The proposed work consists of the routine re-alignment of Singleton Swash, restoration of a natural dune, and improved flushing of an upstream tidal estuary. In detail, Horry County Stormwater is proposing to perform routine re-alignment of Singleton Swash in order to abate its current southern migration. As a result of coastal processes associated with several beach nourishment efforts, Singleton Swash began southerly migrations beginning in 1997, eventually preventing tidal exchange with the Atlantic Ocean. The a-typical migrations have resulted in the loss of upland beach, a protective dune, and threatens structures on adjacent upland property. The frequent swash migrations led to routine realignments of Singleton Swash under Department of the Army permit 2005-2W-180P which authorized realignment activities until June 2017. In an effort to provide a permanent solution to channel migration, an open box culvert design was authorized on May 25, 2016 under SAC-2014-00013, which the applicant will abandon due to unexpected cost estimates. Horry County Stormwater is requesting a 10 year permit to perform routine re-alignment activities which will supersede the previous authorizations. The proposed activities include excavation of 0.57 acres of channel below the High Tide Line (HTL) and filling approximately 0.43 acres below the HTL for dune restoration. Additionally, these activities likely will restore the functions within the upstream estuary that have been diminished due to limited tidal flushing resulting from accumulated sediments within the swash mouth.
NOTE: Due to the dynamic nature of the continual coastal processes ongoing, the figures stated at the time of application may vary slightly during construction activities.
Specific Project Details Provided by the Applicant:
Proposed Construction Methodology:
Construction activities for this project will consist of the deposition of fill material for the re-construction of lost dune within the current location of the migrated swash channel, and routine excavation to re-establish the previous channel location across the beach face. These activities will be accomplished using a combination of bulldozers and tracked excavators and transported with off-road dump trucks. All dredged material will be used for the re-construction of dunes and beach face. Dredging activities will be carried out during low tide events to ensure proper tidal flushing is occurring and to limit suspended sediments from escaping upstream/downstream. Dunes restoration will be constructed to match the existing profile of adjacent undisturbed dunes. Upon the completion of construction, dunes will be stabilized with native vegetation. The newly constructed channel will be graded to match upstream depths.
Proposed Wetland Impacts:
The proposed impacts will result in fill associated with the dune restoration and excavation/dredging for the channel re-location. Specifically, impacts associated with the dune restoration consist of fill within 0.43 acres of the current location of the swash channel (below high tide line). Re-location of the swash channel to its previous location will result in 0.57 acres of excavation below the high tide line within the intertidal beach. Due to the dynamics of the swash and ongoing beach nourishment activities, the applicant is proposing the swash channel relocation within a 300’ area along the beach front.
Long Term Maintenance Activities:
Due to the potential for the ongoing morphological changes of Singleton Swash driven by beach re-nourishment activities and coastal processes, the applicant is proposing a long-term maintenance plan to rely on ongoing swash realignment procedures to maintain proper tidal flushing. This plan will rely on routine onsite observations monitoring the infill of sediments and swash migration which will provide the applicant a proactive approach to avoid future dune erosion and diminished tidal flushing. In addition, the applicant will monitor water levels and maintain the camera on the adjacent Sands Beach Club property which provides real time photo documentation of swash activity. This will help the applicant to determine if a sill is forming at the swash mouth resulting in diminished tidal flushing. Should swash migration occur, the applicant will notify USACE and OCRM prior to commencing the necessary activities to avoid dune erosion and swash migration.
Avoidance and Minimization:
The applicant stated: “Avoidance of impacts to wetland resources was not practicable due to frequent past migrations and the current location of the swash resulting in continual dune erosion and the infill of the swash mouth which has caused diminished tidal flushing within the upstream estuary. The proposed impacts will restore the 0.43 acres of dune that was lost due to the swash migration. These restoration efforts will restore a functional dune protecting inland areas and existing structures. The applicant through careful planning has chosen to limit impacts to only those necessary to restore the swash to its previous location and depth.”
Proposed Mitigation:
The applicant offered no compensatory mitigation for the proposed impacts and stated: “no loss of function or character to the water resources will occur as a result of the proposed corrective actions.”
Project Purpose:
The project purpose as stated by the applicant: “The purpose of the project is to relocate Singleton Swash to its historic location along the beach front in addition to conducting routine realignments during initial stages of annual migrations. These activities will restore and alleviate substantial dune erosion in addition to maintaining vital tidal flushing in the associated estuary.”