Using dredged sediment for underwater barrier sill

The U.S. Army Corps of Engineers, New Orleans District will construct an underwater sill across the bed of the Mississippi River channel to prevent further upriver progression of salt water from the Gulf of Mexico.

Photo courtesy of USACE

The Mississippi River’s volume of water has fallen to a level that allows salt water from the Gulf of Mexico to intrude upstream.

The intrusion of salt water into the river is a naturally occurring periodic condition because the bottom of the riverbed between Natchez, MS, and the Gulf of Mexico is below sea level.

Denser salt water moves upriver along the bottom of the river beneath the less dense fresh water flowing downstream. Under normal conditions, the downstream flow of the river prevents significant upriver progression of the salt water.

However, in times of extreme low volume water flow, unimpeded salt water can travel upriver and threaten municipal drinking water and industrial water supplies.

To arrest the upriver movement of the salt water and reduce the risk to freshwater intakes, USACE will construct an underwater barrier sill near Myrtle Grove, La., using sediment dredged from an area designated for this purpose.

The sill will take approximately two weeks to complete but will demonstrate benefits in advance of completion. The sill has been constructed on four previous occasions in 1988, 1999, 2012 and again in 2022.