Sedimentation significantly influences the operational lifespan and effectiveness of reservoirs, particularly in terms of their ability to supply irrigation and manage water resources. The Logung Reservoir in Central Java, Indonesia, experiences continual sediment deposition driven by erosion within its catchment area. This research estimates the remaining operational lifespan of the reservoir by integrating erosion-driven sediment yield modeling with empirical bathymetric data. The sedimentation rate was derived using the Universal Soil Loss Equation (USLE), which was adjusted using the Sediment Delivery Ratio (SDR) and Trap Efficiency (TE), resulting in an estimated annual sediment inflow of 158,945.2 m³. Conversely, actual sediment accumulation derived from dead storage volume changes over five years was significantly higher at 4,818,622.4 m³ per year. This discrepancy suggests that erosion-based models may underestimate sediment input when conservation measures are not fully accounted for, whereas field measurements provide a more accurate reflection of sediment dynamics. Based on the analysis, the Logung Reservoir’s remaining useful life is estimated at 14.95 years under current sedimentation conditions, and 30.32 years under potential scenarios. These results call attention to the necessity for improved watershed management and sediment control to extend the reservoir’s longevity beyond its original design expectations.