Design Rainfall Revision: A Pilot Study

Overview

A pilot study aiming to explore current techniques in derivation of design rainfalls for Australia is currently in progress. The pilot study area covers southeast Queensland and northeastern New South Wales (Figure 1). The study uses rainfall data from daily and continuously recording rain gauges collected up to December 2004. Results will be compared with design rainfalls published in Australian Rainfall and Runoff 1987 as well as results obtained from similar studies in the area.

Pilot Study Area

Figure 1: Pilot area.

Scope

The scope of the study is to provide design rainfalls for standard durations of 1, 2, 3, 6, 12, 24, 48 and 72 hours and average recurrence intervals of 1, 2, 5, 10, 20, 50 and 100 years.

Data

Data used includes Bureau of Meteorology daily rainfall and pluviograph data, Bureau of Meteorology ALERT (Automated Local Evaluation in Real-Time) rainfall data, as well as rainfall data from the Department of Natural Resources and Mines Queensland (DNRM) and the Department of Infrastructure, Planning and Natural Resources NSW (DIPNR).

Method

The method is based on L-Moments (Hosking, J R M and Wallis, J R, 1997: ‘Regional frequency analysis: An approach based on L-moments’,Cambridge University Press). The method involves evaluating L-moments for each site from the annual maximum rainfall series, and fitting a distribution to the data. For the pilot study the Generalized Extreme Value (GEV) distribution gave the best fit. Regionalisation in the pilot study is based on the region-of-influence approach.

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