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DEVELOPMENT OF SOFTWARE FOR THE OPERATION OF WONOGIRI RESERVOIR AT FLOOD PERIOD

The floods of Bengawan Solo River Basin had caused a lot of losses lately. Therefore, flood control as one of important disaster mitigation efforts becomes urgent measure to manage flood in the upstream catchment area of Bengawan Solo River Basin. The flood prone area with high risk damage is flood plain of along main river and tributaries that located at the city of Surakarta, Karanganyar, and Sragen. In order to improve the performance of flood control, one relevant alternative is through an integrated system for the operation of opening gates of spillway at Wonogiri Reservoir. Lack of hydrological information, often causes uncertainty of operation of spillway’s gates to release water without problem at the downstream. An appropriate software to integrate hydrological information in the catchment area of Wonogiri Reservoir and opening gates of spillway need to be developed.

The developed software consists of three simulation models. First is rainfall-runoff simulation model of flood forecasting to estimate inflow hydrograph based on the catchment response of each watershed that contributes runoff into the reservoir storage. The second model is simulation of flood routing to obtain opening gates of spillway in flood period and the third model is the recommendation of the optimal spillway’s gates opening by considering the reservoir water level, the estimated inflow hydrograph and the condition of the downstream area. Simulation of flood forecasting is conducted by utilizing hydrological information from 14 rainfall gauges and base flow from 8 watersheds. The output of flood forecasting model is the total inflow hydrographs from 8 watersheds. The output of flood routing can be used as valuable consideration to assist the decision maker in determining the optimal hourly outflow discharge under constraint of downstream bankfull capacity of 400 m³/s and maximum reservoir water level +139.1 MSL.

Result of the software development with compiler PHP of MySQL shows real-time hydrological information each rainfall station, base flow from each watershed, initial water level of reservoir and initial opening gates of spillway. Accuracy of water balanced calculation is less than 1%. This performance indicates that the model can be applied to improve the performance of flood control at the upstream of Bengawan Solo River Basin.

Keywords : Flood forecasting, flood routing, flood control, bankfull capacity.