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Analysis of the magnitude and frequency of floods in Colorado

Water-Resources Investigations Report 99-4190

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Abstract

Regionalized flood-frequency relations need to be updated on a regular basis (about every 10 years). The latest study on regionalized flood-frequency equations for Colorado used data collected through water year 1981. A study was begun in 1994 by the U.S. Geological Survey, in cooperation with the Colorado Department of Transportation and the Bureau of Land Management, to include streamflow data collected since water year 1981 in the regionalized flood-frequency relations for Colorado. Longer periods of streamflow data and improved statistical analysis methods were used to define regression relations for estimating peak discharges having recurrence intervals of 2, 5, 10, 25, 50, 100, 200, and 500 years for unregulated streams in Colorado. The regression relations can be applied to sites of interest on gaged and ungaged streams. Ordinary least-squares regression was used to determine the best explanatory basin or climatic characteristic variables for each peak-discharge characteristic, and generalized least-squares regression was used to determine the best regression relation. Drainage-basin area, mean annual precipitation, and mean basin slope were determined to be statistically significant explanatory variables in the regression relations. Separate regression relations were developed for each of five distinct hydrologic regions in the State. The mean standard errors of estimate and average standard error of prediction associated with the regression relations generally ranged from 40 to 80 percent, except for one hydrologic region where the errors ranged from about 200 to 300 percent. Methods are presented for determining the magnitude of peak discharges for sites located at gaging stations, for sites located near gaging stations on the same stream when the ratio of drainage-basin areas is between about 0.5 and 1.5, and for sites where the drainage basin crosses a flood-region boundary or a State boundary. Methods are presented for determining the magnitude of peak discharges for sites located at gaging stations, for sites located near gaging stations on the same stream when the ratio of drainage-basin areas is between about 0.5 and 1.5, and for sites where the drainage basin crosses a flood-region boundary or a State boundary.

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Analysis of the magnitude and frequency of floods in Colorado
Series title:
Water-Resources Investigations Report
Series number:
99-4190
Edition:
-
Year Published:
2000
Language:
ENGLISH
Publisher:
U.S. Department of the Interior, U.S. Geological Survey : Information Services [distributor],
Description:
iii, 35 p., (1 folded) :ill., maps ;28 cm.