Researcher Finds Sea Of Sand Along Coastal Zone With Potential To Replenish Beaches

Steve Boss, assistant professor of geosciences at the University of Arkansas, and Bill Hoffman of the North Carolina Geological Survey quantified an underwater mountain of sand seaward of Cape Hatteras that could help replenish beaches along the North Carolina Outer Banks. When Boss and Hoffman examined Diamond Shoals, an extensive sand deposit off Cape Hatteras, they found somewhere between 1.6 and 3.8 billion cubic yards of sand.

If all the sand could be used to nourish beaches, it would be enough to build a beach 1 mile long, 200 yards wide and 30 feet deep every year for the next 500-1000 years. However, most of this sand lies beneath waters under Federal jurisdiction, and it's likely that only the portion within three nautical miles of shore, which is under state jurisdiction, would ever be considered for use. The sand within state waters is estimated to be between 256 million to 712 million cubic yards.

"Sand is becoming a valuable commodity," Boss said. It can cost $1.5 to 2 million to replenish a mile of beach. Worldwide, beaches are shrinking, creating problems for people who visit, live and travel along their sandy banks.

Boss and Hoffman presented their findings at a recent meeting of the Outer Banks Task Force in Nags Head, N.C. The task force includes the U.S. Army Corps of Engineers, the Federal Highway Administration, the U.S. Fish and Wildlife Service, the National Park Service, the National Marine Fisheries Service, the North Carolina Department of Environmental and Natural Resources, the North Carolina Department of Transportation, and officials from Hyde and Dare counties in North Carolina. The task force seeks to preserve and minimize impact on the natural barrier island system while maintaining roads and access to North Carolina's outer banks. Every year storms and erosion threaten to wipe out North Carolina Highway 12, which runs down the spine of the barrier islands. A long-range plan for protection of the corridor will consider 19 alternatives, which include beach nourishment and dune restoration, a raised highway like the one that runs through the Florida Keys, enhanced ferry service and bridges from the mainland to islands.

Boss and his colleagues studied the prospect of sand availability in four locations and will report their other findings at subsequent meetings.

In 1994 Boss and his colleagues began surveying the ocean floor from Oregon Inlet to Cape Hatteras and westward from Cape Hatteras to Ocracoke Inlet. They used sound waves bounced off the ocean floor to produce "images" of the seafloor and the layers beneath it. They also used side-scan sonar, which produces images that look almost like an aerial photograph.

"This gives us a 'fish's eye view' of the bottom, which can also tell us a lot about what types of sediment might be present," Boss said.

The researchers combined 1,200 miles of data from these two techniques with sample cores drilled from the seafloor to determine different ocean bottom types. Then they created three-dimensional images of the different layers. This allowed the researchers to create a topographic map of the seafloor, indicating thick and thin sediment layers. From this they can calculate the volume of sediment, often sand, in a given area, Boss said.

The task force report focuses on one of four spots where Boss and Hoffman collected data from 1994-96 -- the portion that includes the Cape Hatteras sand.

A finite resource experiencing an ever-increasing demand, sand is rapidly disappearing from coasts worldwide -- for both geological and man-made reasons, Boss said.

During the last ice age, the ocean levels were 300 feet lower. Warming temperatures and melting glaciers have caused the water to creep up the shoreline. And in some areas, man-made dams have shrunk the sediment which usually finds its way to ocean shores.

In coastal states like North Carolina, the loss of beaches means more danger for waterfront property -- particularly during hurricane season. One solution has been to replenish sandy beaches by pumping sand from offshore sources onto the shoreline -- a temporary fix which has to be repeated every 3-5 years. Therefore states must continually seek sources of sand.

Other factors besides money figure into the sand replenishment equation.

Shrinking beaches threaten historic landmarks -- like the Cape Hatteras Lighthouse. The ocean has crept to within 120 feet of the 208-foot tall building, so it is being moved 2,900 feet inland in an attempt to save it. Other buildings may fall into the ocean if the beaches aren't built up, beach replenishment proponents argue.

Federal Emergency Management Agency officials, however, oppose beach replenishment because they feel it encourages development in potentially dangerous areas, Boss said.

"Whatever decision is going to be made, it will not be limited by availability of sand near Cape Hatteras," Boss said. "The decision to exploit the sand resource will depend upon other factors -- economics, logistics, social concerns, public perceptions and environmental concerns."