Louisiana has undertaken a major coastal wetland restoration project that will attempt to reverse land loss and ecosystem degradation in large portions of the state’s coastal wetlands. The images above highlight one of the project’s key efforts: the Davis Pond Freshwater Diversion Structure. Engineers have drilled into the levee on the southern bank of the Mississippi near Luling, Louisiana, and built an 11,000-foot-long, 120-foot-wide outflow channel that leads to a ponding area to the southeast. When the diversion structure is open, Mississippi River water will flow into the ponding area and percolate southward toward the coast through a series of existing lakes.
The Landsat images above show the Davis Pond area in 1999 (top), three years into the project’s construction, and in December 2003, just two weeks after a full-capacity test-run of the structure. In the upper left corner is the Mississippi River (looking greenish in 1999 and tan in 2003). The diversion structure’s outflow channel stretching southeastward from the south bank is a narrow, straight line. In 1999, the channel stopped short at the intersection with east-west running U.S. Highway 90 (the gray horizontal line). By 2003, the brownish line of the channel extended fully into the ponding area.
The four-day test run of the structure began on November 30, 2003, and ended on December 3, but the effects were still apparent on December 15, when the bottom image was captured. The Davis Pond area was nearly filled with water carrying high volumes of sediment, which turned the water bright blue. As intended, the Mississippi River water can be seen spilling over from the ponding area into Lake Cataouatche, at the bottom right corner of the scene. From there, the water moved southward into Lake Salvador, and from there into the Barataria Bay estuary along the Gulf of Mexico.
Deterioration of Louisiana’s coastal zone is largely due to the elaborate levees built up around the Mississippi to control flooding that disrupts agriculture, shipping, and people’s lives. The spring floods also renewed the coastal marshlands, bringing nutrients, freshwater to balance salt water intrusion, and new sediment to counter erosion and subsidence (sinking). In the absence of these floods, the coastal marshes and wetlands have been subsiding and becoming increasingly salty and polluted. Marsh vegetation has declined. These problems have drastically reduced the number of commercial and recreational fish and shellfish—including oysters and shrimp—and put stress on resident and migratory waterfowl populations.
Engineers and natural resource managers have reason to be hopeful about the project’s chances of restoring natural habitat. A similar project constructed 15 miles south of New Orleans in 1991 has created new marshland, renewed vegetation, and tripled oyster production on public lands. For more information about the Davis Pond Freshwater Diversion Structure, visit the New Orleans District Website of the U.S. Army Corps of Engineers.