Assessment of Performance Wonogiri Dam in Service of Water Needs Due to The Impact of Erosion and Sedimentation

Abstract

Wonogiri Dam administratively located in Wonogiri Regency exactly in the upper reaches of Bengawan Solo Watershed. Wonogiri Dam is a multipurpose dam which is used as irrigation, raw water, hydroelectric power plant and flood control. The high impact of erosion and sedimentation became main issue in Wonogiri Dam caused by changes in land use at upstream area. Within 25 years the capacity of Wonogiri Reservoir was reduced by 65 million m3 from 440 million m3 in 1980 to 375 m3 in 2005 as recorded. One of parameter that used for assessment of the dam performance depends on erosion and sedimentation. This study aims to determine assessment of performance Wonogiri Dam in service of water needs due to erosion and sedimentation. Erosion and sedimentation analysis can be determined by using USLE (Universal Soil Loss Equation) and SRD (Sedimen Delivery Ratio) methods. As the result showed that erosion in Wonogiri Watershed has high erosion potential which gain 3,2 million m3/year. The Keduang Sub Watershed shows the highest level of erosion potential, which is between 1.175 million m3/year. The sedimentation rate result in Wonogiri Dam considered relatively high with rate value 1,948,000 m3/year. There for it is necessary that a comprehensive sedimentation management system is needed in the Wonogiri Watershed from both side, in technical and non technical aspect, such as reforestation or dredging activities. Based on the results of the analysis of the impact of erosion and sedimentation, it can be concluded that the performance evaluation of the Wonogiri Dam is include in the sufficient category because many activities have been carried out to restore the reservoir function to its original condition.