The Army Corps of Engineers has introduced navigational structures into the channels called chevrons, bendway weirs and wing dikes, which are used to make the river more accessible to navigation by huge boats. These structures "basically impede the flow, much like speed bumps impede a car's ability to go down the road quickly," says Criss. "These channel structures are intended to benefit the navigation industry, and they actually make flooding worse by constricting the channel."
The great barges that travel the mighty Mississippi need 9 feet of water to maneuver safely. Dredging to make sure that the channel is deep enough at all times is expensive. So the Army Corps of Engineers puts in place structures to try to keep the channel deep enough, and consistent enough for shipping commerce to continue, even on the driest day of the driest month of the year.
One such structure is a wing dike, essentially a big rock wall built perpendicular to the bank to concentrate the flow of water on the other side of the channel. Under flooding conditions, the dike can hasten the height of the water. Another structure, called a bendway weir, is an underwater wall, up to 50 feet high, built in the bends in the river to keep the river wall from being eroded and keeping the channel in place. "Bendway weirs are entirely invisible at the surface," explains Pinter. "They are vertical walls built at the bottom of the channel to direct the flow into the navigational portion of the channel."
Finally, chevrons, some in the shape of the St. Louis arch, are great piles of boulders placed in the river, designed to divert the flow to one side. Chevrons make one side of the river flow very quickly, and the other side have very low flow. "They slow down the water during flood stages, and cause flood stages to rise," says Kusky.
It's humans, not biblical downpours, that have raised the Mississippi River water level 10 to 15 feet higher in the past 100 years. "We've made the river flow through a much narrower channel, and we've put these piles of rocks in the river which slow down the flow," says Kusky. "The only place for the water to go is to rise upward and increase the height of the floods."
To get a sense of how much the Mississippi has been changed over the years, Criss notes that on June 26, 2008, in St. Louis, a day when the river was high, but not breaking through the levees, the river stage was just over 37.5 feet. In the entire period between 1850 and World War II, there was only one time, in 1903, that the river was higher at St. Louis, and that time it was just 6 inches higher. Since World War II, it's been higher than last Thursday 11 times. "We've changed the conveyance of the rivers, their ability to carry the water away, and we've walled off the river from their natural flood plain," says Criss. "What's the river going to do? It's going to rise and rise and rise."
The U.S. Army Corps of Engineers denies that its structures built for navigation have contributed to flooding. "The U.S. Army Corps of Engineers does not agree with the conclusions that have been drawn concerning any connection between especially engineered river training navigation structures and flooding," says Alan Dooley, a spokesperson for the St. Louis District, U.S. Army Corps of Engineers. While Dooley wouldn't respond to specific charges leveled by the scientists, he does add: "We recently have entered into a scientific, in-person exchange of ideas with the gentlemen who have expressed these viewpoints and believe that this process is the best and most productive avenue for a professional dialogue. We hope to continue our discussions and exchanges of ideas in the future."
The gentlemen in question would like to see the Army Corps stop the construction right away. Instead of building more bendway weirs, wing dikes or chevrons, the scientists argue that the Army Corps should dredge to keep the rivers navigable for shipping. The shipping industry could use smaller barges, and wouldn't need such a deep channel to accommodate them. "We've progressively increased the demand on how deep the channel needs to be," says Criss. "Why must we run quarter-mile-long barges on these rivers? On the Rhine, they use smaller boats, and they might have to hire a few more guys to run them."
The perennial answer to managing the Mississippi is to build more levees, but that's the wrong way to the future, say the scientists. Until we dial back the building, heavy rains will remain bad news for people who live or work in a flood plain.
"Nobody is saying we should go around the country tearing down all the levees, because they're protecting homes, businesses and farms," says Kusky. "But right now there are also many places up and down the river system where new levee systems are being built or being proposed. Those are the kind of things that we should stop right now. There's no reason to build new levees and advertise new homes on the flood plain. It's not safe anymore."
About the writer
Katharine Mieszkowski is a senior writer for Salon.
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