Mobile and Airborne Lidar Scanning to Assess the Impacts of Hurricane Harvey to the Beach and Foredunes on North Padre Island, Texas, USA

Hurricane Harvey made landfall on August 25, 2017 around 10:00 PM near Rockport, Texas as a category 4 hurricane, devastating coastal regions and becoming one of the costliest hurricanes on record. Harvey had sustained winds of about 215 km/h, an estimated minimum pressure of 937 mb, and storm surges between 1.8 and 3 meters. Flooding on North Padre Island at Packery Channel was measured at about 1.43 ft MHHW and at Bob Hall Pier was measured at 1.07 ft MHHW. These strong winds, surge levels, and wave impact resulted in rapid change in the beach and foredune structure. This study utilized a mobile lidar system (MLS) for rapid post-storm damage assessment of the beach and foredune structure along a section of sandy beach on North Padre Island, Texas located roughly 50 km to the south of San Jose Island where the storm first made landfall. MLS data were collected on September 5, 2017, 11 days after Harvey made landfall. The system, made by LidarUSA, is a Velodyne HDL-32E, collects about 700,000 points per second, has a +/- 2 cm accuracy, has a 100 m range, as is considered to be a shorter range, lower cost lidar scanner. Pre-Harvey airborne topo-bathymetric lidar data were collected in 2016 by the UASCE Joint Airborne Lidar Bathymetry Technical Center of Expertise (JALBTCX). To measure the impacts of Harvey to the beach and foredunes, the airborne and mobile lidar datasets were compared. First, the datasets were post-processed to remove non-ground points and systematic biases were adjusted between the surveys by using static features, such as roadways, captured in the study area. Once the elevation biases were removed, digital elevation models (DEMs) of the beach and foredune terrain were generated and used to investigate changes in beach geomorphology, including foredune and sub-aerial beach profiles, sediment loss, and shoreline change. Although significant coastal erosion was observed at the study site, results show that changes to the beach and dune system were relatively minor compared to the coastal erosion experienced along San Jose Island where the storm made landfall.