Great Rivers News

Mother Nature Takes a Hand in Floodplain Restoration

By Cate Harrington

Everything was going according to plan at the Mollicy Farms unit of the Upper Ouachita National Wildlife Refuge in northern Louisiana… until Mother Nature intervened.

After an extremely wet spring, the Ouachita River rose above flood stage on May 23 and spilled over several low spots on a 30-foot-tall levee separating the river and a portion of its floodplain. The levee failed catastrophically at two locations along the northwest segment, and water rushed into the 16,000-acre Mollicy unit, inundating agricultural land that had been restored to bottomland hardwood forest over the past 12 years.

A levee breach was just what The Nature Conservancy and the U.S. Fish & Wildlife Service had in mind, except that the partners have 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,” said Steve Haase, a Nature Conservancy biohydrologist working on the project.

While the May breach was not in the partners’ plans, it doesn’t significantly affect the reconnection project, but it will change the timeline as work cannot commence until the site dries out.

Reconnecting the Ouachita River and Its Floodplain

Once a vast expanse of bottomland hardwood forest seasonally inundated by the floodwaters of the Ouachita River, the Mollicy Farms unit was separated from the river in the late 1960s and early 1970s by a 17-mile-long levee so that the land could be used for agriculture.

In the 1990s, the Conservancy helped the U.S. Fish and Wildlife Service acquire much of the Mollicy unit and add it to the national wildlife refuge. The Fish and Wildlife Service planted more than three million bald cypress, oak and ash trees and a host of other native species on almost 11,000 acres of the refuge to restore the floodplain forest.

The partners were planning to breach the levee 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,” said Keith Ouchley, director of The Nature Conservancy in Louisiana.

“Fish would come into the floodplain to spawn in the spring, and the area was a mecca for waterfowl and other wildlife,” Ouchley added. “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.”

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.

“This doesn’t change our plans, but it does change our timeline,” said Steve Haase. “We’ll need to wait for the site to dry out. 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.”

Several partners including the Conservancy, Louisiana State University, the University of Louisiana at Monroe and the U.S. Geological Survey will monitor the project area for several years to see what kind of changes occur in water quality, as well as to fish, amphibians and other wildlife populations.

The project, which is believed to be the largest floodplain reconnection project in the Mississippi River Basin and one of the largest in the entire United States, will alleviate flooding downstream, improve water quality and restore 25 square miles of valuable fish and wildlife habitat.

“We hope that the Mollicy Farms site will be a model for floodplain reconnection and restoration up and down the Mississippi River,” Ouchley commented. “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.”

Watch a video about the project. This video is also available on the Conservancy’s Louisiana web site (see What’s News).