Post-Florence Renourishment Project - Phase II (2020)
HOW TO INTERPRET THE PROGRESS MAPS
for The Post Florence Renourishment Project (Phase II)
Phase II of the Post Florence Renourishment Project will utilize 1,995,000 cubic yards (cy) of sand obtained from the Offshore Dredged Material Disposal Site (ODMDS) associated with Morehead City Federal Navigation Project. West Emerald Isle (EI), Salter Path (IB), Pine Knoll Shores (PKS), and West Atlantic Beach will receive 345,000 cy, 140,000 cy, 990,000 cy, and 520,000 cy, respectively along 9.5 miles of shorelines in four discrete reaches depicted in the Project Construction Map above. As a mental picture, a conventional dump truck holds roughly 12 cubic yards of wet sand. The project is scheduled to be conducted between January 1 to April 30, 2020 and therefore within the construction window established to limit impacts to biological resources. The dredging contract has been awarded to Great Lakes Dredge & Dock and the ocean-certified, self-contained hopper dredges Liberty Island and Ellis Island will be employed for the project - similar to the Phase I effort in 2019.
Hopper dredges utilize dragheads affixed to trailing-arm suction pipes mounted on both sides of the vessel (port and starboard). The dragheads loosen the sand on the bottom off the seafloor and deliver the material to the vessel’s “belly” via the suction arms. Subsequent to completing a “cut” and filling the hopper, the dredge will travel and discharge (pump) sand via a buoyed pipeline located offshore that extends to the pre-construction dry beach. A secondary “T-valve” discharge pipe is used to transport material in one direction (east or west), then the other along the beach to complete approximately 1 - 2 mile sections as lengths of pipe are added and subsequently broken down. The buoyed pipeline and T-valve assembly is subsequently transited down the beach until the nourishment reaches have been filled. Dredged sand will be bulldozed into general construction specifications for subsequent grading into final contours, possibly tilled, and opened for recreational use. The dredges Liberty Island has a maximum capacity of 6,540 cy and the Ellis Island 14,800 cy under optimal conditions.
Project engineers use “stations” positioned along the beach to monitor construction progress and to verify in-place volumes of sand pumped on the beach by dredging contractors. The progress maps above provide detailed views of the Post Florence Renourishment Project (Phase II) reaches to be completed in 2020 with the location/identification of the station numbers and the location of buoyed pipelines. The shaded areas in red represent the completed portions of the project and will be updated on a weekly basis (at least) throughout construction.
The station numbers included in the progress maps conveniently correspond to thousands of linear feet along the beach. For instance, the distance between station “825+00” (Iron Steamer Access) and “896+00” (Memorial Park Access) on the Reach 9 - Pine Knoll Shores Area of Detail graphic above is 7,100 feet. If you visit the beaches of Bogue Banks this winter, you may see wood or metal stakes at the base of the dunes that will identify these station numbers as such.
PROJECT PLANNING & IMPLEMENTATION
The geographical extents and basic geometries of the Phase II, Post Florence Renourishment Project are included in the accompanying "Key Documents" on top of this webpage, and the project was formulated based upon design and cash-flow considerations. Every municipality along Bogue Banks has or is scheduled to receive sand between the Phase I and Phase II projects while maximizing the local and State funding we have in hand to address all of the more critically eroded areas along the Island, coupled with any FEMA funding that has been received to date. Weeks Marine and Great Lakes Dredge & Dock furnished bids for the Phase II effort with the former (Great Lakes) providing the lowest awardable bid price. Great Lakes was also our Phase I contractor. Phase III of the Post-Florence Renourishment Project is tentatively scheduled for winter 2020-2021 and will encompass Central and Western Emerald Isle.
In cross-section going from the top of the dune seaward, the beachfill will be contoured by; (1) tying into the existing, eroded frontal dune at +12 or +13 feet NAVD 88 and maintaining that top dune elevation at vary lengths as one progresses seaward, (2) the slope of the newly constructed frontal dune will be graded on a 5:1 slope to the elevation of +6 feet NAVD 88, (3) the beach berm (flat part of the beach) will be extended from that point seaward at +6 feet NAVD 88 at varying lengths, and (4) the slope of the fill from the berm crest out to sea will be on a 20:1 slope. The newly created dune crest and dune slope will be planted (vegetated) with Sea Oats as part of the contract (see typical cross-section above).
The borrow source for this nourishment effort is the Offshore Dredged Material Disposal Site (ODMDS) associated with Morehead City Federal Navigation Project. This dump site is essentially a repository for dredged material historically extracted from the Outer Harbor reach of the navigation channel and based upon experiences with a 2004 and 2007 Section 933 Project that utilized channel material for beach nourishment and 2004, 2007, 2013. and 2019 post hurricane projects that actually utilized the ODMDS; we expect the sand quality to be excellent. This also makes intuitive sense, because for the most part, the shoal material that enters the navigation channel at Beaufort Inlet is sand that has traveled from adjacent beaches. Construction, or deepening material that resides in the ODMDS should be avoided. To this effect the firm of Moffatt & Nichol, who has been retained by the Bogue Banks communities as the engineering consultant for the Post-Florence Renourishment Project, has performed additional sediment sampling and analyses in the ODMDS to hone the areas of beach quality sand.