Towards a new regional flood frequency analysis method for Tasmania

This paper compares a number of regional flood frequency analysis (RFFA) methods for Tasmania using data from 53 catchments. The analysis uses a Bayesian generalised least squares (BGLS) regression approach in developing prediction equations for selected flood quantiles (Quantile Regression Technique - QRT) or the first 3 moments of the LP3 distribution (Parameter Regression Technique - PRT). In forming the regions two methods are used: in the fixed region approach all the 53 sites are assumed to form one region; in the region of influence (ROI) approach, a region is formed around each of the 53 sites based on the minimum model error variance. The developed prediction equations are validated using one-at-a-time cross validation. It has been found that ROI outperforms the fixed regions and that QRT-ROI and PRT-ROI methods perform very similarly. The findings from this study and other on-going studies will form the basis of recommendations for new RFFA methods in ARR for Tasmania