Application of a Distributed Hydrologic Model to the November 17, 2004, Flood of Bull Creek Watershed, Austin, Texas

Abstract

This study presents a hydrologic analysis of a flood event that took place over a small urbanizing watershed in Austin, Texas. The physically based, distributed-parameter gridded surface subsurface hydrologic analysis (GSSHA) hydrologic model was used to simulate the watershed response to a very high-intensity rain event. The hydrologic model was forced by both gauge-observed and multisensor precipitation estimator (MPE) rainfall input. Observed discharge was compared to GSSHA-generated hydrograph under various degrees of representation of the watershed physiography. In addition, simulation hydrographs by GSSHA using five different model grid sizes were compared in order to evaluate the effect of grid size on model predictions. The simulation hydrograph for the model using a 30-m grid cell generally compared well to the observed flow data once the effects of storm water detention were simulated. The comparison of simulation results from models using 30, 60, 90, 120, and 150 m grid size highlighted the loss of accuracy as the model grid size is increased. Driving the hydrologic model by data from the two rain gauges existing on the watershed resulted in significant overestimation of the runoff.