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Journal of the South African Institution of Civil Engineering

Print version ISSN 1021-2019

Abstract

NORTJE, J H. Estimation of extreme flood peaks by selective statistical analyses of relevant flood peak data within similar hydrological regions. J. S. Afr. Inst. Civ. Eng. [online]. 2010, vol.52, n.2, pp. 48-57. ISSN 1021-2019.

This paper describes a new Regional Estimation of Extreme Flood Peaks by Selective Statistical Analyses (REFSSA) method to estimate extreme flood peaks from regional flood peak data. The method differs from current regional flood frequency analysis (RFFA) methods or approaches in that an additional separate statistical analysis is performed on "record maximum flood peaks" within a "similar hydrological region". Suitability of the method is demonstrated for the estimation of extreme flood peaks with annual exceedance probabilities between 0,001 (1/1 000) and 0,0001 (1/10 000) for two major hydrological regions in South Africa, and for catchment sizes between 100 and 7 000 km2. The applicability of the method for catchments outside these regions and limits has not been fully tested mainly due to a shortage of verified data. The theory and a practical example are presented. Excellent results have been obtained so far, displaying high correlation coefficients between extreme flood peak data and regression lines, namely 0,99 on average on log-normal scale. The method is considered to have universal application, especially in climates experiencing outlier type of extreme flood peaks.

Keywords : hydrology; extreme flood peak estimation; regional flood frequency analysis; regionalisation; regression.

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