Unnatural disaster: human factors in the Mississippi floods.

It’s happened again. For the third time in 15 years the Mississippi River massively burst its banks this spring, inundating tiny Missouri towns such as Winfield (population 720) and Foley (population 178), causing potentially billions of dollars’ worth of destruction—although the damages are still being assessed—and hiking corn prices to $8.00 a bushel in the wake of the lost crop. On 22 April 2008 scientists with the U.S. Geological Survey (USGS) measured the largest water volume on the lower Mississippi River since 1973, with a flow of 1.8 million ft3/sec, enough to fill more than 20 Olympic-size swimming pools in 1 second. 
 
The environmental fallout from the 2008 floods is still being assessed. The danger of floodwater is not simply that its level is too high, says Robert Criss, a geologist at Washington University. “Floodwaters are heavily polluted with sewage and filth, commonly bearing counts of coliforms, fecal Streptococcus, and other bacteria of many thousands per deciliter,” he explains. “The waters are laden with contaminants including agrochemicals, oils, detergents, and toxic metals. They are highly turbid, typically bearing particulate loads a hundredfold or more higher than normal river waters.” Those pollutants, contaminants, and sediments can be carried into homes, where the lingering dampness promotes mold growth. Moreover, floodwater pools trapped behind failed levees serve as breeding grounds for mosquitoes, flies, and other disease vectors. 
 
Meanwhile, observers are asking how such devastating floods could have occurred again so soon. The massive flooding is attributed largely to torrential spring rains in the Upper Mississippi Valley, which Paul Rydlund, a supervisory hydrologist with the USGS Missouri Water Science Center, says were even greater than those preceding the record-breaking 1993 Midwest flood. But as heavy as those rains were, the question in the minds of some is whether they were made worse by structures such as levees and other man-made interventions wrought upon the Mississippi River over time.


The Hand of Man
Changes to the river are hardly a latter-day phenomenon. John Anfinson, a historian with the National Park Service's Mississippi National River and Recreation Area, notes that the early French explorers of the sixteenth and seventeenth centuries recognized that to capture the economic potential of the Mississippi "you have to harness the river; you have to make it behave." That harnessing began with the settlement of New Orleans in the early 1700s, where the first levees were thrown up to create a city that actually lies below sea level. Thereafter, Anfinson says, "The levee system started growing upriver and the navigation system [i.e., dredging and channeling endeavors] started growing downriver." In the centuries that followed, shipping and agricultural interests pressed Congress to allow alteration of the river. Deepening channels made shipping easier, and construction of levees permitted farming and the establishment of towns and cities along the river's banks.
Many experts point to levees as a major culprit in flood devastation. Levees narrow the flow of the water, preventing it from spreading out into the floodplain and forcing it to move faster, explains geologist Jeffrey Mount, who directs the Center for Watershed Sciences at the University of California, Davis. As a bolus of floodwater moves down a river, levees can get overwhelmed in their work. "The dark secret that no one wants to share is that there are two kinds of levees: those that have failed and those that will fail," Mount says. And when that levee fails with a massive wall of water pressing on it, the water rushes with great force onto the land behind the levee. "The power of water is a function of the difference in elevation between the top of the water and the adjacent land," Mount explains. "So the greater that difference, the more powerful the flow that comes out onto that land in terms of its velocity and its power to erode." Wing dams on the river are another factor in exacerbating floods, says Criss. These rock jetties, situated roughly perpendicular to the riverbank, aid shipping by preventing the accumulation of sediment so the river channel stays deeper. Deeper water moves faster, meaning the impact of floods can be greater.
Criss points to another problem: "There are general changes to the land that decrease the permeability of soils. As we convert our forests and prairies and fields to subdivisions, we increase the rate of runoff [into the river]-that's the ubiquitous footprint of man." According to geologist Nicholas Pinter of Southern Illinois University Carbondale, one particular land use change is quite serious-tile drainage. Because many agricultural soils are too poorly drained to naturally serve as good farmland, farmers install subsurface drains ("tiles"). "When it rains," Pinter says, "the water comes out of farm fields faster than it would otherwise."

Ripe for Disaster?
Land development in floodplains is a perilous exercise, according to Gerald Galloway, a professor of engineering at the University of Maryland and former commander of the U.S. Army Corps of Engineers (USACE). For one thing, he says, developers rely heavily on floodplain maps issued by the Federal Emergency Management Agency (FEMA) that demarcate where we can expect so-called 100-year floods-the sort of flood that can be expected once every 100 years. People erroneously believe if they are outside that demarcation they are safe. However, Galloway cautions, such maps are estimates only. Moreover, he says, "The records of the past don't necessarily match the pattern we're in right now in terms of the weather." Criss agrees, saying that the rivers of today are not the rivers of the past, and that there is simply not enough historical information on which to base the notion of a 100or 500-year flood. Besides, at many places, he argues that what have been called 100-year floods are now 10-year floods due to a combination of changing conditions over time.
Larry Buss, who chairs the USACE National Nonstructural/Flood Proofing Committee, says that when a levee is built in compliance with the requirements of the National Flood Insurance Program, there is no longer any floodplain management in the area behind the levee. All kinds of new development can then occur in the area landward of the levee as if the floodplain no longer exists-when in fact it does.
"Politically, it's more acceptable if politicians come to people and say 'I'm going to remove the flood threat from you by supporting building a levee so you can live in that floodplain as if the floodplain no longer existed even though flood risk remains,'" Buss says. "That's more politically acceptable than telling them 'I'm supporting a buyout' or 'I'm supporting a relocation plan where we'll move you to high ground and have you safe from floods forever.'" However, when the levee does have a problem, the damages are much greater than they might have been because of the increased development in vulnerable areas.
Buss says the U.S. approach to levees has been too focused on what he calls short-term economic/political gain that is ultimately transformed into long-term economic/political loss when major flooding results in levee failure or overtopping and then catastrophic flood damages and perhaps loss of life. In these cases, he says, there is a major disconnect between those who make land use decisions (i.e., local communities) and those who pay for the ill-starred consequences of those decisions (i.e., state and federal taxpayers).

The Role of the Corps
Noting the impact of man-made modifications of the river, critics question the judgment of the USACE in carrying out such modifications. "The Corps comes in with a community-by-community project with measures like levees, and it looks at that levee; it doesn't look at the whole Mississippi as a system. And that's a problem," says A 392 VOLUME 116 | NUMBER 9 | September 2008 • Environmental Health Perspectives

Spheres of Influence | Unnatural Disaster
The Mississippi River snakes through downtown LaGrange, Missouri, 21 June 2008. Many engineers and floodplain managers believe the risks that come with siting towns in floodplains are unacceptably high.

Larry Larson, executive director of the Association of State Floodplain Managers.
Pinter charges that the USACE has failed to examine the possibility of elevated flood risk in many navigational engineering projects, including a $5.3 million project in 2007 to construct three arc-shaped chevrons and other structures in the St. Louis Harbor area. The chevrons work much like wing dams, but they are located wholly in the river rather than extending from the shore. Composed of rock, they are designed to lessen the need for continual dredging of St. Louis Harbor, deepen the river bottom, and straighten the flow of the river.
"The benefit of those structures was calculated versus their cost," says Pinter. "The benefit was reduced dredging to help maintain the navigation channel. The cost was the construction cost with no calculation whatsoever of the additional financial cost in terms of elevated flood risk." But Robert Davinroy, chief of river engineering at the Corps' St. Louis office, says the USACE did examine the question of elevated flood risk. "We know how these structures work," he says. "They're submerged by about twelve feet when the river gets to flood stagethey have no effect on flood heights." He adds there are no data to show the chevrons have any effect on the height of floods.
As far as levees go, Galloway argues that the USACE is quite interested in understanding the impact of these structures on floods. "In the greater St. Louis area the Corps has been asking [Congress] for money for a study to see what is the cumulative effect of a lot of little levees. So far they haven't gotten the money. People are not as much interested in learning that sort of information as they are in building levees," says Galloway, referring to those legislators and constituents who view levees as flood protection. For example, a 20 September 2007 article in Time magazine that sharply criticizes a USACE flood control project in Missouri notes that Senator Kit Bond (R-MO) and Representative Jo Ann Emerson (R-MO) were responsible for pushing the project through.
Politics and pressure do play significant roles in the selection of which projects to fund, notes Representative Eddie Bernice Johnson (D-TX), who chairs the Water Resources and Environment Subcommittee of the House Transportation and Infrastructure Committee. For instance, she says the USACE might initially say that a given project is not necessary. "The next time around they've been under so much pressure, they'll go along with it. I've seen that happen," she asserts. She says the pressure comes from local citizens through their representatives for projects that "shouldn't be funded," and the prospects for changing the system are dim.
Moreover, Galloway observes that when Congress authorizes a USACE project, the money for it is quickly appropriated. But when it comes to appropriating money to remedy any environmental problems resulting from the project, Congress is very slow to allocate funds, an observation Johnson says is "probably true." A 2005 Government Accountability Office report titled Wetlands Protection: Corps of Engineers Does Not Have an Effective Oversight Approach to Ensure That Compensatory Mitigation Is Occurring took the Corps' mitigation efforts to task when it comes to restoring wetlands as part of mitigation efforts, labeling USACE guidelines as "vague and internally inconsistent." However, by the time the same office issued the 2008 report Compensatory Mitigation for Losses of Aquatic Resources, mitigation efforts had reportedly improved and the USACE was meeting mitigation requirements except for the stipulation that any concern voiced about a project receive a 60-day review.