Assessment of Reservoir Sedimentation and Mitigation Measures using 2D Hydrodynamic Modeling: Case Study of Pandanduri Reservoir, Indonesia

Abstract In this paper, the accumulated sediment in the Pandanduri Reservoir, Indonesia with a storage capacity of 27 million m 3 was evaluated and estimated by means of a 2D numerical model (MIKE 21 FM). This model was employed to simulate the sediment transport along the river into the reservoir with a total modeled area of 3.15 km 2 and 5 km of the tributary river. The field measurement and sediment sampling in the tributary river were conducted in order to analyze the sediment parameters and later used for the calibration of the numerical model. According to the computational results, the current sedimentation rate was 53,075 m 3 /year, which came from the main tributary river (Suradadi River). One of the proposed alternatives was to design a check dam structure downstream of the Suradadi River so that the sediment transport continuity could be interrupted, thus reducing the river sedimentation rate. Based on the numerical results, adding a check dam upstream of the reservoir could reduce the sedimentation rate of up to 30%. Therefore, the reservoir sedimentation rate reached 34,690 m 3 /year due to the sediment trapping at the upstream river. The 2D model also showed the sedimentation pattern in the reservoir, where most of the sediment accumulated in the middle of the reservoir near the spillway. In conclusion, it is recommended to combine the check dam structure with mechanical excavation and flushing to eliminate the deposited sediment and increase the reservoir lifetime.