Temporal Rainfall – A Risk-Based Approach

Recent hydrological modelling for a major project in Australia by WSP Opus has highlighted a number of differences in the flood modelling methodologies adopted between Australia and New Zealand. One significant difference was the use of a risk- based approach to temporal rainfall patterns to enable critical events to be identified. This is required by the latest issue of Australian Rainfall and Runoff (Ball et al. 2016). The use of a risk-based approach for hydrological modelling and design purposes is increasing throughout the Australasian stormwater industry. Specifically, the use of a sensitivity analysis for assessing the potential effects of climate change is already being requested by some Local Councils in New Zealand, and Australian Rainfall Runoff 2016 (ARR 2016).

Hydrological modelling in Australia and New Zealand has highlighted the importance of the temporal pattern of the design rainfall to the outputs from hydraulic models and calculations. This paper builds on that earlier work (McConchie & Belleville 2010) which noted “The temporal pattern of the design rainfall needs to be accommodated within any rainfall-runoff model if it is to produce realistic hydrological outputs…the actual temporal distribution of storm rainfall at any specific location may be distinctly different to the generalized distribution. This will result in unique storm runoff which must be related to that of the design event.