One of the most significant problems facing landowners along Maryland’s coastal environment is shore erosion – a natural, yet unrelenting process. Through the years, landowners have tried many tactics to protect their property including informal dumping of recycled concrete materials and old tires to more traditional erosion control techniques such as groins, bulkheading and riprap revetments. Unfortunately, these approaches have a number of problems, ranging from obvious visual impacts to the elimination of valuable fringing wetlands and sand beaches that help improve water quality and support wildlife.

However, in recent years landowners have increasingly turned to a “living shorelines” approach to control erosion and provide critical habitat through strategic placement of marsh plants, stone, and sand. During the mid 1980s “soft” shoreline stabilization alternatives were referred to as “nonstructural shore erosion control” which incorporated many elements of today’s “living shorelines” techniques. Some emerging practices place even greater emphasis on habitat creation and less on erosion control. Living shoreline treatments are designed with the intention of maintaining or minimally disrupting normal coastal processes, such as sediment movement along the shoreline and protection and restoration of wetlands.

Coastal engineers, shore erosion control experts and experienced marine contractors benefit from a working knowledge of coastal processes and their effects on shoreline structures. Much of what we know about the interactive forces of land and water in the coastal zone comes from understanding coastal geomorphology.

Coastal geomorphology is the study of coastal landforms, including their origin, evolution and the processes that shape them. Physical processes such as wind, waves, longshore currents, erosion and sediment deposition all work together to create dynamic coastal landforms. These and other forces give rise to familiar landforms depicted in the diagram below including: a “tombolo” – aspit or bar that connects an island or rock to fastland; a “bar” – a raised or submerged mound of sand or other material built in shallow water by waves and currents; a “spit” – a small point of land or narrow shoal projecting into a body of water from the shore.

Tidal wetlands often form on the leeward side of these landforms and in other protected environments along slow moving tidal streams, embayments and coves. Over time, coastal plants and wildlife have adapted to and are dependant upon these special coastal environments. Understanding what geomorphological changes might result from erosion control and other shoreline structures is critical to the sustainable management of dynamic coastal landforms, wetlands and sensitive living resources.

Two traditional and widely used means of shore erosion control are groins and bulkheads. Either of these structures may be good solutions in certain situations. However, even when carefully designed, these approaches can have unintended consequences for people and wildlife.

Groins are structures built out from the shoreline, typically perpendicular to the beach. A single groin builds up beach material on the updrift side of the groin but can seriously erode sediment on the downdrift side. Land downdrift of the last groin will most likely require additional protection, unless a transition section of progressively shorter groins or a spur is provided. Usually, a series of groins or groin “field” is designed by coastal engineers to stabilize a stretch of natural or artificially nourished beach against erosion due to continuing losses of beach material.

Bulkheads or light duty seawalls are best used to retain soil and prevent land from sliding channelward, rather than to prevent active erosion. Over time, bulkheads often fail due to continued erosion at the base of the wall and eventual failure of the metal, wood or fasteners. If the bulkhead is not protected from wave scour and set deeply into a stable bottom, it might ultimately collapse. If the bulkhead is not tall enough or anchored into fastland at each end, storm driven waves can erode fill material from behind the wall – causing failure. Aquatic life can also be harmed from arsenic, chromium, copper, creosote tars from old impregnated timber and other contaminants that leach out from pressure treated lumber bulkheads. The vertical design of bulkheading placed in open waters, permanently reduces the availability of refuge habitat for small fish and attachment surfaces for algae and micro-organisms that serve as important food sources for invertebrates and some fish. Terrapins, habituated for many generations, may nest against a bulkheaded beach where their eggs are drowned by subsequent, often increasing tide levels.

After marsh plants are planted, they begin to reduce erosion in several way. First, marsh vegetation forms a dense, flexible mass of stems that help dissipate wave energy as water moves through the marsh. Second, as the wave energy decreases, sediment transported from shallow waters is deposited in the marsh – causing a build-up or “accretion” of the shoreline.

Finally, as root matter from the plants forms dense root-rhizome mats, the marsh elevation builds vertically and the sediment becomes two to three times stronger than unvegetated soils. This is especially important during the wintertime when plant stems provide much less resistance to waves.

While marsh grass alone can control erosion along very low wave energy shorelines, structural support is needed to maintain a marsh in areas where fetch exposure exceeds 1/2 mile. Fetch is the distance or width of waterbody over which winds blow against the shore.