Are More Dams The Flood Fix?

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This weekend was another wet one for NSW. Reports indicate 20,000 people are isolated by floodwaters in the north of the state and emergency services have likewise been inundated with thousands of calls for help. The NSW floods, now over a month long, come close on the heels of the latest disaster in Queensland.

Tony Abbott’s $30 billion solution is to build up to 100 new dams to prevent flooding, mainly in northern Australia, coupled with a $500 million expansion of Sydney’s Warragamba dam.

Let’s be clear — this is a recycled idea from two years ago when Queensland, NSW and Victoria were reeling from flood after severe flood. The dams are not just for flood protection; Abbott also wants them for irrigation, "drought-proofing" and making hydro power too. That rather complicates the problem. Dams for multiple purposes contain inherent contradictions and are thus difficult to manage.

We might have seen that at Wivenhoe Dam (a structure with both water supply and flood mitigation roles) two years ago, when the dam mangers were in all probability caught, at the end of a long drought, between the imperatives of water conservation and flood mitigation (not to mention a flawed operating manual).

To begin with, we should scotch the idea that Australia can be made anything like drought- or flood-proof — at least within any sense of investment sanity. Those goals are far beyond us economically, and the use of dams on the scale needed would deny many floodplains the periodic soakings they need.

Alternatively they would destroy much productive land or wilderness. We do not have a surfeit of either.

Consider just how many dams would be needed to make a meaningful difference to a severe flood at, say, Rockhampton on the Fitzroy River. A decent number of the 100 dams Abbott seeks would be needed in that basin alone. Every significant tributary would have to be dammed, along with the main stem of the river ─ probably in several locations. And that assumes suitable sites could be found.

When serious flooding occurs, people are attracted to the idea of dams as the solution. Or they want to dredge the rivers, or drain the floodwaters via tunnels or canals to rivers that are not in flood. In other words they want water-storing and water-moving solutions. Frequently, these have only a limited place in flood mitigation thinking that deals in terms of environmental sustainability or budgetary responsibility.

Flood management does not offer easy, single-solution fixes. It is about choosing, from among many strategies, the ones that are most appropriate in particular areas. Dams may have a role here, though generally not a large one. Dredging and the creation of drainage grids have little place.

Levees are worth considering, though not in deltaic environments where rivers branch into several courses or where the potential reach of floods is great ─ for example at Windsor, north-west of Sydney, where one flood reached a level more than 18 metres (six floors on a tall building) above "normal", non-flood levels.

Flood bypasses may have a place in some environments, as may flood retention basins which are commonly used on creeks within urban areas.

All these devices store or re-direct flood flows. But much of the best flood mitigation focuses not on nature but on the human domain. Properties in the most hazardous locations can be purchased by councils, the buildings demolished and their former sites left to floodwaters. Or dwellings can be raised so their floors are above the levels which most floods reach.

All these measures have been used in NSW, where something of the order of $1.3 billion in today’s terms was invested in flood mitigation between the early 1960s and 2007. Governments at all three levels contributed (usually on a 2:2:1 federal:state:local basis).

More than 40 towns got a measure of protection using levees, many retention basins were constructed, and a lot of dwellings were raised or removed. The benefits in places like Grafton, where numerous floods have been kept out of the town since the levees were built around 1970, have been enormous in terms of damage and trauma avoided. The dollar benefits appear to have far outweighed the costs.

Moreover, the state government made it possible for councils to discourage development in flood-liable locations, crimping the tendency to build more and more on floodplains and add to community vulnerability.

The Federal Government also invested in flood warning services, developed largely by the Bureau of Meteorology. The result is that we now have excellent flood prediction services on our main rivers.

Not that all this has been easy to sustain. Floodplain management initiatives in NSW have stalled somewhat over the past decade, the Federal Government having scaled down its monetary contributions. Councils have found it harder to fund new initiatives as a result and schemes which have passed the standard benefit-cost and environmental tests have not been implemented.

Flood warnings have not given the protection they might have because people don’t understand them. The predictions themselves speak only of the heights that will be reached at specified gauges, which by themselves mean little to most people. More work is need to add value to the bureau’s predictions so that people in flood-prone locations understand in advance what a coming flood will mean to them and what they need to do to protect their belongings.

Persuasive messages which motivate people to act are also needed. These are rarely heard.

The proof of the deficiencies of our flood warning services is not hard to find. Recent floods have seen many examples of people reacting not to warning messages, but to the water itself when they see it rising near their homes. Their reactions have been too little and too late, and much has been lost which could have been saved. The evidence has been piled high on the kerbs of many streets in Brisbane, Rockhampton, Bundaberg and elsewhere ─ but not Grafton, where the levees held back floodwaters that peaked above eight metres.

There is much that can be done to mitigate the effects of flooding. Dams may have a role, but it is too easy to think of water-controlling, nature-dominating mechanisms as central to flood management. That is the way of ages past, and it has an inbuilt capacity to fail. Better to think of the problem as one requiring education and land use management as well as flood-modifying measures like levees.

NSW has used many of the available measures, Queensland few. It is no surprise that Queensland has suffered more from recent flooding. It has never taken flood mitigation seriously, and it has allowed much unwise development on floodplains. By contrast NSW for more than four decades had flood management and floodplain development strategies that were among the world’s best.

Flood management is about people as well as floodwaters. It is not primarily about dams.

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