Physical modeling of wave transmission for submerged and emergent breakwaters used in living shorelines

Breakwaters used in living shoreline projects are referred to as engineered reefs and are used to modify wave characteristics along estuarine shorelines in such a way as to promote ecological and biological enhancement, with stabilization of the shoreline often an expressed goal. Studies show engineered reefs are a successful alternative to traditional rubble mound breakwaters in the environmental aspect; however, the true success of these structures has not been quantified in terms of wave energy dissipation. Through physical modeling of engineered reefs using the University of South Alabama's wave basin, much of the engineering design related to wave energy was determined. The testing included bagged oyster shell breakwaters, apex-truncated square concrete pyramids, and ReefBLKs SM subjected to multiple wave forms and water depths. Results from the testing showed that wave transmission through bagged oyster shell and concrete pyramid devices can mostly be explained using published methodologies. In terms of structure geometry, the non-dimensional height, h c/d, is the primary factor when designing the engineered reefs. The bagged oyster shell and ReefBLKsSM are more effective in attenuating shorter wavelengths while concrete pyramids are more effective in attenuating longer wavelengths. The dependence of structure performance on wave period is a new finding.