Assessing the performance of regional flood frequency analysis methods in South Africa

Jj Nathanael,Mjc Horan,Jc Smithers

doi:10.4314/wsa.v44i3.06

Abstract

In engineering and flood hydrology, the estimation of a design flood associates the magnitude of a flood with a level of exceedance, or return period, for a given site. The use of a regional flood frequency analysis (RFFA) approach improves the accuracy and reliability of estimates of design floods. However, no RFFA method is currently widely used in South Africa, despite a number of RFFA studies having been undertaken in Africa and which include South Africa in their study areas. Hence, the performance of the current RFFA approaches needs to be assessed in order to determine the best approaches to use and to determine if a new RFFA approach needs to be developed for use in South Africa. Through a review of the relevant literature it was found that the Meigh et al. (1997) method, the Mkhandi et al. (2000) method, the Görgens (2007) Joint Peak-Volume (JPV) method and the Haile (2011) method are available for application in a nationwide study. The results of the study show that the Haile method generally performs better than the other RFFA methods; however, it also consistently underestimates design floods. Due to the poor overall performance of the RFFA methods assessed, it is recommended that a new RFFA method be developed for application in design flood practice in South Africa.

Highlights

Flood disasters are considered to be the predominant and most frequently occurring natural hazard and are responsible for the most fatalities worldwide (Doocy et al, 2013)
The application of both the general extreme value (GEV) and log-Pearson Type 3 (LP3) distributions for design flood estimation in South Africa have been advocated by a number of studies (Görgens, 2007; Van der Spuy and Rademeyer, 2010)
The Görgens (2007) study developed regional approaches based on design floods estimated using both the GEV and LP3 distributions

Summary

Introduction

Flood disasters are considered to be the predominant and most frequently occurring natural hazard and are responsible for the most fatalities worldwide (Doocy et al, 2013). The loss of life and economic loss caused by floods can occur at both small and large scales (Hubbart and Jones, 2009). Economic losses resulting from flood events have increased globally from an average of US$ 7 billion per year in the 1980s to approximately US$ 24 billion per year between 2001 and 2011 (Kundzewicz et al, 2013). A media release by Shiceka (2011) for the Ministry of Cooperative Governance and Traditional Affairs in South Africa indicated that infrastructure damage as a result of flooding in the North West, Northern Cape, and KwaZuluNatal Provinces in 2011 amounted to approximately R6 million, R50 million, and R300 million, respectively. With a growing population, increasing urbanisation and climate change, the risks that flood events pose are becoming more severe, which requires researchers to improve the accuracy and reliability of methods used for flood estimation (Wiltshire, 1986; Smithers and Schulze, 2000)

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Conclusion