Defensive Living Shoreline Structures
Groins In areas with limited sand in its transport system, down-drift impacts of groins can be significant. Photo by Shoreline Studies Program
Groins Groins can be effective shore protection when sand is in a great enough supply, and they can accumulate enough sand to create a wide beach that protects the base of the bank. Photo by Shoreline Studies Program
Bulkhead Since bulkheads are typically made of wood and were built years ago, many are deteriorating. Once they fail, they no longer provide shore protection. Transitional structures, such as spurs, on either side of the bulkhead breach and grading of the eroding bank could help create a stable pocket beach at the site. Photo by Shoreline Studies Program
Bulkhead A bulkhead that has deteriorated to the point of failure. Because it is in a low energy area, marsh grasses have already colonized the nearshore tidal region indicating that creating a living shoreline shore protection system is a viable option for this site. Photo by Shoreline Studies Program
Bulkhead Bulkheading and bulkhead replacement with riprap provides shore protection of upland structures, but they also have created many areas of the Bay and its tributaries that do not have a natural intertidal zone. Photo by Shoreline Studies Program
Yorktown Beach A combination system of revetment and breakwaters. The revetment protects the low backshore where a significant amount of structures could be impacted by storms. Flooding cannot be avoided, but the riprap revetment can take the brunt of storm waves potentially reducing damage. The offshore breakwaters add to the shore protection by modifying the waves during high water levels with the sand absorbing some of the energy. Photo by Shoreline Studies Program
Riprap Riprap revetment with graded bank. While this system should provide good shore protection since it provides base of bank protection and a graded bank that storm waves should be able to run up, coastal habitats are noticeably absent. Without any vegetation to act as a filter, pollutants such as sediment, herbicides, and fertilizers will run off into the Bay not only during storm events but also during every rainfall. Photo by Shoreline Studies Program
In order to maintain a more natural coastal profile, the Shoreline Studies Program at VIMS prefers to use Living Shoreline methods for shore stabilization. Living shorelines consist of sand, plants, and rocks that create a sloped land/water interface to protect the base of the bank, but the site-specific conditions determine the most effective configuration of these elements for shore protection.
Hard structures like revetments, bulkheads, and groins, armor and stabilize the shoreline landward of the living shoreline structure. They are often considered defensive structures since they typically defend the shoreline, but don't necessarily provide a habitat component.
Revetments
Rock or riprap revetments have sloped and rough faces that decrease wave reflection and, therefore, bottom scour. The upland bank can be graded to enhance shore protection since the large storm waves would run up the graded bank rather than erode it. However, there is often no buffer between the upland and the revetment that allows filtering of run off and, in most cases, no vegetation occurs riverward of a revetment. These structures are an effective “last line of defense” in high energy environments, but can be overtopped during storms.
In some cases, revetments may be recommended in areas that are not suitable for Living Shorelines either because the nearshore is too deep, or the structures are too close to the shoreline.
Bulkheads
Bulkheads exist along many shorelines of Chesapeake Bay. While these structures protect upland structures, they create a hard barrier between the upland and the water. The intertidal zone often disappears as erosion continues, such that no vegetation lives in front of the structure which displaces animal life. In addition, many bulkheads are mowed to their edge, which results in no filters for pollutants (sediment, fertilizer, animal waste, etc.) being washed into the Bay.
Since most bulkheads were historically constructed of wood, they will deteriorate over time and eventually fail. They tend to be reinforced or replaced with revetments. However, bulkheads that have been built in low energy areas and are now deteriorating could be removed and replaced with a living shoreline.
Groins
Groins are common sites around Chesapeake Bay. These structures are built perpendicular to the shoreline in order to capture sand from the alongshore transport system. Groins can be effective erosion control techniques if they capture enough sand to create a wide beach that may mitigate storm surge and waves. However, many areas of the Bay are sand-limited, which reduces the effectiveness of groins. These structures are typically built from wood and deteriorate over time, but can be reinforced with rock. Groins interrupt the sand transport system and can cause increased erosion downdrift.