Coastal Change Hazards: Hurricanes and Extreme Storms

Hurricane Ike

Pre-Storm and Post-Storm 3D Lidar Topography: Bolivar Peninsula, TX

An airborne lidar survey of post-storm topography was completed September 17, 2008, on the Texas coast between Port Lavaca and Port Arthur. Comparisons of the post-storm elevation data to lidar data collected in September 2005, well 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.

Location index for comparison of pre-storm and post-storm lidar elevations on Bolivar Peninsula, TX. The square box describes the focus area for this lidar comparison. The green line is Ike's storm track.

The hardest hit area was the Bolivar Peninsula, where storm surge elevations exceeded the island elevation, leading to inundation, overwash and extreme coastal change. This coastal change and corresponding damage to houses can be seen in oblique photo comparisons. Lidar observations provide a more quantitative estimate of coastal change.

Comparisons of the pre- and post-storm lidar topographic surveys show significant changes. The top figure (2005 survey) contains many high elevation (red) squares that correspond to houses. Many of these squares are missing in the middle figure (2008, post-Ike survey). The missing houses appear again in the bottom figure (elevation change between surveys) as areas of high erosion (red). Also apparent in the bottom figure is an area of high erosion along the shoreline. This represents the loss of beach and dunes due to inundation and overwash processes. Immediately landward of the erosion feature, there is deposition (blue) showing landward movement of at least some of the eroded sand.

Above: September 2005 Lidar Survey Above: September 2008 Lidar Survey Above: Coastal Change Lidar topography from Bolivar Peninsula, TX. These false-color images of the topography show the elevations obtained from lidar missions conducted in September 2005 (top) and in September 2008, immediately after Ike's landfall (middle). The coastal change between the two dates (bottom) is determined from the difference between the two data sets. For the coastal change figure, red indicates at least 1 meter of erosion and blue indicates at least 1 meter of deposition. Note that the spatial coverage of the two data sets differs. The 2008 mission had more extensive coverage than the 2005 mission in this area. Arrows indicate location of pre- and post-storm photo comparisons for Location 1, Location 2, and Location 3.

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