Comparison of Flood Hydrograph of Manikin Dam Watershed Using Synthetic Unit Hydrograph Method, HEC-HMS and Rain on Grid Model with HEC-RAS 2D

Abstract

Manikin watershed is located in Kuaklalo Village which borders Bokong Village, Taebenu Subdistrict, Kupang Regency, East Nusa Tenggara Province which has an area of 49.31 km2 with a river length of 8.62 km which has a semi-arid climate with a fairly high annual rainfall of around 1000 - 1500 mm. This study aims to compare the design flood discharge and peak hour with Nakayasu Synthetic Unit Hydrograph (HSS) method, GAMA I, HEC-HMS and rainfall discharge model with HEC_RAS 2D in Manikin Dam watershed. In this study, 6-hour rainfall with
a return period of 50 years and 100 years was used. Based on the analysis results, the calculation of the hydrological numerical model flood discharge with the HEC-HMS method with a return period of 50 years and 100 years is 511.90 m³/s and 599.30 m³/s with a peak time at the 4th hour. The peak discharge values
obtained using the Nakayasu Synthetic Unit Hydrograph and GAMA I methods with a return period of 50 years and 100 years are 342.11 m³/s, 381.14 m³/s and 406.44 m³/s, 456.13 m³/s, and the peak time obtained at SUH Nakayasu is 3 hours and GAMA I is 4 hours. Numerical model results with HEC-RAS 2D v6.6 with 6
hours of rainfall on the grid obtained peak discharge Hydrograph values for the 50-year and 100-year return periods of 494.86 m³/s and 604.88 m³/s, with the peak time at the 5th hour. Therefore, the largest peak discharge and peak time results were obtained from the HEC-HMS method among the three SUH formulas and HEC-RAS calculations