Investigation of design rainfall temporal patterns in the Gold Coast region of Queensland

Design rainfall temporal pattern is a major source of uncertainty in rainfall-based design flood estimation methods. The Australian Rainfall and Runoff 1987 (ARR87) adopted the Method of Average Variability to derive design rainfall temporal patterns for Australia. It is assumed that the use of these temporal patterns along with representative values of other inputs to the rainfall runoff modeling can preserve the frequency of input rainfall depth in the final flood peak estimate. Although this assumption is questionable, the use of more holistic approach of design flood estimation such as Monte Carlo simulation technique or continuous simulation has not yet been widely accepted by the industry. It will take a while to develop design data and application tools for application with the Monte Carlo simulation and continuous simulation techniques and hence the ARR87 design temporal patterns will remain in use with the Design Event Approach for a while. This paper presents a simple windows-based tool that can be used with sufficient ease to derive design temporal patterns from region-specific data of longer lengths adopting the Method of Average Variability, the ARR87 procedure. This windows-based tool is applied in the Gold Coast region in Queensland to derive new design temporal patterns and it is found that the ARR87 design temporal patterns for the Gold Coast region result in significantly smaller estimated design floods for larger duration storms as compared to the newly derived design temporal patterns.