Florence Replenishment Project (2019)
Area of Detail - (Reach 1 - East EI)
Area of Detail - (Reach 2 & 3 – Indian Beach/Salter Path)
|Typical Cross Section
1/22/19 – Great Lakes Dredge & Dock should begin mobilizing land- and water-based pipe, heavy equipment, personnel, etc. towards the latter parts of February and although the schedule is tentative, dredging/pumping could begin the first week of March.
HOW TO INTERPRET THE PROGRESS MAPS
for The Post Florence Renourishment Project
The Post Florence Renourishment Project will utilize 945,446 cubic yards (cy) of sand obtained from the Offshore Dredged Material Disposal Site (ODMDS) associated with Morehead City Federal Navigation Project. Emerald Isle (EI), Indian Beach (IB), and the unincorporated area of Salter Path (SP) will receive 617,131 cy, 271,905 cy, and 56,410 cy, respectively along 5.2 miles of shorelines in three discrete reaches depicted in the Project Construction Map above. As a mental picture, a conventional dump truck holds roughly 15 cubic yards of dry sand. The project is scheduled to be conducted between the March 1 to April 30, 2019 construction window established to limit impacts to biological resources, and the dredging contract has been awarded to Great Lakes Dredge & Dock. The ocean-certified, self-contained hopper dredges Liberty Island and Ellis Island will be employed for the project. Great Lakes will utilize the area near the "Dog Leg" 4WD Ramp in EI as their main equipment staging facility and point of beach access for heavy equipment.
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 reaches to be completed in 2019 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 throughout the construction.
The station numbers included in the progress map conveniently correspond to thousands of linear feet along the beach. For instance, the distance between station “418+00” (15th Street) and “473+00” (5th Street) on the Reach 1 - East Emerald Isle Area of Detail graphic above is 5,500 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 Post Florence Renourishment Project are included in the accompanying maps below and the project is essentially a re-formulation of a nourishment project that was planned for this winter (2018-19) along the shorelines of EI, IB, and SP. Hurricane Florence passed by Bogue Banks in September 2018 and just before the project was bid. This same reach of beach lost ~945,000 cubic yards of sand in the wake of Florence and accordingly we re-focused our efforts, made a few slight changes, and re-termed our project to the Post-Florence Renourishment Project (Phase I). This best describes what we are trying to accomplish, and is more consistent for FEMA reimbursement purposes. Decisions from FEMA concerning reimbursement for beach nourishment or their “428” program, which provides a fixed-cost number in lump-sum will be made later this year (2019). Great Lakes Dredge & Dock furnished the lone bid for the project bid totaling $20,109,385. We have internally added some safety-net, contingency funding that increases the total to $20,910,385. Maps and a Fact Sheet summarizing the cost schedule and geographic ranges of the project are below. Phase II of the Post-Florence Renourishment Project is tentatively scheduled for winter 2019-2020 and will encompass Central and Western EI, Pine Knoll Shores, and East Atlantic Beach.
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 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 and Bitter Panicum as part of the contract (see typical cross-section below).
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, and 2013 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.