AS the Mississippi River was expected to reach a record crest of 47 feet here yesterday - just five feet less than the height of the city's flood wall - an inevitable question throughout the Midwest bobs like a cork on top of the muddy crest: In addition to the heavy rains, why did all this flooding happen?
Over the last few weeks, much public debate has centered on the practices and culpability of the Army Corps of Engineers in the flooding of the Mississippi, which washed through a neighborhood here Sunday. Hundreds left when sandbags couldn't hold back water from a storm channel.
"After every flood we get blamed," says Gary Dyhouse, a hydrologist with the corps for 26 years. "But we have built a very good system of levees to withhold water," he says, "and to prevent more water from coming here to St. Louis, for instance. Without the levees and reservoirs, it would be much worse."
Environmentalists say this kind of reasoning overlooks the fact that flooded conditions along the heavily damned upper Mississippi are now the worst ever. Since the 1900s, the Army Corps of Engineers has built some 500 dams and about 10,000 miles of levees, nearly all designed to control the flow of rivers at a cost of $25 billion.
Brig. Gen. Stanley Genega, director of civil works for the corps, says this investment in federal levees and dams has prevented more than $200 billion in flood damages since 1937, including $8.2 billion in the Midwest.
"There are 36 reservoirs up the river from here," Mr. Dyhouse says. "At a minimum, those reservoirs lop off three to four feet from the crest here."
Not many environmentalists seem to agree with Dyhouse. "What we have today is a kind of a man-made disaster," says James Tripp, general counsel for the Environmental Defense Fund in New York. "The construction of levees, to an extraordinary degree, restricted flood-plain capacity, and rivers respond to these kinds of restrictions, whether they are tributary dams or levees or channelization."
Without dams and levees to contain them, rivers naturally follow a meandering pattern. They can spread out over nearby lower areas leaving sediment behind and enriching the soil.
The wetlands, backwaters, and side channels help a river adapt and change. Flood plains absorb water slowly and then release it slowly. Ecologists contend that dams change the temperature of water and alter the nutrient patterns of organisms.
Because of levees, farming, and development, Missouri has lost nearly 80 percent of its wetlands over the last 60 years.
"Some of that is due to federal projects that seemed reasonable in the 1920s and '30s," Dyhouse says. "The corps built dams, and the Mississippi was narrowed. There were trade-offs made then which didn't [take into account] the ramifications of the decisions. Environmental restoration is part of the corps's plans today."
The Mississippi serves as the catch basin for parts of 35 states and Canada. The end result of the slow modifications and alterations to the river over the years, according to environmentalists, is a river that runs much narrower, more swiftly, and is very much "engineered," although the flooding today proves somewhat that the river balks at the experience.
"If you channel the river, it moves faster," Mr. Tripp says, "and if it goes faster, then levees prevent it from overtopping. Going faster also means there is more upstream erosion. The river starts carrying more sediment, which has to be deposited in various places, changing the bottom topography and configuration."
In June, Missouri had nearly three times the normal amount of rain.
Over the past two weeks, some locations have had as much as five times the usual amount. With the jet stream flowing steadily to the northeast, the effect has been to hold in place plenty of heavy storm systems. "A stationary front has been hanging over the Midwest for more than six weeks," Dyhouse says.
So much water is pouring by St. Louis that Dyhouse estimates that it will reach over 900,000 cubic feet a second, or just over 7 million gallons, early this week.
In 1992, a federal task force on flooding concluded that some aspects of flood control worked well. But flood damage had cost the American taxpayer more than twice as much a year in the 1990s as in the years just before World War II, according to the Environmental Defense Fund.
Kevin Coyle, the president of American Rivers, a Washington-based group that monitors rivers, suggests a number of ideas to help restore some natural characteristics to the Mississippi. He says that, as much as possible, the river should be linked again with natural flood plains. He says that if levees are rebuilt after this flood, they should be built well away from the river.
If new levees are built, priority protection should go to communities to prevent damage and loss of life, he says.
Finally, he wants a new national flood-insurance program that rewards communities for keeping flood plains natural and unbuilt.