The Lower Mississippi River is essentially a ditch, a navigation channel that carries barges. Wing dams, dikes set perpendicular to the bank, direct the force of the current to the center of the river to assure a deep navigation channel. Closing dams across side channels that run between islands and the bank make it impossible for the river to adopt a side channel as its main channel.
Now The Nature Conservancy has supported a Corps of Engineers study to the tune of $400,000 that will examine the possibilities of opening these side channels. Of that $400,000, $200,000 comes from Wells Fargo. The study is due out in 2014.
The engineers have never done such a study on the Lower River, south of its confluence with the Ohio. But the St. Louis District of the Corps of Engineers has been opening up side channels for years and has an instructive video on YouTube.
From the Mississippi: A Visual Biography:
“The St. Louis District devised a tabletop model on which they could test ways to move water and sediment around and create habitat for fish in the remaining Middle River side channels. The small scale allowed them to model each side channel individually. They could try out various schemes: modify existing river wing dams, notch or remove closing dams across the heads of side channels, install chevron dikes or traditional dikes or hard points in the side channels, or dredge excess sediment from them.
“Notches in closing dams allowed water to flow through and scour sediment from side channels. Removing them altogether was better. Hard points, mini-wing dams constructed of rock or wood and set in side channels, forced water to scour side channels without a significant build-up of sediment between points. At the same time hard points scoured deep holes, habitat for fish, particularly catfish, under the points. Small chevron dikes, “C”-shaped dikes, allowed water to flow around them and open up side channels, while producing a scour hole on the inside of the dike for fish habitat. Once the collaborators understood the dynamics of creating habitat in each channel, it was an easy step to move on to constructing the improvements.
“At the end of the 1990s the collaborators went on to develop the Mississippi River Side Channel Rehabilitation and Conservation Project with the aim of restoring the twenty-three remaining side channels on the Middle River and ten of those that had closed completely. They carried their plan beyond restoring the channels themselves to acquiring land adjacent to the channels. Given the additional land they could reforest the banks of the channels, some of which were farmed clear up to their edges; reestablish the ridge and swale bottomland topography, where water flowing through the channels eroded or deposited sediment on the banks; regain cut bank habitat, places where fish could rest and nest; provide the public with access to the side channels for recreation and education. They noted that in some cases it would make more sense for private individuals, industry, or organizations such as The Nature Conservancy the American Land Conservancy and to acquire the lands bordering the channels.”
As a part of the Middle Mississippi Side Channel program, the engineers examined Calico Chute and found it in pretty good shape. After the U.S. Fish and Wildlife Service established the Middle Mississippi National Wildlife Refuge in 2000, the agency considered including Calico Island in the refuge, should the funds ever become available to purchase the island from its present owner.
Attempts to create a side channel through the Jefferson Barracks Dike Field by notching the northern most wing dam opened up a pond at the head of the dike field, but failed to create a side channel along the true bank of the river.
The Corps video linked above shows that the engineers have taken their methods for opening side channels a step beyond notching closing dams. They are using SCEDs, wing dams that direct some of the river’s current into the closed side channels.
Filed under: Mississippi River, Side channels | Tagged: deep holes, lower mississippi river, navigation channel, riddles point, side channels, The Nature Conservancy, Wells Fargo, wing dams, youtube |