The Initiation of a National Flood Studies Programme for South Africa: Overview and Progress to Date

Floods have an impact on human survival, economic development and environmental sustainability through loss of life and significant economic loss as a consequence of the failure of structures (e.g. dams and culverts).  Estimates of design floods are required for the design of hydraulic structures and to quantify the risk of failure of the structures. Information on flooding is also essential for the development of safe human settlements, particularly in low lying areas.

Historical records of floods are used to both directly estimate design floods from the observed gauged data and to develop methods to estimate the design floods at ungauged sites. The longer the period of available gauged flow data, the more reliable the design floods and methods. Most of the methods currently used for design flood estimation in South Africa were developed in the late 1960s and early 1970s and are in need of updating with more than 40 years of additional data currently available and with new approaches used internationally.  In addition, climate change is expected to influence the magnitude and frequency of flooding, and hence this increased variability in flows need to be accounted for when determining flood risk.

Given the above, the South African National Committee on Large Dams identified the urgent need to update the data and methods used for design flood estimation in South Africa and, in conjunction with the Water Research Commission, initiated a National Flood Studies Programme (NFSP) to update these.  This paper will briefly summarise the performance of empirical, event-based deterministic and regional approaches currently used in South Africa and will provide an overview of new developments to date. This will include updates to design rainfall and probable maximum precipitation estimation, the identification and recommendation of the best probability distribution to use in flood frequency analyses, the development of regional quantile regression and index flood approaches, the determination of locally derived Curve Numbers for the SCS model using both observed and simulated flows, the investigation of an ensemble approach for the SCS-SA model, and the development of a continuous simulation approach to flood estimation on a national scale.