HURRICANE IVAN'S COASTAL IMPACTS AS REVEALED BY AIRBORNE LIDAR

In a cooperative effort between the U.S. Geological Survey, NASA, and Corps of Engineers, the impact zone of 2004’s Hurricane Ivan was surveyed with airborne lidar before and after landfall. The surveys were conducted using NASA’s EAARL (Experimental Advanced Airborne Research Lidar) and Corps of Engineers’ CHARTS (Compact Hydrographic Airborne Rapid Total Survey), and included all of the Gulf-front sandy beaches of Alabama and the Florida Panhandle. The before and after surveys were compared and show extensive beach and dune changes as well as the opening of new inlets through barrier islands. The kinds of impacts varied along the coast dependent on the coast’s elevation. For example, the coast is low, generally less than 2 m NAVD, along the barrier islands near Gulf Shores, AL close to where the right eyewall, and the hurricane’s strongest winds, made landfall. Here, the barrier islands were completely inundated by storm surge. The sea-level gradient between Gulf and back bays drove a strong landward current that transported sand across the island and into the back bays and opened a new inlet. In contrast, ten kilometers to the east in Orange Beach, AL, the topography was higher and the response of the system was dune erosion of over 20 m. In places, the vertical scour approached 3 m and undermined structures including several five-story condominium towers that had been built on top of dunes. These are the largest buildings to ever be completely destroyed in the United States by a hurricane.