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 Restoration Design

Introduction

The grounding of the M/V Wellwood impacted the reef’s surface, flattening corals below the vessel’s hull and creating pits in patchy areas along the reef. The purpose of the restoration is to restore the M/V Wellwood grounding and stabilize the additional injury caused by the 1998 storm season. Restoring and stabilizing the injured reef will prevent further injury to the reef system, provide structural restoration to mimic the original relief, and re-establish biological communities. The goal is to ultimately restore the reef, to the greatest extent practicable, to a state similar to that which existed before the injury occurred.

Project Description

Side view of module construction including placement and layout for securing the module to the reef. (Image: Florida Keys National Marine Sanctuary)

The project involves the restoration of fourteen separate reef sites damaged from the 1984 grounding of the M/V Wellwood on Molasses Reef. The fourteen sites, located in close proximity to each other, range in the degree of damage suffered as a result of the grounding. The project consists of the placement of twenty-two dome shaped reef modules in the fourteen reef sites. Each reef repair site will be compared to the adjacent undamaged coral reef in order to repair the reef to an ambient structure representative of the conditions of both the adjacent reef and the reef prior to the grounding.

The intent of the repair at each site is to firmly anchor the reef modules and replicate the approximate reef crest elevation around the perimeter or each reef module. The reef modules consist of a reinforced concrete slab with the construction of a hollow concrete and limestone dome, on top of the slab weighing approximately 3500 pounds each.

In general, the modules will be placed and anchored to natural reef by a process of pumping tremie concrete beneath and around the base of the module, which will lock it into the natural reef structure. In some places, the reef site will be excavated to provide an area large and deep enough to place and anchor a reef module. In other instances, deeply damaged sites will require a build-up or filling process to elevate the bottom sufficiently to place a reef module. A specialized concrete mixture will be prepared and placed around limestone rock to build-up some of the reef sites sufficiently for reef module placement, and in all locales, to anchor the modules to the natural reef. Limestone material in the form of boulders or smaller stone will be used as a filler material to build up the perimeter around reef repair sites to retain tremie concrete, and to provide a repair surface (dressing) similar to the natural reef. At the direction of NOAA personnel at the repair site, each site will be dressed with limestone rock in order to replicate as near as possible the appearance of the adjacent reef, by pressing the rock into the finished concrete surface or securing rock with mortar, at each repair site. The final product at each of the fourteen repair sites will be the establishment of a reef module, or multiple modules, with the surrounding repair area dressed with limestone rock to create a more natural appearance.

Mold used in restoration process Mixing cement during restoration process Restoration process image

Construction of reef module (left to right): 1. Photo of form assembly with rebar in place and sand drain plug (sand placed in module during construction was later removed). 2. Cement poured into base. 3. Base poured with sand and limestone -- rebar on top. After the construction, the sand was washed out to create cavities for critter habitat. (Photos: Florida Keys National Marine Sanctuary)

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Reef Site Preparation

Each of the fourteen sites damaged by the grounding of the M/V Wellwood have varying degrees of area damaged and of depth of damage. The extent of the damage at the sites ranges from severe structural damage to the reef to minor loss of surface reef material. It is NOAA’s plan to treat each of the 14 sites, regardless of the extent of damage. A minimum of one reef module will be placed at each of the 14 damaged sites, with a final repair surface approximately level with the adjacent reef surface. In some instances, the pits in the reef must be built-up through the placement of tremie-pour concrete with embedded rock and with rebar reinforcement to elevate the surface suffieciently for the placement of the reef module(s). In order for the modules to be sufficiently anchored into the natural reef, the module must be recessed into the natural reef by a minimum of eight inches to a maximum of ten inches. In the case of the damaged site being to shallow or small a surface area for securing a module, the reef will be minorly excavated in order to sufficiently anchor the module. All excavated material will be removed from the project site and disposed of in a landfill, or as directed. Ultimately, each reef site will require filling, excavation, or a combination of both to create a level surface for the placement of the reef modules.

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Attention to Aesthetics

Steps will be taken to minimize concrete surface exposure and maximize the exposure of limestone surfaces through placement of limestone on concrete surface to mimic the natural aesthetics and relief of the Molasses reef. The exposed surfaces will feature as much limestone rock as possible and surfaces of significant size with mortar or concrete faces will be minimized.

Photo of completed module ready for placement in one of the 14 restoration sites. (Photo: Florida Keys National Marine Sanctuary)



 

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