Evaluation of sediment management for two large reservoirs in Lombok island

Sedimentation is an important issue in reservoir rehabilitation and maintenance. This problem is worsened by seasonal water scarcity as a characteristic of arid catchments. Worldwide loss of storage capacity due to sedimentation is much higher than the increase of capacity by the construction of new reservoirs. Further, sedimentation hinders the safe operation of not only shallow reservoirs but also deep reservoirs by means of turbidity currents which sporadically transport large volumes of sediments down to the dams. This study analyses the real case of Pengga reservoir and Batujai reservoir located in Central Indonesia. Selected sediment management alternatives were analysed and evaluated based on technical, social and environmental criteria. Evaluation of sediment management alternatives was conducted by utilising the REServoir CONservation (RESCON) tool. Results showed that, first, both flushing techniques and hydrosuction are feasible whereas dredging and trucking are not. Secondly, the flushing technique outweighs the Hydrosuction Sediment Removal (HSRS) method. Thirdly, application of the HSRS method in both reservoirs shares one thing in common, i.e. it requires an appropriate combination of the number of suction pipes as well as minimum suction pipe diameters. Lastly, there are some differences in the details of implementation of the flushing technique to both reservoirs