Hydrological Dynamics and Geo-Hazard Risks: A Case Study of Cikamiri Sub-Watershed

Abstract

Hydrological dynamics occur as a result of massive land cover changes in the Cikamiri sub-watershed, Garut, Indonesia. Changes in the hydrological patterns increase the frequency of hydrometeorological hazards in the Garut region. This study aims to analyse water balance dynamics and multi-disasters in data-scarce regions by integrating the FJ Mock model, Revised Universal Soil Loss Equation (RUSLE) and Flash Flood Potential Index (FFPI). Rainfall and spatial data from 2016 to 2025 were used to simulate the relation between water availability and land vulnerability with soil and rock types. The results show a decrease in Soil Moisture Capacity (SMC), resulting in weak watershed retention functions. The average discharge of the Cikamiri Sub-watershed 69.8 mm/month with high surface runoff  and a combination of high erosion rates severe creates zones of significant landslide and flash flood vulnerability in the Cikamiri River flow. The results of the FFPI integration show a high concentration of vulnerability zones in areas with steep slopes and non-vegetation cover of 17.12% or 1,070.23 ha. This vulnerability affects the downstream area of the Cikamiri River, which flows into the Cimanuk River Basin. The geo-hazard modelling is consistent with the history of disasters in the study area, which were triggered by sediment accumulation and extreme peak discharge. Slope direction and contour analysis serve as the final validation of the analysis. The findings indicate the need for river basin management focused on the upstream and downstream areas of the Cikamiri sub-watershed, with improvements to drainage infrastructure and control of land clearing in the catchment area. The study provides a basic spatial framework for local governments in developing spatial risk-based development policy planning