Flood management is not mostly about grand engineering schemes

Lloyd Hamilton (On Line Opinion, 11/2/2013) makes some useful points about the management of flooding in south-east Queensland, especially when he says there is no single solution and that several different measures are needed. But the general direction of the solutions he advances should be rejected. Mitigation is not solely, or even largely, about capturing floodwaters or moving them elsewhere.

We need to see flooding as a problem caused by human actions and behaviour, not as a problem caused by nature that needs to be controlled. And we need to stop trying to 'flood-proof' Queensland: it simply can't be done. For one thing it would be prohibitively expensive, and for another it would have disastrous consequences environmentally. It could deny floodplains the occasional soaking they need to be healthy, and it could lead to the loss of productive land and valued wilderness.

When people experience the horrors of bad floods, it is natural that they seek relief. In general, they think of engineering solutions ─ like dredging the rivers or building more dams. But dredging is rarely a useful approach: just look at the huge volumes of water that are stored on floodplains and the comparatively small carrying capacity of river channels. And there is no point in making rivers deeper close to sea level. That will simply mean more sea water in the lower reaches.

Dams can play a part in flood mitigation, but not as large a part as is commonly supposed. The coastal rivers on which most of our big towns and cities are situated have many tributaries, and to prevent flooding they'd all have to be dammed. This would be enormously expensive. In any case most of the best sites for dams have already been utilised and the amount of land that would be drowned by building more dams would be prohibitive. And there would still be flooding when heavy rain fell downstream of the dams.

Hamilton's solutions suffer ─ as his piece recognises several times ─ from several weaknesses. Digging big tunnels to move water from one river to another would be extremely costly, and it would have little worthwhile impact if all the catchments he mentions (the Brisbane, North Pine and Logan) were in flood at the same time as happens periodically. And he notes correctly that low-lying, flat areas are not the best areas for storing water behind dams.

Straightening the Brisbane River would be disastrous. The steeper gradient and faster flows would exacerbate erosion, banks would slip into the river and the channel would become wider, shallower and more silted. These were the results when the Hunter River, in NSW, was straightened as it was from the late nineteenth century. Productive land was lost to slumping and the river's ability to carry flood flows was reduced. There was no useful gain except that boats had shorter journeys ─ but that benefit was lost when the river silted up and became too shallow to navigate in times of low flow.

Far better to look first not at modifying the environment but doing something about what humans have done and keep doing. Over the decades we have built our towns and cities largely on floodplains ─ and we have done little to protect them from the flooding they will inevitably have to bear. Few councils in Queensland have ever studied floods properly, and many have not mapped where floodwaters flow. The result is that subdivisions have been built in places that are certain to be inundated. In recent years we have seen large areas of new houses ─ Emerald is one place among several that come to mind ─ flooded well above their floors. They have been built in the wrong places.

Developers have been allowed to focus on areas where development is easy rather than where it is appropriate. Yet we have no shortage of land that could be developed away from the reach of flooding.

And because of the lack of flood studies, information has not been gathered to allow councils to advise people of the risks they take in buying or building on floodplains. Thus they are shocked when floodwaters overwhelm them. They are also shocked when their insurance premiums grow to become unaffordable, which in some cases means they stop taking out insurance. That creates the potential for personal financial ruin.

The legacy of decades of development on floodplains is that we have allowed the problem to grow, slowly but massively. In the best of all worlds governments would simply buy the properties in flood-liable areas and resettle people ─ but that would cost hundreds of billions of dollars. It might happen on a piecemeal basis, as it has in Grantham in the Lockyer Valley where the town is being virtually relocated, but to buy back much of Townsville, Bundaberg, Rockhampton, Brisbane or the Gold Coast is simply untenable. The most we could afford to do is to buy the most seriously flood-prone properties and turn them over to recreation, farming or parkland.

In some cases we can protect what is already there, and we can certainly stop further development that will exacerbate the problem. Many things could be done by way of protecting people from past developmental mistakes. In some locations levees could be built, and in others floodwaters could be 'trained' away from urban areas. Retention basins could be constructed to 'store' stormwater or creek flooding and let it go slowly once downstream levels have fallen. We could raise the floors of houses.

And we could work at ensuring that people understand that their properties are on floodplains, understand flood warnings and know when a warning means they should act to raise their belongings and evacuate. We could raise low sections of roads so they can function as evacuation routes rather than trapping people when floodwaters flow over them. Raising roads could also help prevent communities from becoming isolated during floods, which always causes great inconvenience, economic disruption and sometimes distress.

These measures will cost a lot, and none of them is perfect or will 'solve' the problem of flooding by itself. Levees, for example, are not appropriate where floodwaters can be very deep (as when there is a 'choke' downstream which slows flood drainage) or in very flat areas (such as deltas) where rivers branch into several channels. Educating people about floods is not cheap, and it is often opposed and undermined by vested interests such as the real estate industry which believes ─ usually with precious little evidence ─ that it will reduce property values.

What is needed is a mix of measures tailored to the varying situations of different flood-liable areas. To work out which measures suit, the flood problem has to be studied and mapped, and measures chosen that fit the local circumstances and provide benefits that outweigh the costs of implementing them. Expert hydraulic and engineering analysis will be needed.

Experience around the world shows that levees often fit the bill, though they can be overtopped in big floods and it must be realised by those living behind them that they are not a complete solution. Flood warning systems also have a place, at least when people are educated to use them effectively. The creation of flood storage capacities in dams may have a role too, though not everywhere and usually to a smaller degree than people believe.

Queensland has had four successive summers of serious flooding in which some communities have been badly flooded more than once. There are signs that pressure is building to force the state government to take action. It needs to ensure that the action it takes is sensible, will reduce the flood problem without creating environmentally deleterious effects and will be cost-effective.

Here's a way forward. An agreement should be sought, involving all three levels of government, to invest in the management of flooding. It would seek to prevent the problem from being exacerbated by continued inappropriate development, and it would determine what means of flood mitigation would be appropriate in different locations. This would require councils and governments to examine the problem, community by community, and to devise cost-effective treatments. Community involvement would be necessary along the way.

Political courage and a strong investment of funds will be needed, over decades. Queensland could, if it chose to do so, spend a small number of billions of dollars over the next few decades.

If it spends wisely it will reap the benefits that many communities in NSW have won since, late in the 1950s and after a similar period of repeated, severe flooding, the three levels of government developed a partnership to invest in flood mitigation and better management of development on floodplains. For decades funding was committed on a 2:2:1 (federal:state:council) basis on measures to reduce the impacts of flooding. Much successful flood mitigation was achieved.

Grafton, in northern NSW, is an example of what can be done. Since the current levees were completed in 1970, no fewer than eleven floods have been kept out of the residential and commercial areas of the town. Since 2000 alone four big floods have been excluded, with damage saved amounting to perhaps $800 million. The levees, if they were built today, would cost in the order of $30 million, with a few hundred thousand dollars having to be spent on their upkeep each year. The ratio of benefits to costs there has been very high.

Grafton is but one case of effective flood mitigation in NSW. More than 40 other NSW towns have had levees constructed, and many retention basins have been built. Some dams were constructed with 'airspace' in which to store floodwaters. Houses in the most hazardous flood prone locations have been purchased, at market price, and then removed to allow clear passage to floodwaters. Many houses have been lifted bodily, and in some areas roads have been raised at low points to give them a measure of flood security. There has been investment in flood prediction services and in helping people to understand warnings and apply them to their own actions when floods threaten.

And for years NSW had regulations which at least placed a crimp on the tendency for councils to allow unwise development in flood-liable areas. The regulations have been weakened somewhat over the past decade in favour of simplifying development regimes, but that is a story for another day. Suffice to say that NSW will probably regret the recent loosening of its regulatory regime for new development and the reduction of investment in flood mitigation.

But much has been gained in NSW in terms of making flooding more manageable. What was done was not without environmental impact, but the impacts on nature were much less deleterious than would result from the adoption of the prescriptions Hamilton advocates.

We need to stop trying to control, dominate and overpower floods by means of grand engineering works. Making nature submit to our will is expensive and likely to fail. That is the way of decades past. We need to do more, though, to make it possible for communities to live more effectively and safely with flooding.