Flood mitigation: so much to do, especially in Queensland

Let’s look at the recent history of Brisbane and the difference between the great flood of 1974 and the one the city has just experienced. In 1974 there were only a few dams upstream, and many people lived in low-lying areas near the river. Thousands were flooded out in the Australia Day flood that year, and in response the state government built Wivenhoe Dam as a flood mitigation structure though with a component for urban water supply. Brisbane became convinced that the dam would "contain" future floods. And development on the floodplains of the city was allowed to proceed apace.

What happened? Two weeks ago, in a flood that peaked in Brisbane a metre lower than the 1974 flood, thousands more dwellings were inundated over their floorboards. A lesser flood did vastly more damage. There is a great irony here, and some important messages..

Almost certainly - though this will be tested in the coming enquiries - the dam helped reduce the peak level of the flood through Brisbane and therefore prevented many more houses from being inundated. But the dam controls only half the catchment above Brisbane. Lockyer Creek, the Bremer River and Oxley Creek all enter the river below the dam. And Wivenhoe itself got to the point that it was filling rapidly and releases became unavoidable.

The event made two points that are not widely acknowledged. The first is that a flood mitigation dam can only mitigate a flood. It cannot eliminate it. Secondly, to increase development on floodplains is to increase community vulnerability.

There is another point that has been glossed over in the debate. It is that if thousands of people are to live on floodplains we must ensure that they understand the risk and will act appropriately when floods threaten their properties.

There was evidence this month at Brisbane, as at Rockhampton, Bundaberg and many other places, that most people neither understand nor trust the flood warnings that are issued. Many ignored them until they could see the floodwaters rising rapidly near their homes, only then starting to protect their belongings. Few sought to move items to higher ground away from their properties. The responses were too little and too late, people were caught short and many lost possessions that could have been saved.

Despite the generosity of government relief payments and the well-subscribed flood appeal, many will suffer great financial hardship. Some will never fully recover. There will be emotional damage as well.

And this leads to another conclusion: flood education, which should be a prerequisite for those who live on floodplains, is sadly lacking in Australia. Information is provided, but not teaching. With few exceptions, councils and governments have not invested in flood education. The result is that people, not knowing they live on floodplains, do not comprehend the risks they face. Moreover they come to believe in myths - for example that a flood mitigation dam offers them complete protection. And they do not understand that they must act swiftly on flood warnings if they are to save their belongings and be spared from the later realisation that they are under-insured or not covered by their existing policies.

We have a long way to go to realise how we can protect ourselves from floods. Multi-pronged action is needed from governments to help us here.

One final point: flood damage in NSW has grown much more slowly over the past half century than in Queensland. The difference lies in the varying effectiveness of floodplain management initiatives in the two states. NSW has done much with levees, buybacks, house raising and other measures at the local level and created at least some brake on inappropriate development on floodplains. Queensland built dams and allowed development to continue largely untrammelled.