Saltwater "Wedge" Advances To Mile 43 Upstream From Mississippi Delta Thanks To Drought & Low Flow
Low water in the Mississippi River has allowed a “wedge” of saltwater from the Gulf of Mexico to work its way up to mile marker 43, just above the Plaquemines Parish community of Jesuit Bend, but is not yet considered a threat to New Orleans, St. Bernard or Jefferson water supplies, officials with the Army Corps of Engineers said Thursday. Plaquemines Parish officials have measured elevated salinity levels at water intakes in Boothville and Venice, but the lower end of the parish has access to freshwater from a pipeline from Belle Chasse, said Will Veatch, a corps hydrologist. The pipeline was installed after low river events in 1988 and 1999.
Denser, heavier saltwater flows upriver beneath fresh water flowing downstream when the river’s flow drops below normal. The federal drinking water standard for salt is 250 parts per million, which could be violated if the wedge’s upper level reaches the water intakes.
If officials believe the wedge is four weeks away from fouling the upriver freshwater intakes, the corps will block the saltwater from moving upstream by building an underwater sill of dredged sediment at mile marker 63.7, 31 miles below the Canal Street ferry.
But that’s not a threat until the leading edge of the wedge has moved 15 to 25 miles upstream of the intakes, Veatch said, and he said corps officials still don’t believe that will happen this summer.
EDIT
http://www.nola.com/environment/index.ssf/2012/07/saltwater_wedge_moving_up_the.html
