Integrated assessment of land-use change, erosion, and reservoir sedimentation in a tropical volcanic watershed: Implications for sustainable watershed management in Indonesia

Abstract

Reservoir sedimentation is a major challenge affecting the long-term sustainability of water resources infrastructure in tropical watersheds. In the Upper Brantas River Basin, Indonesia, rapid land-use change and intensive agricultural activities have accelerated soil erosion and sediment delivery into the Sengguruh and Sutami reservoirs, significantly reducing their storage capacity and operational performance. This study aimed to evaluate the spatial distribution of erosion hazards, quantify sedimentation rates, and assess the effectiveness of soil and water conservation strategies in reducing sediment inflow into both reservoirs. An integrated approach combining the Universal Soil Loss Equation (USLE), Sediment Delivery Ratio (SDR), and Normalized Difference Vegetation Index (NDVI) analyses was applied using geospatial datasets, hydrological observations, sediment sampling, and land-use data for 2017 and 2023. The results indicate that annual erosion in 2023 reached 26.9 million tons/year in the Sengguruh watershed and 7.5 million tons/year in the Sutami watershed, with corresponding sediment delivery ratios of 8.34% and 9.30%, respectively. Land-use conversion from agricultural areas to built-up land substantially increased erosion susceptibility, particularly in steep upstream regions. Spatial analysis further revealed that moderate-to-very-high erosion hazard classes covered more than 62% of the watershed area. Reforestation and gully-plug interventions showed measurable, although limited, reductions in erosion and sedimentation rates, decreasing sediment delivery by up to 0.83%. The findings demonstrate that long-term sediment control in tropical volcanic watersheds requires integrated watershed management combining ecological restoration, structural conservation measures, and community-based land management. This study provides an important scientific basis for sustainable reservoir sediment management in rapidly developing tropical river basins.