Methods for estimating peak discharge and flood boundaries of streams in Utah

Water-Resources Investigations Report 83-4129




Equations for estimating 2-, 5-, 10-, 25-, 50-, and 100-year peak discharges and flood depths at ungaged sites in Utah were developed using multiple-regression techniques. Ratios of 500- to 100-year values also were determined. The peak discharge equations are applicable to unregulated streams and the flood depth equations are applicable to the unregulated flow in natural stream channels. The flood depth data can be used to approximate flood prone areas. Drainage area and mean basin elevation are the two basin characteristics needed to use these equations. The standard error of estimate ranges from 38% to 74% for the 100-year peak discharge and from 23% to 33% for the 100-year flood depth. Five different flood mapping methods are described. Streams are classified into four categories as a basis for selecting a flood mapping method. Procedures for transferring flood depths obtained from the regression equations to a flood boundary map are outlined. Also, previous detailed flood mapping by government agencies and consultants is summarized to assist the user in quality control and to minimize duplication of effort. Methods are described for transferring flood frequency data from gaged to ungaged sites on the same stream. Peak discharge and flood depth frequency relations and selected basin characteristics data, updated through the 1980 water year, are tabulated for more than 300 gaging stations in Utah and adjoining states. In addition, weighted estimates of peak discharge relations based on the station data and the regression estimates are provided for each gaging station used in the regression analysis. (Author 's abstract)

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Methods for estimating peak discharge and flood boundaries of streams in Utah
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Water-Resources Investigations Report
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U.S. Geological Survey,
vi, 77 p. :ill., maps ;28 cm.