Results of N.C. beach-erosion study are inconclusive

Terminal groins have caused sand to build in some places, erode at some places. They've expanded habitat for shorebirds and turtles in some places, and diminished it at some places. And when beaches are widened and channels are dredged in the vicinity, it's difficult to determine what's going on.

Findings in a study on five groins, including at Oregon Inlet, done for the North Carolina Coastal Resources Commission at the behest of the General Assembly, were largely inconclusive, a final report released this month shows.

Terminal groins are long, low-slung sand-trapping structures, usually concrete or rock, that stretch into the ocean off the ends of barrier islands or near inlets.

"The basic conclusion is there's really no smoking gun one way or the other," said Tom Jarrett, senior coastal engineer with Wilmington-based Coastal Planning & Engineering of North Carolina and a member of a CRC-created science panel that oversaw the study.

"The deal here is that most of these structures are not stand-alone structures. They're complemented by other strategies like beach fill."

The Coastal Resources Commission will review the report at a meeting Thursday, CRC spokeswoman Michele Walker said.

Since 2002, state law has banned the use of most hardened structures such as breakwaters, jetties, groins and seawalls because they're known to cause downdrift erosion, but they're permitted in order to save certain other structures or navigational channels.

Until then, they had been restricted since the 1980s, but could be permitted with a variance.

Walker said that various options are expected to be presented to the CRC, including, maintain the status-quo on the ban; amend the ban to give the CRC authority to grant variances to permit terminal groins with conditions; or retain the ban but give the CRC the authority to develop a rule for permitting the groins, including a petition review by the CRC.

Before the Oregon Inlet terminal groin was built in 1991, the Herbert C. Bonner Bridge was in danger of being undermined, the historic life-saving station was threatened, the northern tip of Pea Island National Wildlife Refuge was eroded away, and the inlet was steadily creeping south.

The 3,125-foot rock wall built on the southeast side of the inlet is widely credited with solving those problems, but there have been concerns that it caused erosion further down the coast.

The report found that there was moderate erosion over the second mile down the beach, but by the fifth mile, the beach starts building.

Material dredged from the Oregon Inlet channel has been deposited off Pea Island since dredging began in the mid-'80s, said Jarrett, a retired engineer with the Army Corps of Engineers who had helped design the groin as part of the planning for the never-built Oregon Inlet jetty project.

Jarrett said that the law that ordered the terminal groin study and gave the CRC the authority to consider permitting them does not allow for building groins at any location except at an inlet.

That's a disappointment to the town of Nags Head, which was hoping a groin could be used to anchor a planned shoreline widening project at the south end of rapidly eroding South Nags Head.

"It would help the sand to stay there longer," said Mayor Bob Oakes.

"We still think it would help the nourishment project's effectiveness and lifespan."

Catherine Kozak, (252) 441-1711, cate.kozak@pilotonline.com