Breakwater Overtopping and Transmission Characteristics Associated with Living Shoreline Functional Attributes

A series of physical model tests were performed to explore what, if any, functional benefits in wave protection and damping are associated with various structural augmentations to a traditional breakwater intended to also serve as habitat creating or enhancing. The augmentations are in structural and geometric form and are intended to make large-scale alterations to wave behavior and transmission, and as such, do not involve secondary small-scale measures, such as fronting seagrass meadows of vegetated edges. Those would be considered “opportunities” to further increase the ecological value but were felt to have a limited functional impact or likely value, given the scale of wave aggression. The model test results revealed significant performance deviations from traditional overtopping transmission formulas and experience. Raising the interior breakwater core allowed for a significant lowering of the required breakwater crest height for the same incident wave conditions. Flattening of the front face slope, combined with a reduction in armor size to better achieve bio compatibility, gave improved results but reached a limiting beneficial level. The biggest impact on the reduction of wave overtopping and transmission was found with the introduction of quasi-two-dimensional protruding fronting reef ridges. Similar beneficial results were noted for lee-side habitat ponds where perched pools of water intended as juvenile fish nurseries co-serve as stilling basins in severe wave events before transmitting onward to shore. Incorporating these new design elements into the design of a breakwater offers opportunities to improve visual aesthetics by lowering breakwater crest heights and creating breakwater geometries, which better emulate natural landforms. Such solutions are more conducive to recreating habitat while still retaining the needed wave-mitigating properties of the breakwater.