Comparison of Direct Runoff Values Between Numerical Model and Convolution of Synthetic Unit Hydrograph Method

Abstract

This paper compares the results of direct runoff obtained by a numerical model of the shallow water equations (SWE) with the synthetic unit hydrograph (SUH) methods generally used in Indonesia. It is known that such SUH methods are still empirical, thus making it difficult for users to determine a representative method. Meanwhile, the hydrodynamic approach such as the SWE numerical model can achieve more accurate results in predicting the direct runoff compared to the SUH methods, because the model itself is derived mathematically based on the physical processes. The findings indicate that the direct runoff predicted using the SWE numerical model (HEC-RAS 5.0.7) produced more accurate results for the peak discharge with an average error of -0.07%, the peak time with an average error of 19.77%, and the shape of the hydrograph with the smallest Root Mean Square Error (RMSE) from all the cases tested. Therefore, it can be concluded that in the future the use of a hydrodynamic approach is highly recommended for the direct runoff prediction. This paper was also aimed to be used as a reference in the development of new, more accurate SUH method in the future.