Oysters' Integration on Submerged Breakwaters Offers New Adaptive Shoreline Protection in Low-Energy Environments in the Face of Sea Level Rise

Abstract

Sea level rise (SLR) and increasing storm frequency threaten coastal environments. Engineering solutions such as breakwaters will become ineffective for wave attenuation and erosion control due to SLR. As a natural alternative, oysters create three-dimensional, complex reef structures that attenuate wave energy and increase sedimentation rates. If coupled with breakwaters, oysters may maintain breakwaters' efficiency over time as they are expected to grow with SLR. Here, we measured bathymetric changes over 3 years (via GPS) and wave dampening due to four-made intertidal breakwaters within a small cove of the Choptank River (MD, USA). Then, we modeled the coupling of such gray structures with oysters through Delft3D-SWAN to evaluate the performances of such hybrid solutions on coastal protection, under future scenarios of SLR and climate change. Modeling hydrodynamic results showed a gradual reduction in wave attenuation due to SLR. However, when oysters were included in the modeling, wave dampening in 100 years was 75% and 60% greater than gray breakwaters, at high and low tides, respectively. Morphodynamic results showed increasing net export of sediment from the coast due to SLR. Oyster addition also provided shoreline protection and sediment retention in 100 years compared with the use of breakwaters alone, thanks to oysters' capability to grow with SLR. The coupling between oysters and breakwaters may represent a valuable and effective methodology to protect our coast over a changing climate and a rising sea, where optimal conditions for oyster survivability occur and are maintained over time.