2D numerical modeling of the Jeneberang River Flood due to the overflow of the Bili-Bili Dam

Abstract

High rainfall at the end of January 2019 in South Sulawesi, especially in the upstream area of the Jeneberang watershed, caused an increase in the height and volume of water in the Bili-Bili dam reservoir. The elevation of the water level was recorded on January 22, 2019 at 18:00 WITA reaching +101.87 m ASL above the normal water level elevation of +99.50 m ASL. In accordance with the spillway door operating pattern, if the water level exceeds the normal water level elevation limit, the dam floodgates must be opened to prevent dam collapse. To find out the impact caused, it is necessary to numerically model the flow velocity, depth, and inundation area in the downstream area of the Jeneberang river caused by overflow of discharge from the Bili-Bili Dam spillway. The data used are the flow hydrograph data from the outflow of 10-hour dam outflow as an upstream boundary condition and the rating of the rubber dam rating curve downstream of the Jeneberang river as a downstream boundary condition. The 2D research area focuses on 2 sub-districts directly adjacent to the Jeneberang river, namely Pallangga and Somba Opu sub-districts. From the results of flood simulations using the 2D HEC-RAS numerical model, the flow velocity is between 0.57m / s to 4.84 m / s, the depth is between 1.70 m and 7.38 m, and the inundation area is 1.7 km2. These results were then calibrated with the results of observations and measurements in the field of the former high flood inundation in the building and the results of interviews with the affected communities which found that the simulation results correlated well at the seven points of measurement in the field using RMSE which is 0.37.