Response and Recovery of Barrier Island Breaches Documented by the USGS Extreme Storms Program

The U.S. Geological Survey initiated a national Extreme Storms Program in the mid-1990s to document coastal-landform changes resulting from hurricanes, northeasters, and El-Niño storms. One of the program's goals is to acquire a pre-storm baseline of coastal imagery to compare to post-storm datasets. The USGS modeled its aerial photography initiative after Dr. Shea Penland's program to map the Gulf Coast with geo-positioned video and still images from a low-altitude aircraft. The photography supplements the airborne laser altimetry (Lidar) flights that provide quantitative measurements of the coast. The aerial photo collection (>30,000 images) is now being converted into a geodatabase.

The database can be used to compare the impact of Hurricane Katrina on the Chandeleur Islands, LA, to nine other storm-induced breaches observed in the southeastern United States since 1996. A major impact of Katrina was the inundation of the entire northern 5.3 km portion of the Chandeleur island chain. By contrast, other storm-induced breaches range from small inlets less than 100 m wide to the 2.4-km-wide breach at Dauphin Island, AL, initially formed after Hurricane Ivan and expanded after Hurricane Katrina. The average distance of the breach to the track of the storm is 65 km, but two breaches are located over 100 km away reoccupying channels from earlier storms. Most breaches plot on the right front quadrant of the eye track with onshore winds, except for the Dauphin Island breach, which occurs 39 km west of landfall for Hurricane Ivan. Whereas all the other breaches are stable or are accreting, the continued erosion in the northern Chandeleur Islands indicates the island system may be out of equilibrium. Future work will use the geomorphology of the mapped breaches to infer where new breaches may occur while continuing to monitor the processes shaping the Chandeleur Islands.