File:Underwater Sill Augmentation in Mississippi River 26 Sept 2023 - 6.jpg

English: U.S. Army Corps of Engineers personnel visited the site of the underwater sill in the Mississippi River on Sept. 26, 2023, to provide media with the most up-to-date images and information from the sill augmentation site. USACE is building up the current sill to an elevation of -30 feet while maintaining a 620-foot-wide navigation lane at -55 feet to allow for deep draft navigation. Dredging work on the augmented sill began Sept. 24 and is expected to be completed within 24 days. The initial sill, which was completed in July 2023, was constructed to an elevation of -55 feet, which means the top of the sill was 55 feet below the surface of the river. The current National Weather Service Mississippi River forecast indicates the river volume will fall to historic lows over the next several weeks. 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. 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 (cfs) because the mass of fresh water is no longer capable of preventing saltwater from moving into the below-sea-level river channel. (U.S. Army photo)