FOLLY BEACH — Lunnette Kinard’s family has rented cottages on the east end of this island for 60 years. She’s never seen the erosion so bad, she says.

By the numbers

From the beach renourishment study by Tim Kana of Coastal Science and Engineering, published in Shore & Beach:59 : Beach renourishment projects in South Carolina between 1954 and 2010.62.6: Miles of beach renourished.7: Percent of nourished shoreline that has lost beachfront despite renourishment.$351 million: Total cost of projects in 2010 dollars.$5,000 to $50,000: Per- linear-foot value of developed oceanfront shoreline in South Carolina.$39: Per-foot cost of renourishing beaches.

Waves are washing out sand from under the foundations of homes for almost a mile — from the Washout to the old Coast Guard property on the bank of Lighthouse Creek and its iconic, oceanswept lighthouse.

One bad storm and that entire stretch of beach could be lost like the overwashed, closed Folly Beach County Park on the island’s other end.

When she drove out to see it the other day, “I was just sick,” she said.

Folly Beach is being eaten away on both ends by wave erosion exacerbated by the loss of the flow of sand now trapped at the Charleston jetties.

But a study by beach renourishment guru Tim Kana, of Coastal Science and Engineering, suggests that periodically restoring sand on the island not only has kept it from losing beach, but has added beach overall.

Kana’s recently released study drives right to the crux of the argument whether a groin — a barrier to stop erosion — is needed at the county park to help save it. The park can’t stop losing sand without one, he said.

The study indicates the beach at Folly gained nearly 78 acres between 1987 and 2006, after three rounds of renourishment.

The problem areas on Folly — the east and west end and various spots between — are just that, hot spots of focused erosion, Kana said.

The dynamics of what’s happening at the park are different from what’s happening at the lighthouse end, simply because one is on one side of an inlet and one is on the other, he said in an interview.

Inlet sandbars are the X factor in the debate whether a groin at the beach park is needed. The Coastal Conservation League is opposing a permit for the groin, a barrier to stop sand flowing in the shore current, because of concern that it would rob sand from a nearby shorebird rookery and feeding ground in Stono Inlet.

The league’s opposition is based on “consensus scientific opinion” that “terminal groins such as this will almost certainly deprive the downdrift beaches of sand,” according to its comments to state regulators.

Kana argues that most of Folly Beach is partly protected by the remnants of a series of old groins now largely buried by sand. The groins abruptly end just before the county park, and that keeps renourishment from being more effective there.

“It goes against the basis of shore protection: uniformity of protection,” he said.

The lighthouse end is losing sand to the inevitable wash-away and re-forming nature of sandbars moving downstream from the inlet, much like the Wild Dunes dilemma on Isle of Palms.

The park at the other end is upstream of the sandbar-laden Stono Inlet. The inlet “is a giant pool of trapped sand,” Kana said — as much as 200 times more sand than a single groin can stop, so the park groin wouldn’t have much effect on Bird Key Stono or Skimmer Flats, the rookery and feeding grounds.

The key itself has been moved by sandbar shoaling three times since the early 1900s, and the flats gradually are now becoming the new key, he said.

“That’s just the nature of this particular world; there’s just so much sand in it,” he said. “These ephemeral land forms, nobody wants to de-stabilize them, no question.” But they are controlled by the inlet, not by the sand flow along the county park, he said.

For the overall South Carolina coast, the study indicates about two-thirds of developed beaches have been renourished; about 80 percent of them are in better condition today than they were in the 1980s before renourishment started.

“It’s surprising how much better a condition most of the coast is in compared to 30 years ago,” Kana said.

The study suggests that some $350 million in today’s dollars that were spent on the sand-restoration projects were well spent, compared to tourism and property value dollars.

Reach Bo Petersen at 937-5744, @bopete on Twitter or Bo Petersen Reporting on Facebook.