Flood modeling and baseline study in urban and high population environment: A case study of Majalaya, Indonesia

The Majalaya area is a vital part of the Bandung Metropolitan Area economy, exemplifying an urbanized area prone to annual flooding in Indonesia. Even though multiple flood events occur yearly, Majalaya's floods have not received much attention. This study aims to simulate the 22 February 2018 flood event that caused massive damage to properties and the surrounding environment. The study used gauged and satellite precipitation measurements, stream flow re-cords, Indonesian National DEM (DEMNAS), Light Detection and Ranging (LiDAR), and primarily surveyed topographic terrain data for flood modeling using HEC-HMS and HEC-RAS. The modeled flood extents were compared with the crowdsourced flood extent of a recent large flood event recorded by the local community. The observed and modeled hydrographs were very similar, with a Nash-Sutcliffe Efficiency (NSE) of 0.88 and a root-mean-square error (RMSE) of 11.93. The disparities between the simulated and observed flood extend were identified, including the limitation of modeling, alteration of flow characteristics due to trash clogging, and the quality of crowdsourced flood records. Based on the flood simulation, the study identifies recommendations to manage the flood risk: increasing river conveyance, creating a large reten-tion basin, and creating a designated floodway, while avenues for further studies are recommended.