FOLLY BEACH - Out beyond the new groin at the Charleston County park here lies the only orphaned stretch of sand on this island.

The park beach was renourished last year. Pipes now are pumping sand to renourish the rest of the five miles of beach. But that project will end where the park sand begins.

The far western tip of the island won't get any new sand. It remains in the wash of Stono Inlet tides, a huge tidal pool carving its beach. What once was a stretch of maritime forest behind is now only a few shredded trees. Nearly a decade of storms and high wave erosion have torn it to little more than a moonscape since the 2008 renourishment tapered sands along that stretch.

What the tip has going for it, counterintuitively, is the groin. Groins are barriers, usually made of rock or wood, built from the dunes into the ocean. They are controversial because they interrupt the flow of sand in shore currents, building beach sand upstream but depleting it downstream.

Conservationists opposed the Folly Beach park groin because of that, and almost derailed the renourishment.

In other words, the groin would be the last thing you'd think would help renourish the beach beyond it. But it's not that simple.

While holding the renourished sand in the park, the groin is allowing a steady seep of that sand in winds and storm tides to somewhat fill in the "orphaned" beach. That seep is, in fact, a design feature that was required by the U.S. Army Corps of Engineers as part of the park renourishment permit, because the groin would have made it problematic to "taper" renourishment sand along the beach tip.

"It's working so far," said Scott Harris, College of Charleston geology professor, who is monitoring the renourishment project for the Charleston County Park and Recreation Commission. "The groin has stabilized that part of the island very effectively, as far as we can tell right now. It's keeping erosion from taking out the few remaining maritime trees," he said.

It appears to be working for more than the island. The Coastal Conservation League originally opposed the groin, because the staff was concerned that it would rob sand from the Bird Key Stono, or Skimmer Flats, a valuable shorebird rookery in the inlet past the beach. The league agreed to hold off challenges to give the groin a chance to work.

Aerial surveys by Scott's team indicate that sand is building up just under the tideline on the rookery's ocean side, Scott said.

That's good news, so far, said Katie Zimmerman, league program director.

"We're going to keep our eye on it," she said. "Time will tell how this will pan out."

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