The U.S. Army Corps of Engineers (USACE) contracted Weeks Marine to build the saltwater sill at Mile 63.8 AHP with the cutterhead dredge J.S. CHATRY. The sill is a barrier to the migration upriver of the saltwater wedge to protect freshwater intakes at approximately Mile 74 AHP. Weeks completed the barrier’s construction to the targeted elevation – 55 feet during dredging operation from July 11 to July 27 (2023). The U.S. Coast Guard (USCG) removed all transit restrictions related to the sill’s construction on July 27. The USACE will continue to monitor the location of the saltwater wedge although the long-range river forecasts indicate the Carrollton Gage will remain over 2.0 feet for the next month. The forecasts suggest the saltwater wedge will remain below the sill for the time being. No further actions are anticipated but remain possible.
This is the first time the sill’s construction has been required in back-to-back years as it was constructed during last year’s low water event also by Weeks Marine (October 2022). The hydrology of the Mississippi River is ever changing as 2019 was the first time the Bonnet Carré Spillway had been operated in back-to-back years (2018/2019) and twice in the same year and briefly in 2020 (three years in a row). The USACE last measured the saltwater wedge on July 17, 2023, and reported it was at Mile 52.2 AHP.
The stage at Cairo (IL) at 0900 hours today was 12.34 feet with a 24-hour change of + 0.02 feet and tomorrow’s forecast predicts a slight fall to 11.9 feet. The following chart details the stage readings at Cairo, IL over the last two month (June 3 to August 3).The National Weather Service’s (NWS) Extended Streamflow Prediction forecast the stages at Cairo will continue arise until cresting at 16.4 feet on August 8 and then begin a slow fall to 7.5 feet on August 30 (2023).
The NWS recently confirmed the country is being influenced by the prevailing El Nino weather pattern, that can be linked at times to higher precipitation levels “precipitation increases significantly”. Although the location of precipitation is also a critical factor in increasing stages on the Mississippi River.
During 2019 and 2020 there was a lot of media attention focused on increased precipitation leading to more high river stages with multiple records being set such as the increased operation of the Bonnet Carré Spillway. The Spillway was operated in back-to-back years 2018/2019 for the first time ever and repeated in 2019/2020 and then the first and only time (so far) the flood control structure was operated twice in the same year 2019. One of the caveats related to the increased precipitation forecasts was that more extreme weather events would also increase – thus extreme droughts or increased low water events were included in the same weather briefings. However, there has not been a crest recorded on the Carrollton Gage higher than 14.5 feet since 2020 the last operation of the Bonnet Carré Spillway with a crest of 17.61 feet on April 16, 2020, eclipsing the crest from 2019 at 17.25 feet on May 10, 2019.