Excessive Sedimentation

 

Where the Mississippi traverses through Louisiana it used to fork into many different rivers that drained to the coast, depositing all the sand and sediment across a large area along the coast. These deposits were vital to building our vanishing coastline; however, the Corps dammed nearly every one of those outlets, leaving just one channel with a few smaller channels stemming out to the coast. As a result, the water and sediment cannot spread and disperse as it once did and the delta can no longer grow. Much of that sediment is now diverted into the Atchafalaya Basin and the rest is lost forever into the depths off the continental shelf.

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 At the same time, the oil companies began digging canals throughout the coast. When the oil companies dredged canals, they accelerated the erosion of the coastal marshes.  As these marches eroded, the sea water began to come up the canals, through the marsh, and into the cypress forests, killing cypress trees and destroying our last line of defense from hurricanes and tropical storms. Furthermore, drilling by oil companies results in subsidence. As the sea level continues to rise, we are losing our coast at a rate of roughly a football field every fifty minutes.

The last dam the Corps built was in the Atchafalaya River. The Corps realized that they could not control the floods with the Mississippi levees alone so they created a spillway, a place to release flood waters. They put levee systems that were twenty miles apart (on average), cutting the surface of the Atchafalaya Basin by less than 50%. The last structure they put in was a power plant. Here, they realigned the power plant dam at the end of the curve of the river, which is where most of the Mississippi River bedload moves. This structure was created in an effort to divert up to 65% of the Mississippi River’s sediment load along with 25% of the flow. The Corps created one big channel; distributaries from the channel were dammed and realigned, diverting sediment from the main channel into the distributaries. The oil companies dug pipeline and access canals crisscrossing the Basin, disrupting the natural hydrology, accelerating siltation and impairing water quality. While there once were all manner of lakes, bayous and waterways in the interior of the Basin fed by the Atchafalaya River water, between the Corps and the oil companies, they destroyed roughly 75% of the Basin’s streams, lakes and bayous. This loss leaves only 25% of the historical swamps, lakes and bayous within the levee system and much of it is severely degraded.

Sedimentation continues to play a primary role in the destruction and loss of valuable wetlands. All these manipulations from the Corps, the presence of illegal spoil banks left behind from oil and gas pipeline projects, coupled with industrial interests and state-backed projects which exacerbate the accretionary process, result in a dire need to save the remaining swamps from becoming bottomland hardwood forests. Once the swamps are filled with sediment, they cannot be replaced. This process creates serious repercussions for ecological integrity and public safety in the face of climate change, extreme weather events and sea level rise. “There is only a little portion left that we have here, and we are fighting tooth and nail to protect it” proclaims Basinkeeper Dean Wilson. 

 

 
Atchafalaya Basinkeeper
P.O. Box 410
Plaquemine, LA 70765 basinkeeper@gmail.com
cell: 225-685-9439
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