Spine. Width varies. Printer is to 

determine final width and adjust spine and co
COVER: Arkansas River near Buena Vista, Colorado.

Photograph by Michael Lewis, U.S. Geological Survey.
Regional Regression Equations 

for Estimation of Natural Streamflow 

Statistics in Colorado

By Joseph P. Capesius and Verlin C. Stephens

Prepared in cooperation with the Colorado Water Conservation Board and the

Colorado Department of Transportation

Scientific Investigations Report 2009–5136

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Capesius, J.P., and Stephens, V.C., 2009, Regional regression equations for estimation of natural streamflow statistics 

in Colorado: U.S. Geological Survey Scientific Investigations Report 2009–5136, 46 p.

Library of Congress Cataloging-in-Publication Data

Capesius, Joseph P.

Regional regression equations for estimation of natural streamflow

statistics in Colorado / by Joseph P. Capesius and Verlin C. Stephens

 p. cm. -- (Scientific investigations report ; 2009-5136)

“Prepared in cooperation with the Colorado Water Conservation Board and the

Colorado Department of Transportation.”

Includes bibliographic references.

ISBN 978-1-4113-2562-3

1. Stream measurements--Colorado. 2. Streamflow--Colorado. 3. Regression 

analysis. I. Stephens, Verlin C. II. Geological Survey (U.S.) III. Colorado

Water Conservation Board. IV. Colorado Dept. of Transportation. V. Title. VI.

Series: Scientific investigations report ; 2009-5136.

GB1225.C6C36 2009

551.48’309788021--dc22

2009039729
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................1

Description of Study Area ...................................................................................................................3

Previous Studies ...................................................................................................................................3

Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado.........4

Definition of Hydrologic Regions of Colorado..................................................................................4

Selection of Stations ............................................................................................................................4

Selection of Stations for Peak-Streamflow Statistics ...........................................................4

Selection of Stations for Other Streamflow Statistics.........................................................15

Computation of Streamflow Statistics and Basin and Climatic Characteristics......................15

Peak-Streamflow Frequency ...................................................................................................15

Annual- and Monthly-Mean Streamflow and Flow-Duration Curves ...............................15

Minimum and Maximum 7-Day Streamflow..........................................................................15

Basin and Climatic Characteristics ........................................................................................16

Computation of Regional Regression Equations ...........................................................................17

Generalized Least-Squares Regression ................................................................................17

Weighted Least-Squares Regression.....................................................................................18

Discussion of Selection of Variables......................................................................................18

Application and Limitations of Regional Regression Equations .................................................19

Summary........................................................................................................................................................28

Acknowledgments.......................................................................................................................................29

Selected References...................................................................................................................................29

Supplemental Information..........................................................................................................................33

Figures

1. Boundaries of hydrologic regions and locations of streamflow gaging 

stations in Colorado and adjacent States.................................................................................2

2. Summary of variables and regression diagnostics for regional equations ......................18

3. Regional regression equations for the Mountain hydrologic region.................................20

4. Regional regression equations for the Northwest hydrologic region ...............................22

5. Regional regression equations for the Rio Grande hydrologic region ..............................24

6. Regional regression equations for the Southwest hydrologic region...............................26

7. Regional regression equations for the Plains hydrologic region .......................................28

Tables

1. Drainage-basin and climatic characteristics at streamflow-gaging 

stations used for regional regression analysis........................................................................5

2. Basin and climatic characteristics evaluated for use in regional 

regression equations .................................................................................................................16

3. Sources of data used to compute basin and climatic characteristics..............................17

4. Streamflow-gaging stations used in the development of the regional 

streamflow regression equations ............................................................................................35
iv

Conversion Factors and Datum

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

acre-foot per day (acre-ft/d) 0.01427 cubic meter per second (m3/s)

acre-foot per year (acre-ft/yr) 1,233 cubic meter per year (m3/yr)

acre-foot per year (acre-ft/yr) 0.001233 cubic hectometer per year (hm3/yr)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum.
Abstract

The U.S. Geological Survey (USGS), in cooperation 

with the Colorado Water Conservation Board and the Colorado 

Department of Transportation, developed regional regression 

equations for estimation of various streamflow statistics that are 

representative of natural streamflow conditions at ungaged sites 

in Colorado. The equations define the statistical relations between 

streamflow statistics (response variables) and basin and climatic 

characteristics (predictor variables). The equations were developed using generalized least-squares and weighted least-squares 

multilinear regression reliant on logarithmic variable transformation. Streamflow statistics were derived from at least 10 years 

of streamflow data through about 2007 from selected USGS 

streamflow-gaging stations in the study area that are representative of natural-flow conditions. Basin and climatic characteristics 

used for equation development are drainage area, mean watershed elevation, mean watershed slope, percentage of drainage 

area above 7,500 feet of elevation, mean annual precipitation, 

and 6-hour, 100-year precipitation. For each of five hydrologic 

regions in Colorado, peak-streamflow equations that are based on 

peak-streamflow data from selected stations are presented for the 

2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year instantaneous-peak 

streamflows. For four of the five hydrologic regions, equations 

based on daily-mean streamflow data from selected stations are 

presented for 7-day minimum 2-, 10-, and 50-year streamflows 

and for 7-day maximum 2-, 10-, and 50-year streamflows. Other 

equations presented for the same four hydrologic regions include 

those for estimation of annual- and monthly-mean streamflow 

and streamflow-duration statistics for exceedances of 10, 25, 50, 

75, and 90 percent. All equations are reported along with salient 

diagnostic statistics, ranges of basin and climatic characteristics 

on which each equation is based, and commentary of potential 

bias, which is not otherwise removed by log-transformation of 

the variables of the equations from interpretation of residual plots. 

The predictor-variable ranges can be used to assess equation 

applicability for ungaged sites in Colorado.

Introduction

The U.S. Geological Survey (USGS), in cooperation with the Colorado Water Conservation Board and the 

Colorado Department of Transportation, developed regional 

regression equations for estimation of various streamflow 

statistics that are representative of natural streamflow conditions in Colorado. Accurate estimates of various streamflow 

statistics are important for water-resource management, 

stream-related structural design, stream-hazard identification, and water-quality management. Streamflow statistics 

routinely are needed for ungaged watersheds that lack nearby 

streamflow-gaging stations (stations) from which streamflow 

statistics could be directly computed. Regional regression 

equations are a common tool used to estimate streamflow 

statistics at ungaged sites across the Nation and Colorado.

Regional regression equations are based on statistical 

relations between (1) streamflow statistics of interest computed 

from applicable records of the stations and (2) basin and climatic 

characteristics, for which data are typically readily available. 

The use of regional equations, along with expressions of predictive uncertainty, generally represents a reliable and cost-effective 

means for estimating streamflow statistics at ungaged sites.

Purpose and Scope

The purpose of this report is to present regional regression 

equations, by hydrologic region, for estimation of streamflow 

statistics for naturally flowing streams in Colorado (fig. 1). The 

equations were developed using the statistical relations between 

streamflow statistics (response variables) and basin and climatic 

characteristics (predictor variables). The current (2009) study 

updates or refines the equations provided by Kircher and others 

(1985) and Vaill (1999) and uses streamflow data collected after 

those studies were completed. Each of these previous studies is 

described in the section “Previous Studies.”

For each of five hydrologic regions in Colorado, peakstreamflow equations based on peak-streamflow data from 

selected stations are presented for the 2-, 5-, 10-, 25-, 50-, 

100-, 200-, and 500-year instantaneous-peak streamflows (peak 

streamflow). For four of the five hydrologic regions, minimum 

and maximum 7-day streamflow (7-day, T-year) equations 

based on daily-mean streamflow data from selected stations are 

presented for 7-day minimum 2-, 10-, and 50-year streamflows 

as well as for 7-day maximum 2-, 10-, and 50-year streamflows. 

Other equations presented for the same four hydrologic regions 

include those for estimation of annual- and monthly-mean 

streamflow and streamflow-duration statistics for exceedances 

of 10, 25, 50, 75, and 90 percent. The streamflow-duration 

statistics collectively are referred to as the “flow-duration 

curve.” The flow-duration values, presented in this report as 

Regional Regression Equations for Estimation of 

Natural Streamflow Statistics in Colorado

By Joseph P. Capesius and Verlin C. Stephens
2 Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado

Figure 1. Boundaries of hydrologic regions and locations of streamflow gaging stations in Colorado and adjacent States.

Q10th, Q25th, Q50th, Q75th, and Q90th, indicate the percentage 

of days that a given daily-mean streamflow is exceeded. For 

example, a 10-percent flow-duration value (Q10th) is calculated 

as the daily-mean streamflow at a given station that is exceeded 

10 percent of the time or 10 percent of the days. Finally, this 

report also describes some limitations associated with the equations, which includes an assessment of prediction errors and 

assessment of equation applicability for ungaged sites.

The study area of equation applicability is limited to 

Colorado, even though the study area was extended to include 

stations within a 50-mile boundary or buffer surrounding 

Colorado. The study area was extended 50 miles beyond 

the Colorado for the sole purpose of equation development.

The regional equations for peak-streamflow estimation were 

developed using annual peak-streamflow data collected through 

water year 2006 (October 1, 2005, through September 30, 2006). 

The remaining equations, with the exception of the 7-day, T-year 

minimum streamflow equations, were developed with data 

through water year 2007. The 7-day, T-year minimum streamflow 

equations were developed with data collected through climate 

year 2007 (April 1, 2006, through March 31, 2007). The choice of 

climate year in lieu of water year explicitly was made because the 

climate year designation splits the daily-mean streamflow record 

at a time (spring) in which streamflows for a given station generally are larger than at the water year (autumn) or even calendar 

year transition.

36°

38°

40°

110° 108° 106° 104° 102°

COLORADO

WYOMING

NEBRASKA

KANSAS

UTAH

ARIZONA

NEW MEXICO

TEXAS

OKLAHOMA

Denver

White River

Green River

Colorado River

Colorado River

San Juan River

Ani mas River

Ladder C reek

Republican River

Arikaree River

Arkansas River

Platte River

Cache La Poudre River

Huerfano River

North Platte River

Gunnison River

North Platte River

Purgatoire River

Rio Grande

S a n JuanR

PiedroRiver

Yampa River

South

Platte River

Green

River

Dolores River

Mountain

Region Plains

Region

Northwest

Region

Rio Grande

Region

Southwest

Region

Base from U.S. Geological Survey digital data, 2005, 1:2,000,000

Colorado State Plane Central projection

0 50 100 MILES

0 50 100 KILOMETERS

EXPLANATION

Streamflow-gaging station

Continental Divide

Hydrologic regional boundaries
Introduction 3

The study is limited by type of statistical procedures 

used to define the relation between streamflow statistics 

and basin and climate characteristics. These procedures 

included generalized least-square and weighted least-square, 

multilinear regression based on base-10 logarithmic transformations of all included variables. The authors recognize that 

other transformations of variables could be used.

The study was limited to the use of several selected 

basin and climatic characteristics described in the section 

“Basin and Climatic Characteristics.” These characteristics are drainage area; mean watershed slope; mean annual 

precipitation; mean watershed elevation; 6-hour, 100-year 

precipitation; and percentage of drainage area above 

7,500 feet of elevation.

The equations reported here, as well as equations in all 

the studies referenced, are or were scoped to estimate natural 

streamflow statistics for ungaged sites. To clarify, the equations 

are based on analysis of streamflow data representing streamflow conditions relatively unaffected by anthropogenic influences such as regulation and diversion or return flows such as 

from a municipality or mining operation, or urban development 

in a basin. Kircher and others (1985) provide the most quantitative description of natural streamflow. Those authors defined 

natural streamflow as streamflow from drainage basins relatively unaffected by urban development or water-management 

activities such as substantial reservoir storage, streamflow 

diversions, or return flows of previously diverted streamflow. 

Further, those authors defined natural streamflow as streamflow 

having less than about 10 percent of the mean-annual streamflow volume at the station affected by anthropogenic activity. 

The definition by Kircher and others (1985) was used in the 

current (2009) study. Also, the selection of stations used for the 

current (2009) study was influenced by those stations selected 

by Kircher and others (1985), Vaill (1999), and the authors’ 

general knowledge of hydrologic systems in Colorado.

Description of Study Area

Colorado has a varied and diverse terrain and climate. 

The State lies within the headwaters of the major river 

basins of the Colorado River, Missouri River, Rio Grande, 

and Arkansas River. The geographic variation in Colorado 

is well characterized by three major physiographic provinces, 

which trend north to south across the State (Fenneman, 1931).

Encompassing about 40 percent of Colorado on the east, 

the Great Plains Province is characterized by rolling grasslands 

broken by occasional hills and bluffs and shallow river valleys. Elevations in the Great Plains range from near 3,500 feet 

at the eastern border of Colorado to about 6,000 feet in the 

foothills of the Rocky Mountains at the western edge of the 

province. The Great Plains have low relative humidity, plentiful sunshine, limited precipitation, substantial and persistent 

wind, and substantial diurnal variability in air temperatures. 

Annual temperature extremes generally range from –10 to 

–15o Fahrenheit in winter to about 100o Fahrenheit in summer. Most precipitation occurs as rain during April through 

September, largely in the form of thunderstorms. Mean annual 

precipitation in the Great Plains ranges from 9 to 18 inches per 

year (Colorado State University, 2008). Precipitation tends to 

decrease from the eastern border of the Great Plains to a minimum near the foothills at which point it increases rapidly with 

the increase in elevation of the foothills (Western Regional 

Climate Center, 2008).

Encompassing central Colorado from north to south, 

the Southern Rocky Mountains Province lies west of the 

Great Plains and is characterized by several mountain ranges. 

Elevations range from about 6,000 feet to more than 14,000 feet. 

The mountain ranges are characteristically separated by steep 

valleys and high intermontane parks. The climate of the Southern 

Rocky Mountains is strongly affected by differences in elevation. Wide variations occur within short distances. Similarly, 

temperature varies with elevation and decreases with increased 

elevation (Colorado Geological Survey, 2003; Colorado State 

University, 2008; Western Regional Climate Center, 2008). Mean 

annual precipitation is dominated by snowfall and increases with 

elevation from about 10 inches per year to more than 60 inches 

per year. Snowfall tends to be associated with eastern-moving 

winter storms, which originate from the Pacific Ocean and tend to 

produce more snow on the windward side of the mountain ranges 

than on the leeward.

Encompassing much of the western quarter of Colorado 

from north to south, the Colorado Plateaus Province is located 

between the Utah border to the west and the Southern Rocky 

Mountains to the east. The terrain is characterized by mesas 

and plateaus separated by steep and rugged canyons. Like 

the Great Plains, the Colorado Plateaus Province has low 

relative humidity, plentiful sunshine, limited precipitation, and 

substantial and persistent wind. Climatic variability is extreme 

over relatively short distances because of the microclimates 

created by the highly irregular landscape. Below 9,000 feet 

in elevation, mean annual precipitation ranges from 9 to 

18 inches per year, whereas, high elevations (above 9,000 feet) 

receive in excess of 32 inches per year. Snowfall is a substantial component of annual precipitation at high elevations. 

However, intense summer thunderstorms can account for 20 

to 40 percent of the annual precipitation (Robson and Banta, 

1995; Colorado Geological Survey, 2003; Colorado State 

University, 2008).

Previous Studies

Many reports document regression equations developed 

for estimating streamflow statistics in Colorado. Patterson 

(1964 and 1965), Patterson and Somers (1966), and Matthai 

(1968) developed regression equations for major river basins 

in Colorado. Headman and others (1972) developed equations for streamflow statistics based on channel geometry. 

The first statewide regional regression study, which focused 

on peak streamflow, was conducted by McCain and Jarrett 
4 Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado

(1976). The hydrologic regions, as described in the section 

“Definition of Hydrologic Regions of Colorado,” originally 

were defined by McCain and Jarrett (1976) and subsequently 

adopted by Kircher and others (1985). Kircher and others 

(1985) developed regional regression equations for a range 

of high- and low-streamflow characteristics for streams in 

western Colorado by using USGS streamflow data collected 

through 1983. Their study is the last regional regression study 

for nonpeak streamflow statistics in Colorado. Livingston 

and Minges (1987) developed equations for the estimation of 

peak streamflows for small drainage basins (less than about 

20 square miles) in the Great Plains part of eastern Colorado. 

Vaill (1999) developed regional regression equations for peak 

streamflow in Colorado. Vaill (1999) used peak streamflow 

data collected through 1993 for his study, which represents 

the most recent regional regression study relative to the current 

(2009) study for peak streamflow. Other regional regression 

studies of various streamflow statistics include Waltemeyer 

(2006) and Thomas and others (1997); however, those studies 

included only parts of Colorado because of study-specific 

focus in bordering States.

Regional Regression Equations for 

Estimation of Natural Streamflow 

Statistics in Colorado

The development of regional regression equations for 

the estimation of natural streamflow statistics in Colorado is 

composed of four major steps:

1. Definition of distinct hydrologic regions,

2. Selection of stations for inclusion in multilinear regression analysis and distribution of the selected stations into 

their respective hydrologic regions,

3. Computation of streamflow statistics and basin and 

climate characteristics for the stations, and

4. Computation of the regression equations for each streamflow characteristic for each hydrologic region as applicable.

These steps are further described in the four sections that follow.

Definition of Hydrologic Regions of Colorado

For the current study and several previous studies, five 

hydrologic regions were defined. These are the Mountain, 

Northwest, Rio Grande, Southwest, and Plains regions (fig. 1). 

These regions are the same as those originally defined by McCain 

and Jarrett (1976) and adopted by Kircher and others (1985). A 

hydrologic region is qualitatively defined as a region of similar 

hydrology and climatology.

The five hydrologic regions of Colorado were defined 

on the basis of the physiographic and climatic characteristics 

that were used to develop best-fit regression equations. 

The Mountain region is identified as that region of central 

Colorado above about 7,500 feet in elevation located between 

the Colorado-Wyoming border and the Rio Grande basin. The 

Mountain region encompasses the headwaters of most major 

river basins in Colorado where the annual peak streamflow generally is produced by snowmelt runoff. The Northwest region is 

defined as the northwestern part of Colorado below 7,500 feet 

and encompassing substantial areas of the Yampa, White, and 

Gunnison River basins. The Rio Grande region ranges in elevation from about 5,000 feet near the Colorado–New Mexico 

border to more than 14,000 feet in the northern parts and 

encompasses the Rio Grande basin. The Southwest region is 

defined as the region located south of the Gunnison River basin 

and west of the Rio Grande basin and encompasses the Dolores, 

Animas, and San Juan River basins. The Plains region is east of 

the Rocky Mountains and below 7,500 feet in the South Platte 

River basin and below 9,000 feet in the Arkansas River basin.

Selection of Stations

Various selection criteria were used to develop the list of 

selected stations for regression analysis reported here. This section details the selection criteria used.

Selection of Stations for PeakStreamflow Statistics

A comprehensive list of all USGS streamflow stations 

within 50 miles of the Colorado border was acquired from 

the National Water Information System (NWIS) database 

(U.S. Geological Survey, 2008). From the comprehensive 

list of candidate stations, those stations with at least 10 years 

of streamflow record identified as representative of natural 

streamflow conditions were selected for this study.

Subsequently, multiple stations on the same stream 

course were evaluated for data similarity as judged by relative drainage-area magnitude. If the relative drainage-area 

magnitude was less than a factor of 2.5, data were considered 

similar. In such cases, stations with the longer applicable record 

were selected. The reason for excluding stations on the basis of 

relative drainage-area and stream-course equality enhances the 

quantity of independent streamflow information (as represented 

by stations and their respective data). This exclusion process 

was used in Vaill (1999) and serves the purpose of removing 

redundant data or hydrologic information from the data base. 

At the completion of the selection process, 422 stations were 

identified, with a combined total of 13,054 years of record, and 

were used in the development of peak-streamflow equations. A 

map showing the location of the stations is provided in figure 1, 

and each station, ancillary information, and basin and climatic 

characteristics are listed in table 1. The “home page” of each 

station can be accessed online at http://waterdata.usgs.gov/nwis/

nwisman/?site_no=STATION&agency_cd=USGS, where the 

word STATION is replaced by the eight-digit station number. 

The home pages provide authoritative station names and other 

identifying characteristics.
Table 1. Drainage-basin and climatic characteristics at streamflow-gaging stations used for regional regression analysis.—Continued[LATDEG, latitude in decimal degrees; LNGDEG, longitude in decimal degrees; YRSPK, years of record for peak streamflow; YRSANN, years of record for annual streamflowsquare miles; S, mean watershed slope, in percent; P, mean annual precipitation, in inches; E, mean watershed elevation, in feet; A7500, percentage of A above 7,500 feet elevation 100-year precipitation, in inches; NA, not applicable, station operated as peak-only or flood-hydrograph station]

Station

number

Hydrologic

region LATDEG LNGDEG YRSPK YRSANN A S P E 

06614800 Mountain 40.4961 105.8650 33 34 1.5 43.2 47.1 11,246 06616000 Mountain 40.5494 106.0211 32 32 20.5 25.7 30.9 9,794 06617100 Mountain 40.7411 106.2795 25 24 182.1 16.8 24.4 9,275 06618500 Mountain 40.7264 106.2906 25 24 255.4 13.7 20.5 8,994 06619000 Mountain 40.8616 106.3372 11 10 475.9 14.1 21.3 9,027 06620400 Mountain 41.1833 106.2700 10 NA 22.1 8.9 31.7 9,726 06621000 Mountain 41.0811 106.3075 26 25 118.1 12.8 23.5 9,118 06622000 Mountain 41.0500 106.5256 12 NA 107 21.7 30.4 9,168 06622500 Mountain 41.2083 106.5173 14 13 59.8 22.6 35.5 9,484 06622700 Mountain 41.3702 106.5206 47 47 38.1 18.5 35.3 9,403 06623800 Mountain 41.0236 106.8248 42 43 65.8 23.2 44.3 9,457 06624500 Mountain 41.2139 106.7784 18 15 201.5 24.3 39.5 9,048 06627500 Northwest 41.4000 107.0006 10 10 34 14.3 30.3 8,384 06629100 Northwest 41.6989 106.6267 13 NA 14.4 22.9 21.3 8,146 06630800 Mountain 41.6530 106.3453 13 NA 8.9 7.6 15.8 7,759 06631000 Northwest 41.7166 106.3172 11 9 191.4 10.9 22.4 8,319 

06631100 Mountain 41.6400 106.3053 13 NA 25.5 11.5 23.4 8,483 

06632400 Mountain 41.5852 106.2228 41 53 62.8 19.7 35.3 9,799 06696980 Mountain 39.3394 105.9117 14 8 23.7 31.6 29 11,296 06699005 Mountain 39.2869 105.6958 14 NA 230.2 18.4 20.8 10,152 06700500 Mountain 39.2089 105.3036 58 NA 92.6 33.7 29.6 10,054 06706000 Mountain 39.4572 105.6586 36 60 126.9 34.8 24.3 11,009 06707000 Plains 39.4089 105.1758 60 NA 475.7 31.7 25 9,464 06709500 Plains 39.4844 105.0025 41 NA 302.6 18.9 21.5 6,987 06710385 Mountain 39.6328 105.3367 23 NA 103.2 31.9 24.8 9,606 06710400 Mountain 39.6305 105.3217 14 NA 22.2 25.7 23.1 8,303 06710600 Plains 39.6803 105.1978 10 NA 7.6 28.2 20.3 7,207 06710990 Plains 39.6158 105.2322 13 NA 43.6 23.4 22.8 7,987 

06711000 Plains 39.6355 105.1686 27 NA 50.2 25.1 22.4 7,826 

06712000 Plains 39.3558 104.7633 67 NA 167.9 7.3 20.6 7,093 06716500 Mountain 39.7658 105.6261 49 53 146.6 44.5 27.1 11,182 06717400 Mountain 39.7164 105.5714 12 5 43.7 36.9 25 10,642 06719500 Plains 39.7505 105.2489 62 NA 392.3 39.2 24.4 9,962 06721500 Mountain 40.2189 105.5283 15 16 32.5 40.8 38.2 10,825 06722500 Mountain 40.0908 105.5144 24 24 13.4 33.6 38.3 11,119 06723000 Mountain 40.1667 105.4444 19 5 27.8 37.3 31.4 9,959 06725500 Mountain 39.9617 105.5044 51 87 36.5 35.3 33.2 10,345 06726900 Plains 40.0117 105.3486 12 NA 3.9 24.6 20.6 7,294 06729000 Mountain 39.9147 105.5019 7 10 43.6 32.8 30.9 10,174 06730300 Plains 39.8778 105.2772 24 NA 15.2 36.4 23.5 8,255 06732000 Mountain 40.3453 105.5856 18 18 24.6 45.0 40.8 10,503 06739500 Plains 40.4539 105.1989 9 NA 134.1 29.9 20.4 7,421 06748200 Mountain 40.5516 105.6269 13 13 3.6 44.3 24.8 11,027 
Table 1. Drainage-basin and climatic characteristics at streamflow-gaging stations used for regional regression analysis.—Continued [LATDEG, latitude in decimal degrees; LNGDEG, longitude in decimal degrees; YRSPK, years of record for peak streamflow; YRSANN, years of record for annual streamflowsquare miles; S, mean watershed slope, in percent; P, mean annual precipitation, in inches; E, mean watershed elevation, in feet; A7500, percentage of A above 7,500 feet elevation 100-year precipitation, in inches; NA, not applicable, station operated as peak-only or flood-hydrograph station] Station number Hydrologic region LATDEG LNGDEG YRSPK YRSANN A S P E 

06748510 Mountain 40.6386 105.6617 13 13 0.9 22.4 24 10,878 06748530 Mountain 40.6230 105.5650 13 13 12.4 26.7 20 9,833 06748600 Mountain 40.6469 105.4936 23 23 92.6 28.9 21.3 9,866 06755000 Plains 41.1264 105.1944 35 21 13.5 10.4 18.9 7,808 06758200 Plains 39.3372 104.4755 10 NA 115.4 7.0 19.8 7,002 06758250 Plains 39.6130 104.4508 10 NA 6.5 5.7 18.1 5,923 06758700 Plains 39.4925 104.1633 10 NA 2.7 9.2 17.3 5,849 06761900 Plains 41.2564 104.0811 22 NA 0.6 1.7 15.5 5,300 06762500 Plains 41.2278 103.8931 64 NA 1,216.1 4.0 15.6 5,850 06762600 Plains 41.3197 104.0808 25 NA 7.6 2.0 16.8 5,339 06821300 Plains 39.5200 103.4436 11 NA 6.8 2.6 16.3 5,348 06821400 Plains 39.9067 102.2694 11 NA 19.8 2.2 18.2 3,899 06823500 Plains 40.0394 101.8667 65 NA 176.8 4.3 18.3 3,654 06825500 Plains 39.5755 102.2521 26 NA 268.9 3.0 17.7 4,333 06844700 Plains 39.2853 101.4660 22 NA 85.7 1.6 19.5 3,619 06844800 Plains 39.3206 101.6329 33 NA 20.1 1.0 19.5 3,698 06858500 Plains 39.0179 101.3479 33 NA 696.2 2.5 18 3,964 07079500 Mountain 39.2597 106.3406 11 11 51.2 33.4 25.3 11,433 07081000 Mountain 39.2642 106.3409 14 11 45.7 22.8 22 10,800 07082000 Mountain 39.2697 106.3950 8 21 23.8 32.8 30.8 11,146 07083000 Mountain 39.1722 106.3892 60 61 23.5 49.0 34.5 11,955 07089000 Mountain 38.8128 106.2222 48 NA 68.5 45.8 22.2 11,380 07091000 Mountain 38.7336 106.1600 20 NA 83 47.1 22.5 11,379 07093500 Mountain 38.5214 105.9897 14 NA 211.6 36.1 18.3 10,096 07093775 Plains 38.4672 105.8600 23 NA 211 22.7 13.8 9,356 07095000 Plains 38.1861 105.4836 66 NA 320.5 19.5 21.2 9,189 07096500 Plains 38.4364 105.1914 32 NA 436.3 26.2 16.7 8,428 07099100 Plains 38.3742 104.9642 11 NA 213.8 27.9 20.4 8,143 07099230 Plains 38.4650 104.8272 28 NA 62.2 25.1 19.2 6,860 07105920 Plains 38.6817 104.8586 12 NA 11 48.7 24 8,832 07105945 Plains 38.7075 104.8466 28 NA 6.8 48.5 22.5 8,193 07107500 Plains 38.0517 104.7936 18 NA 171.4 28.6 22.1 7,964 

07114000 Rio Grande 37.4200 105.0528 46 NA 53.1 35.4 27.3 9,883 07118000 Plains 37.3864 104.6658 11 NA 140.1 27.0 22 8,062 

07120620 Plains 37.5547 104.0216 21 NA 15.6 6.2 14.7 5,582 07121500 Plains 38.0031 103.6561 41 NA 510.9 3.9 13.6 4,871 07124300 Plains 37.1147 104.6053 18 NA 100.1 25.5 19.5 7,366 07125100 Plains 37.2000 104.1941 13 NA 79.1 10.0 15.6 6,077 07125500 Plains 37.1684 104.1450 14 NA 162.2 13.5 18 6,642 07126100 Plains 37.3045 104.0155 16 NA 84.8 2.8 14 5,479 07126200 Plains 37.3456 103.9580 41 NA 161.4 2.8 14.3 5,521 07126325 Plains 37.4242 103.9202 24 NA 48.7 4.4 14.1 5,330 07126390 Plains 37.4928 103.8280 21 NA 48.6 4.6 13.9 5,161 
Table 1. Drainage-basin and climatic characteristics at streamflow-gaging stations used for regional regression analysis.—Continued[LATDEG, latitude in decimal degrees; LNGDEG, longitude in decimal degrees; YRSPK, years of record for peak streamflow; YRSANN, years of record for annual streamflowsquare miles; S, mean watershed slope, in percent; P, mean annual precipitation, in inches; E, mean watershed elevation, in feet; A7500, percentage of A above 7,500 feet elevation 100-year precipitation, in inches; NA, not applicable, station operated as peak-only or flood-hydrograph station]

Station

number

Hydrologic

region LATDEG LNGDEG YRSPK YRSANN A S P E 

07126415 Plains 37.5153 103.7255 23 NA 48.7 11.2 13.9 4,981 07126470 Plains 37.5439 103.6322 16 NA 421.3 8.6 15.6 5,607 07126480 Plains 37.5892 103.6483 21 NA 56.1 11.3 14.1 4,968 07133200 Plains 37.7242 102.7405 11 NA 2.4 5.2 16 4,431 07138600 Plains 38.5250 101.6216 39 NA 25.2 1.1 17.7 3,650 07138650 Plains 38.4811 101.4882 20 NA 500.3 1.4 17 3,858 07153500 Plains 36.9875 103.4241 33 NA 529.2 13.5 17.2 6,251 07154400 Plains 36.8833 103.0183 53 NA 112.2 11.8 16.7 5,087 07154650 Plains 36.8978 102.9016 22 NA 24.9 12.0 17.2 4,555 07155100 Plains 36.7722 102.8049 18 NA 10.6 1.8 17.1 4,624 07155590 Plains 37.1220 101.8979 35 NA 2,926.6 8.4 17.0 5,001 07155900 Plains 37.1909 101.8988 34 NA 57.1 0.6 17.3 3,669 07156010 Plains 37.2584 101.7754 15 NA 411.3 0.9 17.2 3,946 07156100 Plains 37.5000 101.7616 15 NA 584.2 1.5 17 4,411 07156220 Plains 37.6264 101.7616 32 NA 813.3 1.6 17 4,149 07156600 Plains 37.3353 101.0504 33 NA 21.5 1.7 18.6 2,983 07199000 Plains 36.7872 104.4622 40 NA 199.1 23.6 20.1 7,594 07201000 Plains 36.9058 104.4361 48 NA 14.6 23.8 20.9 7,608 07201200 Plains 36.8308 104.3333 30 NA 5.2 16.2 19 7,120 07203000 Plains 36.6817 104.7867 76 NA 295.2 23.7 20.6 8,016 07204000 Rio Grande 36.5539 105.2678 69 NA 78.8 26.3 21.1 9,405 07204500 Rio Grande 36.4853 105.2656 68 NA 73.2 19.4 23.6 9,151 07205000 Rio Grande 36.5186 105.2753 72 NA 10.5 28.1 21.7 9,405 07206400 Rio Grande 36.5264 105.1750 40 NA 7.2 48.2 25.9 9,810 07207500 Plains 36.5739 104.9461 57 NA 185.4 27.4 21.5 8,589 07208500 Plains 36.3725 104.9689 83 NA 60.1 24.2 26.2 9,550 

07211000 Plains 36.3603 104.5986 75 NA 949 21.6 20.7 8,106 

07225500 Plains 36.3259 103.9255 12 NA 268.7 6.2 17.2 6,532 07227295 Plains 36.3889 103.3186 42 NA 1.2 2.0 16.2 5,182 07232500 Plains 36.7214 101.4896 57 NA 2,033 3.0 17.3 4,463 07232650 Plains 36.5564 102.7866 12 NA 33.9 1.1 16.6 4,593 08216500 Rio Grande 37.8561 106.9275 32 31 34.2 40.5 30.6 11,473 08218500 Rio Grande 37.7519 106.8300 36 37 91.9 35.7 37.4 10,723 08219500 Rio Grande 37.6569 106.6492 80 80 210.6 31.3 38.2 10,398 08220500 Rio Grande 37.5917 106.4500 47 38 52.7 30.7 33.6 10,507 08223500 Rio Grande 37.4903 106.2595 25 23 30.7 34.6 31.8 10,356 08224500 Rio Grande 38.2203 106.0897 59 58 45.4 35.8 18.8 10,405 08227000 Rio Grande 38.1633 106.2906 87 87 516.9 22.8 20.8 9,949 08227500 Rio Grande 38.0136 105.6928 46 34 12.9 64.6 30.1 11,294 08230500 Rio Grande 37.8597 106.3195 57 39 106.2 27.6 26.5 10,056 08231000 Rio Grande 37.8133 106.3186 68 47 62.2 27.8 31.1 10,259 08236000 Rio Grande 37.3747 106.3348 54 65 107.6 33.7 38.4 10,872 
Table 1. Drainage-basin and climatic characteristics at streamflow-gaging stations used for regional regression analysis.—Continued [LATDEG, latitude in decimal degrees; LNGDEG, longitude in decimal degrees; YRSPK, years of record for peak streamflow; YRSANN, years of record for annual streamflowsquare miles; S, mean watershed slope, in percent; P, mean annual precipitation, in inches; E, mean watershed elevation, in feet; A7500, percentage of A above 7,500 feet elevation 100-year precipitation, in inches; NA, not applicable, station operated as peak-only or flood-hydrograph station] Station number Hydrologic region LATDEG LNGDEG YRSPK YRSANN A S P E 

08240500 Rio Grande 37.3747 105.2950 59 48 52.7 41.2 23.2 10,492 08241500 Rio Grande 37.4250 105.4150 58 37 182.9 25.1 19.4 9,169 08242500 Rio Grande 37.4472 105.4258 67 67 40.2 32.5 22.3 10,152 08245500 Rio Grande 37.3539 106.5250 14 17 44.2 35.0 45 11,218 08246500 Rio Grande 37.0539 106.1875 43 97 281.6 27.8 35.3 10,481 08247500 Rio Grande 36.9931 106.0386 82 67 115.7 14.6 25.2 9,353 08248000 Rio Grande 36.9822 106.0736 88 88 152.8 21.7 30.6 9,861 08248500 Rio Grande 37.1770 105.8781 59 59 372.9 15.2 23.5 9,192 08252500 Rio Grande 36.8983 105.2544 68 NA 25.6 23.5 26.9 10,599 08253000 Rio Grande 36.8969 105.2603 70 NA 18.5 29.9 28.7 11,023 08253500 Rio Grande 36.8842 105.2811 69 NA 2.2 39.2 29.6 11,313 08255000 Rio Grande 36.9528 105.4103 10 NA 11.2 35.0 27 10,929 08263000 Rio Grande 36.8292 105.5478 32 25 10.6 41.7 28.9 10,973 08264000 Rio Grande 36.6223 105.3895 24 14 19.2 37.6 30.2 11,077 08265000 Rio Grande 36.7034 105.5686 75 77 112.2 42.4 26.3 10,149 08267500 Rio Grande 36.5419 105.5561 70 73 37.1 55.2 28.3 10,389 08268500 Rio Grande 36.5322 105.6856 51 67 66.6 43.1 23.3 9,401 08269000 Rio Grande 36.4394 105.5036 72 56 63 40.2 25.1 9,608 08275000 Rio Grande 36.3756 105.5492 19 17 60.8 31.2 24.6 9,040 08275500 Rio Grande 36.2989 105.5817 50 52 80.4 32.7 27.7 9,352 08275600 Rio Grande 36.3320 105.5789 24 23 38 33.5 26.6 9,362 08281200 Rio Grande 36.9556 106.5367 13 NA 28.1 25.8 34.2 9,724 08284000 Rio Grande 36.6986 106.5575 24 NA 50.6 15.6 26.1 8,856 08284100 Rio Grande 36.6625 106.6331 51 52 475.3 20.2 30.2 9,304 08284500 Rio Grande 36.6681 106.7048 34 28 192.5 13.6 20 7,792 08286650 Rio Grande 36.3172 106.4853 33 NA 143.9 15.6 18.9 8,140 08288000 Rio Grande 36.3917 106.2395 33 19 48 20.2 24.6 9,157 08289000 Rio Grande 36.3497 106.0442 75 75 411.9 20.2 19.7 8,492 09012500 Mountain 40.2533 105.8114 10 8 45.8 42.5 36.8 10,680 09016500 Mountain 40.1125 105.7497 27 28 47.8 50.2 35.8 10,641 09020000 Mountain 40.1805 106.0092 19 18 109.2 29.5 25.8 9,630 09024000 Mountain 39.9000 105.7767 20 97 27.8 38.9 32.8 10,767 09026500 Mountain 39.9100 105.8783 33 73 32.8 36.3 29 10,738 09032000 Mountain 39.9500 105.7656 14 73 19.9 29.7 30.5 10,453 09032500 Mountain 39.9975 105.8236 17 26 51.1 27.0 28.7 9,973 09033000 Mountain 40.0508 105.7775 21 19 8.1 23.3 34.8 10,509 09033500 Mountain 40.0867 105.7947 10 9 11.7 29.3 26.5 9,538 09034000 Mountain 40.0853 105.9553 5 23 295.9 26.6 25.8 9,756 09034500 Mountain 40.0833 106.0881 28 86 823.9 29.7 26.7 9,737 09034900 Mountain 39.7603 105.9064 41 42 5.5 49.7 32.3 11,793 09035500 Mountain 39.7789 105.9283 28 50 16.4 46.0 30.7 11,559 09035700 Mountain 39.7972 106.0261 32 42 35.2 42.1 28.6 11,106 
Table 1. Drainage-basin and climatic characteristics at streamflow-gaging stations used for regional regression analysis.—Continued[LATDEG, latitude in decimal degrees; LNGDEG, longitude in decimal degrees; YRSPK, years of record for peak streamflow; YRSANN, years of record for annual streamflowsquare miles; S, mean watershed slope, in percent; P, mean annual precipitation, in inches; E, mean watershed elevation, in feet; A7500, percentage of A above 7,500 feet elevation 100-year precipitation, in inches; NA, not applicable, station operated as peak-only or flood-hydrograph station]

Station

number

Hydrologic

region LATDEG LNGDEG YRSPK YRSANN A S P E 

09035800 Mountain 39.8005 106.0264 41 42 8.8 37.5 28.3 10,945 09035900 Mountain 39.7958 106.0306 41 42 27.4 42.1 28.7 10,989 09036500 Mountain 39.9075 106.0172 10 10 13.9 36.8 28.2 10,526 09039000 Mountain 40.2175 106.3131 40 40 44.6 36.7 28.3 9,869 09040000 Mountain 40.1575 106.2834 37 36 75.7 30.0 23.2 9,266 

09041100 Mountain 40.2405 106.3736 13 13 11.5 25.2 20.6 8,907 

09046530 Mountain 39.4930 106.0447 10 8 11.1 34.2 28 11,034 09047000 Mountain 39.6139 106.0520 44 50 128.2 31.8 27 10,913 09047500 Mountain 39.6055 105.9431 58 58 57.8 41.9 29.8 11,497 09047700 Mountain 39.5944 105.9725 49 50 9.1 35.2 26.2 10,879 09050100 Mountain 39.5753 106.1106 49 50 92.2 35.3 29 11,238 09052400 Mountain 39.7280 106.1734 26 28 8.6 48.9 31.8 11,199 09052800 Mountain 39.7630 106.1925 27 28 14 52.8 32.5 11,029 09055000 Mountain 39.8528 106.2678 10 9 7.6 25.8 24.4 9,600 09058610 Mountain 39.7039 106.4575 33 33 3.3 28.2 28.9 10,024 09058700 Mountain 39.6983 106.4456 40 40 3 22.5 27.6 9,848 09058800 Mountain 39.7317 106.4267 38 40 3.6 28.2 29.6 10,575 09059500 Northwest 39.8000 106.5839 62 63 93.4 33.0 25.8 9,722 09060500 Mountain 40.0411 106.6559 28 28 47.8 18.8 29.3 9,390 09063200 Mountain 39.5222 106.3236 40 43 9.5 34.0 26.7 10,823 09063400 Mountain 39.5228 106.3361 43 44 23.8 34.2 28.1 10,721 09064500 Mountain 39.4733 106.3678 32 71 58.2 38.0 27.8 10,922 09065100 Mountain 39.5680 106.4125 46 47 34.2 47.0 30.8 11,184 09065500 Mountain 39.6258 106.2781 50 53 14.5 50.5 30.5 11,116 09066000 Mountain 39.5964 106.2650 51 53 12.5 31.7 28 10,713 09066100 Mountain 39.6400 106.2934 40 44 4.5 60.1 31.4 11,088 09066150 Mountain 39.6436 106.3025 33 41 5.3 58.0 30.6 11,074 09066200 Mountain 39.6483 106.3231 40 43 6.1 53.5 28.5 10,904 09066300 Mountain 39.6458 106.3823 42 43 5.9 36.9 25.7 10,504 09066400 Mountain 39.6828 106.4014 43 44 7.4 30.7 26.6 10,399 09066500 Mountain 39.6147 106.4400 12 12 101 40.6 27.9 10,305 09067005 Mountain 39.6317 106.5225 11 11 395.1 37.1 26.7 10,456 09068000 Mountain 39.5572 106.7631 22 22 71.5 39.5 26.1 9,951 09069500 Mountain 39.5455 106.9348 11 12 62.6 35.4 24.7 9,689 09070000 Mountain 39.6494 106.9537 60 61 944.6 33.6 23.1 9,481 09071300 Mountain 39.7166 107.3103 20 20 6.5 9.6 42.7 10,771 09073500 Mountain 39.1894 106.8145 13 43 107.4 42.0 28.6 11,215 09073700 Mountain 39.2139 106.6559 16 16 6.1 47.9 31.9 11,762 09073800 Mountain 39.1964 106.6900 10 10 8.6 36.7 29.9 11,439 09073900 Mountain 39.1889 106.7184 10 10 6.6 28.1 28.9 11,263 09074000 Mountain 39.2058 106.7975 43 44 42.1 34.1 28.8 10,890 09074800 Mountain 39.0875 106.8123 25 25 32.3 46.9 36.4 11,431 
Table 1. Drainage-basin and climatic characteristics at streamflow-gaging stations used for regional regression analysis.—Continued [LATDEG, latitude in decimal degrees; LNGDEG, longitude in decimal degrees; YRSPK, years of record for peak streamflow; YRSANN, years of record for annual streamflowsquare miles; S, mean watershed slope, in percent; P, mean annual precipitation, in inches; E, mean watershed elevation, in feet; A , percentage of A above 7,500 feet elevation 

7500 

100-year precipitation, in inches; NA, not applicable, station operated as peak-only or flood-hydrograph station] Station number Hydrologic region LATDEG LNGDEG YRSPK YRSANN A S P E 

09075700 09077200 09077800 09078000 09078100 09078200 09078500 09080300 09081600 09082800 09083000 09084000 09085200 09085300 09085400 09089500 09091100 09091500 09092000 09092500 09093000 09095000 09096000 09096500 09096800 09097500 09097600 09104500 09107000 09110000 09110500

09111500

091120000911250009113300091135000911450009115500

091170000911800009119000

09122000

MountainMountainMountainMountainMountainMountainMountainMountainNorthwestMountainNorthwestMountainNorthwestNorthwestNorthwestMountain

NorthwestNorthwestNorthwest

NorthwestNorthwest

NorthwestMountainMountainMountainMountainMountainNorthwestMountainMountainMountain

MountainMountainMountainMountainMountainMountainMountain

MountainMountainMountainMountain

39.123639.245539.241739.330839.358939.334239.342839.361739.232239.329739.330539.466739.605339.609139.5978

39.3311

39.531639.677839.6200

39.471939.5669

39.453339.223639.250539.236139.272239.325039.086438.860338.664438.8644

38.869738.824438.664438.765538.702238.5419

38.4117

38.497238.559738.521738.2914

106.9053106.5314106.5931106.6581106.5684106.5753106.6659106.8206107.2273107.3334107.2245107.0523107.4484107.4348107.4239

107.5801107.7140107.6984107.7634

107.8326

108.1109

108.3170107.8020107.8406107.6339107.8506107.8423108.1267106.5667106.8453

106.9098106.9695106.8528106.8481107.0584106.9984106.9498

106.4228106.7261106.6364106.9409

107.1145

25

99

281516391450161415181514

4914

8

20

30

24231337155912242420

12251276122678

55142468

18

251919411717411452161415171413

44

NA

1519

30

23221259155912202597

11

241485122581

56142470

18

35.318.9

11.5

88.910.7

7.2

42.312.4

167.3

27.975.430.323.815.8

6.2

64.263.434.9

137.1

7.9

141.5323.1

22.880.449.8

143

9.35.3

127.6477.1

89.268.932.9

289.3

47.7

119.3

1,010

148.3425.9106.9

1,059.9

339.9

60.253.448.441.048.238.037.744.049.422.130.930.438.134.940.6

26.523.433.532.4

29.0

34.642.220.417.417.520.636.921.527.330.9

40.736.837.834.232.228.629.8

31.226.338.324.2

26.4

44.336.133.231.632.631.929.526.839.53432.62735.834.128.9

29.920.226.122.9

29.4

21.220.231.234.330.326.730.934.126.623.9

38.233.63231.731.927.325.6

21.418.323.418.6

21.1

11,38411,84611,598

10,975

11,204

10,89110,54610,10310,166

9,4639,1689,4909,7169,6619,010

8,7327,2438,5507,972

9,406

8,1347,6249,3659,7439,3518,6229,5899,862

10,92410,647

10,88310,33610,80810,27210,202

9,894

10,210

10,237

9,606

10,619

9,733

10,432
Table 1. Drainage-basin and climatic characteristics at streamflow-gaging stations used for regional regression analysis.—Continued[LATDEG, latitude in decimal degrees; LNGDEG, longitude in decimal degrees; YRSPK, years of record for peak streamflow; YRSANN, years of record for annual streamflowsquare miles; S, mean watershed slope, in percent; P, mean annual precipitation, in inches; E, mean watershed elevation, in feet; A7500, percentage of A above 7,500 feet elevation 100-year precipitation, in inches; NA, not applicable, station operated as peak-only or flood-hydrograph station]

Station

number

Hydrologic

region LATDEG LNGDEG YRSPK YRSANN A S P E 

09122500 Mountain 38.5608 107.3167 11 11 58.2 46.0 27.4 9,862 09123500 Mountain 38.0250 107.3084 13 12 120.5 45.9 34.1 11,435 09124500 Mountain 38.2989 107.2301 69 70 339.2 42.7 28.2 10,884 09125000 Mountain 38.4878 107.4151 27 27 35 38.5 22.7 9,674 09126000 Mountain 38.2572 107.5467 15 53 67 49.6 32.7 10,862 09127500 Mountain 38.5519 107.5062 21 18 42.3 29.4 20.5 9,631 09128500 Northwest 38.7278 107.5067 58 59 43.4 43.6 25.6 9,165 09130500 Northwest 39.0133 107.3584 19 19 132.9 28.9 28.7 8,694 09130600 Mountain 39.1308 107.5753 10 10 7.3 18.3 29.8 9,418 09132500 Northwest 38.9258 107.4342 72 74 525.6 33.0 28.5 8,886 09132900 Mountain 39.0322 107.6137 13 13 2.4 20.9 34 10,397 09134500 Northwest 38.9264 107.7937 29 29 34.7 17.1 33.5 9,723 09136200 Northwest 38.7830 107.8378 24 23 5,247.4 28.9 22.0 9,444 09137800 Northwest 38.9447 108.0281 12 12 10.8 17.4 32.8 9,663 09139200 Mountain 38.9836 107.9720 12 12 12.2 18.6 37.7 10,153 09140200 Mountain 38.9866 107.9437 12 12 5.6 16.1 38.3 9,969 09141200 Northwest 38.9580 107.9187 12 12 10.5 17.3 33.9 9,381 09143500 Northwest 38.9016 107.9212 90 82 39.1 16.8 35.7 9,464 09144200 Northwest 38.7878 107.9953 23 22 197 17.6 24.4 8,034 09146000 Southwest 38.0311 107.6751 16 16 75.2 58.4 38.1 11,267 09146400 Southwest 38.0736 107.8512 15 15 14.1 38.5 30.9 10,215 09146500 Southwest 38.0933 107.8137 16 16 16.5 50.3 35.2 10,939 09146600 Southwest 38.1455 107.9198 12 12 8.2 11.8 25.8 9,053 09147000 Southwest 38.1778 107.7584 49 49 97.2 28.1 26.3 9,163 09147100 Mountain 38.1494 107.6448 18 18 45.6 55.6 33.7 10,721 09149450 Northwest 38.5553 108.0459 13 NA 102.7 15.3 18.2 7,839 09150500 Northwest 38.7350 108.1617 24 23 249.1 18.3 17.4 7,274 09153400 Northwest 39.3086 108.9837 10 10 168.4 41.8 15.5 6,525 09163700 Southwest 38.9639 109.3368 15 NA 90.1 15.5 9.9 4,980 09165000 Southwest 37.6389 108.0604 53 54 105.6 38.2 36.1 10,631 09166500 Southwest 37.4725 108.4976 92 96 505.2 32.3 31.2 9,694 09168100 Southwest 37.8767 108.5831 29 29 147 27.6 21.5 7,932 09168700 Southwest 38.0258 108.8148 12 NA 1.7 9.7 12.9 5,836 09169500 Southwest 38.3103 108.8854 40 41 2,028.6 22.7 21.9 7,862 09172000 Southwest 37.9583 108.0059 18 18 33.4 31.2 32.1 10,041 09172500 Southwest 38.0425 108.1323 70 70 309.5 37.6 30.3 9,944 09174500 Southwest 38.2736 108.3629 10 9 38.4 16.1 19.7 7,645 09175000 Southwest 37.9758 108.3279 12 18 53.7 16.9 26.2 8,687 09175500 Southwest 38.2178 108.5665 53 53 1,068.6 22.6 23.7 8,483 09177500 Southwest 38.5189 109.1098 23 NA 15.4 16.0 30.3 8,986 09181000 Southwest 38.7250 109.3451 13 5 20.5 44.7 13.8 5,637 09182000 Southwest 38.5928 109.2657 24 23 7.9 41.1 31.8 9,468 
Table 1. Drainage-basin and climatic characteristics at streamflow-gaging stations used for regional regression analysis.—Continued [LATDEG, latitude in decimal degrees; LNGDEG, longitude in decimal degrees; YRSPK, years of record for peak streamflow; YRSANN, years of record for annual streamflowsquare miles; S, mean watershed slope, in percent; P, mean annual precipitation, in inches; E, mean watershed elevation, in feet; A7500, percentage of A above 7,500 feet elevation 100-year precipitation, in inches; NA, not applicable, station operated as peak-only or flood-hydrograph station] Station number Hydrologic region LATDEG LNGDEG YRSPK YRSANN A S P E 

09182600 Southwest 38.9528 109.6590 15 NA 5.8 31.7 11.1 5,743 09183000 Southwest 38.6128 109.5798 31 29 163 14.8 9.6 4,807 09184000 Southwest 38.5622 109.5140 47 43 77.1 29.6 19.9 7,104 09185200 Southwest 38.4000 109.4507 15 NA 15.2 25.1 15 6,669 09185500 Southwest 38.2433 109.4401 22 21 357.9 9.7 14.2 6,586 09187000 Southwest 38.0625 109.5743 17 8 114.3 32.8 17.2 7,338 09216400 Northwest 41.5594 109.5112 16 NA 45.9 16.7 9.5 7,042 09216537 Northwest 41.6394 108.1293 24 NA 34.4 7.0 7.9 7,011 09216550 Northwest 41.6750 108.7368 21 NA 153 7.9 8.5 6,976 09216600 Northwest 41.4569 108.9423 22 NA 8.1 15.1 9.2 6,982 09216700 Northwest 41.4833 108.9673 18 NA 481.9 12.5 11.2 7,317 09216900 Northwest 41.5327 109.3810 24 NA 1.3 34.2 8.8 6,827 09224810 Northwest 41.4597 109.6229 17 NA 12.1 10.2 8.6 6,654 09224820 Northwest 41.4250 109.6160 20 NA 3.6 11.4 8.6 6,566 09224840 Northwest 41.4111 109.6021 17 NA 1.3 15.0 8.6 6,553 09224980 Northwest 41.3736 109.6451 17 NA 414.9 7.6 9.9 6,840 09225200 Northwest 41.1705 109.6101 20 NA 6.7 15.9 10.3 6,653 09225300 Northwest 41.0611 109.6188 21 NA 11.9 12.2 10.6 6,578 09229450 Northwest 41.0205 109.6801 10 NA 525.3 15.8 19.3 8,541 09235600 Northwest 40.7680 109.3190 35 36 24.9 19.9 20.5 8,139 09238500 Northwest 40.4080 106.7870 20 13 42.3 19.6 47.1 9,493 09239500 Northwest 40.4836 106.8323 99 99 567.4 21.7 31.5 8,782 09241000 Mountain 40.7175 106.9159 69 68 216.5 27.3 38.1 9,106 09244100 Northwest 40.3341 107.1392 18 18 34.5 25.2 26.3 8,292 09245000 Northwest 40.6697 107.2851 44 43 67.7 20.4 30.7 8,414 09245500 Northwest 40.6805 107.2873 15 15 21.4 22.7 31.4 8,461 09249000 Northwest 40.3125 107.3201 19 18 144.1 23.8 33.7 9,063 09250000 Northwest 40.1936 107.7323 34 NA 63.3 21.3 24.3 7,906 09251500 Northwest 40.9905 107.0442 10 10 115.4 21.0 33.5 8,707 09251800 Northwest 41.0425 106.9572 10 9 13 26.8 47 9,458 09253000 Northwest 40.9994 107.1434 60 60 252.7 22.4 32.8 8,546 09253400 Northwest 41.1322 107.0692 12 NA 12.7 24.1 48.6 9,573 09255000 Northwest 40.9825 107.3828 76 76 149.8 19.4 30.5 8,390 09256000 Northwest 41.0978 107.3819 38 36 332.4 15.3 26.6 7,837 09257000 Northwest 41.0283 107.5492 59 46 1,010.9 18.6 27.8 8,001 09257500 Northwest 40.8766 107.4645 10 NA 8.4 18.9 38.1 9,011 09258000 Northwest 40.9155 107.5217 39 39 24.8 18.7 28.2 8,066 09258200 Northwest 41.3400 107.6712 12 NA 51.2 7.4 13.1 6,927 09258900 Northwest 41.1319 107.6465 14 NA 920.5 8.7 13 6,988 09259500 Northwest 40.8405 107.5151 11 NA 8.5 17.6 31.4 8,405 09260000 Northwest 40.5486 108.4243 83 86 4,035.8 11.7 16.6 7,063 09263700 Northwest 40.3000 109.1340 15 NA 63.1 19.2 12.6 6,468 
Table 1. Drainage-basin and climatic characteristics at streamflow-gaging stations used for regional regression analysis.—Continued[LATDEG, latitude in decimal degrees; LNGDEG, longitude in decimal degrees; YRSPK, years of record for peak streamflow; YRSANN, years of record for annual streamflowsquare miles; S, mean watershed slope, in percent; P, mean annual precipitation, in inches; E, mean watershed elevation, in feet; A7500, percentage of A above 7,500 feet elevation 100-year precipitation, in inches; NA, not applicable, station operated as peak-only or flood-hydrograph station]

Station

number

Hydrologic

region LATDEG LNGDEG YRSPK YRSANN A S P E 

09263800 Northwest 40.3166 109.2173 14 NA 9.4 10.1 9.2 5,379 09264000 Northwest 40.7333 109.6785 11 11 26.6 10.1 29.2 9,929 09264500 Northwest 40.7333 109.7035 12 12 19.9 18.2 32.2 10,480 09266500 Northwest 40.5775 109.6221 94 92 101.5 20.7 27.4 9,452 09268000 Northwest 40.6263 109.8201 37 36 44.6 20.8 31.8 10,353 09268500 Northwest 40.6427 109.8110 44 43 8.8 24.5 30.9 10,138 09268900 Northwest 40.6594 109.7510 29 29 7.5 18.0 30.5 10,030 09269000 Northwest 40.6500 109.7618 18 17 10.4 19.1 29.5 9,832 09270500 Northwest 40.5263 109.6057 35 35 116.2 24.7 26.7 9,279 09271800 Northwest 40.4166 109.7507 15 NA 4.3 20.8 12.7 6,542 09300500 Northwest 40.3019 109.8532 28 22 544.6 21.6 23.1 8,833 09302450 Mountain 40.0503 107.4689 25 25 21.6 21.8 30.3 8,971 09302500 Mountain 40.0383 107.4881 12 12 59.9 25.8 37.8 9,814 09303000 Northwest 39.9875 107.6145 50 56 259.4 25.2 35.5 9,551 09303300 Mountain 39.8433 107.3348 20 20 52.2 21.5 42.1 10,585 09303320 Mountain 39.8428 107.3367 14 14 7.4 14.2 41.8 10,667 09304000 Northwest 39.9744 107.6253 46 47 176.5 27.2 36.9 9,852 09304500 Northwest 40.0336 107.8623 98 103 760.3 24.9 30.9 8,938 09306007 Northwest 39.8261 108.1831 25 24 177.3 32.7 19.9 7,634 09306036 Northwest 39.8250 108.1993 12 11 3.6 14.3 16.7 6,933 09306039 Northwest 39.8266 108.2076 11 11 1.2 13.8 16.4 6,744 09306042 Northwest 39.8336 108.2206 18 16 1.1 15.4 16.5 6,671 09306052 Northwest 39.8141 108.2437 11 9 7.9 19.5 17.3 7,213 09306058 Northwest 39.8372 108.2443 11 11 48.3 28.8 18.1 7,473 09306200 Northwest 39.9211 108.2976 41 42 505.8 27.9 18.7 7,419 09306240 Northwest 39.8883 108.5284 11 11 9.2 28.3 20.5 7,876 09306242 Northwest 39.9203 108.4729 33 33 31.7 24.2 19.2 7,542 09306255 Northwest 40.1686 108.4012 28 29 262.5 19.5 16.7 6,878 09306800 Northwest 39.7533 109.3548 19 19 323.3 29.2 15.9 7,157 09307500 Northwest 39.5664 109.5874 27 27 300 37.6 17.5 7,772 09308000 Northwest 39.9389 109.6485 26 17 902.7 28.5 15.1 7,112 09328900 Southwest 38.9422 109.8212 10 NA 22.9 37.8 12.1 6,110 09339900 Southwest 37.3897 106.8412 45 45 65.4 44.4 43 10,235 09340000 Southwest 37.3695 106.8923 46 45 90.8 45.7 41.5 10,071 09340500 Southwest 37.4856 106.9303 17 16 39.9 46.9 51 11,081 09341500 Southwest 37.3920 106.9073 29 28 85.6 43.3 45 10,380 09342000 Southwest 37.3695 106.9403 13 12 24 40.2 39.9 9,890 09342500 Southwest 37.2667 107.0078 75 72 280.8 38.9 38.8 9,738 09343000 Southwest 37.2128 106.7945 37 36 57.9 46.7 39.2 10,026 09343500 Southwest 37.1936 106.9053 18 17 23.1 32.5 33.1 9,264 09344000 Southwest 37.0853 106.6895 41 59 69.2 43.3 40.1 10,255 09345200 Southwest 37.0756 106.8111 8 25 13.4 26.0 33.2 9,608 
Table 1. Drainage-basin and climatic characteristics at streamflow-gaging stations used for regional regression analysis.—Continued [LATDEG, latitude in decimal degrees; LNGDEG, longitude in decimal degrees; YRSPK, years of record for peak streamflow; YRSANN, years of record for annual streamflowsquare miles; S, mean watershed slope, in percent; P, mean annual precipitation, in inches; E, mean watershed elevation, in feet; A7500, percentage of A above 7,500 feet elevation 100-year precipitation, in inches; NA, not applicable, station operated as peak-only or flood-hydrograph station] Station number Hydrologic region LATDEG LNGDEG YRSPK YRSANN A S P E 

09346000 Southwest 37.0028 106.9075 36 71 176 32.3 31.4 9,180 09346200 Southwest 36.9333 107.0006 39 NA 129.5 18.1 20.9 7,637 09347500 Southwest 37.4286 107.1934 14 13 82.6 41.9 37.8 10,137 09349800 Southwest 37.0883 107.3978 44 45 624.9 29.3 27.2 8,564 09350800 Southwest 36.7231 107.2797 49 NA 60.2 18.2 18 7,394 09352900 Southwest 37.4775 107.5437 43 45 72.5 57.9 39.5 11,350 09355000 Southwest 37.0111 107.5970 56 56 58.3 16.7 17.4 6,940 09357200 Southwest 36.4667 107.9173 35 NA 0.2 14.4 10.5 6,934 09357230 Southwest 36.5900 108.1848 21 NA 0.3 9.9 9.6 5,958 09357500 Southwest 37.8331 107.5995 47 47 57.6 54.4 44.7 11,936 09358550 Southwest 37.8197 107.6637 14 15 20.1 54.5 40.5 11,445 09359000 Southwest 37.7975 107.6953 14 13 44.4 51.9 41.2 11,571 09361000 Southwest 37.4219 107.8451 50 48 168.4 46.7 33.7 9,592 09361400 Southwest 37.3342 107.9095 20 6 25.5 53.9 34.1 9,413 09361500 Southwest 37.2792 107.8803 83 95 709.6 46.6 35.9 10,146 09362000 Southwest 37.6039 107.8937 22 22 63.2 33.0 24.8 8,174 09363000 Southwest 37.3253 107.7490 45 42 97.4 34.1 34.4 9,999 09363100 Southwest 37.1397 107.7534 23 23 17.8 6.8 16.9 6,762 09365500 Southwest 37.2897 108.0406 92 90 33.4 49.2 39.8 10,228 09366000 Southwest 37.1189 108.1987 23 22 75.6 23.3 21.4 7,835 09366500 Southwest 36.9997 108.1887 86 87 309.3 18.0 20.3 7,605 09367400 Southwest 36.7861 108.2259 27 4 1.1 15.3 9.8 5,650 09367530 Southwest 36.7333 108.3006 35 NA 3 7.6 9.2 5,503 09367550 Southwest 36.7667 108.3701 21 NA 4.6 6.6 9 5,468 09367561 Southwest 36.7733 108.4412 16 15 136.3 13.0 10.7 5,776 09367950 Southwest 36.7244 108.5915 30 18 4,390.7 7.3 9.9 6,328 09367980 Southwest 36.7706 108.7262 17 NA 21.7 3.5 7.9 5,227 09368020 Southwest 36.9258 108.7250 21 NA 2.1 6.1 8.8 5,334 09368500 Southwest 37.3817 108.2581 16 15 39.5 26.3 33.4 9,705 09369000 Southwest 37.3703 108.2315 15 14 12.1 43.0 33.1 9,690 09369500 Southwest 37.3739 108.2306 15 13 12.1 25.3 31 9,388 09371000 Southwest 37.0275 108.7415 72 78 526.7 26.4 19 7,216 09371300 Southwest 37.3475 108.4829 11 NA 4.5 22.6 17.3 6,856 09372000 Southwest 37.3242 109.0157 56 56 347.5 15.5 14.9 6,407 09378170 Southwest 37.8467 109.3696 21 22 8.4 27.7 26.8 8,621 09378630 Southwest 37.7556 109.4765 41 42 3.8 35.7 26.3 8,680 09378650 Southwest 37.6808 109.4626 17 18 37.4 26.1 22.5 7,917 09378700 Southwest 37.5606 109.5787 29 23 205 28.9 15.4 6,807 09379000 Southwest 37.2661 109.6757 10 9 278.9 22.8 10.6 5,861 09379030 Southwest 36.3333 109.6243 15 NA 76.9 12.3 8.3 5,905 09379060 Southwest 36.4694 109.4062 14 NA 1.3 3.3 8.9 5,826 09379300 Southwest 37.2167 109.8173 15 NA 64.4 21.1 8.6 5,383 
Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado 15

Selection of Stations for Other 

Streamflow Statistics

Many USGS streamflow-gaging stations in the study 

area operate as peak-only or flood-hydrograph stations and as 

such do not record daily-mean streamflow data. However, the 

remaining streamflow statistics or “other streamflow statistics” 

(nonannual peak) considered in this report are computed 

from continuous daily-mean streamflow. Hence, a subset of 

the 422 stations needed to be identified for the purposes of 

this study.

Stations used for development of equations for 

estimating the annual- and monthly-mean flow characteristics, the minimum and maximum streamflow characteristics, 

and the flow-duration curve are a subset of the 422 stations 

described in the previous section. A total of 288 sites with a 

combined record of 9,877 years of annual mean streamflow 

were selected. These stations are identified in table 1 as those 

with an applicable count of annual streamflow values. The 

actual number of stations used in the other streamflow-statistic 

equations is slightly reduced to counts between 210 and 280 

because of factors such as the presence of zero-flow values or 

periods of partial streamflow record.

Finally, the authors concluded that the number of 

stations in the Plains hydrologic region was inadequate for 

regression-equation development for any of the streamflow 

statistics other than peak streamflow. Additionally, the presence of substantial record of zero flows at many stations 

throughout the region, which is attributed in part to the lack 

of abundant precipitation and sandy soils, makes direct 

application of conventional regional-regression techniques, 

such as shown in this report, difficult and any resulting equations of questionable applicability.

Computation of Streamflow Statistics 

and Basin and Climatic Characteristics

The methods used for computing the streamflow statistics 

and basin and climatic characteristics used in the development 

of the regression equations are described in this section. The 

resulting streamflow statistics and basin and climate characteristics are used as the respective response and predictor variables 

in the regression analysis.

Peak-Streamflow Frequency

The annual peak-streamflow data by station were used 

to estimate station-specific peak-streamflow magnitude by 

recurrence intervals, such as the 100-year peak streamflow. 

Peak streamflow estimates by station and T-year recurrence 

interval provide the basis for computing regional peakstreamflow regression equations.

The station-specific peak-streamflow values used for this 

report were computed using the computer program PeakFQ

(Flynn and others, 2006) for all annual-peak streamflows 

representative of natural-flow conditions. PeakFQ is based 

on the guidelines for estimating peak-streamflow frequency 

that are described by the Interagency Advisory Committee on 

Water Data (1982). The guidelines are commonly referred to 

by practitioners as “Bulletin 17B.”

The Bulletin 17B guidelines fit a Pearson Type III distribution to the product moments of the logarithms of annual 

peak streamflow. The product moments are mean, standard 

deviation, and skew. To compensate for effects of short record 

at a station, station skew is combined or weighted with a 

generalized value that is derived from a generalized skew 

map, which is included in Bulletin 17B. The program also 

provides for conditional probability adjustments for sites with 

zero-flow values for the annual peak. All other default settings 

of PeakFQ were used, and the program was operated in a 

batch or automated mode by using default settings to estimate 

station-specific, peak streamflow by recurrence intervals for 

this study. These station-specific, peak-streamflow values are 

considered the results of intermediate computations and are 

not reported here.

Annual- and Monthly-Mean Streamflow 

and Flow-Duration Curves

Daily-mean streamflow data for the 288 stations were 

used to compute the annual- and monthly-mean streamflows and the station-specific flow-duration curves. Not all 

288 stations could be used, however, because of zero-flow 

conditions. Four sites have annual-mean streamflow values 

of zero, and various stations have one or more monthly-mean 

streamflows of zero. Station-specific annual- and monthlymean streamflows and flow-duration curve values provide 

the basis for developing regional equations for estimation 

of these streamflow statistics. Annual-mean streamflows are 

computed as the arithmetic mean of all annual-mean streamflows representative of natural-flow conditions. Monthlymean streamflows are computed as the arithmetic mean of 

all monthly-mean streamflows representative of natural-flow 

conditions. The flow-duration values are computed by sorting 

or ranking the daily-mean streamflow data and linearly interpolating to the five exceedance percentiles of interest (10, 25, 

50, 75, and 90).

Minimum and Maximum 7-Day Streamflow

Minimum- and maximum 7-day, T-year streamflows are 

computed from analysis of the 7-day minimum and maximum 

daily-mean streamflow for each year of record representative 

of natural-flow conditions. The 7-day, T-year statistics are the 

minimum or maximum consecutive 7-day mean streamflow 
16 Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado

Table 2. Basin and climatic characteristics evaluated for use in regional regression equations.

[NED, National Elevation Dataset; PRISM, Parameter-Elevation Regressions on Independent Slopes Model; km, kilometer; NOAA, National Oceanic and 

Atmospheric Administration; DAYMET, Daymet project]

Characteristic Unit Datasets used

Drainage area square

miles

Watershed Polygon generated using StreamStats process

Maximum elevation feet 10-meter NED

Minimum elevation feet 10-meter NED

Relief (difference between maximum and minimum elevations) feet 10-meter NED

Mean watershed elevation feet 10-meter NED

Mean watershed slope (not channel slope) percent 10-meter NED

Percentage of area with slopes greater than 30 percent percent 10-meter NED

Percentage of area with slopes greater than 30 percent and facing north percent 10-meter NED

Percentage of area with slopes greater than 15 percent percent 10-meter NED

Percentage of area with slopes greater than 15 percent and facing north percent 10-meter NED

Percentage of area above 7,500 feet percent 10-meter NED

Mean annual precipitation inches PRISM 4 km,a 8 kmb

6-hour, 2-year precipitation inches NOAA-Atlas 14,c NOAA-Atlas 2d

24-hour, 2-year precipitation inches NOAA-Atlas 14,c NOAA-Atlas 24

6-hour, 100-year precipitation inches NOAA-Atlas 14,c NOAA-Atlas 2d

24-hour, 100-year precipitation inches NOAA-Atlas 14,c NOAA-Atlas 2d

Mean annual number of wet days days DAYMET a

Used for Colorado, Utah, Arizona, New Mexico, and Wyoming.

b

Used for Nebraska, Kansas, Oklahoma, and Texas.

c

Used for Utah, Arizona, and New Mexico.

d

Used for Colorado, Wyoming, Nebraska, Kansas, Oklahoma, and Texas.

expected to occur once every T-years or that has an exceedance probability of 1/T, and these statistics provide the basis 

for developing regional equations for estimation of minimum 

and maximum 7-day streamflow.

Minimum- and maximum-streamflow frequency statistics 

were estimated using the methods described by Riggs (1972) 

implemented by the computer program SWSTAT (Lumb and 

others, 1990). The use of SWSTAT in the context of this report 

requires the explicit assumption that the log-Pearson Type III 

distribution is simultaneously suitable for low- and high-flow 

frequency analysis in Colorado. The general approach implemented by SWSTAT includes the following: Annual series of 

the minimum or maximum 7-day streamflows by station are 

computed by a “sliding window,” and the product moments of 

mean, standard deviation, and skew of the logarithms of the 

streamflow values are computed. Finally, a log-Pearson Type 

III distribution is fit to the product moments, and the quantiles 

for the 2-year, 10-year, and 50-year recurrence intervals are 

extracted to produce the station-specific minimum and maximum 7-day, T-year streamflow statistics.

Basin and Climatic Characteristics

Based on the results of previous regional streamflow 

studies conducted in Colorado and neighboring States 

(Kircher and others, 1985; Thomas and others, 1997; Vaill, 

1999; Hortness and Berenbrock, 2001; Berenbrock, 2002; 

Miller, 2003; Hortness, 2006; Waltemeyer, 2006; and Kenney 

and others, 2007) and on the availability of readily accessible 

data, a total of 17 characteristics (11 basin and 6 climatic 

characteristics) that are listed in table 2 were evaluated as 

candidate predictor variables in the regression analysis. For 

each of the 422 stations utilized in this study for the development of the regression equations, values for all 17 characteristics were calculated using various techniques involving 

geographic information system technology and multiple data 

sources that are listed in table 3.

Exploratory graphical and statistical analysis of relations between the basin and climatic characteristics was 

conducted to narrow the list of candidate characteristics into 

those that are appropriate or applicable variables for regression analysis. The graphical and statistical analysis considered 

strength of correlation or concordance, linearity, and crosscorrelation between variables. For example, mean annual 

precipitation and mean watershed elevation are strongly 

related in Colorado; so, to a degree, having one is equivalent 

to having the other. The decision process also is influenced 

by the number of stations (degrees of freedom) by region. 

The graphical and statistical analysis resulted in selection 

of the six predictor variables of drainage area (A) in square 

miles; mean watershed elevation (E) in feet; mean watershed slope (S) in percent; percentage of drainage area above 

7,500 feet of elevation (A7500); mean annual precipitation (P) 

in inches; and 6-hour, 100-year precipitation (6P100) in inches. 

Only these six variables are considered for the remainder of 

this report.
Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado 17

Table 3. Sources of data used to compute basin and climatic characteristics.

Dataset name Source description

Parameter-elevation Regressions on Independent 

Slopes Model climate mapping system (PRISM)

Total Precipitation (30-year average, 1971–2000)

Daly, Christopher, Nielson, R.P., and Phillips, D.L., 1994, A statistical-topographic 

model for mapping climatological precipitation over mountainous terrain: Journal 

of Applied Meteorology, v. 33, no. 2, p. 140–158, accessed August 15, 2007, 

at http://www.prism.oregonstate.edu/products/

Daily surface weather and climatological summaries Daymet Project, Daily surface weather and climatological summaries at 1-kilometer 

resolution over the conterminous United States, accessed August 15, 2007, at 

http://www.daymet.org

Precipitation frequency atlas for the Western 

United States (National Oceanic and Atmospheric 

Administration Atlas 14)

Bonnin, G., Martin, D., Lin, B., Parzybok, T., Yekta, M., and Riley, D., 2006, Precipitation frequency Atlas of the United States: National Weather Service, National Oceanic 

and Atmospheric Administration Atlas 14, Volume 1, version 4.0, accessed August 16, 

2007, at http://hdsc.nws.noaa.gov/hdsc/pfds/docs/NA14Vol1.pdf

Precipitation frequency atlas for the Western 

United States (National Oceanic and Atmospheric 

Administration Atlas 2)

Miller, J.F., Frederick, R.H., and Tracy, R. J., 1973, Precipitation frequency 

Atlas of the United States: National Weather Service, National Oceanic and 

Atmospheric Administration Atlas 2, Volume III, accessed August 16, 2007, 

at http://www.nws.noaa.gov/oh/hdsc/noaaatlas2.htm

National Elevation Dataset (NED) 10-meter resolution U.S. Geological Survey, 2007, National elevation dataset: accessed August 13, 2007, 

at http://ned.usgs.gov/

Computation of Regional Regression Equations

The computation of the regional regression equations 

is described in this section. Multilinear regression was used 

to define statistical relations between each of the streamflow 

statistics and two or more basin and climatic characteristics. 

A description of the principles of regional regression is beyond 

the scope of this report. Descriptions of the principles are 

available in references such as Helsel and Hirsch (2002) or 

Montgomery and others (2001). For the current (2009) investigation, logarithmic transformations (base-10) were made on 

all streamflow statistics and basin and climatic characteristics 

prior to the development of the regression equations. The 

data were logarithmically transformed in order to increase 

linearity between the regression variables and to acquire a 

constant variance of the regression residuals. For the A7500 

variable, which is presented as a percentage from 0 to 100, a 

value of 1 percent was added before logarithmic transformation to avoid null values associated with the inability to take 

a logarithm of zero.

For the current (2009) investigation, two forms of related 

regression techniques were used—generalized least-squares 

(GLS) and weighted least-squares (WLS) regression analysis. 

GLS regression was used exclusively to compute equations 

for peak-streamflow and 7-day minimum and maximum 

streamflow estimation. WLS was used exclusively to compute 

equations for annual- and monthly-mean streamflow and flowduration curve estimation.

Generalized Least-Squares Regression

The regionalized regression equations for computing the 

peak-, minimum-, and maximum-streamflow equations were 

developed using the GLS method described by Stedinger 

and Tasker (1985) and Tasker and Stedinger (1989). For the 

regional streamflow-frequency regression analysis reported 

here, GLS regression was preferred over WLS regression 

because GLS is an extension of WLS that accounts for cross 

correlation between response variables. WLS regression 

only accounts for differences in station record length and 

uncertainty in the station-specific streamflow statistics and 

assumes independence between response variables. A summary of variables, units, and regression diagnostics reported 

for the GLS and WLS regression equations is shown in 

figure 2.

The regression equations from GLS regression for 

estimation of peak, minimum, and maximum streamflow 

are listed by region in the left-hand page of figures 3–7. The 

figures identify the streamflow statistic, the regression method, 

the number of respective stations used to develop the equations, numerical values of regression diagnostics, and a “check 

mark” that signifies the general reliability of the equation 

based on inspection of residual plots. For the 7-day minimum 

streamflow equations the station count decreases as the recurrence interval increases because of increases in the number 

of zero values in the station-specific estimates of the 7-day 

minimum streamflow.

Figures 3–7 provide appropriate GLS-regression diagnostics for each equation. These are the standard error of prediction, the pseudo R-squared statistic, and the standard model 

error. Readers are directed to Stedinger and Tasker (1985) 

and Tasker and Stedinger (1989) for details. Each equation 

is statistically significant with a p-value less than 0.01. The 

ranges of the predictor variables also are listed in the figures. 

These ranges can be used to assess equation applicability. The 

applicability of the equations for ungaged sites with basin 

and climate characteristics outside the range of the predictor 

variables is questionable.
18 Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado

Regression Equation Response Variables

Variable Variable definition

QT T-year peak streamflow, in cubic feet per second

7

QT

min 7-day, T-year minimum streamflow, in cubic feet per second

7

QT

max 7-day, T-year maximum streamflow, in cubic feet per second

Qann Annual-mean streamflow, in cubic feet per second

Qmonth Monthly-mean streamflow by abbreviation, in cubic feet per second

Q#th Daily-mean streamflow as exceedance probability as percent, in cubic feet per second

Regression Equation Predictor Variables

Variable Variable definition

A Drainage area, in square miles

A7500 Percentage of A above 7,500 feet of elevation plus 1

E Mean elevation of watershed, in feet

P Mean annual precipitation, in inches

6

P100 6-hour, 100-year precipitation, in inches

S Mean watershed slope, in percent

Regression Equation Diagnostics for GLS and WLS Regression Equations

Diagnostic Diagnostic Definition

SEP Standard error of prediction (WLS and GLS), in percent

adjR2 100 × adjusted R-squared (WLS only), dimensionless

pseudoR2 100 × pseudo R-squared (GLS only), dimensionless

SME Standard model error (GLS only), in percent

√ Mark that qualifies (see text) the reliability of regression residuals

Figure 2. Summary of variables and regression diagnostics for regional equations. GLS, Generalized Least Squares; WLS, 

Weighted Least Squares.

Weighted Least-Squares Regression

The regionalized regression equations for computing 

the annual-and monthly-mean streamflow equations and 

the equations for the flow-duration curve were developed 

using WLS regression. For the regional regression analysis reported here, WLS regression was preferred over GLS 

regression because GLS regression was specifically developed 

for use with T-year type streamflow statistics and is difficult 

to extend to other streamflow statistics. The weights used 

for the WLS regression for the annual-mean and monthlymean equations are based on the variance of the logarithms 

of the observed values. Specifically, stations with lesser 

variance received greater weighting. The weights for flowduration equations are based on length of available record 

in years. The equations for estimating monthly- and annualmean streamflows and flow-duration curves for four of the 

five hydrologic regions are listed in figures 3–7. Equations 

were not developed for the Plains hydrologic region for 

reasons outlined in section “Selection of Stations for Other 

Streamflow Statistics.”

The figures also provide appropriate WLS-regression 

diagnostics for each equation. These include the standard error 

of prediction and the adjusted R-squared statistic. Each equation is statistically significant with a p-value less than 0.01. 

Readers are directed to standard texts on regression such as 

Helsel and Hirsch (2002) or Montgomery and others (2001) 

for details. Similar to the GLS-regression equations, the ranges 

of the predictor variables also are listed in the figures.

Discussion of Selection of Variables

The six selected basin and climatic characteristics were 

examined as predictor variables for the regression equations reported in figures 3–7. Regression-equation development is an inherently iterative process, and the modeler must 
Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado 19

balance several competing objectives, including the tradeoff 

between number of variables to include in the equation and 

the degrees of freedom (data points) used to estimate 

regression coefficients.

One goal in the early stages of regression-equation 

development is to identify and select those basin and climatic 

characteristics that have a statistically significant effect on the 

dependent variables and to generally exclude those predictor 

variables having limited influence. For example, P and E are 

strongly coupled in the study area in which the latter influences the former through orographic effects that enhance the 

formation of precipitation; hence, it is not always optimal to 

have both variables present in an equation. Other variables can 

be selected on professional judgment and logic and confirmed 

by statistical significance. For example, A is a vital predictor 

variable for streamflow statistics and is the only common variable used in all regional equations developed by Kircher and 

others (1985) and Vaill (1999). For the regression equations 

reported here, A is similarly included.

The selection of variables also is influenced by various regression diagnostics such as statistical significance (as 

measured by p-values), residual standard error, the distribution 

of regression residuals, several coefficient-of-determination 

statistics (R-squared statistics) or R-squared-like statistics 

(pseudo R-squared for the GLS regression; see Griffis and 

Stedinger [2007]) and others. Selection of variables can 

also be influenced by the preference to maintain a consistent 

structural form to a set of estimating equations in order to 

help ensure physically consistent estimates. By maintaining a 

regionally consistent set of included variables in the equations 

with ensembles of T-year peak streamflow, situations such as 

the 50-year peak streamflow being estimated as less than the 

25-year peak streamflow are virtually eliminated. By maintaining a regionally consistent set of included variables in the 

equation ensembles for monthly streamflow, a smooth monthto-month variation in estimated streamflow, which is presumably more reflective of actual seasonal variations, is provided.

Application and Limitations of Regional 

Regression Equations

Application and limitations of the regional regression 

equations in figures 3–7 exist. The number of equations 

reported here is too large for a comprehensive discussion 

of the subtle details of each. However, all of the equations 

reported in the figures are statistically significant, with a 

p-value less than 0.01, and represent reasonably reliable 

equations that were developed from USGS data, available 

sample sizes, and techniques that are within the scope of 

the report.

The authors have assessed each equation and assigned 

a qualification as a “boxed check mark” to each equation 

based on visual interpretation of the residual plots (not 

reported here) for each equation. A boxed check mark is 

provided in figures 3–7 for each equation for which no bias 

was identified. A boxed check mark is not provided for those 

equations for which the residual plots indicate that bias (as 

either overestimation or underestimation) could exist for some 

combinations of basin and climatic characteristics. Such biases 

are indicated by nonlinear relations in the residual plots or the 

presence of heteroscedasticity (nonconstant variance). The 

magnitude and direction of bias are difficult to systematically 

quantify and mitigate for each of those equations within the 

scope of this report. For each of the equations listed in the 

figures, however, the qualification provides a mechanism by 

which the potential for biased estimation can be communicated to practitioners.

All streamflow statistics estimated from the equations 

are considered to be associated with natural basin and climatic 

characteristics and are not representative of anthropogenically 

influenced conditions, such as site-specific situations involving 

factors like the placement or removal of a dam or substantial 

diversion and return flows. In general, the equations and their 

associated errors are most valid for ungaged watersheds with 

basin and climatic characteristics well within the ranges of the 

predictor variables for each equation. Estimates and associated 

errors for ungaged sites having basin or climate characteristics 

outside the reported range of the independent variables are less 

applicable and could be erroneous. As a result, consideration 

of these and other limitations requires substantial judgment 

on the part of the practitioners for reliable application of the 

regional equations for estimation of natural streamflow statistics in Colorado.

The USGS has developed a Web-based computer program called StreamStats (Ries and others, 2004). The 

software facilitates the computation of streamflow statistics 

using regional regression equations or other procedures that 

have been published previously. StreamStats allows 

the user to obtain streamflow statistics for both gaged and

ungaged sites by selecting a specific stream location on a 

map interface. If the location of interest lacks a station, the 

algorithms in StreamStats delineate the watershed for 

the location, compute basin and climatic characteristics, 

and provide estimates of the streamflow statistics using the 

available regression equations. In general, the computational 

algorithms used to generate basin and climatic characteristics 

for the regression equations reported here are consistent with 

those of StreamStats. As a result, predictor variables 

used to develop the equations presented in this report are 

compatible for use with StreamStats, which represents 

a unique contribution to ungaged-site, regional-streamflow 

estimation in Colorado. Finally, regression equations reported 

here for Colorado have been included in StreamStats to 

ease the computation of estimates of streamflow statistics 

for practitioners.
20 Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado

Figure 3. Regional regression equations for the Mountain hydrologic region.

Summary of Variables, Units, and Regression Diagnostics is shown in figure 2.

Q A S P

Q A S P

Q

2

2 05 0 78 0 17 2 10

5

1 51 0 77 0 16 1 85

10

1

10

10

10

=

=

=

−

−

−

. . . .

. . . .

. . . .

. . . .

.

20 0 77 0 14 1 71

25

0 90 0 75 0 16 1 55

50

0 68 0

10

10

A S P

Q A S P

Q A

=

=

−

− . . .

. . . .

. .

75 0 16 1 45

100

0 46 0 75 0 14 1 35

200

0 28 0 75

10

10

S P

Q A S P

Q A

=

=

−

− S P

Q A S P

0 13 1 26

500

0 06 0 74 0 15 1 14 10

. .

. . . . = −

7 2

1 99 0 82 2 08

7 10

1 38 0 85 1 78

7 50

10

10

1

Q A P

Q A P

Q

max . . .

max . . .

max

=

=

=

−

−

0−0.94 0.85 1.57 A P

7 2

26 56 1 13 1 26 5 85

7 10

33 76 1 20 2 25 7

10

10

Q A P E

Q A P E

min . . . .

min . . .

=

=

−

− ..

min . . . .

20

7 50

18 56 1 17 1 86 3 56 Q = 10 A P E −

√

√

√

√

√

√

√

√

√

√

√

√

√

√

SEP = 49,

SEP = 44,

SEP = 41,

SEP = 40,

SEP = 39,

SEP = 36,

SEP = 36,

SEP = 33,

SEP = 89,

SEP = 153,

SEP = 126,

SEP = 46,

SEP = 35,

SEP = 31,

pseudoR2

 = 83,

pseudoR2

 = 86,

pseudoR2

 = 87,

pseudoR2

 = 88,

pseudoR2

 = 88,

pseudoR2

 = 90,

pseudoR2

 = 90,

pseudoR2

 = 91,

pseudoR2

 = 80,

pseudoR2

 = 67,

pseudoR2

 = 72,

pseudoR2

 = 86,

pseudoR2

 = 92,

pseudoR2

 = 94,

SME = 48,

SME = 43,

SME = 40,

SME = 39,

SME = 37,

SME = 34,

SME = 34, and

SME = 31.

SME = 87,

SME = 148, and

SME = 122.

SME = 45,

SME = 34, and

SME = 30.

Peak Streamflow Equations for Mountain Hydrologic Region

Minimum Streamflow for Mountain Hydrologic Region

Maximum Streamflow for Mountain Hydrologic Region

Generalized least-squares (GLS) regression, 141 stations

Approximate range of predictor variables

Generalized least-squares (GLS) regression, 124, 118, and 111 stations

Approximate range of predictor variables

Generalized least-squares (GLS) regression, 130 stations

Approximate range of predictor variables

A: 1–1,060 square miles; S: 7.6–60.2 percent; and P: 18–47 inches

A: 1–1,060 square miles; P: 18–47 inches; and E: 8,600–12,000 feet elevation

A: 1–1,060 square miles and P: 18–47 inches
Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado 21

Figure 3. Regional regression equations for the Mountain hydrologic

region.—Continued

Summary of Variables, Units, and Regression Diagnostics is shown in figure 2.

Q A P

Q A P

Q

10th

25th

50th

=

=

=

−

−

−

10

10

10

2 64 0 89 2 22

2 86 0 96 1 92

2 6

. . .

. . .

. 9 0 98 1 49

2 85 1 01 1 40

3 46 1 10 1 59

10

10

A P

Q A P

Q A P

. .

. . .

. . .

75th

90th

=

=

−

−

Q A P

Q A P

Q A

ann

oct

nov

=

=

=

−

−

−

10

10

10

2 31 0 88 1 71

3 29 0 97 1 98

3 14 0

. . .

. . .

. . .

. . .

. . .

98 1 78

2 90 1 00 1 52

2 99 1 02 1 53

10

10

P

Q A P

Q A P

Q

dec

jan

feb

=

=

=

−

−

10

10

10

2 92 1 02 1 46

2 87 1 06 1 42

2 95 1 14

−

−

−

=

=

. . .

. . .

. .

A P

Q A P

Q A P

mar

apr

1 64

1 60 0 94 1 44

1 29 0 82 1 52

2

10

10

10

.

. . .

. . .

Q A P

Q A P

Q

may

jun

jul

=

=

=

−

−

− . . .

. . .

. . .

80 0 84 2 23

2 73 0 85 1 91

2 93 0 92 1 84

10

10

A P

Q A P

Q A P

aug

sep

=

=

−

−

√

√

√

√

√

√

√

√

√

√

√

√

√

√

SEP = 11,

SEP = 19,

SEP = 21,

SEP = 21,

SEP = 24,

SEP = 26,

SEP = 24,

SEP = 19,

SEP = 21,

SEP = 21,

SEP = 56,

SEP = 61,

SEP = 32,

SEP = 19,

SEP = 29,

SEP = 29,

SEP = 39,

SEP = 72,

adjR2

 = 93,

adjR2

 = 89,

adjR2

 = 90,

adjR2

 = 89,

adjR2

 = 88,

adjR2

 = 88,

adjR2

 = 89,

adjR2

 = 92,

adjR2

 = 87,

adjR2

 = 87,

adjR2

 = 72,

adjR2

 = 75, and

adjR2

 = 86.

adjR2

 = 90,

adjR2

 = 88,

adjR2

 = 88,

adjR2

 = 86, and

adjR2

 = 82.

Annual and Monthly Mean Streamflow for Mountain Hydrologic Region

Flow-Duration Curve for Mountain Hydrologic Region

Weighted least-squares (WLS) regression, 129 stations

Approximate range of predictor variables

Weighted least-squares (WLS) regression, 129 stations

Approximate range of predictor variables

A: 1–1,060 square miles and P: 18–47 inches

A: 1–1,060 square miles and P: 18–47 inches
22 Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado

Figure 4. Regional regression equations for the Northwest hydrologic region.

Summary of Variables, Units, and Regression Diagnostics is shown in figure 2.

7 2

34 73 0 83 8 56

7 10

38 52 0 90 9 42

7 50

10

10

Q A E

Q A E

Q

min . . .

min . . .

min

=

=

−

−

= − 10 36. . 44 0 94 8.84 A E

7 2

7 19 1 03 3 60

7500

1 25

7 10

5 35 1 00 2 48

10

10

Q A P A

Q A P

max . . . .

max . . .

=

=

−

− A

Q A P A

7500

1 31

7 50

3 90 0 94 1 80

7500

1 23 10

.

max . . . . = −

Q A A P

Q A A P

2

5

=

=

− −

− −

10

10

1 15 0 75

7500

0 41 2 15

0 49 0 76

7500

0 54 2

. . . .

. . . .00

0 10 0 75

7500

0 63 1 93

0 35 0 75

7500

0 7

10

10

Q A A P

Q A A

10

25

=

=

− −

−

. . . .

. . . 2 1 82

0 65 0 74

7500

0 77 1 74

0 93 0 74

7500

10

10

P

Q A A P

Q A A

.

. . . .

. .

50

100

=

=

−

−

− =

=

0 81 1 65

1 20 0 73

7500

0 85 1 56

1 53 0 72

10

10

. .

. . . .

. .

P

Q A A P

Q A

200

500 A P 7500

−0 8. . 8 1 44

√

√

√

√

√

√

√

√

√

√

√

√

SEP = 113,

SEP = 88,

SEP = 79,

SEP = 74,

SEP = 74,

SEP = 75,

SEP = 76,

SEP = 79,

SEP = 212,

SEP = 280,

SEP = 338,

SEP = 86,

SEP = 59,

SEP = 51,

pseudoR2 = 72,

pseudoR2 = 75,

pseudoR2 = 77,

pseudoR2 = 79,

pseudoR2 = 79,

pseudoR2 = 79,

pseudoR2 = 79,

pseudoR2 = 79,

pseudoR2 = 42,

pseudoR2 = 41,

pseudoR2 = 39,

pseudoR2 = 84,

pseudoR2 = 89,

pseudoR2 = 90,

SME = 108,

SME = 84,

SME = 75,

SME = 70,

SME = 69,

SME = 70,

SME = 70, and

SME = 72.

SME = 199,

SME = 259, and

SME = 307.

SME = 82,

SME = 56, and

SME = 48.

Peak Streamflow Equations for Northwest Hydrologic Region

Minimum Streamflow for Northwest Hydrologic Region

Maximum Streamflow for Northwest Hydrologic Region

Generalized least-squares (GLS) regression, 90 stations

Approximate range of predictor variables

Generalized least-squares (GLS) regression, 52, 47, and 42 stations

Approximate range of predictor variables

Generalized least-squares (GLS) regression, 59 stations

Approximate range of predictor variables

A: 1–5,250 square miles; A7500: 0–100 percent, and P: 8–49 inches

A: 5–5,250 square miles; E: 6,880–10,480 feet

A: 5–5,250 square miles, P: 8–49 inches, and A7500: 0–100 percent
Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado 23

Figure 4. Regional regression equations for the Northwest hydrologic

section.—Continued

Summary of Variables, Units, and Regression Diagnostics is shown in figure 2.

Annual and Monthly Mean Streamflow for Northwest Hydrologic Region

Flow-Duration Curve for Northwest Hydrologic Region

Weighted least-squares (WLS) regression, 56 stations

Approximate range of predictor variables

Weighted least-squares (WLS) regression, 62 stations

Approximate range of predictor variables

A: 1–5,250 square miles and P: 8–49 inches

A: 1–5,250 square miles and P: 8–49 inches

Q A P

Q A P

Q A

ann

oct

nov

=

=

=

−

−

−

10

10

10

4 98 0 95 3 32

4 32 1 01 2 54

4 68 1

. . .

. . .

. . .

. . .

. . .

08 2 62

4 53 1 07 2 46

4 73 1 05 2 62

10

10

P

Q A P

Q A P

Q

dec

jan

feb

=

=

=

−

−

10

10

10

4 63 1 14 2 46

4 39 1 14 2 36

4 77 1 06

−

−

−

=

=

. . .

. . .

. .

A P

Q A P

Q A P

mar

apr

3 02

4 54 0 96 3 40

6 90 1 00 4 87

4

10

10

10

.

. . .

. . .

Q A P

Q A P

Q

may

jun

jul

=

=

=

−

−

− . . .

. . .

. . .

37 0 83 3 09

3 03 0 84 1 98

2 62 0 92 1 55

10

10

A P

Q A P

Q A P

aug

sep

=

=

−

−

Q A P

Q A P

Q

10th

25th

50th

=

=

=

−

−

−

10

10

10

6 03 1 03 4 23

5 86 1 05 3 72

6 0

. . .

. . .

. 7 1 05 3 61

6 91 1 07 3 98

8 32 1 06 4 80

10

10

A P

Q A P

Q A P

. .

. . .

. . .

75th

90th

=

=

−

−

√

√

√

√

√

√

√

√

√

SEP = 29,

SEP = 85,

SEP = 66,

SEP = 61,

SEP = 66,

SEP = 56,

SEP = 43,

SEP = 66,

SEP = 47,

SEP = 61,

SEP = 52,

SEP = 78,

SEP = 99,

SEP = 52,

SEP = 56,

SEP = 66,

SEP = 91,

SEP = 223,

adjR2 = 88,

adjR2 = 78,

adjR2 = 83,

adjR2 = 82,

adjR2 = 81,

adjR2 = 85,

adjR2 = 90,

adjR2 = 85,

adjR2 = 84,

adjR2 = 82,

adjR2 = 68,

adjR2 = 67, and

adjR2 = 70.

adjR2

 = 86,

adjR2 = 85,

adjR2 = 83,

adjR2 = 80, and

adjR2 = 70.
24 Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado

Figure 5. Regional regression equations for the Rio Grande hydrologic region.

Summary of Variables, Units, and Regression Diagnostics is shown in figure 2.

Q A P

Q A P

Q A P

2

3 00 1 00 2 46

5

2 04 0 95 2 02

10

1 55 0 93 1

10

10

10

=

=

=

−

−

−

. . .

. . .

. . .

. . .

. . .

.

80

25

1 01 0 91 1 55

50

0 66 0 89 1 39

100

0 19

10

10

10

Q A P

Q A P

Q

=

=

=

−

−

− A P

Q A P

Q A P

0 87 1 17

200

0 03 0 86 1 11

500

0 52 0 84 0 85

10

10

. .

. . .

. . .

=

=

−

7 2

44 17 1 03 10 71

7 10

46 35 1 09 11 15

7 50

10

10

Q A E

Q A E

Q

min . . .

min . . .

m

=

=

−

−

in . . . = − 10 49 44 1 13 11 88 A E

7 2

3 83 0 98 2 89

7 10

2 22 0 92 2 11

7 50

10

10

1

Q A P

Q A P

Q

max . . .

max . . .

max

=

=

=

−

−

0−1 3. . 8 0 86 1 7. 4 A P

√

√

√

√

√

√

√

√

√

√

√

√

√

√

SEP = 67,

SEP = 57,

SEP = 54,

SEP = 52,

SEP = 51,

SEP = 51,

SEP = 52,

SEP = 54,

SEP = 111,

SEP = 189,

SEP = 165,

SEP = 81,

SEP = 55,

SEP = 31,

pseudoR2

 = 80,

pseudoR2

 = 83,

pseudoR2

 = 84,

pseudoR2

 = 84,

pseudoR2

 = 85,

pseudoR2

 = 85,

pseudoR2

 = 84,

pseudoR2

 = 84,

pseudoR2

 = 51,

pseudoR2

 = 37,

pseudoR2

 = 47,

pseudoR2

 = 68,

pseudoR2

 = 77,

pseudoR2

 = 94,

SME = 64,

SME = 55,

SME = 51,

SME = 49,

SME = 48,

SME = 48,

SME = 49, and

SME = 49.

SME = 103,

SME = 170, and

SME = 148.

SME = 76,

SME = 52, and

SME = 30.

Peak Streamflow Equations for Rio Grande Hydrologic Region

Minimum Streamflow for Rio Grande Hydrologic Region

Maximum Streamflow for Rio Grande Hydrologic Region

Generalized least-squares (GLS) regression, 44 stations

Approximate range of predictor variables

Generalized least-squares (GLS) regression, 28, 27, and 24 stations

Approximate range of predictor variables

Generalized least-squares (GLS) regression, 31 stations

Approximate range of predictor variables

A: 2–517 square miles and P: 19–45 inches

A: 13–517 square miles and E: 8,600–12,000 feet elevation

A: 13–517 square miles and P: 19–45 inches
Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado 25

Figure 5. Regional regression equations for the Rio Grande hydrologic

region.—Continued

Summary of Variables, Units, and Regression Diagnostics is shown in figure 2.

Annual and Monthly Mean Streamflow for Rio Grande Hydrologic Region

Flow-Duration Curve for Rio Grande Hydrologic Region

Weighted least-squares (WLS) regression, 32 stations

Approximate range of predictor variables

Weighted least-squares (WLS) regression, 32 stations

Approximate range of predictor variables

A: 2–517 square miles and E: 7,790–11,500 feet

A: 2–517 square miles and E: 7,790–11,500 feet

Q A E

Q A E

Q

ann

oct

nov

=

=

=

−

−

−

10

10

10

33 58 1 12 8 24

32 88 0 95 8 04

24 7

. . .

. . .

. 9 0 90 6 02

17 71 0 86 4 26

13 34 0 83 3 18

10

10

A E

Q A E

Q A E

. .

. . .

. . .

dec

jan

=

=

−

−

Q A E

Q A E

Q

feb

mar

apr

=

=

=

−

−

−

10

10

10

11 68 0 87 2 75

9 32 0 97 2 14

5 09

. . .

. . .

. A E

Q A E

Q A E

1 10 1 16

37 25 1 26 9 23

61 30 1 23 15 22

10

10

. .

. . .

. . .

may

jun

=

=

−

−

Q A E

Q A E

Q

jul

aug

sep

=

=

=

−

−

−

10

10

10

53 30 1 07 13 17

43 00

1 03

10 59

4

. . .

.

.

.

1 4. . 9 0 99 10.19 A E

Q A E

Q A E

Q

10th

25th

50th

=

=

=

−

−

−

10

10

10

32 35 1 13 8 04

41 33 1 07 10 18

. . .

. . .

38 61 0 96 9 46

42 09 0 90 10 30

50 71 0

10

10

. . .

. . .

. .

A E

Q A E

Q A

75th

90th

=

=

−

− 89 12 42 E .

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

SEP = 47,

SEP = 26,

SEP = 26,

SEP = 36,

SEP = 36,

SEP = 29,

SEP = 21,

SEP = 56,

SEP = 61,

SEP = 61,

SEP = 52,

SEP = 26,

SEP = 29,

SEP = 61,

SEP = 39,

SEP = 52,

SEP = 107,

SEP = 179,

adjR2

 = 72,

adjR2 = 72,

adjR2 = 73,

adjR2 = 68,

adjR2 = 66,

adjR2 = 74,

adjR2 = 82,

adjR2 = 75,

adjR2 = 71,

adjR2 = 74,

adjR2 = 72,

adjR2 = 80, and

adjR2 = 75.

adjR2

 = 66,

adjR2 = 72,

adjR2 = 64,

adjR2 = 48, and

adjR2 = 44.
26 Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado

Figure 6. Regional regression equations for the Southwest hydrologic region.

Summary of Variables, Units, and Regression Diagnostics is shown in figure 2.

Peak Streamflow Equations for Southwest Region

Minimum Streamflow for Southwest Region

Maximum Streamflow for Southwest Region

Generalized least-squares (GLS) regression, 78 stations

Approximate range of predictor variables

Generalized least-squares (GLS) regression, 46, 37, and 33 stations

Approximate range of predictor variables

Generalized least-squares (GLS) regression, 59 stations

Approximate range of predictor variables

A: 1–4,390 square miles and A7500: 0–100 percent

A: 4–4,390 square miles, P: 10–51 inches, E: 5,600–11,600 feet

A: 4–4,390 square miles and P: 10–51 inches

Q A A

Q A A

Q

2

1 67 0 64

7500

0 10

5

2 13 0 62

7500

0 19

10

2 36

10

10

10

=

=

=

−

−

. . .

. . .

. A A

Q A A

Q A A

0 61

7500

0 23

25

2 61 0 60

7500

0 27

50

2 77 0 59

7

10

10

. .

. . .

. .

−

− =

= 500

0 30

100

2 91 0 59

7500

0 33

200

3 04 0 58

7500

0

10

10

−

−

−

=

=

.

. . .

. .

Q A A

Q A A .

. . .

36

500

3 21 0 58

7500

0 39 Q A = 10 A−

7 2

22 24 1 16 1 51 4 65

7 10

18 74 0 97 1 35 3

10

10

Q A P E

Q A P E

min . . . .

min . . .

=

=

−

− .

min . . . .

88

7 50

26 29 0 49 0 11 6 45 Q A = 10 P E −

7 2

4 07 0 99 3 10

7 10

2 68 0 93 2 44

7 50

10

10

1

Q A P

Q A P

Q

max . . .

max . . .

max

=

=

=

−

−

0−1 8. . 6 0 89 2 0. 3 A P

√

√

√

√

√

√

√

√

√

√

√

√

√

√

SEP = 90,

SEP = 71,

SEP = 67,

SEP = 66,

SEP = 67,

SEP = 69,

SEP = 71,

SEP = 75,

SEP = 226,

SEP = 255,

SEP = 354,

SEP = 64,

SEP = 43,

SEP = 33,

pseudoR2

 = 67,

pseudoR2

 = 52,

pseudoR2

 = 33,

pseudoR2

 = 88,

pseudoR2

 = 93,

pseudoR2

 = 95,

pseudoR2

 = 70,

pseudoR2

 = 75,

pseudoR2

 = 77,

pseudoR2

 = 78,

pseudoR2

 = 78,

pseudoR2

 = 78,

pseudoR2

 = 77,

pseudoR2

 = 77,

SME = 87,

SME = 69,

SME = 64,

SME = 63,

SME = 63,

SME = 65,

SME = 67, and

SME = 70.

SME = 207,

SME = 226, and

SME = 300.

SME = 61,

SME = 40, and

SME = 30.
Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado 27

Figure 6. Regional regression equations for the Southwest hydrologic

region.—Continued

Summary of Variables, Units, and Regression Diagnostics is shown in figure 2.

Annual and Monthly Mean Streamflow for Southwest Region

Flow-Duration Curve for Southwest Region

Weighted least-squares (WLS) regression, 57 stations

Approximate range of predictor variables

Weighted least-squares (WLS) regression, 57 stations

Approximate range of predictor variables

A: 1–4,390 square miles and P: 10–51 inches

A: 1–4,390 square miles and P: 10–51 inches

Q A P

Q A P

Q A

ann

oct

nov

=

=

=

−

−

−

10

10

10

4 37 0 91 2 98

4 80 1 00 2 89

4 59 0

. . .

. . .

. . .

. . .

. . .

91 2 78

4 22 0 91 2 45

4 28 0 96 2 39

10

10

P

Q A P

Q A P

Q

dec

jan

feb

=

=

=

−

−

10

10

10

3 97 0 98 2 18

3 79 1 00 2 12

4 98 1 12

−

−

−

=

=

. . .

. . .

. .

A P

Q A P

Q A P

mar

apr

3 11

5 16 1 01 3 63

6 13 1 05 4 30

5

10

10

10

.

. . .

. . .

Q A P

Q A P

Q

may

jun

jul

=

=

=

−

−

− . . .

. . .

. . .

19 0 91 3 58

4 60 0 94 2 95

8 72 0 98 5 46

10

10

A P

Q A P

Q A P

aug

sep

=

=

−

−

Q A P

Q A P

Q

10th

25th

50th

=

=

=

−

−

−

10

10

10

5 44 1 02 3 79

5 27 1 00 3 40

5 0

. . .

. . .

. 8 0 98 3 01

5 99 1 02 3 37

7 30 1 01 4 11

10

10

A P

Q A P

Q A P

. .

. . .

. . .

75th

90th

=

=

−

−

√

√

√

√

√

√

√

√

√

√

√

√

SEP = 56,

SEP = 85,

SEP = 91,

SEP = 91,

SEP = 207,

SEP = 32,

SEP = 107,

SEP = 61,

SEP = 52,

SEP = 56,

SEP = 32,

SEP = 21,

SEP = 24,

SEP = 36,

SEP = 134,

SEP = 297,

SEP = 134,

SEP = 134,

adjR2

 = 85,

adjR2 = 77,

adjR2 = 76,

adjR2 = 75,

adjR2 = 77,

adjR2 = 83,

adjR2 = 82,

adjR2 = 95,

adjR2 = 88,

adjR2 = 85,

adjR2 = 63,

adjR2 = 64, and

adjR2 = 79.

adjR2

 = 85,

adjR2 = 78,

adjR2 = 75,

adjR2 = 78, and

adjR2 = 72.
28 Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado

Figure 7. Regional regression equations for the Plains hydrologic region.

Summary

 The U.S. Geological Survey (USGS), in cooperation 

with the Colorado Water Conservation Board and the Colorado 

Department of Transportation, developed regional regression 

equations for estimation of various streamflow statistics that are 

representative of natural streamflow conditions in Colorado. 

Accurate estimates of various streamflow statistics are important for water-resource management, stream-related structural 

design, stream-hazard identification, and water-quality management. Streamflow statistics routinely are needed for sites in 

ungaged watersheds (ungaged sites) that lack nearby streamflow-gaging stations (stations) from which streamflow statistics 

could be directly computed. Regional regression equations are a 

common tool used to estimate streamflow statistics at ungaged 

sites across the Nation and Colorado.

Regional regression equations are based on statistical 

relations between (1) streamflow statistics of interest computed 

from applicable records of the stations and (2) basin and climatic 

characteristics, for which data are typically readily available. The 

use of regional equations generally represents a reliable and costeffective means for estimating streamflow statistics at ungaged 

sites, along with expressions of predictive uncertainty.

The purpose of this report is to present regional regression 

equations by hydrologic region for estimation of streamflow 

statistics for naturally flowing streams in Colorado. The equations were developed using the statistical relations between 

streamflow statistics (response variables) and basin and climatic 

characteristics (predictor variables).

For each of five hydrologic regions in Colorado, peakstreamflow equations that are based on peak-streamflow data 

from selected stations are presented for the 2-, 5-, 10-, 25-, 50-, 

100-, 200- and 500-year instantaneous-peak streamflows (peak 

streamflow). For four of the five hydrologic regions, minimum 

and maximum 7-day streamflow (7-day, T-year) equations 

based on daily-mean streamflow data from selected stations are 

presented for 7-day minimum 2-, 10-, and 50-year streamflows, 

as well as for 7-day maximum 2-, 10-, and 50-year streamflows. 

Other equations presented for the same four hydrologic regions 

include those for estimation of annual- and monthly-mean 

streamflow and streamflow-duration statistics for exceedances of 

10, 25, 50, 75, and 90 percent. The streamflow-duration statistics 

collectively are referred to as the “flow-duration curve.” The 

flow-duration values, presented in this report as Q10th, Q25th, 

Q50th, Q75th, and Q90th, indicate the percentage of days that a 

given daily-mean streamflow is exceeded. For example, a 10-percent flow-duration value (Q10th) is calculated as the daily-mean 

streamflow at a given station that is exceeded 10 percent of the 

time or 10 percent of the days. Finally, this report also describes 

some limitations associated with the equations, including an 

assessment of prediction errors and assessment of equation applicability for ungaged sites.

The regional equations for peak-streamflow estimation were 

developed using annual peak-streamflow data collected through 

water year 2006 (October 1, 2005, through September 30, 2006). 

The remaining equations, with the exception of the 7-day, T-year 

minimum streamflow equations, were developed using data 

through water year 2007. The 7-day, T-year minimum streamflow 

equations were developed using data collected through climate 

year 2007 (April 1, 2006, through March 31, 2007).

The study was limited to the use of several selected 

basin and climatic characteristics including drainage area; 

mean watershed elevation; mean watershed slope; percentage 

of drainage area above 7,500 feet of elevation; mean annual 

precipitation; and 6-hour, 100-year precipitation.

Peak Streamflow Equations for Plains Hydrologic Region

Generalized least-squares (GLS) regression, 69 stations

Approximate range of predictor variables

Summary of Variables, Units, and Regression Diagnostics is shown in figure 2.

A: 0.5–2,930 square miles and 6P100: 2.4–5.1 inches

Q A P

Q A P

Q A

2

1 26 0 52

6 100

0 35

5

0 94 0 57

6 100

1 64

10

0 85 0

10

10

10

=

=

=

. . .

. . .

. . .

. . .

. .

59

6 100

2 15

25

0 84 0 61

6 100

2 57

50

0 85 0 62

6 100

2

10

10

P

Q A P

Q A P

=

= .

. . .

. . .

79

100

0 88 0 63

6 100

2 98

200

0 95 0 63

6 100

3 37

500

10

10

Q A P

Q A P

Q

=

=

= 100 81 0 64

6 100

. . 3 5. 9 A P

√

√

√

√

√

√

√

√

SEP = 183,

SEP = 142,

SEP = 136,

SEP = 137,

SEP = 139,

SEP = 141,

SEP = 160,

SEP = 141,

pseudoR2

 = 40,

pseudoR2

 = 54,

pseudoR2

 = 58,

pseudoR2

 = 62,

pseudoR2

 = 64,

pseudoR2

 = 65,

pseudoR2

 = 65,

pseudoR2

 = 70,

SME = 174,

SME = 134,

SME = 128,

SME = 128,

SME = 129,

SME = 131,

SME = 147, and

SME = 128.
Selected References 29

The computation of the regional regression equations used 

multilinear regression to define statistical relations between each 

of the streamflow statistics and two or more basin and climatic 

characteristics. For the investigation, logarithmic transformations 

(base-10) were made on all streamflow statistics and basin and 

climatic characteristics prior to the development of the regression 

equations. The data were logarithmically transformed to increase 

linearity between the regression variables and to acquire a constant variance of the regression residuals.

For the investigation, two forms of related regression techniques were used—generalized least-squares (GLS) and weighted 

least-squares (WLS) regression analyses. GLS regression was 

used exclusively to compute equations for peak-streamflow and 

7-day minimum and maximum streamflow estimation. WLS was 

used exclusively to compute equations for annual- and monthlymean streamflow and flow-duration curve estimation.

The regionalized regression equations for computing the 

peak-, minimum-, and maximum-streamflow equations were 

developed using the GLS method. For the regional streamflowfrequency regression analysis reported here, GLS regression 

was preferred over WLS regression because GLS is an extension 

of WLS that accounts for cross correlation between response 

variables. WLS regression only accounts for differences in station 

record length and uncertainty in the station-specific streamflow 

statistics and assumes independence between response variables.

WLS regression was used for the development of regionalized regression equations for computing the annual- and 

monthly-mean streamflow equations and the equations for the 

flow-duration curve. WLS regression was preferred over GLS 

regression because GLS regression was specifically developed 

for use with T-year type streamflow statistics and is difficult 

to extend to other streamflow statistics. The weights used for 

the WLS regression for the annual-mean and monthly-mean 

equations are based on the variance of the logarithms of the 

observed values. The weights for flow-duration equations are 

based on length of available record in years.

Appropriate diagnostics for each of the equations are 

reported. These are standard error of prediction in percent (GLS 

and WLS), the adjusted R-squared statistic in percent (WLS 

only), the pseudo R-squared statistics in percent (GLS only), and 

the standard model error in percent (GLS only). Each of the equations is statistically significant with p-values less than 0.01. The 

ranges of the predictor variables also are provided. These ranges 

can be used to assess equation applicability. The applicability of 

the equations for ungaged sites with basin and climate characteristics outside the range of the predictor variables is questionable.

Application and limitations of the regional regression equations exist. All of the equations reported in the figures are statistically significant and represent reasonably reliable equations that 

have been developed from USGS data, available sample sizes, 

and techniques that are within the scope of the report.

The authors have assessed each equation and assigned 

a qualification to each equation based on visual interpretation of the residual plots (not reported here) for each equation. 

For some equations the residual plots indicate that bias (as 

either overestimation or underestimation) could exist for some 

combinations of basin and climatic characteristics. Such biases 

are indicated by nonlinear relations in the residual plots or the 

presence of heteroscedasticity (nonconstant variance). The magnitude and direction of bias are difficult to systematically quantify 

and mitigate for each of those equations within the scope of this 

report. For each of the equations listed in the figures, however, 

the qualification provides a mechanism by which the potential for 

biased estimation can be communicated to practitioners.

All streamflow statistics estimated from the equations are 

considered to be associated with natural basin and climatic characteristics and are not representative of anthropogenically influenced conditions, such as site-specific situations involving factors 

like the placement or removal of a dam or substantial diversion 

and return flows. In general, the equations and their associated 

errors are most valid for ungaged watersheds with basin and 

climatic characteristics well within the ranges of the predictor 

variables for each equation. Estimates and associated errors for 

ungaged sites having basin or climate characteristics outside the 

reported range of the independent variables are less applicable 

and could be erroneous. As a result, consideration of these and 

other limitations requires substantial judgment on the part of the 

practitioner for reliable application of the regional equations for 

estimation of natural streamflow statistics in Colorado.

Acknowledgments

The authors recognize John England of the Bureau 

of Reclamation and William H. Asquith, Kenny Eng, 

Robert Jarrett, Terry Kenney, Julie Kiang, and Karen Ryberg 

of the USGS for providing invaluable technical guidance and 

review for this study and report.

Selected References

Berenbrock, Charles, 2002, Estimating the magnitude of peak 

flows at selected recurrence intervals for streams in Idaho: 

U.S. Geological Survey Water-Resources Investigations 

Report 2002–4170, 59 p. 

Bonnin, G., Martin, T., Lin, D., Parzybok, B., Yekta, M., and 

Riley, D., 2006, Precipitation frequency Atlas of the United 

States: National Weather Service, National Oceanic and 

Atmospheric Administration Atlas 14, Volume III, accessed 

August 16, 2007, at http://www.nws.noaa.gov/oh/hdsc/

PF_documents/Atlas2_Volume3.pdf

Colorado Geological Survey, 2003, Ground water atlas of 

Colorado: Colorado Geological Survey Special Publication 

Number 53, 210 p.

Colorado State University, 2008, Precipitation map of Colorado: 

Fort Collins, Colorado State University, accessed July 28, 

2008 at http://waterknowledge.colostate.edu/prcp_map.htm
30 Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado

Daly, Christopher, Nielson, R.P., and Phillips, D.L., 1994, A 

statistical-topographic model for mapping climatological 

precipitation over mountainous terrain: Journal of Applied 

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2007 at http://www.prism.oregonstate.edu/products/

Daymet Project, daily surface weather and climatological 

summaries at 1 km resolution over the conterminous United 

States, accessed August 15, 2007, at http:://www.daymet.org

Fenneman, N.M., 1931, Physiography of the western United 

States: McGraw-Hill, Inc., New York, 534 p.

Flynn, K.M., Kirby, W.H., and Hummel, P.R., 2006, User’s 

manual for program PeakFQ, Annual flood frequency 

analysis using Bulletin 17B guidelines: U.S. Geological 

Survey Techniques and Methods book 4, chap. B4, 42 p.

Griffis, V.W., and Stedinger, J.R., 2007, The use of GLS 

regression in regional hydrologic analyses: Journal of 

Hydrology, v. 344, p. 82–95.

Headman, E.R., Moore, D.O., and Livingston, R.K., 1972, 

Selected streamflow characteristics as related to channel 

geometry of perennial streams in Colorado: U.S. Geological 

Survey Open-File Report 72–160, 24 p.

Helsel, D.R., and Hirsch, R.M., 2002, Statistical methods in 

water resources: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 4, chap. A3, 510 p.

Hortness, J.E., 2006, Estimating low-flow frequency statistics 

for unregulated streams in Idaho: U.S. Geological Survey 

Scientific Investigations Report 2006–5035, 31 p.

Hortness, J.E., and Berenbrock, C. 2001, Estimating monthly 

and annual streamflow statistics at ungaged sites in Idaho: 

U.S. Geological Survey Water Resources-Investigations 

Report 2001–4093, 36 p.

Interagency Advisory Committee on Water Data, 1982, Guidelines for determining flood flow frequency: U.S. Geological 

Survey, Office of Water Data Coordination, Bulletin 17B of 

the Hydrology Subcommittee, 183 p.

Jarrett, R.D., and Costa, J.E. , 1988, Evaluation of the flood 

hydrology in the Colorado Front Range using precipitation, 

streamflow and paleoflood data for the Big Thompson River 

basin: U.S. Geological Survey Water-Resources Investigations Report 87–4117, 37 p. 

Jarrett, R.D., and Tomlinson, E.M., 2000, Regional interdisciplinary paleoflood approach to assess extreme flood potential: Water Resources Research, v. 36, no. 10, p. 2957–2984. 

Kenney, T.A., Wilkowske, C.D., and Wright, S.J., 2007, 

Methods for estimating magnitude and frequency of peak 

flows for natural streams in Utah: U.S. Geological Survey 

Scientific Investigations Report 2007–5158, 28 p.

Kircher, J.E., Choquette, A.F., and Richter, B.D., 1985, 

Estimation of natural streamflow characteristics in western 

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Livingston, R.K., and Minges, D.R., 1987, Techniques for 

estimating regional flood characteristics of small rural 

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72 p.

Lumb, A.M., Kittle, J.L., and Flynn, K.M., 1990, Users 

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236 p.

Matthai, H.F., 1968, Magnitude and frequency of floods in the 

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491 p.

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Miller, K.A., 2003, Peak-flow characteristics of Wyoming 

streams: U.S. Geological Survey Water-Resources Investigations Report 2003–4107, 79 p.

Montgomery, D.C., Peck, E.A., and Vining, G.G., 2001, 

Introduction to linear regression analysis—Wiley series 

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U.S. Geological Survey Water-Supply Paper 1683, 475 p.
Selected References 31

Ries, K.G. III, Steeves, P.A,, Coles, J.D., Rea, A.H., and 

Stewart, D.W., 2004, StreamStats—A U.S. Geological Survey Web application for stream information: 

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book 4, chap. B1, 18 p.

Robson, S.G., and Banta, E.R., 1995, Ground water atlas of the 

United States, Segment 2—Arizona, Colorado, New Mexico, 

Utah: U.S. Geological Survey Hydrologic Investigations 

Atlas 730–C.

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

analysis I—Ordinary, weighted, and generalized leastsquares compared: American Geophysical Union, Water 

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Tasker, G.D., and Stedinger, J.R., 1986, Regional skew with 

weighted LS regression: American Society of Civil Engineers Journal of Water Resources Planning and Management, v. 112, no. 2, p. 225–237.

Tasker, G.D., and Stedinger, J.R., 1989, An operational GLS 

model for hydrologic regression: Journal of Hydrology, 

v. 111, p. 361–375.

Thomas, B.E., Hjalmarson, H.W., and Waltemeyer, S.D., 1997, 

Methods for estimating magnitude and frequency of floods 

in the southwestern United States: U.S. Geological Survey 

Water-Supply Paper 2433, 195 p.

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accessed August 13, 2007, at http://ned.usgs.gov/

U.S. Geological Survey, 2008, National Water Information 

System—NWISWeb: accessed on various dates in 2008 at 

http://waterdata.usgs.gov

Vaill, J.E., 1999, Analysis of the magnitude and frequency 

of floods in Colorado: U.S. Geological Survey WaterResources Investigations Report 99–4190, 35 p.

Waltemeyer, S.D., 2006, Analysis of the magnitude and 

frequency of peak discharges for the Navajo Nation in 

Arizona, Utah, Colorado, and New Mexico: U.S. Geological 

Survey Scientific Investigations Report 2006–5306, 42 p.

Western Regional Climate Center, 2008, Climate of Colorado: Western Regional Climate Center, URL accessed 

on July 28, 2008 at http://www.wrcc.dri.edu/narratives/

COLORADO.htm

Supplemental Information

Table 4. Streamflow-gaging stations used in the development of the regional streamflow regression equations.—Continued[Peak flow, 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year peak flow; Maximum 7Q2, maximum 7-day, 2-year flow; Maximum 7Q10, maximum 7-day, 10-year flow; Maximum 7Qflow; Minimum 7Q2, minimum 7-day, 2-year flow; Minimum 7Q10, minimum 7-day, 10-year flow; Minimum 7Q50, minimum 7-day, 50-year flow; Flow duration, 10-, 25-, 50-, 75X, station used in the development of regional regression equation for the indicated streamflow characteristic and hydrologic region; --, station not used in the development of rethe indicated streamflow characteristic and hydrologic region]

Station 

number Station name

Hydrologic

region

(fig. 1)

Streamflow characteristic

Peak

flow

Maximum Minimum 

7Q2 7Q10 7Q50 7Q2 7Q10 7Q50 An

06614800 Michigan River near Cameron Pass, CO Mountain X X X X X X X 06616000 North Fork Michigan River near Gould, CO Mountain X X X X X X -- 06617100 Michigan River at Walden, CO Mountain X X X X X X X 06618500 Illinois Creek at Walden, CO Mountain X X X X X X -- 06619000 Michigan River near Cowdrey, CO Mountain X X X X X -- -- 06620400 Douglas Creek above Keystone, WY Mountain X X X X -- -- 06621000 Douglas Creek near Foxpark, WY Mountain X X X X X X X 06622000 Big Creek at Big Creek Ranger Station, WY Mountain X -- -- -- -- -- -- 06622500 French Creek near French, WY Mountain X X X X X X X 06622700 North Brush Creek near Saratoga, WY Mountain X X X X X X X 06623800 Encampment River above Hog Park Creek, near 

Encampment, WY

Mountain X X X X X X X 

06624500 Encampment River at Encampment, WY Mountain X -- -- -- -- -- -- 06627500 Jack Creek at Matheson Ranch near Saratoga, WY Northwest X -- -- -- -- -- -- 06629100 Rattlesnake Creek near Walcott, WY Northwest X -- -- -- -- -- -- 06630800 Bear Creek near Elk Mountain, WY Mountain X -- -- -- -- -- -- 06631000 Medicine Bow River near Medicine Bow, WY Northwest X -- -- -- -- -- -- 

06631100 Wagonhound Creek near Elk Mountain, WY Mountain X -- -- -- -- -- -- 

06632400 Rock Creek above King Canyon Canal, near Arlington, WY Mountain X X X X X X X 06696980 Tarryall Creek at Upper Station near Como, CO Mountain X X X X -- -- -- 06699005 Tarryall Creek below Rock Creek near Jefferson, CO Mountain X -- -- -- -- -- -- 06700500 Goose Creek above Cheesman Lake, CO Mountain X -- -- -- -- -- -- 06706000 North Fork South Platte River below Geneva Creek, 

at Grant, CO 

Mountain X X X X X X X 

06707000 North Fork South Platte River at South Platte, CO Plains X -- -- -- -- -- -- 06709500 Plum Creek near Louviers, CO Plains X -- -- -- -- -- -- 06710385 Bear Creek above Evergreen, CO Mountain X -- -- -- -- -- -- 06710400 Cub Creek at Evergreen, CO Mountain X -- -- -- -- -- -- 06710600 Mount Vernon Creek near Morrison, CO Plains X -- -- -- -- -- -- 06710990 Parmalee Gulch at Mouth, at Indian Hills, CO Plains X -- -- -- -- -- -- 

06711000 Turkey Creek near Morrison, CO Plains X -- -- -- -- -- -- 

06712000 Cherry Creek near Franktown, CO Plains X -- -- -- -- -- -- 06716500 Clear Creek near Lawson, CO Mountain X X X X X X X 06717400 Chicago Creek below Devils Canyon near Idaho Sprgs CO Mountain X X X X X X X 06719500 Clear Creek near Golden, CO Plains X -- -- -- -- -- -- 06721500 North St. Vrain Creek near Allens Park, CO Mountain X X X X X X X 06722500 South St. Vrain Creek near Ward, CO Mountain X X X X X X X 06723000 Middle St. Vrain Creek near Allens Park, CO Mountain X X X X -- -- -- 06725500 Middle Boulder Creek at Nederland, CO Mountain X X X X X X X 
Table 4. Streamflow-gaging stations used in the development of the regional streamflow regression equations.—Continued [Peak flow, 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year peak flow; Maximum 7Q2, maximum 7-day, 2-year flow; Maximum 7Q10, maximum 7-day, 10-year flow; Maximum 7Qflow; Minimum 7Q2, minimum 7-day, 2-year flow; Minimum 7Q10, minimum 7-day, 10-year flow; Minimum 7Q50, minimum 7-day, 50-year flow; Flow duration, 10-, 25-, 50-, 75X, station used in the development of regional regression equation for the indicated streamflow characteristic and hydrologic region; --, station not used in the development of rethe indicated streamflow characteristic and hydrologic region] Station number Station name Hydrologic region (fig. 1) Streamflow characteristic Peak flow Maximum Minimum 

7Q2 7Q10 7Q50 7Q2 7Q10 7Q50 An

06726900 Bummers Gulch near El Vado, CO Plains X -- -- -- -- -- -- 06729000 South Boulder Creek near Rollinsville, CO Mountain X X X X X X X 06730300 Coal Creek near Plainview, CO Plains X -- -- -- -- -- -- 06732000 Glacier Creek near Estes Park, CO Mountain X X X X X X X 06739500 Buckhorn Creek near Masonville, CO Plains X -- -- -- -- -- -- 06748200 Fall Creek near Rustic, CO Mountain X X X X X X X 06748510 Little Beaver Creek near Idylwilde, CO Mountain X X X X X X X 06748530 Little Beaver Creek near Rustic, CO Mountain X X X X X X X 06748600 South Fork Cache La Poudre River near Rustic, CO Mountain X X X X X X X 06755000 South Crow Creek near Hecla, WY Plains X -- -- -- -- -- -- 06758200 Kiowa Creek at Kiowa, CO Plains X -- -- -- -- -- -- 06758250 Kiowa Creek Tributary near Bennett, CO Plains X -- -- -- -- -- -- 06758700 Middle Bijou Creek Tributary near Deer Trail, CO Plains X -- -- -- -- -- -- 06761900 Lodgepole Creek Tributary near Pine Bluffs, WY Plains X -- -- -- -- -- -- 06762500 Lodgepole Creek at Bushnell, Nebr. Plains X -- -- -- -- -- -- 06762600 Lodgepole Creek Tributary No. 2 near Albin, WY Plains X -- -- -- -- -- -- 06821300 North Fork Arikaree River Tributary near Shaw, CO Plains X -- -- -- -- -- -- 06821400 North Fork Black Wolf Creek near Vernon, CO Plains X -- -- -- -- -- -- 06823500 Buffalo Creek near Haigler, NE Plains X -- -- -- -- -- -- 06825500 Landsman Creek near Hale, CO Plains X -- -- -- -- -- -- 06844700 South Fork Sappa Creek near Brewster, KS Plains X -- -- -- -- -- -- 06844800 South Fork Sappa Creek Tributary near Goodland, KS Plains X -- -- -- -- -- -- 06858500 North Fork Smoky Hill River near Mcallaster, KS Plains X -- -- -- -- -- -- 07079500 East Fork Arkansas River near Leadville, CO Mountain X X X X X X X 07081000 Tennessee Creek near Leadville, CO Mountain X X X X X X X 07082000 Lake Fork above Sugar Loaf Reservoir, CO Mountain X X X X X X X 07083000 Halfmoon Creek near Malta, CO Mountain X X X X X X X 07089000 Cottonwood C below Hot Springs, near Buena Vista, CO Mountain X -- -- -- -- -- -- 07091000 Chalk Creek near Nathrop, CO Mountain X -- -- -- -- -- -- 07093500 South Arkansas River near Salida, CO Mountain X -- -- -- -- -- -- 07093775 Badger Creek, Lower Station, near Howard, CO Plains X -- -- -- -- -- -- 07095000 Grape Creek near Westcliffe, CO Plains X -- -- -- -- -- -- 07096500 Fourmile Creek near Canon City, CO Plains X -- -- -- -- -- -- 07099100 Beaver Creek near Portland, CO Plains X -- -- -- -- -- -- 07099230 Turkey Creek above Teller Reservoir near Stone City, CO Plains X -- -- -- -- -- -- 07105920 Little Fountain Creek above Keaton Reservoir, near 

Fort Carson, CO 

Plains X -- -- -- -- -- -- 

07105945 Rock Creek above Fort Carson Reservation, CO Plains X -- -- -- -- -- -- 07107500 St. Charles River at Burnt Mill, CO Plains X -- -- -- -- -- -- 
Table 4. Streamflow-gaging stations used in the development of the regional streamflow regression equations.—Continued[Peak flow, 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year peak flow; Maximum 7Q2, maximum 7-day, 2-year flow; Maximum 7Q10, maximum 7-day, 10-year flow; Maximum 7Qflow; Minimum 7Q2, minimum 7-day, 2-year flow; Minimum 7Q10, minimum 7-day, 10-year flow; Minimum 7Q50, minimum 7-day, 50-year flow; Flow duration, 10-, 25-, 50-, 75X, station used in the development of regional regression equation for the indicated streamflow characteristic and hydrologic region; --, station not used in the development of rethe indicated streamflow characteristic and hydrologic region]

Station 

number Station name

Hydrologic

region

(fig. 1)

Streamflow characteristic

Peak

flow

Maximum Minimum 

7Q2 7Q10 7Q50 7Q2 7Q10 7Q50 An

07114000 Cucharas River at Boyd Ranch, near La Veta, CO RioGrande X -- -- -- -- -- -- 07118000 Apishapa River near Aguilar, CO Plains X -- -- -- -- -- -- 

07120620 Big Arroyo near Thatcher, CO Plains X -- -- -- -- -- -- 07121500 Timpas Creek at Mouth near Swink, CO Plains X -- -- -- -- -- -- 07124300 Long Canyon Creek near Madrid, CO Plains X -- -- -- -- -- -- 07125100 Frijole Creek near Alfalfa, CO Plains X -- -- -- -- -- -- 07125500 San Francisco Creek near Alfalfa, CO Plains X -- -- -- -- -- -- 07126100 Luning Arroyo near Model, CO Plains X -- -- -- -- -- -- 07126200 Van Bremer Arroyo near Model, CO Plains X -- -- -- -- -- -- 07126325 Taylor Arroyo below Rock Crossing, near Thatcher, CO Plains X -- -- -- -- -- -- 07126390 Lockwood Canyon Creek near Thatcher, CO Plains X -- -- -- -- -- -- 07126415 Red Rock Canyon Creek at Mouth near Thatcher, CO Plains X -- -- -- -- -- -- 07126470 Chacuaco Creek at Mouth near Timpas, CO Plains X -- -- -- -- -- -- 07126480 Bent Canyon Creek at Mouth near Timpas, CO Plains X -- -- -- -- -- -- 07133200 Clay Creek Tributary near Deora, CO Plains X -- -- -- -- -- -- 07138600 White Woman C Tributary near Selkirk, KS Plains X -- -- -- -- -- -- 07138650 White Woman C near Leoti, KS Plains X -- -- -- -- -- -- 07153500 Dry Cimarron R near Guy, NM Plains X -- -- -- -- -- -- 07154400 Carrizozo Creek near Kenton, OK Plains X -- -- -- -- -- -- 07154650 Tesesquite Creek near Kenton, OK Plains X -- -- -- -- -- -- 07155100 Cpld Springs Creek near Wheeless, OK Plains X -- -- -- -- -- -- 07155590 Cimarron River near Elkhart, KS Plains X -- -- -- -- -- -- 07155900 North Fork Cimarron River Tributary near Elkhart, KS Plains X -- -- -- -- -- -- 07156010 North Fork Cimarron River at Richfield, KS Plains X -- -- -- -- -- -- 07156100 Sand Arroyo Creek near Johnson, KS Plains X -- -- -- -- -- -- 07156220 Bear Creek near Johnson, KS Plains X -- -- -- -- -- -- 07156600 Cimarron River Tributary near Moscow, KS Plains X -- -- -- -- -- -- 07199000 Canadian River near Hebron, NM Plains X -- -- -- -- -- -- 07201000 Raton Creek at Raton, NM Plains X -- -- -- -- -- -- 07201200 Chicorica Cr Tributary near Raton, NM Plains X -- -- -- -- -- -- 07203000 Vermejo River near Dawson, NM Plains X -- -- -- -- -- -- 07204000 Moreno Creek at Eagle Nest, NM RioGrande X -- -- -- -- -- -- 07204500 Cieneguilla Cr near Eagle Nest, NM RioGrande X -- -- -- -- -- -- 07205000 Sixmile Creek near Eagle Nest, NM RioGrande X -- -- -- -- -- -- 07206400 Clear C near Ute Park, NM RioGrande X -- -- -- -- -- -- 07207500 Ponil Creek near Cimarron, NM Plains X -- -- -- -- -- -- 07208500 Rayado Creek near Cimarron, NM Plains X -- -- -- -- -- -- 

07211000 Cimarron River at Springer, NM Plains X -- -- -- -- -- -- 

07225500 Ute Creek near Gladstone, NM Plains X -- -- -- -- -- -- 
Table 4. Streamflow-gaging stations used in the development of the regional streamflow regression equations.—Continued [Peak flow, 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year peak flow; Maximum 7Q2, maximum 7-day, 2-year flow; Maximum 7Q10, maximum 7-day, 10-year flow; Maximum 7Qflow; Minimum 7Q2, minimum 7-day, 2-year flow; Minimum 7Q10, minimum 7-day, 10-year flow; Minimum 7Q50, minimum 7-day, 50-year flow; Flow duration, 10-, 25-, 50-, 75X, station used in the development of regional regression equation for the indicated streamflow characteristic and hydrologic region; --, station not used in the development of rethe indicated streamflow characteristic and hydrologic region] Station number Station name Hydrologic region (fig. 1) Streamflow characteristic Peak flow Maximum Minimum 

7Q2 7Q10 7Q50 7Q2 7Q10 7Q50 An

07227295 Sandy Arroyo Tributary near Clayton, NM Plains X -- -- -- -- -- -- 07232500 Beaver River near Guymon, OK Plains X -- -- -- -- -- -- 07232650 Aqua Frio Creek near Felt, OK Plains X -- -- -- -- -- -- 08216500 Willow Creek at Creede, CO RioGrande X X X X X X X 08218500 Goose Creek at Wagonwheel Gap, CO RioGrande X X X X X X X 08219500 South Fork Rio Grande at South Fork, CO RioGrande X X X X X X X 08220500 Pinos Creek near Del Norte, CO RioGrande X X X X X X X 08223500 Rock Creek near Monte Vista, CO RioGrande X X X X X X X 08224500 Kerber Cr above Little Kerber Cr near Villa Grove, CO RioGrande X X X X X X -- 08227000 Saguache Creek near Saguache, CO RioGrande X X X X X X X 08227500 North Crestone Creek near Crestone, CO RioGrande X X X X X X X 08230500 Carnero Creek near La Garita, CO RioGrande X X X X X X -- 08231000 La Garita Creek near La Garita, CO RioGrande X X X X X X X 08236000 Alamosa River above Terrace Reservoir, CO RioGrande X X X X X X X 08240500 Trinchera C above Turners Ranch, Nr Ft Garland, CO RioGrande X X X X X X X 08241500 Sangre De Cristo Creek near Fort Garland, CO RioGrande X X X X X -- -- 08242500 Ute Creek near Fort Garland, CO RioGrande X X X X X X -- 08245500 Conejos River at Platoro, CO RioGrande X X X X X X X 08246500 Conejos River near Mogote, CO RioGrande X X X X X X X 08247500 San Antonio River at Ortiz, CO RioGrande X X X X -- -- -- 08248000 Los Pinos River near Ortiz, CO RioGrande X X X X X X X 08248500 San Antonio River at Mouth, near Manassa, CO RioGrande X X X X -- -- -- 08252500 Costilla Creek above Costilla Dam, NM RioGrande X -- -- -- -- -- -- 08253000 Casias Creek near Costilla, NM RioGrande X -- -- -- -- -- -- 08253500 Santistevan Creek near Costilla, NM RioGrande X -- -- -- -- -- -- 08255000 Ute Creek near Amalia, NM RioGrande X -- -- -- -- -- -- 08263000 Latir Creek near Cerro, NM RioGrande X -- -- -- -- -- -- 08264000 Red River near Red River, NM RioGrande X X X X X X X 08265000 Red River near Questa, NM RioGrande X X X X X X X 08267500 Rio Hondo near Valdez, NM RioGrande X X X X X X X 08268500 Arroyo Hondo at Arroyo Hondo, NM RioGrande X X X X X X X 08269000 Rio Pueblo De Taos near Taos, NM RioGrande X X X X X X X 08275000 Rio Fernando De Taos near Taos, NM RioGrande X X X X X X X 08275500 Rio Grande Del Rancho near Talpa, NM RioGrande X X X X X X X 08275600 Rio Chiquito near Talpa, NM RioGrande X X X X X X X 08281200 Wolf Creek near Chama, NM RioGrande X -- -- -- -- -- -- 08284000 Rito De Tierra Amarilla at Tierra Amar, NM RioGrande X -- -- -- -- -- -- 08284100 Rio Chama near La Puente, NM RioGrande X X X X X X X 08284500 Willow Creek near Park View, NM RioGrande X X X X -- -- -- 
Table 4. Streamflow-gaging stations used in the development of the regional streamflow regression equations.—Continued[Peak flow, 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year peak flow; Maximum 7Q2, maximum 7-day, 2-year flow; Maximum 7Q10, maximum 7-day, 10-year flow; Maximum 7Qflow; Minimum 7Q2, minimum 7-day, 2-year flow; Minimum 7Q10, minimum 7-day, 10-year flow; Minimum 7Q50, minimum 7-day, 50-year flow; Flow duration, 10-, 25-, 50-, 75X, station used in the development of regional regression equation for the indicated streamflow characteristic and hydrologic region; --, station not used in the development of rethe indicated streamflow characteristic and hydrologic region]

Station 

number Station name

Hydrologic

region

(fig. 1)

Streamflow characteristic

Peak

flow

Maximum Minimum 

7Q2 7Q10 7Q50 7Q2 7Q10 7Q50 An

08286650 Canjilon Creek above Abiquiu Reservoir, NM RioGrande X -- -- -- -- -- -- 08288000 El Rito near El Rito, NM RioGrande X X X X X X X 08289000 Rio Ojo Caliente at La Madera, NM RioGrande X X X X X X X 09012500 North Inlet at Grand Lake, CO Mountain X X X X X X X 09016500 Arapaho Creek at Monarch Lake Outlet, CO Mountain X X X X X X X 09020000 Willow Creek near Granby, CO Mountain X X X X -- -- -- 09024000 Fraser River at Winter Park, CO Mountain X X X X X X X 09026500 St. Louis Creek near Fraser, CO Mountain X X X X X X X 09032000 Ranch Creek near Fraser, CO Mountain X X X X X X X 09032500 Ranch Creek near Tabernash, CO Mountain X X X X X X -- 09033000 Meadow Creek near Tabernash, CO Mountain X X X X X X X 09033500 Strawberry Creek near Granby, CO Mountain X X X X X -- -- 09034000 Fraser River at Granby, CO Mountain X X X X X X X 09034500 Colorado River at Hot Sulphur Springs, CO Mountain X X X X X X X 09034900 Bobtail Creek near Jones Pass, CO Mountain X X X X X X X 09035500 Williams Fork below Steelman Creek, CO Mountain X X X X X X X 09035700 Williams Fork above Darling Creek, Nr Leal, CO Mountain X X X X X X X 09035800 Darling Creek near Leal, CO Mountain X X X X X X X 09035900 South Fork of Williams Fork near Leal, CO Mountain X X X X X X X 09036500 Keyser Creek near Leal, CO Mountain X X X X X X X 09039000 Troublesome Creek near Pearmont, CO Mountain X X X X X X X 09040000 East Fork Troublesome Creek near Troublesome, CO Mountain X X X X X X X 

09041100 Antelope Creek near Kremmling, CO Mountain X X X X X X -- 

09046530 French Gulch at Breckenridge, CO Mountain X X X X X X X 09047000 Blue River at Dillon, CO Mountain X X X X X X X 09047500 Snake River near Montezuma, CO Mountain X X X X X X X 09047700 Keystone Gulch near Dillon, CO Mountain X X X X X X X 09050100 Ten Mile Creek below North Ten Mile Creek, at Frisco, CO Mountain X X X X X X X 09052400 Boulder Creek at Upper Station, near Dillon, CO Mountain X X X X X X X 09052800 Slate Creek at Upper Station, near Dillon, CO Mountain X X X X X X X 09055000 Otter Creek above Green Mountain Reservoir, CO Mountain X X X X X X X 09058610 Dickson Creek near Vail, CO Mountain X X X X X -- -- 09058700 Freeman Creek near Minturn, CO Mountain X X X X X -- -- 09058800 East Meadow Creek near Minturn CO Mountain X X X X X X X 09059500 Piney River near State Bridge, CO Northwest X X X X X X X 09060500 Rock Creek near Toponas, CO Mountain X X X X X X X 09063200 Wearyman Creek near Red Cliff, CO Mountain X X X X X X X 09063400 Turkey Creek near Red Cliff, CO Mountain X X X X X X X 09064500 Homestake Creek near Red Cliff, CO Mountain X X X X X X X 
Table 4. Streamflow-gaging stations used in the development of the regional streamflow regression equations.—Continued [Peak flow, 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year peak flow; Maximum 7Q2, maximum 7-day, 2-year flow; Maximum 7Q10, maximum 7-day, 10-year flow; Maximum 7Qflow; Minimum 7Q2, minimum 7-day, 2-year flow; Minimum 7Q10, minimum 7-day, 10-year flow; Minimum 7Q50, minimum 7-day, 50-year flow; Flow duration, 10-, 25-, 50-, 75X, station used in the development of regional regression equation for the indicated streamflow characteristic and hydrologic region; --, station not used in the development of rethe indicated streamflow characteristic and hydrologic region] Station number Station name Hydrologic region (fig. 1) Streamflow characteristic Peak flow Maximum Minimum 

7Q2 7Q10 7Q50 7Q2 7Q10 7Q50 An

09065100 Cross Creek near Minturn, CO Mountain X X X X X X X 09065500 Gore Creek at Upper Station, near Minturn, CO Mountain X X X X X X X 09066000 Black Gore Creek near Minturn, CO Mountain X X X X X X X 09066100 Bighorn Creek near Minturn, CO Mountain X X X X X X X 09066150 Pitkin Creek near Minturn, CO Mountain X X X X X X X 09066200 Booth Creek near Minturn, CO Mountain X X X X X X X 09066300 Middle Creek near Minturn, CO Mountain X X X X X X 09066400 Red Sandstone Creek near Minturn, CO Mountain X X X X X X X 09066500 Gore Creek near Minturn, CO Mountain X X X X X X X 09067005 Eagle River at Avon, CO Mountain X X X X X X X 09068000 Brush Creek near Eagle, CO Mountain X X X X X X X 09069500 Gypsum Creek near Gypsum, CO Mountain X X X X X X X 09070000 Eagle River below Gypsum, CO Mountain X X X X X X X 09071300 Grizzly Creek near Glenwood Springs, CO Mountain X X X X X -- -- 09073500 Roaring Fork River at Aspen, CO Mountain X X X X X X X 09073700 Hunter Creek above Midway Creek, near Aspen, CO Mountain X X X X X X X 09073800 Midway Creek near Aspen, CO Mountain X X X X X X X 09073900 No Name Creek near Aspen, CO Mountain X X X X X X X 09074000 Hunter Creek near Aspen, CO Mountain X X X X X X X 09074800 Castle Creek Above Aspen, CO Mountain X X X X X X X 09075700 Maroon Creek Above Aspen, CO Mountain X X X X X X X 09077200 Fryingpan River near Ivanhoe Lake, CO Mountain X X X X X X X 09077800 South Fork Fryingpan River at Upper Station, near Norrie, CO Mountain X X X X X X X 09078000 Fryingpan River at Norrie, CO Mountain X X X X X X X 09078100 North Fork Fryingpan River above Cunningham C, near Norrie, CO Mountain X X X X X X X 09078200 Cunningham Creek near Norrie, CO Mountain X X X X X X X 09078500 North Fork Fryingpan River near Norrie, CO Mountain X X X X X X X 09080300 Rocky Fork Creek near Meredith, CO Mountain X X X X X X X 09081600 Crystal River above Avalanche Creek, near Redstone, CO Northwest X X X X X X X 09082800 North Thompson Creek near Carbondale, CO Mountain X X X X X X X 09083000 Thompson Creek near Carbondale, CO Northwest X X X X X X X 09084000 Cattle Creek near Carbondale, CO Mountain X X X X X X X 09085200 Canyon Creek above New Castle, CO Northwest X X X X X X X 09085300 East Canyon Creek near New Castle, CO Northwest X X X X X X X 09085400 Possum Creek near New Castle, CO Northwest X X X X X X X 09089500 West Divide Creek near Raven, CO Mountain X X X X X -- -- 

09091100 Mamm Creek near Silt, CO Northwest X -- -- -- -- -- -- 

09091500 East Rifle Creek near Rifle, CO Northwest X X X X X X X 
Table 4. Streamflow-gaging stations used in the development of the regional streamflow regression equations.—Continued[Peak flow, 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year peak flow; Maximum 7Q2, maximum 7-day, 2-year flow; Maximum 7Q10, maximum 7-day, 10-year flow; Maximum 7Qflow; Minimum 7Q2, minimum 7-day, 2-year flow; Minimum 7Q10, minimum 7-day, 10-year flow; Minimum 7Q50, minimum 7-day, 50-year flow; Flow duration, 10-, 25-, 50-, 75X, station used in the development of regional regression equation for the indicated streamflow characteristic and hydrologic region; --, station not used in the development of rethe indicated streamflow characteristic and hydrologic region]

Station 

number Station name

Hydrologic

region

(fig. 1)

Streamflow characteristic

Peak

flow

Maximum Minimum 

7Q2 7Q10 7Q50 7Q2 7Q10 7Q50 An

09092000 Rifle Creek near Rifle, CO Northwest X X X X X X X 09092500 Beaver Creek near Rifle, CO Northwest X X X X X X X 09093000 Parachute Creek near Parachute CO Northwest X X X X X -- -- 09095000 Roan Creek near De Beque, CO Northwest X X X X X X X 09096000 Plateau Creek at Upper Station, near Collbran, CO Mountain X X X X X X -- 09096500 Plateau Creek near Collbran, CO Mountain X X X X X X X 09096800 Buzzard Creek below Owens Creek, near Heiberger, CO Mountain X X X X -- -- -- 09097500 Buzzard Creek near Collbran, CO Mountain X X X X X X -- 09097600 Brush Creek near Collbran, CO Mountain X X X X X X X 09104500 Mesa Creek near Mesa, CO Northwest X X X X X X X 09107000 Taylor River at Taylor Park, CO Mountain X X X X X X X 

09110000 Taylor River at Almont, CO Mountain X X X X X X X 09110500 East River near Crested Butte, CO Mountain X X X X X X X 

09111500 Slate River near Crested Butte, CO Mountain X X X X X X X 

09112000 Cement Creek near Crested Butte, CO Mountain X X X X X X X 09112500 East River at Almont CO Mountain X X X X X X X 09113300 Ohio Creek at Baldwin, CO Mountain X X X X X X X 09113500 Ohio Creek near Baldwin, CO Mountain X X X X X X X 09114500 Gunnison River near Gunnison, CO Mountain X X X X X X X 09115500 Tomichi Creek at Sargents, CO Mountain X X X X X X X 09117000 Tomichi Creek at Parlin, CO Mountain X X X X X X X 09118000 Quartz Creek near Ohio City, CO Mountain X X X X X X X 09119000 Tomichi Creek at Gunnison, CO Mountain X X X X X X X 

09122000 Cebolla Creek at Powderhorn, CO Mountain X X X X X X X 09122500 Soap Creek near Sapinero, CO Mountain X X X X X X X 09123500 Lake Fork at Lake City, CO Mountain X X X X X X X 09124500 Lake Fork at Gateview, CO Mountain X X X X X X X 09125000 Curecanti Creek near Sapinero, CO Mountain X X X X X X X 09126000 Cimarron River near Cimarron, CO Mountain X X X X X X X 09127500 Crystal Creek near Maher, CO Mountain X X X X X X X 09128500 Smith Fork near Crawford, CO Northwest X X X X X X X 09130500 East Muddy Creek near Bardine, CO Northwest X X X X X X X 09130600 West Muddy Creek near Ragged Mountain, CO Mountain X X X X X X X 09132500 North Fork Gunnison River near Somerset, CO Northwest X X X X X X X 09132900 West Hubbard Creek near Paonia, CO Mountain X X X X X X X 09134500 Leroux Creek near Cedaredge, CO Northwest X X X X X X X 09136200 Gunnison River near Lazear, CO Northwest X X X X X X X 09137800 Dirty George Creek near Grand Mesa, CO Northwest X X X X X X X 09139200 Ward Creek near Grand Mesa, CO Mountain X X X X X X X 
Table 4. Streamflow-gaging stations used in the development of the regional streamflow regression equations.—Continued [Peak flow, 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year peak flow; Maximum 7Q2, maximum 7-day, 2-year flow; Maximum 7Q10, maximum 7-day, 10-year flow; Maximum 7Qflow; Minimum 7Q2, minimum 7-day, 2-year flow; Minimum 7Q10, minimum 7-day, 10-year flow; Minimum 7Q50, minimum 7-day, 50-year flow; Flow duration, 10-, 25-, 50-, 75X, station used in the development of regional regression equation for the indicated streamflow characteristic and hydrologic region; --, station not used in the development of rethe indicated streamflow characteristic and hydrologic region] Station number Station name Hydrologic region (fig. 1) Streamflow characteristic Peak flow Maximum Minimum 

7Q2 7Q10 7Q50 7Q2 7Q10 7Q50 An

09140200 Kiser Creek near Grand Mesa, CO Mountain X X X X X X X 09141200 Youngs Creek near Grand Mesa, CO Northwest X X X X X X X 09143500 Surface Creek at Cedaredge, CO Northwest X X X X X X X 09144200 Tongue Creek at Cory, CO Northwest X X X X X X X 09146000 Uncompahgre River below Ouray, CO Southwest X X X X X X X 09146400 West Fork Dallas Creek near Ridgway, CO Southwest X X X X X X X 09146500 East Fork Dallas Creek near Ridgway, CO Southwest X X X X X X X 09146600 Pleasant Valley Creek near Noel, CO Southwest X X X X X X 09147000 Dallas Creek near Ridgway, CO Southwest X X X X X X X 09147100 Cow Creek near Ridgway, CO Mountain X X X X X X X 09149450 Dry Creek near Olathe, CO Northwest X -- -- -- -- -- -- 09150500 Roubideau Creek at Mouth, near Delta, CO Northwest X X X X X X X 09153400 West Salt Creek near Mack, CO Northwest X X X X -- -- -- 09163700 Cisco Wash near Cisco, UT Southwest X -- -- -- 09165000 Dolores River below Rico, CO Southwest X X X X -- -- -- 09166500 Dolores River at Dolores, CO Southwest X X X X X X X 09168100 Disappointment Creek near Dove Creek, CO Southwest X X X X X -- -- 09168700 Disappointment Creek Tributary near Slick Rock, CO Southwest X -- -- -- -- -- -- 09169500 Dolores River at Bedrock, CO Southwest X X X X X X X 09172000 Fall Creek near Fall Creek, CO Southwest X X X X X X X 09172500 San Miguel River near Placerville, CO Southwest X X X X X X X 09174500 Cottonwood Creek near Nucla, CO Southwest X X X X -- -- 09175000 West Naturita Creek near Norwood, CO Southwest X X X X X -- -- 09175500 San Miguel River at Naturita, CO Southwest X X X X X X X 09177500 Taylor Creek near Gateway, CO Southwest X -- -- -- -- -- -- 09181000 Onion Creek near Moab, UT Southwest X X X X X X X 09182000 Castle Creek above Diversions, near Moab, UT Southwest X X X X X -- -- 09182600 Salt Wash near Thompson, UT Southwest X -- -- -- -- -- -- 09183000 Courthouse Wash near Moab, UT Southwest X X X X X -- -- 09184000 Mill Creek near Moab, UT Southwest X X X X X X X 09185200 Kane Springs Canyon near Moab, UT Southwest X -- -- -- -- -- -- 09185500 Hatch Wash near La Sal, UT Southwest X X X X -- -- -- 09187000 Cottonwood Creek near Monticello, UT Southwest X X X X -- -- -- 09216400 Greasewood Canyon near Green River, WY Northwest X -- -- -- -- -- -- 09216537 Delaney Draw near Red Desert, WY Northwest X -- -- -- -- -- -- 09216550 Deadman Wash near Point of Rocks, WY Northwest X -- -- -- -- -- -- 09216600 Cutthroat Draw near Rock Springs, WY Northwest X -- -- -- -- -- -- 09216700 Salt Wells Creek near Rock Springs, WY Northwest X -- -- -- -- -- -- 09216900 Bitter Cr Tributary near Green River WY Northwest X -- -- -- -- -- -- 
Table 4. Streamflow-gaging stations used in the development of the regional streamflow regression equations.—Continued[Peak flow, 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year peak flow; Maximum 7Q2, maximum 7-day, 2-year flow; Maximum 7Q10, maximum 7-day, 10-year flow; Maximum 7Qflow; Minimum 7Q2, minimum 7-day, 2-year flow; Minimum 7Q10, minimum 7-day, 10-year flow; Minimum 7Q50, minimum 7-day, 50-year flow; Flow duration, 10-, 25-, 50-, 75X, station used in the development of regional regression equation for the indicated streamflow characteristic and hydrologic region; --, station not used in the development of rethe indicated streamflow characteristic and hydrologic region]

Station 

number Station name

Hydrologic

region

(fig. 1)

Streamflow characteristic

Peak

flow

Maximum Minimum 

7Q2 7Q10 7Q50 7Q2 7Q10 7Q50 An

09224810 Blacks Fork Tributary No 2 near Green River, WY Northwest X -- -- -- -- -- -- 09224820 Blacks Fork Tributary No 3 near Green River, WY Northwest X -- -- -- -- -- -- 09224840 Blacks Fork Tributary No 4 near Green River, WY Northwest X -- -- -- -- -- -- 09224980 Summers Dry Creek near Green River, WY Northwest X -- -- -- -- -- -- 09225200 Squaw Hollow near Burntfork, WY Northwest X -- -- -- -- -- -- 09225300 Green River Tributary No 2 near Burntfork, WY Northwest X -- -- -- -- -- -- 09229450 Henrys Fork Tributary near Manila, UT Northwest X -- -- -- -- -- -- 09235600 Pot Creek Above Diversions, near Vernal, UT Northwest X X X X -- -- -- 09238500 Walton Creek near Steamboat Springs, CO Northwest X X X X X X X 09239500 Yampa River at Steamboat Springs, CO Northwest X X X X X X X 09241000 Elk River at Clark, CO Mountain X X X X X X X 09244100 Fish Creek near Milner, CO Northwest X X X X X X X 09245000 Elkhead Creek near Elkhead, CO Northwest X X X X X X -- 09245500 North Fork Elkhead Creek near Elkhead, CO Northwest X X X X X -- -- 09249000 East Fork Williams Fork near Pagoda, CO Northwest X X X X X X X 09250000 Milk Creek near Thornburgh, CO Northwest X -- -- -- -- -- -- 09251500 Middle Fork Little Snake River near Battle Creek, CO Northwest X X X X X X X 09251800 North Fork Little Snake River near Encampment, WY Northwest X X X X X X X 09253000 Little Snake River near Slater, CO Northwest X X X X X X X 09253400 Battle Creek near Encampment, WY Northwest X X X X X X X 09255000 Slater Fork near Slater, CO Northwest X X X X X X X 09256000 Savery Creek near Savery, WY Northwest X X X X X X -- 09257000 Little Snake River near Dixon, WY Northwest X X X X X X X 09257500 Willow Creek near Baggs, WY Northwest X -- -- -- -- -- -- 09258000 Willow Creek near Dixon, WY Northwest X X X X X X -- 09258200 Dry Cow Creek near Baggs, WY Northwest X -- -- -- -- -- -- 09258900 Muddy Creek above Baggs, WY Northwest X -- -- -- -- -- -- 09259500 Fourmile Creek near Baggs, WY Northwest X -- -- -- -- -- -- 09260000 Little Snake River near Lily, CO Northwest X X X X X -- -- 09263700 Cliff Creek near Jensen, UT Northwest X -- -- -- -- -- -- 09263800 Cow Wash near Jensen, UT Northwest X -- -- -- -- -- -- 09264000 Ashley C Below Trout C near Vernal, UT Northwest X X X X X X X 09264500 South Fork Ashley Creek nearVernal, UT Northwest X X X X X X X 09266500 Ashley Creek near Vernal, UT Northwest X X X X X X X 09268000 Dry Fork Above Sinks, near Dry Fork, UT Northwest X X X X X X X 09268500 North Fork Of Dry Fork near Dry Fork, UT Northwest X X X X X X X 09268900 Brownie Canyon Above Sinks, near Dry Fork, UT Northwest X X X X X X X 09269000 East Fork Of Dry Fork near Dry Fork, UT Northwest X X X X -- -- -- 09270500 Dry Fork at Mouth near Dry Fork, UT Northwest X X X X X -- -- 
Table 4. Streamflow-gaging stations used in the development of the regional streamflow regression equations.—Continued [Peak flow, 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year peak flow; Maximum 7Q2, maximum 7-day, 2-year flow; Maximum 7Q10, maximum 7-day, 10-year flow; Maximum 7Qflow; Minimum 7Q2, minimum 7-day, 2-year flow; Minimum 7Q10, minimum 7-day, 10-year flow; Minimum 7Q50, minimum 7-day, 50-year flow; Flow duration, 10-, 25-, 50-, 75X, station used in the development of regional regression equation for the indicated streamflow characteristic and hydrologic region; --, station not used in the development of rethe indicated streamflow characteristic and hydrologic region] Station number Station name Hydrologic region (fig. 1) Streamflow characteristic Peak flow Maximum Minimum 

7Q2 7Q10 7Q50 7Q2 7Q10 7Q50 An

09271800 Halfway Hollow Tributary near Lapoint, UT Northwest X -- -- -- -- -- -- 09300500 Uintah River at Fort Duchesne, UT Northwest X X X X X X -- 09302450 Lost Creek near Buford, CO Mountain X X X X X X X 09302500 Marvine Creek near Buford, CO Mountain X X X X X X X 09303000 North Fork White River at Buford, CO Northwest X X X X X X X 09303300 South Fork White River at Budges Resort, CO Mountain X X X X X X X 09303320 Wagonwheel Creek at Budges Resort, CO Mountain X X X X -- -- -- 09304000 South Fork White River at Buford, CO Northwest X X X X -- -- -- 09304500 White River near Meeker, CO Northwest X X X X X X X 09306007 Piceance Creek below Rio Blanco, CO Northwest X X X X X X X 09306036 Sorghum Gulch at mouth, near Rio Blanco, CO Northwest X -- -- -- -- -- -- 09306039 Cottonwood Gulch near Rio Blanco, CO Northwest X -- -- -- -- -- -- 09306042 Piceance Creek Tributary near Rio Blanco, CO Northwest X -- -- -- -- -- -- 09306052 Scandard Gulch at Mouth, near Rio Blanco, CO Northwest X -- -- -- -- -- -- 09306058 Willow Creek near Rio Blanco, CO Northwest X X X X -- -- -- 09306200 Piceance Creek below Ryan Gulch, near Rio Blanco, CO Northwest X X X X X X X 09306240 Box Elder Gulch near Rangely, CO Northwest X X X X -- -- -- 09306242 Corral Gulch near Rangely, CO Northwest X X X X -- -- -- 09306255 Yellow Creek near White River, CO Northwest X X X X X X -- 09306800 Bitter Creek near Bonanza, UT Northwest X X X X -- -- -- 09307500 Willow Creek above Diversions near Ouray, UT Northwest X X X X X X X 09308000 Willow Creek near Ouray, UT Northwest X X X X X -- -- 09328900 Cresent Wash near Cresent Junction, UT Southwest X -- -- -- -- -- -- 09339900 East Fork San Juan River above Sand Creek, near Pagosa Springs, CO Southwest X X X X X X X 09340000 East Fork San Juan River near Pagosa Springs, CO Southwest X X X X X X X 09340500 West Fork San Juan River above Borns Lake, near Pagosa Springs, CO Southwest X X X X X X X 09341500 West Fork San Juan River near Pagosa Springs, CO Southwest X X X X X X X 09342000 Turkey Creek near Pagosa Springs, CO Southwest X X X X X X X 09342500 San Juan River at Pagosa Springs, CO Southwest X X X X X X X 09343000 Rio Blanco near Pagosa Springs, CO Southwest X X X X X X X 09343500 Rito Blanco near Pagosa Springs, CO Southwest X X X X X -- -- 09344000 Navajo River at Banded Peak Ranch, near Chromo, CO Southwest X X X X X X X 09345200 Little Navajo River Below Lake Oso Diversion Dam, 

near Chromo, CO 

Southwest X X X X X X -- 

09346000 Navajo River at Edith, CO Southwest X X X X X X X 09346200 Rio Amargo at Dulce, NM Southwest X -- -- -- -- -- -- 09347500 Piedra R at Bridge Ranger Station, near Pagosa Spgs, CO Southwest X X X X X X X 
Table 4. Streamflow-gaging stations used in the development of the regional streamflow regression equations.—Continued[Peak flow, 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year peak flow; Maximum 7Q2, maximum 7-day, 2-year flow; Maximum 7Q10, maximum 7-day, 10-year flow; Maximum 7Qflow; Minimum 7Q2, minimum 7-day, 2-year flow; Minimum 7Q10, minimum 7-day, 10-year flow; Minimum 7Q50, minimum 7-day, 50-year flow; Flow duration, 10-, 25-, 50-, 75X, station used in the development of regional regression equation for the indicated streamflow characteristic and hydrologic region; --, station not used in the development of rethe indicated streamflow characteristic and hydrologic region]

Station 

number Station name

Hydrologic

region

(fig. 1)

Streamflow characteristic

Peak

flow

Maximum Minimum 

7Q2 7Q10 7Q50 7Q2 7Q10 7Q50 An

09349800 Piedra River near Arboles, CO Southwest X X X X X X X 09350800 Vaqueros Canyon near Gobernador, NM Southwest X -- -- -- -- -- -- 09352900 Vallecito Creek near Bayfield, CO Southwest X X X X X X X 09355000 Spring Creek at La Boca, CO Southwest X X X X X X X 09357200 Gallegos Canyon Tributary near Nageezi, NM Southwest X -- -- -- -- -- -- 09357230 West Draw near Farmington, NM Southwest X -- -- -- -- -- -- 09357500 Animas River at Howardsville, CO Southwest X X X X -- -- -- 09358550 Cement Creek at Silverton, CO Southwest X X X X X X X 09359000 Mineral Creek near Silverton, CO Southwest X X X X X X X 09361000 Hermosa Creek near Hermosa, CO Southwest X X X X X X X 09361400 Junction Creek near Durango, CO Southwest X X X X X X X 09361500 Animas River at Durango, CO Southwest X X X X X X X 09362000 Lightner Creek near Durango, CO Southwest X X X X X X X 09363000 Florida River near Durango, CO Southwest X X X X X X -- 09363100 Salt Creek near Oxford, CO Southwest X X X X X -- -- 09365500 La Plata River at Hesperus, CO Southwest X X X X X X X 09366000 Cherry Creek near Red Mesa, CO Southwest X X X X -- -- -- 09366500 La Plata River at CO-NM State Line Southwest X X X X X -- -- 09367400 La Plata River Tributary near Farmington, NM Southwest X -- -- -- -- -- -- 09367530 Locke Arroyo near Kirtland, NM Southwest X -- -- -- -- -- -- 09367550 Stevens Arroyo near Kirtland, NM Southwest X -- -- -- -- -- -- 09367561 Shumway Arroyo near Waterflow, NM Southwest X X X X -- -- -- 09367950 Chaco River near Waterflow , NM Southwest X X X X -- -- -- 09367980 Rattlesnake Arroyo near Shiprock, NM Southwest X -- -- -- -- -- -- 09368020 Malpais Arroyo near Shiprock, NM Southwest X -- -- -- -- -- -- 09368500 West Mancos River near Mancos, CO Southwest X X X X X X X 09369000 East Mancos River near Mancos, CO Southwest X X X X X X -- 09369500 Middle Mancos River near Mancos, CO Southwest X X X X X -- -- 09371000 Mancos River near Towaoc, CO Southwest X X X X -- -- -- 09371300 Mcelmo Creek Tributary near Cortez, CO Southwest X -- -- -- -- -- -- 09372000 Mcelmo Creek near CO-UT State Line Southwest X X X X X X X 09378170 South Creek Above Reservoir near Monticello, UT Southwest X X X X X -- -- 09378630 Recapture Creek near Blanding, UT Southwest X X X X -- -- -- 09378650 Recapture Creek below Johnson Creek near Blanding, UT Southwest X X X X -- -- -- 09378700 Cottonwood Wash near Blanding, UT Southwest X X X X -- -- -- 09379000 Cob Wash near Bluff, UT Southwest X X X X -- -- -- 09379030 Black Mountain Wash near Chinle, AZ Southwest X -- -- -- -- -- -- 09379060 Lukachukai Creek Tributary near Lukachukai, AZ Southwest X -- -- -- -- -- -- 09379300 Lime Creek near Mexican Hat, UT Southwest X -- -- -- -- -- -- 
46 Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado

Publishing support provided by:

Denver Publishing Service Center, Denver, Colorado

Manuscript approved for publication, June 17, 2009

Edited by Mary Kidd

Graphics and layout by Joy Monson

For more information concerning this publication, contact:

Director, USGS Colorado Water Science Center

Box 25046, Mail Stop 415

Denver, CO 80225

(303) 236-4882

Or visit the Colorado Water Science Center Web site at:

http://co.water.usgs.gov/

This publication is available online at:

http://pubs.usgs.gov/sir/2009/5136/
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