On Sept. 28, the U.S. Army Corps of Engineers, New Orleans District, began construction of an underwater sill across the bed of the Mississippi River channel to arrest further upriver progression of salt water from the Gulf. The sill was completed on Oct. 10.

In a press release on its website, USACE said, "Mississippi River's volume of water has fallen to a level that allows salt water from the Gulf of America to intrude upstream. The intrusion of salt water into the river is a naturally occurring periodic condition because the bottom of the riverbed between Natchez, Miss., and the Gulf of America 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, unimpeded salt water can travel upriver and threaten municipal drinking water and industrial water supplies," stated USACE.

The construction of the sill is a mitigation feature required as part of the effort to deepen the shipping channel from 40 feet to 45 feet and subsequently to 50 feet. The sill is designed to create a large reservoir to collect and hold salt water for a period of time equal to the increase in duration of the saltwater intrusion caused by the channel deepening, noted the Corps. Here is a link to the location of the wedge as of Oct. 14 and will update if the toe moves upriver: https://www.mvn.usace.army.mil/….

USACE constructed a similar underwater sill in 1988, 1999, 2012, 2022, 2023 and 2024 at river mile 64, near Myrtle Grove, Louisiana, to arrest the progression of saltwater intrusion during that year's low water season. In 2023, USACE augmented the underwater sill from a depth of minus 55 feet to a depth of minus 30 feet when the initial sill was overtopped by salt water moving upriver. A 620-foot-wide navigation lane was kept on the sill at a depth of minus 55 feet to ensure deep-draft shipping continued along the nation's busiest inland waterway, noted the press release.

On Oct. 19, the Mississippi River at New Orleans was at 3 feet above zero gauge. When the river gets low there, off-loading barges to waiting ships can be difficult.

Elsewhere on the Lower Mississippi River, the river level in St. Louis on Oct. 19 is at 0.34 feet above zero gauge and at Memphis, the river is at 8.72 below zero gauge. The USCG will lower drafts on barges and tow sizes if the river keeps falling. This means that shippers have to load less grain in a barge headed to the Gulf but still pay the same freight, which could affect their basis paid to a farmer. Also, cutting back on tow sizes may mean that shippers will have to load more barges to be sure to make contract specs at the Gulf.

As of Oct. 16, CIF (Cost, Insurance, and Freight) corn basis was firm, while CIF soybean basis was weaker. Because of the continued government shutdown, there are no weekly exports sales and shipment reports. However, USDA is still publishing weekly inspections which continues to show strong corn inspections, while soybean inspections have been down, mainly due to China snubbing U.S. soybeans because of the tariff fight with the U.S.

Mississippi River gauge St. Louis: https://water.noaa.gov/…

Mississippi River gauge at Memphis: https://water.noaa.gov/…

Mary Kennedy can be reached at mary.kennedy@dtn.com

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