Engineering Natural Solutions on the Mississippi

A river system forever changed

These interventions on major rivers have unintended consequences. The dams used to manage water levels for navigation slow the river’s flow, creating lake-like conditions that degrade habitat, hinder fish migration and disrupt natural flood cycles. Over time, these changes reduced water quality and fragmented wildlife habitat. And changes on the land also impact the rivers.

“We have altered our landscape significantly. We developed the land, planted row crops and straightened streams—and our large rivers are on the receiving end of all those impacts,” said Bryan Hopkins, TNC Midwest strategy director of great rivers and floodplains. “We’re past the point of letting the river heal itself. We really need to engineer back the functions that provide environmental benefits.”

Richard Raynie, a project manager with the Corps in New Orleans, agrees. He’s worked with the river in Louisiana for 30 years, the bulk of that time spent with the state’s Coastal Protection and Restoration Authority.

“We have to look at the river as a system. It’s a different river system than it was more than 100 years ago, and a lot of ecosystem changes have resulted,” Raynie said. He explained that water control is different in the lower basin where there aren’t locks and dams but more levees. “It’s a less controlled system, so we’re reacting to the water more than controlling it.”

A new paradigm

In most cases, we can’t remove the dams on large rivers, but we can change how water moves through them. By blending engineered infrastructure with natural features like wetlands, islands and floodplains, we can restore critical functions while maintaining navigation and flood protection.

Today, the same agency that built the dams and levees is a key partner in reconnecting floodplains, rebuilding habitat and making communities more resilient.

“One mission of the Corps is navigation, but equally important now is our aquatic ecosystem restoration mission,” said Jill Bathke, a water resource planner with the Corps. “In the last 15 years, the Corps has focused on ways to reestablish a self-regulating system. We’ve shifted the way we manage the system. We are required to think about natural solutions and to think 50 years into the future to make sure the solutions are sustainable.” 

In the lower river, sand dams provide an example of balancing flood control and ecosystem restoration, Raynie explained. Sand dams, a type of temporary levee, help keep water in the river, maintaining the stream power during low levels. During high water, the sand can be distributed in the adjacent wetlands in the delta, helping to restore habitat.

“That’s a key hybrid project that has benefits to both navigation and ecosystem restoration. So the Corps is contemplating multi-faceted solutions, looking at not only navigation and flood risk mitigation, but also ecosystem restoration,” Raynie said.

Partnering to create a resilient Mississippi River basin

Large-scale solutions require massive resources. Partnering with federal agencies like the Corps enables the necessary projects to restore a resilient river basin. TNC builds strong relationships with the Corps at all levels to align local and national priorities. This partnership allows TNC to bring science, data and community input to projects at a basin-level scale, and this additional insight helps the Corps make thoughtful decisions.

“Partnering with organizations like TNC and academic institutions helps add credibility and scientific understanding of the effects of water control structures and how we operate them,” Raynie said. “That specialized knowledge helps us understand the impacts, and it really helps us to have that perspective.”

TNC has a long history of partnering with the Corps to make this happen. Together, we’re finding ways to reconnect floodplains, rebuild habitat and improve resilience for both people and nature.

“When we are working in large river systems, we can’t make adjustments in one part of a river without affecting others. We have to look at the river systemically,” Hopkins explained. “The Corps conducts large studies that help us look at the whole system and make good decisions.”

Bathke works with the Corps Navigation and Ecosystem Sustainability Program (NESP), which serves the dual purpose of maintaining navigation channels and ensuring sustainable solutions.

“These large studies enable the authority and funding for projects and also help the Corps forecast out where we are going to work and help identify opportunities where there aren’t ecosystem restoration projects in place to realize benefits,” Bathke said.

For example, the Corps uses material dredged from the river to create new ecological benefits like building river islands and berms to support habitat and creating forest diversity that supports tree species important to migratory birds.

“The Mississippi River system flows through three of the most important migratory bird flyways in the world,” says Nick Ohde, TNC’s Mississippi River Basin Program director. “When we manage water to attract migratory birds to the floodplain, it benefits hunters, birdwatchers and wildlife alike.”

Remembering Leopold’s words, we can use dams and other structures to manage water levels and mimic the natural function of floodplains. These structures can be used to draw down water for strategic periods of time to expose the mudflats—built-up sediment left behind as the river floods and recedes.

“When we think about healthy, wild rivers, the first thing we think of is probably not dams and levees. But we work with what we have,” said Ohde. “These structures can be really important tools to mimic natural flow patterns of rivers to benefit people and nature.”

Expert use of this ability allows us to mimic the natural pulse of a free-flowing river, which would ebb and flow periodically, exposing its edges for a time, then covering the floodplain again as water levels rise.

Healthy rivers benefit people and nature

“The lock and dam system definitely altered the upper Mississippi River, and it’s changed how we control water levels,” Bathke said. “Our goal is to manage water levels to mimic natural peak and lowering of water levels. Oftentimes that means lowering the water level by just a few inches. This exposes mudflats and allows plants to grow, which can benefit a variety of species that use the river as a migration corridor or as habitat.”

Those mudflats are teeming with life. Creating a pulse of flooding and receding water—just a couple of inches deep—allows seeds to germinate, yielding vegetation that provides food for waterfowl when the plants are exposed in shallow water. Then as the water flows again, those aquatic plants continue to provide food and habitat for myriad freshwater creatures, including macroinvertebrates, which in turn become lunch for fish and migrating birds. Effective use of this pulse allows habitats to evolve, protecting threatened and endangered species, and filters the water, providing communities with a cleaner supply.

“There is so much science and long-term monitoring on the upper Mississippi River that is important to designing sustainable water resource solutions, and we rely on that long-term data to build better projects and support ongoing restoration,” Bathke said.

Sustainable Rivers Program

Throughout the basin, the Sustainable Rivers Program (SRP)—a partnership between TNC and the Corps—helps Corps staff manage dams on smaller rivers and streams for environmental benefits. Together, TNC and the Corps identify areas where small changes in water levels could benefit a particular species of mussel or fish, for example, and work with dam operators to implement the flow change within the operating parameters for that dam.

In Louisiana, the Old River Control Structure keeps the lower Mississippi River in its current channel. Without it, the Mississippi River would change its course and bypass Baton Rouge and New Orleans altogether. Allowing that to happen would have massive economic consequences, so since the 1950s, the Corps has diverted about 30% of the Mississippi River into the Atchafalaya basin. Altering how that 30% is allocated in a small way may deliver big ecosystem benefits. The SRP held a workshop to consider the effects of small changes.

We asked, “If we can turn the knobs differently, what are the impacts?” Raynie said.

We’re collecting data to understand how water flows through the basin and make improvements. For example, holding water on the floodplain a little longer at key times of the year can give fish and crawfish time to spawn, giving a boost to the local fisheries and improving water quality.

“The Atchafalaya River basin is the largest forested wetland in North America and provides critical wildlife habitat, water filtering and flood relief for our communities,” said Bryan Piazza, science director for TNC in Louisiana and the Mississippi River Basin program. “Finding the right balance to protect all of those benefits is key to ensuring this significant resource persists.”

A living laboratory

TNC’s Emiquon Preserve, a 7,000-acre floodplain along the Illinois River in central Illinois, allows staff and partners to better understand how to mimic nature in a controlled environment. A water control structure installed at the connection with the river can let water in and out of the floodplain. Understanding the impacts on both the river and the floodplain is critical to protecting the delicate ecosystem.

“Simply opening an area and allowing water to periodically move into it may appear on the surface to be restoring the function of the river, but we need to ask, is it getting in at the right time of the year, staying for the right length of time for plants to grow and giving the right spawning cues for fish? Emiquon has shown us the need to control how the river is connecting with its floodplain and plan for conservation goals,” Hopkins said.

Emiquon builds on a long history of similar water management projects led by state and federal agencies along the Mississippi River—work that has been refining how infrastructure can support ecological function for decades. Lake Odessa in Iowa was one of the first places on the Mississippi to do that. This large oxbow wetland connected to the Mississippi River is owned by the Corps and managed by Iowa Department of Natural Resources and the U.S. Fish and Wildlife Service. For more than 75 years, state and federal agency staff have used water control structures to try to mimic the river’s natural seasonal pulse.

“I grew up near Lake Odessa,” Ohde said. “It’s easy to take it for granted, but it really is a place where you can see how thoughtful water management can support fish, waterfowl and migratory birds while still working within the reality of how the modern river is managed.”

A resilient river for the future

Restoring the health of our great rivers isn’t about turning back time. It’s about rethinking the tools we already have. The locks, dams and levees that once straightened and constricted these waterways might also hold the key to restoring some of their natural function.

“The Mississippi River is a highly altered system. Just letting a portion of it go back to nature won’t restore a natural system,” Ohde said. “This is why we work with partners to take a holistic approach to restoring the river system.”

Each of these projects helps TNC and its partners, including the Corps, learn together what works under different conditions so we can identify more ways to help the Mighty Mississippi remain resilient for future generations.