Dams and Levees Heighten Flood Danger in a Warming World

Patrick McCully
Sunday, July 29, 2007

This op-ed first appeared in the San Francisco Chronicle, Sunday, July 29, 2007

Floods are the most destructive, most frequent and most costly natural disasters on Earth. And they're getting worse. Large parts of central and western England are underwater in the worst flooding in 60 years. Insurers estimate the damage could reach $6 billion -- on top of the $3 billion in flood losses suffered in northern England in June.

Over the past two months, the monsoon season in Bangladesh, China, India and Pakistan has, conservatively, claimed hundreds of lives. Texas has suffered major flood damage, as have Nebraska, Oklahoma, Kansas, Missouri and North Carolina. Although California's primary water worry right now is drought, increasingly serious floods lie in store for us, too.

Flood damages have soared around the world in recent decades for a variety of reasons. Global warming is worsening storms; we've deforested and paved over watersheds; and more people are living and working on floodplains (there are few better examples of this than the fast-sprawling cities of California's Central Valley). But a key factor behind the spiraling flood damages is the very flood-control measures supposed to protect us. Flood damages soar when engineering projects reduce the capacity of river channels, block natural drainage, increase the speed of floodwaters and cause the subsidence of deltas and coastal erosion. In addition, "hard path" flood control based on dams and levees can ruin the ecological health of rivers and estuaries.

Dams and levees are not fail-proof, and when they do fail, they do so spectacularly and sometimes catastrophically. Worse, they 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's poorly conceived and maintained flood defenses. Sacramento lies at the confluence of the Sacramento and American rivers behind a network of aging levees. California's capital is widely regarded as second only to New Orleans among major U.S. cities in the risk it faces from major flooding.

A warming climate threatens New Orleans with increasingly intense hurricanes and a rising sea level. Similarly, Sacramento is witnessing a long-term trend of increasingly high floods washing down from the Sierra.

The limitations of conventional flood control will become ever more apparent as global warming-induced super-storms test dams and levees far beyond their intended limits. Fortunately there is a better way to deal with floods -- the "soft path" of flood-risk management.

This approach assumes all anti-flood infrastructure can fail and that this failure must be planned for. Instead of spending billions of dollars vainly trying to eliminate flooding, we need to recognize that floods will happen and learn to live with them as best we can. This means reducing the speed, size and duration of floods by restoring river meanders and wetlands, and by improving drainage. It means doing all we can to get out of floods' destructive path with improved warning and evacuation measures. It means developing plans to help communities recover from flood disasters. And it means discouraging development in areas that will inevitably flood.

It also means protecting our most valuable assets. Houses can be raised on stilts, as along the Russian River. By removing levees that protect relatively low-value land, we can help free up funds to maintain essential levees protecting urbanized areas, such as Sacramento.

A sensible flood bill was killed in the California Assembly last August. The bill would have required local governments that approve new developments in flood-risk zones to share liability with the state for damages caused by levee failure. Fortunately, key players in the Legislature are now working with the governor to try to pass this bill, or others with similar intent.

There is more good news. A 10-year, $220 million project to reduce floods on the Napa River will restore tidal marshlands, remove some buildings in the flood zone and set back levees to give the river room to spread. This innovative collaboration between local residents, businesses and government agencies as well as environmentalists, is funded by a Napa County sales tax and the Army Corps of Engineers. Outside the United States, especially in Europe, but also in China, river and wetland restoration-based projects are gaining favor as the preferred strategy to dealing with flood risk.

Despite a growing consensus that mitigation, not elimination, is the only realistic flood policy, there remain powerful interests devoted to outmoded flood control. A notable diehard in California is the Building Industry Association, which strives to kill any enlightened approaches to flood management in Sacramento.

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 save lives, money and property, but also help bring us back healthy rivers and wetlands.

Patrick McCully is executive director of Berkeley-based International Rivers Network. He is author of the recent report "Before the Deluge: Coping with Floods in a Changing Climate."