Abstract:
Floods are among the most common natural disasters around the world, particularly occurs in
the vicinity of rivers. Ethiopia has continuous topographical land arrangement that ranges
from high altitude of highlands to plain lands extending to lowlands, experiences high floods
during rainy season. Curbing the recurrent flooding through addressing the problem and
identifying flood-prone areas; mapping flood hazard, risk and locating the inundated area and
stating some recommendable alternative mitigation measures. The main objective of this study
was to execute flood hazard and risk assessment using GIS and Remote Sensing in Western
Wabe Shebelle River basin. The DEM with high-resolution 30m was used to delineate the
basin watershed in the catchment area 5,040.58
. Multi Criteria Evaluation procedure was
evaluated to meet a specific objective technique to assess flood hazard in the Agarfa
catchment using GIS environment for the selected basin and Eigenvector criteria weight was
calculated for each factor in IDRISI and Excel software. Flood hazard Weighted Overlay with
development factors such as elevation, slope, land cover, rainfall, soil and drainage density.
Flood risk were also Weighted Overlay using the elements of population density, land-use and
the flood hazard layer within the river basin. The study results showed that the downstream
catchment area were more vulnerable to high flood hazard and risk. The best fitted probability
distribution was GEV which calculates the maximum peak discharge of 1,215.46 ⁄ ,
2,595.62 ⁄ , 3,179.53 ⁄ and 4,978.06 ⁄ for a return period of 10, 100, 200 and
1000 years respectively. The inundation map was developed in RAS Mapping tool of HEC GeoRAS; mapping water surface generation and floodplain along the Western Wabe Shebelle
River basin with inundated area of 105.2ha, 143.6ha, 153.9ha, and 178.4ha for 10, 100, 200
and 1000 years of return period, respectively. The flooded area in the return period 1000
years was the highest compared to other return period tested due to the increased stream flow
and the flood depth was excessive that ranges from 0.0015m to 92.6m and hence, the
consequence of the flood on life and property was very high. The mitigation measures must be
taken shall include: taking the application of structural determinations that focuses on
reducing the impacts of flooding on communities and taking the non-structural measures like
land-use control, sampling signal measures, relocations and early flood warnings.
