The Why Files The Why Files --

Katrina + 1: Are we rebuilding in harm's way?


Level the levees?
Water explodes into a surging shower at base of home on the waterAny discussion of the human hand in flooding must deal with levees -- the dikes built to keep water in its "place." As the people of New Orleans learned last year, levees can be a cold comfort. Multiple failures allowed vast flooding; in contrast to claims by the Army Corps of Engineers, little or none of the floods were caused by water that went over the levee tops.

Despite the hazards of wind and water, many people still crave that ocean view. Photo: USGS

"Let no one believe that because you are behind a levee, you are safe," former Army Corps of Engineers General Gerald Galloway told the American Association for the Advancement of Science last February. "You must be prepared to evacuate, and get out of the way." Galloway, who oversaw a major report on the Mississippi-Missouri flooding in 1993, suggests emulating Holland, which mobilized after disastrous floods in 1952 and built protection against 1,250-year flood of the Rhine River, and a 10,000 year flood from the North Sea. "At New Orleans, the failed levees were supposed to protect against a 200-year flood, and they didn't even do that," Galloway observes.

Skeletal remains of a building washed away by flood waters
The storm surge blew out this school, in the New Orleans region. Courtesy Dustin Anderson

Levees have drawbacks, since they are expensive, prone to failure, and will raise the level of inland floods. Nicholas Pinter, who has studied the meeting-ground of the Illinois, Mississippi and Missouri Rivers near St. Louis, says levees narrow and deepen a river channel. That speeds the river and allows barge traffic, but it also reduces the river's water-carrying capacity and its ability to store water during floods. Pinter says levees have caused a surge in flooding around St. Louis. "It's dramatic. Today, floods at St. Louis are 10 to 12 feet higher than they were during the pre-engineering era [before levees were built]. There is a systematic underestimation of the hazard level; the current estimate of the level of the 100-year flood is underestimated by 4 to 5 feet."

A related change is taking place along the coasts, where rising sea levels are increasing flood heights.

Two areas of US will lose wetlands due to rising oceans
Louisiana and the South Atlantic states stand to lose vast amounts of wetlands if the ocean continues rising. That will intensify the damage caused by storm surges. Courtesy Evan Mills, Lawrence Berkeley National Laboratory

On the level?
The question of where to build levees is inextricably linked to the question of where to locate housing, says Jeffrey Mount of the University of California. "We should be making land-use decisions that steer development away from those areas that are most vulnerable. If you live behind a levee, you are at risk. The simplest solution is to keep this land as farms. It's far cheaper to have floodplain management than flood control, period."

Pinter, who has documented rapid development around St. Louis, says, "The first thing levees do is encourage development. It's absolutely the worst thing imaginable. If you could take a static picture now and prevent new development, that would accomplish more than anything."

Stream on over to our "building-in-harm's-way" bibliography.


Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

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