The New Orleans mayor, LaToya Cantrell, signed an emergency declaration for the city on Friday amid concerns about saltwater from the the Gulf of Mexico that has been creeping up the drought-hit Mississippi River in Louisiana.
The declaration came amid concerns the saltwater, which is impacting the river because it is at such low levels, could impact the drinking water of thousands of residents in the next few weeks
The Louisiana governor, John Bel Edwards, said the state would be requesting an emergency declaration from the federal government in the next couple of days as well to get federal funds and agencies involved.
For those who rely on the Mississippi River for drinking water, the saltwater intrusion is a potential health risk, as high concentrations of salt in drinking water may cause people to develop increased blood pressure and corrode drinking water infrastructure.
The saltwater has already entered the drinking water of communities south of New Orleans – from Empire Bridge to Venice, Louisiana – making the water undrinkable for about 2,000 residents and causing water outages at local schools. As the saltwater moves upriver, it could affect the drinking water for another 20,000 people in Belle Chasse. After that it could reach the drinking water intake for the New Orleans community of Algiers, across the river from the French Quarter.
To slow the progression of the saltwater, the army corps of engineers constructed an underwater barrier downriver from New Orleans in July.
On Friday, the corps released an updated timeline of the saltwater intrusion in the river that includes the delay added by the underwater barrier. With the barrier in place, the saltwater would not reach the Belle Chasse drinking water intake until 13 October and the Algiers intake until 22 October.
Governor Edwards said his team is working with the four parishes at the end of the Mississippi River that are already affected by the low river water. “I found out today that the forecast is for above average amounts of precipitation in winter. But that’s still several months away,” he said. “And what we need most in Louisiana right now, for the Mississippi River, we need rain further up north in the Ohio Valley.”
Colonel Cullen Jones of the army corps of engineers said that 10in of rain would be needed across the entire Mississippi Valley to increase the Mississippi River flow high enough to push back the seawater.
The mouth of the Mississippi River is below sea level. Because saltwater is denser than freshwater it is moving underneath the freshwater along the bottom of the river in a wedge shape.
The lowest Mississippi River levels recorded in modern history were in 1988, when seawater entered the water systems of New Orleans for a couple of days before it was pushed back down the river by freshwater. But forecasts show the current day low river levels could become more severe, potentially allowing saltwater to remain in the system from a couple of weeks to a couple of months, said Colonel Jones.
The corps is also working on a plan to deliver 15m gallons to the southern parishes by next week. Together the water treatment systems that could be contaminated with saltwater by 24 October use 36m gallons of water per day.
The barrier was intended to slow the upstream movement of the saltwater, but the salt wedge has overtopped the barrier. Similar barriers were constructed in 1988, 2012 and 2022. This is the first time the barrier has needed to be built in back-to-back years. Last year, the barrier wasn’t overtopped, he added.
Communities along the river are keeping a close eye on the upstream movement of the saltwater wedge and testing the salinity levels near their water system intakes, said Dr Joseph Kanter, the state health officer and medical director for the Louisiana department of health. “Everyone along the river knows where the wedge is and when it’s approaching. That’s not going to be a surprise,” he said.
While salt is not a federally regulated contaminant, it could be a health concern for people who are on low salt diets and for those who are pregnant. The World Health Organization’s drinking water guideline suggests that 200mg of sodium a liter is the threshold at which most people will not want to drink the water because of taste. When saltwater is pumped through a water distribution system it can cause pipes to corrode, potentially leaching heavy metals from the pipes and pipe fittings into drinking water.
But it is difficult to predict which metals might leach from pipes, as distribution systems are all different and some do not have full maps of their systems. “So, a hallmark of the response is going to be frequent testing of the water that is going through the water systems distribution network,” Kanter said.
The corps of engineers is exploring barging river water from upriver to areas being affected by the saltwater intrusion and smaller communities south of Louisiana are sourcing reverse osmosis devices capable of desalinating water, Kanter said. But those measures would probably not be able to replace the amount of water used by New Orleans, which has a population of nearly 370,000 people.
Kanter reiterated that the current estimates are worst-case scenarios.
Multiple days of rainfall in the Missouri and Ohio River Basins would be necessary to increase the freshwater flow of the Mississippi River, said Julie Lesko, a senior service hydrologist with the National Weather Service New Orleans/Baton Rouge office. “When we look at what could happen over a two-week period we’re not seeing anything significant that would make its way down river to alleviate the problems,” she said.
Coastal communities across the US are facing similar challenges with saltwater intrusion, said Allison Lassiter, an assistant professor at the University of Pennsylvania focused on urban water management.
Desalination systems have limitations because they are expensive and don’t produce a lot of water. “This will be a difficult nut to crack,” she said.
Sea level rise will make the conditions that allow saltwater intrusion into the Mississippi River more likely in the future, said Soni Pradhanang, an associate professor of hydrology and water quality at the University of Rhode Island. Climate change is also expected to exacerbate droughts by making them longer and more frequent. “We’re only going to see this happening more,” she said. “Sea level rise will lead to increased salinity as more of this seawater pushes up into the estuaries and inland.”