It is now more than three years since Queensland's disastrous flood summer of 2010-11. A few short weeks saw three quarters of the state declared a disaster area, many towns flooded, thousands of houses taking in water and some being destroyed, and large numbers of people having to evacuate. The communities of the Condamine-Balonne and Lockyer valleys and Ipswich and Brisbane were especially grievously affected. Now, with various proposals devised, under consideration or being implemented, it is possible to see what the state might do to manage flooding in the future.
First, some context. The summer of 2010-11 was actually just the worst of a period of four years of unusually frequent and severe floods which affected virtually all parts of the state. Some places were flooded repeatedly. The previous summer had also been a bad one for flooding, and so were the two that followed. The mayhem seemed to come to an end after ex-Tropical Cyclone Oswald brought record flood heights to Bundaberg and other Burnett River communities in January 2013.
Flood-rich periods can create the momentum for action to manage the effects of flooding. The experience of flood after damaging flood focuses community and governmental minds to a degree that single floods, on individual rivers, cannot. Repeated, widespread and severe flooding creates situations from which comprehensive, far-reaching action can be instituted.
Have minds been focused in Queensland? Is the state seizing the opportunity to better manage this most expensive and disruptive of natural hazards?
The answer is a mixed one. Decisions are being made, but the effort being mounted appears too narrowly based to allow floods to be managed as well as should be possible. An historic opportunity is about to be missed.
About a dozen towns have investigated the building of levees and some like St George and Roma are close to finalising levee-building projects talked about for years. Others have levees planned, but in others again levees will probably not be part of the strategy. Some flood-prone urban areas, like Gympie, Ipswich and Brisbane, have sites that are topographically or otherwise inappropriate for levees to be a significant part of the effort.
On the Brisbane River, the flood mitigation role of Wivenhoe Dam has been much scrutinised and new operating procedures adopted. Henceforth, the dam will not be allowed to fill to the degree that occurred in early 2011. Releases will begin at lower dam levels, with some negative consequences as far as prolonged rural inundation and the isolation of communities upstream of Brisbane are concerned but with the benefit of reduced peak flood heights in built-up areas.
Beyond that, the state government has flagged its intention to build flood mitigation capacity in the form of new dams within the Brisbane River catchment, and to raise the wall of Wivenhoe Dam so more floodwaters can be impounded. Eight potential dam sites are under investigation.
New dams carry the potential to reduce peak flood heights both in Ipswich and Brisbane. But it will be all too easy to exaggerate the benefit, because the flood height reductions will probably be small. It is likely that given similar rainfalls to those of early 2011 they will save only a small minority of the buildings that experienced over-floor inundation in Brisbane on that occasion.
Most of the proposed dam sites are in the headwaters of the river system and will command only small proportions of the catchment. Moreover the economics of dam construction are unlikely to allow them all to be built.
Over time low sections of the Bruce Highway, the state's main transport artery, will be raised. Communities will be cut off less frequently and disruption to the economy will be reduced.
But dams, levees and the raising of roads will not render flood prone areas immune . That is important to recognise, and it is to be hoped that there is no repeat of the situation that followed the building of Wivenhoe from 1977 to 1985. Then, the Bjelke-Petersen government trumpeted the dam as the 'solution' to Brisbane's flood woes.
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