Scientists are not so bullish on nourishment

By on April 5, 2011

A 2009 nor'easter did serious damage in South Nags Head.

Coastal geologist Stan Riggs lived in South Nags Head in the early 1970s, when the beach was wide and houses were few.

“It was wild empty land, and lots of big dunes,” Riggs said in a recent interview. “So that shoreline has moved almost 1,000 feet since then.”

Over the course of his 46-year career, while conducting studies of the Outer Banks, Riggs has been witness to the rapid oceanfront development in Nags Head, the shoreline’s intractable erosion, its seasonal walloping by storms, its sad sandbag-littered diminishment.

A geology professor at East Carolina University, Riggs understands why the tourism-dependent town has aggressively pursued a beach widening project. He is sympathetic to property owners who desperately want to save their homes.

He just doesn’t believe Nags Head’s proposed $34 million beach nourishment project has much, if any, chance of being successful.

Stan Riggs. (ECU photo)

“If you go through a five-year period of no storms — it might last that long. But on the other hand, it’s not unusual to have two, three, five nor’easters,” he said.

“And if we do, it’ll be gone. If they get it on this spring, it could be gone this summer.”

Nags Head officials believe, however, that the sand will last much longer and are moving ahead with financing the project. The town has chosen Great Lakes Dredge and Dock Co. to do the work, which could start by mid-June. But that will depend on what happens to a lawsuit challenging the town’s process for obtaining easements.

No stranger to Outer Banks residents, Riggs has given numerous public presentations about coastal processes, sea level rise, and yes, beach nourishment.

Besides sheer luck in storm-dodging, success or failure with nourishment comes down to the underlying geology, the land under the seawater. Some of it does not lend itself to a stable beach that would respond to sand replenishment, he said. Kitty Hawk, for instance, is sitting on an inner stream divide, a high area between two valleys. Mirlo Beach is located on angled rock.

South Nags Head is often cited as a reason for pushing forward with beach nourishment. It is also viewed as a reason why pumping sand onto the beach could be a bad bet.

And South Nags Head, Riggs said, is part of an area that has always been dominated by inlets and old stream valleys. That means the town, essentially, is planning to put sand on a beach that geologically wants to move.

“I suggest those people never go to Las Vegas — they don’t understand risk at all,” he said.

At a March 16 panel discussion sponsored by the League of Women Voters of Dare County, Dorothea Ames, Riggs’ partner in the ECU geology department, emphasized that statistics may determine an “average” erosion rate, but in reality, an eroding beach may seem stable or even accrete part of the year.

Then one persistent nor’easter, or a series of northeast slams, or one big tropical storm during a spring tide can wipe out a shoreline and the dunes in a matter of hours or days. A powerful nor’easter in November 2009, for example, damaged or destroyed dozens of houses in South Nags Head and consumed much of the shoreline and dune.

Ames was giving her geologist’s counter to the town’s pitch that says its proposed beach nourishment would last 10 years based on erosion history.

“There’s no such thing as an average erosion rate,” she told the small audience. “Most of these projects do not last very long in northeastern North Carolina because there’s high energy.”

South Nags Head’s erosion rate, according to the state, averages 4 to 6 feet per year over 50 years, or a loss of about 275,000 cubic yards since 1994. Sea level rise, Ames said, is only going to worsen the rate.

Great Lakes Dredge and Dock Co. has completed several beach nourishment projects, including this one in Brevard County, Fla. (GLD&D photo)

But another veteran North Carolina coastal scientist was less pessimistic. In a series of slides, Spencer Rogers, an erosion specialist and coastal engineer with North Carolina Sea Grant, illustrated successful long-term, although larger, nourishment projects in locations like Carolina and Wrightsville beaches.

At the same time, he cautioned that beach fill “is a treatment, not a cure” that must be maintained, is not cost effective in high erosion areas and must be a community-scale project. He also said that smaller projects — like the one proposed in Nags Head — could be effective in addressing long-term erosion, but are “not particularly” effective in storm events.

Despite those factors, Rogers said that inaction could be the most expensive choice. At the very least, even if some or all of the sand is lost, nourishment would buy time for Nags Head.

“The controversy over beach nourishment, in my experience, has less to do with beach nourishment than with who’s paying the bills,” he said, responding to an audience question about cost-benefit analysis. “If the issue is who pays, then the other issue is who benefits?”

Some contend that the project, especially one that is not full-scale, will not survive 10 years without having sand replenishment every few years. In addition, federal funds will not be available to rebuild a storm-damaged project without a maintenance component built in from the onset.

In the unfunded 14.1-mile federal nourishment project authorized in 2000 for Kitty Hawk, Kill Devil Hills and Nags Head, the Army Corps of Engineers planned to use about 8 million cubic yards of sand on the 10-mile Nags Head section, with renourishment planned in intervals of about three years. Nags Head plans to use a total of 4.6 million cubic yards in its proposed project.

Surf can come precariously close to the Comfort Inn.

The 50-year total cost of the federal project was estimated at $72 million for construction, with about $18.2 million annually for maintenance. Only $500,000 was appropriated for pre-construction.

Charles “Pete” Peterson, marine science professor at UNC-Chapel Hill, said in a 2006 interview that nourishment projects on average last about five years, with huge variance. One project, he recalled, still had pipeline on it when a storm wiped all the pumped sand away.

A beach must be engineered to certain specifications and maintained regularly to be eligible for permanent repair under Federal Emergency Management Agency rules. The repair must be needed to protect improved property from immediate threat.

But Rogers sidestepped the significance of scale and degree, saying it is too difficult to accurately estimate how a beach like Nags Head will respond.

“The way you really find the performance is to build it and see how it performs,” Rogers said after the presentation.

“One of the nice things about beach nourishment is it doesn’t commit you forever.”

Beach nourishment works great in some places: It’s been very successful in Miami Beach, where the flat nearshore and ocean waves are comparable to those in the Outer Banks’ sounds. Longtime nourishment of about three miles of beach in nearby Sandbridge, Va., has been credited with expanding the shoreline and jacking up property values.

Other effective beach-widening projects in North Carolina were built on less-energetic southeast-facing beaches, and were usually fully-engineered large-scale projects with regular maintenance schedules.

But much of the Outer Banks, including South Nags Head, Riggs said, has steep northeast-facing high-energy beaches. Sediment transport from north to south is some of the highest on the coast. Mirlo Beach, known for having the biggest waves on the East Coast, has a rock offshore that runs north-northeast at an angle that causes storm-driven waves to focus energy toward the beach.

“Nobody goes to Miami Beach to surf,” Riggs said. “I think people need to keep perspective where they are.”

Riggs also has been a member of numerous state science and coastal policy panels. He and Ames co-authored, “Drowning the North Carolina Coast: Sea Level Rise and Estuarine Dynamics” and are two of four authors of “ The Battle for North Carolina’s Coast, ” scheduled for release in September.

Considering that South Nags Head is in the same neighborhood as Oregon Inlet, a stubbornly unruly waterway, Riggs said that beach nourishment there would require a long-term, costly commitment that he compared to having children.

Instead, he believes Nags Head should do what Kitty Hawk has done: start getting the houses off the beach and keep them off the beach. Keep infrastructure on the west side, far from the reach of damaging surf.

“We don’t need to abandon the barrier islands,” he said. “We just have to get smart about living on them.”

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