Batu Flash Flood Modeling Using HEC-HMS for Hydrological Prediction

On November 4th, 2021, there was a hydrometeorological disaster in the form of a flash flood in the Bumiaji District area, Batu City, Malang, East Java. Extreme weather conditions trigger high rainfall due to climate change. When flash floods occur in Batu City, Malang, the results of analysis of satellite imagery and weather radar also show the growth of Cumulonimbus (Cb) clouds, which are intense with a potential distribution of heavy to hefty rainfall in the Batu City area, Malang. In this study, hydrological analysis was carried out using the HEC-HMS model to estimate the magnitude of the flood discharge. The maximum daily rainfall data from the BMKG station closest to the study location is used. The analysis was carried out using spatial data of the seamless digital elevation model (DEM) from the DEM Nasional by observing the flood-affected catchment area. The results of the analysis are the estimated magnitude of flood discharge. The flood discharge in the downstream is 50.6 m3/s for a two-year return period, 60.1 m3/s for a five-year return period, 66.5 m3/s for a ten-year return period, 74.7 m3/s for a 25-year return period, 80.8 m3/s for a 5-year return period, and 86.9 m3/s for 100-year return period. In a future study, it can be used to determine the appropriate channel dimensions and the river’s normalization so that if hefty rainfall occurs again, the impact of the floods can be reduced.