The U.S. Army Corps of Engineers, New Orleans District is working to delay upriver progression of salt water from the Gulf of Mexico by augmenting the sill initially constructed in July 2023.
Construction is underway to increase the existing underwater sill from a depth of -55 feet to a depth of -30 feet. A 620-foot-wide navigation lane will be kept to a depth of -55 feet to ensure deep-draft shipping continues along the nation’s busiest inland waterway.
USACE initially constructed the underwater barrier sill in July 2023 to create an artificial basin to delay the ingress of salt water beyond river mile 64 above Head of Passes. As a result of the river’s prolonged extreme low-flow rate, the underwater sill was overtopped Sept. 20, 2023.
“As a result of continued falling conditions, this existing sill was overtopped and the toe of the saltwater wedge has reached River Mile 69, near the community of Jesuit Bend,” said Col. Cullen Jones, USACE New Orleans District commander. “Our modeling indicates that by augmenting the existing sill, we can support state and local preparedness and response efforts by delaying further upriver progression of the salt water by approximately 10 to 15 days.”
In addition to the sill augmentation, USACE is preparing to transport fresh water to impacted areas. During previous low-water events, such as 1988 and 2012, barging was used to transport fresh water to treatment facilities downriver of the saltwater toe.
“The Corps is securing water barges that will support impacted water treatment facilities by transporting water collected from portions of the river that do not have salinity readings,” said Jones. “This water can then be combined with water at the municipal facility to create a mixture that is safe for treatment.”
The intrusion of salt water into the river is a naturally occurring phenomenon because the bottom of the riverbed between Natchez, Miss., and the Gulf of Mexico is below sea level. Denser salt water moves upriver along the bottom of the river beneath the less dense fresh water flowing downstream. Under normal conditions, the downstream flow of the river prevents significant upriver progression of the salt water. However, in times of extreme low volume water flow, such as what has been occurring this year, unimpeded salt water can travel upriver and threaten municipal drinking water and industrial water supplies. An underwater sill was constructed on four previous occasions in 1988, 1999, 2012 and last year in 2022.
“As new information becomes available, we will reevaluate the projected movement of the salt water and share this information with our partners and the public for their preparedness, readiness, and response,” said Jones.
The U.S. Army Corps of Engineers, New Orleans District, held a press conference Sept. 15, 2023, at their headquarters in New Orleans, La., to discuss planned efforts to address continued low-water conditions on the Mississippi River.
Col. Cullen Jones, USACE New Orleans District commander, briefed media on current steps the Corps plans to take to augment the existing underwater sill while working with the U.S. Coast Guard and navigation industry to maintain navigation along the Mississippi River. In addition, Plaquemines Parish President Keith Hinkley and Governor’s Office of Homeland Security and Emergency Preparedness director, Casey Tingle, spoke to media at the conference about steps to ensure safe and sufficient water supplies for parish residents.“
The current National Weather Service Mississippi River forecasts the river’s volume to fall to historic lows over the next several weeks,” said Jones. “If these conditions occur, the USACE-constructed saltwater barrier sill is expected to be overtopped by saltwater intruding upriver from the Gulf of Mexico, leading to unsafe salinity conditions at municipal water intakes located north of the sill location.
”Efforts under consideration include barging water downriver to municipal treatment facilities and placement of Reverse Osmosis Water Purification Units to allow for treatment of river water with high chloride levels. USACE has already issued a contract to place a reverse osmosis water purification unit at the East Pointe a la Hache Water Treatment Plant.
To mitigate for the Deep Draft Shipping Channel’s influence on the rate of upriver saltwater progression, USACE constructed an underwater barrier sill in July 2023 to create an artificial basin that delays the ingress of saltwater beyond river mile 64 above Head of Passes. An underwater sill was constructed on four previous occasions in 1988, 1999, 2012 and last year in 2022. During previous low-water events, such as 1988 and 2012, barging was used to transport fresh water to treatment facilities downriver of the saltwater wedge.
USACE continues to closely monitor, survey and model the impacts these conditions may have on the river with regards to both navigation and saltwater intrusion from the Gulf of Mexico. Saltwater intrusion is a naturally occurring phenomenon when the river flows fall below 300,000 cubic feet per second because the mass of fresh water is no longer capable of preventing saltwater from moving into the below-sea-level river channel. The current National Weather Service forecast projects river levels falling to approximately 130,000 cubic feet per second in the New Orleans area. These levels represent the lowest river volume in this area since the recorded low of 120,000 cubic feet per second in 1988.
“This low-water event marks the first time underwater sills were required in back-to-back years as a result of saltwater intrusion from the Gulf of Mexico,” Jones added. “However, the New Orleans District is ready to meet this challenge with the best science, engineering data, and technology available.”
Col. Cullen Jones, commander, U.S. Army Corps of Engineers, New Orleans District, inspected progress on repairs to the London Avenue Permanent Canal Closures & Pumps (PCCP) in New Orleans, La., and installation of temporary pumps May 30, 2023, to ensure pump capacity will be met before the start of this year’s Hurricane Season.
In February 2023, USACE and its partners identified corrosion as the primary cause of failure for Pump #1 at the London Avenue PCCP.
Pump #1 is under repair and scheduled to be returned to service before the start of the 2023 Hurricane Season.
Jones interacted with Corps personnel and contractors working onsite to install temporary pumps and complete repairs to the PCCP. He also spoke with residents living close to the job site who had questions about the work being performed at London Avenue.