The Mississippi River meanders through the continental United States for 2,320 miles before emptying into the Gulf of Mexico in Louisiana. This vastness is hard to envision–until you see a new model at the Louisiana State University Center for River Studies, complete with sand and flowing water.
The super-realistic model is part of an effort to understand how the area will be impacted by climate change and other environmental phenomena in the future–and in particular, how the river’s many man-made levees impact southern Louisiana’s ability to replenish its wetlands and stave off sea-level rise. These levees are basically walls that prevent the river’s natural flooding process. The problem is that without the sediment those normal seasonal floods bring to the area, the local wetlands are receding. The state has lost 1,900 square miles of land since the levees were built in the 1930s at the rate of about a football field every hour. This decades-long problem will be exacerbated by climate change-related sea-level rise. If nothing is done, studies have shown that Louisiana’s coast could lose 4,120 square miles over the next 50 years, resulting in billions of dollars of damages. This is already impacting people’s lives: Louisiana is home to some of the country’s first climate change refugees.
That’s where the Center for River Studies‘ giant model of the lower 179 miles of the Mississippi comes in. Clocking in at 10,800 square feet, or about two basketball courts, the model is a way to test and study the impact of a relatively new type of infrastructure intervention called “sediment diversions.” These are structures built along the banks of the river that create channels through the man-made levees. They’re designed to bring sediment from the river out to the areas beyond its banks by mimicking the flooding process. In essence, diversions allow the area to reap the benefits of flooding–in a very controlled manner. If diversions are successful, they can replenish the state’s battered wetlands, counteracting the effects of sea-level rise and saltwater intrusion–problems that will likely worsen because of climate change.
The model also does something else: It gives people a visceral way to understand how the river works and why studying it is so important.
This isn’t LSU’s first model of the Mississippi. In the early aughts, the university and the Coastal Protection Restoration Authority (CPRA), which run the River Studies Center together, built a much smaller, 900-square-foot model to study how the river would respond to sea-level rise. But this new model, which opened this month, gives the scientists far more quantitative tools to examine how the river will react to certain circumstances. The previous model covered about 60 miles of the river, but the new one covers 179 miles–necessary for the scientists to evaluate projects the CPRA is thinking about doing that are further upriver. The new model itself is far more detailed, and uses lightweight plastic fake sand that better mimics the way real sediment moves down the river.
Scientists can change the locations of miniature sediment diversions, as well as the flow rate of the river and other parameters, and then test to see what happens. Because the fake sand moves much faster than real sand, they can simulate one year’s worth of time in one hour. Projectors above the model make it look more realistic and indicate the landscape, coastal features, and diversion locations. “We can look at future projects and how that would impact the river, the movement, flow rates, stages, and ultimately how that might impact river sediment diversions,” says Clint Willson, the center’s director and a professor of civil and environmental engineering.
He plans to do experiments by creating a particular scenario–like what might happen if the CPRA doesn’t build any sediment diversions–and running the physical model for 50 “years” to see what the impact looks like. Then, the scientists can add in a diversion in a particular location, or another, and see how that changes the river and the wetlands 50 years later. “It’s kind of going back to the scientific method,” he says.
Why not just use a computer to do all this modeling? Willson says that using the physical model is actually faster than a computer because of the complexity of the simulations involved. To make the computer models run faster, he says that scientists often use approximations, but comparing the computer’s results to the physical model’s results might help them build better models overall. In essence, it’s another tool to study the river, one that can augment digital methods as well as the work of hydrologists out in the field, working with real-time measurements.
The work is so vital because of the increasing threat of climate change, which is exacerbated in this particular region because the wetlands are sinking as the sea levels are rising. “If you think about those wetlands, a lot of them are not getting replenished,” Willson says. “When you have stresses like storms or future stresses like sea-level rise, they don’t have material to help them bounce back or be more resilient.”
But there’s a delicate balance to be struck–because the Mississippi is a huge driver of the region’s economy. The levees are necessary to navigate the river and protect Louisiana’s coastal industries. “You can’t just break open holes in the levee and let the river water go. The entire Midwest of the United States and the agricultural economy is depending on being able to use barges that go up and down the Mississippi River,” Willson says. “It’s an extremely challenging problem from a political, social, economic, engineering, and ecological perspective.”
That’s the final piece of what the Mississippi River model could do: Act as a physical argument for the importance of the CPRA’s work while doubling as a scientific and educational tool. After all, seeing a giant model of the river is far more interesting than reading scientific papers.
“As engineers and scientists, we love our PowerPoints. You think, I’ll jazz it up, we’ll show animations of our numerical models. But it’s an animation of a computer model,” Willson says. “But to have someone come out and see the river and be convinced that we’re replicating the relevant processes in our physical models, and look at the way it responds, look when the sediment moves? That’s all extremely valuable.”