Prediksi Pola Sebaran Sedimentasi Sebagai Penentuan Umur Guna Waduk (Studi Kasus Bendungan Jragung, Kab. Semarang)

The Jragung Dam in Semarang Regency is designed for a 50-year service life, serving as flood control, irrigation supply, micro-hydropower generation (1,400 kW), tourism, and raw water provision. However, sedimentation can reduce storage capacity and shorten its operational lifespan. This study aims to predict sediment distribution patterns to estimate reservoir service life and develop appropriate sediment management strategies. Hydrological analysis was conducted using the Thomas Fiering and FJ Mock methods, erosion rates were calculated using the Universal Soil Loss Equation (USLE), sediment transport (bed load and suspended load) was analyzed using multiple methods, and distribution modeling was performed with MIKE 21 software. Results indicate an average inflow discharge of 6.20 m³/s and an annual sediment load of 0.753 million m³, dominated by sand fractions (d50 ≈ 1.07 mm). Modeling suggests the reservoir’s service life will be only 39 years, significantly shorter than planned, with sediment deposition concentrated in the upstream and middle reservoir zones. Dredging is proposed as a mitigation strategy, requiring a total removal volume of 20.095 million m³ to extend the reservoir’s service life.