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VIEWPOINT: Dams pose flood risks in a warming world

by (c) Copyright Thomson Reuters 2010. Click For Restrictions. http://about.reuters.com/fulllegal.asp | Thomson Reuters Foundation
Friday, 15 June 2007 00:00 GMT

As climate change picks up pace, traditional flood-control methods could fail spectacularly, argues Patrick McCully, executive director of the International Rivers Network.

Floods are the most destructive, most frequent and most costly natural disasters on earth. And they are getting worse.

In just the first two weeks of June the media reported three flood-related deaths in Switzerland, five in Ghana, nine in Australia, 12 in Iran, 76 in China and more than 135 in Bangladesh. Severe floods were reported in numerous other parts of the world including Northern Ireland, Malaysia, South Africa, Kenya, two Canadian provinces and several U.S. states.

Flood damages have soared in recent decades partly because global warming is leading to more intense storms, and partly because more people are living and working on floodplains.

The United Nations estimates that by 2050 the number of people at risk of damaging floods will double to 2 billion. But a key factor behind the spiralling flood damages are the very flood control measures that are supposed to protect us.

Dams and embankments (known as levees in the United States) can never be fail-proof, and when they fail, they do so spectacularly and sometimes catastrophically. They also provide a false sense of security that encourages risky development on vulnerable floodplains.

When New Orleans was devastated in 2005, the primary cause was not Hurricane Katrina, but the failure of the city&${esc.hash}39;s poorly conceived and maintained flood defences.

The limitations of conventional flood control will become ever more evident as global warming-induced super storms test dams and embankments beyond their intended limits.

Author Jacques Leslie aptly describes dams as "loaded weapons aimed down rivers."

Dams kill because they collapse - as many as 230,000 people died from a chain of dam failures in central China in 1975 - and also because of dam operators&${esc.hash}39; negligence. Sudden releases of monsoon waters from India&${esc.hash}39;s Ukai Dam last year killed 120 people in the downstream city of Surat. The floods caused economic losses of ${esc.dollar}49 billion.

Conventional "hard path" flood control ignores the complex workings of rivers and coasts. Dams, embankments and the straightening and dredging of rivers trigger profound changes in the ways in which water and sediment flow through watersheds.

Flood damages soar when engineering projects reduce the capacity of river channels, block natural drainage, increase the speed of floods, and cause the subsidence of deltas and coastal erosion. In addition, "hard path" flood control often ruins the ecological health of rivers and estuaries.

A better way

There is a better way to deal with floods - the "soft path" of flood risk management. Flood risk management assumes that all anti-flood infrastructure can fail and that this failure must be planned for.

The "soft path" is also based on an understanding that some flooding is essential for the health of riverine ecosystems.

Instead of spending billions of dollars vainly trying to eradicate floods completely, we need to recognize that floods will happen and learn to live with them as best we can.

This means taking measures to reduce their speed and size (for example, restoring meanders and wetlands) and duration (say, improving drainage). It means protecting our most valuable assets, for example by raising houses on mounds or stilts, and defending built-up areas behind carefully planned and well-maintained embankments.

It also means doing all we can to get out of floods&${esc.hash}39; destructive path with improved warning and evacuation measures.

Such practices are already in use in many parts of the world. In northern California, a 10-year, ${esc.dollar}220-million project to reduce floods on the Napa River will restore tidal marshlands, remove some buildings from the flood zone and set back embankments to give the river room to spread.

Communities along France&${esc.hash}39;s longest river, the Loire, persuaded the government to scrap a planned "flood control" dam in favour of river restoration and a new flood warning system. In China, efforts are underway to restore portions of the Yangtze wetlands to act as flood absorption areas.

Despite a growing consensus that mitigation not elimination is the only realistic flood policy, there remains a powerful a faction devoted to outmoded "hard" flood control. Notable among these diehard groups are the U.S. Army Corps of Engineers, the World Bank and the water establishment in India.

An iron triangle of politicians, bureaucrats and dam builders continues to promise salvation through embankments and dams any time a community is struck by a flood (even when such floods have been worsened - or caused - by existing dams and levees).

Improving our ability to cope with floods under the current, and future, climates requires adopting a more sophisticated set of techniques. The "soft path" of flood management should be a core part of efforts to adapt to a changing climate. Such a path will not only reduce deaths and damages, but also save money and bring us healthy rivers and wetlands.

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