Australia's largest catchment scale flood hazard mapping study, the New Era Regional Flood Mapping exercise, shares new innovations to conduct broad-scale flood modelling which enables a better understanding of floodplains - particularly in rural and remote locations.

The 2011 Queensland floods affected more than 75 per cent of the state. Australia’s flood analysis information and flood behaviour data was scarce prior to the disaster, particularly for the state of Queensland. Previous flood models techniques were not complex enough to adequately simulate flooding situations.

The Queensland Floods Commission of Inquiry Final Report (QFCI, 2012) identified several key recommendations, considering in particular the necessity of a risk-based understanding of floodplains, as well as the need to live with floods rather than attempt to control them.

The New Era Regional Flood Mapping study, led by Jo Tinnion, leading floodplain management consultant at BMT WBM Pty Ltd, fills existing knowledge gaps on flood data and presents the benefits of catchment-scale modelling to improve emergency management procedures and regional land use.

“Until recently, models were unable to model much more than 10 million cells and even then the run time could take weeks to run at the desired grid scale,” said Tinnion. “Recent innovations in flood modelling techniques when combined with advances in consumer grade computer technology can help engineers, emergency planners and land use planners better predict flood behaviour.”

The development of a new computational engine for TUFLOW by BMT WBM has enabled significant reductions in the overall model run times (hundreds of times faster than conventional 2D hydraulic models) and thus has greatly facilitated catchment scale flood modelling.

flood after 24hours

Flooding after 24 hours

For instance a model area of 533,000 square kilometres with 149 million active cells and a grid resolution of 62m (a size more than twice that of the UK) can now be run in just over 10 hours. Previously a model this size would take the better part of a year to run.

“In addition, advances in ground surface data collection and in flood modelling proficiency represent the dawn of a new era in floodplain management in Australia where flood risks can be assessed and managed at a holistic whole of river basin level,” Tinnion said.

The use of catchment scale flood models can be used to identify flood prone areas which may require further investigation through more detailed flood studies. It can also be calibrated and used to provide boundaries for more detailed flood modelling. This can assist state agencies and local governments to target investment in those areas at most risk considering the wider impacts across a larger area.

Broad scale catchment modelling can also be applied to assist with regional land use to determine future strategic land use planning, highlighting where potential flooding could impact settlement patterns, infrastructure development and mining and agricultural activities.

In addition, the flood extents and animations produced on a catchment scale can enable emergency managers with no experience of an extreme flood event (or other flood events) to visualise the flood behaviour across an entire catchment.

flood after 96hours

Flooding after 96 hours

Tinnion’s study looked at the Condamine-Balonne catchment, which was badly damaged by the 2011 floods and covers an area of some 128,300 square kilometres – equivalent to 10 per cent of Queensland’s total area.

“The mapping for this catchment identified additional areas of flood storage within the catchment which until now were previously unknown. It can also identify high level breakouts and local connectivity, as well as inform future land use planning decision at a regional level and seek to deliver consistent floodplain management provisions in jurisdictions across the region,” said Tinnion.

“Points of interest and vulnerable infrastructure, including schools and railway stations, have been highlighted which is invaluable for the local emergency managers to help them consider the wider impacts of flooding in areas previously unaffected. It also has the ability to highlight those localities where additional evacuation infrastructure should be provided.”

Dr Ben Taylor, chair of the Engineers Australia Bundaberg Committee said the advances were essential to the betterment and resilience of regional flood-prone communities which have faced the challenges of recovering after flood events like the ones that devastated Central Queensland.

“The engineering profession is committed to protecting high standards and working with local authorities, state and federal governments to assist in the preparedness of the community to deal with natural disasters and crisis situations,” Taylor said.