2011 – Factors Influencing the Estimation of Extreme Floods

Rory Nathan, Peter Hill

This paper provides an overview of the different simulation frameworks used for the estimation of design floods.. For small events the behaviour of many flood modifying factors is highly variable and chaotic, whereas as the magnitude of the event increases so does the organising influence of the dominant meteorologic conditions. The approach to design flood estimation will depend upon the availability of data and the exceedance probabilities of interest. The techniques can vary from frequency analysis of the data recorded at a site to rainfall-runoff modelling with design rainfall inputs derived from regional frequency analysis. For extreme floods, which are of relevance for assessing flood loadings for dams and the assessment of spillway adequacy, the stochastic (Monte Carlo) approach offers a number of advantages over the traditional deterministic approach. Although there has been significant progress in design flood estimation practice in Australia over the last couple of decades there remains many significant research and training needs.