Magnitude and frequency of floods in the United States. Part 13. Snake River basin

Water Supply Paper 1688

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The magnitude of a flood of any selected frequency up to 50 years for any site on any stream in the Snake River basin can be determined by methods outlined in this report, with some limitations. The methods are not applicable for regulated streams, for drainage basins smaller than 10 or larger than 5,000 square miles, for streams fed by large springs, or for streams that have flow characteristics materially different from the regional pattern. The magnitude of a flood for a selected frequency at a given site is determined by using the appropriate composite frequency curve and the mean annual flood for the given site. The mean annual flood is computed from either a formula or a nomograph in which drainage area, mean annual precipitation, and a geographic factor are used as independent variables. The standard error of estimate for the computation of mean annual floods is plus 17 percent and minus 15 percent.

Nine flood-frequency regions (A-I) are defined. In all except regions B and I, frequency relations vary with the mean altitude of the basin as well as with the geographic location; therefore, families of curves are required for 7 of the 9 flood-frequency regions.

The report includes a brief description of the physiography and climate of the Snake River basin to explain the reason for the large variation in mean annual floods, which range from zero to about 27 cubic feet per second per square mile.

Composite frequency curves and formulas for computing mean annual floods are based on all suitable flood data collected in the Snake River basin. Tables show the data used to derive the formula. Following the analysis of data are station descriptions and lists of peak stages and discharges for 295 gaging stations at which 5 or more years of annual flood records were collected pr'or to Sept. 30, 1957. Many flood peak data are not usable in defining the frequency curves and deriving the formula because of large diversions and regulation upstream from the gaging stations.

Additional publication details

Publication type:
Publication Subtype:
USGS Numbered Series
Magnitude and frequency of floods in the United States. Part 13. Snake River basin
Series title:
Water Supply Paper
Series number:
Year Published:
U.S. Government Printing Office
Publisher location:
Washington, D.C.
Contributing office(s):
Utah Water Science Center
Report: xi, 250 p.; 5 Plates: 31.50 x 31.36 inches or smaller
United States
Idaho, Nevada, Oregon, Utah, Washington, Wyoming
Other Geospatial:
Snake River basin