Flood Risk Assessment Using Multi-Criteria Evaluation and Flood Inundation Modelling: The Case of Upper Awash Basin, Ethiopia
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Date
2020
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Addis Ababa University
Abstract
Flood is among the most common widely recognized and destructive natural hazards causing
extensive damage to infrastructure, public and private services, the Environment, the economy and
devastation to human settlements. The objective of this thesis is Evaluation of flood hazard and
risk prone sites: the case of upper awash basin. To achieve the objective flood assessment is
performed using a Multi Criteria Analysis (MCA) in a GIS environment. To produce the flood
hazard seven flood causative factors were considered, these are the reclassified, Elevation, Rainfall
intensity (precipitation), Drainage Density, Elevation, Slope, Distance to River, soil type and Land
use/cover map of the study area. The result has revealed that, 9.18 % of the basin was characterized
by very high flood hazard level and 36.08 % of the study area was characterized by high flood
hazard level. On the other hand 45.14 % of the study area fall under moderate hazard level zone.
The rest of the study area which is 9.46 % and 0.14 % falls under low and very low hazard level
respectively. Flood risk assessment was done by taking the population and land use land cover as
element at risk. Unlike the flood hazard analysis the result of flood risk analysis shows that 4.43,
15.73, 41.35, 28.82 and 9.67 percent of the area of the upper awash basin were subjected to very
low, low, moderate, high and very high flood risk respectively. For flood inundation modelling
Log Normal distribution, Gumbel’s distribution and Log Pearson distributions were compared to
choose best distribution for estimation of discharge at the return period of 5, 10, 25, 50, 100, and
200 year, however flood extent map were prepared for the return period of 50, 100 and 200 year.
From the result of 50 year return period inundation modelling it is observed that most flood depths
are in range of 0.00-0.52m which covers 27% of the total flood extent. The next highest portion is
covered by 0.52-0.91m which is about 22%. Other flood depths 0.91m-1.60m, 1.60-2.47m and
2.47-3.67m takes in decreasing proportion.
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Keywords
Upper Awash Basin, Flood Inundation Modelling, Flood Risk Assessment