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Topic

Wave Run-up on a Highly Dissipative Beach

School of Earth and Ocean Sciences

Date & location

• Monday, January 6, 2025
• 10:00 A.M.
• Bob Wright Centre, Room A319

Examining Committee

Supervisory Committee

• Dr. Jody Klymak, School of Earth and Ocean Sciences, University of Victoria (Co-Supervisor)
• Dr. Johannes Gemmrich, School of Earth and Ocean Sciences, UVic (Co-Supervisor)
• Dr. Brad Buckham, Department of Mechanical Engineering, UVic (Outside Member)

External Examiner

• Dr. Jim Thomson, Department of Civil and Environmental Engineering, University of Washington

Chair of Oral Examination

• Dr. Val Napoleon, Faculty of Law, UVic

Abstract

Long-term observations of wave run-up on were collected using video imagery. The study site is a highly dissipative sand beach on the West Coast of Vancouver Island with seasonally energetic wave behaviour. Spectral analysis of the long-term timeseries was done to characterize the run-up spectrum. These run-up spectra consistently show a peak frequency in the infragravity range, with a frequency dependence of 𝑓^−1.5. This demonstrates a clear spectral shift of the characteristic developed wind-wave spectrum, which has a dominant period of approximately 10 seconds and a frequency dependence of 𝑓⁻⁴. The spectral transformation is consistent with findings from previous run-up studies, although the peak period and frequency dependence of the spectra presented here show an extreme example of this expected spectral evolution. Additional instruments utilized in the analysis include an offshore wave buoy, a Spotter buoy deployed immediately outside the surf-zone, and for a shorter three week period, an RBR pressure sensor that was deployed on the same mooring as the Spotter buoy. Correlations were evaluated between run-up behaviour and sea-state variables to understand wave transformation across the surf-zone, as well as to find useful and practical indicators of heightened wave run-up hazard that can be used by risk managers. Significant wave height (Hs), dominant period (T0), and the parameter √𝐻𝐿 are all positively correlated to run-up extent, with √𝐻𝐿 being the strongest predictor. A positive correlation was also found between large run-up events and the amount of relative infragravity energy present in the incoming wave field. The process of bore-bore capture (BBC) was shown to be a likely mechanism behind the drastic spectral shift to lower peak frequencies. BBC was also shown to drive extreme run-up events, especially when captures occur within the swash zone. Infragravity waves propagating within the surf-zone facilitate additional capture events and therefore indirectly contribute to these large run-up instances. The magnitude of infragravity energy associated with wave groups can be approximated using the crest-trough correlation, which captures the groupiness of the incoming wave field. The crest-trough correlation parameter was used as a proxy for infragravity energy and found to better predict run-up behaviour when included in an empirical parametrization with √𝐻𝐿.