The U.S. Army Corps of Engineers (USACE) awarded a cutterhead dredge contract to Weeks Marine to construct the saltwater sill across the bottom of the Mississippi River Ship Channel to block the saltwater wedge from advancing upriver to protect the freshwater intakes for the City of New Orleans. The sill construction began on Saturday, September 14, 2024, after a short delay related to the approach of Hurricane Francine. Weeks estimates it has completed approximately 82% of the construction of the saltwater barrier to limit the depth of the River to approximately -55 feet. The USACE and Weeks estimate the sill will be completed on Wednesday September 25, 2024, to the height of -55 feet. The cutterhead dredge J.S. CHATRY (Weeks Marine) continues constructing the saltwater sill near Mile 63.7 Above Head of Passes (AHP).
The USACE anticipates that once again the saltwater sill’s elevation will have to be raised to the height of -30 feet with the inclusion of a navigation notch (620 feet wide) to accommodate all ship traffic with the notch remaining at -55 feet. The augmented sill was first constructed last year (2023), the notched sill performed very well but the pilots, U.S. Coast Guard, Weeks Marine and the USACE all did a phenomenal job moving vessels through a one-way buoyed channel with coordinated traffic via the Contact Pilots: COMMUNICATION IS KEY. If the augmented sill is required, there could be a few scheduled 12-hour closures to all vessel traffic this would allow the J.S. CHATRY to focus on sill building without having to allow the dredge to relocate to accommodate passing ship traffic. This was also implemented last year and worked well for completion of the sill to -30 feet, decision based upon measurements after the presently targeted elevation is reached.
The Marine Safety Information Bulletin as distributed by the U.S. Coast Guard that details the navigation transit restrictions is attached, please review the MSIB for complete details.
Also attached is the “U.S. Coast Guard, Captain of the Port New Orleans Navigation Outlook” document released on September 20, 2024. The following information is reproduced from the Navigation Outlook and extends the one-way transit restriction to protect the dredge and equipment while pumping on the deeper areas.
“All vessels are limited to one way traffic from MM 63.5 to 65 AHP confined to a channel 500’ wide. The channel follows the Left Descending Bank (LDB) and is marked on its West side by four white buoys with fixed white all-around lights.
- All vessels transiting this zone shall check-in with and take direction from the Contact Pilot onboard the J.S. CHATRY 30 minutes prior to arrival on Channel 67.
- All vessels shall transit at their slowest safe speed between MM 63.5 to 65 AHP.
- Alliance Anchorage is closed to all traffic.”
Weeks continues to work to build the sill in the deepest areas of the river as priority, vessel traffic and pilots are required to report anticipated transits through the area with a Contact Pilot located on scene with at least 30 minute notice
Last year the USACE raised the sill to an elevation of -30 feet with a 620-foot navigation notch left in to allow one-way vessel traffic through a buoyed one-way channel. The USACE remains concerned that this could be required based on long-range precipitation models, the USACE will continue to monitor the saltwater wedge and precipitation level across the Mississippi River Basin to determine if the sill will require augmentation again.
The following information is reproduced from the latest USACE Saltwater Intrusion Information website:
*****SALTWATER WEDGE INFORMATION******
SALTWATER WEDGE: As of September 17, 2024, the USACE measured the location of the toe of the saltwater wedge at Mile 49.2 AHP.
Saltwater Wedge Information Link: https://www.mvn.usace.army.mil/Missions/Engineering/Stage-and-Hydrologic-Data/SaltwaterWedge/SaltwaterWedgeNow/
The flow in the Mississippi River remains extremely low with the flow at Red River Landing (Mile 302.4 AHP) measured at 197,000 cubic feet per second earlier today.
The stage reading at the Carrollton Gage at 1300 hours today was 2.79 feet with a 24-hour change of + 0.14 feet. A small rise is predicted in the National Weather Service 28-Day “Extended Streamflow Prediction” to 3.8 feet on September 24 and to then begin a slow extended fall to 2.3 feet on October 21 (2024).
