3.27.15-sediment.jpg
Reddish-brown sediment carried by the Mississippi and Atchafalaya rivers can be seen entering Lakes Pontchartrain, Maurepas and Borgne. The most sediment is seen exiting the Mississippi in Plaquemines Parish and the Atchafalaya below and west of Morgan City. Some sediment also is seen moving through Davis Pond into Lake Salvador and Barataria Bay. The image was taken Friday by NASA's MODIS satellite.
(NASA MODIS satellite)
The rising Mississippi and Atchafalaya rivers are carrying a wealth of sediment -- clearly visible from space -- into coastal wetlands, Lake Pontchartrain and other coastal lakes, and the Gulf of Mexico, according to a Friday (Mar. 27) image from NASA's MODIS satellite.
The high-river sediment arrives in southern Louisiana after being washed off farmland in the Midwest along the upper Mississippi River, and similar farmland in the Ohio Valley. A combination of rainfall and melting snow from repeated cold fronts that have crossed those segments of the country in recent weeks has washed the sediment into tributaries of the Mississippi and Ohio rivers.
Louisiana officials hope to build a series of diversions along the Mississippi River in future years to collect sediment from similar spring flood seasons to build new wetlands and nourish existing wetlands in the state. Today, the majority of the sediment is lost to the Gulf of Mexico.
At the Old River Control Structure above Baton Rouge, about 30 percent of the Mississippi's water is diverted into the Atchafalaya River. The sediment is seen flowing south, entering the Gulf through that river's mouth below Morgan City and through the Wax Lake Outlet just to the west. Wetlands have been expanding south of Wax Lake for more than 40 years as a result of similar springtime flooding.
The Mississippi was at 13.69 feet at the Carrollton Gage in New Orleans at 5 p.m. Friday, and is expected to crest on Wednesday at 14.2 feet, well below the official 17-foot flood stage for the city. Floodwalls protect the city from water up to 20 feet.
But water levels have been high enough since Monday to pour a steady stream of sediment-laden water into the Bonnet Carre Spillway in St. Charles Parish, where it is flowing into Lake Pontchartrain, largely hugging the lake's southern shore. Sediment also is visible in Lake Maurepas.
The water began leaking through long wooden slats in concrete bays in the spillway structure that separate the river from the spillway on Monday when the river reached 12.5 feet in New Orleans.
Sediment from the spillway is also visible in Lake Borgne, the Mississippi Sound and along the Chandeleur Islands, after having traveled through the Industrial Canal in New Orleans and then through Gulf Intracoastal Waterway, and also through the Rigolets and Chef Menteur passes at the eastern end of the lake.
On the West Bank, some sediment also is visible flowing through the Davis Pond freshwater diversion into Lake Cataouatche before entering Lake Salvador and Barataria Bay.
The most visible amounts of sediment are seen along the east and west sides of the southern end of the river in Plaquemines Parish, with a wide stream flowing southwest towards the deep Gulf of Mexico.