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Fiedler, JW, Smit PB, Brodie KL, McNinch J, Guza RT.  2019.  The offshore boundary condition in surf zone modeling. Coastal Engineering. 143:12-20.   10.1016/j.coastaleng.2018.10.014   AbstractWebsite

Numerical models predicting surfzone waves and shoreline runup in field situations are often initialized with shoreward propagating (sea-swell, and infragravity) waves at an offshore boundary in 10-30 m water depth. We develop an offshore boundary condition, based on Fourier analysis of observations with co-located current and pressure sensors, that accounts for reflection and includes nonlinear phase-coupling. The performance of additional boundary conditions derived with limited or no infragravity observations are explored with the wave resolving, nonlinear model SWASH 1D. In some cases errors in the reduced boundary conditions (applied in 11 m depth) propagate shoreward, whereas in other cases errors are localized near the offshore boundary. Boundary conditions that can be implemented without infragravity observations (e.g. bound waves) do not accurately simulate infragravity waves across the surfzone, and could corrupt predictions of morphologic change. However, the bulk properties of infragravity waves in the inner surfzone and runup are predicted to be largely independent of ig offshore boundary conditions, and dominated by ig generation and dissipation.

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Okihiro, M, Guza RT, Seymour RJ.  1993.  Excitation of Seiche Observed in a Small Harbor. Journal of Geophysical Research-Oceans. 98:18201-18211.   10.1029/93jc01760   AbstractWebsite

Seiche measured within a small (0.6 by 0.6 km), shallow (12-m depth) harbor is dominated by oscillations in several narrow infragravity frequency bands between approximately 10(-3) and 10(-2) Hz. Energy levels within the harbor are amplified, relative to just outside the harbor in 8.5-m depth, by as much as a factor of 20 at the lowest (grave mode) resonant frequency (approximately 10(-3) Hz) compared to amplifications of roughly 5 at higher resonant frequencies (approximately 10(-2) Hz). At nonresonant frequencies, energy levels observed inside the harbor are lower than those outside. These amplifications are compared to predictions of a numerical model of seiche excited by linear, inviscid long waves impinging on a harbor of variable depth. The amplification of higher-frequency (approximately 10(-2)-Hz) seiches is predicted within a factor of about 2. However, at the grave mode (10(-3) Hz), the observed amplification decreases with increasing swell and seiche energy levels, possibly owing to the sensitivity of this highly amplified mode to dissipation not included in the inviscid model. The energy levels of higher-frequency seiche within the harbor were predicted from the offshore sea and swell spectra by the ad hoc coupling of the linear model for the amplification of harbor modes with a nonlinear model for the generation of bound infragravity waves outside the harbor. The predictions are qualitatively accurate only when the swell is energetic and bound waves are a significant fraction of the infragravity energy outside the harbor.

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Thomson, J, Elgar S, Raubenheimer B, Herbers THC, Guza RT.  2006.  Tidal modulation of infragravity waves via nonlinear energy losses in the surfzone. Geophysical Research Letters. 33   10.1029/2005gl025514   AbstractWebsite

The strong tidal modulation of infragravity (200 to 20 s period) waves observed on the southern California shelf is shown to be the result of nonlinear transfers of energy from these low-frequency long waves to higher-frequency motions. The energy loss occurs in the surfzone, and is stronger as waves propagate over the convex low-tide beach profile than over the concave high-tide profile, resulting in a tidal modulation of seaward-radiated infragravity energy. Although previous studies have attributed infragravity energy losses in the surfzone to bottom drag and turbulence, theoretical estimates using both observations and numerical simulations suggest nonlinear transfers dominate. The observed beach profiles and energy transfers are similar along several km of the southern California coast, providing a mechanism for the tidal modulation of infragravity waves observed in bottom-pressure and seismic records on the continental shelf and in the deep ocean.

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Young, AP, Guza RT, Adams PN, O'Reilly WC, Flick RE.  2012.  Cross-shore decay of cliff top ground motions driven by local ocean swell and infragravity waves. Journal of Geophysical Research-Oceans. 117   10.1029/2012jc007908   AbstractWebsite

Ground motions at the frequencies (between 0.01 and 0.1 Hz) of ocean infragravity and swell waves were observed on a cross-shore transect extending landward from the edge of a southern California coastal cliff. Cliff top ground motions are coherent and in phase with water level fluctuations at the cliff base. Vertical ground motions at infragravity and single frequencies decay rapidly with inland distance from the cliff edge (e-folding scale is about 12 m), and at the edge decrease by several orders of magnitude between high tide when waves reach the cliff base, and low tide when the waterline is about 50 m from the cliff base. The observed cross-shore decay scales are qualitatively consistent with gravitational loading and attraction of water waves at tidally modulated distances from the cliff base. At approximately constant distance from the waterline, ground motions vary roughly linearly with nearshore swell wave energy. In contrast to these locally forced ground motions, double frequency band (0.1-0.2 Hz) cliff top vertical ground motions are remotely generated with spatially uniform magnitudes approximately equal to those observed 14 km inland. Near the cliff edge, ground tilt dominates the observed large (relative to vertical) cross-shore acceleration at infragravity frequencies, contributes significantly to cross-shore acceleration at swell frequencies, and is a small fraction of cross-shore acceleration at higher frequencies.