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Wetlands as Infrastructure



Thompson Bend at Missouri Sister Island, A Point Bar

As a river meanders downstream it shaves sediment from the concave bend, carries it downstream, and deposits it on the convex bend. In time the neck of a point of land--called the point bar--between two bends narrows. In a flood the river can cut a new channel across the narrow neck. The Mississippi threatened to do that at Thompson Bend, just north of the confluence with the Ohio River.

Missouri Sister Island: Dry Bayou/Thompson Bend

Mississippi County, Missouri

South of Horseshoe Lake and just north of its confluence with the Ohio, the Mississippi makes a great S, slightly canted northwest to southwest, enclosing two point bars, Dogtooth Island in Illinois on the west and Dry Bayou/Thompson Bend in Missouri on the east. Both lie within the active floodplain of the Mississippi. Both are given over to rich agricultural land, 10,000 acres in the case of Dry Bayou-Thompson Bend. The distance around the bend is seventeen miles. Given a big enough flood the Mississippi could cut a new channel across the narrow neck of the point bar and shorten that distance to a mile and a quarter. Since 1981 the river has been threatening to do just that.

Flooding in the bend runs two ways: Should the Ohio be in flood and the Mississippi not, it backs up into the Mississippi, causing quiet, lake-like conditions. Should the Mississippi be in flood and the Ohio not, its current rages against point bar as it surges toward a lower Ohio. The river from the upstream bend to the downstream bend drops a half-inch per mile over the seventeen miles. The landscape from the upstream side of the point bar to the downstream side drops fourteen to sixteen feet. Should the Mississippi have its way and cut a new channel it could create a cutoff, destroy thousands of acres of valuable farmland, and erode the mainline levee near Birds Point, less than a mile away. Downstream traffic would stop at upstream of the bend; upstream traffic would stop at Cairo, Illinois. Not even the smallest tow could manage the new channel. Navigation through the old channel would grow iffier by the day as it grew more and more shallow. A rupture in the levee could send a flood cascading as far south as Helena, Arkansas, where the foot of Crowleys Ridge would direct the flood back to the Mississippi through the mouth of the St. Francis River.

In 1981 a thin line of trees anchored the bank of the upstream bend at the mouth of Dry Bayou. A small private levee kept the river out of the adjacent fields, not enough to keep the river from beginning the process of cutting a new channel at the mouth of the bayou. In March the river overtopped its bank, washed out the thin line of trees, broke through the levee, and began cutting a new channel across Dry Bayou-Thompson Bend. It repeated the process in 1983, 1984, and 1985, each time eroding 40,000 tons of topsoil per acre and removing any trees that might be in its way. The farmers, who were losing their fields, and the Corps of Engineers, which was losing its navigation channel, formed an alliance to stop the river from searching out a shorter, steeper route downstream. Over the next fourteen years Lester Goodin and his colleagues, who farmed the point bar, and Jerry Rapp, a hydraulic engineer with the St. Louis District, worked out a solution that was environmentally sound and hydraulically effective. They planted trees.

The Corps of Engineers has long used revetments as infrastructure–first willow mats, then riprap, then concrete mats–to armor the concave bends in the river against erosion. At Dry Bayou-Thompson Bend revetments would be prohibitively expensive and ultimately ineffective. Rapp and Goodin came up with a design that confronted the river with successive vegetative screens, placed perpendicular to its flow-line across the neck of the peninsula. 

Dry Bayou/ Thompson Bend: Lester Goodin’s Tree Screen

Mississippi County, Missouri

In January 1986 Lester Goodin and his partners planted cottonwood stakes and green ash cuttings in the snowy ground. In all they planted 125 acres in green ash, cottonwood, and pecan: screens of hard, fast-growing green ash on the upside of the bend to withstand the force of the current and the debris the river would throw at them; then screens of soft, fast-growing cottonwood to catch the sediment that made it through the ash. They planted pecans, whose nuts were food for migrating ducks, in the fields because they could trim the lower branches and farm underneath them. It was their first effort to stop the Mississippi scouring a new channel through the point bar. By 1993 they had trees sixty to seventy feet tall, facing a 500-year flood.


Tree Screen

Tree Screen




 On the eve of the Flood of 1993, the Ohio River at Paducah, Kentucky was sixteen feet below flood stage. “The headwater of the ‘93 flood was terrific and the Ohio sixteen feet down, it was a real river rapids that came through here.” At Dry Bayou-Thompson Bend the river tried to break through the defense Goodin and Rapp had erected. The flood surged through screen after screen, losing half its power against the first hundred-foot screen. The river deposited more sediment and debris than it scoured as it surged across the point bar. It killed some of the trees, but they remained standing, their roots anchored in the soil. 

The Floods of 1994 and 1995 removed the dead trees, prevented regeneration, and left the point bar vulnerable once again. Rapp and Goodin went about the business of replanting the screens. They varied the species of trees, adding cherrybark and willow oaks, swamp tupelo, and lots and lots of cypress, the first on Tywappity Bottom in 125 years. And, the trees invited more trees. Birds, roosting in the forest, dropped mulberry, box elder, and dogwood seeds. A diverse forest awaited the next big flood.

Out of the Dry Bayou-Thompson Bend project came a commitment from the Corps of Engineers to establish more riparian corridors where necessary along the riverbank, strips of trees three hundred feet deep along twelve miles of restrictive easement. The Corps would compensate landowners for the easements and give them right of first refusal of any timber cut from the easements. 

            U.S. Army Corps of Engineers, St. Louis District, “Thompson Bend Riparian Corridor Project,” http://mvswc.mvs.usace.army.mil/thompson/slideshow.htm;  U.S. Army Corps of Engineers, St. Louis District,  “Thompson Bend Riparian Corridot Project, Project Description,” http://mvs-wc.mvs.usace.army.mil/thompson/projectdescription.htm;  Hatfield, Terrie, “Tree Screen Saves River Channel,” Engineer Update, October 200, Vol. 24, No. 10, http://www.hq.usace.army.mil/cepa/pubs/oct00/story12.htm.






One Response

  1. very nice. Lester Goodin was instrumental in this project and is an expert in flood plain restoration and re-establishing riparian corridors to control erosion.

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