SEDIMENTATION EFFECTS IN RESERVOIR TOWARD THE DECLINING FUNCTION OF FLOOD CONTROL

Abstract

One of the reservoir function is as a flood control, with the principle of flood damming. The reservoir ability to reduce flood depends on the amount of its storage capacity. A river flowing into reservoir velocity will decrease, then consequently the sediment that is carried over by the river will settle. The reduction of the reservoir capacity due to sedimentation will decrease the reservoir capability as a flood control, because the ability to reduce the flood also declines. This research will analyze the magnitude of sediment effect in the reservoir toward the decrease of reservoir function as a flood control. The case study will use data from Wonogiri Dam. Analysis includes comparation magnitude of spill out flood hidrograph on initial condition before the sedimentation, and later condition after sedimentation in reservoir, that is, by comparing the analysis of flood routing hidrograph. The result of data analysis, showed sedimentation that has occured since 1980 to 2005 around 41.10% settled in the dead storage , 13.40% in the operational space, and 0.90% in the flood control space. The analysis result showed that the capability to reduce the reservoir's peak flood due to sedimentation decreases 570 m3/sec, in which originally the reservoir was able to reduce the flood as much as 2575 m3/sec on initial condition, and the reduction capability decreases to only about 2005 m3/sec after sedimentation. I hope the results of this analysis could be used as a reference reservoir management and in particular the management of sediment in the reservoir.