Posted on November 10, 2020
The sand needed to rebuild beaches along South Carolina and other parts of the Southeast will become scarcer over the next 50 years and there may be shortages, an analysis done for the Army Corps of Engineers says.
Some areas today haven’t found enough to fill their need.
The report, by Florida-based firm Taylor Engineering for the Corps, found dire shortages as it counted known “borrow areas” where sand can be harvested as it relates to the next five decades of beach renourishment projects.
In such projects, dredged sand is spit back onto the beach and the Corps is often the agency that leads the work.
Some of the worst shortages were found in South Florida and on that state’s Gulf coast. In South Carolina, the biggest shortage of known sand sources was found in Beaufort County. Some areas, including Charleston and Colleton counties, have already identified enough material to cover future projects.
In Beaufort, which includes Hilton Head Island and fast-eroding Hunting Island State Park, there’s an estimated need for 25 million cubic yards of sand — enough to fill the Great Pyramid of Giza almost eight times.
But only a quarter of that amount has been located in past borrow areas. And with a 55 percent contingency added to account for sea rise and sand that might be lost or deemed unsuitable, the borrow areas cover just 15 percent of the 50-year need.
The report does not account for the possibility that some areas which aren’t participating may start new nourishment projects or the increasingly frequent emergency projects triggered when a tropical storm or hurricane sweeps material off the beach.
Climate change-driven sea-level rise makes the need for sand more urgent. A 2019 study showed an increasing chance of erosion for beaches on the Southeast Atlantic Coast, with three-quarters of the beaches from North Carolina to central Florida facing a high risk of degradation.
Paul T. Gayes, a professor at Coastal Carolina University, said the patterns of beach-building work had already been changing. Often, a federally sponsored project is meant to last as long as a decade.
“If you look at the last many years, we’re not seeing that play out as well as it had been,” he said, with more beaches pushed to do smaller “patching” after a storm causes sudden erosion all at once.
The report has two recommendations: tracking and prioritizing which parts of the region need sand the most, and finding new potential sources, including areas where harvesting sand now may be blocked by regulation.
It does not address, however, a different threat to barrier islands. Sea-level rise poses a particular risk to the “back” or marshy side of these islands opposite the beach, where there’s no sandy slope or dune system to stop water from seeping in.
“We’re seeing the (sea rise) acceleration scientists have projected, and to me, it’s really unfortunate that the Corps is giving coastal communities the impression that we can keep them safe for 50 years,” said Rob Young, director of the Program for the Study of Developed Shorelines at Western Carolina University.
Search for sand
Renourishment projects involve using a dredge boat to suck up a slurry of sand and water out of a river, sandbar or off the ocean floor and then carting it back to shore where the material is emptied onto the beach.
The farther away that sand source is, the longer the trip, and the more expensive it becomes. Not all sand is suitable; if the sediment is too fine, it could wash away easily or make beach water muddy.
Hunting Island State Park in Beaufort County completed one of its regular renourishment projects earlier this year, putting 1.7 million cubic yards of sand on 2 miles of beach at a cost of $10 million. The beach has one of the highest erosion rates on the East Coast, losing 15 to 20 feet of sand a year, Park Manager J.W. Weatherford said.
“It doesn’t surprise me that they would say that Beaufort County is looking for sand,” Weatherford said of the Corps report.
The shoreline of Beaufort County, strewn with islands small and large and several dynamic creeks, causes a dance of sandbars and shoals that change with the tides, Weatherford said.
That dynamism is one of the reasons Scott Liggett, chief engineer for the town of Hilton Head Island, isn’t worried about finding sand in the future.
He said the town’s own surveys have found as many as 60 square miles offshore that could provide future sand, but requires further investigation.
He also said the tidal shoals offshore in Beaufort County are frequently replenished — meaning material that’s sucked up to be put on a beach may be replaced later.
Tim Kana of Coastal Science and Engineering agreed with that finding.
“There’s a lot of sand out in those sand shoals offshore, they just haven’t been confirmed,” he said.
Environmental concerns
In South Carolina, where seawalls on the sandy beach are banned, renourishment has become the main source of protection for communities on the edge of the coast. But it’s a commitment that lasts forever, said CCU’s Gayes.
On the Grand Strand, which includes Myrtle Beach, there have been detailed surveys of the sand that’s available. But it’s in a thin layer offshore, making it harder to do a project that lasts a decade.
“What you may see is more of a chronic effort, a continuous effort, all the time a little bit at a time, rather than gigantic projects every five, 10, 15 years,” Gayes said.
There are also concerns over the environmental impact of sucking up too much material or placing foreign sand on a beach, a condition which is little reviewed. One 2006 study of a nourishment project in North Carolina found that coarser sand meant there was less food for shorebirds on the beach, and fewer ghost crabs, as well.
“There is this suggestion that we would mine every sandy, reasonably accessible bit of (ocean) habitat in the Southeast,” Young said. “What in the world would the environmental impacts of that be?”
Source: postandcourier
