Quantifying the influence of urban development on runoff in South Africa

It is widely accepted that urban development results in larger flood peak discharges with faster catchment response times, larger total runoff volumes and lower base flow volumes. However, these effects have not previously been studied in the context of the specific characteristics of fast-growing urban areas in developing countries, which are generally unregulated. This study quantifies the effects of urban development on runoff, including: a) runoff volumes, b) base flow volumes and c) flood peaks from eight South African catchments using the Mann-Kendall test and Kendall’s τ. Both total runoff and base flow volumes are found to increase with increased development levels and possible reasons for this are discussed. The flood peak analysis finds statistically insignificant trends in most catchments. However, there is an increasing trend in the catchment with the highest proportion of informal development. Recommendations are made for further investigation into reasons for the findings.