Shifting Sands

Scientific study is yielding valuable insights into coastal erosion. Researchers have discovered that permanent structures built in attempts to contain and control erosion — jetties, groins and seawalls — vary in effect between futility and making things worse.

Government and private individuals build these structures in good faith: sometimes to protect roads and houses, sometimes as a strategy to catch and retain sand drifting in the water down the shoreline.

But groins and jetties ultimately have little say against the powerful natural forces that shape the coasts, eating away at one beach only to distribute sand and sediment at another. Indeed, research has revealed the dynamics of the littoral shoreline, a place where the only constant is change.

Residents along the coast, whether on the Island or elsewhere, belatedly are realizing that jetties do little good and more harm in the midst of such forces.

One of the clearest examples can be found a few feet to either side of the jetty between what is known as Pay Beach and the Inkwell in Oak Bluffs. North of the jetty, Pay Beach is broad enough to comfortably accommodate a volleyball game, several games of catch and any number of sunbathers and sandcastle builders from the shore to the seawall. But south of the jetty, the Inkwell is a comparatively narrow strip of beach between the seawall and the sea.

Seawalls cause their own problems, denying the ocean the sediment that otherwise would be washed into the water to build a beach farther down the coast.

Taking down seawalls is unlikely, given the roads, property and houses that they protect.

But that does not mean eroding beaches must be left to languish. Dredging sand from Vineyard harbors, coastal ponds and inlets and piling it on beaches where the sand has been eroding away is a good solution. And dredging offers the double benefit of making ponds and inlets more navigable and increasing their circulation, improving their quality and safeguarding their shellfish.

The solution is not permanent — the sand on some beaches will continue to wear away, requiring continuous replacement — but then ocean coastlines by their nature lack permanence. In the long run, it is better to know and work with the natural flow than to work against it.