EVALUATION OF FLOOD MITIGATION ALTERNATIVES FOR FLOOD PRONE AREA OF UPPER AWASH SUB-BASIN (UPSTREAM OF KOKA DAM)

Flood is a natural process that can happen at any time in a wide variety of locations which causes tremendous losses in terms of property and life, particularly in the Ilu floodplain, of sub-basin. The main objective of this study was to study flood hazard mapping and its mitigation measures using Hydraulic model HEC-RAS, Hec-GeoRAS, and ArcGIS. The adequacy, homogeneity, independency of the data series and that the data come from the same distribution was tested at 95% significance levels for gauging station in the study area by different statistical software (Minitab, SPPSS, Sigma plot). Flood frequency analysis for 2, 5, 10, 25, 50, 100, 200, 500, 1000 and 10000-years return period was done by Gumbel"s, Log Pearson type III, and Log-normal probability distributions based on maximum instantaneous flow recorded at Awash River at 9 stations in sub-basin.
The Goodness of Fit Test (GOF) of these selected flood frequency distributions was conducted using MAE, RMSE, RRMSE, and CC and log-Pearson type III is adopted best fit method with Pearson Correlation of 0.96, 0.99 for Teji near Asgori and Awash at Bello stations respectively. Flood discharges results for Teji near Asgori and Awash at Bello stations have magnitude of 172.81, 181.44, 76.75, 86.12 m3/s for 50 and 100 years return periods respectively.