Flood risk mapping and Vulnerability Analysis of Megech River using 2D hydrodynamic flood modelling
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Date
2012-08
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Addis Ababa
Abstract
The consequences of flooding are complex and far-reaching. These consequences include
direct damage to property and structures, as well as disruption of economic activity and
displacement of affected population, with the attendant costs of evacuation and temporary
accommodation. They include loss of agricultural productivity, including both opportunity as
well as direct damage to crops in various stages of cultivation. They include direct damage to
infrastructure, in addition to disruption of transportation and services, potentially affecting
populations not directly touched by flood waters, and for extended periods of time, not
limited to the period of inundation.
Flood is causing economical, social and environmental damage and lives loss in Ethiopia. In
recent year, the August 2006, flooding is one of the worst flooding events. Understanding of
flood risk is the first step for Flood risk management. Dembia floodplain is a frequently
flooded catchment with Megech River. Flood risk management strategies have not been
developed for this region and there is no spatial planning approach for regional development.
This study focuses on studying the flooding characteristics in the flood plain of the catchment
using two-dimensional (2D) hydrodynamic modelling.
Flood risk mapping is an important aid to a community to take action in the present for the
reduction of future damages, to plane for flood preparedness and response, to develop
infrastructure for reducing flood severity and flood damage, and to guiding development to
avoid increased risk where hazard is frequent. An important aspect of this study is the
development of models and procedures that could be used in generation of flood risk map.
This research was based on four major steps. The first step was to prepare input data for the
modelling, such as topographic mesh, upstream boundary and surface roughness.
Topographic mesh was generated using SMS11.0 based on 53238 x-y-z survey points.
Upstream boundary condition was generated by flood frequency analysis methods.
The second step involves the calibration of the model based on field measured data. The
calibration is performed by manually changing surface roughness coefficient until the good
fit between simulated and measure surface water level is obtained.
The third steps concern simulation and mapping of flood hazard parameters based on model
results respectively. The model results consist of flood depth, flow velocity and surface water
elevation.
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The final step is flood risk mapping. Flood risk map was generated by weighting flood depth,
flow velocity and flood duration. Flood hazard and flood risk maps are important tools to
communicate flood risk to different target groups.
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Keywords
Hydrodynamic modelling