 66.3 80.2 89.9 96.1 21.9 78.4 6.1 56.7

Little Slate Creek 5.9 10.4 35.2 54.2 81.6 93.4 97.7 29.9 85.6 2.5 21.1

Lolo Creek 6.5 11.4 37.5 56.4 83.0 95.2 98.5 30.3 87.5 2.9 25.8

Main Fork Red River 17.9 27.7 65.3 82.3 96.3 99.3 99.8 27.0 96.9 3.8 57.3

Rapid River 16.6 26.3 64.6 82.4 94.9 97.8 99.2 23.2 94.4 3.5 54.9

South Fork Red River 15.0 23.3 56.5 74.1 91.6 97.5 99.2 25.8 92.0 2.8 42.3

Average 26.8 38.0 72.2 85.8 95.8 98.5 99.5 25.0 96.2 3.3 61.5

a

 Values equal to or greater than 99.95 are entered as 100.0.

b

 Bolded values are for the 1.5 year recurrence discharge, used as an estimate for bankfull discharge.
USDA Forest Service RMRS-GTR-131. 2004 23

with Leopold’s (1994) observation that in many streams 

bedload transport begins at discharges greater than the 

average annual discharge.

The size of bedload material being transported also 

increases with discharge. The largest particle in the bedload sample increased with increasing discharge at all 

24 of the study sites where such information is available 

(see figure 8 example). A power curve fit of the largest 

particle size-discharge pairs of data resulted in significant positive relationships (r2

 = 0.37-0.75) for all but one 

site, Lolo Creek (r2 = 0.05) (table 10). The size of the 

largest particle in the bedload samples ranged from 22 

mm to 83 mm for sites where the 76.2 mm square orifice 

Helley-Smith sampler was used and up to 128 mm and 

141 mm at the two sites where the 152.4 mm square orifice sampler was occasionally used at higher discharges. The size of the sampler orifice may have limited 

measurement of large particles in transport at many of 

the sites. Additionally, the short sampling times at any 

given location along the sampling transect and the episodic nature of bedload transport reduce the likelihood 

of capturing large particles that may be occasionally in 

transport. Thus, the largest particle in the bedload sample may be much smaller than the largest particle being transported across the sampling transect during any 

measurement. The bedload sediment size class data for 

most sites also indicate that the larger size classes generally appear in the bedload samples associated with the 

higher discharges.

The results of the painted rock and bedload trap studies and the observations of the size of recently moved 

particles at selected sites all support a hypothesis of 

transport of coarse material making up much of the 

channel bed during high but relatively frequently occurring discharges. At the 10 sites where movement of 

painted rocks was monitored during the snowmelt runoff in 1995, instantaneous peak discharges ranged from 

1.26 to 2.12 Qb. At nine of the 10 sites the largest transported particle was the size of the D83 to D95 of the bed 

surface material and for one site it was the size of the D71

of the bed surface material. The largest particle observed 

to have recently moved during the 1997 snowmelt runoff ranged from the D85 up to the D100 of the bed surface 

material. At these 11 sites, instantaneous peak discharges ranged from 1.75 to 2.46Qb

. At the two Red River 

study sites, the largest particles captured in the bedload 

traps represent the D44 and D54 of the surface bed material. Discharges during the 1997 spring snowmelt evaluation period at the Red River study sites were 1.2Qb

and 1.6Qb, respectively. These observations and measurements of transport of coarse material, coupled with 

conservative estimates of the largest material in transport in the bedload samples, suggest that at most sites 

coarse material, often about the median size of the bed 

material, is in transport at discharges near or slightly 

above bankfull discharge. This is in general agreement 

with the findings of others. Andrews (1984) found that 

in 24 coarse-bed Colorado streams the median diameter 

particle of the bed surface was entrained by discharges equal to or less than bankfull discharge. Particles as 

large as the D90 were entrained by bankfull discharge. 

Ryan and Troendle (1996) report that transport of the 

full range of particle sizes on the bed (up to the limits of 

the sampler) begins between 0.7 and 1.0 of bankfull discharge for a coarse-bed stream in Colorado.

At most sites, the median diameter of the bedload 

sample increases with discharge, but the relationship 

is much weaker than that between the largest particle 

and discharge (table 10). A power curve fit to the median diameter-discharge pairs of data resulted in significant positive relationships (r2

 = 0.08 to 0.52) at 24 of the 

study sites. The power curve relationship was not significant at six of the study sites.

Sand-size material is the major component of the bedload sediment. At 23 sites the predicted transport rate of 

the sand size particles (0.5-2 mm) is larger than predicted transport rates for all other size classes (<0.5, 2-8, 8-

32, >32 mm) across the range of sampled discharges. At 

the remaining sites, the predicted sand transport rate is 

greatest up to some discharge, and then the transport rate 

of larger material becomes greater. To provide additional perspective on sediment sizes in transport, we include 

in table 10 the largest median diameter, the percentage of 

bedload samples with median diameters larger than sand 

(2 mm), and the corresponding minimum discharge, expressed as a ratio of bankfull discharge, when median diameters exceed 2 mm. For example, for bedload samples 

collected at the Selway River study site, while the largest 

median diameter was 55.0 mm, only 2.8 percent of the 

samples (two out of 72) had median diameters exceeding 2 

mm and these occurred at or above discharges of 1.61Qb.

Summary

The web site spreadsheets and documents that accompany this report provide sediment transport and related data for 33 coarse-bed streams and rivers in Idaho. 

These sites span a large range of drainage areas, average annual runoffs, channel sizes, channel gradients, and 

substrate sizes. Our primary purpose is to make these 

data available to potential users.
24 USDA Forest Service RMRS-GTR-131. 2004 

Table 10. Information on size of bedload material for the study sites. Largest particle Median diameter Diameter Largest Percent of Q/Qb or Power b-axisc Power median samples with Q/Q1.5 Particle size class with the Study site eqn.a r2 Trendb mm eqn. r2 Trendb mm median >2 mm ratiod largest transport rate Big Wood River 0.63 + 79 0.08 + 40.7 35.0 0.29Q1.5 0.5-2 mm up to ~1.25Q1.5; 8-32 mm and >32 mm at >1.25Q1.5

e

Blackmare Creek nm 32-64 0.01 +ns 4.0 5.6 0.08 0.5-2 mm at all dischargesBoise River 0.37 + 62 0.05 +ns 35.8 2.4 0.96 0.5-2 mm at all dischargesDollar Creek nm 16-32 0.14 + 2.0 0 0.5-2 mm at all dischargesJohnson Creek 0.69 + 55 0.33 + 4.6 5.6 0.35 0.5-2 mm at all dischargesLittle Buckhorn Creek nm 8-16 0.13 + 1.9 0 0.5-2 mm at all dischargesLochsa River 0.68 + 45 0.08 +ns 3.0 2.8 0.43 0.5-2 mm at all dischargesMiddle Fork Salmon River 0.70 + 83 0.16 + 43.7 51.6 0.71 Q1.5 0.5-2 mm up to ~0.71 Q1.5; 8-32 mm and >32 mm at >1.10Q1.5North Fork Clearwater River 0.64 + 74 0.32 + 19.9 6.9 0.56 0.5-2 mm at all dischargesSalmon River nr Obsidian 0.40 + 72 0.29 + 10.6 38.0 0.90 Q1.5 0.5-2 mm at all dischargesSalmon River nr Shoup 0.72 + 78 0.25 + 48.5 63.9 1.00 Q1.5 8-32 mm and >32 mm at >0.82Q1.5

f

Salmon River bl Yankee Fork nm 32-64 0.33 + 38.9 21.7 0.33 Q1.5 0.5-2 mm up to ~0.69Q1.5; 8-32 mm and >32 mm at >0.79Q1.5Selway River 0.75 + 82 0.29 + 55.0 2.8 1.61 0.5-2 mm at all dischargesSouth Fork Payette River 0.71 + 128 0.17 + 63.8 16.7 0.24 0.5-2 mm at all dischargesSouth Fork Salmon River 0.48 + 27 0.13 + 2.3 1.5 0.77 0.5-2 mm at all dischargesSquaw Creek (USGS) 0.73 + 66.5 0.25 + 10.3 8.7 0.64 0.5-2 mm at all dischargesThompson Creek 0.75 + 68.5 0.20 + 7.1 2.4 0.31 0.5-2 mm at all dischargesValley Creek 0.59 + 141 0.12 + 18.5 34.5 0.26 0.5-2 mm up to ~1.29Qb; 2-8 mm >1.29 QbWest Fork Buckhorn Creek nm 16-32 0.11 + 2.5 14.1 0.20 0.5-2 mm at all dischargesCat Spur Creek nm 25 18.0 0.17 <2 mmgHawley Creek nm 32-64 0.12 + 9.8 12.9 0.39 0.5-2 mm at all dischargesJohns Creek 0.27 + 22 0.01 -ns 5.3 3.6 2.00 0.5-2 mm at all dischargesLittle Slate Creek 0.46 + 30 0.05 +ns 17.5 1.7 0.43 0.5-2 mm at all dischargesLolo Creek 0.05 +ns 55 0.00 -ns 10.2 14.3 0.16 0.5-2 mm at all dischargehMain Fork Red River 0.53 + 60 0.17 + 38.9 5.7 0.08 0.5-2 mm at all dischargesRapid River 0.42 + 62 0.16 + 37.2 20.5 0.09 0.5-2 mm up to ~0.64Qb; >32 mm at >0.64QbSouth Fork Red River 0.70 + 49 0.26 + 3.2 5.9 0.31 0.5-2 mm at all dischargesSquaw Creek (USFS) nm 64-128 0.34 + 5.9 9.7 0.50 0.5-2 mm up to ~2.27 Qb; 2-8 mm >2.27 QbTrapper Creek 0.63 + 41 0.33 + 3.7 3.5 0.29 0.5-2 mm at all dischargesFourth of July Creek 0.75 + 40 0.52 + 3.1 5.1 0.45 0.5-2 mm at all dischargesHerd Creek 0.70 + 60.5 0.41 + 9.7 19.4 0.09 0.5-2 mm up to ~1.30Qb; 2-8 mm >1.30QbMarsh Creek 0.59 + 66 0.18 + 23.4 38.8 0.13 0.5-2 mm at all dischargesa nm = largest particle not measured at this study site. b + represents a trend of increasing size with discharge; - represents a trend of decreasing size with discharge; ns = not significant at alpha = 0.01.c At study sites where the largest particle diameter was not measured, the largest size class represented in the samples is shown. d Ratio of the lowest discharge to either bankfull or the 1.5 year recurrence discharge when the median diameter of a bedload sample was >2 mm. e A few exceptions occur at lower discharges; refer to web-site data files and graphs. f Only two of the 61 bedload samples were at discharges < Q1.5. g Limited data and a few exceptions occur. h A few exceptions occur; refer to web-site data files and graphs.
USDA Forest Service RMRS-GTR-131. 2004 25

Streamflow at all of the study sites is dominated by 

the melting of snow and flows typically peak in April, 

May, or June. Average annual runoff for the study watersheds ranges from 3.7 to 36.3 inches in response to large 

differences in average annual precipitation. Average 

annual discharge averages 0.21 of bankfull discharge 

(range 0.11-0.40). The bankfull discharge for most of 

these sites is a relatively frequent event with an average 

recurrence frequency of about 1.5 years.

Since a significant snowpack develops at all of these 

sites, a large proportion of the annual runoff occurs during a relatively short period of time, typically during the 

spring and early summer. Discharges equal to or larger 

than the bankfull discharge, on average, occur 3.3 percent of the time (12.1 days/year) and account for 19.7 

percent of the annual streamflow. Discharges less than 

the average annual discharge, on average, occur 75.0 

percent of the time (273.9 days per year) and account 

for 31.6 percent of the annual streamflow. The remaining 48.7 percent of the streamflow is associated with discharges between Qa

 and Qb that, on average, occur 21.7 

percent of the time (79.3 days per year).

Bankfull discharge increases with increasing drainage area and average annual precipitation. Width, average depth, average velocity, and gradient at bankfull 

discharge are strongly related to both bankfull discharge 

and drainage area. However, bankfull discharge is the 

better predictor since it incorporates differences in precipitation inputs not reflected in drainage area.

The channel bed at all the study reaches is armored. 

The D50 of the surface material was larger than the subsurface material and the ratio of the surface to subsurface 

median diameters ranged from 1.9 to 7.2 indicating the 

presence of an armor layer. Armoring has been linked to 

sediment supply being less than the ability of the stream 

to transport that load (Dietrich and others 1989).

Both bedload and suspended sediment transport 

increases with stream discharge. The relationships 

between sediment transport and discharge using the loglog model (equation 1) resulted in statistically significant 

(alpha=0.01) models for all sites for both total bedload 

and suspended sediment transport. The exponents in the 

power function form of the model (equation 2) exhibit 

a very wide range from 1.489 to 5.749 (average 2.711) 

for total bedload transport and 1.362 to 3.997 (average 

2.289) for suspended sediment transport. Emmett and 

Wolman ( 2001) state that a principal factor influencing 

the value of the exponent in the bedload transport equation is sediment supply limitation due to both the availability and mobility of bed material. They suggest that 

supply limitations can occur due to a streambed armor 

layer of large particles and that large bedload transport 

rates cannot occur until the armor layer is disturbed.

At most sites, the suspended sediment transport is 

larger than the bedload transport over the entire range of 

discharges when sediment transport was measured. At 

bankfull discharge, suspended sediment transport makes 

up the majority of the sediment load for all but five study 

sites. In general, as watershed size increases, suspended 

sediment accounts for an increasing percentage of the 

total sediment in transport.

The value of the exponent in the sediment transport 

power equations exerts much control over the range 

of flows most responsible for sediment transport. As 

the exponent increases, a larger proportion of the sediment load is associated with higher discharges that occur a smaller portion of the time. On average, discharges 

equal to or larger than bankfull discharge transport 61.5 

percent of the bedload sediment. Discharges less than 

average annual discharge only transport about 3.8 percent of the bedload sediment. The remaining 34.7 percent of the bedload is transported by discharges between 

average annual discharge and bankfull discharge.

The size of bedload material being transported also 

increases with discharge. At all sites where the largest 

particle in the bedload sample was measured, there was 

a positive relationship between particle size and discharge. At most sites there was also a positive relationship between the median size of the bedload sample and 

discharge; however, these relationships were often very 

weak. Sand size material is a major component of the 

bedload sediment and at 23 of the study sites the transport rate of the sand is larger than rates for any other size 

class across all measured discharges. This is in agreement with Leopold’s (1992) observation for gravel-bed 

streams that the largest portion of the bedload is sand.

Observations and measurements of transport of 

coarse material using painted rocks and bedload traps 

and the measurements of the largest particle in the bedload samples suggest that at most sites coarse material (often about the median size of the bed material) is 

moved at discharges near or slightly above bankfull discharge. This is in general agreement with the findings of 

others (Andrews 1984; Ryan and Troendle 1996).

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designed to meet the needs of the National Forest managers, 

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