Roughness Values for Overland Flow in Subcatchments

Abstract
A simple method is presented for assigning Manning roughness coefficients n to overland flow segments in kinematic wave models. The resulting n‐value for each subcatchment reflects its imperviousness and its land use. This approach has been incorporated into a kinematic wave model, and its application is here demonstrated on a catchment in Singapore. One storm record was used for calibration purposes, and this yielded extreme Manning n‐values of 0.02 and 0.30 for pure impervious and pervious sections, respectively. The calibrated model was then tested on two other storms for verification. Good agreements between simulated and measured hydrographs were obtained.

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