Subsidence Induced Collapse of the Mississippi Delta System

Sherwood M. Gagliano, Ph.D., 1260 Main Street, Baton Rouge, LA 70802: sgagliano@coastalenv.com, Karen M. Wicker, Ph.D., 1260 Main Street, Baton Rouge, LA 70802: kwicker@coastalenv.com

The Mississippi River drives one of the largest and most biologically productive ecosystems of North America. The delta ecosystem is an important platform for human activity. It is a producer of oil and gas, a hub of navigation, a center for refineries, and is rich in agriculture, fisheries, and cultural resources. Its transportation infrastructure and power plants are important for Louisiana and the nation. The delta ecosystem that provides this platform is collapsing. It is not just eroding; it is being submerged and invaded by the sea. The Gulf shoreline is shifting many miles inland; moving northward from Grand Isle to Covington.

How do we know this? A number of scientists have and continue to study this phenomenon. It is instructive to compare results of two study groups: Robert Morton funded by the U.S. Geological Survey and S. M. Gagliano funded by the U.S. Army Corps of Engineers. Morton et al. studied the effects of geological fault movement on subsidence and land loss at “hotspots” in Lafourche and Terrebonne Parishes. They concluded that withdrawal of oil and produced water in oil fields was the primary cause of land subsidence and submergence. Gagliano et al. conducted a series of studies of the relationships between geological fault movement and subsidence in coastal Louisiana. They initially concluded that fault movement was primarily related to basin tectonics, but later work demonstrated that the Morton team’s conclusion that fluid withdrawal is the primary cause is correct.

Denial is not a solution. Two of the most instructive areas of study have been Empire and Bastian Bay. The fault hazard must be further delineated for future land use, resource management planning and coastal restoration.