ANALISIS DEBIT BANJIR PADA SUB DAERAH ALIRAN SUNGAI (DAS) TABUK, PERBANDINGAN METODE HIDROGRAF SATUAN SINTETIK (HSS) SCS DAN SNYDER

Abstract

Floods are a natural disaster that can occur during the rainy season in various watershed areas across many regions of Indonesia. Continuous heavy rainfall causes rivers to exceed their capacity, leading to flooding. The Sungai Tabuk subdistrict, one of the rice product areas, was also affected by flooding, which will disturb rice production. This research aims to compare two methods for calculating a design flood using proper software, which has not been found in previous studies in this area. We chose a hydrological model simulation using the HEC-HMS software to determine the magnitude of the flood discharge. The data was collected by two processes: field research for primary data and data received from other institutions for secondary data. The data was analyzed by comparing two methods available in the software: the SCS and the Snyder unit hydrograph (HSS), and it was processed to create a rainfall-runoff model using both of them. The simulation results with observations dated January 1, 2021, using the Mononobe distribution method by SCS and Snyder, are as follows: the SCS method at the outlet had a higher discharge: 974,4 m³/s, whereas the Snyder method had a discharge of only 957,5 m³/s. The differences in the results can be attributed to the differences in the parameters and calculation methods. In contrast, the discharge observed in the field was 39.072 m³/s. It can be seen that the discharge values from the HEC-HMS software are significantly higher than the discharge values obtained in the field, because the discharge was a regular flow instead of a design one. A further study that can reveal why the difference was relatively high and how to overcome the problem is needed.