EVALUATION OF SUSTAINABLE SEDIMENT MANAGEMENT IN SENGGURUH RESERVOIR CONSIDERING AGE AND TRAPPING EFFICIENCY
Keywords:Trap efficiency, Brown, Churchill, Sedimentation, Dredging, Flushing
Trap efficiency is essential in governing the sedimentation process, as the volume of sediment trapped in a reservoir depends on it. The trap efficiency values were a tool to evaluate sustainable reservoir sediment management scenarios in Sengguruh. Theoretically, the reservoir could trap much sediment with higher trap efficiency values. However, along with the age of a reservoir, the sediment trap efficiency decreased. This paper aims to analyze long-term historical records of sediment trap efficiency and to evaluate the scenarios of sustainable sediment management in the Sengguruh Reservoir. Results indicated that after its completion in 1988, the sediment trap efficiency of Sengguruh Reservoir has continued to fluctuate yearly instead of conservation efforts. The trap efficiency sharply reduced during the initial impounding in 1988–1989. Later, in 1990–1994, the depletion rate became mild as introduced sediment dredging works. In February 2004, a massive landslide and flash flood in the upper catchment produced more sediment transported to the Sengguruh reservoir. Therefore, the trap efficiency remained low, between 15 and 20%. The predicted value of future trap efficiency with Brown's method yielded slightly lower values than the Churchill method but still gave good results compared to observed values. With the dredging-only scenario, the future trap efficiency varied between 15% and 20%. In contrast, the combination of dredging and flushing yielded a value between 20% and 35%. Further, dredging 310,000 m3 annually and flushing 1,200,000 m3 every three years provided better trap efficiency results for future sustainable sediment management in the Sengguruh Reservoir.