Posted on October 9, 2023
The Army Corps of Engineers has known for decades that its continual efforts to deepen the Mississippi River for bigger ships would eventually trigger the saltwater crisis that has now gripped the New Orleans area for weeks.
“This is certainly something that everybody knew was going to happen,” said Cecil Soileau, a retired Corps engineer who warned in a 1990 report that dredging the lower river would threaten the region’s drinking water.
That report, written with two other Corps engineers, said “a substantial body of historical evidence pointed to channel deepening as the major cause of increases in frequency and duration of saltwater intrusion events.”
While drought in the Midwest has drastically cut downriver flows this year, dredging to make way for larger cargo ships was the key to bringing the Gulf of Mexico’s salty water to New Orleans’ doorstep, said Soileau, who was chief of the hydrology and hydraulics branch of the Corps’ New Orleans division before he retired in 1993.
“We have droughts every 20 or 30 years,” he said. “We had them in 1930s, 1953, 1988. But it didn’t seem to bother us before Southwest Pass was deepened. Now it takes a lot more fresh water to keep the salt water from coming in.”
Had the lower river not been deepened to 55 feet in recent years, the salt water likely would have halted near Alliance, about 20 miles downriver from New Orleans, Soileau said.
Instead, the wedge of salt water snaking up the Mississippi has sullied water supplies in south and central Plaquemines Parish and is expected to make water unsafe to drink in communities closer to New Orleans in the coming weeks. The Corps has predicted the salt water will reach the water plant intakes in Belle Chasse, Dalcour and St. Bernard Parish later this month and New Orleans’ West Bank and Gretna in late November. Forecasts updated on Thursday indicate salt might not reach harmful levels at New Orleans’ east bank plant and at the plant in East Jefferson.
Deepening the river gives heavier salt water more room to build up under the lighter fresh water, eventually forming a mass that the weakening downriver flows can’t budge.
The Corps has repeatedly acknowledged that channel deepening exacerbates saltwater intrusion, but agency officials have stressed in recent weeks that the current crisis is more an act of God than man.
“Saltwater intrusion in the Mississippi River during extreme low water has been a naturally occurring phenomenon since before the deepening of the river,” Corps spokesperson Ricky Boyett said.
Had the lower river not been deepened to 55 feet in recent years, the salt water likely would have halted near Alliance, about 20 miles downriver from New Orleans, Soileau said.
Instead, the wedge of salt water snaking up the Mississippi has sullied water supplies in south and central Plaquemines Parish and is expected to make water unsafe to drink in communities closer to New Orleans in the coming weeks. The Corps has predicted the salt water will reach the water plant intakes in Belle Chasse, Dalcour and St. Bernard Parish later this month and New Orleans’ West Bank and Gretna in late November. Forecasts updated on Thursday indicate salt might not reach harmful levels at New Orleans’ east bank plant and at the plant in East Jefferson.
Deepening the river gives heavier salt water more room to build up under the lighter fresh water, eventually forming a mass that the weakening downriver flows can’t budge.
The Corps has repeatedly acknowledged that channel deepening exacerbates saltwater intrusion, but agency officials have stressed in recent weeks that the current crisis is more an act of God than man.
“Saltwater intrusion in the Mississippi River during extreme low water has been a naturally occurring phenomenon since before the deepening of the river,” Corps spokesperson Ricky Boyett said.
Sill solution?
Before the most recent dredging effort, which aimed last year for a depth of 50 feet but actually reached 55 feet south of Venice, Corps studies indicated salt water could become an issue for Plaquemines for about 10 days during low-water periods. It was an optimistic prediction; Plaquemines has had to contend with saltwater contamination since July — a period of more than three months.
To slow the salt water, the Corps built an underwater dam, called a sill, in July. But the sill was easily overwhelmed, prompting the Corps to begin emergency work late last month to elevate it to within 30 feet of the river’s surface. The work, which continues, hasn’t halted the salt water’s progress, although Corps officials think it has made a difference.
Boyett stressed that the Corps has taken other steps to mitigate the salt water, including sending water by barge to Plaquemines and several upgrades to the area’s water systems.
A temporary sill worked fairly well when river levels plummeted in 1988, but the crisis was also eased by a shift in weather that brought more fresh water downriver just before New Orleans’ water supplies were fouled.
In his 1990 report, Soileau said New Orleans leaders began searching for emergency sources of water as the salt water approached.
“After devoting local resources to find solutions that were timely, it became evident there weren’t any,” he wrote 33 years ago.
The saltwater wedge of ‘88 should have raised concerns about efforts to dig out more of the river bottom, Soileau said.
“It demonstrated what would happen if we went deeper.”
Warnings from ’81
Soileau wasn’t the first to sound the alarm about river dredging and water supplies.
When the Corps first proposed deepening the channel from 40 feet to 55 feet south of Baton Rouge, in the early 1980s, several government agencies and environmental groups protested.
In a 1981 letter, the Louisiana Department of Health urged the Corps to reconsider its plan, stressing that the “increased salinity in drinking water supplies … is one of considerable health significance.”
The state Department of Natural Resources was more pointed. In a letter that same year, Director Michael Bourgeois said he was “uncomfortable” with the Corps’ “dismissal … of saltwater intrusion as only a minor problem.”
“The problem is hardly minor given the fact that a major metropolitan area depends on the Mississippi River for its freshwater supplies,” he wrote.
The Environmental Defense Fund predicted New Orleans’ current water crisis in its letter to the Corps. A deeper channel, the group wrote in 1981, “would result in movement of the saltwater wedge to a point where New Orleans and other communities would have to find alternative sources of water.”
Forty-two years later, New Orleans and Jefferson Parish have been scrambling to do exactly that. They are developing plans to spend upwards of $300 million on emergency pipelines to pull water from farther upriver. Schools and hotels have been buying pallet loads of bottled water, and hospitals are investing in expensive saltwater filtration systems.
Trade vs. tap water
The Corps has been clearing the way for ship travel in the Mississippi for almost a century. As ships have increased in size, the Corps has made sure the river has increased in depth.
While the number of cargo ships has grown by less than 10% over the past decade, the capacity of these vessels has ballooned by 65%, according to the Institute of Shipping Economics and Logistics.
Deepening the Mississippi ensures that Louisiana ports remain competitive, said U.S. Sen. Bill Cassidy, R-Baton Rouge.
“Bigger ships carrying more cargo means more jobs and economic opportunity for Louisiana and the nation,” Cassidy said after the first two phases of dredging were completed last year.
The river handles 450 million tons of grain, fuel, chemicals and other exports each year, and accounts for almost 20% of all waterborne commerce in the U.S., according to a 2018 Corps report.
If residents of south Louisiana are angry about the recent threats to their drinking water, business leaders say they need to realize the Mississippi has another role: superhighway.
“It’s not just for [supplying] fresh water; it’s for commerce,” said Sean Duffy, executive director of the Big River Coalition, which began lobbying to deepen the channel in 2012. “Channel deepening puts us in competition to ship cargo around the world. It helps American farmers. It brings cost down for all Americans.”
The latest deepening effort drew far less opposition than the one in 1981. The Corps’ 2018 environmental analysis of the project generated only a few dozen comments. Over the course of two public meetings about the deepening, salt water wasn’t mentioned by either Corps staff or attendees, according to transcripts.
Salty Future?
Soileau isn’t surprised people had forgotten the risks. If the last big water scare hadn’t happened as far back as 1988, when many local leaders were teenagers, maybe they’d have foreseen the danger.
“If it had been more recent, maybe it would have triggered greater concern,” he said. “It’s probably something we should have anticipated, but we simply don’t look down the road far enough.”
If the Mississippi must serve the dual and sometimes conflicting purposes of supplying water and conveying ships, it’s clear that a hastily built sill isn’t enough to protect water supplies, Soileau said.
He recommends reviving the idea of a monumental gate at the mouth of the river. Once considered by the the Corps in the early ‘80s, but cast aside due to the complexity and cost, a gate or lock system could swing shut when the Gulf threatens to invade.
Building a five-mile span of steel and concrete on a soggy, rapidly eroding river delta would have a “rather astronomical” price tag, Soileau admits, and the Corps has no plans to pursue such a project.
So perhaps the New Orleans area will need to brace itself for a saltier future.
“I don’t know any other solution,” he said. “These things with salt water — they’ve happened in the past, and it’s going to happen in the future.”
