U.S. Army Corps of Engineers (USACE) EMERGENCY RESPONSE SALT WATER SILL CONSTRUCTION:
Weeks Marine continues dredging with their cutterhead dredge J.S. CHATRY to build the salt water sill (barrier) at Mile 63.8 Above Head of Passes (AHP), Weeks now indicates the sill is expected to be completed by tomorrow, Friday, October 21, 2022 to the present targeted elevation -55 feet (between -55 and -52 feet). Due to the difficulties in evenly achieving that height the USACE allowed Weeks a variance in the sill height, the sill is now expected to be completed to this first targeted elevation by tomorrow (Friday, October 21, 2022)
Weeks is also working to grade down a few areas down that were built slightly higher than the allowed -52 feet and will knock these areas down to be within the accepted variance (-55 feet to -52 feet) that will not require adjustment to the maximum draft recommendation on the Mississippi River Ship Channel of 50 feet. The expected schedule is for the construction of the sill be to be completed tomorrow and for the buoys and one-traffic to be controlled by the Contact Pilots until the buoys are removed, expected to occur on Saturday (October 22, 2022).
Upon completion of this first stage, Weeks will move the J.S. CHATRY upriver to resume work on a restoration project using dredged material from the Alliance Anchorage.
The one-way traffic controlled by the Contact Pilot will continue until the buoys are removed and the U.S. Coast Guard officially rescinds or adjusts the details in the Marine Safety Information Bulletin (expected October 22, 2022).
The USACE will keep monitoring the situation and if the sill elevation needs to be constructed higher, then the sill building process will resume with a similar configuration and the J.S. CHATRY and equipment returning in the same foot print (expected).
The saltwater wedge has reached the location of the barrier and is both rising and mixing with freshwater, the USACE will continue to monitor the movement of the saltwater and salinity measurement at the sill, a rough estimate is that the USACE will know over the next week if the sill height will need to be increased above 52 feet. If the sill is constructed higher than 52 feet, maximum draft reductions should be expected and could be implemented with little notice.
THE DECISION TO BUILD ABOVE -52 FEET WILL DETERMINE A LOT ABOUT PROMPT ADJUSTMENTS TO MAXIMUM DRAFT RECOMMENDATIONS.
Weeks Marine offered the following update this morning: (drag barge is being utilized to knock down areas higher than 52 feet)
“On 10.19.22 the Dredge JS Chatry continued a second pass in Cut 2 of the Saltwater Sill borrow area from STA 38+00-42+70.
The Tug Sea Lion continued conducting drag barge operations throughout the daytime working on leveling any areas of mounded material.
Spill Barge operations will continue throughout today. We are approaching the design template completion for the barrier sill with current efforts being focused on filling in the side slopes of the sill.”
The Marine Safety Information Bulletin (MSIB) as developed by the U.S. Coast Guard and the Navigation Bulletin released by the U.S. Army Corps of Engineer are both attached.
The channel restrictions detailed in the MSIB are reproduced below:
All vessels are limited to one wav traffic from MM 63.65 to 63.91 AHP confined to a channel soo· 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 T/V CAPT SAM 30 minutes prior to arrival on Channel 67.
- All vessels shall transit at their slowest safe speed between MM 63.5 to 65 AHP.
- All vessels anchoring in Alliance Anchorage shall maintain a minimum 2,500’ separation from the J.S. CHATRY. Additionally. the northern most 600′ of the anchorage is closed. Vessels anchored may be required to vacate at the discretion of the Contact Pilot.
- The Contact Pilot is the Coast Guard’s Designated Representative.
- These measures will remain in effect until rescinded/adjusted at a future date.
The one-way traffic for shallow- and deep-draft traffic will be controlled by the Contact Pilot on the CAPT SAM 24-hours until the construction of the salt water sill is completed (MSIB rescinded or adjusted).
The graph below is reproduced from the National Oceanic and Atmospheric Administration’s (NOAA) National Weather Service website and represents an experimental product to account for the complexity of accurately predicting long-range precipitation. This forecast projects stage levels based on expected precipitation for 2 days (top) and 16 days (bottom) and was developed within the North American Ensemble Forecast System (NAEFS) computer model and highlights Quantitative Precipitation Forecasts (QPF). Along with the forecasts, a shaded area is also provided to indicate uncertainty for the forecast each day in the future. These plots are experimental and not an official forecast product.
Sean M. Duffy, Sr.
Standing By Channel: (504) 338-3165
Big River Coalition