if you want to see how dunes work compare Bradley Beach to Belmar after the storm.
Bradley had 20' high dunes which were started in 2001 with wooden snow fencing and recycled Christmas trees. The dunes were full of grasses and dune vegetation too, like a fortified wall of sand.
Their huge dunes saved the boardwalk and much of the ocean front properties. The dunes got wiped out by the storm but they served their purpose.
Belmar had these little 3' dunes next to their boardwalk, more like landscaping areas. Now they have no boardwalk and the town suffered extensive flooding and damage. They are already talking about building the same silly little boardwalk, and maybe putting in a sea wall as well...complete waste of 16 million dollars.