Abstract
M. Sc. (Environmental Management)
The 2010/2011 floods saw the City of Johannesburg and many other municipalities in
South Africa declared disaster ridden due to the number of deaths, homeless citizens and
loss of property. Conventional Geographic Information System (GIS) approach is used to
map flood vulnerable areas using floodlines while social surveys assess at-risk population
through impacts of a hazard. This study then tests the hypothesis that combined approach
to identify and map flood vulnerable areas is better than independent approaches, using
Diepsloot township as a case study. Starting with aerial photographs as a base layer,
ArcGIS 10™ was used to conduct spatial analysis of the flood-prone areas using the 1:50-
and 1:100-year floodlines. The results mapped out dwellings vulnerable to flooding along
the floodplains only. The survey probed the people’s perceptions, experiences and coping
strategies with flooding. Findings from the field survey revealed some key observations, as
follows:
The perception of 95% of respondents is that flooding is a major environmental
challenge in Diepsloot township as confirmed by their experiences;
61% attributed this to construction of dwellings within floodplains; and
71% agreed that how strong a dwelling is in terms of construction materials also
determines its vulnerability to flooding.
In addition to floodplains, other sections of the settlement were identified through local
knowledge as being vulnerable to various types of flooding - fast-flowing water, ponding
and slope run-off. Dwellings on hill-slopes and besides storm water drains were identified
as vulnerable to flooding. Slope measurements over the area were done using contours
which corroborated these further areas of flood vulnerability as both low-lying and high
slopes. Due to poor layout of dwellings, vulnerable units could not be counted but the
extent was visible in the mapping. Long-term coping strategies and adaptation measures do
seem to be in place, without interventions from municipal authorities. The combined
approach for flood vulnerability assessment proved successful in creating a practical and
affordable means to create a more comprehensive assessment, called for local knowledge
engagement in policy development to mitigate flood disaster risk in the Gauteng City-
Region.