Unusual Beach Changes Induced by Hurricane Irma with a Negative Storm Surge and Poststorm Recovery.

Cheng, J. and Wang, P., 2019. Unusual beach changes induced by Hurricane Irma with a negative storm surge and poststorm recovery. Journal of Coastal Research, 35(6), 1185–1199. Coconut Creek (Florida), ISSN 0749-0208. The coast of west-central Florida, facing the Gulf of Mexico, experienced Hurricane Irma with a negative surge of 1.1 m and a highly oblique northerly approaching wave in September 2017. This unusual hydrodynamic condition provides an opportunity to investigate the effect of surge and incident wave direction on morphology changes. Beach profiles, spaced at 300 m apart, along a 15-km stretch of beach were surveyed 2 weeks prior to the passage of Hurricane Irma and 1 week after and continued for up to 5 months after the passage to obtain Irma-induced erosion as well as post-Irma recovery. Owing to the occurrence of negative surge, the profile volume of the dune field remained mostly stable. The majority of beach erosion occurred below mean sea level, with a considerable amount of sediment transported seaward of the depth of closure. This is opposite to the conservation of beach profile volume above depth of closure under several earlier storms with a positive surge. The alongshore variation of overall beach profile volume erosion demonstrates a southward decreasing trend, due to a southward decreasing wave height as controlled by the northerly incident wave. After the passage of Irma, minor beach volume recovery occurred during the calm period of the fall season. Opposite to the typical erosive beach in winter, the most substantial beach accretion and onshore bar movement were observed during the following peak winter season as beach/bar evolved toward equilibrium. The profile volume in the dry beach region experienced a complete recovery in the first 5 months after Hurricane Irma. Shoreline change is a valid proxy for beach volume change during both the erosive and the recovery phase of Irma. The systematically measured beach profiles provide a solid dataset to calibrate process-based models to study beach morphodynamics. [ABSTRACT FROM AUTHOR]