Analysis of runoff from small drainage basins in Wyoming

Abstract

A rainfall-runoff model was used to synthesize long-term records of runoff volume and peak discharge from long-term records (73 years) of rainfall and evaporation. The long-term data was transferred from a base station, Cheyenne, Wyoming, to 13 other weather stations in Wyoming. Volume and peak discharge frequencies were developed for the intermontane areas on 22 drainage basins smaller than 11 square miles relative to rainfall at the nearest weather station. Runoff volumes and peak discharges were related to basin parameters with a high degree of correlation. Flood volumes were related to drainage area, maximum relief and basin slope. Flood peaks were related to drainage area, maximum relief, basin slope, and channel slope. A dimensionless hydrograph was developed to define the characteristics shape of flood hydrographs to be expected from small drainage basins in Wyoming. The method requires a peak discharge in cubic feet per second and a volume in acre-feet to produce a synthetic hydrograph. Some selectivity was used in the development to avoid multipeak events or unusually shaped hydrographs. An investigation of storage behind a highway embankment with a culvert to allow outflow, has shown that the single fast-rising peak is most important in culvert design. Single peaks cause higher water elevations behind embankments than do multi-peak events of the same magnitude and volume. The study was limited to simple box culverts with inlet control. /FHWA/