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Kedurus River serves to drain flood discharge originating from the upper reaches of Gresik City and empties into Kali Mas Surabaya. In the rainy season, the West Surabaya area is often flooded due to the Kedurus River runoff. This study aims to analysis and simulate flooding with numerical methods, so flood prone areas due to overflowing Kedurus River can obtained. Flood simulation was carried out with the HEC-RAS software that combines 1-dimensional and 2-dimensional flow. In flood simulation, Nakayasu Synthetic Unit Hydrograph is used as the boundary of upstream conditions and the Stage Hydrograph as the downstream condition boundary. To create a river model, DEM data and hydrograph-data are used with certain return periods. The results of the analysis and simulation obtained depth, speed, duration and extent of flooding so that it can be obtained flood risk map of West Surabaya area. This flood risk map can be used for planning control and early warning.