Integrating Oyster Castles into Living Shorelines to promote coastal
bays resilience to Sea Level Rise
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 ripraps to
dissipate wave energy which prevent marsh boundary erosion and
facilitate sedimentation. Currently, ripraps are built with rocks which
cannot adapt to SLR to continue attenuating wave energy. Alternatively,
oyster castles are modular cinder blocks for building breakwaters and
coastal structures that initiate the development of oyster reefs which
can grow equivalently with SLR. Thus, oyster castle breakwaters can
adapt to SLR while retaining their breakwater function. This research
used Delft3D and SWAN to model the effects of climate changes,
especially SLR, on coastal morphology with 3 domain configurations: 1)
only marsh, 2) traditional living shoreline with riprap and 3) living
shoreline with oyster castle. We built a model comparing marsh
deposition between these coastal structures over time, and determined
the most important parameters affecting living shoreline evolution. All
domains were 2 km wide by 1 km in length to mimic coastal bay
conditions. Model runs were set up for a temporal scale of 150 days.
This duration was increased by a morphological factor of 150 to project
our results to 30 and 60 years. The parameters tested 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 castle
into living shorelines, and increase marsh density to enhance sediment
deposition and coastal resilience. Our modelling efforts focus on
quantifying the impacts of coastal processes on created marsh dynamics.