Risk analysis of debris and non-debris flow in the Cisokan river flood event

¹ Bandung Institute of Technology, Magister Study Program of Water Resources Management, Faculty of Civil and Environmental Engineering, Jl. Ganesha 10, Bandung, West Java Province, 40132, Indonesia
² Bandung Institute of Technology, Water Resources Engineering Research Group, Faculty of Civil and Environmental Engineering, Jl. Ganesha 10, Bandung, West Java Province, 40132, Indonesia

^* Corresponding author: nugrohoeka@itb.ac.id

Abstract

Cisokan River is one of the main inflow rivers of Cirata Reservoir aside from Citarum River. Cisokan River is the second largest contributor to Cirata inflow after Citarum River. In May of 2023 Cisokan River experienced instances of flash flood disasters that submerged houses in Cianjur Regency, one of the affected villages is Ciranjang Village. Several news outlets reported that this flood also left debris and mud in the affected areas, which indicated that the flood was debris flow. This study conducts the risk analysis resulting from debris and non-debris flow with the changes in river cross-section due to sedimentation. In this study, modeling was carried out employing a Digital Elevation Model (DEM) map and utilizing the Hec-RAS software. One focus of the modeling was on simulating the Newtonian (non-debris) and non-Newtonian (debris), comparing the results and analyzing the risk from both. The result showed that the non-Newtonian flow’s flood inundated area is larger than the Newtonian flow’s, which means the high flood risk area of debris flow is 12.5% larger than the non-debris flow’s high flood risk area.