Inundation Numerical Modeling in the Eastern Part of Surabaya

Inundation in Surabaya is a problem year after year, especially in the eastern part of Surabaya. The river which is located in eastern Surabaya direct to the sea. East Surabaya has varying inundation heights ranging from 0.10 to 0.80 meters. One of the causes of inundation in eastern Surabaya is land use change. In addition, the eastern part of Surabaya is relatively low and close to the sea. When sea level is higher than water level from river so that water cannot flow to downstream and that one of the causes of inundation in eastern Surabaya. Inundation simulation are made with 1D and 2D models on HEC-RAS. Ananlysis of the inundation model in eastern Surabaya using the upstream boundary condition as return period flood discharge and the condition of the downstream boundary condition as water level. Then process map data and do a model descritization. Then do calibration so that the model get near to existing condition. There are 4 inundation simulation scenario in this research. The fourth difference in the scenario is the upstream boundary conditions. The upstream boundary conditions used for the four scenarios are 2, 5, 10, and 25 years return period flood discharge. In addition, pump are also used as existing conditions. The result of the four scenarios are then made inundation maps based on area and depth. Flood discharge with 2, 5, 10, and 25 years return peiod for inundation simulations are 33.28 m3 /s, 39.71 m3 /s, 43.765 m3 /s, and 48.68 m3 /s. The result of inundation simulation based on depth are 0.05 to 0.82 meters. The result of inundated area by simulation is 0.20 to 8.5 ha. This map is used as reference in determining the priority scale of inundation handling in Eastern Surabaya. It can be concluded from the result of simulations with inundation impacts based on the area and depth of inundation in Mulyorejo District