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Storm- and tide-induced infragravity dynamics at an intermediate-to-dissipative microtidal beach
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  • Lorenzo Melito,
  • Luca Parlagreco,
  • Saverio Devoti,
  • Maurizio Brocchini
Lorenzo Melito
Università Politecnica delle Marche

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Luca Parlagreco
Italian Institute for Environmental Protection and Research
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Saverio Devoti
Italian Institute for Environmental Protection and Research
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Maurizio Brocchini
Università Politecnica delle Marche
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Abstract

Numerical simulations of a range of wave climates and tide conditions made with the model XBeach are exploited to study propagation, evolution, dissipation, and reflection patterns of infragravity waves (IGW) at the intermediate-to-dissipative beach of Sabaudia (Tyrrhenian sea, Italy). On the basis of a novel calibration process performed using field swash properties collected by a nearby monitoring station, the model reproduces swash characteristics with good skill (Willmott index of agreement D = 0.61-0.79). IGW at Sabaudia beach evolve exclusively as bound long waves (BLW) growing across the shoaling region for both mild and intense wave climate. BLW release occurs still in the inner shoaling zone and, thus, may not be strictly connected with wave breaking inception, as usually assumed. Furthermore, values of the dimensionless bed slope βH at which transition from steep- to mild-slope behaviour occurs are higher that traditional threshold. Finally, although the small tide (0.4 m between MHWS and MLWS; tide range/breaking wave amplitude ratios between 0.14 and 1.1) does not alter bulk IGW reflection significantly, low tide is effective in reducing onshore IGW fluxes and, ultimately, reflection coefficients R2 selectively for intermediate IG frequencies. Our study, for the first time, gives clear evidence that the tide has a role in determining frequency-dependent IGW dynamics and altering the dissipative state of a mild sloping beach also in a microtidal environment.