Floodplain Inundation Modeling and Mapping for Geray River: Nile Basin, Ethiopia

Flood is among the most devastating natural hazards in the world claiming lives and properties more than any other natural phenomena. During high flow, the Geray River flooded the vicinity of the area and causes loss of cultivated land and life. The objective of this study describes the flood extent and depth in the Geray River for different flow conditions. This research involves the integration of HEC-HMS, HEC-RAS, and GIS to develop a regional model for floodplain determination and modeling analysis representation. The hydrologic model is calibrated using of HEC-HMS for daily time series data for return periods of 2, 10, 25, 50 and 100 years. One dimensional hydraulic model HEC-RAS with HEC-GeoRAS interface in coordination with ArcGIS was applied for the analysis. The result of the hydrologic model by HEC-HMS showed a flow value of 109.1m 3 /sec, 214.9m 3 /sec, 274.4m 3 /sec, 318.4m 3 /sec and 362.7m 3 /sec for return periods of 2, 10, 25, 50 and 100 respectively. Accordingly, the flooded area generated, for the mentioned return periods are 0.87km 2 , 1.08km 2 , 1.16km 2 , 1.23km 2 and 1.29km 2 respectively. The classification of flood depth area showed most of the flooding area had water depth less than 1.5m.