Levees: Do They Work Too Well?

By J. Madeleine Nash/Chicago

A river view is a priceless asset, or so the residents of Davenport, Iowa, believed. Now, however, they are realizing that their postcard vistas came at a price. Two weeks ago, the town, which had chosen not to build a levee, was swamped by millions of gallons of murky water. Yet while Davenport flooded, the business district of nearby Rock Island, Illinois, barely got its feet wet. Reason: in 1971 Rock Island decided to build a rock-and-clay floodwall.

In spite of the impression created by images of levees and houses being overrun by rising waters, the mounds of earth and rock built to contain the Mississippi around population centers have by and large worked. At week's end, along 600 miles of swollen, surging river, most major levees continued to hold.

The problem, ironically, is that the enormous system of levees built up over more than 200 years may be working too well. As the flood recedes and cities like Davenport begin the dismal task of cleaning up, sharp questions are being raised about the wisdom of the nation's approach to flood control, and the cost, both financial and environmental, of a program that relies on man-made structures to contain the mighty river. Over the past seven decades, the U.S. Army Corps of Engineers has spent billions of dollars constructing an elaborate flood-control network, including 7,000 miles of levees, along the Mississippi and the rivers that feed it. The system was intended to protect the communities that sprang up on the river's edge, and most of the time it has. But many environmentalists believe that, over the years, the corps's attempts to control the Mississippi have backfired. Left to its own devices, a flooding river spreads horizontally, filling its natural floodplain and enriching it with fertile, alluvial soil. Along the Mississippi, however, this pattern of natural flow has been increasingly blocked by a patchwork of levees.

The effect is that an increasingly pent-up river rises higher, moves faster downstream, and is more prone to back up like a clogged drain, increasing the pressure on unfortified areas. "The water has to go somewhere," says aquatic ecologist Richard Sparks of the Illinois Natural History Survey, "and if we don't allow it to spread out, the only direction it can go is up."

Nowhere are these effects more dramatic than in the Mississippi Delta, which used to be replenished every year with rich alluvial deposits. Now the soil, laden with nutrients, is carried by the river, bypasses the Delta and falls into the Gulf of Mexico, where it is contributing to algae blooms and threatening the fisheries. The Delta is sinking, with the result that the levees keeping the river at bay have to be periodically raised.

But it is ordinary human activity -- not just the Corps of Engineers -- that has robbed the Mississippi basin of its most precious resource: the wetlands and riparian forests that once absorbed excess rainwater like so many giant sponges. In fact, the displacement of this natural flood-control system by an artificial one may, over time, increase the number of record-busting floods.

Even critics of the corps concede that protecting existing cities and towns is appropriate. Hannibal, Missouri, can only be thankful that it has just completed construction of a new $8 million floodwall, without which the Mark Twain home and museum would now be underwater. But absolutely critical to stemming future flood losses, a federal task force concluded last year, is protection of riverine floodplains from further development. In some cases it may even prove cost effective to relocate entire flood-prone communities. "We need to start giving land back to the river," says Larry Larson, head of Wisconsin's floodplain program. "If we don't, sooner or later the river will take it back."