Prepared in cooperation with

U.S. Department of Agriculture, Forest Service

Estimating the Magnitude of Bankfull Flows for 

Streams in Idaho

Water-Resources Investigations Report 03–4261

U.S. Department of the Interior

U.S. Geological Survey

 The following errors were corrected on June 16, 2004: Page 6, table 2, description of basin slope, "feet per mile"

 was changed to "percent"; Page 9, table 3, headnote, basin slope in "feet per mile" was changed to basin slope in

"percent"; Page 17, appendix A, headnote, "feet per mile" was removed. 
Estimating the Magnitude of 

Bankfull Flows for Streams in 

Idaho

By Jon E. Hortness and Charles Berenbrock

Prepared in cooperation with

U.S. Department of Agriculture, Forest Service

Water-Resources Investigations Report 03–4261

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior U.S. Department of Agriculture

Gale A. Norton, Secretary Ann M. Veneman, Secretary

U.S. Geological Survey U.S. Forest Service

Charles G. Groat, Director Dale Bosworth, Chief

U.S. Geological Survey, Reston, Virginia; 2004

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Hortness, J.E., and Berenbrock, Charles, 2004, Estimating the Magnitude of Bankfull Flows for Streams in Idaho: U.S. 

Geological Survey Water-Resources Investigations Report 03–4261, 37 p.
iii

Contents

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

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

Purpose and scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Description of study area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Previous investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Compilation of data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Basin and climatic characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Peak-flow data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Determination of regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Estimation methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Application of methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Example 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Example 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Computer program for regional regression equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

References cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Appendix A. Basin and climatic characteristics for streamflow-gaging stations in Idaho 

and bordering States used in regional regression analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Appendix B. Peak flows at selected recurrence intervals for streamflow-gaging stations 

in Idaho and bordering States used in regional regression analysis . . . . . . . . . . . . . . . . . . . . 27

Appendix C. (XT Λ-1

 X)-1 matrices for the T-year (T = 1.5, 2, and 2.33) regional regression 

equations for Idaho . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
iv

Figures

1. Map showing locations of streamflow-gaging stations in Idaho and bordering 

States used in regional regression analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2. Map showing locations of regions in Idaho used in regional regression 

analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3. Graph showing joint distribution of drainage area and mean basin elevation, 

and minimum covering ellipsoid for gaged sites in region 3, Idaho . . . . . . . . . . . . . . . . . 10

Tables

1. Selected data sources used to obtain basin and climatic characteristics for 

regional regression analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2. Description of selected basin and climatic characteristics used in the final 

predictive equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3. Predictive regression equations and their accuracy in estimating peak flows for 

ungaged sites on unregulated and undiverted streams in Idaho . . . . . . . . . . . . . . . . . . . 9

Conversion Factors, Water Year Definition, and Vertical Datum

Water year: In U.S. Geological Survey reports dealing with surface-water supply, a water year is 

the 12-month period, October 1 through September 30. The water year is designated by the calendar year in which it ends; thus, the water year ending September 30, 2001, is called the “2001 

water year.”

Sea Level: In this report, “sea level” refers to the North American Vertical Datum of 1988 

(NAVD of 1988)—a vertical control datum established by the minimum-constraint adjustment of 

Canadian-Mexican-United States leveling observations and held fixed at Father Point/Rimouski, 

Quebec, Canada.

Multiply By To obtain

cubic foot per second (ft3/s)

foot (ft)

foot per mile (ft/mi)

inch (in.)

inch per year (in/yr)

mile (mi)

square mile (mi 2

)

0.02832

0.3048

0.1894

2.54

2.54

1.609

2.590

cubic meter per second (m3

/s)

meter (m)

meter per kilometer (m/km)

centimeter (cm)

centimeter per year (cm/yr)

kilometer (km)

square kilometer (km2

)
Estimating the Magnitude of Bankfull Flows 

for Streams in Idaho

By Jon E. Hortness and Charles Berenbrock

Abstract

Methods for estimating magnitudes of peak 

flows with recurrence intervals of 1.5 and 2.33 

years were developed for ungaged sites on streams 

throughout Idaho. These peak flows represent the 

magnitudes at and near bankfull stage and are 

needed for quantification of water rights required 

to maintain or restore fish and wildlife habitats and 

riparian vegetation. Data from a previous report 

detailing methods for estimating magnitudes with 

recurrence intervals of 2 to 500 years were used in 

this study.

Generalized least-squares regression techniques were used to calculate the final coefficients 

and measures of accuracy for the regression equations for each of nine regions. The equations relate 

basin and climatic characteristics to peak flows 

with recurrence intervals of 1.5 and 2.33 years. The 

basin and climatic characteristics used to develop 

the equations included drainage area, mean basin 

elevation, forested area, mean annual precipitation, 

basin slope, north-facing slopes greater than 30 percent, and slopes greater than 30 percent. Average 

standard errors of the regression model ranged from 

+150 to -60.1 percent, and average standard errors 

of prediction ranged from +165 to -62.2 percent. 

The range of prediction errors was narrowest, 

-48.9 to -32.9 percent, for region 5.

A computer program was developed to automate the calculations required for the regional 

regression calculations. Results from this program 

comprised calculated peak flows, site-specific standard errors of prediction, and the 90-percent confidence intervals for the estimates.

INTRODUCTION

Introduction. 

Estimates of the magnitude and frequency of peak 

flows are used for a variety of purposes, such as the 

design of bridges, culverts, and flood-control structures, and the management and regulation of flood 

plains. For these purposes, peak-flow recurrence intervals generally are 50 years or greater. However, there 

is increasing interest in peak flows with a more frequent recurrence interval and their role in maintaining 

aquatic and riparian ecosystems. Of particular interest 

are those peak flows necessary for mobilization of 

streambed sediments to maintain long-term fish habitat 

and channel capacity.

The U.S. Forest Service (USFS) in Idaho has been 

involved in the quantification of instream flows as part 

of the ongoing Snake River Basin Adjudication, as well 

as for general planning and administrative purposes. 

One key component of instream flows proposed by the 

Forest Service is the high flow regime necessary to sustain long-term aquatic and riparian ecosystems. Methods used to estimate the range of flows that constitute 

this high flow regime include using bankfull discharge 

or a percentage of bankfull discharge.

Most hydrologists agree that peak flows with a 

recurrence interval of about 1.5 years best represent 

bankfull flows. Leopold (1994) stated that the recurrence interval of bankfull discharges generally ranges 

from 1 to 2.5 years and that the 1.5-year peak flow is a 

reasonable average. Similarly, a regional study completed by Castro and Jackson (2001) suggests that the 

average recurrence interval for bankfull flows in the 

Pacific Northwest States (Oregon, Washington, and 

Idaho) is 1.4 years, and the 1.5-year interval is suggested for use in Idaho. Emmett (1975) also found that 

the average recurrence interval for bankfull discharges 

in the upper Salmon River Basin is about 1.5 years.

Currently, peak-flow recurrence interval information is available only for gaged sites (sites where 

streamflow-gaging stations, or gages, have been established) that have at least 10 years of annual peak-flow 

record. Berenbrock (2002) developed regional peakflow regression equations for ungaged streams in 

Idaho; however, the minimum recurrence interval for 
Kootenai

River Priest

River

Spokane

River

St

River

Joe

Pend

Oreille

Lake

Coeur

d'Alene

Lake

Fork

Clark

Bitterroot River

Clearwater

Lochsa

Selway

River

River River

Dworshak

Reservoir

Salmon

River

Snake

River

Grande

Ronde

Sandpoint

Coeur

d'Alene

Lewiston

3

4

5

17 16

11 14

2

1

24

22

23

10

15

18

21

68

55

41 40

44 39 38

43

46 47

48

52

51

50

36

65

64 80

83 73

84, 85

86

70

74 146

144 143

61

60

62

63

56

32

154

153

30

152

138

140

128

127

148

149

130

132

135 136

134

133

131

142

6 7

8

13

27

26

25

9

12

19

69

20

49

45

42

35

37

34

28

79

78

54

67

66

87

53

81

88

82

77

76

72

75

71

91 90

151

150

89

129

139 137

147 145

141

59

57

58

33

155

31

29

Stud

are

IDAHO

WASHINGTON

OREGON

MO

NEVADA UTAH

EXPLA

Gaging stati number ( acteristics 

39
River

Weiser

River

Lemhi

River

Salmon

River

River

Snake

Boise

River

River

Malheur

River

Owyhee

River Bruneau

Snake

River

Raft

River

Portneuf

River

R

Blackfoot

Snake

Henrys

River

BeaLak

Bear

American

Falls

Reservoir

River

Lost

Big

River Wood

Big

Pa

Res

Salmon

Fork

Pahsimeroi River

River

Lost

Little

Creek

Birch

Lucky

Peak

Lake

Salmon

Boise

Twin

Falls

Pocatello

Idaho

Falls

King

Hill

199

200

222

221

223

227

192 190

193

191 194

189

174

106

107

104

103

120

118

110

122

224

228 126 197

196

125 175

99

116

115 117

256

109

108

111

114

112

198

220

219 218

182 213 186

180

185 181

183 211

216

217

207

204

205

322 201 

332

33

326

202

203

210

206

209

208

179

215

178

157

171

93 97 94

101

98

95

96 168

165

166

159 

262

161

160

167

253

252 250

233

248

245

243

236

28

264

254

289 2

288 257

269

270

234

231 232

238

240

260

291

230

229 

124

123

121

119

113

107

173

195

105

176

172

100

102

255

163

92

235

169

164

170

177

156 158

162

271

273

272

184 212

214

187

226

225

321

261

285

283

258 286

259

290 287

263

265

266

268

267

241

237

239

242

244

246

251

249

247

188

0 40 20 

0 40 20 60 

Base from U.S. Geological Survey digital data,1:2,000,000, 1999;Transverse Mercator projectionFactor at central meridian: 0.99960Longitude of central meridian: -114° 00'

Latitude of origin: 42° 00'

False easting (meters): 500,000.0False northing (meters): 100,000.0

Figure 1. Locations of streamflow-gaging stations in Idaho and bordering States used in regional regression analysis.
4 Estimating the Magnitude of Bankfull Flows for Streams in Idaho

these equations was 2 years and did not include the 

2.33-year recurrence interval, which is also a standard 

output from the U.S. Geological Survey (USGS) floodfrequency program.

In 2003, using data obtained for Berenbrock’s 

2002 study, the USGS conducted a study in cooperation with the USFS to develop additional regional 

regression equations that can be used to estimate bankfull flows. The equations developed in this study will 

provide more accurate estimates of bankfull flows for 

ungaged streams in Idaho.

Purpose and Scope

This report documents the development of regression equations used for estimating the magnitude of 

peak flows with recurrence intervals of 1.5 and 2.33 

years. Equations for peak flows with a 2-year recurrence interval estimated previously by Berenbrock 

(2002) also are presented. Data from Berenbrock’s 

study of 333 gaging stations with at least 10 years of 

record through water year 1997 were used to develop 

the regression equations for this study. The equations 

are in the same format and were developed for the 

same regions as those provided in Berenbrock’s study. 

Standard errors of estimates are included to help predict the reliability and accuracy of each equation.

Description of Study Area

The study area (fig. 1) is the entire State of Idaho 

and areas of adjacent States where particular drainage 

basins cross over State boundaries. The adjacent States 

partially included in the study area are Washington, 

Oregon, Nevada, Utah, Wyoming, and Montana. The 

northern and central parts of the area comprise mainly 

rugged, mountainous terrain; broad plains and mildly 

sloping valleys and hills predominate in the south. 

Geologic features across the study area consist of sedimentary, igneous, and metamorphic rocks ranging in 

age from Precambrian to Holocene (Bond, 1978). The 

granitic Idaho batholith is the major structural feature 

in the central part of the study area, and basalt covers 

much of the southern and western parts (Ross and Savage, 1967).

Most precipitation in the study area results from 

storms moving inland from the Pacific Ocean. The 

amount of precipitation varies widely and is greatly 

affected by topography. Precipitation ranges from less 

than 10 in/yr on the Snake River Plain in south-central 

Idaho to 60 to 70 in/yr in the central mountains of 

Idaho (Molnau, 1995). Precipitation is greatest during 

the winter and the most significant amounts are a direct 

result of orographic effects. Spring and summer thunderstorms in the southern part of the study area sometimes produce large amounts of precipitation. Resulting streamflow varies geographically and seasonally 

and can be affected by land use and vegetation. During 

much of the year, streamflow in most unregulated 

streams in the study area is minimal base flow; during 

April, May, June, and July, streamflow is significantly 

higher, primarily as a result of snowmelt. Occasionally 

during the winter months, large frontal systems carrying warmer air release moisture as rain on the snowpack and frozen ground, which results in rapid snowmelt and high runoff rates, particularly at elevations 

less than 6,000 ft above sea level (National Oceanic 

and Atmospheric Administration, 1971).

Acknowledgments

The authors recognize the hard work and dedication of the many USGS hydrologic technicians and 

hydrologists in collecting, processing, and storing the 

peak-flow data necessary for the completion of this 

report. Also, the authors appreciate the assistance of 

the many Federal, State, and local agencies that financially support operations of streamflow-gaging stations 

throughout Idaho where peak-flow data are collected.

PREVIOUS INVESTIGATIONS

Previous Investigations. 

Emmett (1975) developed equations that related 

bankfull discharge to other channel-geometry and flow 

characteristics in the upper Salmon River Basin in 

south-central Idaho. The main assumption in the study 

was that river channels are shaped by the dominant 

flow, which was defined as the bankfull flow. Only 

equations for the 1.5-year recurrence interval flood 

(assumed to be the bankfull flow) were developed 

during Emmett’s study.

Harenberg (1980) developed several sets of 

regression equations for Idaho on the basis of channelgeometry and basin characteristics. He developed 

equations to predict the 1.25-, 2-, 5-, 10-, 25-, 50-, and 

100-year peak flows at ungaged sites. The characteristics in the final equations were bankfull width, drainage 
Compilation of Data 5

area, and 24-hour rainfall intensity for the 2-year recurrence interval. He used fewer gaging stations than previous flood-frequency studies because channel-geometry characteristics could not be determined at every 

gaging station. He demonstrated that standard errors 

were smaller when channel-geometry variables were 

included with basin characteristics in regression equations, but standard errors in his study were 20 to 30 

percent larger than those in Berenbrock’s (2002) study; 

Berenbrock’s dataset was approximately twice as large 

as Harenberg’s. Regional regression equations for estimating streamflow statistics in the Western United 

States were developed by Hedman and Osterkamp 

(1982). The regression equations were developed for 

various streamflow statistics using channel geometry. 

However, data from only three gages in Idaho (located 

on tributaries to the Snake River) were used in their 

analysis.

COMPILATION OF DATA

Compilation of Data. 

All data used to develop regression equations for 

estimating peak flows with recurrence intervals of 1.5 

and 2.33 years were obtained from the report by Berenbrock (2002). These data consisted of basin and climatic characteristics and peak-flow records for each of 

the relevant gaging stations. In addition, the regional 

boundaries determined by Berenbrock (2002) also 

were used in this study.

Basin and Climatic Characteristics

Use of the same independent variables in each of 

the peak-flow equations for a specific region ensures 

that the correlation structure among the streamflow statistics for each region is preserved so that estimates of 

the statistics are stable and consistent (Haan, 1977). 

For this reason, equations developed in this study use 

the same independent variables (basin and climatic 

characteristics) as the equations developed by Berenbrock (2002) for each region. Thus, the same seven basin and climatic characteristics used by Berenbrock—

drainage area (DA), mean basin elevation (E), forested 

area (F), mean annual precipitation (P), basin slope 

(BS), north-facing slopes greater than 30 percent 

(NF30), and slopes greater than 30 percent (S30)—

also were used in this analysis. Data sources used to 

obtain these characteristics are listed in table 1, general 

descriptions of the seven characteristics used in the 

final equations are listed in table 2, and basin and climatic characteristic values obtained for each gaging 

station are listed in appendix A (back of report; table 4

Table 1. Selected data sources used to obtain basin and climatic characteristics for regional regression analysis

[Multiply meter by 3.281 to obtain foot; multiply kilometer (km) by 0.6214 to obtain mile]

Dataset name Source description

National Elevation Dataset (NED)

Basin characteristics were calculated using 30-meter resolution digital elevation data; 

http://gisdata.usgs.gov/ned/default.asp

National Elevation Dataset 

Hydrologic Derivatives (NED-H)

Hydrologic derivatives of NED data were developed using procedures similar to those in Stage 1 

processing, using a custom projection for Idaho; 

http://edcnts12.cr.usgs.gov/ned-h/about/Stage1.html

National Land Cover Dataset (NLCD)

Vogelmann, J.E., Sohl, T.L., Campbell, P.V., and Shaw, D.M., 1998, Regional land cover 

characterization using Landsat Thematic Mapper data and ancillary data sources: Environmental 

Monitoring and Assessment, v. 51, p. 415– 428 

(http://edcwww.cr.usgs.gov/programs/lccp)

Idaho map of mean annual 

precipitation1

Molnau, M., 1995, Mean annual precipitation, 1961– 1990, Idaho: Moscow, University of Idaho, 

Agricultural Engineering Department, State Climate Program, scale 1:1,000,000 

(http://snow.ag.uidaho.edu/Climate/reports.html)

Western United States average 

monthly or annual precipitation2

Daly, C., and Taylor, G., 1998, Western United States average monthly or annual precipitation, 

1961– 90, Oregon: Portland, Water and Climate Center of the Natural Resources Conservation 

Service, grid-cell resolution 4 km (http://www.ocs.orst.edu/prism/prism_new.html)

1 Used for areas in Idaho.

2 Used for areas outside of Idaho.
6 Estimating the Magnitude of Bankfull Flows for Streams in Idaho

in Berenbrock, 2002). Detailed information concerning 

how these values were obtained can be found in Berenbrock’s report (2002, p. 5).

Peak-Flow Data

Peak-flow data from 333 gaging stations (fig. 1; 

appendix B, back of report) with at least 10 years of 

record through water year 1997 (Berenbrock, 2002) 

were used in this analysis. These data represented naturally occurring flows that were not affected by regulation or large irrigation diversions. Most data were from 

continuous-record sites where stage is recorded at a 

fixed interval, typically ranging from 15 to 60 minutes. 

Some data were collected at crest-stage sites where 

only the peak, or highest stage that occurs between site 

visits (usually several months), is recorded.

Determination of Regions

Because of the need for stable and consistent estimates at a specific site, the same region boundaries 

defined by Berenbrock (2002) also were used in this 

analysis. This resulted in nine separate study regions 

and one undefined region (fig. 2). The undefined region 

is almost entirely made up of the area commonly referred to as the eastern Snake River Plain. This area 

includes several dams, major irrigation diversions, 

springs with extremely large discharges, and channel 

bottoms with very high infiltration rates. Because flows 

influenced by these conditions cannot be characterized 

by a regional regression approach, this area was not 

included in the analysis. More detailed information on 

how the regional boundaries were determined can be 

found in previous reports by Berenbrock (2002, p. 8) 

and Hortness and Berenbrock (2001, p. 6).

ESTIMATION METHODS

Estimation Methods. 

Regional regression equations that can be used to 

estimate the magnitude of peak flows with recurrence 

intervals of 1.5 and 2.33 years at ungaged sites were 

developed during this study. Equations for estimating 

peak flows with a recurrence interval of 2 years that 

were developed by Berenbrock (2002) also are 

included for comparison.

Regression techniques were used to define a set of 

predictive equations that related peak flows with recurTable 2. Description of selected basin and climatic characteristics used in the final predictive equations

[Multiply meter by 3.281 to obtain foot; multiply kilometer (km) by 0.6214 to obtain mile]

Characteristic Description

Drainage area (DA)

Drainage area of the basin that contributes surface runoff, in square miles; estimated using 

Arc/Info Grid with 30-meter resolution digital elevation models (DEMs)

Mean basin elevation (E)

Mean elevation of the basin, in feet above sea level; estimated using Arc/Info Grid and 

averaging elevations using 30-meter resolution DEMs

Forested area (F)

Area of the basin containing forest, in percent of total drainage area; estimated using 

Arc/Info Grid with a 37-meter resolution land cover grid

Mean annual precipitation (P)

Mean annual precipitation over the entire drainage area, in inches; estimated using Arc/Info 

Grid with a combination of 500-meter (within Idaho) and 4-km (outside of Idaho) resolution 

precipitation grids

Basin slope (BS)

Average slope of the basin, in percent; estimated using the “average maximum technique” 

in Arc/Info Grid with 30-meter resolution DEMs

North-facing slopes greater than 

30 percent (NF30)

Area of north-facing slopes with slopes greater than 30 percent, in percent of drainage area; 

estimated using the “average maximum technique” in Arc/Info Grid with 30-meter 

resolution DEMs

Slopes greater than 30 percent (S30)

Area with slopes greater than 30 percent, in percent of drainage area; estimated using the 

“average maximum technique” in Arc/Info Grid with 30-meter resolution DEMs
Estimation Methods 7

American

Falls

Reservoir

Bear

Lake

Pend

Oreille

Lake

Coeur

d'Alene

Lake

Idaho

Falls

Lewiston

Salmon

Sandpoint

Coeur

d'Alene

Boise

Twin

Falls

Pocatello

King

Hill

2

5

1

3

4

6

8

7b

7a

0 40 20 60 100 MILES 80

0 40 20 60 100 KILOMETERS 80

Base from U.S. Geological Survey digital data, 1:2,000,000, 1999;

Regions based on Hydrologic Unit Boundaries, 1:2,000,000, 1999;

Transverse Mercator projection

Factor at central meridian: 0.99960

Longitude of central meridian: -114° 00'

Latitude of origin: 42° 00'

False easting (meters): 500,000.0

False northing (meters): 100,000.0

Figure 2. Locations of regions in Idaho used in regional regression analysis.

EXPLANATION

Region and identification number for which specific

 regression equations were developed (see table 3)

Undefined area

2
8 Estimating the Magnitude of Bankfull Flows for Streams in Idaho

rence intervals of 1.5 and 2.33 years to selected basin 

and climatic characteristics for each region in Idaho. 

The initial step involved performing a flood-frequency 

analysis of the peak-flow data for each gaging station 

to determine the peak-flow values for selected recurrence intervals. Next, all the peak-flow, basin, and climatic characteristic data were transformed to base-10 

logarithms to obtain a linear regression model and to 

achieve equal variance about the regression line. Equal 

variance about the regression line satisfies the basic 

assumption that the distribution of errors is normal and 

constant throughout the range (Riggs, 1968). Prior to 

the transformation, a value of 1 was added to data that 

were a measure of percentage (such as forest cover) to 

ensure that no 0 values, which cannot be transformed, 

were present. Also, mean basin elevation (E) values 

were divided by 1,000 to allow for more convenient 

coefficients in the final equations.

Finally, using the same explanatory variables for 

each region as defined by Berenbrock (2002), generalized least-squares (GLS) regression techniques were 

used to calculate the final coefficients and measures of 

accuracy for the regression equations for each region. 

GLS techniques (Stedinger and Tasker, 1985) can 

account for correlation between sites, differences in 

record lengths, and variability of peak flows at gaged 

sites. These factors are accounted for by assigning different weights to each observation of the peak flow on 

the basis of its contribution to the total variance of the 

sample flow statistic. A more detailed discussion of 

how GLS accounts these factors can be found in Berenbrock’s (2002, p. 13) report.

RESULTS

Drainage area (DA), mean basin elevation (E), 

mean annual precipitation (P), forest cover (F), northfacing slopes greater than 30 percent (NF30), basin 

slope (BS), and slopes greater than 30 percent (S30) 

were the explanatory variables that were included in 

regression equations. No equation included more than 

three explanatory variables, and region 7b was the only 

region that included only one explanatory variable 

(DA).

The standard error of the regression model and the 

average standard error of prediction also are listed in 

table 3. The standard error of the regression analysis 

(model) is a measure of how well the regression model 

fits the data used to construct it. This error term also is 

often referred to as the standard error of estimate. The 

average standard error of prediction is the sum of two 

components—model error plus sampling error—

which results from estimating model parameters from 

samples of the population. The model error is a characteristic of the model and is a constant for all sites. The 

sampling error for a given site, however, depends on 

the values of the explanatory variables used to develop 

the peak-flow estimate at that site and, thus, varies 

from site to site. The standard error of prediction provides a better overall measure of a model’s predictive 

reliability than does the model error. A more rigorous 

mathematical description of these errors and how to 

convert them from logarithms (base-10 units) to percent errors is given in a report by Pope and Tasker 

(1999, p. 12).

Standard errors of the model were different for 

each region and for each recurrence interval (table 3). 

The largest and smallest average standard errors of the 

model were +150 and -60.1 percent (region 7b, Q1.5) 

and + 42.9 and -30.0 percent (region 5, Q2.33), respectively. Similarly, the largest and smallest average standard errors of prediction were +165 and -62.2 percent 

(region 7b, Q1.5) and +45.9 and -31.5 percent (region 

5, Q2.33), respectively (table 3). Overall, region 5 

equations would be expected to have the smallest error 

and region 7b equations would be expected to have the 

largest error. The larger errors associated with the 

region 7b equations likely result from use of a small 

number of gaging stations (17) in a region of more 

diverse geology, which can have unknown effects on 

small peak flows.

LIMITATIONS

Limitations. 

The average standard errors of prediction given in 

table 3 represent the general measure of how well the 

regional regression equations will estimate peak flows 

when they are applied to ungaged sites. The accuracy 

of the equations will be reduced if the values of explanatory variables are outside the range of the values used 

to develop the equations. The magnitude of this reduction in accuracy is unknown. Standard errors of prediction vary from site to site, depending on the values of 

the explanatory variables for each site. The standard 

errors of prediction will be smaller for sites where values of the explanatory variables are near the mean of 

their range. If the value of an explanatory variable used 
Limitations 9

Table 3. Predictive regression equations and their accuracy in estimating peak flows for ungaged sites on unregulated and 

undiverted streams in Idaho

[Q, peak flow, in cubic feet per second; DA, drainage area, in square miles; E, mean basin elevation, in feet; F, percentage of 

forest cover in the basin; P, mean annual precipitation, in inches; NF30, percentage of north-facing slopes greater than 30 percent; S30, percentage of slopes greater than 30 percent; and BS, average basin slope, in percent]

1 From Berenbrock (2002, table 7, p. 16 –18). 2 Exponent for (E/1,000) is zero which is equivalent to multiplying by one; (E/1,000)0 = 1. 3 Data were based on 30 gaging stations. The 1.5-year peak flow was below the base flow for gaging station 13301800, and thus was excluded from the 

analysis. 4 Data were based on 27 gaging stations. The 1.5-year peak flow was below the base flow for gaging station 13172200, and thus was excluded from the 

analysis.

Peak-flow regression equations for given recurrence interval

Standard error of model

(percent)

 Standard error

of prediction

(percent)

Region 1 (Data were based on 21 gaging stations)

Q1.5 = 0.748 DA0.802 (E/1,000) 3.28 (F + 1)-0.283

1Q2 = 2.52 DA0.775 (E/1,000) 3.32 (F + 1)-0.504

Q2.33 = 3.90 DA0.764 (E/1,000) 3.32 (F + 1)-0.577

+76.7 to -43.4

+69.0 to -40.8

+65.1 to -39.4

+87.1 to -46.5

+78.4 to -43.9

+73.9 to -42.5

Region 2 (Data were based on 44 gaging stations)

Q1.5 = 0.508 DA0.901 (E/1,000) 0.132 P0.926

2Q2 = 0.742 DA0.897 P0.935

Q2.33 = 0.863 DA0.894 (E/1,000)-0.0587 P0.941

+61.4 to -38.1

+60.2 to -37.6

+59.9 to -37.4

+65.5 to -39.6

+64.2 to -39.1

+63.9 to -39.0

Region 3 (Data were based on 26 gaging stations)

Q1.5 = 12.6 DA0.879 (E/1,000)-0.161

1Q2 = 26.3 DA0.864 (E/1,000)-0.502

Q2.33 = 45.0 DA0.856 (E/1,000)-0.849

+98.1 to -49.5

+78.3 to -43.9

+70.5 to -41.3

+108 to -52.0

+86.4 to -46.4

+77.9 to -43.8

Region 4 (Data were based on 60 gaging stations)

Q1.5 = 9.49 DA0.903 (E/1,000) 0.055

1Q2 = 16.3 DA0.893 (E/1,000)-0.121

Q2.33 = 20.3 DA0.890 (E/1,000)-0.193

+89.2 to -47.2

+80.5 to -44.6

+77.2 to -43.6

+92.6 to -48.1

+83.5 to -45.5

+80.1 to -44.5

Region 5 (Data were based on 46 gaging stations)

Q1.5 = 0.0157 DA1.01 P 2.34 (NF30 + 1)-0.696

1Q2 = 0.0297 DA 0.995 P 2.20 (NF30 + 1)-0.664

Q2.33 = 0.0388 DA0.990 P 2.13 (NF30 + 1)-0.651

+45.6 to -31.3

+43.6 to -30.4

+42.9 to -30.0

+48.9 to -32.9

+46.7 to -31.8

+45.9 to -31.5

Region 6 (Data were based on 31 gaging stations)

3Q1.5 = 1.41·10-4 DA0.904 P3.25

1Q2 = 2.58·10-4 DA0.893 P3.15

Q2.33 = 4.16·10-4 DA0.882 P3.04

+72.4 to -42.0

+71.2 to -41.6

+68.9 to -40.8

+78.1 to -43.8

+76.5 to -43.4

+74.2 to -43.6

Region 7a (Data were based on 28 gaging stations)

4Q1.5 = 0.699 DA0.758 (E/1,000) 1.213

1Q2 = 2.28 DA0.759 (E/1,000) 0.769

Q2.33 = 3.99 DA0.760 (E/1,000) 0.544

+86.9 to -46.5

+74.8 to -42.8

+71.1 to -41.6

+95.6 to -48.9

+82.3 to -45.2

+78.3 to -43.9

Region 7b (Data were based on 17 gaging stations)

Q1.5 = 7.82 DA0.606

1Q2 = 10.2 DA0.611

Q2.33 = 11.4 DA0.613

+150 to -60.1

+131 to -56.6

+123 to -55.1

+165 to -62.2

+143 to -58.8

+134 to -57.3

Region 8 (Data were based on 60 gaging stations)

Q1.5 = 1.23 DA0.958 BS 0.984 (S30 + 1)-0.421

1Q2 = 1.49 DA0.942 BS 1.15 (S30 + 1)-0.563

Q2.33 = 1.59 DA0.936 BS 1.23 (S30 + 1)-0.623

+88.7 to -47.0

+82.9 to -45.3

+81.0 to -44.7

+93.0 to -48.2

+86.9 to -46.5

+84.8 to -45.9
10 Estimating the Magnitude of Bankfull Flows for Streams in Idaho

in the regression equations is near its extreme (maximum or minimum, appendix A), the equations might 

result in unreliable and erroneous estimates. For example, figure 3 shows a “cloud of common values” for the 

two explanatory variables used in regression equations 

for region 3. If the maximum value for drainage area 

and the minimum value for mean basin elevation were 

used, this combination would plot outside the cloud of 

common values and, thus, any equations used might 

result in unreliable estimates.

Generating basin characteristic values using 

source datasets or methods other than those described 

in this study also will result in estimates of unknown 

reliability. The standard errors for each equation are 

applicable only if the datasets presented in table 1 and 

methods described in table 2 are used to obtain the 

required basin characteristics.

The regression equations are not applicable for 

streams that exhibit significant gains and (or) losses as 

a result of flow from springs or seepage through highly 

permeable streambeds. The equations also are not 

applicable for streams affected by irrigation diversions 

or large dams that regulate streamflow. The Boise River 

downstream from Lucky Peak Lake, the Clearwater 

River downstream from Dworshak Reservoir, and the 

entire Snake River in Idaho are examples of stream 

reaches within the study area for which the regional 

regression equations are not applicable.

Finally, the regional regression equations might 

not be reliable for sites in heavily urbanized basins. 

Techniques for estimating peak flows for urban streams 

are presented in a report by Sauer and others (1983).

APPLICATION OF METHODS

Application of Methods. 

In the subsequent paragraphs, specific examples 

are given for calculating peak flows. The first example 

addresses the situation where the drainage area for an 

ungaged site is located completely within one region. 

The second example addresses the situation where the 

drainage area of the specified site encompasses parts of 

two separate regions. It is important to note that the 

coefficients and exponents in the predictive equations 

are rounded to three significant figures. Thus, the final 

peak-flow estimate derived from these equations will 

have an accuracy no greater than to three significant 

figures.

Example 1

A 1.5-year peak-flow estimate for an ungaged site 

in region 5 is needed. The required basin characteristics for region 5 regional regression equations were 

determined to be the following: DA = 480.5 mi2; 

P = 28.33 in.; and NF30 = 21.5 percent. Then

Q1.5 = 0.0157 DA1.01 P2.34 (NF30 + 1)-0.696 (1)

Q1.5 = 0.0157 (480.5) 1.01 (28.33) 2.34 (21.5 + 1)-0.696

Q1.5 = 2,300 ft3/s

On the basis of the range of the average standard 

errors of prediction given in table 3, about 67 percent 

of all estimates at this site will be between 1,580 and 

3,360 ft3/s (-31.5 to +45.9 percent). Put another way, 

there is about a 67-percent certainty that the “true” 

value of Q1.5 is between 1,580 and 3,360 ft3/s. Instead 

of calculating these equations (table 3) manually, a 

computer program explained in the section titled 

“Computer Program for Regional Regression Equations” can be used. This computer program also calculates the error of prediction and the 90-percent confidence interval for individual estimates for each recurrence interval and for each region.

Example 2

A 1.5-year peak-flow estimate is needed for an 

ungaged site in region 4 with a drainage basin encompassing parts of regions 4 and 5. The procedure is 

similar to that given in example 1, except the regional 

regression equations need to be solved for each of the 

associated regions and the results averaged or apporlog (Drainage area)

1.00

0.75

0.50

0.25

0

-1 1 0 2 3 4

log (_______________) 1000 Mean basin elevation

Minimum

covering

ellipsoid

Cloud of

common values

Figure 3. Joint distribution of drainage area and mean basin elevation,

and minimum covering ellipsoid for gaged sites in region 3, Idaho.
Computer Program for Regional Regression Equations 11

tioned according to the fraction of the contributing 

drainage area that is in each region (Sando, 1998). 

The required basin characteristics for region 4 and 5 

equations were determined to be the following: 

DA = 853.0 mi2; P = 35.4 in.; E = 5,125.6 ft; and 

NF30 = 23.6 percent. The part of the drainage area 

in region 4 is 622.0 mi2 and the part in region 5 is 

231.0 mi2.

(1) REGION 4 EQUATION

Q1.5 = 9.49DA0.903 (E/1,000)-0.055 (2)

Q1.5 = 9.49 (853.0)0.903 (5,125.6/1,000)-0.055

Q1.5 = 3,845 ft3/s

(2) REGION 5 EQUATION

Q1.5 = 0.0157 DA1.01 P2.34 (NF30 + 1)-0.696 (3)

Q1.5 = 0.0157 (853.0)1.01 (35.4)2.34 (23.6 + 1)-0.696

Q1.5 = 6,497 ft3/s

(3) AREA-WEIGHTED AVERAGE OF THE 1.5-YEAR PEAK 

FLOWS

Qu=Qxn

DAxn + QxnDAxn (4)

where

 Qu is peak flow for the selected flood frequency for 

the ungaged site,

 Qx is estimated peak flow using the equation for the 

selected region,

DAx is drainage area for the selected region,

DA is total drainage area upstream from the ungaged 

site, and

xn is selected region where n = 1 through 9.

Q1.5 = 3,845 (622.0/853.0) + 6,497 (231.0/853.0)

Q1.5 = 4,560 ft3/s

The regional regression equation computer program also can be used to estimate the peak-flow values 

in this example. The program would need to be executed twice, once for region 4 and once for region 5. 

Then, the average value would need to be estimated 

manually by weighting according to drainage area 

(area-weighted average), as shown in equation 4.

COMPUTER PROGRAM FOR REGIONAL 

REGRESSION EQUATIONS

Computer Program for Regional Regression Equations. 

As part of the previous peak-flow study by Berenbrock (2002), a computer program was adapted to calculate peak flows using regional regression equations. 

The program also calculates the associated site-specific 

errors of prediction for ungaged sites. Regression equations for 1.5 and 2.33 recurrence interval peak flows 

developed during this study (table 3) have been added 

to this program. The computer software package 

includes an executable program file and other supporting files. The software package and instructions for 

downloading, installing, and executing the program 

are available from the Idaho District home page on 

the World Wide Web at http://idaho.usgs.gov/PDF/

wri024170/program.html The executable program 

idregeq.exe will calculate estimated peak flows for the 

regional regression equations presented in table 3 of 

this report and in table 7 of Berenbrock’s (2002) report. 

This program must be executed in a disk operating system (DOS) and the user will be prompted to input data 

for ungaged sites.

The regional regression equations can be calculated manually, but the program allows more convenient and efficient calculation of the errors of prediction. The errors of prediction for ungaged sites are 

calculated by matrix algebra using the weighted matrix 

(XT Λ-1 X)-1 obtained from GLS analysis. Further 

explanation for computing the error of prediction 

is given in a report by Hodgkins (1999), and the 

(XT Λ-1 X)-1 matrices for each recurrence interval 

and region are shown in appendix C of this report 

(back of report) and in table 9 of Berenbrock’s (2002) 

report.

To execute the regional regression program, enter 

the program’s name (idregeq.exe) in a DOS window. 

The program will ask for the name of an output file to 

save program results, an identifier (name and/or number) of the ungaged site, the region number where the 

ungaged site is located, and the value for each explanatory variable used in the region’s regional regression 

equations. Results will be displayed on the screen, and 

all program results will be saved in a single output file 

no matter how many times the program repeats. Results 

from each program execution comprise calculated peak 

flows, site-specific standard errors of prediction (SE), 

and 90-percent confidence intervals for the estimates. 

A more detailed discussion explaining the use of the 

() () DA DA
12 Estimating the Magnitude of Bankfull Flows for Streams in Idaho

regional regression program, how to interpret the 

results, and cautions to be aware of can be found in 

the previous report by Berenbrock (2002, p. 22).

SUMMARY

Recent increased interest in the biological, geomorphic, and environmental effects of varying river 

flows has highlighted the need for information regarding annual peak flows with relatively short recurrence 

intervals. Peak flows with recurrence intervals between 

1.5 and 2.33 years, often referred to as bankfull flows, 

are important for mobilization of streambed sediments 

(cleansing), maintenance of width and depth features 

of the channel, and maintenance of riparian vegetation. 

Currently, this information is available only for gaged 

sites that have at least 10 years of annual peak-flow 

record. Berenbrock (2002) developed regional peakflow regression equations for ungaged streams in 

Idaho; however, the minimum recurrence interval for 

these equations was 2 years and did not include the 

2.33-year recurrence interval. Recognizing the need for 

this additional information, the U.S. Geological Survey, in cooperation with the U.S. Forest Service, conducted a study to develop additional regional regression equations that can be used to estimate bankfull 

flows.

Basin and climatic characteristics, peak-flow 

records, and regional boundaries presented by Berenbrock (2002) were used in this study to develop regional regression equations for estimating peak flows 

with recurrence intervals of 1.5 and 2.33 years. Basin 

and climatic characteristics and peak-flow records were 

included for 333 gaging stations with at least 10 years 

of record through water year 1997. The State was 

divided into 10 regions, which included one undefined 

region in the area of the eastern Snake River Plain.

Because of the need for stable and consistent estimates of peak flows in each region, the same explanatory variables used by Berenbrock (2002) also were 

used in this study for each region. Generalized leastsquares regression techniques then were used to calculate the final coefficients and measures of accuracy for 

the regression equations for each region. Average standard errors of the model ranged from +150 to -60.1 

percent, and average standard errors of prediction 

ranged from +165 to -62.2 percent. As the recurrence 

intervals increased, the magnitude and the range between the errors decreased. The ranges of standard 

errors of the model and standard errors of prediction 

were narrowest for region 5.

The estimating equations might not yield reliable 

results for sites with basin characteristic values outside 

of the range of values used to develop the equations. 

The equations are not applicable for regulated streams 

or those affected by significant gains and (or) losses 

owing to spring flow, seepage through highly permeable streambeds, or irrigation diversions.

A computer program (idregeq.exe) automates the 

calculations required for the regional regression calculations. Results from this program comprise calculated 

peak flows, site-specific standard errors of prediction, 

and the 90-percent confidence intervals for the estimates.

REFERENCES CITED

References Cited. 

Berenbrock, Charles, 2002, Estimating the magnitude 

of peak flows at selected recurrence intervals for 

streams in Idaho: U.S. Geological Survey WaterResources Investigations Report 02–4170, 59 p.

Bond, J.G., 1978, Geologic map of Idaho: Moscow, 

Idaho Bureau of Mines and Geology, 1 sheet, 

scale 1:500,000.

Castro, J.M., and Jackson, P.L., 2001, Bankfull discharge recurrence intervals and regional hydraulic 

geometry relationships: Patterns in the Pacific 

Northwest, USA: Journal of the American Water 

Resources Association, v. 37, no. 5.

Emmett, W.W., 1975, The channels and waters of the 

upper Salmon River area, Idaho: U.S. Geological 

Survey Professional Paper 870 – A, 115 p.

Haan, C.T., 1977, Statistical methods in hydrology: 

Ames, Iowa State University Press, 378 p.

Harenberg, W.A., 1980, Using channel geometry to 

estimate flood flows at ungaged sites in Idaho: 

U.S. Geological Survey Water-Resources Investigations 80–32, 39 p.

Hedman, E.R., and Osterkamp, W.R., 1982, Streamflow characteristics related to channel geometry of 

streams in Western United States: U.S. Geological 

Survey Water-Supply Paper 2193, 17 p.

Hodgkins, Glenn, 1999, Estimating the magnitude of 

peak flows for streams in Maine for selected 

recurrence intervals: U.S. Geological Survey 
References Cited 13

Water-Resources Investigations Report 99–4008, 

45 p.

Hortness, J.E., and Berenbrock, Charles, 2001, Estimating monthly and annual streamflow statistics 

at ungaged sites in Idaho: U.S. Geological Survey 

Water-Resources Investigations Report 01 – 4093, 

36 p.

Leopold, L.B., 1994, A view of the river: Cambridge, 

Mass., Harvard University Press, 298 p.

Molnau, M., 1995, Mean annual precipitation, 1961–

1990, Idaho: Moscow, University of Idaho, Agricultural Engineering Department, State Climate 

Program, scale 1:1,000,000. Also available at 

URL http://snow.ag.uidaho.edu/Climate/

reports.html

National Oceanic and Atmospheric Administration, 

1971, Climates of the states, climate of Idaho, in

Climatography of the United States: Silver Spring, 

Md., no. 60–10, 18 p.

Pope, B.F., and Tasker, G.D., 1999, Estimating the 

magnitude and frequency of floods in rural basins 

of North Carolina: U.S. Geological Survey WaterResources Investigations Report 99 – 4114, 44 p.

Riggs, H.C., 1968, Some statistical tools in hydrology: 

U.S. Geological Survey Techniques of WaterResources Investigations, Book 4, Chap. A1, 39 p.

Ross, S.H., and Savage, C.N., 1967, Idaho earth science: Moscow, Idaho Bureau of Mines and Geology, 285 p.

Sando, S.K., 1998, Techniques for estimating peakflow magnitude and frequency relations for South 

Dakota streams: U.S. Geological Survey WaterResources Investigations Report 98– 4055, 48 p.

Sauer, V.B., Thomas, W.O., Jr., Stricker, V.A., and Wilson, K.V., 1983, Flood characteristics of urban 

watersheds in the United States: U.S. Geological 

Survey Water-Supply Paper 2207, 63 p.

Stedinger, J.R., and Tasker, G.D., 1985, Regional 

hydrologic analysis 1—ordinary, weighted, and 

generalized least squares compared: American 

Geophysical Union, Water Resources Research, 

v. 21, no. 9, p. 1421–1432.
[ This page intentionally left blank ]
Appendix A. Basin and climatic characteristics for streamflow-gaging stations in Idaho and bordering 

States used in regional regression analysis

Appendix B. Peak flows at selected recurrence intervals for streamflow-gaging stations in Idaho and 

bordering States used in regional regression analysis

Appendix C. (XT Λ- 1

 X)- 1 matrices for the T-year (T = 1.5, 2, and 2.33) regional regression equations 

for Idaho
[ This page intentionally left blank ]
ging station name

eek near Leonia, ID 55.3 4,686.9 92.0 48.30 37.1 21.8 69.4

near Bonners Ferry, ID 17.6 3,189.5 77.1 30.05 26.7 28.8 40.8

at Naples, ID 16.0 3,498.6 92.6 31.27 24.3 13.7 27.8

 at Moravia, ID 133.1 3,257.0 72.6 30.36 21.2 9.7 27.0

near Bonners Ferry, ID 26.6 5,194.4 78.7 42.20 40.6 18.3 70.2

eek near Copeland, ID 12.5 4,084.4 94.5 29.15 25.4 5.8 33.2

on Creek near Porthill, ID 29.9 5,347.3 89.5 41.32 46.4 22.7 81.4

k near Porthill, ID 71.1 5,054.2 70.4 46.14 37.0 19.8 62.3

ek near Clark Fork, ID 1.1 4,844.3 96.1 57.78 50.2 9.1 91.6

reek at Clark Fork, ID 115.1 4,648.5 82.4 54.32 43.2 20.3 71.8

near Colburn, ID 121.4 4,280.6 62.6 38.15 32.2 15.9 52.4

ek near Dover, ID 3.1 2,519.6 89.4 30.00 17.9 3.7 11.9

 at outlet of Priest Lake near Coolin, ID 596.6 3,941.3 79.0 38.79 28.9 13.7 46.3

ek near Coolin, ID 10.6 3,258.6 97.6 30.58 35.0 16.6 59.3

eek near Dalkena, WA 68.2 3,622.5 79.6 36.71 30.1 20.0 51.8

near Colville, WA 82.5 3,520.8 89.4 37.74 29.6 13.9 46.2

ver at Kettle Falls, WA 1,011.0 2,904.3 77.0 27.57 22.3 9.0 28.2

ane River at Elk, WA 84.4 2,459.0 65.2 28.22 13.2 4.1 10.4

near Chattaroy, WA 31.0 2,683.7 65.3 27.61 15.3 4.4 9.0

lch near Spokane, WA 4.4 2,245.2 23.9 19.37 9.7 0.6 2.6

ane River at Dartford, WA 634.9 2,397.7 54.6 25.11 12.2 2.8 9.4

ek near Libby, MT 23.7 5,275.3 66.4 52.96 54.1 26.7 82.4

ek near Libby, MT 11.3 5,466.8 76.7 52.64 48.3 30.0 71.2

 at Troy, MT 125.0 4,069.2 87.3 43.94 38.5 21.0 62.8

reek near Yaak, MT 2.4 4,299.5 81.5 31.61 27.4 0.5 37.2

eek near Yaak, MT 5.7 4,627.2 96.9 40.99 33.9 30.1 63.5

uly Creek near Yaak, MT 7.8 4,468.8 96.7 38.86 35.9 26.7 72.6

 Creek at Missoula, MT 79.9 5,708.4 79.3 37.04 36.9 16.7 57.6

k near Hamilton, MT 5.1 7,064.0 51.8 50.32 42.5 19.5 73.4

eek near Corvallis, MT 26.1 6,649.7 50.4 60.87 57.0 32.1 82.8

 near Victor, MT 3.3 6,684.3 73.4 54.70 37.9 22.0 69.2

reek near Stevensville, MT 29.0 6,557.7 60.4 55.58 58.8 28.8 89.6

above Sleeman Creek, near Lolo, MT 249.2 5,272.8 84.7 46.82 35.3 19.1 58.9

c characteristics for streamflow-gaging stations in Idaho and bordering States used in regional regression analysis

ation; F, percentage of forest cover in the basin; P, mean annual precipitation; BS, average basin slope; NF30, percentage of 

ent; S30, percentage of slopes greater than 30 percent; mi2, square miles; ft, feet; in., inches; ID, Idaho; MT, Montana;

ngton; WY, Wyoming; Y.N.P., Yellowstone National Park]

NF30

(percent)

REGION 2

DA

(mi2)

E

(ft)

F

(percent)

BS

(percent)

S30

(percent)

P

(in.)

REGION 1

17
ging station name

Creek near Superior, MT 12.0 4,648.3 88.2 39.04 41.2 27.3 76.2

imber Creek near Haugan, MT 2.6 4,669.2 96.0 48.34 32.8 1.6 54.3

ver near St. Regis, MT 43.6 4,843.4 88.3 44.49 47.2 30.4 84.6

Little Joe Creek near St. Regis, MT 14.4 4,854.3 89.8 42.42 45.6 28.5 83.1

River near Thompson Falls, MT 641.5 4,567.1 85.8 29.56 30.0 15.9 47.0

eek at Thompson Falls, MT 181.5 4,437.3 93.1 43.68 43.5 27.8 79.6

Coeur d’Alene River above Shoshone Creek, 334.0 3,947.0 89.7 48.25 40.8 24.7 75.6

Prichard, ID

Coeur d’Alene River at Enaville, ID 893.7 3,835.9 88.9 45.38 41.9 25.4 77.6

eek at Mullan, ID 3.1 5,212.4 93.2 49.41 46.7 33.1 83.0

k at Wallace, ID 15.0 4,411.0 94.2 41.53 49.6 31.2 88.8

Coeur d’Alene River at Silverton, ID 105.6 4,615.4 89.8 42.52 45.8 27.5 82.3

y Creek near Kellogg, ID 4.5 3,648.3 91.8 40.23 48.0 13.6 89.3

Coeur d’Alene at Elizabeth Park near Kellogg, ID 181.8 4,301.2 88.5 43.34 45.8 27.2 82.5

Coeur d’Alene River near Pinehurst, ID 287.1 4,096.4 83.5 45.09 44.6 26.9 80.7

ene River at Cataldo, ID 1,207.4 3,878.0 87.3 45.01 42.3 25.5 77.8

k near Cataldo, ID 24.8 4,316.0 85.6 54.84 41.8 27.9 81.6

r at Calder, ID 1,024.5 4,545.6 89.8 46.95 41.3 24.7 74.4

River near Santa, ID 272.6 3,592.6 80.6 37.73 25.1 12.5 34.9River at Lotus, ID 434.5 3,465.5 82.2 35.63 23.8 11.4 31.7

ek near St. Maries, ID 7.1 3,308.1 86.4 31.71 30.3 23.5 51.3

reek Tributary at Plummer, ID 2.0 2,966.3 35.9 20.00 15.2 1.5 9.9

ek below North Fork, near Hayden Lake, ID 21.5 3,564.7 95.1 38.75 41.8 25.3 81.2

er near Lowell, ID 1,913.1 5,511.8 82.8 40.58 44.2 24.1 785.6

Creek near Lowell, ID 6.2 3,814.8 93.7 33.22 42.7 39.6 80.2

apoose Creek near Powell Ranger Station, ID 4.5 4,832.2 82.4 47.61 47.2 17.1 87.9

 near Powell Ranger Station, ID 12.2 4,817.1 86.5 48.18 48.7 13.9 88.5

near Lowell, ID 88.3 4,467.2 91.3 46.34 34.7 13.7 55.7

er near Lowell, ID 1,179.4 5,197.2 88.2 46.62 38.5 20.4 63.5

Clearwater River at Bungalow Ranger Station, ID 997.5 4,888.8 82.2 52.47 39.0 22.1 68.1

Clearwater River near Canyon Ranger Station, ID 1,294.2 4,732.9 82.9 51.40 40.4 22.7 69.9

k near Bovill, ID 3.0 3,716.0 86.8 48.07 32.0 27.6 55.6

otlatch River near Bovill, ID 42.7 3,617.2 86.0 42.67 26.3 14.0 36.4

reek Tributary near Latah, WA 2.3 2,693.4 1.1 20.41 11.4 1.7 1.9

Rock Creek Tributary near Fairfield, WA 0.6 2,720.9 7.9 19.91 11.0 2.6 3.2

ek Tributary near Moran, WA 2.0 2,671.8 9.9 18.97 17.2 0.9 2.0

reek at Spokane, WA 674.9 2,647.1 19.4 20.83 10.5 2.3 6.7

(mi2) (ft) (percent) (in.)

REGION 2 -- Continued

REGION 3

(percent) (percent) (percent)

P BS NF30

aracteristics for streamflow-gaging stations in Idaho and bordering States used in regional regression analysis--Continued

DA E F S30

18
ging station name

k below Kearney Gulch near Asotin, WA 170.5 3,752.2 30.5 23.01 35.4 20.7 57.5

Draw near Clarkston, WA 2.0 1,472.6 0.2 11.90 12.7 0.9 3.9

s Creek near Craigmont, ID 8.2 4,040.1 10.7 20.00 8.9 0.2 1.0

ver at Kendrick, ID 453.7 2,969.1 59.8 29.51 18.2 5.5 17.8

ek near Lapwai, ID 268.9 3,149.2 30.7 19.31 18.9 7.7 22.2

at mouth near Clarkston, WA 7.5 1,458.4 0.2 12.08 8.6 0.1 1.4

eek near Central Ferry, WA 67.2 1,898.5 0.0 16.12 14.2 2.3 6.7

River near Starbuck, WA 431.8 2,943.7 23.7 23.98 26.4 11.9 36.0

 Tributary near Polatch, ID 2.9 3,156.8 87.6 28.67 24.3 17.8 27.1 near Potlatch, ID 35.8 2,977.9 46.4 24.92 18.7 5.0 19.8

er near Potlatch, ID 316.0 3,165.1 63.4 30.07 21.2 9.0 25.8er at Colfax, WA 491.7 2,963.6 41.7 26.93 17.7 6.2 17.8

Creek near Moscow, ID 2.4 3,694.1 79.3 29.55 27.4 10.0 41.1

eek at University of Idaho, at Moscow, ID 17.6 2,844.2 12.5 24.53 11.8 1.0 6.0

Palouse River at Pullman, WA 126.9 2,745.5 6.9 23.76 11.9 0.8 3.3

at Creek at Pullman, WA 27.1 2,652.2 0.6 23.23 10.0 0.0 0.0

er below South Fork at Colfax, WA 788.7 2,842.0 27.4 25.33 15.5 4.2 12.1

at Pine City, WA 304.6 2,527.0 1.6 19.00 9.1 0.5 1.2

Creek near Colfax, WA 189.8 2,691.9 0.0 20.97 10.5 0.5 1.1

near Walla Walla, WA 48.5 2,342.9 18.4 30.10 21.4 8.9 23.7

ouchet River near Dayton, WA 106.2 3,820.0 59.8 42.10 38.9 21.0 65.9

ver at Bolles, WA 363.3 2,928.8 31.7 30.50 27.3 13.4 38.5

d Creek at Arrowrock Reservoir, ID 20.8 5,198.1 36.8 19.08 39.8 18.4 70.7

eek near Idaho City, ID 4.8 5,313.2 60.4 22.08 32.9 26.2 57.4

k above Robie Creek, near Arrowrock Dam, ID 397.0 5,070.8 66.3 24.76 31.3 16.7 51.0

k near Arrowrock Dam, ID 16.0 4,680.6 65.0 23.34 39.8 23.4 70.6

k near Arrowrock, ID 424.4 5,024.2 65.0 24.48 31.7 17.0 52.0

ey Creek near Eagle, ID 19.2 4,017.4 8.0 19.42 24.3 9.3 30.2

near Eagle, ID 59.4 3,963.4 11.7 20.39 25.3 8.8 34.3

Malheur River above Beulah Reservoir near 342.5 5,360.8 52.7 23.79 21.6 6.0 23.2

d Creek near Horseshoe Bend, ID 7.0 3,882.5 0.0 17.16 23.9 15.2 26.3

 Creek near Emmett, ID 55.2 4,099.3 4.8 15.88 23.6 7.3 28.0

reek near Emmett, ID 6.2 3,804.1 1.7 12.88 22.9 2.9 21.4

h Weiser River near Tamarack, ID 4.0 4,947.6 81.5 39.75 27.3 3.2 41.5

er at Tamarack, ID 36.6 4,654.2 87.8 34.61 22.3 4.9 27.1

Weiser River near Council, ID 2.3 6,883.5 76.0 40.00 27.0 16.9 36.5

REGION 3 -- Continued

NF30 S30

(mi2) (ft) (percent) (in.) (percent) (percent) (percent)

DA

aracteristics for streamflow-gaging stations in Idaho and bordering States used in regional regression analysis--Continued

E BS F P

REGION 4

19
ging station name

er at Starkey, ID 105.4 4,969.7 88.1 32.34 26.5 10.7 38.0

er near Council, ID 391.9 4,668.2 64.6 29.64 24.2 9.6 32.7

k Weiser River near Mesa, ID 86.1 5,430.2 74.1 34.00 27.4 11.1 38.3

er near Cambridge, ID 596.4 4,636.5 58.2 29.23 23.5 8.7 30.6

near Cambridge, ID 55.3 4,751.8 42.3 22.43 26.4 10.0 37.9

er River near Indian Valley, ID 79.5 5,313.9 67.1 28.23 26.9 11.2 36.5

er near Weiser, ID 1,448.3 4,141.3 32.7 22.23 19.3 6.4 22.1

k near Weiser, ID 56.8 4,846.2 55.4 22.12 31.6 10.6 53.4

near Midvale, ID 4.3 3,233.7 1.1 10.00 15.7 0.5 6.1

Burnt River near Whitney, OR 110.8 4,901.1 81.6 25.11 18.7 4.5 17.7

Burnt River above Barney Creek near Unity, OR 38.9 5,823.5 91.6 28.59 28.2 16.9 42.0

er near Baker, OR 205.2 5,224.6 74.5 24.67 26.5 9.6 40.8

k above Skull Creek near New Bridge, OR 155.7 5,742.6 67.6 47.53 40.5 14.5 63.7

Gulch near Richlavel, OR 6.7 3,581.4 1.4 24.97 25.4 3.1 32.3

lee Creek at Brownlee Ranger Station, ID 7.4 5,913.0 79.2 30.00 44.9 18.5 78.9

River at Brownlee Dam, ID 177.1 5,037.5 62.2 27.53 29.4 14.3 43.3

near Oxbow, OR 298.5 4,287.7 50.2 33.71 27.4 9.8 40.0

er above Gumboot Creek, OR 99.8 6,374.4 64.6 56.25 37.0 21.0 58.7

Creek near Homestead, OR 4.1 5,192.1 75.4 37.19 33.5 18.5 53.2

near Tamarack, ID 15.1 4,742.2 93.0 35.36 27.4 6.7 45.0

on River at Riggins, ID 576.1 5,421.1 71.8 29.61 33.4 15.5 51.5

Skookumchuck Creek near White Bird, ID 15.3 5,031.2 69.3 30.22 30.6 15.8 44.2

er at White Bird, ID 13,418.3 6,753.8 58.3 24.72 37.7 19.1 60.3

k near Grangeville, ID 5.0 3,961.5 33.1 24.22 11.7 8.5 10.9

de River at La Grande, OR 687.4 4,582.0 68.4 27.57 20.3 6.5 21.8

reek near Union, OR 104.1 5,263.8 85.9 39.66 28.6 10.6 40.8

k near Imbler, OR 24.8 5,515.7 77.1 43.58 21.3 6.3 20.8

Creek near Joseph, OR 29.6 7,461.3 47.0 64.64 57.2 22.9 87.0

er near Lostine, OR 71.5 6,893.5 52.1 56.69 49.2 22.1 77.2

near Wallowa, OR 72.1 5,804.7 67.2 44.74 45.6 23.2 75.0

er at Minam, OR 239.2 5,699.5 66.4 46.47 43.5 21.3 70.5

Creek near Elk City, ID 9.1 5,052.5 93.9 36.37 27.9 11.9 42.3

Clearwater River near Elk City, ID 260.8 5,095.1 91.7 35.30 24.1 10.1 28.8

ek near Golden, ID 14.2 4,880.8 94.3 35.81 35.0 9.5 57.9

Clearwater River near Grangeville, ID 843.4 5,116.5 91.8 34.88 29.7 14.0 42.4

Creek near Stites, ID 13.8 3,142.8 57.6 31.08 24.8 16.6 32.0

Clearwater River at Stites, ID 1,168.3 4,546.6 70.5 31.31 25.7 11.9 35.1

River at Kamiah, ID 4,827.4 4,956.2 77.4 38.29 36.2 19.1 58.6

(percent) (percent) (percent)

REGION 4 -- Continued

(mi2) (ft) (percent) (in.)

aracteristics for streamflow-gaging stations in Idaho and bordering States used in regional regression analysis--Continued

DA E F P BS NF30 S30

20
ging station name

near Greer, ID 241.4 3,528.6 84.1 31.53 22.6 8.4 25.5

h Creek at Pierce Ranger Station, ID 6.4 3,539.5 92.2 40.00 17.5 1.1 8.5

near Orofino, ID 5.2 2,955.8 82.6 29.82 18.0 7.2 17.7

River at Orofino, ID 5,507.9 4,736.4 76.6 37.36 34.4 17.7 54.5

Walla Walla River near Milton, OR 61.9 4,273.1 68.3 46.44 46.3 21.9 74.7

Walla Walla River near Milton, OR 42.6 3,640.0 57.2 42.17 42.1 23.9 71.2

near Walla Walla, WA 58.8 3,933.2 68.6 47.97 50.5 28.8 85.5

near Walla Walla, WA 17.1 3,136.4 45.7 40.52 38.3 24.9 68.8

itterroot River near Conner, MT 379.3 6,361.7 78.6 28.42 33.2 18.1 55.1

reek near Hamilton, MT 88.1 6,676.0 86.4 29.55 38.8 22.5 67.5

Bitterroot River near Stevensville, MT 73.0 6,495.2 79.6 30.60 36.5 21.3 62.0

reek near Florence, MT 20.8 5,389.4 62.1 24.51 39.1 24.2 69.3

k near Ketchum, ID 17.3 8,558.1 59.0 34.44 45.9 24.1 72.1

River near Ketchum, ID 137.5 8,204.0 55.8 31.42 40.6 20.8 67.5

ch near Ketchum, ID 10.5 7,373.5 61.5 30.69 42.5 32.9 79.2

ngs Creek at Guyer Hot Springs, near Ketchum, ID 92.6 7,696.0 59.7 35.77 42.6 23.1 77.8

River at Hailey, ID 627.6 7,685.6 43.2 29.35 42.7 22.1 74.0River near Bellevue, ID 786.2 7,347.3 35.5 26.45 40.2 20.8 69.3

near Fairfield, ID 11.8 6,496.3 30.1 19.80 33.4 13.1 62.2

ver near Rocky Bar, ID 22.1 7,274.7 61.3 41.26 32.6 15.7 46.8

ek near Lowman, ID 10.0 5,796.4 52.1 32.14 24.2 7.8 29.9

 near Twin Springs, ID 831.6 6,415.7 50.2 32.42 44.3 23.2 75.1

Boise River near Featherville, ID 641.6 7,025.2 50.6 34.72 42.1 21.5 74.4

 near Bennett, ID 133.6 6,276.7 22.4 22.40 29.3 11.4 47.3

near Anderson Ranch Dam, ID 55.6 6,171.1 59.2 32.16 33.6 14.0 59.3

eek nr Lowman, ID 11.3 6,623.7 49.9 32.33 44.6 14.7 76.2

Payette River at Lowman, ID 449.3 6,824.5 54.3 34.51 46.7 23.2 76.6

 at Lowman, ID 16.5 5,793.4 63.3 31.40 39.5 25.9 72.2

eek near Crimes Pass, ID 10.0 4,779.2 68.8 26.49 46.3 16.1 83.7

 near McCall, ID 3.6 7,255.3 60.3 49.73 22.5 2.5 23.4

Payette River above Jumbo Creek, near McCall, ID 48.7 6,921.9 71.6 37.22 42.1 16.5 67.9

Payette River above Reservoir near McCall, ID 51.7 6,905.7 72.6 36.82 41.0 15.7 65.6

k at Smiths Ferry, ID 8.6 5,514.1 87.7 28.13 19.8 3.6 18.3

ek near Stanley, ID 14.9 8,255.9 57.7 41.59 35.4 22.1 56.9

er near Obsidian, ID 93.9 8,181.1 56.9 34.66 32.8 17.8 53.1

e Creek near Obsidian, ID 35.6 8,161.5 47.1 44.47 37.6 19.0 60.4

k at Stanley, ID 148.9 7,318.8 63.0 23.94 26.1 12.0 37.0

(percent) (percent) (percent)

REGION 4 -- Continued

(mi2) (ft) (percent) (in.)

aracteristics for streamflow-gaging stations in Idaho and bordering States used in regional regression analysis--Continued

DA E F P BS NF30 S30

REGION 5

21
ging station name

er below Valley Creek, at Stanley, ID 510.4 7,786.2 54.9 29.61 30.4 14.6 45.2

k Salmon River near Clayton, ID 187.3 7,992.1 74.5 27.11 41.0 22.7 71.1

er below Yankee Fork, near Clayton, ID 811.1 7,791.6 61.9 27.95 33.6 17.1 53.7

k near Clayton, ID 7.6 7,809.8 78.1 22.53 47.1 16.6 87.1

k Salmon River near Cape Horn, ID 133.8 7,482.6 70.8 28.40 26.6 11.6 40.2

 Creek near Cape Horn, ID 181.7 7,060.3 70.1 30.02 20.2 7.6 24.7

k Salmon River near Yellow Pine, ID 1,038.7 7,189.7 68.9 29.00 38.4 20.3 64.1

ear Big Creek, ID 451.5 6,981.2 78.6 28.71 44.3 24.6 74.0

Salmon River near Knox, ID 91.7 6,631.3 88.7 37.46 31.7 18.3 52.9Salmon River near Krassel Ranger Station, ID 329.3 6,381.8 83.7 33.62 38.0 19.9 63.8

outh Fork Salmon River at Stibnite, ID 19.3 7,724.4 83.7 34.05 35.3 20.4 62.6outh Fork Salmon River near Stibnite, ID 42.9 7,619.9 77.3 30.88 40.8 22.8 72.5outh Fork Salmon River near Yellow Pine, ID 106.9 7,404.6 78.2 30.02 41.7 22.2 73.0

eek at Yellow Pine, ID 216.4 7,135.2 91.7 34.31 28.2 11.3 40.7

er near Burgdorf, ID 100.5 6,963.9 82.7 43.91 24.8 10.7 61.8

Salmon River near Warren, ID 1,164.0 6,696.9 81.2 33.15 37.4 18.4 60.5

er near French Creek, ID 12,228.0 6,913.7 57.4 24.41 37.8 19.3 60.4

Creek below Muddy Creek near Dell, MT 277.0 7,928.2 14.5 18.82 24.1 10.1 31.8

r Creek near Dillon, MT 349.0 6,940.1 28.9 19.22 18.8 5.6 19.6

 above reservoir near Alder, MT 525.5 7,235.2 26.0 22.93 20.1 6.2 20.5

k at Eighteenmile Shearing Corral, near Kilgore, ID 228.4 6,943.3 39.4 26.84 12.8 3.2 12.8

k at Camas, ID 393.9 6,428.8 22.9 21.10 8.6 1.9 7.5

nyon at Spencer, ID 4.0 6,820.0 58.0 17.33 24.8 11.2 33.1

ek at Spencer, ID 123.2 7,027.5 29.9 20.29 19.6 7.9 23.5

ek at Dubois, ID 238.7 6,696.9 24.4 19.42 16.7 5.1 18.8

near Goldburg, ID 16.2 8,734.8 49.7 26.30 32.6 10.9 53.0

eek near Goldburg, ID 74.2 8,380.5 54.1 23.79 32.7 14.2 53.7

Big Lost River at Wild Horse, near Chilly, ID 114.7 8,659.7 58.1 29.80 43.1 22.0 72.1

ver at Howell Ranch, near Chilly, ID 440.4 8,626.3 37.9 26.96 37.8 17.9 60.8

ar Creek above Diversion 3, near Mackay, ID 8.4 9,461.0 21.0 26.61 66.2 17.1 94.2

eek near Clayton, ID 6.1 7,298.7 69.6 20.81 36.6 24.9 61.5

Creek near Clayton, ID 29.5 7,618.4 68.9 22.60 47.7 23.5 85.8

k near Clayton, ID 6.4 7,520.2 66.3 21.74 40.8 21.2 68.3

k below Bruno Creek, near Clayton, ID 71.6 7,729.2 73.0 25.17 36.3 16.3 60.2

er Creek near Clayton, ID 18.3 8,951.8 39.2 31.98 41.3 23.5 64.3

almon River near Clayton, ID 540.2 8,092.5 31.7 26.00 38.2 20.6 62.7

h near Clayton, ID 9.3 7,015.7 9.4 20.99 36.3 16.8 63.5

(percent) (percent) (percent)

REGION 5 -- Continued

(mi2) (ft) (percent) (in.)

aracteristics for streamflow-gaging stations in Idaho and bordering States used in regional regression analysis--Continued

DA E F P BS NF30 S30

REGION 6

22
ging station name

ek near Challis, ID 84.6 7,780.8 62.4 25.59 37.2 18.3 62.0

k above Diversion near May, ID 17.9 8,178.6 45.4 21.25 51.4 26.7 87.5

k near May, ID 20.0 7,926.5 40.7 20.24 47.9 24.1 80.6

er at Salmon, ID 3,746.1 7,397.5 37.3 21.63 33.4 16.7 52.9

r near Lemhi, ID 907.1 7,430.9 24.3 15.62 25.2 11.9 36.9r at Salmon, ID 1,258.0 7,108.2 24.9 15.26 26.4 12.4 39.1

Creek at Gibbonsville, ID 32.5 6,184.7 90.9 25.32 45.2 18.8 86.3

ek near North Fork, ID 20.5 6,707.4 83.9 27.88 41.3 20.7 75.8

Salmon River at North Fork, ID 210.3 6,258.1 77.8 22.87 43.6 23.1 78.0

ek near Shoup, ID 520.7 7,028.2 80.2 24.00 38.6 20.9 62.2

er near Shoup, ID 6,236.7 7,154.3 41.1 20.37 33.3 16.6 52.8

r above Hot Springs Creek near Deeth, NV 389.8 6,589.8 2.3 15.19 17.5 5.3 21.8

k near Paradise Valley, NV 176.2 6,210.4 4.1 21.88 21.0 8.3 26.4

Creek near Mc Dermitt, NV 225.4 5,890.4 1.4 17.00 17.3 4.3 17.2

uinn River near McDermitt, NV 137.9 6,117.4 2.1 22.24 22.2 10.0 28.0

d Blitzen River near Frenchglen, OR 204.7 6,197.6 22.4 29.07 16.2 5.5 15.2

 near Denio, NV 86.7 6,025.9 3.9 16.86 23.1 9.0 31.2

h near Glenns Ferry, ID 0.7 6,089.9 1.3 25.00 30.7 1.7 53.2

on Creek at Stout Crossing near Glenns Ferry, ID 14.2 5,927.8 3.0 23.47 25.2 8.3 36.8

 Creek near Charleston, NV 3.6 7,067.5 1.3 24.49 27.4 6.6 38.9

eek near Rowland, NV 57.6 6,597.0 3.6 19.58 25.7 11.9 35.2

ver at Jarbidge, NV 22.6 8,260.7 37.8 33.79 48.8 22.7 85.8

 near Jarbidge, NV 25.8 7,069.6 13.7 22.42 17.9 7.7 18.8

arbidge River near Three Creek, ID 84.9 7,603.0 24.5 24.77 35.3 16.1 55.2

reek near Jarbidge, NV 3.5 7,028.8 8.4 22.15 16.8 7.1 14.1

reek near Bruneau, ID 243.7 5,170.0 0.0 13.81 10.1 2.3 7.4

Creek near Bruneau, ID 103.4 5,067.4 0.1 14.22 13.2 3.8 11.5

k Tributary near Grasmere, ID 4.5 4,856.2 0.0 10.00 8.0 0.0 0.2

k near Oreana, ID 16.7 3,879.7 2.1 9.79 11.4 4.2 11.0

Reynolds Creek near Reynolds, ID 0.4 6,821.4 40.2 15.00 17.5 6.0 10.4

eynolds Creek near Reynolds, ID 0.2 6,810.7 3.3 25.00 13.3 0.4 0.6

reek at Toolgate Weir near Reynolds, ID 18.7 6,133.6 38.4 21.22 23.0 11.1 24.9

k near Reynolds, ID 12.5 4,883.0 11.1 13.64 21.1 7.7 21.6

ek near Reynolds, ID 13.1 5,001.8 5.5 14.66 26.1 9.7 36.3

reek at Outlet Weir near Reynolds, ID 91.8 5,015.7 12.4 14.83 20.2 7.2 20.7

w Creek Tributary near Marsing, ID 1.8 4,447.6 0.0 10.00 14.3 0.1 8.3

k above Lone Tree Creek, near Jordan Vallley, ID 454.2 5,781.8 38.9 26.15 19.5 5.8 21.8

REGION 6 -- Continued

REGION 7a

S30

(mi2) (ft) (percent) (in.) (percent) (percent) (percent)

E F

aracteristics for streamflow-gaging stations in Idaho and bordering States used in regional regression analysis--Continued

DA P BS NF30

23
ging station name

 near Boise, ID 9.1 3,605.5 0.0 10.23 3.2 0.0 0.0

 at Warmsprings near Vale, OR 535.3 4,133.8 0.8 12.26 17.4 3.7 15.3

d River above Elkhorn Reservoir, near Malad City, 107.1 6,070.2 8.1 13.20 17.7 6.1 17.8

 above Campbell Creek, near Malad City, ID 12.5 5,986.6 9.4 15.08 17.5 4.7 17.9

 above Evans Dividers, near Malad City, ID 34.0 5,883.8 11.1 16.79 20.8 6.6 24.4

 near Park Valley, UT 28.7 6,681.4 0.7 17.00 17.5 3.7 13.7

ek near Herman, ID 26.7 6,477.2 14.9 15.65 9.0 0.6 1.4

ek below Tex Creek near Ririe, ID 431.4 6,422.9 19.2 16.61 13.3 2.8 8.4

ost Creek near McCammon, ID 3.9 6,767.0 41.5 24.88 42.4 21.8 77.0

k near McCammon, ID 367.4 5,587.7 9.0 14.30 16.8 6.4 20.2

Pocatello Creek near Pocatello, ID 14.0 5,756.2 7.7 15.00 21.2 8.0 17.3

eek near Pocatello, ID 407.3 5,545.4 7.3 16.28 16.4 6.9 18.7

ek near Yost, UT 7.9 8,483.9 40.7 23.66 32.3 29.7 51.8

k near Elba, ID 81.2 6,460.8 16.3 17.39 23.5 12.2 33.0

ek near Oakley, ID 52.4 6,339.4 6.2 17.39 28.1 14.4 41.3

 near Rock Creek, ID 81.6 6,350.2 9.4 14.46 31.6 13.8 48.7

reek near Gooding, ID 2.1 5,624.1 0.0 10.00 10.1 0.2 2.0

reek near Garfield Guard Station, ID 12.3 8,395.8 30.8 25.00 47.4 12.7 79.0

 River at Campbell Ranch near Carey, ID 263.4 7,045.9 17.9 22.03 34.9 13.5 57.5

ver near West Yellowstone, MT 434.9 7,900.0 93.9 42.30 11.3 2.4 7.9

below Pole Creek near Frontier, WY 128.6 8,466.6 72.8 31.97 20.4 5.0 19.5

ek above reservoir, below La Chapelle Creek, 58.5 7,971.5 25.4 21.62 9.6 0.3 1.2

Evanston, WY

k near Geneva, ID 45.4 7,243.6 24.8 23.80 26.5 8.1 36.9

near Geneva, ID 38.1 7,448.4 51.3 26.84 27.9 8.3 42.9

k near Wyoming-Idaho State Line, WY 113.8 7,330.7 36.5 25.13 27.4 8.7 40.7

Creek at Irrigators Weir, near Montpelier, ID 50.6 7,360.5 28.5 21.49 32.0 14.1 52.6

n Creek at Bloomington, ID 24.3 7,684.3 37.6 35.10 27.4 15.7 40.5

n Creek near Georgetown, ID 21.9 7,824.2 55.4 26.14 40.6 19.6 70.8

reek near Soda Springs, ID 17.2 7,598.6 75.5 30.73 29.9 15.1 47.3

 at Fivemile Meadows, near Soda Springs, ID 42.5 6,193.0 1.2 18.42 5.1 0.8 3.4

 near Soda Springs, ID 50.9 6,184.9 2.3 18.19 6.1 1.7 5.5

d Creek near Cleveland, ID 62.4 6,720.9 40.4 23.61 20.9 5.8 21.8

 near Mink Creek, ID 68.4 6,534.7 40.0 26.57 28.6 14.9 42.4

k Tributary near Treasureton, ID 4.7 5,837.2 2.2 15.10 17.4 4.8 10.3

near Preston, ID 30.4 7,384.3 53.7 36.05 31.3 13.9 49.4

REGION 8

(in.) (percent)

REGION 7b

(mi2) (ft) (percent) (percent) (percent)

aracteristics for streamflow-gaging stations in Idaho and bordering States used in regional regression analysis--Continued

DA E F P BS NF30 S30

REGION 7a -- Continued

24
ging station name

bove Maple Creek near Franklin, ID 23.2 5,691.9 2.5 14.22 19.8 5.1 18.0

 near Richmond, UT 16.3 7,655.4 62.2 40.94 49.4 30.6 86.6

r at south boundary of Y.N.P., WY 477.4 7,232.2 82.6 47.68 15.9 5.6 14.8

r above Jackson Lake at Flagg Ranch, WY 502.5 8,199.4 82.8 47.42 15.8 5.5 14.7

ek at Moran, WY 162.7 8,134.7 72.4 36.25 20.3 6.1 20.8

Creek Tributary near Moran, WY 2.5 9,690.1 39.2 39.20 22.8 2.8 23.2

k above Lava Creek near Moran, WY 330.1 8,951.0 59.7 37.05 27.0 12.1 33.9k near Moran, WY 370.2 8,815.8 60.2 35.58 26.3 11.5 32.8

e River at Kelly, WY 608.0 8,863.0 62.6 31.62 23.3 8.3 26.9e River at Zenith, WY 627.2 8,792.9 61.5 31.27 22.8 8.1 26.3

k near Jackson, WY 10.7 8,291.9 75.7 34.72 40.3 21.0 71.2

near Bondurant, WY 4.7 8,030.8 94.9 26.96 26.5 7.6 38.8

 Creek near Bondurant, WY 2.8 7,773.4 82.4 25.46 22.8 6.7 25.2

near Bondurant, WY 58.2 8,078.6 71.6 28.09 35.1 17.7 55.5

te Creek at mouth near Bondurant, WY 82.7 8,559.5 54.5 31.02 38.6 16.1 60.8

er near Jackson, WY 561.3 7,961.5 60.9 26.68 30.3 12.7 42.6

near Jackson, WY 46.9 7,459.6 65.6 28.89 32.7 18.4 50.5

k near Jackson, WY 9.0 7,274.0 72.5 23.64 35.6 26.5 64.7

near Alpine, WY 3.9 7,938.7 38.8 30.63 53.6 7.7 88.7

 above reservoir, near Alpine, WY 448.8 8,105.3 72.2 34.91 35.1 16.7 54.5

near Smoot, WY 3.2 7,568.8 68.8 27.87 18.7 3.2 11.9

ear Smoot, WY 48.2 8,010.1 73.4 32.89 28.0 9.3 40.5

d Creek near Smoot, WY 25.7 8,647.5 73.4 39.48 45.1 21.6 81.3

 near Afton, WY 27.7 8,496.0 72.3 39.33 49.3 20.7 84.9

 near Fairview, WY 113.8 8,441.5 34.5 29.44 24.9 9.9 33.2

Creek near Bedford, WY 20.1 8,469.4 54.0 40.81 49.7 20.1 80.7

n near Freedom, WY 3.3 7,087.4 50.8 28.44 27.9 4.5 40.2

ek above reservoir near Alpine, WY 108.1 7,017.8 59.3 26.69 27.5 12.4 40.4

k above reservoir near Alpine, WY 36.5 7,962.0 46.8 31.08 51.5 25.2 83.1

bove reservoir near Irwin, ID 58.5 7,908.8 59.5 34.15 49.8 26.6 81.4

above reservoir near Irwin, ID 78.3 7,187.5 56.1 26.74 38.8 22.6 69.7

eek near Macks Inn, ID 20.9 8,273.4 57.8 30.06 34.6 11.8 49.3

r at Warm River, ID 131.1 6,675.6 69.3 31.78 9.1 1.5 5.5

reek at Warm River, ID 123.7 6,418.3 65.4 35.26 10.6 1.3 5.4

reek near Bechler Ranger Station Y.N.P., ID 85.4 7,912.5 87.7 56.03 6.9 0.2 3.3

near Squirrel, ID 333.6 7,540.3 83.6 52.87 11.0 2.4 7.8

near Chester, ID 512.9 6,974.2 63.3 42.64 9.9 2.1 6.4

Creek near Victor, ID 3.0 8,287.6 77.8 40.89 45.1 37.0 86.6

REGION 8 -- Continued

BS NF30 S30

(mi2) (ft) (percent) (in.) (percent) (percent) (percent)

DA E F P

aracteristics for streamflow-gaging stations in Idaho and bordering States used in regional regression analysis--Continued

25
ging station name

k near Victor, ID 21.8 8,499.6 65.1 54.17 41.7 23.4 68.3

 above South Leigh Creek, near Driggs, ID 341.4 7,302.9 39.7 31.73 23.6 13.3 34.5

 near Tetonia, ID 479.2 7,200.1 38.2 30.33 21.5 11.5 30.0

near Tetonia, ID 17.5 6,551.9 15.7 16.55 9.2 0.4 1.8

 near St. Anthony, ID 874.8 6,920.9 36.1 27.65 19.0 9.1 24.3

k near Henry, ID 14.3 6,881.2 28.3 20.00 18.0 5.3 18.2

(percent) (percent) (percent)

REGION 8 -- Continued

(mi2) (ft) (percent) (in.)

DA E F P BS NF30 S30

26

characteristics for streamflow-gaging stations in Idaho and bordering States used in regional regression analysis--Continued
Number

of years

of known

Period of known peak flows peak

 1,240 1,050 1,330 1929-80 50

 42 29 49 1928-31, 33, 35-38, 74 11

 154 127 167 1961-80 19

 929 773 1,000 1928-74 45

 524 407 583 1928-34, 72-79 15

 338 298 356 1959-81 23

 602 524 637 1928-59 32

 1,930 1,680 2,040 1928-71 43

 42 29 51 1962-81 20

 3,140 2,880 3,260 1989-99 11

 2,580 2,240 2,740 1959-82 24

 36 33 38 1961-71 11

 4,830 4,240 5,100 1913-48 35

 64 51 70 1962-71 18

 506 405 556 1951-97 47

 298 324 328 1940-86 47

 1,150 881 1,280 1923-97 75

 109 99 114 1949-79 31

 137 117 146 1962-75 14

 22 14 27 1950, 62-75 15

 1,290 1,030 1,410 1929-32, 47-97 55

 642 530 696 1933, 37-44, 48, 54, 59-69, 74 23

 226 191 243 1960-92 33

 2,170 1,850 2,330 1945-57, 74, 83-96 28

 27 22 30 1960-74 15

 128 109 137 1960-78 19

 170 141 184 1960-74 15

 1,270 1,100 1,350 1899, 1948, 58-59, 61-64, 66-67 10

 148 123 160 1958-73 16

 627 572 651 1947-69, 72 24

 109 89 119 1958-73 16

 810 701 860 1948-53, 58-73 22

 1,670 1,470 1,760 1951-60, 72, 74 12

 67 50 76 1961-79, 82 20

 39 31 43 1961-75, 79 16

 4,410 3,420 4,900 1911-17, 34, 48, 54, 59-75 27

 180 154 192 1960-74 15

 2,310 1,830 2,550 1948, 56-97 43

 1,590 1,310 1,720 1956-97 42

 6,040 4,840 6,620 1951-97 47

 15,100 12,000 16,600 1940-97 58

 104 88 111 1961-71, 73-80 19

 376 281 425 1968-97 30

 1,660 1,390 1,790 1968-88 21

 73 56 81 1962-71 10

 1,940 1,500 2,160 1987-99 13

 3,660 2,820 4,080 1988-97 10

Appendix B. Peak flows at selected recurrence intervals for streamflow-gaging stations in Idaho and bordering

States used in regional regression analysis

[ND, not determined because peak flow is below base flow]

1.5 1

2 2.33 

Peak flow, in cubic feet per

second, for given recurrence

intervals, in years

REGION 1

REGION 2

27
Number

of years

of known

Period of known peak flows peak

 18,800 15,200 20,600 1911-97 66

 587 476 641 1967-71, 73-81 14

 15,500 12,900 16,800 1911-12, 21 -97 79

 3,060 2,350 3,420 1966-97 32

 4,780 3,750 5,290 1912, 21-66 45

 113 97 121 1961-71, 74 12

 67 56 73 1961-81 21

 319 239 360 1948-97 43

 25,500 22,400 27,000 1911, 30-99 71

 73 57 81 1962-71 10

 78 67 84 1962-71 10

 267 212 294 1962-71 10

 1,710 1,570 1,770 1958-67 10

 18,700 16,400 19,800 1911-12, 30-99 72

 16,300 14,600 17,100 1945-69 25

 18,800 16,300 19,900 1967-97 33

 58 46 64 1960-71, 73-79 19

 644 539 694 1960-71 12

 55 35 66 1961-70, 72-76 16

 25 22 27 1962-76 15

 18 11 22 1954-73 20

 6,510 4,950 7,270 1948-97 50

 405 276 476 1960-82, 91-96 30

 17 6 26 1959-76 18

 47 31 56 1961-65, 67-71, 74-81 18

 6,210 5,130 6,720 1945-71 26

 816 527 977 1975-97 23

 78 55 158 1963-77 15

 651 452 757 1964-78 15

 1,490 1,010 1,750 1915-17, 29-31, 59-90, 95-97 41

 56 46 61 1961-71 11

 799 631 882 1961-71, 74-81 19

 3,580 2,810 3,970 1915-19, 67-97 36

 4,530 3,690 4,930 1956-79 24

 12 10 13 1956-59, 61, 63-64, 66-71 13

 331 261 365 1979-97 19

 1,040 797 1,170 1934-42, 48, 59-81 33

 396 316 435 1935-40, 48, 60-79 27

 5,600 4,420 6,180 1963-95 33

 1,840 1,310 2,120 1962-79 18

 865 646 976 1954-79 26

 522 359 610 1949-53, 55-67 18

 858 657 959 1944-51, 56-68 21

2,190 2,770 3,060 1906-89 84

 91 63 107 1914-18, 39-43, 55 11

 13 10 15 1939-41, 51-71 24

 1,650 1,220 1,860 1951-97 47

intervals, in years

States used in regional regression analysis--Continued

Peak flow, in cubic feet per

second, for given recurrence

1.5 2.33 1

2 

Appendix B. Peak flows at selected recurrence intervals for streamflow-gaging stations in Idaho and bordering

REGION 3

REGION 4

REGION 2--Continued

28
Number

of years

of known

Period of known peak flows peak

 62 47 70 1951-71 21

 1,930 1,510 2,130 1916-54 39

 51 32 62 1955-59, 61-71 16

 94 58 114 1955-68 14

 882 647 1,000 1904-82, 84-94 90

 78 61 87 1961-71, 73-80 19

 938 753 1,030 1957, 62-82, 97 23

 92 55 114 1962-71 10

 39 32 42 1960-77 18

 484 395 527 1937-71, 74-75, 97 38

 55 51 57 1933-35, 37-43 10

 991 793 1,090 1939-49, 56 12

 2,910 2,390 3,160 1937-41, 43-53, 56 17

 817 668 880 1911-13, 20-21, 37-49, 56, 81-82, 85-88, 97 26

 4,770 3,840 5,220 1939-97 59

 266 210 293 1939-62, 97 25

 729 601 791 1923-27, 38-71, 97 40

 9,720 7,600 10,800 1890-91, 1895-1904, 11-14, 53-97 61

 420 337 461 1911-13, 19337-65 32

 67 53 73 1962-71 10

 686 583 734 1967-80 16

 73 59 79 1964-81 18

 708 568 775 1904-16, 20-25, 27-68 61

 2,020 1,760 2,140 1958-97 40

 89 71 98 1964-65, 67-81 17

 91 66 103 1962-71 10

 903 692 1,010 1979-96 18

 2,570 2,010 2,840 1967-96 30

 1,640 1,510 1,700 1945-53  ̊ ̊9

 72 60 78 1965-75 11

 199 167 214 1937-38, 46-59, 62-71 26

 4,900 4,160 5,240 1948, 51-99 48

 138 110 151 1960-71 12

 61,600 52,200 66,000 1894, 1911-99 88

 98 66 115 1961-72 12

 3,260 2,670 3,540 1904-09, 11-15, 18-23, 26-89 81

 749 640 800 1912, 15, 18-19, 26, 97 75

 405 348 431 1938-50 13

 540 459 578 1915, 24-78 56

 1,580 1,420 1,650 1913, 26-91, 95-97 70

 923 801 979 1915, 24-85, 95-97 66

 3,110 2,700 3,290 1913, 66-97 33

 90 71 99 1962-71 10

 1,930 1,660 2,050 1945-74 30

 91 74 98 1962-81 16

 5,000 4,330 5,310 1911-20, 23-63 51

 186 159 198 1961-71 11

 6,560 5,360 7,120 1964-99 36

1.5 

Appendix B. Peak flows at selected recurrence intervals for streamflow-gaging stations in Idaho and bordering

States used in regional regression analysis--Continued

1

2 2.33 

Peak flow, in cubic feet per

second, for given recurrence

intervals, in years

REGION 4--Continued

29
Number

of years

of known

Period of known peak flows peak

 53,000 46,500 55,900 1911-65 55

 2,140 1,710 2,340 1980-99 20

 123 104 133 1962-81 19

 109 74 127 1962-71, 74-81 18

 54,200 47,600 57,100 1931-33, 35-38, 65-99 42

 776 637 844 1903, 07, 09-16, 32-91 70

 489 385 541 1930, 33-69 38

 890 686 994 1914-17, 40-97 62

 317 240 356 1940-42, 44-71 31

 2,340 1,950 2,520 1956-73 18

 659 572 699 1948-54, 58-79 29

 342 275 373 1920, 22-24, 38-73 40

 51 41 55 1958-73 16

 170 139 184 1962-71 10

 905 762 972 1948-71 24

 40 27 47 1962-71 10

 495 427 526 1941-58 18

 2,290 1,800 2,520 1915-97 83

 1,660 1,230 1,880 1912-96 85

 54 42 60 1961-72 11

 332 279 357 1958, 63-71, 73-76, 78-80 17

 102 84 111 1962-71 10

 6,610 5,520 7,120 1871-72, 1911-99 91

 4,400 3,670 4,730 1945-97 53

 655 536 712 1946-56 11

 513 439 548 1945-56 12

 151 123 165 1962-71, 73-80 18

 4,230 3,620 4,510 1941-99 59

 148 116 164 1962-71 10

 35 27 38 1962-71 10

 346 309 363 1962-71 10

 1,340 1,160 1,430 1946-97 52

 1,280 1,080 1,370 1926-45 20

 89 71 97 1962-71, 73-80 18

 143 125 151 1963-71  ̊ ̊9

 517 460 542 1941-52 12

 482 436 503 1941-52 12

 1,000 848 1,070 1911-13, 21-74, 93-99 63

 3,070 2,620 3,270 1926-60, 74 36

 1,470 1,180 1,610 1921-49, 74 29

 4,970 4,180 5,330 1922-91 70

 33 24 38 1963-72 10

 1,660 1,420 1,760 1929-72, 74 45

 2,110 1,800 2,250 1922-60 39

 8,870 7,390 9,570 1973-81  ̊ ̊9

 3,780 3,300 3,990 1945-58 14

 1,030 893 1,090 1929, 31-60 31

 3,330 2,800 3,580 1967-99 29

2.33 

REGION 5

Appendix B. Peak flows at selected recurrence intervals for streamflow-gaging stations in Idaho and bordering

States used in regional regression analysis--Continued

Peak flow, in cubic feet per

REGION 4--Continued

second, for given recurrence

intervals, in years

1.5 1

2 

30
Number

of years

of known

Period of known peak flows peak

 173 143 188 1929-42, 83-97 29

 352 293 380 1929-40 12

 953 823 1,010 1929-43 15

 2,930 2,510 3,130 1929-99 71

 1,400 1,230 1,480 1943-52 10

 11,400 9,880 12,100 1932-48 13

 61,500 55,000 64,300 1945-56 12

 331 262 365 1946-53, 60-91 40

 393 290 444 1921-32, 46-53, 55-58, 60-73, 75 39

 968 822 1,040 1939-97 59

 808 628 897 1937-53, 69-73 22

 454 336 513 1925-97 73

7.3 9.8 11 1962-71 10

 307 233 344 1941-52, 69-93 35

 264 197 297 1921-73, 83-87 57

 135 109 147 1962-71 10

 379 319 407 1961-73 13

 742 611 803 1944-97 54

 2,150 1,780 2,320 1904-14, 20-97 89

 183 163 192 1963-73, 80-84 16

6.7 8.9 10 1963-71, 74 10

 123 86 143 1973-97 25

4.4 7.4 9.2 1971-97 27

 252 178 291 1973-97 25

 206 161 227 1970-86 17

 1,590 1,280 1,730 1929-38, 73-81 19

 85 49 107 1962-71 10

 246 206 265 1944-63 20

 147 123 158 1962-71, 73-76, 78-80 17

ND 21 26 1962-71 10

 8,490 6,930 9,220 1912-16, 20-97 83

 910 702 1,010 1956-97 42

 988 747 1,110 1929-43 15

 97 74 109 1962-71 10

 139 116 150 1962-80 19

 556 476 592 1930-39 10

 1,760 1,440 1,910 1945-77 33

 13,500 11,400 14,400 1945-81 37

 375 273 429 1943-80, 82-97 54

 393 242 483 1922-27, 29-33, 35-97 74

 454 268 564 1949-97 49

 407 307 457 1949-81 33

 1,380 1,040 1,540 1911-16, 18-21, 30, 38-98 72

 111 84 124 1911, 22-23, 25-91 70

3.8 5.7 6.5 1960-71 12

 87 68 97 1961-71, 73-80 19

 23 15 27 1963-79 17

1.5 1

2 2.33 

REGION 7a

Appendix B. Peak flows at selected recurrence intervals for streamflow-gaging stations in Idaho and bordering

States used in regional regression analysis--Continued

Peak flow, in cubic feet per

REGION 6

REGION 5--Continued

second, for given recurrence

intervals, in years

31
Number

of years

of known

Period of known peak flows peak

 188 127 221 1964-78 15

 302 240 333 1963-78 16

 81 55 96 1929-32, 54-71 22

 444 373 478 1963-78 16

8.1 12 14 1939-49, 63, 66-97 44

 165 81 219 1939-49 11

 140 80 177 1961-71, 73-80 19

 23 16 27 1961-71, 74-76, 78-80 17

ND 43 56 1965-78 14

3.8 5.1 5.8 1963-93 31

3.2 4.2 4.6 1966-93 28

 169 125 191 1964-90 27

 85 51 105 1964-93 30

 63 35 81 1963-93 31

 322 184 404 1961-71, 73-80 19

5.4 10 13 1946-52, 55-71 24

 1,960 1,560 2,160 1961-80 19

 59 33 75 1904-06, 10-17, 22-23, 38-62, 64-85 59

 1,470 862 1,820 1963-79 17

 109 74 129 1912-13, 32, 41-69 32

 65 50 73 1939-61 23

 120 100 129 1941-43, 47-52  ̊ ̊9

5.1 10 13 1959-73 15

 208 165 228 1963-71  ̊ ̊9

 787 595 883 1978-79, 86-97 14

 14 11 15 1961-71 11

 298 250 321 1955-97 43

 22 17 25 1961-1971 11

 214 154 246 1985-94 10

 69 56 75 1960-89 30

 176 127 202 1957-67, 71 12

 50 39 56 1911-16, 19-30, 32-97 84

 200 150 224 1910-13, 39, 44-74 36

 23 17 26 1961-76, 78-80 19

 106 90 113 1963-71  ̊ 9

 880 689 974 1920-26, 41-58 25

 1,360 1,210 1,430 1914-17, 19-73, 84-96 70

 771 601 852 1953-98 46

 335 233 390 1958-97 39

 147 110 165 1940-51 12

 165 119 188 1940-51 12

 400 271 469 1950-92 43

 99 82 107 1943-79 37

 150 124 162 1961-86 26

 50 43 53 1940-56 17

 121 103 130 1961-86 26

 73 57 80 1965-86 22

Appendix B. Peak flows at selected recurrence intervals for streamflow-gaging stations in Idaho and bordering

REGION 8

REGION 7a--Continued

States used in regional regression analysis--Continued

Peak flow, in cubic feet per

second, for given recurrence

intervals, in years

1.5 1

2 2.33 

REGION 7b

32
Number

of years

of known

Period of known peak flows peak

 187 161 198 1913-26 14

 372 300 407 1939-86 48

 355 334 364 1943-52 10

 45 30 53 1961-80 20

 591 536 616 1947-52, 56-62, 70-84, 86 37

 558 527 571 1940-1952 13

 200 187 206 1944-52, 71-72, 79-89 22

 5,360 4,960 5,530 1914-15, 19-25 9

 8,030 6,490 8,760 1984-97 14

 2,510 2,120 2,680 1918, 45-97 52

 41 35 44 1964-74 11

 4,080 3,690 4,250 1966-97 32

 4,090 3,800 4,210 1918, 45-60 17

 3,180 2,900 3,310 1918, 45-58 15

 2,700 2,240 2,920 1917, 88-97 12

 79 62 86 1945-97 53

 13 12 14 1950-92 43

 15 13 16 1943-79 37

 612 520 655 1961-86 26

 292 213 333 1982-92 11

 3,750 3,320 3,950 1918, 45-58 15

 391 341 413 1965-86 22

 128 111 135 1914-17, 19-73, 84-96 70

 21 18 23 1953-98 46

 3,290 2,800 3,510 1918, 37-38, 54-97 47

 47 36 52 1940-51 12

 250 213 266 1932-57 25

 242 210 256 1933-57 24

 505 453 528 1943-80 38

 227 197 241 1946-49, 62-67 10

 263 236 274 1932-43 12

 44 32 51 1961-71 11

 924 800 980 1954-71, 74 19

 200 175 211 1918, 54-71 19

 464 407 490 1918, 1954-71 19

 517 447 549 1918, 34-36, 54-71 22

 258 227 272 1963-80 18

 461 392 493 1912-14, 18-32 18

 605 500 653 1912-14, 18-32 18

 502 429 535 1984-97 14

 3,550 3,150 3,730 1905-09, 18-97 85

 3,540 3,120 3,730 1920-97 78

 38 33 41 1962-71 10

 280 253 292 1962-71 10

 1,460 1,260 1,550 1962-97 36

 1,270 1,070 1,350 1930-32, 34, 40-57 22

 84 47 107 1962-80 19

 3,380 2,890 3,610 1890-93, 1903-09, 20-97 88

 283 206 322 1963-71, 74-80 16

 From Berenbrock (2002, table 7, p. 16-18).

Appendix B. Peak flows at selected recurrence intervals for streamflow-gaging stations in Idaho and bordering

States used in regional regression analysis--Continued

REGION 8--Continued

Peak flow, in cubic feet per

second, for given recurrence

intervals, in years

1.5 1

2 2.33 

1

33
34

Appendix C. (XT Λ-1 X)-1 matrices for the T-year (T = 1.5, 2, and 2.33) regional regression equations for 

Idaho

[Some numbers are in scientific notation; DA, Drainage area; E, mean basin elevation; F, percentage of forest cover in the basin;

P, mean annual precipitation; NF30, percentage of north-facing slopes greater than 30 percent; BS, average basin slope; and S30, percentage of 

slopes greater than 30 percent]

(XT

 

Λ-1 X)

-1 matrix

REGION 1

1.5-year recurrence interval

 CONSTANT DA E F 

 0.81690 -0.15522E-01 0.89824E-01 -0.44334 

 -0.15522E-01 0.58304E-02 0.23381E-02 0.23234E-02

 0.89824E-01 0.23381E-02 0.30674 -0.14033 

 -0.44334 0.23234E-02 -0.14033 0.27410 

2-year recurrence interval

 CONSTANT DA E F 

 0.70947 -0.13937E-01 0.74767E-01 -0.38336 

 -0.13937E-01 0.50165E-02 0.20736E-02 0.22620E-02

 0.74767E-01 0.20736E-02 0.26166 -0.11881 

 -0.38336 0.22620E-02 -0.11881 0.23590 

2.33-year recurrence interval

 CONSTANT DA E F 

 0.66262 -0.13362E-01 0.66824E-01 -0.35660 

 -0.13362E-01 0.46295E-02 0.19920E-02 0.23076E-02

 0.66824E-01 0.19920E-02 0.23977 -0.10808 

 -0.35660 0.23076E-02 -0.10808 0.21843 

REGION 2

1.5-year recurrence interval

 CONSTANT DA E P 

 0.41277 0.10637E-02 0.75114E-01 -0.28223 

 0.10637E-02 0.13788E-02 0.31021E-02 -0.33895E-02

 0.75114E-01 0.31021E-02 0.26254 -0.15515 

 -0.28223 -0.33895E-02 -0.15515 0.23833 

2-year recurrence interval

 CONSTANT DA E P 

 0.39901 0.98739E-03 0.72212E-01 -0.27258 

 0.98739E-03 0.13325E-02 0.30477E-02 -0.32694E-02

 0.72212E-01 0.30477E-02 0.25340 -0.14973 

 -0.27258 -0.32694E-02 -0.14973 0.23015 

2.33-year recurrence interval

 CONSTANT DA E P 

 0.39651 0.94449E-03 0.71247E-01 -0.27060 

 0.94449E-03 0.13240E-02 0.30554E-02 -0.32384E-02

 0.71247E-01 0.30554E-02 0.25199 -0.14864 

 -0.27060 -0.32384E-02 -0.14864 0.22848 

REGION 3

1.5-year recurrence interval

 CONSTANT DA E 

 0.97938E-01 -0.54908E-02 -0.17862 

 -0.54908E-02 0.43918E-02 -0.54067E-02

 -0.17862 -0.54067E-02 0.40646 

2-year recurrence interval

 CONSTANT DA E 

 0.72994E-01 -0.40438E-02 -0.13200 

 -0.40438E-02 0.31745E-02 -0.38284E-02

 -0.13200 -0.38284E-02 0.29798 
35

Appendix C. (XT Λ-1 X)-1 matrices for the T-year (T = 1.5, 2, and 2.33) regional regression equations for 

Idaho—Continued 

(XT

 

Λ-1 X)

-1 matrix

 

REGION 3 – Continued 

2.33-year recurrence interval

 CONSTANT DA E 

 0.64627E-01 -0.35647E-02 -0.11614 

 -0.35647E-02 0.27364E-02 -0.31926E-02

 -0.11614 -0.31926E-02 0.26035 

REGION 4

1.5-year recurrence interval

 CONSTANT DA E 

 0.88119E-01 -0.81369E-03 -0.12446 

 -0.81369E-03 0.19964E-02 -0.43262E-02

 -0.12446 -0.43262E-02 0.19417 

2-year recurrence interval

 CONSTANT DA E 

 0.76068E-01 -0.75066E-03 -0.10719 

 -0.75066E-03 0.17192E-02 -0.36670E-02

 -0.10719 -0.36670E-02 0.16698 

2.33-year recurrence interval

 CONSTANT DA E 

 0.71908E-01 -0.73895E-03 -0.10117 

 -0.73895E-03 0.16203E-02 -0.34200E-02

 -0.10117 -0.34200E-02 0.15742 

REGION 5

1.5-year recurrence interval

 CONSTANT DA P NF30 

 0.30088 -0.68338E-02 -0.17085 -0.22671E-01

 -0.68338E-02 0.17285E-02 0.37080E-02 -0.19055E-02

 -0.17085 0.37080E-02 0.10729 0.12335E-02

 -0.22671E-01 -0.19055E-02 0.12335E-02 0.19957E-01

2-year recurrence interval

 CONSTANT DA P NF30 

 0.27767 -0.62717E-02 -0.15755 -0.21191E-01

 -0.62717E-02 0.15842E-02 0.33900E-02 -0.17302E-02

 -0.15755 0.33900E-02 0.98903E-01 0.12712E-02

 -0.21191E-01 -0.17302E-02 0.12712E-02 0.18410E-01

2.33-year recurrence interval

 CONSTANT DA P NF30 

 0.27113 -0.61759E-02 -0.15377 -0.20656E-01

 -0.61759E-02 0.15500E-02 0.33331E-02 -0.16851E-02

 -0.15377 0.33331E-02 0.96490E-01 0.12389E-02

 -0.20656E-01 -0.16851E-02 0.12389E-02 0.17942E-01

REGION 6

1.5-year recurrence interval

 CONSTANT DA P 

 0.77207 -0.21098E-01 -0.53388 

 -0.21098E-01 0.34260E-02 0.10154E-01

 -0.53388 0.10154E-01 0.37746 

2-year recurrence interval

 CONSTANT DA P 

 0.73182 -0.19589E-01 -0.50715 

 -0.19589E-01 0.32568E-02 0.93413E-02

 -0.50715 0.93413E-02 0.35932 
36

Appendix C. (XT Λ-1 X)-1 matrices for the T-year (T = 1.5, 2, and 2.33) regional regression equations for 

Idaho—Continued 

(XT

 

Λ-1 X)

-1 matrix

 

REGION 6 – Continued 

2.33-year recurrence interval

 CONSTANT DA P 

 0.69863 -0.18807E-01 -0.48392 

 -0.18807E-01 0.31155E-02 0.89783E-02

 -0.48392 0.89783E-02 0.34272 

REGION 7a

1.5-year recurrence interval

 CONSTANT DA E 

 0.36664 -0.12482E-01 -0.44083 

 -0.12482E-01 0.36699E-02 0.87481E-02

 -0.44083 0.87481E-02 0.54890 

2-year recurrence interval

 CONSTANT DA E 

 0.27535 -0.10043E-01 -0.32931 

 -0.10043E-01 0.29644E-02 0.69738E-02

 -0.32931 0.69738E-02 0.40923 

2.33-year recurrence interval

 CONSTANT DA E 

 0.26053 -0.95514E-02 -0.31118 

 -0.95514E-02 0.27689E-02 0.67052E-02

 -0.31118 0.67052E-02 0.38613 

REGION 7b

1.5-year recurrence interval

 CONSTANT DA 

 0.63666E-01 -0.33265E-01

 -0.33265E-01 0.20590E-01

2-year recurrence interval

 CONSTANT DA 

 0.52959E-01 -0.27639E-01

 -0.27639E-01 0.17103E-01

2.33-year recurrence interval

 CONSTANT DA 

 0.48930E-01 -0.25516E-01

 -0.25516E-01 0.15787E-01

REGION 8

1.5-year recurrence interval

 CONSTANT DA BS S30 

 0.15000 -0.11962E-01 -0.19540 0.96505E-01

 -0.11962E-01 0.32557E-02 0.83896E-02 -0.36495E-02

 -0.19540 0.83896E-02 0.33323 -0.18960 

 0.96505E-01 -0.36495E-02 -0.18960 0.11656 

2-year recurrence interval

 CONSTANT DA BS S30 

 0.13509 -0.10754E-01 -0.17622 0.87079E-01

 -0.10754E-01 0.29289E-02 0.75498E-02 -0.32850E-02

 -0.17622 0.75498E-02 0.30082 -0.17123 

 0.87079E-01 -0.32850E-02 -0.17123 0.10528 

2.33-year recurrence interval

 CONSTANT DA BS S30 

 0.13042 -0.10377E-01 -0.17020 0.84129E-01

 -0.10377E-01 0.28276E-02 0.72849E-02 -0.31706E-02

 -0.17020 0.72849E-02 0.29073 -0.16553 

 0.84129E-01 -0.31706E-02 -0.16553 0.10180 
U.S. Geological Survey Water-Resources Investigations Report 03–4261

Hortness and Berenbrock— Estimating the Magnitude of Bankfull Flows for Streams in Idaho—