In a move that echoes the approach taken by the Netherlands, which has long wrestled with such problems, a nascent movement made up of activists and city leaders victimized by flooding is pushing for “natural river defenses.” They want to set the rivers free, if just a little.
Departing from the U.S. Army Corps of Engineers’ long-term strategy of hemming in rivers with levees and dams, cities and counties are buying up homes and farms and relocating residents to restore flood plains and wetlands. They’re moving levees back from the water’s edge. And they’re ditching steep concrete channels in favor of gently sloped green spaces.
“For decades we’ve treated levees as the only line of defense” against floods, said Andrew Fahlund, senior vice president of American Rivers, which advocates for healthy waterways. “They ought to be the last line of defense.”
Champions of natural river defenses say the Corps will have to adapt its tactics as the world warms. Warmer air holds more water vapor, which can trigger more intense deluges, said Kenneth Trenberth, a senior scientist at the National Center for Atmospheric Research.
Levees “will be under a lot more pressure if climate scientists are correct,” said Sandra Postel, a fellow at National Geographic and the Post Carbon Institute. She thinks the record Mississippi floods this year — on top of a “thousand-year” deluge in Tennessee last year and widespread flooding in the Upper Midwest in 2008 — will prompt greater adoption of natural flood defenses.
The Dutch — often considered water management experts — are further along with their policy of developing more natural defenses. They’re lowering dikes in some areas and moving them back, creating more space for rivers to flood safely.
The strategy is intended to help the rivers “cope with a lot more water than they do now,” said spokeswoman Esther van Dijk.
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