Modeling 100 year ARI floods in South Australian Catchments

Abstract

This paper presents the results of a regional flood study undertaken for South Australia (SA). In the first part of the study suitability of the Generalized Extreme Value (GEV) distribution fitted by LH moments for characterising at-site flood behaviours is investigated. Visual assessments through probability plots as well as an objective assessment through Monte-Carlo simulations were conducted to identify the most appropriate order of LH moments from L, L2 and L4 for fitting the GEV distribution function to annual maximum series for the 23 selected catchments. In the second part, the selection of the most appropriate form of the least squares regression based on the estimated error covariance matrix and the development of the regional prediction model were undertaken. The GEV fitted by L4 moments was selected for at-site flood frequency analyses considering the bias and relative efficiency estimates of the quantile estimates. Based on the estimated error structure, the Generalized Least Squares (GLS) regression approach was identified as the best technique to develop the regional model. Reliability of the model predictions was demonstrated by using 3 randomly selected test catchments