Flood Inundation Mapping With Integration Of GIS And Hydraulic Model (HEC- RAS) For Early Warning In Dechatu Catchment, Dire Dawa City, Eastern Ethiopia

Abstract

Nowadays, extraordinary floods are common in many parts of Ethiopia causing a lot oflosses to human lives as well as damage to property. Historically, Dire Dawa City has beenvulnerable to flash flooding from rainfall, in particular of the Dechatu Catchment. Theobjective of this study is to constitute flood inundation maps for Dechatu Catchment. In orderto achieve the objective, the integrate of spatial technology of GIS and hydraulic model(HEC-RAS) were used as tools. ASTER DEM and Landsat 8 OLI image were used as primaryparameter to generate geometric data such as Triangulation Irregular Network (TIN),streamline, river bank, flow paths, manning?�?s n value and cross section cutline. The Fulleremperical method is used for determining the peak flow discharge for return periods of 5, 10,25, 50 and 100 years and the result is found to be 460.05m3/s, 890.23 m3/s, 1450.49m3/s,2110.61m3/s and 4148.01m3/s respectively. In HEC-RAS, river geometry, boundaryconditions, manning?�?s n value of different land cover and peak discharge for different returnperiods were inputted and then steady flow analysis was carried out. The result of Steadyflow analysis shows that water surface elevation in the longitudinal profile increase withincreasing return period. The flood inundation maps produced clearly indicate that areaswith 94.48ha, 123.16ha, 140.13ha, 152.76ha and 172.63ha inundated by 5,10,25,50 and 100year return period respectively. Also the maximum water level was obtained for the 100 yearflood frequency. Generally, high water depth occurred along the main channel and spreadsgradually to the floodplains. The current study also suggested that flood prone areas were atthe middle and downstream along the banks of the river. Thus, integration of GIS andhyd