Seagrass Mitigation after Previous Beach Renourishment Projects

Village of Key Biscayne

2006-2011 Pipeline Corridor Seagrass Mitigation

The 2002 beach nourishment construction included permitted impacts along the offshore pipeline corridor of 0.14 acres of seagrass. These impacts were caused by the placement of the submerged pipeline along the 6,000-foot corridor from the offshore borrow areas southeast of Key Biscayne to the beach. The pipeline connected the hydraulic dredge pumping the sand slurry to the beach for fill placement. The initial dredge pipeline was installed in 2000 as beach construction commenced.  Due to delays in construction, this pipeline remained in place for approximately 2 years, and a second pipeline was installed by the contractor once beach fill placement eventually commenced in the spring of 2002.  Both pipelines were removed in late 2002 at the completion of construction. 

From 2004-2005, Miami-Dade DERM documented 0.32 acres of seagrass impacts in the pipeline corridor, which represented an increase of 0.18 acre over the permitted acreage.

For mitigation of these impacts, 0.28 acres of seagrass were to be restored within the pipeline corridor and in the form of prop scar restoration within seagrass beds in Biscayne Bay. 

The Village negotiated with the environmental regulatory agencies, State of Florida Department of Environmental Protection (DEP) and Miami-Dade County Department of Environmental Resource Management (DERM), for seagrass mitigation related to these impacts. The agencies required a total of 1.33 acres of off-site seagrass mitigation, and the affected seagrass areas along the pipeline corridor recovered naturally. This acreage incorporated all non-permitted impacts, permitted impacts, and increases due to the time delay in mitigation implementation.

  • Area A Restoration - 2008:

    Seagrass surveys, mitigation planning and permitting commenced in 2006-2008. In 2008, the first phase of seagrass mitigation in Area A was completed in southern Miami-Dade County consisting of a total of 0.42 acres. Mitigation consisted of mapping prop scars within the seagrass beds, harvesting  of appropriate "donor" seagrass, and transplanting the donor grass to the scars. In addition, bird stakes were installed to promote seagrass restoration. A portion of the mitigation areas are located in the Florida Keys National Marine Sanctuary (FKNMS). Continued negotiations with the Florida DEP precluded prop scar restoration in areas of Biscayne Bay, as the Office of Coastal and Aquatic Managed Areas (CAMA) of the DEP would not allow the harvesting of donor seagrass from within the northern portion of Biscayne Bay Aquatic Preserve (BBAP).  Therefore, additional areas were mapped in southern Miami-Dade County outside of the BBAP and outside of Biscayne National Park.

  • Areas A, B, D and Monroe County Restoration - 2010:

    To continue with the mitigation implementation to achieve the total mitigation requirement of 1.33 acres, additional areas for prop scar restoration were mapped. In early 2010, a total of 33 sites covering 0.61 acres were restored with a combination of sediment placement to restore the scars along with seagrass transplanting and bird stake installation. These areas were in Areas A, B and D, with a small portion of the restoration area in northern Monroe County.

  • Biscayne National Park Restoration - 2011:

    With the lack of suitable restoration areas outside of the BBAP, the Village entered into a Memorandum of Understanding (MOU) with the Biscayne National Park to restore the remaining 0.33 acres of seagrass mitigation park within the park boundaries. In September 2011 the restoration was completed with the placement of sediment fill, transplanting of appropriate donor seagrass, and installation of bird stakes.

Monitoring of the restoration areas is ongoing, and to date the success criteria have been met or exceeded in accordance with the permit conditions.




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