Flood Risk Analysis (Case Study of Upper Awash River from Wonji to Awash Malkessa)
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Date
2021-09
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Addis Ababa University
Abstract
Flood is probably the greatest devastating, wide spread and frequently natural hazard of
the world wide that producing several socioeconomic and environmental consequences
within the affected floodplain. In Ethiopia, Awash River basin is one of the areas
affecting by flood plain problem and among Awash River basin, wonji to awash
melkessa is one the most frequently severed area by floodplain along Awash River, for
those flood risk analysis is so important.
The main objective of this study was flood inundation mapping and quantifies the risk of
flood on the area by using hydrological model HEC-HMS for peak flood forecasting for
different return period and GIS extension HEC-GeoRAS integration with hydraulic
model HEC-RAS for flood inundation mapping. For hydrological model (HEC-HMS)
daily rainfall and stream flow data of 16 years from (1998-2013 G.C) was used. Among the
data used eight years for calibration and five years for validation of HEC-HMS model at
wonji Gauged station. HEC-RAS model was calibrated and validated using satellite
imaginary Landsat-7 flood event and observed flood event of September, 06/2000 and
September, 22/2007 G.C respectively. The missing values were filled by using normal
ration method for daily precipitation data. Consistent data was checked by double mass
curve method. The initial and constant loss method was selected for loss method and for
transform method Clark unit hydrography was applied.
The estimated peak flood by hydrological model (HEC-HMS) was 147.2m3/s, 161.9m3/s,
329.4m3/s, 409.5m3/s and 506.8m3/s for 5year, 10year, 25years, 50years and 100year
return period correspondingly. The flood inundated area corresponding to peak flood
were 1052.7 hectare, 1086.9 hectare, 1429.5 hectare, 1559.1 hectare and 1694.1 hectare
respectively. The total crop losses were calculated for flood inundated area, for 5 years
and 100 year return period of crop loss were 75501.6 quintal and 121503 quintal
correspondingly.
Thus finding of the study may help in planning and management of flood plain area to
mitigate probable disaster through technical approach.
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Keywords
Arc GIS, HEC-HMS, HEC-RAS, Flood inundation map