A DISTRIBUTED DYNAMIC WATERSHED MODEL1

Abstract

ABSTRACT:A distributed watershed model was developed to mathematically simulate overland and channel flow for a single‐event storm. The modeled watersheds in the study were subdivided into rectangular grid elements. All hydrologically significant parameters, such as land slope, rainfall and precipitation excess, were assumed to be uniform within each element. The Green‐Ampt method was adopted to generate precipitation excess for each element during the simulation period. A two‐dimensional diffusion wave model was used for overland flow routing and an iterative Alternative Direction Implicit scheme was used to solve the simultaneous overland flow equations. Once the overland flow became inflow to the channel, a one‐dimensional dynamic wave flood routing technique, based on a four‐point, implicit, non‐linear finite difference solution of the St. Venant equation of unsteady flow, was applied. A limited number of comparisons were made between simulated and observed hydrographs for areas of about one square mile. Given the appropriate parameters, the model was able to accurately simulate runoff for single‐event storms. This paper describes a distributed watershed model developed to simulate overland and channel flow. Comparisons were made between simulated and observed hydrographs for three watersheds. The model was able to accurately simulate the runoff for single‐event storms using 61‐m by 61‐m (200 ft by 200 ft) watershed grid elements.