Participatory GIS approach to flood risk assessment of informal settlements : the case of Cape Town
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2012-02
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Abstract
Rural-urban migrations have contributed to the steady increase in the population of Cape Town. Many of the migrants have settled in informal settlements because they cannot afford to rent or buy decent housing. Many of these settlements are however located on marginal and often poorly drained land. Consequently, most of these settlements are prone to flooding after prolonged rainfall. Current flood risk management techniques implemented by the authorities of the Cape Town City Council (CTCC) are ideal for formally planned settlements but are not designed to support informal settlements. In fact, owing to a lack of information about the levels of flood risk within the individual settlements, either the CTCC has often been uninvolved or it has implemented inappropriate remedies within such settlements. Various authors purport that the inadequate flow of information between all the stakeholders has hampered development of sustainable flood risk management strategies. This study sought to investigate a methodology that the CTCC could use to improve flood risk assessment.
Using two case studies of flood-prone informal settlements in Cape Town, this study proposed a methodology for the collection and integration of community-based information into a Geographic Information System (GIS) that can be used by the CTCC for risk assessment. In addition, this research also demonstrated the use of a participatory multi-criteria evaluation (MCE) for risk assessment. Two questionnaires were used to collect community-based information. The shack outlines of the two informal settlements were digitized using aerial imagery from the CTCC. Responses to the questionnaires were captured using spreadsheets and linked to the corresponding shacks in the GIS. Risk weights were subsequently calculated using pairwise comparisons for each household, based on their responses to the questionnaires. The risk weights were then mapped in the GIS to show the spatial disparities in risk.
It was found that flood risk assessment should transcend the traditional analysis of the physical impact of floods. Also, any other hazards in the area of interest should be taken into account when doing flood risk assessment. The risk maps showed that flood risk could vary based on factors such as income, sanitation, exposure to hazards and inefficient mitigation measures.
This work contributes to the body of Participatory GIS (PGIS) and MCE. The overall contribution of this work lies in demonstrating a practical participatory approach to data collection and the use of MCE for risk assessment in informal settlements in Cape Town.
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INFORMAL SETTLEMENTS, FLOODING, FLOOD RISK MANAGEMENT, PARTICIPATORY GIS, MULTI-CRITERIA EVALUATION, COMMUNITY PARTICIPATION, SOUTH AFRICA--CAPE TOWN, RURAL URBAN MIGRATION, FLOOD CONTROL, NATURAL DISASTERS, DISASTER PREPAREDNESS, GEOGRAPHIC INFORMATION SYSTEMS, GEOSPATIAL INFORMATION MANAGEMENT, RISK ASSESSMENT, MULTIVARIATE ANALYSIS, CASE STUDIES