Flood of evidence


Furious floods

Too many floods

Fewer trees = more floods?

Wetlands and floods

Flood prevention: the earthmover approach
















 















Sandbag levee in St. Genevieve, Mo.
Courtesy FEMA.
































 





























photo of the Big Muddy reserve The Big Muddy reserve.
U.S. Fish & Wildlife Service








 








A barge string makes its way up the Mississippi River, which has been converted into a barge canal with dikes, levees, dams and channelization.

Copyright David Tenenbaum.


Structural solution -- or problem?
Animation of three narrow rivers inside their banks and levees before the flood. Three swollen rivers during the flood, then sand deposits after the flood receded. Three views of the junction of the Mississippi, Missouri and Illinois Rivers: before, during and after the great flood of 1993. The pinkish sand in the last pic was left by the flooding river. Some deposits were six feet deep, enough to destroy farmland.
Courtesy NASA.
If the destruction of wetlands and forests can unintentionally increase river flooding, what about intentional construction in rivers and floodplains? In the United States, as in many other countries, floodplains have been a focus of development. Simply, people like to live near rivers -- for farming, water, transportation, and, once, waste disposal.

In many major American rivers, the U.S. Army Corps of Engineers has built a wide range of navigation and flood-control structures:

  • Dams create lakes for irrigation, navigation and flood control.

  • Channels allow ships and barges to haul bulk commodities like oil and grain.

  • Levees (dikes built parallel to the flow) restrain the river, helping form deep navigation channels and offering a semblance of protection to land in the floodplain.

a levee with sandbags and flooded river Throughout the 20th century, the Corps built and maintained an extensive system of locks, dams and levees on the Mississippi and Missouri Rivers, which drain most of the United States, east of the Rockies.

To farmers, barge companies and real estate interests, levees are critical for taming the rivers. But to environmentalists, they are artificial restraints that promote reckless development and farming in the floodplain. Certainly, some major rivers have been sundered from their floodplains. The Lower Missouri River, for example, occupies only about 10 percent of the floodplain, says Galat (see "Flooding to Restore... " in the bibliography).

Plain flood
The natural role of a floodplain is to carry excess water during periods of heavy runoff, but when the floodplain is walled off behind levees, the artificially narrow river must rise higher to compensate. "For the same discharge rate, rivers rise higher than they used to," says Galat. "It doesn't take a rocket scientist to figure that one out."

And while levees do protect farms and towns during minor floods, the flood of 1993 demonstrated that giant floods will still reclaim the floodplain, no matter how high the levees.

The logical move, says Galat, is to get out of the line of fire -- to move away from rivers that refuse to be tamed. That's been done, to some extent: After the 1993 flood, several towns were relocated above the Mississippi and Missouri River floodplains.

But Galat observes that development is continuing in the floodplain. "There was a lot of fanfare about moving towns, but in the big scale, it was just fanfare. There's been little fundamental change in floodplain management." Malls and homes are being built smack in the floodplain, he observes, behind restored levees. Eventually, these levees will break again, he predicts, if the water does not simply rise above them.

Galat is one of many river scientists who favor putting the floodplain back to work as natural damper on flood heights and source of wildlife habitat. Since the 1993 flood, he says, 50,000 acres of floodplain in Missouri alone have been returned to the floodplain by opening levees in areas like the Big National Muddy Fish and Wildlife Refuge.

Like wetlands and forests, there are limits to how much levee removal can help. No matter how much he favors returning the floodplain, Galat insists this would not affect gigantic floods like the '93 on the Mississippi-Missouri system -- so many levees broke that the rivers occupied essentially their entire historical floodplains -- and still produced a whopper of a flood. In other words, even if some levees were removed, the river would likely run over the remainder during epic floods.

Rather than worrying about floods like the 1993 edition, which only come every 100 years or so, Galat says it's more sensible to examine what the effects of "messing with the river" are on the floods that occur every couple of years or so. The height of these floods, he says, is profoundly increased by building levees, wetland loss, deforestation, stream channelization and changes in land use in the watershed.

Five barges are being pushed upriver by a tug, visible in the background. Each barge appears to be more than 100 feet long.
What have we done to the flooding picture?
Galat insists that channelization and building "was not sensible," but rather reflected "the human attitude that technology will solve all your problems. The flood situation is part of the arrogance of humanity and technology" that we can live above nature. With river alterations and development in floodplains, he says, "the bottom line is that you will pay sooner or later" in the next flood. The costly and futile struggle against floods reflects a mistaken assumption, Galat concludes. "A flood is not a disturbance of a river. The absence of a flood is a disturbance of a river."

Water's rising! Check out our flood bibliography before it gets too wet...



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