Water Resources of Idaho

Estimating the Magnitude of Peak Flows at Selected Recurrence Intervals for Streams in Idaho by Charles Berenbrock

Water Resources Investigations Report 02-4170

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NOTE: This report was updated July 25, 2007 to add an errata page. Table 4 of this report contains a typographical error. On page 30, in the row for Map No. 56, Selway River near Lowell, ID, the value for S30 (percent) is listed as 785.6. The correct value is 75.6.

This report documents estimation of the magnitude of peak flows at recurrence intervals of 2, 5, 10, 25, 50, 100, 200, and 500 years. Two methods, the log-Pearson Type III distribution and the drainage-area ratio, are presented for estimating peak flows for gaged sites and for ungaged sites near gaged sites on the same stream. Two methods based on regression analysis are presented for estimating peak flows for ungaged sites on unregulated and undiverted streams in Idaho -- the regional regression method and the region-of-influence method. Standard errors of estimate, calculated to show the predictive reliability of each method, are described in terms of their applications and limitations.

This report is available online -- view report (1838K). Download computer program for regional regression equations. For further information concerning this report please contact Charles Berenbrock - (208)387-1301. If you encounter problems viewing this report, please contact Tim Merrick by phone at (208)387-1305 or email at trmerrick@usgs.gov.