The U.S. Army Corps of Engineers, New Orleans District began construction of an underwater sill Oct. 11 across the bed of the Mississippi River channel to prevent further upriver progression of salt water from the Gulf of Mexico.

The Mississippi River’s volume of water has fallen to a level that allows salt water to intrude upstream. Salt water from the Gulf of Mexico moves upriver in a wedge shape that may stretch up approximately 20 miles from the bottom to the surface of the river.

To stop the salt water from moving upriver and reduce the risk to freshwater intakes, the New Orleans District began construction of an underwater barrier sill at river mile 64, which is near Myrtle Grove, Louisiana, to arrest the progression of saltwater intrusion.

The sill is being created using sediment dredged from a designated area just upstream for this purpose. Throughout the construction phase, the U.S. Army Corps of Engineers will test salinity levels in the river to determine where the saltwater wedge is and how high the sill may need to be built.

Currently, the greatest risk associated with the salt water intrusion is the appearance of unsafe salinity levels at municipal drinking water intakes in Plaquemines Parish. Additionally, the U.S. Coast Guard has issued navigation restrictions around the sill construction site from river mile 63.5 to 64.

The New Orleans District and U.S. Coast Guard are closely coordinating with the navigation industry to ensure vessel traffic in the river is not significantly impacted. Draft restrictions may be issued as construction of the sill progresses.