A distributed dynamic watershed model

Abstract

A distributed watershed model was developed to mathematically simulate routing overland and channel flow for a single-event storm. The watersheds used 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. Soil property and land use were the major factors in defining a hydrologic response unit. 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 adopted to solve the simultaneous equations. Once the overland flow became inflow to the channel, 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. Limited number of comparisons were made between simulated and observed hydrographs for areas of about one square mile. Given the appropriate parameters, the model accurately simulated runoff for a single-event storm.