Abstract
AbstractWe use a numerical model, already validated for this purpose, to simulate the effect of wave frequency spread on wave transformation and swash amplitudes. Simulations are performed for planar beach slope cases and for offshore wave spectra whose frequency spread changes over realistic values. Results indicate that frequency spread, under normally approaching waves, affects swash amplitudes. For moderately dissipative conditions, the significant infragravity swash increases for increasing values of the offshore frequency spread. The opposite occurs under extremely dissipative conditions. The numerical analysis suggests that this inverted pattern is driven by the effect that different distributions of incoming long‐wave energy have on low‐frequency wave propagation and dissipation. In fact, with large frequency spreads, wave groups force relatively short subharmonic waves that are strongly enhanced in the shoaling zone. This process leads to an infragravity swash increase for increasing frequency spread under moderately dissipative conditions in which low‐frequency energy dissipation in shallow water is negligible or small. However, under extremely dissipative conditions, the significant low‐frequency energy dissipation associated with large frequency spreads overturns the strong energy growth in the shoaling zone eventually yielding an infragravity swash decrease for increasing frequency spread.
Highlights
As a result of the interaction with the seabed, a rapid evolution of wave properties occurs in the nearshore with waves changing their shape, breaking and driving shoreline/runup oscillations in the swash region (Elfrink & Baldock, 2002)
As a result of the relatively low Iribarren numbers considered in this work (ξ0 < 0.56), swash spectra are dominated by oscillations at IG frequencies (f < fp∕2) showing saturation at incident SS bands (f > fp∕2)
Numerical simulations show an IG swash variability induced by incident wave frequency spread with a pattern that inverts over two Iribarren number ranges
Summary
As a result of the interaction with the seabed, a rapid evolution of wave properties occurs in the nearshore with waves changing their shape, breaking and driving shoreline/runup oscillations in the swash region (Elfrink & Baldock, 2002). Understanding and predicting runup oscillations have been a research topic for decades considering that the motion of water running up and down the beach drives change in the morphology (Butt & Russell, 2000), affects infiltration (Horn, 2002; Turner & Masselink, 1998), is relevant to ecological studies dealing with the distribution of macrofauna (McArdle & McLachlan, 1992), and its estimation is needed to define coastal hazards and setback lines (Vousdoukas et al, 2012). The predictor of R has been obtained using 10 data sets and developing a linear regression between R and offshore variables (like significant wave height Hs0√and wavelength L0) and beach slope β. A considerable number of field, laboratory, and numerical studies have tackled a variety of aspects of processes related to low-frequency swash and its variability
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