The Mississippi River was closed temporarily to shipping traffic in New Orleans on Wednesday as contractors began building an underwater barrier that the Army Corps of Engineers says will stop the advance of salt water threatening drinking water in the New Orleans area. Due to low water levels in the Mississippi River, salt water has been moving far upriver and was at the outskirts of New Orleans by Wednesday, nearly 90 miles north of the mouth of the Mississippi.
Also Wednesday, Plaquemines Parish issued an advisory to residents living in the parish that high levels of sodium and chloride were being measured in drinking water.
River traffic had to be closed for about 3 miles while the Great Lakes Dredge & Dock Co. installed a pipeline needed in building the massive underwater sill. The river was expected to be reopened Wednesday evening.
The company will dredge sediment to build up the barrier at a point near Myrtle Grove in Plaquemines. The company was given an $8.1 million contract to do the work. The barrier is expected to be done in 45 days.
Ricky Boyett, a corps spokesman, said the sill will begin pushing the salt water back into the Gulf in about two weeks. The salt water is expected to be stopped by the sill and then pushed out by the flow of the river. The corps says underwater sills have stopped salt water intrusion in the past. Sills were constructed in 1988 and 1999.
Typically the rush of freshwater down the Mississippi River keeps salt water contained to the southernmost portions of the river. But in times of drought the Gulf’s salt water can move farther inland. The river’s stage has been a couple feet below the mean average at New Orleans.
During the construction of the barrier, river traffic will be reduced to one lane as it passes the construction zone, Boyett said.