Transformation and morphological impact of low-frequency waves during hurricane attack
Anarde, Katherine Alyse
Bedient, Philip B
Doctor of Philosophy
Field measurements of wave, current, and sediment dynamics in the nearshore environment during extreme events are scarce due to energetic waves and rapid bed level changes that can damage or shift instrumentation. Overestimation of storm processes in many morphodynamic models highlight a need for high-resolution field data during extreme storm events to improve and validate model forecasts of coastal storm hazards and impacts. To address this data and knowledge gap, this thesis offers insights into the physical processes that contribute to coastal flooding and drive morphological change during storms by providing new field data, methodological frameworks, and detailed analysis of water levels, currents, and sediment transport on two mild-sloping beaches along the Texas Gulf coast (U.S.A) during Hurricane Harvey (2017). Measurements of storm hydrodynamics are linked to post-storm changes to coastal landforms using sedimentological data, beach profile surveys, and topographic maps derived from imagery collected by unmanned aerial vehicles. The comprehensive data set acquired during Hurricane Harvey is evaluated in multiple studies to examine the role of low-frequency surface ocean waves in driving coastal change and inland flooding during hurricane impact. Herein, "low-frequency waves" collectively refers to waves with frequencies spanning the infragravity (IG) band (0.003-0.04 Hz) and just below the IG band (~0.4-3 mHz), termed very low frequency (VLF) waves. Key findings include 1) IG wave growth and energy loss in the very nearshore and into the back-barrier bay during island overwash is frequency-dependent; 2) VLF variability in nearshore water levels can be classified as small-amplitude meteotsunamis, that when amplified, may present a flood hazard in this region; 3) the morphological evolution of barrier-island cuts during hurricane impact is influenced by competing wave-driven and back-barrier processes; and 4) sequential far-field storms may aid in the recovery of barrier beaches. The results obtained in this thesis will be used to inform validation studies to improve numerical simulations of the transformation and morphological impact of low-frequency waves toward better prediction of coastal hazards.
infragravity waves; hurricanes; meteotsunami; overwash; barrier island