Runoff and Peak Discharges Using Green‐Ampt Infiltration Model

Abstract

The Green‐Ampt infiltration model is used to predict runoff from 12 rangeland and cropland watersheds in Montana and Wyoming. Soil parameters derived from data in standard USDA soil surveys are used, and 99 rainfall events are modeled. The runoff distributions obtained from the model are then used with a hydrograph model to predict the peak discharge from the watershed. Procedures are applied that adjusted the Green‐Ampt infiltration parameters for various cover and condition classes. The model is applied to areas of up to 54 sq mi with a wide variety of soil and cover conditions. The runoff volumes and peak discharges are compared with the measured values and with those predicted by the Soil Conservation Service (SCS) curve‐number procedure. The Green‐Ampt model predicted both the runoff volume and peak discharge better than the curve‐number model. The standard error of estimate was less for the Green‐Ampt model in nine of 12 watersheds for runoff volumes and in 11 of 12 watersheds for peak discharges.