Application of Storm Erosion Index (SEI) to parameterize spatial storm intensity and impacts from Hurricane Michael

Hurricane Michael made landfall as a Category 5 Hurricane on 10 October 2018 between Mexico Beach, Florida and Tyndall Air Force Base in Panama City Beach, Florida causing damages totaling $25 billion (Beven et al. 2019). While damages were caused by both wind and surge, this paper is solely concerned with the surge induced damages which were observed predominantly within 50 km (27 nmi) of the hurricane’s path. Generally, regions to the east of Hurricane Michael’s landfall sustained the most severe damages and appear consistent with the spatial gradient in peak water levels. This gradient was marked; with surge induced damage concentrated in the immediate vicinity of Mexico Beach and attenuating significantly over distances as little as 37 km (20 nmi) to the west in Panama City Beach and east in Port Saint Joe (Kennedy, in review). The gradient in erosion was also pronounced, with Panama City Beach experiencing an average erosion rate of 0.4 m3/m (3.9 cy/ft) while Mexico Beach and Cape San Blas experienced rates approximately three (1.1 m3/m or 11.5 cy/ft) and five (1.7 m3/m or 18.5 cy/ft) times that. For inherent reasons, the pronounced gradient in surge damages and erosion values are of primary interest to coastal researchers and managers. Storm Erosion Index (SEI), developed by Miller and Livermont (2008) combines the three primary drivers of coastal erosion (wave height, total water level, and storm duration) into a physically meaningful form to evaluate storms based on their erosion potential. Here, SEI is applied to explore these spatial variations at seven distinct regions within the Florida Panhandle and are compared to the observed impacts for both erosion and structural damages. These regions include: (west to east) Panama City Beach, Tyndall Air Force Base (AFB), Mexico Beach, Cape San Blas, Port St. Joe, St. Vincent Island, and St. George Island. Empirically, the cumulative SEI relates well with the observed beach erosion; while the Peak Erosion Intensity (PEI) was found to better capture the trends in structural damages. By capturing the spatial variation of the storm intensity, SEI and PEI are therefore proposed as a viable engineering demand parameter with potential applications in community scale fragility curves.