Low river allowing saltwater to threaten drinking supplies

MISSISSIPPI RIVER — The Army Corps of Engineers said yesterday it would construct an underwater sill in the Mississippi River as it seeks to stop saltwater from threatening drinking water supplies in the New Orleans area.

It’s needed because water levels in the drought-stricken Mississippi have gotten so low that the river is nearly at sea level, allowing salt water from the Gulf of Mexico to move far inland.

The federal U.S. Drought Monitor shows nearly two-thirds of the lower 48 states are experiencing some form of drought, and the Department of Agriculture has declared more than half of the nation’s counties — nearly 1,600 in 32 states — as natural disaster areas. More than 3,000 heat records were broken over the last month.

At the latest check on Monday, salt water was on the outskirts of New Orleans, 85 miles upriver from where the Mississippi empties into the Gulf. The river’s fresh water is used by New Orleans and surrounding towns and industry.

The corps planned to issue bids on Tuesday to get work started on building a sill designed to stop the salt water from moving upriver and affecting freshwater intake valves for Belle Chasse, a town in Plaquemines Parish south of New Orleans. The sill is created by mounding sediment at the bottom of the river to create a dam-like structure that can halt the dense salt water flowing under the freshwater.

Mike Stack, the chief of emergency management for the corps in New Orleans, said the sill is needed because of the most recent long-range forecast for water levels.

Billy Nungesser, the president of Plaquemines, said he planned to declare a state of emergency today because of the saltwater threat. The parish said it wanted to make sure there were adequate plans in place if the need for fresh water arises.

Plaquemines Parish said neighboring Jefferson Parish was ready to supply drinking water should that become necessary. But the parish said it did not expect to have to close any of its freshwater intakes in the immediate future.

The corps says underwater sills have stopped saltwater 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 southern-most portions of the river. But in times of drought the Gulf’s salt water can move farther inland. On Monday, the river’s stage was a couple feet below the mean average at New Orleans.

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