Author(s): P. W. Jordan; K. Sih; P. I. Hill; N. Nandakumar; P. E. Weinmann; R. J. Nathan
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Keywords: Design flood estimation; Design rainfall intensities; Australi
Abstract: The Areal Reduction Factor (ARF) for a particular catchment area, given design rainfall burst duration and annual exceedance probability (AEP) represents the ratio between the areal design rainfall and the representative point design rainfall for the catchment. Australian Rainfall and Runoff (1987) recommended areal reduction factors based on studies in the United States. This paper describes the derivation of ARF equations for the last remaining region in Australia without specific ARFs, NSW and the ACT. Data from the entire period of daily rainfall record at more than 6000 sites across NSW and the ACT was assembled. Representative circular “catchments” were formed for areas between 125 and 8000 km2 and the data were analysed for each of these catchment sizes to produce ARF estimates for each combination of duration between 1 and 5 days and AEP between 1 in 2 and 1 in 100. Two homogeneous regions were established in NSW and the ACT for estimation of ARFs, with the dividing line based on the predominant mechanisms of heavy precipitation. Separate equations were derived for both of these regions using the same functional form as in the other states. Interim equations were also derived, so that the ARF equations apply for all durations between 1 hour and 120 hours and catchment areas between 1 and 10,000 km2. These revised ARF equations are consistent with recently developed equations for the adjoining states and are recommended for application by flood hydrologists and drainage designers working in NSW and ACT.
Year: 2011