USACE EMERGENCY RESPONSE SALTWATER SILL CONSTRUCTION:
Today’s update from Weeks Marine on the construction of the saltwater sill reported construction operations continue to effectively and to safely pass traffic in the one-way adjusted channel with traffic management coordinated via the Contact Pilot on the cutterhead dredge J.S. CHATRY.
Weeks expects to make minor adjustments to the two of the four buoys installed to mark the alternate channel over the next few days. The Crescent and Federal Pilots approved the realignment of the two buoys to assist Weeks. The one-way traffic extends from Mile 63.91 Above Head of Passes [AHP] to Mile 63.65 AHP (buoyed channel). Weeks and Pilots report no challenges with vessel transits to this point.
The J.S. CHATRY began dredging with a two-hour test on July 11 and then commenced 24-hour dredging operations on the morning of July 12 – operations have continued non-stop successfully since. The first targeted elevation of the saltwater sill is – 55 feet (with allowance of a few feet higher) this first phase of construction is expected to be achieved over the next 7-10 days. Upon reaching the first target elevation the USACE will continue testing of salinity levels to see if the sill will require being built higher off the bottom (draft restrictions could become necessary but will not be required if the sill stays at the first targeted elevation – at this time construction to a higher barrier is not expected).
The Navigation Bulletin released by the U.S. Army Corps of Engineers and the Marine Safety Information Bulletin (MSIB) issued by the U.S. Coast Guard to document the Vessel Traffic Service Safety Measure with the official transit conditions are attached. The following transit restrictions begin at 1200 hours on July 11, 2023, as reproduced from the MSIB:
“All vessels are limited to one way traffic from MM 63.65 to 63.91 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 shall check-in with and take direction from the Contact Pilot onboard the J.S. CHATRY 30 minutes prior to arrival on Channel 67.
Please see attached MSIB for complete details. (The Alliance Anchorage extends from Mile 65.8 AHP to Mile 63.8 AHP).
*Two of the buoys marking the adjusted channel will be relocated, the coordinates of the buoys listed in the MSIB will not be revised to match the realignment, but new coordinates will be shared with the relevant pilot associations and the contact pilots on board the dredge. |
| Saltwater Sill Diagrams below provided by the USACE:
Sill Location (USACE): Sill Diagram Rendering with footnotes for correctness below (USACE)
The saltwater sill can be thought of as an underwater levee on the bottom of the Mississippi River designed to capture the saltwater wedge and cease its migration upriver.
The USACE measured the saltwater wedge at Mile 57.2 AHP on July 6, 2023, and predicted the wedge would reach Mile 59.8 AHP by July 7, 2023.
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With You,
Sean
Sean M. Duffy, Sr.
Executive Director
Standing By Channel: (504) 338-3165
Big River Coalition
