Adaptation measures are typically grouped into three categories: hard armoring, soft stabilization, and managed retreat.
Throughout most of the 20th century, the favored method of holding onto retreating shores was the construction of hard points to prevent the movement of sand and protect the roads and buildings behind them. Seawalls, groins, revetments, and jetties built by the Army Corp of Engineers (or following their guidelines) have come to define much of the nation’s coasts. Unfortunately, in addition to being very expensive, hard armoring protects the land directly behind it at the expense of its surroundings. By interrupting natural processes that have operated for millennia, down-current beaches and wetlands shrink or disappear as they are deprived of the sand needed to replenish themselves.
Locally, we are less reliant on hard armoring, but there are locations (e.g., the Oak Bluffs harbor) where pre-existing commercially important development will almost certainly be preserved (at great expense) by continuing to maintain and expand hard shoreline protection. The town beach at Squibnocket demonstrates both the value and ultimate limitations of this approach. Without the seawall, the sand beach would be located far inland today and the parking lot long gone, possibly leading to the loss of public access. Construction of the seawall has therefore bought time to enjoy a valuable town resource. However, that time has run out, and the town must now plan not only for the possibility of losing the beach, but also the challenge of decommissioning a seawall and parking lot before they crumble into the sea.
More temporary, but less harmful, solutions involve the nourishment of beaches with new sand or stabilization with natural materials. In Massachusetts, beach nourishment is made more challenging due to strong restrictions on offshore mining of sand. Nourishment projects on Martha’s Vineyard are especially difficult, as the only sufficiently large sources of sand nearby are considered by the Division of Marine Fisheries to be valuable fish and shellfish habitat that would be damaged by the mining process. More realistic at the moment, and currently ongoing at many of our eroding beaches, are stabilization projects using biodegradable materials and the planting of native species to stabilize the sand. This is the area of adaptation where ingenuity and technological innovation could be most valuable.
While the previous two categories may roughly correspond to the methods of the past and the present, respectively, the Vineyard’s future may be characterized mostly by retreat, whether by choice or not. A 2011 report from the EPA dismisses shoreline armoring and soft stabilization as generally too expensive and/or ecologically damaging. The EPA now strongly advocates for managed retreat through the promotion of rolling easements and other methods to encourage compliance (such as reducing government support for coastal development and protection, and making it clear to homeowners that they will not receive assistance to rebuild following losses). A recent report from the state on adaptation measures takes a more favorable view of soft stabilization but also emphasized the need to minimize what they term “repetitive losses,” a goal that is antithetical to continuation of expensive temporary measures, and which can only truly be accomplished through retreat.
Choices regarding adaptation measures will pit various economic interests against one another, for example those of homeowners and the shellfish industry. Protection of valuable residential real estate threatens the shellfish industry, whether it is the destruction of wetlands through building of revetments and groins, or damage to offshore fishing areas caused by sand mining for beach nourishment. Island-wide planning is essential to balance these interests and to coordinate action in more cost-effective and less ecologically damaging ways. A local shoreline vulnerability study would be invaluable to assist in this planning.
The largely natural
shoreline (apart from the harbors and downtown areas) is a crucial aspect of
the Vineyard’s local character. Coupled with the high costs of the other
adaptation measures, this suggests that in many locations some sort of retreat
will occur, whether well-planned or not. It is in our interest to manage
coastal development now to both facilitate successful managed retreat efforts,
and to reduce the economic cost and environmental damage of poorly managed (or
accidental) retreat where it occurs.
Excerpted from the Sea Level Rise chapter of the VCS Climate Change report