Geomorphologic Rainfall‐Runoff Model: Incorporating Philip's Infiltration Expression

Abstract

This paper presents a watershed discharge hydrograph simulation model, based on the hydraulically based geomorphologic instantaneous unit hydrograph (IUH), developed by Kirshen and Bras (1983). This IUH was derived as a function of watershed geomorphology and the response of streams to lateral inflows, determined by solving one‐dimensional linearized equations of motion. The effective rainfall is calculated here to be equal to the gross rainfall minus the infiltration losses, presented with Philip's expression coupled with an empirical equation for soil moisture computation. Consideration is given to the role of mountainous terrain in runoff generation. For mountainous watersheds, the mountain runoff is regarded as a water depth on the alluvial channels. The effective rainfall depth is calculated to be equal to this water depth plus the rainfall depth minus the infiltration losses. The simulation model is verified through applications for three gauged watersheds in Saudi Arabia. A comparison is made between the observed and simulated hydrographs, and evaluation of the model results and limitations is provided.