New rain data paves way for better flood mapping

New local rainfall data will provide more reliable and up-to-date flood information and pave the way for Moreton Bay Regional Council to update its flood mapping.

The data was collated by WMA Water managing director Mark Babister in a project initiated by Brisbane City, Ipswich City and Lockyer Valley Regional and Moreton Bay Regional councils.

Council Drainage Waterways and Coastal Planning co-ordinator Alan Charteris told last week’s Council meeting that because previous data collated by the Bureau of Meteorology was based on much broader information base, the figures from local rain gauges were not taken into account.

“It was smooshed over because you were looking at gauges in different locations and trying to drag that into our region,” Mr Charteris said.

“The update draws on 30 years more data and more significantly draws on data sets that are specific to our region, right down to the gauges that the council runs themselves.

“We know that rainfall is quite patchy and there are specific rainfall patterns that occur as a result of our ranges, our topography.”

More accurate information

The four councils commissioned WMA Water to oversee the project after noticing limitations in the Bureau’s 2016 Intensity-Frequency-Duration (IFD) design rainfall data, which is used to help design flood and drainage infrastructure and as a base for developing design event flood maps and flood levels.

The project aimed to unearth information that more accurately represented local rainfall conditions than the data gathered by the Bureau in the 2016 IFD, which is used along with data from 1987.

It used rainfall figures collected by an extensive network of council rain gauges across the four Local Government Areas, which was not used by the Bureau of Meteorology in 2016.

A report to last week’s Council meeting says the 2020 IFD project was peer reviewed by an expert hydrologist, who found that the “methodology has been applied competently and innovatively” and that the “approach is better suited to high station density areas such as south-east Queensland”.

The review concluded that “the work is a significant improvement on the BoM 2016 IFD tables”, the report said.

“Over the long-term, it is expected that utilising the best available data will enable better building practices in the floodplain and reduced economic impact from flood damages.”