Regional flood estimation in Australia: an overview of the study in relation to the upgrade of Australian rainfall and runoff

Regional flood estimation methods are used for estimation of design floods in ungauged catchments, which is required in the design of culverts, small to medium sized bridges, causeways, farm dams, soil conservation works and many other water resources management tasks. in Australia, the regional flood estimation methods have not been upgraded since 1987. Recently, the National Committee on Water Engineering has taken necessary steps to upgrade Australian Rainfall and Runoff (ARR). In the context of ARR upgrade, Project 5 Regional flood methods focuses on collation of a national database, development and testing of various regional flood estimation methods, which will form the basis of recommendation of new regional flood estimation methods in the upcoming revised edition of ARR. This paper focuses on the data preparation and preliminary studies on various regional flood estimation methods. The data from 703 gauged stations across Australia has been collated and the initial investigations show that a regression based approach can provide more accurate design flood estimates than the Probabilistic Rational Method. The initial results of time trend analysis show that about 30% of stations' annual maximum flood series are affected by trends; although further investigation is needed before any firm conclusion can be made about the trends in Australian flood data. A region of influence approach (ROI) is being investigated for developing regional flood prediction equations where the database of all the Australian states will be combined. In the ROI approach, to develop a prediction equation for an ungauged catchment of interest, the nearby 30 to 50 gauged stations will be included in the region. The national regional flood estimation database is expected to be updated periodically in future.