Drainage-basin and channel-geometry multiple- regression equations are presented for estimating design-flood discharges having recurrence intervals of 2, 5, 10, 25, 50, and 100 years at sites on unregulated rural streams in Iowa. Statewide drainage-basin equations were developed with average standard errors of prediction that ranged from 38.6 to 50.2 percent. Drainage-basin characteristics were quantified for 164 streamflow-gaging stations using a geographic-information-system procedure to process topographic maps and digital cartographic data. The significant drainage-basin characteristics identified included contributing drainage area; relative relief; drainage frequency; and 2-year, 24-hour precipitation intensity. Statewide and regional channel-geometry equations that are dependent on whether a stream has been channelized were developed with average standard errors of prediction for the statewide channel-geometry equations that ranged from 41.0 to 68.4 percent and for the regional channel-geometry equations from 30.3 to 70.0 percent. Channel-geometry characteristics were measured onsite and on topographic maps for streams at 157 streamflow- gaging stations. The significant channel-geometry characteristics identified for the statewide and regional regression equations included bankfull width and bankfull depth for natural channels and active-channel width for channels affected by channelization.
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USGS Numbered Series
Estimating design-flood discharges for streams in Iowa using drainage-basin and channel-geometry characteristics
Water-Resources Investigations Report
U.S. Geological Survey ;
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