The effects of large-scale breakwaters on shoreline vegetation

Abstract

In response to shoreline erosion and coastal wetland loss, living shorelines have been implemented as a natural alternative to shoreline hardening. In high wave energy systems, “hybrid” living shoreline designs incorporating large-scale breakwaters have been increasingly chosen to restore and conserve wetlands. However, evaluations of the effectiveness of breakwaters at preserving natural shorelines and promote the growth of shoreline plantings are limited. To evaluate the effectiveness of large-scale breakwaters at protecting or restoring marshes in high wave energy environments, we conducted an experimental planting and shoreline monitoring program landward of eight-year-old breakwaters and adjacent no breakwater sites along Bon Secour Bay, Alabama. Results showed that breakwaters help natural marsh to maintain its cover at a high level (70%), but have little impact on shoreline planting. Furthermore, breakwater presence reduced the pressure for upland migration, allowing natural marsh patches to expand seaward. Without breakwater protection, fringing marsh retreated upland significantly. Cumulatively, this study suggests that large-scale breakwaters could have an impact on preserving fringing marsh vegetation in high wave energy environments though their effectiveness into the future will require adaptive management in response to local sea-level rise.