Optimum Rainfall Interval and Manning’s Roughness Coefficient for Runoff Simulation

Abstract

To simulate a runoff hydrograph from an overland plane or from a catchment that is subject to natural rainfall, the use of a computer model is essential. To develop such a model, among other parameters, the modeler is required to specify rainfall interval, rainfall data for that interval, and Manning’s roughness coefficient (Manning’s n ) of the plane or catchment surface. To evaluate Manning’s n for runoff simulation, it is common to use the hydrograph fitting technique. With this technique, the simulated hydrographs are actually dependent on the rainfall data and, hence, the rainfall interval. The Manning’s n is, therefore, also dependent on the rainfall interval. In this technical note, using rainfall and runoff data over a concrete plane, a concrete catchment, and an asphalt plane, the optimum rainfall interval and the corresponding optimum Manning’s n have been evaluated. Five rainfall intervals were used in the evaluation, which ranged from 0.25 min to 4.0 min . The evaluation shows that: (1) for ca...