Separating the surf from the mainland, dunes are a critical protective barrier.  When storm surge threatens inland areas, it’s often the only thing standing in the way.  Dunes aren’t just piles of sand, they’re an ecosystem of dune grass, small shrubs and other plants adapted to survive this hostile environment.  Birds and other animals live in this buffer zone, protected from the waves and wind.

The MVP tenant in the dune is dune grass.  Its deep roots literally hold the dune together, creating a more resilient barrier when the winds and waves kick up.  Wind blows the sand against the dune, where it is trapped by the grass and helps to build the dune up, grain by grain.  Wave action erodes the sand, and the cycle continues.

Complicating this endless dance are humans.  People walking in the dunes trample the grass, creating paths that erode in the wind.  The other contributor to erosion of the dunes in some areas is the jetty.  Jetties are constructed by the U.S. Army Corps of Engineers and serve to stop erosion of the beach while also trapping sand between each.  Jetties are essentially piles of boulders stacked in a pyramid and running perpendicular to the beach.  Trapping sand, they serve their desired purpose when engineered properly.
When jetties are constructed without regard for the downward drift the can destroy the protective dunes and dramatically change the beach.  In Quogue, New York, a part of the Hamptons on Long Island, jetties built in 1992 stopped the natural drift of sand from Shinnecock Inlet and wiped out the dunes.  This exposed the homes that line the coast in this area to storm surge.  Visiting the beach in Quoque ten years after the construction of the jetties, I was shocked at how much the beach had changed.  The double dune was gone, and so was the pristine sloping sandy beach.  It was a great lesson in responsible civil engineering.
The dunes on Plum Island have faced similar threats over the years.  The jetties built on either side of the Merrimack River serve to stabilize the drift of sand, hopefully keeping the channel wider and deeper than it might otherwise be.  Sand that would otherwise clog the channel is better served as a barrier beach.  Were it only so simple.  Jetties, while built with good intentions, can be a blessing or a curse, depending on where you are on the beach.  While the wind and waves are far more powerful over time than the jetties, the impact they’ve had is transformative here and now.  Dunes, while appearing timeless, are fragile ecosystems that need protection from people.