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Louisiana

Largest Floodplain Restoration in Mississippi River Basin


Flooding at Mollicy Farms

In 2009 and 2011, high water levels created flood conditions at Mollicy Farms along the Ouachita River in Moorehouse Parish.

Floodplains by Design

Healthy floodplains can help increase flood protection, recharge aquifers, and improve wildlife habitat. This animated feature illustrates how we can harness these rich ecosystems to benefit both people and wildlife.

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Reconnecting the Ouachita River to Its Floodplain

The project is the largest floodplain reconnection and reforestation in the United States.

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US FWS manager, Kelby Ouchley, and TNC Board member, Tommy Barham, looking at the Mollicy floodplain. 

"With the levees in place, fish are cut off from the floodplain and rainwater gets trapped inside the levee where it sits on the trees for too long, which can kill young trees." 

Keith Ouchley, director of The Nature Conservancy in Louisiana

Floodplain Reconnection

The Nature Conservancy is working with partners to reconnect 25 square miles of former floodplain forest back to Louisiana’s Ouachita River, which is located within the Mississippi River Basin.

The $4.5 million restoration project, the largest in the history of the Louisiana Chapter, includes removing portions of the 17-mile-long, 30-foot-tall levee constructed more than 30 years ago. Believed to be the largest floodplain reconnection project in the Mississippi River Basin and one of the largest in the entire United States, the project will help alleviate flooding downstream, improve water quality (reduce both nutrients and sediments) and restore valuable fish and wildlife habitat.

This is a great example of private-public partnership that has relied upon funding from diverse partners that include the Louisiana Department of Environmental Quality, Coypu Foundation, Coca-Cola, Environmental Protection Agency, Freeport-McMoRan Copper & Gold Foundation, Shapiro Foundation, North American Wetland Conservation Council, LA CAT and many others.

“We believe the values associated with this type of restoration are many—from wildlife habitat and water quality improvement to floodwater storage—and we hope to prove that here at Mollicy, “ says Keith Ouchley, director of The Nature Conservancy in Louisiana.

 

Reconnecting the Ouachita River and Its Floodplain

Mollicy Farms was once part of a vast expanse of bottomland hardwood forest seasonally inundated by the floodwaters of the Ouachita River. It was deforested and separated from the river via the aforementioned levee in the late 1960's so that the land could be used for agriculture.

In 1998, the Conservancy helped the U.S. Fish and Wildlife Service acquire much of Mollicy Farms and add it to the Upper Ouachita National Wildlife Refuge. The Fish and Wildlife Service planted more than three million bald cypress, oak and ash trees on almost 11,000 acres of the refuge to restore the floodplain forest.

TNC and USFWS planned to breach the levee in 2009 to restore the connection between the river and its floodplain that is not only critical to the long-term health of the forest but to the fish and other aquatic life in the Ouachita River.

“Before the levee was constructed around the Mollicy Farms unit, the river would flood each year in late winter and early spring, overflowing its banks and seeping through the bottomland hardwood forest,” says Ouchley.

“Fish would come into the floodplain to spawn in the spring, and the area was a mecca for waterfowl and other wildlife,” Ouchley adds. “With the levees in place, fish are cut off from the floodplain and rainwater gets trapped inside the levee where it sits on the trees for too long, which can kill young trees like those planted at Mollicy in recent years.”

Mother Nature Intervenes

Everything was going according to the restoration plan at Mollicy Farms… until Mother Nature intervened.

After an extremely wet spring in 2009, the Ouachita River rose to a historic flood stage on May 23 and spilled over several low spots on the levee. The levee failed catastrophically at two locations and water rushed into the 16,000 acre Mollicy unit. A levee breach is just what TNC and USFWS had in mind, although they had planned to breach the levee themselves.

A levee breach was just what The Nature Conservancy and the U.S. Fish and Wildlife Service had in mind, except that the partners had spent more than a year planning a $4.5 million project to permanently breach the Mollicy levee themselves.

“This is a perfect example of how real world conservation is sometimes quite different from textbook conservation,” says Steve Haase, a Conservancy biohydrologist for the Louisiana chapter working on the project.

While the May breach was not in the partners’ plans, it did not significantly affect the reconnection project

Plans May Go Awry, But All is Not Lost

The partners hoped to avoid a catastrophic breach to minimize the amount of sediment that would be washed onto the floodplain or downstream due to rapid water movement from the Ouachita through the levee. They were also concerned that, if the breach holes were too small, there would be no good way to get the water from the Ouachita back out of the floodplain, which could be detrimental to the newly planted trees.

"We'll need to wait for the site to dry out," says Haase. "Then we'll widen the two existing breaches, make needed connections to existing internal drainages to ensure better drainage of the site, and proceed with construction of the additional breaches as planned."

The Future of Mollicy Farms

We’ll have completed our first 3 years of monitoring the project area to determine changes in water quality, as well as to fish, amphibians and reptiles. Our data indicate that many species have begun using the historic floodplain again. Bird use, especially waterfowl and wading birds, have come back to Mollicy Farms in great numbers (one winter survey indicated over 70,000 geese and ducks on the site). Water quality parameters (nutrients and sediments) coming off the site into the river have not dramatically improved yet, but are expected to as restoration proceeds.

The next phase of the restoration involves restoring the internal hydrology of the floodplain. We intend to recreate a semblance of the network of bayous and embedded wetlands that historically would hold water on Mollicy. By holding water longer and slowing down the velocity of water flowing back to the river as floodwaters recede, we anticipate that nutrient and sediment export to the river will be minimized.

In addition to continued monitoring, we will begin this work in summer 2013 with the Mollicy Bayou restoration. This will involve creating almost 3 miles of bayou and embedded wetlands. Other work will involve plugging straight-line agricultural ditches, removal of roads, culverts and other impediments to historic hydrologic function.

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