Mr. Powers had a thought about that. In the past, he said, the beach stayed open with even more erosion than last year. But that was before the fashionable crowds came. “Now it gets more attention,” he said, and left it at that. No point in spoiling a beautiful day.

But in fact, Rockaway Beach has always gotten a lot of attention — almost $270 million in restoration efforts since 1930 (in today’s dollars), as of the latest tabulation by the Program for the Study of Developed Shorelines at Western Carolina University . That’s more than any other beach in the country. The federal government has replenished the sand at least 37 times.

Andy Coburn, associate director of the program, said that what we call beach erosion might more accurately be called shoreline migration, the island’s natural response to changing currents and “human interactions.” The Rockaways want to move westward, but we won’t let them. Thus the unceasing need for more sand.