Comparison of Wave Energy Dissipation between Two Living Shoreline Systems in a Sheltered Estuary

Abstract:

Living shorelines have the potential to provide shoreline protection as well as, habitats for wildlife. There are many designs proposed however, there has not been quantitative comparisons of their performance in wave attenuation. This study was intended to determine the effectiveness of different living shorelines for dissipating wave energy. Measurements were made in a low wave energy environment along the Lafayette River in Norfolk, Virginia around a marsh sill and an oyster reef. To compare the wave energy dissipation of the living shorelines in the river, pressure sensors were deployed on the offshore and onshore sides of each structure for 27 days in September and October of 2019. Using Wave Analysis Toolbox OCEANLYZ, a spectral analysis was performed. The waves approaching the site were found to be small with a maximum significant wave height of 9 cm. The small wave height was attributed to the dominant wind speed of 2-4 m/s in the south west direction. The marsh sill was fully submerged only 28% of the deployment time while the oyster was fully submerged 94% of the 27-day period. Wave attenuation was dependent on elevation of water level relative to structure/reef height such that dissipation decreased with an increase in water level. A breaking threshold was considered at the point where wave height was larger than 0.625 of water depth above structure/reef crest. Analysis of wave damping shows that spectral significant wave height was reduced under both breaking and non-breaking conditions for the sill and oyster reef. The spectral analysis results revealed that the marsh sill was more effective at attenuating wave energy. This study could help coastal engineers in the future with determining the effectiveness of living shoreline structures in estuaries and low wave energy environments.