APPLICATION OF REMOTE SENSING AND GROUND-PENETRATING RADAR TECHNOLOGIES TO ASSESS DAMAGE CAUSED BY HURRICANE IAN IN SOUTHWEST FLORIDA

Remote sensing (UAV-flown LiDAR), geospatial analysis, and ground-penetrating radar (GPR) are being used to map and monitor the morphosedimentary condition of Southwest Florida’s (Collier and Lee Counties) coastal zone to both chronicle the impacts of climate change (through sea-level rise and storminess) and inform resiliency planning by local governments, unincorporated communities, and State Parks and Federal Reserves. The pre-event baseline condition was mapped using either drone LiDAR in the spring and summer of 2022, prior to Hurricane Ian, or using NOAA 2018 fixed-wing LiDAR for those regions not flown before Ian’s arrival. Hurricane Ian made landfall as a strong category 4 storm on 28 September 2022 in northern Lee County. Its slow forward progression, intense winds, and trajectory, generated ideal conditions for an extreme surge, reaching as high as 4.6 m NAVD88. Two surge-related processes influenced coastal geomorphology. Flood surge, due to its extreme height, created “overwash and inundation regime” impacts (after Sallenger) and transported shelf sands to the back dune environment, transgressing the foredune and lowering crest height. Flood surge overwashed several barrier islands and caused extensive flooding damage, destruction of poorly constructed or low elevation buildings, and loss of life. Ebb surge returned flood waters at a lower elevation which caused prolific erosion, creating ebb surge channels that transected the foredune and backshore and undercut foundations of structures located seaward of or up to the coastal construction control line. A comparison of pre- and post-storm digital elevation models reveals: the processes causing these geomorphic effects, the spatial variability of coastal vulnerability, the quantification of sediment gains and losses, and, most importantly, invaluable insight for restoration strategies and the building of resilience capacity. GPR surveys complement the geospatial analyses by revealing the prehistory of late Holocene storm surge erosion. GPR traces, from surveys oriented parallel the shoreline but high on the backshore or foredune, exhibit channel-forms consistent with ebb surge processes. This work clearly demonstrates that certain regions are chronically eroded, further illuminating vulnerabilities.