Sediment impact on capacity loss in Bili-Bili reservoir: An integrated assessment

• Long term bathymetric analysis reveals a 35% storage loss in Bili-Bili Reservoir. • 3D morphometric and predictive modeling (R² = 0.94) quantify sediment evolution. • Sediment-control structures retain ∼57% of total sediment inflow (2011- 2024). • Findings establish a transferable adaptive management framework for tropical basins. Reservoir sedimentation critically threatens the long-term sustainability of water infrastructure in tropical monsoon basins. This study presents an integrated assessment of sediment accumulation, morphodynamic evolution, and storage capacity loss in the Bili-Bili Reservoir, Indonesia, based on multi-year bathymetric surveys conducted in 1997 (baseline) to 2024. Multitemporal bathymetric datasets were combined with three-dimensional morphometric reconstruction and exponential predictive modeling (R² = 0.94) to quantify spatiotemporal sediment distribution and forecast future storage decline. The results indicate a 35% reduction in total storage from 375 × 10⁶ m³ at commissioning to 243.85 × 10⁶ m³ in 2024 with projections suggesting a 50% loss by 2048 under current management practices. The 2004 Mount Bawakaraeng landslide contributed an unprecedented sediment inflow of approximately 3.8 × 10⁶ m³ yr⁻¹, while post-2011 sediment-control structures retained approximately 57% of total sediment inflow. Bathymetric evidence further demonstrates progressive upstream deltaic aggradation, reducing hydraulic efficiency and effective storage capacity. Unlike previous short-term or empirical studies, this research introduces a multi-decadal, data-driven framework that explicitly links sedimentation processes with infrastructure performance and management outcomes. The findings provide a quantitative benchmark for reservoir sustainability and inform adaptive sediment management strategies consistent with Indonesia’s IWRM framework. This approach offers a transferable methodology for sediment-prone reservoirs across tropical regions under increasing hydroclimatic variability.