Scientists Study Coastal Erosion at Cape Hatteras, North Carolina


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Scientists Study Coastal Erosion at Cape Hatteras, North Carolina

By John Warner, Jeff List, Rob Thieler, Jesse McNinch, Kevin Haas, George Voulgaris, and Marinna Martini
July 2010

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A strange sight was observed on the beaches at Cape Hatteras, North Carolina, last February. A large white vehicle—or was it a boat?—drove across the sandy beach, headed directly into the crashing waves, and maneuvered out to sea. The Light Amphibious Resupply Cargo (LARC) vehicle, operated by the U.S. Army Corps of Engineers (USACE) from Duck, North Carolina, was part of a multi-organizational coastal-erosion study involving scientists from the U.S. Geological Survey (USGS), the USACE, the University of South Carolina, and Georgia Tech Savannah, in cooperation with the National Park Service Outer Banks Group. The study investigated processes responsible for alongshore delivery of sediment to the cape's point, and the mechanisms that transport sediment from the point farther offshore.

Above left: The Light Amphibious Resupply Cargo (LARC) vehicle transporting divers and gear into the surf zone for deployment of oceanographic instruments. [larger version]

Above center: Jetpump used to to insert pipes. [larger version]

Above right: Long pipes were jetted into the seafloor to support instruments on a cantilever arm. [larger version]

The study involved many different types of field activities. We deployed oceanographic instruments in the nearshore to measure surface waves and ocean currents. The surf zone is a challenging environment, and the deployment of instruments here requires specialized gear and highly trained personnel. The LARC transported divers into the surf zone, where they used a jetpump to insert long pipes into the sandy seafloor. The divers then attached instruments to the pipes, which held the instruments in place during the study.

Above: North Carolina coastline, showing location of Cape Hatteras. [larger version]

Other instruments measured the spatial variability of surface currents, using a WERA very high frequency (VHF) radar system. The WERA, which has separate transmit and receive arrays, was installed along the dune line at a site occupied by the lighthouse before it was moved inland about 10 years ago to protect it from coastal erosion. The WERA measured surface currents as far out as 14 km from shore and approximately 14 km along the coast, on a grid with spacing approximately 150 m on a side.

Above: WERA radar system used to measure the speed and direction of surface currents. [larger version]

The speed and direction of currents in the surf zone were measured remotely with a camera mounted atop the Cape Hatteras Lighthouse. The camera took pictures during daylight hours at a rate of 3.3 frames per second, and the images were recorded on a computer. Processing of the images will track foam lines to estimate the speed and lateral variability of currents moving alongshore (near and generally parallel to the coastline).

Above left: Cape Hatteras Lighthouse. [larger version]

Above right: A camera mounted on the upper railing of the Cape Hatteras Lighthouse collected imagery used to measure the speed and direction of currents in the surf zone. [larger version]

We performed a dye study to estimate alongshore-transport rates and to learn what dye could reveal about lateral mixing in the surf zone. Uranine dye, a nontoxic substance, was placed in dissolvable bags and deployed from a sophisticated launching mechanism (large slingshot). Photographs taken from a single-engine aircraft flying at 1,000 ft are being analyzed to infer alongshore-transport directions.

Above left: Dissolvable bag containing uranine dye. [larger version]

Above right: USGS personnel launch a bag of uranine dye into the surf zone. [larger version]

Above: Aerial photographs revealed the path of the tracer (bright green) in the nearshore.

CLARIS (Coastal Lidar and Radar Imaging System) uses lidar (light detection and ranging) to measure coastal topography and X-band radar to estimate offshore bathymetry (water depths). [larger version]

A Coastal Lidar and Radar Imaging System (CLARIS) used lidar (light detection and ranging) to measure dune heights and beach topography, and X-band radar to measure the intensity of breaking waves, which is used to estimate offshore bathymetry. The CLARIS system is ideal for measuring offshore bar locations and sand movement during storms when powerful waves are breaking.

The deployment was covered by a local online news organization, the Island Free Press, in an article and slide show posted February 18, 2010.

This project is part of a larger study—the Carolina Coastal Change Processes Project—led by USGS Coastal and Marine Geology Program scientists in Woods Hole, Massachusetts, to understand regional sediment dynamics along the coastline of North and South Carolina. Visit the Cape Hatteras Field Study to learn more about the work described in this article. A similar study conducted last year on Diamond Shoals was highlighted in the Sound Waves article "USGS Studies Sediment Transport at Cape Hatteras, North Carolina."

We thank the following personnel for their dedication and hard work during the deployment: USGS divers Chuck Worley, Dann Blackwood, Sandy Baldwin, Michael Casso, BJ Reynolds, and Jordan Sanford; photographer Don Bowers; USGS technicians Jonathan Borden and Brandy Armstrong; USACE LARC personnel Ray Townsend, Jason Pipes, and Mike Forte; Georgia Tech Savannah students Stephanie Smallegan, Adam Sapp, Thomas Gay, and Xiufeng Yang; University of South Carolina technicians and students Jeff Morin and Kumar Nirnimesh; and Virginia Institute of Marine Science student Kate Brodie.