Urban flood risk management: a case study of Aboabo, Kumasi.
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Date
October, 2016
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Abstract
Floods are a serious global issue attracting attention and research from academia, the media and other international discourse. Consequently, they have become critical national issues especially with African countries who lack the financial resources and technical knowhow to mitigate its impacts. The Aboabo community (a suburb of Kumasi), located in the transitional forest zone of Ghana has become vulnerable to the devastating effects of flooding in recent times due to climate change, exponential population growth, and rapid urbanization. In order to reverse this trend and lessen the debilitating impacts of flooding on this community, there is a need for the development of a flood risk map which will form the basis of any future flood management and planning activities. This study presented a holistic approach in the development of a flood risk map and discusses its significance in Flood Risk Management.
In order to create a digital representation of the study area, a Digital Elevation Model (DEM) was created. Hydrological analysis necessary to determine flow direction and accumulated flow (resulting from e.g. rainfall, surrounding streams) was performed on the depressionless DEM of the study area. Reclassified slope angles (i.e. high slope areas, medium slope areas, and low slope areas) and stream buffer zones (within 50m of stream network) were added in ArcGIS environment to generate flood risk maps. The flood risk maps showed three risk zones -High risk, medium risk zone and low risk zone. To further demonstrate the potential of flooding in these three risk zones, a simulation-based approach was adopted. A simple vector-based method which only required the extents of flood levels in simulating flood extent based on the derived drainage lines, their depth and their capacity to hold rainfall run-off was used. With the aid of the elevation measure, flood water levels were selected. The flood contours showed the extent of flood at a given flood level. The flood model extents were further overlaid on a geo-referenced Google Earth image of the study area which visibly demonstrated areas at risk in the event of floods. Based on existing literature, questionnaires and interviews were administered to respondents in the Community and stakeholders to investigate the causes and effects of floods. With over 84% response rates, majority of the residents attributed the cause and effect of flooding to lack of drains/choked drains and gradual weakening of buildings respectively.
The research clearly demonstrated the application of GIS through hydrological analysis, carrying out flood simulations and the administering of questionnaires and interviews with stakeholders, is very essential in providing guidelines for Flood Risk Mapping.
Description
A thesis submitted to the Department of Geomatic Engineering, Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the degree of Master of Science.