Last week, I wrote about how riprap consists of a cluster of medium-sized rocks placed at the base of a seawall to prevent erosion. The same concept is put to work when creating a living shoreline, but the rock gets moved offshore. As I’ve written in this blog before, living shorelines are created when property owners plant vegetation along an eroding shoreline instead of putting up a hard surface like a wooden seawall or concrete revetment. Native emergent grasses and rushes (or mangroves, down south!) are planted in the soggy soil between high and low tide, and once they take root they can hold the shoreline in place effectively.

However, in most locations you can’t just plant grasses and let them go. Incoming wave action often proves too strong and will uproot these small, vulnerable plants. So, to give them a fighting chance to take root and thrive, breakwaters are created just offshore to absorb the wave energy and create a quite area for new plants to grow.

The breakwaters work under the same basic concept as riprap—waves hit the rock and energy is broken up away from the shoreline. Breakwaters vary widely in size and composition. At Pensacola’s largest living shoreline effort, Project Greenshores, designers used limestone rock and chunks of broken up airport runway. Bags of collected oysters were used as breakwaters at less wave-intense Bayou Texar. At a seagrass restoration area along Pensacola Beach’s Quietwater Beach, the breakwaters were built of large precast reef balls, which are typically used as underwater artificial reefs.

When designing, it is best to leave space between the breakwaters, staggering them so they don’t create a wall. The idea is for them to slow water down but not block it entirely. Some designs are more effective than others, with success varying widely depending on layout and the geomorphology of the water body and shoreline. It is wise to work with a regulatory agency or environmental consultant when designing a living shoreline, as placement of breakwaters and vegetation need to be well-planned.

As described in the graphic above, another hybrid technique involves sills, which are rows of rock or oyster material placed parallel directly against the shoreline near the planted grasses. These would only be used in quieter waters, and are rarely seen in local restoration projects.

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