The dramatic trade-off “reactivated the flood plain,” in engineer-speak. It also highlighted limitations in the long-term strategy of hemming in rivers with levees and dams, then pushing farms and towns up against the river walls.
“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.”
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.
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.
Oft-flooded Napa, Calif., calls its $400 million project the “living river.” Confronted in the 1970s with a Corps plan to turn the downtown riverbank into a concrete channel, citizens said no. Instead, in 1998, voters said yes to relocating 13 bridges, buying out some 100 homes and businesses and restoring 900 acres of wetlands.
The project, now about two-thirds complete, according to Mayor Jill Techel, dug the city’s Veterans Memorial Park into a bowl for holding floodwaters. The wine-tasting destination’s downtown now features a tiered trail that doubles as a spillway for the Napa River when it swells.
Nonetheless, the town flooded again on New Year’s Eve 2005. Although the project was incomplete, Techel said, the town drained in 24 hours instead of the usual two to three days. The new wetland area “was a sponge,” she said. “It took all that water.”
And in Pierce County, Wash., the Puyallup River — which has flooded 15 times over the past 20 years — will soon spread out a bit more. Engineers have started pushing back levees, mile by mile. The straightened, channelized river could no longer handle the increased snowmelt from Mount Rainier, said county engineer Dennis Dixon. “After 100 years, we’re seeing that’s not quite working.”
Meanwhile, Cedar Rapids, Iowa, has been buying out 1,300 homes and 100 businesses in a flood plain inundated by the town’s “800-year-flood” of 2008, said Mayor Ron Corbett. “We’re really moving people out of harm’s way,” he said, to establish a 220-acre “floodable greenway.”
But on May 3, the city’s voters narrowly rejected a one-cent increase in the sales tax to pay for revamped, gently sloped levees. The Corps also rejected part of the plan, leaving the city to search for other funding. The project is now jeopardized, Corbett said.
Napa had better luck with the Corps, obtaining partial funding from an organization that has long favored steep levees and straight, deep main channels — geometry that drives floodwaters downriver fast and high.
Corps officials declined to comment.
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. A report published in the journal Nature in February concluded that North America experienced an excess of deluges in the second half of the 20th century and fingered greenhouse gas-driven atmospheric warming as a partial cause.
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 the world’s water management experts — are further along with their policy of developing more natural defenses.
For centuries, the Dutch waged a stunningly successful war against water, building levees and using windmills to pump the lowlands dry and give their citizens “droge voeten,” or dry feet. Vast tracts of land have been won back from the wet: More than 60 percent of the population lives at or below sea level.
But the aggressive tactics came at a cost, said Dale Morris, senior economist at the Royal Netherlands Embassy. The country has been gradually sinking inside its giant defenses and is crossed by increasingly tempestuous rivers rampaging seaward behind ever-bigger dikes.
The threat of devastating flooding in 1993 and 1995 — caused by wet weather and snowmelt — and an ominous mix of demographic and climate changes, including the promise of heavier winter rains, suggested disaster lay ahead. It was only a matter of time before the rivers burst their man-made banks and swamped the densely populated surroundings.
Hence a 21st-century government vision for sustainable water management, which involves lowering dikes in some areas and moving them back, inviting the rivers to flood and creating space for them to do so safely.
Called “ruimte voor de rivier” or “room for the river,” the strategy is intended to help the rivers “cope with a lot more water than they do now,” said spokeswoman Esther van Dijk. It involves about 35 projects — including relocating dikes, deepening riverbeds and even permanently turning farmland back into flood plain — at a cost of more than $3 billion. The effort is expected to be complete by 2015. Households and neighborhoods, meanwhile, do their part by finding ways to store stormwater temporarily, by using cisterns or flooding public parking garages.
All involve trade-offs. Among the parcels of land identified to quell the restless rivers, Morris said, is one along the Waal River in the eastern part of the country. Once slated for development, he said, the land has instead been turned into a park that can be inundated if pressure on the riverbank rises.
The scale is different along the mighty Mississippi, but similar “economic and human capital is at risk,” Morris said. The Dutch, who have offered advice on integrated water management in several parts of the United States, such as along the Sacramento River in California, have not been asked to advise on this year’s flooding on the Upper Mississippi, he said. “Not all the Dutch practices are applicable” to the U.S. river, he said, but “some of them clearly are.”
Most of all, Morris said, the Dutch strategy represents a psychological shift. It amounts to an acknowledgment that if you want to keep your head above water, you have to be prepared to get your feet wet.