EVALUASI PERBANDINGAN KERUGIAN EKONOMI AKIBAT BANJIR PADA KONDISI EKSISTING DAN NORMALISASI (Studi Kasus: Sungai Cisadane, Banten)

Abstract

This study examines the effectiveness of the Cisadane River normalization plan based on rainfall data, land cover, and the characteristics of the Cisadane Watershed. This research aims to determine the 2, 5, 10, 25, 50, and 100-year return period flood discharge and to design the new Cisadane River cross section. Flood inundation modeling is also carried out to determine the effectiveness of Cisadane River normalization and flood losses in existing and normalized conditions. Flood inundation modeling will be carried out using HEC-RAS V.6.4.2 software based on the value of flood discharge from rain data processing. Rainfall data is processed using the Thiessen Polygon method to obtain average rainfall values, then processed using the Normal, Gumbel and Log Pearson III methods to produce design rainfall. The design rainfall is then tested using Chi Kuadrat and Smirnov-Kolmogorov method in order to obtain a design rainfall that is able to represent the rainfall data. The selected design rainfall is further processed using the Mononobe equation to obtain rainfall intensity and hourly rainfall values. The characteristics of the Cisadane watershed are processed using the HSS Nakayasu method to produce a unit hydrograph value. The result of rainfall data processing is the value of the design flood discharge for the return period of 2, 5, 10, 25, 50, and 100 years. The 25-year return period flood discharge is used as the basis for designing the new Cisadane River cross section and is also used in flood inundation modeling for normalization conditions. From the flood inundation modeling using HEC-RAS software, it can be seen that the Cisadane River normalization program is able to reduce the flood inundation formed at the 100-year return period by 86.17%. Meanwhile, the flood losses in the existing conditions and normalization at the 11-year return period are IDR 11,735,421,018 and IDR 608,400,810 respectively.