National Assessment of Storm-Induced Coastal Change Hazards

Pre- and Post-Storm Photo Comparisons – Cape Lookout, NC to Oregon Inlet, NC

The barrier island coast between Cape Lookout and Cape Hatteras has a very different orientation than the coast between Cape Hatteras and Oregon Inlet; in fact, together, they form nearly a right angle. This difference in orientation has contributed to differences in impact on each coast during the passage of Hurricane Irene. The more southerly facing reach from Lookout to Hatteras was impacted directly by the storm's strongest winds in the right-front quadrant. Model results (by Coastal Emergency Risk Assessment using ADCIRC) estimated that maximum storm surge along the ocean-facing side of the barrier islands from Cape Lookout to Cape Hatteras was roughly 2 m. Additionally, 7-m wave heights observed on the open coast contributed to both setup and runup. The resulting impacts to the coast included dune erosion, overwash, and potentially dune retreat, as indicated below in the before and after images. In contrast, as the counterclockwise circulation of the storm moved across the broad Pamlico Sound after landfall, the winds eventually blew from west to east creating a storm surge, in addition to waves and wave setup, on the sound-side of the barrier island between Cape Hatteras and Oregon Inlet. ADCIRC indicated that the soundside storm surge also reached roughly 2 m. The ocean-side surge levels were lower than the sound-side levels, and where the island was lower than the surge level, the surge may have flowed from sound to ocean potentially contributing to the formation of five breaches carved between Cape Hatteras and Oregon Inlet, several of which severed NC Highway 12.

Location index of photographs. Each location includes photos and/or photo-pairs showing changes that occurred during Hurricane Irene. The green line shows Hurricane Irene's track.

Location 1: Vertical aerial photographs of Core Banks, NC, from June 12, 2010 (upper, acquired by USDA) and August 28, 2011 (lower, acquired by NOAA one day after landfall of Hurricane Irene). The red line in the lower photo is the location of the oceanfront shore on June 12, 2010. This location is 30-35 km northeast of landfall and in the hurricane's right-front quadrant. A breach has been cut through the barrier island. This is not an unusual occurrence at this location; inlets have been observed here in other photography. Such inlets close naturally by infilling with sand over weeks and months, then reopen during storms like Irene. [larger version]

Location 2: Oblique aerial photographs of Ocracoke Island, NC, from May 6, 2008 (top, pre-storm) and August 30, 2011 (bottom, post-storm, acquired three days after landfall of Hurricane Irene). The yellow arrow in each image points to the same feature. Overwash deposits of sand extend over the road after the storm. Heavy equipment is at work clearing the road, which appears buried rather than destroyed. Overwash extended tens of meters landward of the road into the marsh grasses on the sound-side of the island. [larger version]

Location 3: Oblique aerial photographs of Hatteras Village, NC, from May 6, 2008 (top, pre-storm) and August 30, 2011(bottom, post-storm, acquired three days after landfall of Hurricane Irene). The yellow arrow in each image points to the same cottage. Note that the dunes seaward of the cottages may have steepened by wave impacts (the collision regime), but it is not clear with this data. Our lidar results will confirm whether dune erosion occurred. Cottages here appear not to have been significantly impacted by waves and surge. [larger version]

Location 4: (Upper image) Oblique aerial photograph near Rodanthe, NC, looking south along the coast on August 30, 2011, three days after landfall of Hurricane Irene. Oblique aerial photographs of central part of upper image from May 6, 2008 (middle, pre-storm) and August 31, 2011 (lower, post-storm). The yellow arrow in each image points to the same cottage. A breach was carved through the barrier island, severing NC Highway 12. The storm surge was approximately 2 m high on the sound-side and was less on the ocean-side. Flow from the sound to the ocean may have played a role in cutting the breaches between Oregon Inlet and Cape Hatteras. [larger version]

Location 5: (Upper image) Oblique aerial photograph of Pea Island National Wildlife Refuge, NC, looking north along the coast on August 30, 2011, three days after landfall of Hurricane Irene. Oblique aerial photos of the central part of upper image from May 6, 2008 (middle, pre-storm) and August 31, 2011 (lower, post-storm). The yellow arrow in each image points to the same cottage. At this location, two breaches were carved through the island, severing NC Highway 12. With the storm surge higher on the island's sound-side, currents flowing from sound to ocean may have contributed to creating these breaches. [larger version]