Analysis of Land Cover Changes Impact on Design Flood Estimation Case study: Upper Cimanuk Watershed in Garut City

Abstract

The unexpected flooding events that occurred in the years 2021 and 2022 in the city of Garut became unforeseen incidents. According to the National Disaster Management Agency (BNPB), the flood disasters were caused by several factors, one of which was changes in land cover. Based on this background, this research is conducted to examine the causes of changes in flood discharge that have occurred in the city of Garut due to land cover changes from the years 2000, 2010, and 2020. The evaluation of the factors causing the flood magnitude is performed by conducting a hydrological analysis in the Cimanuk Watershed. An analysis of land cover changes using the ArcGIS application to create land cover samples and HEC-HMS application was conducted to determine the percentage increase in discharge and to understand the percentage of land cover changes that occurred in the Cimanuk Watershed. The data used included satellite image maps, digital elevation models (DEM), rainfall intensity, and cross-sectional data. The accuracy of the simulation was assessed using the Nash-Sutcliffe Efficiency (NSE). The simulation results show an increase in the inflow discharge into Garut city ranging from 23.7% to 32.2% for each return period. The NSE value obtained for the model was 0.83, indicating that the HEC-HMS hydrological model performed well.