OS038-03
Comparisons between laboratory experiments and a theoretical model of intermittent edge wave excitation

Monday, 14 December 2020: 05:38
Virtual
Xuelin Ding1, Giovanni Coco2, Paolo Blondeaux3, Giovanna Vittori3, Robert T Guza4, Colin Whittaker5, Roland Garnier6, Robert A Dalrymple7, Zhangping Wei8 and Pedro Lomonaco9, (1)University of Auckland, School of Environment, Auckland, New Zealand, (2)University of Auckland, Auckland, New Zealand, (3)University of Genova, Genova, Italy, (4)University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, (5)University of Auckland, Civil and Environmental Engineering, Auckland, New Zealand, (6)AZTI, Marine Research, Basque Research and Technology Alliance (BRTA), Pasaia, Spain, (7)Johns Hopkins University, Department of Civil Engineering, Baltimore, MD, United States, (8)Johns Hopkins University, Baltimore, MD, United States, (9)Oregon State University, Corvallis, OR, United States
Recorded Presentation
Abstract:
Edge waves are coastal waves trapped near the shore by reflection and refraction. Previous studies show the clear excitation mechanism of edge waves under monochromatic wave conditions via phase locking and nonlinear growth. However, how efficiently the mechanism would work under random incident waves remains unclear.

This study compares laboratory measurements with a theoretical model of edge wave growth under monochromatic and random incident waves. Compared to the narrow-band random incident waves assumed by the model, incident waves during experiments had larger amplitudes, wider frequency spectra and faster-varying amplitudes.

Despite the differences, the theoretical model predicted the main features of edge wave excitation observed in the laboratory. During the experiments, edge waves grew continuously until equilibrium under monochromatic incident waves but were present intermittently under random incident waves. The theoretical model also predicted continuous and intermittent growth under monochromatic and random incident waves, respectively. Broad-band incident wave conditions led to the smallest predicted and measured edge wave amplitudes. However, incident waves characterized by the smallest (finite) frequency spread did not necessarily result in the largest edge wave amplitudes both during experiments and in theory. The runup signals were decomposed into incident and edge wave contributions. Consistent with the theoretical model, the laboratory results showed that the coupling between phases of incident waves and edge waves ensured a positive net energy flux to the edge waves during the initial growth. Meanwhile, uncoupling phases or decreased incident wave amplitudes resulted in a negative net energy flux, thus decreased edge wave amplitudes both in the predictions and measurements.

This study provides a clear example of how the hydrodynamics of the nearshore with random incident waves differ from that with monochromatic incident waves. The implications of this study show that many morphodynamic models that assume monochromatic waves will require more attention.

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