161-8 Beyond the Breakwaters: Contrasting the Impacts of Anthropogenic Modifications on Developed and Undeveloped Barrier Islands along the Virginia Coast, USA.

Session: Dynamics of Natural and Built Environments

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Anthropogenic modifications to coastal systems are known to alter natural coastal dynamics ranging from longshore sediment transport to barrier-island migration. The role of these coastal management strategies in shaping the morphodynamics of developed barrier islands has been the focus of numerous previous studies; however, less is known about the influence and persistence of anthropogenic modifications on adjacent, undeveloped barrier islands. This study examines the impacts of shoreline stabilization efforts on the morphology of adjacent portions of a developed (Wallops Island) and undeveloped (Assawoman Island) barrier island along the US Mid-Atlantic coast. Using a combination of historical digital elevation models (2005–2021), satellite imagery (2016–present), and seasonal real-time kinematic GPS elevation profiles (2024–present), we assess the decadal to annual influences of anthropogenic modifications on the shoreline position and beach volume of Wallops and Assawoman islands. In 2011, beach nourishment on Wallops Island led to accretion of up to 57 m³/m along the subaerial beach and concurrent shoreline advance of up to 80 m. By 2014, up to 75 m³/m of sediment had eroded from the beach, resulting in up to 30 m of shoreline retreat. Most of the eroded sediment was transported downdrift to Assawoman Island, with up to 95 m³/m of accretion along the subaerial beach and shoreline advance of up to 31 m. Continued erosion threatening government infrastructure along Wallops Island prompted the installation of two sets of 2–3, shore-parallel, detached breakwaters in 2021 and additional beach nourishment. Some sediment has since been trapped landward of these structures, intensifying erosion and shoreline retreat within 1 km downdrift of each breakwater set. Sediment trapping also led to a reduction in sediment fluxes to Assawoman Island, contributing to shoreline retreat rates of up to 28 m/yr since 2021. Both management decisions resulted in the immediate protection of Wallops Island and associated infrastructure yet had divergent impacts on the downdrift Assawoman Island: sediment from the 2011 nourishment contributed to transient downdrift accretion, while sediment trapped behind the breakwaters since 2021 has exacerbated downdrift erosion. Given the vulnerability of beaches and barrier islands to accelerating relative sea-level rise and the increasing need for shoreline protection along developed coastlines, this study highlights both the intended benefits and unintended consequences of anthropogenic interventions on interconnected barrier-island systems.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9759

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