Wonogiri reservoir operation pattern after the construction of new spillway for flood control

Abstract

Wonogiri reservoir in upstream Bengawan Solo experienced sedimentation problems that endanger its operation. Much of sediments come from Keduang watershed. To overcome this problem, closure dike was constructed to localize the sediment from Keduang watershed. The dike divides the reservoir into main and sediment storage reservoirs, each has its spillway. This paper presents results of the study on Wonogiri Reservoir operation during flood period after dike construction. The study followed a two-step calculation. It updated the design flood by employing rainfall data frequency analysis and Collins unit hydrograph. Flood routing was subsequently done by applying level pool method. Two conditions were considered, namely existing condition whose initial water level was +135.3 meters and new condition whose initial water level was +136.3 meters. The study reveals an increase of the flood discharge to Wonogiri reservoir by 7.7% and 3.6% for the 60 year and 500 year floods, respectively, as compared to the previous study of Pradipta (2014). The study shows that Wonogiri reservoir is prone to overtopping under 500 year flood. It is recommended to lower the control water level of the new spillway.

The Development of Ungauged-Catchment Integrated-Similarity Unit Hydrograph to Estimate Inflow of Wonogiri Reservoir

“…The results showed that the T p of the 1982 Design was 13 hours while Pradipta (2014) used 5 hours for all the design flood types. Moreover, Perum Jasa Tirta I (2020) was discovered to have produced 8, 7, and 17-hour for 60-year, 1.2×100-year, and PMF design, respectively while Wijayanti et al (2021) predicted a 5-hour which was similar to the findings of Pradipta (2014) for 1.2×100-year flood and PMF but a 4-hour for the 60-year flood. Meanwhile, the T p obtained for the 60 and 1.2×100-year floods in this study were 4 hours when the rainfall was distributed in a 5-hour duration and but the value changed to 5 hours at a 6-hour duration.…”

“…The hydrologic model was validated using rainfall-runoff events and data obtained from previous investigations (Nugroho, 2015). The results obtained from this study were also compared to those of previous investigations (Pradipta, 2014;Perum Jasa Tirta I, 2020;Wijayanti et al, 2021).…”

“…A five-hour duration was also used for further analysis based on ground-rainfall characteristics of 60 and 1.2×100-year design flood and the 24-hour rainfall was discovered to be distributed for the PMF as presented on the right side of Figure 8. The flood hydrograph characteristics observed were compared with those reported in previous studies (Pradipta, 2014;Perum Jasa Tirta I, 2020;Wijayanti et al, 2021) in the following Table 5. The results showed that the T p of the 1982 Design was 13 hours while Pradipta (2014) used 5 hours for all the design flood types.…”

“…It was built mainly to control and mitigate floods in the Bengawan Solo River basin (Nugroho, 2015). Due to the issue of sedimentation, the reservoir was split into two including the sediment storage reservoir (SSR) to trap the sediments from the Keduang watershed and the main reservoir (MR) to deliver water to the downstream areas (Jayadi et al, 2018;Morris, 2020;Wijayanti et al, 2021). The only catchments with rainfall and water level monitoring stations in the Wonogiri Reservoir watershed are Keduang, Temon, and Wuryantoro (Oktavia, 2013).…”

Operational analysis of South Bali's integrated regional water company related to the Sidan Dam operational plan

“…Dams are one of the water supply infrastructures both for irrigation and clean water in Indonesia. This dam was built in a location that is calculated to provide maximum storage and is technically safe (Wijayanti et al, 2021;Heydari et al, 2015;Ahmadi et al, 2017;Kartini & Permana, 2016).…”