Contractors have built about 150 feet of Bald Head Island’s terminal groin, an arm-shaped pile of giant rocks designed to trap sand and reduce erosion on South Beach.

Crews are digging a 32- to 40-foot-wide trench in the sand, then placing rock-filled geotextile mattresses on the leveled surface. After that, they’re stacking large boulders on the specially constructed mattress pads.

Work is going slowly because the contractors have to pump water from the excavation and make sure the construction area is perfectly flat and at exactly the correct elevation, said Chris McCall, shoreline protection manager and assistant village manager.

“The terminal groin is moving along,” McCall said. “They are putting the rocks in place.” Orion Marine Group crews place a six-by-20-foot mattress on the construction centerline, then place additional pads on each side of the center mattress.

The mattresses go down first so that the heavy boulders won’t subside into the sand.

McCall said the crew was averaging eight to 10 mattresses a day. They are staging mainland operations just east of American Marine Co. on the Intracoastal Waterway at Oak Island.

When finished, the terminal groin will be 1,300 feet long and reach into the Atlantic about 300 feet. It is designed to capture some, but not all, of the sand that washes by in the longshore current.

Four community-based terminal groins are allowed in North Carolina under a 2011 law. Other beaches seeking to build groins are Holden Beach, Ocean Isle Beach and Figure Eight Island.

Construction is expected to wrap up in October. Technicians will monitor the groin’s performance for at least two years before the project engineer decides whether to add another 600 feet to the structure.

Source State Port Pilot