Once again, a wedge of salt water is moving up the Mississippi River from the Gulf of Mexico, threatening drinking water supplies and forcing the U.S. Army Corps of Engineers to construct an underwater sill to slow its advance.
This phenomenon, which used to happen about once a decade, has now required a response three years in a row. There are a number of factors at work — sea level rise, low rivers and the deepening of the channel for shipping among them. In addition, natural cuts in the levee downriver, like Neptune Pass and Mardi Gras Pass, bleed fresh water out and allow salt water to advance.
Last year, the salt water forced some residents in lower Plaquemines to go for months using only bottled or trucked-in water. It damaged appliances and forced a hurried response by federal, state and local officials who rushed to put reverse-osmosis machines on water intakes to reduce salinity, costing millions of dollars.
In Orleans and Jefferson, which are far more heavily populated, new pipelines were proposed to bring fresh water from farther upriver in order to keep salt levels below safety thresholds. Those ended up not being needed, but the threat was enough to illustrate the water supply's precariousness for hundreds of thousands of residents.
Thankfully, this year's wedge is predicted to be less of a problem than last year's. Current forecasts have it impacting the water plants in Port Sulphur and Point a la Hache, as well as one in the Boothville-Venice area that is already being affected. Plaquemines Parish officials have rented reverse-osmosis machines and are prepared to pipe water downriver from Belle Chasse to combat the problem. Unlike last year, the Corps does not anticipate needing to barge fresh water to those places.
Areas farther upriver, like St. Bernard, Orleans and Jefferson parishes, are not expected to be impacted this year.
There is still some variability in that forecast. While the wedge's advance was slowed by Hurricane Francine's heavy rains, a lot rides on how much rain falls across the Midwest and whether enough of it flows down the Mississippi to push out the salt water.
The wedge's repeat appearance highlights the challenge that faces much of south Louisiana. Higher seas, increased management of the river and climate instability mean that the old ways of doing things are unlikely to be sufficient going forward.
In Plaquemines, installing permanent reverse-osmosis machines is cost-prohibitive, officials have said. Instead, they are looking at ways to increase pumping capacity from the Belle Chasse water plant, which is much farther upriver than the ones near Boothville, Port Sulphur and Point a la Hache.
These improvements, they hope, will make dealing with the saltwater wedge less of a crisis and more of an adjustment. After all, events like this are the new normal.