FLOOD HYDROGRAPH ANALYSIS USING SYNTHETIC UNIT HYDROGRAPH, HEC-HMS, AND HEC-RAS 2D UNSTEADY FLOW PRECIPITATION ON-GRID MODEL FOR DISASTER RISK MITIGATION

This study presents a flood hydrograph numerical modeling of the Keser watershed for disaster risk mitigation and water resources management for an emergency action plan (EAP) on the Tugu dam. Several formulations for calculating peak discharge, which are associated with information on flood design in Indonesia are regulated in SNI 2415:2016 regarding the procedure of flood discharge calculation and design. This information is important and related to water structure dimensions, risk, costs, and reliability. The complexity of watershed conditions affects the hydrograph shape and volume. Hence, a performance analysis is needed to identify the best current hydrograph model. In this study, the performance of Nakayasu, Gamma 1, and Snyder SUH was analyzed and compared with the numerical modeling using the HEC-RAS 2D hydrodynamics precipitation on grid and HEC-HMS numerical model in the Keser watershed with one-hour rainfall height of 114.92 mm (R50). Based on the calculation results, the hydrologic numerical model flood discharge calculation using HEC-HMS method was 451.1 m3/s. The peak discharge values obtained using the Nakayasu, Gamma, and Snyder methods were 424.2, 410.4, and 439.4 m3/s, respectively. The results of the numerical model with HEC-RAS 2D v6.3 with uniform precipitation on the grid obtained a peak discharge hydrograph value of 420.98 m3/s. Therefore, the highest peak discharge results were obtained from the HEC-HMS method among the three SUH formulas and HEC-RAS calculations. Hence, the deviation of peak discharge value using three SUH, HEC-HMS, and HEC-RAS was obtained under 10%.