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Louisiana’s Plan to Combat Wetlands Loss Brings Mississippi River Sediment Back Home

The top minds in wetlands ecology, hydrology, and geology from across the world have spent half a century investigating Louisiana’s unprecedented, catastrophic coastal land loss. And, after poring through volumes of data, comparing maps, and examining soil content, tides, wind, subsidence, rising sea levels, and numerous other factors, the one question nearly all of these experts ask when it comes to reversing loss and sustaining the system is, ‘Why not use the Mississippi River?’ After all, the Mississippi and its oft-shifting delta are responsible for building nearly all of South Louisiana’s extensive network of swamps, marshes, tree-lined ridges, and barrier islands over 10,000-plus years.

It’s just in the last 100 years that the silt, clay, and sand carried by the mighty Mississippi have largely lost contact with the wetlands, due to flood-control and navigation levees meant to tame the channel. Construction of innumerable oil- and gas-field canals and man-made navigation channels have also altered water flows, driving saltwater deep into marshes and swamps. The result has been the loss of nearly 2000 square miles of coastal lands.

That’s why, since 2013, the TRCP and our partners in saltwater fisheries conservation have recommended using oil-spill recovery funds to build diversions along the Mississippi River that will allow the flow of silt and sediment to imperiled wetlands east and west of the river. Now, regional agencies are closer than ever to making this happen.

Diversions of water and sediment will capture some of the land-building materials currently being lost to the deep waters of the Gulf as shown in this spring-time sediment plume and direct them into shallower marshes and open water to rebuild and sustain wetlands. Image courtesy of NASA.

Diversions of water and sediment will capture some of the land-building materials currently being lost to the deep waters of the Gulf as shown in this spring-time sediment plume and direct them into shallower marshes and open water to rebuild and sustain wetlands. Image courtesy of NASA.

After more than a year of intensive modeling and examinations of potential impacts, the Water Institute of the Gulf and Louisiana’s Coastal Protection and Restoration Authority has determined to move forward with two diversions. The Mid-Barataria Diversion, near the town of Myrtle Grove on the west bank of the river, is expected to move as much as 75,000 cubic feet of sand- and silt-laden waters per second to build and sustain more than 25,000 acres of marsh. On the east side, the Mid-Breton Diversion will move as much as 35,000 cubic feet per second to build and sustain 15,000 acres of wetlands. Even with these two diversions, nearly 60,000 acres of wetlands near Bird’s Foot Delta are expected to vanish in the next 50 years, but without these projects, coastal experts project the loss of 250,000 acres of coastal wetlands in that time.

The agencies project that there are changes on the way, but these changes do not include devastation to towns and fisheries, as some have predicted. Building and sustaining wetlands using diversions will increase water levels in the basins—probably more than two feet in the Barataria Basin, which is expected to be periodically between early February and early July, and less than that in the Breton Basin. This water will make its way into surrounding lakes, bays, and, eventually, the Gulf of Mexico. Also, as expected, salinity levels will drop in both basins when diversions are operating and return quickly as flows are reduced in the summer and fall. This is similar to what currently happens in these areas, especially in the Breton Basin where there are many existing outlets for river water.

The good news for anglers: The diversions will be a boon to fish habitat, with more nutrients and greater interaction of fresh- and saltwater expected to stimulate forage production and expand the food available for popular recreational fish like speckled trout, redfish, flounder, black drum, and largemouth bass. Again, this mimics what is already happening in areas where existing diversions and natural crevasses create a smorgasbord of crawfish, crabs, shrimp, bluegill, shad, mullet, and menhaden.

There will, however, be impacts from freshwater on existing oyster leases, though the modeling shows no long-term, overall reduction in oyster biomass. Oyster harvesters want the state to identify where productivity will increase, decrease, or cease to exist—a reasonable request that the Louisiana Department of Wildlife and Fisheries and CPRA should make a top priority.

Overall, it’s an optimistic time for Gulf sportsmen, conservationists, and scientists. It seems that, after decades of watching our wetlands vanish, the Mississippi River will finally be given the chance to heal the Louisiana coast. “We are moving forward with addressing coastal land loss in a way that we’ve never done before,” says CPRA Chairman Chip Kline. “We are excited.”

We’re excited, too.

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  1. Turning the Tide – Environment & Society Spring 2016 - April 4, 2016

    […] Louisiana’s Plan to Combat Wetlands Loss Brings Mississippi River Sediment Back Home […]

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