The Mississippi River Delta formed over the last 7,000 years as the Mississippi River carried sediment accumulated from all over North America and deposited it at the mouth of the river along what is now Louisiana’s coastline. When enough sediment stacks up under water, plant communities begin to thrive and develop, encouraging new sediment to accumulate until new land is formed.
But by the mid-20th century, the US Army Corps of Engineers had installed a series of water control structures along the lower portion of the Mississippi River to prevent it from changing its course, thereby protecting the ports of Baton Rouge and New Orleans. As a result, this natural sediment cycle was halted, and the sediment that once built land along the coastline was lost into the deeper waters of the Gulf of Mexico.
“To restore the health and vitality of the Mississippi River Delta not only now, but for years to come, it is vital that all of the sediment is treated like the precious resource it is and every effort is made to maximize its capture for coastal restoration,” says Alisha Renfro, staff scientist with the National Wildlife Federation. “The sand and mud carried by Mississippi River and its tributaries is the foundation and the lifeblood of the delta.”
Levees built for flood protection and navigation have almost entirely cut off the river’s flow of fresh water, mud and sand that once built and helped sustain the wetlands and barrier islands of the delta. In addition, dams upriver have trapped sediment upriver reducing the total sediment load that winds its way down to Louisiana.
Despite the reduction in sediment carried by the river, the Mississippi is still mighty with nearly 90 million tons of sediment passing the city of Belle Chasse each year. The sediment transported by the Mississippi River is comprised of sand and mud. By the time the river reaches Louisiana, sand makes up roughly 20 to 30 percent of the total sediment load carried by the river, while mud makes up the remaining 70 to 80 percent.
While some sediment does escape the river where the levee end on the east side of the river and at the Bird Foot Delta, the mud and sand is bypassing most of Barataria Bay and Breton Sound’s marshes. In order to capture and fully reap the benefits of all the sediment that river carries, both marsh creation and sediment diversion projects need to be employed in the best locations possible. Marsh creation projects can use sediment – mostly sand – dredged from the river to restore land in strategic locations. Reliance on this type of project alone means missing out on nearly 70 percent of the sediment carried by the river. Sediment diversion projects tap into both the sand the mud carried by the river to build new land and to help sustain the existing wetlands, that in the absence of sediment input, are rapidly disappearing. Together these projects can allow us to can create a healthy and more resilient future for coastal Louisiana.