THE IMPACT OF HURRICANE IKE AND ANTHROPOGENIC MODIFICATION ON FOLLET’S ISLAND OUTWASH CHANNELS: FORMATION AND DYNAMICS

Hurricane Ike made landfall at Galveston Island on September 13th, 2008. The category 2 hurricane had wind speeds of over 110 mph and a storm surge of 2.6 meters. Offshore directed flows associated with elevated back-barrier water levels after Ike made landfall carved out 31 outwash channels on Follet’s Island. The outwash channels are oriented perpendicular to the shoreline and cut from the beach through the dune and their upstream heads terminate near County Route 257 (Bluewater Highway). Ongoing analysis of sediment cores, lidar data, and aerial imagery of Follet’s Island, Texas, contributes to the understanding of geomorphology and sedimentology of barrier islands and outwash channels, especially those in a highly modified barrier island landscape. In this study, six lidar datasets spanning 18 years were analyzed to track evolution of the outwash channels since their initial formation. The perimeter of each outwash channel was digitized using ArcGIS. Then morphologic metrics of area and change through time were calculated. Additionally, an investigation into the anthropogenic modification to the shoreline via beach nourishment and dune restoration was conducted to add context to observed morphologic change. Data from American Shore and Beach Preservation Association and the Center for Developed Shorelines indicate 24.98 million cubic meters of sediment was emplaced during 130 engineered nourishments, spanning the Texas Gulf Coast between 1992 - 2019. Despite the enormous volume of emplaced sediment, this is taken to be a minimum estimate of anthropogenic modification, as beach driving and wrack scraping are common practices, and are not accounted for. Since the original formation of the outwash channels in 2008, the elevation of the primary foredune has been restored through beach and dune engineering, and 16 channels infilled. As of Sept. 2024, 15 of the original outwash channels remain open as brackish ponds, providing wetland habitat. Improved understanding of the geomorphology of barrier islands and outwash channels through natural processes (e.g., tropical cyclones) and engineering projects can inform management decisions for beach nourishment and ecosystem preservation and provide insight into the geomorphic evolution of barrier islands.