Coastal Change Hazards: Hurricanes and Extreme Storms

Hurricane Frances

Hurricane Frances. Image copyright WSI Corporation. [larger version]

Category-2 Hurricane Frances came ashore on the central east coast of Florida on September 5, 2004. The U.S. Geological Survey (USGS), NASA and U.S. Army Corps of Engineers (USACE) are cooperating in a research project investigating coastal change that occurred during Hurricane Frances.

On September 8th, the USGS acquired aerial video and still photography from Daytona Beach to West Palm Beach, Florida. On September 9th, coastal topography of essentially the same region was surveyed using NASA's EAARL (Experimental Advanced Airborne Research Lidar), a laser mapping system. These data will be compared to an earlier survey conducted in June 2004 by the USACE using CHARTS (Compact Hydrographic Airborne Rapid Total Survey). The comparison will detect the magnitude and spatial variability of coastal changes such as beach erosion and overwash deposition. These data will be used to develop and test predictive models of coastal impacts from severe storms. The data will be made available to local, state and federal agencies for purposes of disaster recovery and erosion mitigation.

Preliminary Assessment

Based on the USGS aerial video and stills from the area north of landfall, i.e. from Stuart to Vero Beach, FL, the impact of Hurricane Frances in regard to coastal change was not as severe as the impact of 2003's Category-2 Hurricane Isabel (Hurricane Isabel Storm Impact Studies) on the Outer Banks of North Carolina. During Isabel, many oceanfront structures were destroyed and overwash was extensive where waves overtopped the crest of beach or dune and drove sand landward covering roads and infrastructure. In contrast, during Frances, there were few structures destroyed and overwash occurred only sporadically along the coast (see examples below). However, the coastal-change impacts of Frances were felt over 250 km of coast, from landfall near Stuart to north of Daytona Beach. This broad impact zone was in contrast to Hurricane Charley's narrow zone of 20-40 km, because of that storm's small size and rapid forward speed that limited the development of storm surge along the coast (Hurricane Charley Storm Impact Studies).

The before and after lidar data acquired in both the Charley and Frances impact zones will be compared to test and extend these assessments quantitatively.

Index map showing locations of pre- and post-storm photo pairs.

Another overwash deposit (to the right of the middle oceanfront house) at Floralton Beach. Note the damaged roof of the house to the left of the middle house. [larger version]

Oceanfront house destroyed by waves and erosion on North Hutchinson Island. This type of destruction was more the exception than the rule; most oceanfront structures survived with little or no apparent damage. Note how the vegetation/dune line is now more landward than before the storm, indicating erosion. Also note the remains of a protective seawall on the beach. [larger version]

Overwash deposits near Ft. Pierce. Here waves and storm surge overtopped the crest of the beach and drove sand landward covering vegetation and the road. Overwash deposits like this developed sporadically along the coast. [larger version]