Chicago — Those recent floods that hit parts of the Midwest so hard are the immediate result of unusually heavy and persistent winter rains.
But much of the damage wrought, according to veteran flood watchers and environmentalists, can be traced over the longer run to a mix of government and developer policies - policies that, in effect, have encouraged people to build near flood-prone areas and have caused smaller amounts of water to make an increasingly large impact.
''A storm of that magnitude in December is exceedingly rare,'' notes University of Illinois climatologist Wayne Wendland. ''If it had been snow, the same amount of water would probably have been spread around over several days and the flooding would have been alleviated.''
Yet many homes damaged in floods in Illinois, Arkansas, and Missouri were situated near flood walls and dams aimed precisely at controlling heavy amounts of water. Certainly the increase in flood control projects (the nation now has some 60,000 dams, for instance) has had some benefits. The problem, critics contend, is that the projects often have been doled out on a pork-barrel basis rather than by need. Also, they don't begin to solve the whole problem. Yet because the projects are there, many people assume it is safer to build closer to water than they otherwise would.
''A lot of flood-control projects are in the long-run detrimental because they give people a false sense of security that water won't be a problem,'' says Dr. John Marlin, a biologist with the Central States Resource Center.
In addition, many people who already have homes close to water where flooding has left its mark reason that it won't happen again soon. And many say they can't afford to move. At the very least, says Chuck Hoffman of the American Rivers Conservation Council, Washington should not encourage rebuilding on a flood site, as it did with mobile homes near Wilkes-Barre, Pa., after the Susquehanna River flooded in 1972. Two years later another flood hit. ''That was just poor planning,'' he says.
In spite of a more than $15 billion federal investment over the years in flood-control projects, the rate of flood damage in the United States increases each year. The US Army Corps of Engineers, which built many of the projects, contends damages would be at least five times greater without the dams, levees, and flood walls.
Still, structural solutions can handle onlya limited amount of water.
Certainly developer and government practices, which include filling in traditional swamp and wetland water-holding areas, the straightening of steams in river tributaries, and the construction of narrower, deeper navigational channels for shipping in major rivers, have played a significant role in flood damage.
''We're paving in the wetlands,'' says Oliver Houck, a Tulane University law professor specializing in environmental law. ''By destroying the holding capacity of the northern reaches of all our rivers, more water goes downstream faster than it used to. We need to slow it down, reopen some of the plumbing, and restore some of that natural storage capacity.''
One result of the varied policies: Less water now can do more damage. For instance, St. Louis University geologist Charles Belt has documented that construction of the main channel of the Mississippi River has resulted in a three-foot hike in its level over the last 50 years or so. Though water levels at St. Louis reached their highest point in the floods of 1973, a higher volume of water had passed by at least eight times in past years.
''Rains that used to just water our lawns now threaten our homes - we've turned it into an enemy,'' Professor Houck insists.
''The situation is making major floods out of minor ones,'' agrees Brent Blackwelder, Washington representative of the Environmental Policy Center. ''The flood control crisis is really a man-made one.''
That point was underscored in a National Science Foundation study on flood mitigation issued two years ago. It urged any federally funded development of flood hazard areas to carry a legal requirement that certain conditions (such as flood proofing or raising a structure's foundation) be met.
Environmentalists say the flood-control emphasis must shift from one of building more structures to better management of flood plain areas. They suggest using more of these as parks or recreation areas. They also urge better and more widely available mapping of flood-prone areas and installation of flood warning systems.