Application of HEC‑RAS and HEC‑GeoRAS model for Flood Inundation Mapping, the case of Awash Bello Flood Plain, Upper Awash River Basin, Oromiya Regional State, Ethiopia

Abstract

Flood is the devastating natural events as it causes massive destructive of life, economy and infrastructure. The main objective of this study was food inundation mapping using HEC-RAS model: the case of Awash Bello food plain, Upper Awash River basin, Ethiopia. River geometry, annual peak food, and boundary conditions are the most important input parameters for RAS preprocessing. The river cross-sections along the food plain were extracted using HEC-Geo RAS. Annual peak food frequency analysis for diferent recurrence intervals (i.e., 2, 5, 10, 25, 50, and 100 years) was computed using the calibrated and validated HEC-HMS model based on a 25 years (1990–2015) hydro-meteorological data collected from Ministry of Water Resources Irrigation and Electricity and National Meteorological Agency, respectively. The model result depicted the food extreme value for the respective recurrence interval was 526, 610, 828.8, 1072.8, 1263.6, and 1461.3 m3 /s, respectively. For more reliability, the HEC-HMS model outputs were compared with the food extreme value obtained from Log Pearson type-III, General Pareto and Gumbel extreme value distribution function and it was found the HEC-HMS model result for every recurrence interval was higher than the extreme value distribution function outputs. After verifying the acceptability of the HEC-HMS model result, the verifed peak food was inserted into HEC-RAS model and food inundation mapping for diferent recurrence intervals were executed. The HEC-RAS model outcome indicated that the food inundation mapping area for 2, 5, 10, 25, 50, and 100-year recurrence intervals, respectively, was 71.475, 76.630, 89.150, 100.290, 105.160, and 109.462 km2 . Finally, it was realized that the whole Awash Bello food plain is under the infuence of food inundation due to the intensive rainfall event.