Three days after Cyclone Kirrily crossed the coast at Townsville on 25th January 2024 the Bureau of Meteorology issued warnings of a slow-moving trough likely to form over southeast Queensland, warning of local moderate to heavy rainfall and possible floods. In the five weeks since Cyclone Jasper in mid-December 2023, ants and snakes, animals always attuned to weather changes, had already started moving to higher ground.
The region’s humidity is stifling, low-lying areas are collecting puddles with some roads cut and the ground is soaked from a wet summer. These are the perfect confluence of events that can lead to flooding.
It is worth remembering that in Brisbane’s 1974 flood Cyclone Wanda brought a rain depression that drenched the entire Brisbane River catchment. In 1893, two massive floods followed a cyclone in February. Disaster-hardened Queenslanders will be mindful that cyclone season is not over yet.
Flood warnings have been issued for Laidley Creek, Lockyer Creek and the Bremer River as locals watch the waters rise and local councils are on alert. Why are these catchments important? All of them are downstream of Wivenhoe Dam. Should heavy rain falls into these unregulated catchments they flow into the Brisbane River and can cause Brisbane flooding.
It is an often-misunderstood flood fact is that only half (52%) of the Brisbane River is regulated by Wivenhoe and Somerset dams. But many people in Brisbane believe that Wivenhoe Dam will protect them; it can save the city from flooding. But the Wivenhoe Dam myth is a fallacy.
Wivenhoe Dam, 150 kilometres from the mouth of the Brisbane River, was approved by Cabinet in 1971 and fast-tracked after the 1974 floods. Premier, Joh Bjelke-Petersen, announced that the dam ‘would be pushed ahead as quickly as possible for flood mitigation’. Three times the size of Somerset Dam (completed in 1959), Wivenhoe could increase Southeast Queensland’s water supply by 80 per cent, store five years water supply, and hold 1,970,000 megalitres in temporary flood storage.
At the opening of Wivenhoe Dam in October 1985 Joh Bjelke-Petersen fuelled the myth declaring that he ‘doubted if the 1974 flood could occur again because the dam would absorb an enormous quantity of water before any had to be released’. Newspapers propagated the myth of flood proofing, The Courier Mail proclaiming ‘Flood Threat Past: Sir Joh’ and The Sunday Mail declaring that with Wivenhoe Dam ‘Brisbane should see an end to major floods’. Brisbane residents readily pinned their hopes on the dam as their great protector. Decades of real estate agents, property owners, and local and state governments have either promoted their myth, or supported it through silence or inaction to prevent development on the floodplain.
When Brisbane experienced the 2011 floods, the Queensland Flood Commission of Inquiry, the media, and a class action perpetuated misinformation that Wivenhoe Dam can save Brisbane from floods if operated correctly. The floods in 2022, largely caused in north Brisbane by inundation from creeks and overland flow from heavy rain (outside the dam’s catchment), should have helped dispel the fallacy that the dams “flood-proof” Brisbane, but the myth endures.
The perception of safety is an illusion. Dams can mitigate floods and reduce flood heights, but they cannot prevent them. The water release strategy can minimise flood heights downstream by managing the flows, but dams have a finite capacity. Ultimately, water must be released. The safety of the dam cannot be risked. If the dam wall breaks, there would be uncontrolled flow and southeast Queensland’s water supply would be severely compromised for years.
It is nature that determines the character of the flood and the efficacy of the dam. The location, intensity and timing of rainfall will determine the location, duration, and extent of the flooding. Hydrologists refer to floods, that occur upstream of the dam as favourable floods. Unfortunately, a downstream or unfavourable flood is just as likely, and Wivenhoe Dam can play only a minimal role.
Floods will come again and they may be bigger than those previously experienced. Climate change may bring more frequent and greater floods and our current flood mitigation strategies and dependency on dams will not be enough to protect Brisbane.
Perpetuating the Wivenhoe myth is dangerous. It creates false hope that floods can be prevented and puts lives and property at risk. It does nothing to dissuade people from building on the floodplain or for regulators to reconsider land use plans, sustainable designs or building materials, or policies that will relocate people from danger and seek other forms of flood mitigation.
As the Bureau of Meteorology issues flood warnings, Brisbane residents would be wise not to rely on Wivenhoe Dam to save them.
Dr Margaret Cook is an environmental historian whose research interests concentrate on the dynamic between humans and nature over time with a focus on water.
Margaret joined Griffith University in the Australian Rivers Institute as a Research Fellow in 2022 working with Professor Sue Jackson on the Water Cultures (Murray Darling Basin) ARC project. Margaret is the author of “A River with a City Problem: A History of Brisbane Floods“.
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