Evaluation of direct runoff volumes and simulation of peak discharges

Abstract

The main goal of this study is to estimate the direct runoff from storm rainfalls and to simulate peak discharges occurred in a headwater catchment in Hong Kong. With application of the straight line method, inflection point method and one parameter filter method, the baseflow volumes are separated, and the direct runoff volumes are computed for the storms occurred in the headwater catchment during the period from 2007 to 2010. Totally, there are 20 storm events to be analyzed, and the associated runoff coefficients are computed. Among three methods, one parameter method is the most suitable one to provide the baseflow separation and direct runoff volumes, and the result by using the method shows that average direct runoffs contribute about 63% of flood peak discharges, and the direct runoff ratios are less than 38%. To further explore the direct runoff features, direct runoff hydrographs are simulated and analyzed by using regression method, runoff coefficient method and SCS method. Among them, the runoff coefficient method gives the best result in predicting the cumulative direct runoff volumes, while the regression method is found to be the worst for simulating direct runoff hydrographs for small storms (rainfall depth < 10 mm).