Dams not always the answer to flooding

13 January 2011

The current deluge and floods near Brisbane fills us all with shock and awe. Clearly, such events demonstrate the high variability of the Australian climate and the power of the water. Care for the affected people in the area is the first priority. However, the deluge has rekindled the debate about dams. Calling for the building of new dams is not a good response to a very wet La Nina year. Floods are natural occurring phenomena in Australia, and a dam is often the first thing that springs to mind to control floods. However, there are other and more innovative ways to adapt to the natural occurring floods and future increasing climatic variability.

Risk can be defined as the combination of occurrence (how often something occurs) and damage (how bad it is). The traditional focus in flood management has been to minimise the occurrence by building dams and river control structures. There are however three main reasons why new dams are not the solution to the current and future flooding in Australia. Firstly, the worst floods are the largest floods; this means that to reduce the risk of large floods we have to overdesign our dams. This results in low efficiency and high costs as the dams would be mostly empty, as in the last 10 years of drought. Secondly, multiple purposes for dams, such as power generation and water storage, counteract the flood prevention role. For flood prevention the dam needs to be as empty as possible, while for irrigation water storage or power generation the dam needs to be as full as possible. As a result the risk of early spilling is increased resulting in floods downstream. Wivenhoe dam above Brisbane is trying to spill water as quickly as possible causing at least some of the downstream flooding. Thirdly, there is a large body of international research that highlights the detrimental effects of dams on the environment and this is one of the key drivers for the current Murray Darling Basin plan. The Australian climate is highly variable (the land of droughts and flooding rains) and this creates its natural beauty and diversity. Floods are a key element of this environment, while dams change water quality and temperature with detrimental effects on flora and fauna.

Finally dams tend to give a false sense of security to people living below dams and in floodplains; they believe that they are 100% safe, which is never the case. Evidence of this is emerging in some of the reactions in flood affected areas around Brisbane as well.

As alternatives, activities in the traditional catchment management area are still very much needed, such as increasing infiltration and slowing down the water before it reaches the stream. Increases in vegetation and banning removal of vegetation in sensitive areas are key to this.

Relatively new and as a result of the international work on the impact of dams, many countries (such as the U.S.A. and in Europe) are looking at alternative way by focussing on the second part of the risk equation (reducing damage) rather than occurrence. The large floods in the Mississippi in 1993 and floods in Europe in the Rhine and Elbe have further forced some of this rethinking. This involves limiting development in floodplains to allow the river to run freely. Spreading out the floods lowers the peak and thus limits the damage. This would involve identifying different ways of living and working in flood prone areas, while still protecting high value assets. Reassessing development regulations and possibly moving homes or businesses might be part of the solution. People living in flood prone areas can be compensated or assisted to be "flood ready", similar to people living in bush fire risk areas. Rerouting of floodwaters to certain areas of the floodplain could be another option.

For Australian agriculture, this also requires developing flexible and responsive cropping systems, taking full advantage of the wet years and making do in the very dry years.

For this to be effective, flood risk forecasting, particularly at the long range, needs more focus. There is significant forecasting at the short range, but full interpretation of long range climate patterns, their influence on Australia, and their possible changes due to climate change still needs more work. While we are able to predict the La Nina pattern, we are not yet able to accurately predict the impact or risk of such a pattern for different areas. Reanalysis of the current flooding events in Queensland will assist with this for the future.

So far Australia has not yet looked at the opportunities of "living with floods" rather than "fighting floods" in detail.

Contact: Associate Professor Willem Vervoort

Phone: 02 8627 1054

Email: 3f5904064a084d4222052f2522112d75355203022d0c05515c3f5c061e