With the first anniversary of the Brisbane floods upon us, there are lessons still to be learned.
As the debate on last year’s Queensland floods continues, it’s important that we don’t lose sight of the significant environmental costs of such events and, equally important, the environmental consequences of proposed management responses.
This is according to Professor Jon Olley, deputy director of Griffith University’s Australian Rivers Institute.
“In addition to the damage bill for property, public infrastructure, crops and livestock are the longer-term costs associated with the loss of productive farmland through soil erosion.
“More difficult to quantify in dollar terms are the environmental costs of poor water quality in rivers, water storages and coastal waterways, not only from failed sewage treatment plants but also from the transport of vast amounts of sediment, nutrients and other contaminants scoured from catchments upstream.
“There is little doubt that the flooding outcome for Brisbane would have been much
worse without Wivenhoe Dam.
“With hindsight it is easy to argue authorities could have reduced the flooding by partially emptying the dam in the weeks before the deluge.
“However, it is operated to meet our water supply needs as well as mitigate floods — and
the memory of drought and water shortages are still fresh.
“In future, we could take a more risk-averse approach to flooding but we would
also need to accept the associated financial and environmental costs of an increased
dependence on desalination and recycling.
“Options for building other water storages in southeast Queensland of sufficient size
to capture floodwaters of the scale we witnessed are extremely limited — not only
because of the lack of suitable dam sites but also because of the resulting loss of valuable agricultural and urban land from inundation.
“We also need to weigh up the significant environmental effects of dams on rivers and estuaries downstream.
“It is worth remembering too that when the catchments are saturated and storages are
full, they offer limited protection from intense and sustained rainfall events, such as the one we witnessed last year.
“It is simply not possible to flood-proof against all extreme weather events.”
Regarding whether we can better plan urban developments on floodplains, Professor Olley says there are still lessons to be learnt about the design of homes close to waterways to minimise damage to property and, if necessary, provide opportunity for safe evacuation during flood events.