Coastal Change Hazards: Hurricanes and Extreme Storms

Hurricane Gustav

Pre- and Post-Storm 3D Lidar Topography: Dauphin Island

Airborne lidar surveys of post-storm topography were collected September 5 – 8, 2008, on the barrier-island coasts of Louisiana, Mississippi, and Alabama that were impacted by Hurricane Gustav. Comparisons of the elevation data to lidar surveys collected before the storm are used to characterize the nature, magnitude, and spatial variability of hurricane-induced coastal changes, such as beach erosion, overwash deposition, and island breaching.

The central portion of Dauphin Island, AL, located over 270 km (168 mi) from hurricane landfall, experienced overwash as waves and surge transported sand across the island. Comparisons between the June 2007 and post-Gustav lidar surveys (bottom figure) reveal erosion along the Gulf-front beaches and deposition of sand inland.

Dauphin Island, AL, 2007 and 2008. Three-dimensional view of lidar-based topography measured in June 2007 and on September 8, 2008. Blue represents elevations below mean high water. Lower elevations are represented by brown shades; higher elevations are greens and reds. The view is looking west along the island with the Gulf of Mexico to left. In the 2007 image, a 3.5-m (~11-ft) emergency berm that was built after Hurricane Katrina (2005) is seen in green on the Gulf-side of the island. In the 2008 image, the emergency berm is conspicuously absent. [larger versions: 2007 image | 2008 image]

Dauphin Island, AL, 2008. Three-dimensional view of changes in island elevation between June 2007 and September 8, 2008. Red indicates areas of elevation loss (erosion) and green indicates areas of elevation gain (accretion). The view is looking west along the island with the Gulf of Mexico to left. The emergency berm built after Hurricane Katrina was completely eroded, and sand was deposited inland. Overwash along the road was cleared prior to the lidar flight. Piles of cleared sand are seen in green along the north side of the road. The patches of red and green on the houses are an artifact of data processing. Large green rectangles on the ground are locations of houses built since Hurricane Katrina. [larger version]

Note: The results presented here are considered preliminary and have not been thoroughly reviewed or edited. They are based on preliminary data that may be updated as the survey accuracy improves in future processing steps such as application of the precise ephemeris for GPS satellites, offset checks using ground control surveys, checks for laser calibration and mounting errors, and full application of data quality control, assurance and editing procedures.

Coastal and Nearshore Mapping with Scanning Airborne Laser (Lidar)
USGS