It is now more than two years since Queensland's disastrous summer of flooding, and there have been several bad floods since both west of the Great Dividing Range and near the coast. The time is right for asking what directions the state might be taking in terms of managing the problems caused by floods.
Soon after the floods of 2010-11 the federal government instituted a levy to raise funds for the recovery process, and later it allocated money for mitigation works at Ipswich and Roma. Now the state government wants to bring in another levy to raise a billion dollars for infrastructure protection over the next five years. Numerous mayors, several state ministers and the premier have made it clear that serious action must be taken to mitigate the effects of flooding. The time for flood mitigation, long lacking in Queensland, appears to have arrived.
But what do our politicians intend to do? Where is the state heading in its attempts to deal with the most costly agent of natural disaster that it has to cope with?
The many pronouncements made so far suggest that the approach taken will be a narrow one. Levees, new dams with flood storage capacities and the raising of major roads where they cross floodplains have been mentioned frequently, but it will be disappointing if the effort is limited to measures such as these. They have parts to play, but the best flood management is much more multi-faceted. It protects infrastructure and communities from floodwaters but it also seeks to limit the future growth of the problem itself. In addition it seeks to improve community responses to floods.
The most effective flood mitigation goes beyond merely controlling the water. It is also about living with the inevitability of flooding. There are many mitigation options.
Let's look first of all at the possibilities for flood control. Here we should reject grand schemes like cutting canals to allow water to be shifted from rivers in flood to rivers which are not: these would be hugely expensive and unlikely to be cost-effective. Building many small dams in the headwaters of rivers is also not likely to be worthwhile in cost-benefit terms and they will be environmentally very damaging. Likewise dredging river beds adds little to rivers' flood carrying capacity, because the channels are small and at most can carry only much smaller volumes of floodwater than the adjacent floodplains. In any case the floodplains must be drenched periodically in the interests of environmental health.
Then there are flood mitigation dams, which are expensive and have potential flood control impacts which are often overstated: remember Wivenhoe? Good sites are not always easy to find, such dams destroy wilderness or productive land and there will need to be a lot of them if they are to make substantial contributions.
Levees can be very effective, though it is rarely possible to build them high enough to keep out the biggest floods. But in association with diversion banks and floodway bypasses, if necessary with velocity control banks to reduce the erosive power of floodwaters, they can play a major part in protecting urban areas. Not all environments are suitable, though: where flood heights are great (for example upstream of major topographical 'chokes' on rivers) or where rivers break into several channels (as in deltas) levees are inappropriate.
Small dams called retention basins also have value in built-up areas, as does the lowering of ground levels to trap water and keep it out of streams until peak flows have passed. The lowering of sports fields and even residential yards in large numbers has been of considerable value in mitigating flooding in western Sydney.
All these options help prevent flooding or reduce its severity. They increase the separation of property and other assets from flooding.
Beyond the flood-modifying measures, altering the existing built environment by raising houses on site or by purchasing and removing buildings from locations where flood flows occur also offer significant possibilities. In 2006 Campbell Newman as Lord Mayor of Brisbane proposed a buyback of severely flood-prone properties along Brisbane's creeks, but there was no support from the ALP government of the day. Yet this measure, like house-raising, has frequently been utilised in NSW and elsewhere.
Other approaches have been given less prominence in recent discussions. Rarely have we heard about changing our approach to the use of floodplain land, for example by prohibiting the future building of residential premises (and indeed commercial ones) there. Yet doing this would actually strike at the core of the problem, which is the legacy of decades of inappropriate decisions mainly by local governments. Gradually, inexorably, we have increased our vulnerability to the flood threat to the point that it has become a huge problem. Sooner or later we must stop making the problem even worse.
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