Jonathan Leathers, University of Maryland College Park

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Abstract:

Living shorelines are native marsh plantings that control coastal erosion and provide coastal resilience to sea level rise (SLR) by migrating upland during SLR. Living shorelines require breakwaters to dissipate wave energy to prevent marsh boundary erosion and facilitate sedimentation. Currently, breakwaters are built with riprap which cannot adapt to SLR. Alternatively, oyster castles are modular cinder blocks for building breakwaters that initiate the development of oyster reefs which can adapt to SLR by growing equivalently with rising sea level. This research used Delft3D to model the effects of SLR on coastal morphology with 3 domain configurations: 1) only marsh, 2) traditional living shorelines with riprap and 3) living shorelines with oyster castles. The model objectives included comparing marsh deposition between oyster castle and riprap breakwaters and determining the important parameters affecting living shoreline evolution. All domains were 2 km wide by 1 km in length to mimic coastal bay conditions. Simulations were set for a temporal scale of 150 days and increased by a morphological factor of 150 to project for 60 years. Experimental parameters included vegetation density, nearshore slope, SLR, and suspended sediment concentration (SSC). Oyster castles facilitated greater marsh deposition than riprap at +8.9 mm under current sea level, +3.5 mm with SLR of 0.4 m, and +3.3 mm with SLR of 0.8 m. Increased nearshore slope and higher SSC both increased sediment deposition in the marsh. Increased sea level and higher marsh density decreased maximum bed shear stress. Therefore, coastal restoration efforts should strive to integrate oyster castles into living shorelines and increase marsh density to enhance sediment deposition and coastal resilience. These modelling efforts focused on quantifying the impacts of coastal processes on marsh dynamics and building the framework of a model for use in future research.