Flood Risk Analysis in Informal Settlements of Cape Town

Many of the settlements in Cape Town are located on marginal and often poorly drained land.  Because of this, most of these settlements are prone to flooding after rainfall.  The current flood risk management techniques are not designed to support informal settlements, but this study sought to investigate that the previous method could use to improve the flood risk assessment.  During the period from 1996 and 2005, 290 flood-disasters happened in Africa alone which left 8,183 people dead and 23 million people affected, causing $1.9 billion economic losses.  Floods were the most frequent natural disaster in Africa during this period and the frequency of the disasters are expected to increase in the future.

                Risk is assessed by the following equation: Risk = Hazard x Exposure x Vulnerability.  Based on this equation, if any of the three elements increase or decrease then the risk increases or decreases respectively.  Studies into the level of vulnerability of an environment or community to a particular hazard will invariably provide insight into the magnitude of risk of the environment or the community to that hazard.  This study therefore adopted vulnerability as an indicator of risk: Regional Vulnerability = Damage potential + Coping capacity.  The study focused on assessing these prescribed factors in an informal settlement in Cape Town.

                Graveyard Pond is an informal settlement located in Philippi, a suburb of Cape Town.  This settlement is particularly prone to flooding because it is located in an area designated as a catchment pond.  As you can see in the picture, housing was built in the lowest part of the settlement.

                The magnitude of vulnerability is inversely proportional to the magnitude of the associated weight.  Weights were allocated to the individual households based on their responses to disasters experienced.  The weights for the hazards were then mapped along with the weights for sanitation and disease, and income, ultimately showing overall vulnerability by averaging out the weights.

                This study made the ranking significantly simpler by assessing all the alternatives at once rather than ranking them against each other.


http://www.sajg.org.za/index.php/sajg/article/viewFile/27/11