Atchafalaya River Basin

Many years ago, The Nature Conservancy bought some land in a swampy, remote part of the Atchafalaya Basin and began measuring water depth, turbidity, temperature, levels of dissolved oxygen and other data. The information would give TNC’s scientists a baseline for future work at TNC’s Atchafalaya Preserve.

“For 10 years since that initial collection, we have been measuring the same data and submitting it to the State of Louisiana’s Atchafalaya Basin Program,” says Joe Baustian, TNC’s senior ecologist in Louisiana. “It was, and remains, information that has never been assembled before.”

Specifically, Baustian and a revolving team of researchers from local universities set up instruments at seven locations in this remote part of the watershed. Each station is carefully placed to remain discreet from the others to ensure that the continuous measurements account for every kind of condition, from severe flooding to drought. A priority for TNC and the partners is to observe changes happening over time attributable to conserving habitat on land and restoring natural flows in waters, or to emerging threats related to pollution and new weather patterns.

A decade in, the numbers speak for themselves. In one study, the researchers compared female crawfish living in swamps fed by oxygen-rich river water with counterparts living in water made hypoxic by human modifications to the floodplain’s natural flow patterns.

“Over 10 years, our researchers observed that female crawfish in the hypoxic waters were smaller and laid fewer eggs,” says Christopher P. Bonvillain, Ph.D., professor and graduate program coordinator at Nicholls State University’s Department of Biological Sciences. “These findings support restoring hydrology to reduce water stagnation to benefit the crawfish population.”

Restoring natural water flows in the basin would benefit the area’s crawfish populations, which fuel the leading wild-caught crawfish industry in the nation. Letting water flow and filter as it moves through the swamp also maintains oxygen levels to benefit other wildlife and improves the quality of water flowing through the larger Atchafalaya Basin.

“When the river connects to its floodplain swamps, we see a near immediate improvement in dissolved O₂, and things remain good as long as the water is flowing,” adds Baustian.

According to Baustian and TNC’s university partners, research like this is critical to informing restoration efforts and demonstrating the potential for on-the-ground improvements. TNC will continue monitoring these conditions as well as pursuing opportunities to enhance ecological functioning in the Atchafalaya Basin.

The Nature Conservancy’s Sustainable Rivers Project (SRP) substantially advanced its goals when partners recently gathered to revive a project at the Old River Control Structure (ORCS) after a two-year pause. Managed by the U.S. Army Corps of Engineers, the ORCS is responsible for maintaining the water flowing down the Atchafalaya and Mississippi River basins.

In 2002, TNC and the Corps launched a collaborative effort to find more sustainable ways to manage river infrastructure to optimize benefits for people and nature. Now known as the Sustainable Rivers Project, this collaboration has grown from eight rivers in 2002 to 44 rivers in 2022, influencing 12,079 miles of U.S. waterways and including 90 associated reservoirs and dams.

The SRP focuses on determining flow requirements for rivers and then creating operating plans for dams that incorporate these flows. In April, TNC and the Corps held an SRP Flows Workshop, gathering representatives from federal and state agencies, universities, nonprofits and local communities from throughout the two river basins. The participants pooled their expertise around this infrastructure’s management plan, discussing what is and is not working with the distribution of water flowing between the Mississippi River and the Atchafalaya River.

“For decades, the ORCS has supported a 70/30 split, diverting 30 percent of the combined flow of the Mississippi and Red River flows into the Atchafalaya River Basin while allowing the remaining 70 percent to run its course down the Mississippi River,” says Bryan Piazza, TNC’s Louisiana director of science and facilitator of the SRP Flows Workshop. “Before revisiting whether the status quo remains ideal, we needed to bring as many experts together as possible to determine what is required throughout the year, and across years, to promote the ecological and economic health of these watersheds.”

In response to that need, the workshop participants spent two days digging into and using the latest science to develop hydrographs (graphic illustrations of annual flow patterns) that explore and compare alternatives against the current 70/30 flow split. Specifically, the scientists used software provided by the Corps to generate and compare hydrographs that would potentially alter current flows to provide optimum conditions for three specific targets:

• fish and crawfish production
• water quality across the swamp
• forest health

With the workshop complete and alternate hydrographs in hand, next steps include testing those hydrographs with a hydrodynamic computer model to assemble maps and a summary for the Corps that will outline how the alternate flow patterns affect the targets. Ideally, as these flow regimes are refined, they will be tested in real time and could lead to a shift in management of the ORCS to benefit people and nature.

“The ORCS flow regime was set up in 1963 based on what was happening at that time,” adds Piazza. “Since then, the water flow down the Mississippi River has changed, the coast has changed, and the climate has changed. These are reasons why we are grateful for this opportunity to explore these questions and revisit new approaches to the management of the ORCS that could support wildlife, flood protection and economic prosperity for communities who depend upon these rivers.”