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Water-Resources Investigations Report 03-4188
Version 1.10

Estimating the Magnitude and Frequency of Peak Streamflows for Ungaged Sites on Streams in Alaska and Conterminous Basins in Canada

Prepared in cooperation with

By Janet H. Curran, David F. Meyer, and Gary D. Tasker


Estimates of the magnitude and frequency of peak streamflow are needed across Alaska for floodplain management, cost-effective design of floodway structures such as bridges and culverts, and other water-resource management issues. Peak-streamflow magnitudes for the 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year recurrence-interval flows were computed for 301 streamflow-gaging and partial-record stations in Alaska and 60 stations in conterminous basins of Canada. Flows were analyzed from data through the 1999 water year using a log-Pearson Type III analysis. The State was divided into seven hydrologically distinct streamflow analysis regions for this analysis, in conjunction with a concurrent study of low and high flows. New generalized skew coefficients were developed for each region using station skew coefficients for stations with at least 25 years of systematic peak-streamflow data.

Equations for estimating peak streamflows at ungaged locations were developed for Alaska and conterminous basins in Canada using a generalized least-squares regression model. A set of predictive equations for estimating the 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year peak streamflows was developed for each streamflow analysis region from peak-streamflow magnitudes and physical and climatic basin characteristics. These equations may be used for unregulated streams without flow diversions, dams, periodically releasing glacial impoundments, or other streamflow conditions not correlated to basin characteristics. Basin characteristics should be obtained using methods similar to those used in this report to preserve the statistical integrity of the equations.


Description of Study Area
Determination of Drainage-Basin Characteristics
Determination of Streamflow Analysis Regions
Estimating Peak Streamflows at Gaged Sites
Regional Equations for Estimating Peak Streamflows
Procedures for Estimating Peak Streamflow Magnitude and Frequency
Appendix A. Years of Record for Annual Peak Streamflows Used in This Report
Appendix B. Accuracy of Estimating Equations

This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.

Download the report (PDF, 5.7 MB)

Select Plate 1 (PDF, 3.84 MB) to view or print.

Revision History

Other downloadable items:

Tools for Estimating Streamflow

Computer program to compute peak-streamflow frequencies, standard error of prediction, confidence limits, and equivalent years of record for ungaged sites (ZIP file, 138 KB). After downloading, unzip using WINZIP (evaluation version available free at Run the program by double-clicking reg.exe. The program expects the file split.cmn to be in the same folder as reg.exe. View the FORTRAN code by opening reg.for.


Regression equations for estimating 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year peak streamflows for unregulated streams in Regions 1-7, Alaska and conterminous basins in Canada (table 3, 28 KB)


Data for Figure 2, Relation of discharge to drainage area for selected recurrence intervals for the Yukon River, Alaska and Canada. (15 KB)


Generalized skew and summary statistics for Regions 1-7, Alaska and conterminous basins in Canada (table 2, 15 KB)


Station information and peak-streamflow statistics for streamflow-gaging and partial-record stations in Alaska and conterminous basins in Canada (table 4, 299 KB)


Document Accessibility: Adobe Systems Incorporated has information about PDFs and the visually impaired. This information provides tools to help make PDF files accessible. These tools convert Adobe PDF documents into HTML or ASCII text, which then can be read by a number of common screen-reading programs that synthesize text as audible speech. In addition, an accessible version of Acrobat Reader 5.0 for Windows (English only), which contains support for screen readers, is available. These tools and the accessible reader may be obtained free from Adobe at Adobe Access.

For additional information contact:

Alaska Science Center, Water Resources Office
U.S. Geological Survey
4230 University Drive, Suite 201
Anchorage, AK 99508-4664

Please visit for more information about USGS activities in Alaska.

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