Hydrologic modeling for watershed erosion control

Abstract

The watershed manager, hydrologist and design engineer are always faced with the problem of taking a particular action and making decision under uncertainty. This report explains and applies a method to be used in the design of floodwater retarding structures, and sediment storage reservoirs and to evaluate the effects of land treatment practices on the watershed hydrographs for ungaged watersheds or where precipitation records are available but streamflow data do not exist. The suggested procedure for estimating runoff hydrograph and sediment yield consists of obtaining parameter estimates from available precipitation data for a probabilistic rainfall model. The model is used to generate two 100-year and 20 ten-year simulation runs of precipitation events through the Monte Carlo procedure. The synthetic records were converted to runoff and sediment yield by means of the Soil Conservation Service equation (rainfall-runoff equation) and the modified universal soil loss equation, respectively. For determining the runoff curve number or hydrologic soil cover complex number for the W-1BX, a stochastic procedure was used. A regression analysis from available data which related rainfall to runoff was run and then through the SCS equation, the curve number was computed. To present the suggested procedure, the flood of July 16, 1975, was used and compared with the computed runoff hydrograph. The computed sediment yield with the proposed flood retarding structure was compared with the computed sediment yield of W-IBX in present condition.