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Floods May Worsen as the Climate Changes


Uncharted Waters
Floods May Worsen as the Climate Changes

November 30, 2008 By

It has become apparent as floods increase in number and severity that terms like "100-year flood" are outdated and so are the country's strategies for protecting citizens against major events -- save some forward-thinking communities.

Experts warn that reliance on decrepit levee systems and continued buildup of floodplain areas, combined with warmer temperatures and more rain, will result in more death and damage from flooding. They urge a more balanced approach to flood management to mitigate this looming threat.

In spring 2008, floods killed more than 20 people around the country, destroyed tens of thousands of homes and inundated cropland, resulting in rising commodity prices. Much of the damage occurred in the Midwest where flooding was termed "historic." In Missouri during a 36-hour period, four rivers crested at record levels March 17-19. These "historic" floods are occurring more often than calculations suggest they should.

In 1993, Midwest flooding caused more than $15 million of damage and killed 50 people. That flood, called the Great Flood of 1993, was estimated by the Army Corps of Engineers as perhaps a 250-year flood.

In 2001, Bob Criss, professor of earth and planetary sciences at Washington University in St. Louis, wrote that the 1993 flood was, in reality, a 30- or 50-year flood. "They said I was Chicken Little," Criss said. But he feels vindicated by recent events. "We're seeing more floods and worse ones," he said.

There's been progress at mitigating these risks in areas like Tulsa, Okla., and the Pacific Northwest, where progressive strategies have controlled flooding. But overall it's been slow, with a continuation of the same philosophies.

"We, as emergency managers, have to start saying, 'Look, we have to take a much broader view, otherwise as our climate changes, this is going to be a big deal,'" said Bob Freitag, a former emergency manager with FEMA [Federal Emergency Management Agency] and currently professor of urban design and planning at the University of Washington. "We, as emergency managers, see everything that goes wrong: all the mistakes that were made on that stream -- upstream in terms of fencing it in, removing all storage, removing the forest that provides detention. All those failures -- we see [them] at a point when it comes downstream and destroys homes."

 

Warming Trend

According to the National Climatic Data Center, the Earth's summer temperature rose above average for the 30th straight year in 2008.

Some areas of the country are experiencing more rainfall instead of snow, which means more severe flooding in the spring. "The Governmental Panel on Climate Change has said that in many cases, we're going to see less water in an area because of climate change, but when it comes it's going to be the gullywasher," said Gerry Galloway, a civil engineer and former brigadier general who was assigned by the White House to lead a committee assessing the Great Flood of 1993.

In response, most areas are trying to funnel more water through narrower channels, the age-old strategy. In the Midwest, the Army Corps of Engineers is deepening channels with wing dikes and other structures to allow more water to pass through.

"That's what they think they're going to do," Criss said. "You might be able to do that locally with continued maintenance and dredging, but thinking they're going to change the bottom of the river for any significant difference is folly."

The idea of creating narrower, deeper channels has been the Midwest's flood-control philosophy for more than 100 years, but 19th-century maps show the Mississippi River is no deeper now than it was then, Criss said. "How do you dig a hole in the bottom of a river? You don't, and thinking that we can is not very bright."

Any dredging done on the bottom of a river, in this


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