2008 – Design Rainfall Issues in South East Queensland

Terry Malone

Abstract: Recent studies in SE Queensland for existing and proposed dams and other flood studies have highlighted a number of issues with respect to the design event approach in deriving and applying design rainfalls to calibrated runoff routing models.

The estimation of design rainfall depths for frequent to large events is usually done by the intensity-frequent-durations (IFD) methods outlined in Australian Rainfall and Runoff (AR&R) or CRC-Forge.

The design temporal patterns applied to these rainfall depths are critical in the estimation of design floods as are the adopted loss rates.

This paper describes the methods used to derive the design rainfall and some of the issues which arose in their application in the design event approach to assessing design floods. It uses examples at several locations in studies undertaken by SunWater and refers to similar issues encountered in other studies.

Implications for flood studies are outlined.

Keywords: design rainfall, design floods, CRC-FORGE, IFD, temporal patterns, SunWater, Queensland.

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