On September 18, 2003, Hurricane Isabel pounded the northern Outer Banks of North Carolina. At the U.S. Army Corps of Engineers (USACE)'s Field Research Facility in Duck, 125 km north of where the eye wall cut across Hatteras Island, the category 2 storm generated record conditions for 27 years of monitoring: an 8.1-m wave height measured at a wave-rider buoy in 20 m of water, and a 1.5-m storm surge.
In a cooperative program between the U.S. Geological Survey (USGS) and the National Aeronautics and Space Administration (NASA), airborne lidar (NASA's EAARL [Experimental Advanced Airborne Research Lidar]) was used to survey the beaches and dunes along a 350-km-long reach from Cape Henry at the mouth of Chesapeake Bay to Cape Lookout, NC.
With the accurate long-range forecast by the National Oceanic and Atmospheric Administration (NOAA)'s National Hurricane Center, we were able to acquire a prestorm survey only 2 days before Isabel's landfall. A poststorm survey flown 3 days after impact allows detection of coastal change.
In addition to lidar surveys, USGS personnel from St. Petersburg, FL, and Woods Hole, MA, made other assessments. Dennis Krohn, Karen Morgan, and Russ Peterson photographed and videotaped the impact zone from a twin-engine plane operating out of St. Petersburg's Albert Whitted Field (see oblique aerial photographs).
A ground team consisting of USGS personnel Jeff List, Hilary Stockdon, Meg Palmsten, and Abby Sallenger, plus University of South Florida (USF) graduate student Laura Fauver, drove in a four-wheel-drive vehicle from Virginia Beach, VA, to a new breach through Hatteras Island, southwest of Cape Hatteras, traveling on the beach where possible.
Billy Reynolds negotiated numerous roadblocks and set up his global-positioning-system (GPS) base station (in support of EAARL) where the eye wall cut across Hatteras Island. Amar Nayegandhi processed part of the EAARL data within a week of landfall, using ALPS, the Airborne Lidar Processing System developed by John Brock and his group; and Kristy Guy created the grayscale lidar images that accompany this article.
Preliminary analyses of the EAARL data from Hatteras Island show extensive beach changes and dune erosion, as well as destruction of infrastructure and buildings, particularly in Hatteras Village.
The most extensive beach changes were associated with the opening of a breach (approximately 500 m wide and divided into three separate channels) that completely severed the island. The main breach (see top photograph in this article), and a smaller one several kilometers to the south (not shown), occurred at minimums in both island elevation and island width. (Note that the EAARL data shown here did not extend across the entire island width, which was determined from other sources.)
Storm-surge estimates are being generated by NOAA, using the standard SLOSH (Sea, Lake, and Overland Surges from Hurricanes) model, and will provide sea-level approximations on either side of the island; gradients in sea level may have generated currents that could have carved the breach. Calculated sea-level gradients will be coupled with EAARL topography and topographic change to determine vulnerability criteria for breach openings on barrier islands.
The USACE is tasked with closing the breach so that NC Highway 12 can be rebuilt to provide access to Hatteras Village. The plan is to pump sand through pipes from a flood-tidal delta approximately 6 km away and choke off the tidal currents that now scour the breach floor and keep it open. Within 10 days of landfall, we were able to provide the USACE with high-resolution topographic data to assist in their efforts.
In addition, the USACE conducted bathymetric surveys of the breach and acoustic profiling of its poststorm tidal currents. Collectively among the USGS, NASA, USACE, and NOAA, the Hurricane Isabel breach is likely the most extensively ever monitored and offers the opportunity to develop and thoroughly test models of breach development.
in this issue:
Impacts of Hurricane Isabel