Study on Wonogiri Reservoir Operation Performance for Flood Control Purposes Using New Operation Rules

Abstract

To overcome the Wonogiri Reservoir sedimentation problem, a closure dike and a new spillway have been built that separates the reservoir into the main reservoir (MR) and sediment storage reservoir (SSR). This study assesses the dam safety through reservoir flood routing simulation with the flood control water level (CWL) of +135.8 m. The new reservoir operation rules and the design flood of Q60, Q500, andPMF were used to estimate the maximum reservoir water level and the total outflow discharge. The results show that for the Q60 and Q500 the reservoir water level has not reached CWL until the end of the fourth day, so it is vulnerable to the risk of dam overtopping. Besides, the freeboard does not to comply with the dam safety requirements and the maximum outflow discharge for the PMF is much higher than the expected flood control capacity. It is necessary to update the reservoir operating regulations by changing the reservoir water level limit and the opening of the two spillway gates. The results showed that although the reservoir water level in the MR and SSR can be controlled not to exceed the EFWL, the total discharge from the PMF still exceeds the maximum limit.