n Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese - Statistical analysis of extreme floods : technical paper

Abstract

In this paper it is demonstrated that widespread, severe floods are caused by infrequent, but not rare, meteorological phenomena, including tropical cyclones and cut-off low pressure systems. The magnitude of the severe floods relative to the series of annual maximum floods at any one site can be readily determined, but all direct statistical analysis methods seriously under-estimate their frequency of occurrence. This is demonstrated by the statistical analyses of wide area, severe flood-producing rainfall. The statistical analyses confirm that the widely used log Pearson type 3 distribution using conventional moment estimators, remains the preferred method for the statistical analysis of hydrological and meteorological data, but that no direct statistical analysis methods can be used with confidence for return periods exceeding 50 years. Procedures for overcoming these difficulties are presented in an accompanying paper on the standard design flood.