MORPHOSEDIMENTARY IMPACT OF HURRICANE IAN (2022) STORM SURGE ALONG THE GULF COAST OF SOUTHWEST FLORIDA: LESSONS FOR BUILDING RESILIENCE CAPACITY

Hurricane Ian made landfall in Southwest Florida, USA, on 28 September 2022 as a Category 4 storm exhibiting many of the characteristics associated with recently intensified storminess (e.g., rapid fueling, slow forward motion, large diameter). The extreme storm surge severely impacted the coastal geomorphology of the barrier islands and mainland beaches, resulting in wholesale destruction and loss of life in many communities. To assess the morphosedimentary impact of the storm, our research included: 1) high-resolution topographic mapping using UAV-flown LiDAR pre- and post-event; 2) post-storm bathymetric surveys using fixed-wing LiDAR flown by U.S. Army Corps of Engineers, and 3) imaging of partially buried surge channel structures using ground-penetrating radar (500/750 MHz GPR) for comparison with pre-Ian conditions. Pre- and post-event digital elevation models were used to assess sediment volume changes and to extract topographic profiles. Incoming storm surge, because of its extreme height, resulted in “overwash and inundation regime” impacts, placing the erosional capacity of wave energy well above the substrate. As a result, incoming surge caused sand transport via sheet overtopping, overwash and overtop fan deposition, and foredune deflation and retrogradation. Ebb-surge return, however, caused channelized erosion principally on the foredune and upper berm, sites that may not necessarily anneal through fairweather aggradation. It also induced substantial damage to infrastructure just behind the coastal setback boundary. Narrower barrier segments that experienced ebb-surge incision from Ian were breached by ~1.5-2.0-m-deep scour channels, similar to those imaged by GPR prior to the event, thereby allowing for identification of chronic erosional hot spots. In contrast, strandplains exhibited greatest resilience, with limited overtopping and lack of channels. The qualitative and quantitative observations are being shared with all coastal residents, but particularly with the municipalities of Sanibel, Fort Myers Beach, and Naples, three of the most seriously impacted coastal communities. Ultimately, these databases will inform regional hydrodynamic (Delft3D) and morphodynamic (XBEACH) modeling efforts for anticipating and adapting to future storm impacts.