New regional flood frequency estimation (RFFE) method for the whole of Australia : overview of progress

The regional flood frequency estimation (RFFE) modes in Australian Rainfall and Runoff (ARR), referred to as 'ARR RFFE 2012' are in the process of finalisation. The methods will allow the derivation of design flood estimates for annual exceedance probabilities (AEP) of 50% to 1% for catchments of 1 to 1,000 km 2 anywhere in Australia. This paper gives an overview of the ARR RFFE 2012 method, covering data preparation, recommendation of the final test method and the development of the application tool in collaboration with WMA Water (Sydney). In the development of the final test method, a total of 676 gauged catchments have been used to create six regions covering Australia. A Bayesian generalised least squares (GLS) regression technique has been adopted to develop prediction equations. A regionalised Log Pearson Type 3 (LP3) distribution is recommended to derive design flood estimates for ungauged catchments in the range of AEPs of 50% to 1%. For all the regions, the proposed prediction equations use only two predictor variables, catchment area and design rainfall intensity. An application tool has been prepared, which automates the application of the AR R RFFE 2012 method. The user is required to input latitude, longitude and catchment area to obtain design flood quantiles and associated uncertainty estimates with 90% confidence limits.