The Swamp Stomp

Volume 15, Issue 24

Images taken from NASA’s MODIS satellite clearly show that the rising Mississippi and Atchafalaya rivers are pouring an abundance of sediment into coastal wetlands, Lake Pontchartrain and other coastal lakes, and the Gulf of Mexico.

Having been washed into the Mississippi River by a combination of rainfall and melting snow at farmlands across the Midwest and Ohio Valley, sediment is gushing into southern Louisiana. Officials hope to construct a series of diversions along the Mississippi River in the coming years to collect the increased amount of sediment that is expected to continue its journey south in future spring floods. The sediment would then be used to create new wetlands in order to nourish the existing wetlands.

30 percent of the Mississippi River’s water is diverted into the Atchafalaya River at the Old River Control Structure above Baton Rouge. Satellite imagery displays that the sediment is entering the Gulf of Mexico, which is where the majority of sediment is lost, through the Atchafalaya River’s mouth below Morgan City and through the Wax Lake Outlet to the west. The wetlands off of Wax Lake have been expanding south for over 40 years due to similar springtime flooding.

While water levels remain below the official 17-foot flood stage for the city, the water levels have been high enough to pour a constant stream on sediment-laden water into the Bonnet Carre Spillway in St. Charles Parish. From there the sediment is carried into Lake Pontchartrain where it mainly settles on the lake’s southern shore. Increased sediment is also noticeably visible in Lake Maurepas.

When the river grew to 12.5 feet in New Orleans, water began to escape through the long wooden slats in concrete bays in the spillway structure. As a result, sediment from the spillway became visible in Lake Borgne, the Mississippi Sound, and along the Chandeleur Islands after it traveled through the Rigolets and Chef Menteur passes at the eastern end of the lake.

The West Bank also acts as a deposit zone for some sediment flowing through the Davis Pond freshwater diversion into Lake Cataouatche before entering Lake Salvador and Barataria Bay. The most visible amount of sediment, however, are along the east and west sides of the southern end of the river in Plaquemines Parish, with a broad stream flowing towards the Gulf of Mexico.

Despite this immense increase in sediment, criticism from oyster growers and commercial fishers remain against the plans to build the necessary diversions.

In response to such criticisms, Garret Graves, chairman of Louisiana’s Coastal Master Plan, claimed, “People are out there making allegations that are not supported. . . We’re moving forward with the master plan. We’re moving forward with designing four of the largest diversions. And we’re building them.”

These diversions are expected to produce 300 square miles of new land by 2060, while other projects also in the master plan would create marshland using sediment collected from the Mississippi River. The master plan is still determining the best places to build projects that will allow the state to withstand water level heights in the coming century, but it seems apparent that these diversions are necessary to cope with the increased flooding expected in the coming years.