Sunday, May 9, 2004
North Carolina’s disappearing coast
RALEIGH – RALEIGH — North Carolina’s coast is disappearing.
Each year, rising sea level gently floods more land in Eastern North Carolina as faraway glaciers melt.
And every so often, relentless northeasters and ferocious hurricanes come along, pounding and grinding the ocean shoreline as well as the state’s nearly 4,000 miles of estuarine shoreline — the waterfronts lining the shallow sounds, broad rivers and wide tidal creeks.
The combination of those natural phenomena is gobbling up North Carolina real estate at a surprising rate — consuming perhaps 1,250 acres per year. The shoreline in northeastern North Carolina is receding at an average rate of about 2.7 feet per year.
“We are shrinking, dramatically,” says coastal geologist Stan Riggs, who has studied modern coastal systems for 40 years and advises local, state and federal governments about the impacts of natural forces and human development on coastal zones.
Riggs and his associate Dorothea Ames have just published a new book documenting the effects of sea-level rise and storms on our coastal area. “Drowning the North Carolina Coast: Sea-Level Rise and Estuarine Dynamics” notes that the rapid submersion of shoreline has happened before — and means that little will ultimately survive.
“The processes of change continues to take its toll today as every no’easter and hurricane place their mark upon the shifting sands of time,” the book notes. “If the rapid rates of coastal evolution continue, no great remnants from our present coastal civilization will survive into antiquity. This is our coastal heritage.”
The book’s front and back covers show a vivid picture of what can happen — the loss of about 50 linear feet of a 75-foot-tall sand and clay bluff on the Chowan River near Albemarle Sound in a period of two to three hours during last fall’s Hurricane Isabel.
A storm surge of 5 to 8 feet, combined with 80 mile-per-hour winds and gusts to 95, reduced a significant bluff to a sandy clay beach. “It was not a good place to be,” says Riggs, distinguished research professor at East Carolina University in Greenville.
Riggs and Ames, assistant scientist at ECU and Riggs’ longtime research associate, analyzed 21 specific estuarine sites using data that goes back decades to determine how the shore has changed. They not only have documented the astonishingly rapid average erosion rate of 2.7 feet of shoreline each year in northeastern North Carolina, but also computed that the receding shoreline claimed 119 acres of upland and 246 acres of wetlands that scientists say are critical to absorbing runoff and filtering pollutants from coastal waters.
By their calculations, the average loss of land in the 1,593-mile estuarine region that Riggs first mapped in 1978 is 629 acres per year.
But Riggs takes it one step further: Because he mapped only about 50 percent of the shoreline in that 1978 study, the real loss of land would be much greater over the entire region if the erosion rate is the same — 478 acres of upland and 780 acres of wetlands, for a total of 1,258 acres.
Riggs and Ames’ book is “a wakeup call that we have huge issues confronting us,” said Todd Miller, founder of the N.C. Coastal Federation. “That estuarine fringe is one of the most productive environmental resources on Earth, and North Carolina is way behind the curve in regulating the estuarine shoreline.”
If it sounds unlikely that North Carolina might be losing more than 1,250 acres of its land each year to rising sea level and bad storms, Riggs understands the skepticism. He didn’t believe it himself when Ames showed him data not long ago about the shoreline of Dare County on the western side of Pamlico Sound. Riggs was so sure the data were wrong that he bet her a bottle of wine — a good red Australian — that the shoreline could not have receded by 171 feet in just five years.
They re-surveyed with a highly accurate Trimble GPS and ran the data again. Riggs lost. “That was a tremendous recession of land that I could not tell had changed,” Riggs said. “Until we had the ability to survey it, we weren’t able to document that change.”
These observations are not just idle exercises. The drowning of the N.C. coast has significant consequences — and not just for those who might have a cottage in the way. As sea level rises and storms take their toll on the shoreline, a great variety of things happens. As Isabel showed, storms erode not just sand and clay but also peat deposits and other organic matter. When all that material in the water column begins to decay, it consumes oxygen in the water. Fish have nothing to breathe. “We had massive fish kills after that,” said Riggs.
As waters rise, wetlands disappear — and if development has already consumed inland areas that might have become new wetlands, wildlife loses its habitat. Animals have fewer places to roam. Stormwater runoff from higher land, unchecked by wetlands that once absorbed it, rushes straight into the estuaries and fouls water quality. Fin fish and shellfish suffer from the pollutants that stormwater brings. A vicious cycle continues.
The shape of the state changes, too. North Carolina’s famous Outer Banks, a chain of thin sand banks that gives the state its signature eastern profile and its fearsome capes, will begin to submerge as rising seawater claims significant portions of Core Banks near Cape Lookout, Ocracoke Island to the north and Hatteras Island. Riggs and Ames say these barrier islands “are like icebergs, with only a small portion rising above the sea surface, and the greatest portion hidden below sea level.”
Riggs figures that in the short-term future — perhaps a decade or two, or even within a year or so if a catastrophic Category 5 hurricane were to strike the banks head-on — much of the banks will go under. The narrow inlets that now hyphenate the coast will become much wider bodies of water.
Hurricane Isabel might have created that kind of damage, had it not diminished in ferocity and come ashore as only a Category 2 storm, he said. “The barrier islands already are shrinking significantly,” said Riggs. During Isabel, “they eroded on the front side, they eroded on the back side. … We came within a couple of inches of having three new inlets.”
In a century or perhaps two, Riggs and Ames warn, the Outer Banks would largely submerge. Pamlico Sound would become Pamlico Bay. The Alligator River would become Alligator Sound after much of Roanoke Island goes under water.
Sea-level rise and storms are natural processes. Shorelines exist to absorb the enormous physical energy of storms — and sandy shorelines are efficient absorbers of energy.
But Riggs and Ames point out that human alterations have hastened erosion and shoreline recession. Dredging of sand for beaches elsewhere has depleted the natural store of sand that nature often uses to replenish beaches. And what Riggs calls “Raleigh-style development” of entire neighborhoods in coastal areas causes problems for the people who buy homes in those areas.
“A lot of people don’t like vegetation on their shoreline, but the minute they clear it and open up their view, they create the opportunity for erosion,” he said. “They may think vegetation is snaky, but any vegetation you maintain on the shoreline is better than none. … The moment you open it up, it becomes like a wound, and it festers.”
Those who live in the Piedmont and mountain areas of the state may not realize this fundamental principle, Riggs said: Land in those regions doesn’t change a lot. “You buy a piece of property with four boundaries, and you can count on having that 100 years from now, or 200 years from now,” he said. “On the coast, that’s not the same. We have energy that changes the (shape of the) land, and we are in the process of drowning the coast.”
Riggs points to the wisdom of coastal residents in an earlier time, when they built homes on the sound sides of the Outer Banks where they were somewhat protected. It’s not the coastline that is fragile, he points out, but the human superstructure built on it. “There’s a reason the old timers built little beach cottages — they could be picked up or rebuilt without destroying the system,” Riggs said.
`DROWNING THE NORTH CAROLINA COAST’: “The glaciers are still melting today, sea level continues to rise, and the ocean slowly but relentlessly continues to flood the coastal lands of North Carolina. … There is no guaranteed permanency to any characteristic or feature within the North Carolina coastal system.”
EROSION | This 75-foot-tall sand and clay bluff stood on the western shore of the Chowan River near Albemarle Sound in August 2003. Hurricane Isabel struck on Sept. 18, 2003, gouging away 50 feet of the Chowan River shoreline in a few hours and reducing the high bluff to the broad sand beach shown in a photo taken on Oct. 6, 2003. The dramatic erosion shows the results of the enormous energy that storms can focus on North Carolina’s ever-changing shoreline. Stan Riggs used the photos as the front and back cover of a new book he wrote with Dorothea Ames.
Eroded remnants of barrier islandsNew transgressive barrier islands
Observer Associate Editor Jack Betts can be reached at firstname.lastname@example.org.