IMPACT OF HURRICANE ISABEL ON THE NORTH CAROLINA COAST

During September 2003, Hurricane Isabel impacted the northern Outer Banks of North Carolina creating record wave and surge conditions. At the Army Corps of Engineer’s Field Research Facility in Duck, 125 km north of landfall, the Category 2 storm generated a significant wave height (at a waverider in 20 m of water) of 8.1 m and storm surge of 1.5 m—both records for twenty-seven years of monitoring.

In a cooperative effort between USGS and NASA, airborne lidar (NASA’s EAARL – Experimental Advanced Airborne Research Lidar) surveyed the beaches and dunes before and after Isabel’s landfall from Cape Henry, VA (at the mouth of Chesapeake Bay) to Cape Lookout, NC. With the accurate long-range track forecast by NOAA’s National Hurricane Center, EAARL was able to survey two days before landfall providing an outstanding baseline to detect change. The post-storm survey was obtained three days following landfall.

Hurricane Isabel’s impacts were considered by observers to be the most extensive along the Outer Banks since the late seventies, and perhaps since the 1962 Ash Wednesday northeaster. Near where the eyewall cut across Hatteras Island, EAARL measurements showed that foredune retreat locally exceeded 25 m and, in places, the dunes were completely eroded. Extreme dune erosion extended north from Cape Hatteras for at least 180 km to Sandbridge, VA. In many places along that reach, overwash breached the dunes and covered roads with up to ~1 m of sand. The most extensive beach and dune changes were caused by a ~500 m wide breach that severed Hatteras Island southwest of Cape Hatteras. EAARL data indicate that the main breach, and a smaller one several kilometers to the south, occurred at minima in both island elevation and island width. The before and after lidar data quantify changes associated with dune erosion, overwash, and breach formation and should be valuable for testing models of storm impacts on coasts.