Wave Attenuation Through Submerged Oyster Aquaculture Cages

Coastal and estuarine shorelines are some of the most eroded in the world due to their sensitivity to sea-level rise and increased wave energy from storms and human industrial and recreational interactions. Much of Maine’s coastline is formed by “bluffs” or steep cliffs made of loose granular material that, depending on their stability, can be highly erosive. Small amount of coast is sandy beach (5%), but loss is an economic concern. 

With the abundance of aquaculture in the waters of Maine, as well as previous research in shellfish based coastal protection, the opportunity exists to combine aquaculture and coastal defense in Maine, given the prevalence of coastal erosion in the area as an issue, and the large economic sector of shellfish farming.  

This study looks to examine this potential by quantifying the wave attenuating properties of submerged oyster aquaculture cages, using in-situ wave measurements and a Smooth Particle Hydrodynamics computational fluid dynamic model. Wave decay of up to 80% for ~4 second waves was seen over 30 m of oyster cages, where less-steep waves and shorter waves were attenuated more. Added mass drag dominated wave attenuation compared to friction, supported by KC (Keulegan Carpenter Number). Wave attenuation likely affected mean water levels through gradients in radiation stresses, and set up in mean water levels reached up to 5 cm when including tidal currents, indicating that scaled-up versions of bottom oyster farms could have implications on coastal circulation in semi enclosed systems.  

Future research should explore optimization of bottom oyster farms to reduce a broader range of wave environments, while assessing the secondary effects of wave attenuation on ambient hydrodynamics.  

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