Simulating storm waves in the nearshore area using spectral model: Current issues and a pragmatic solution

Abstract

Short waves are of key importance for nearshore dynamics, particularly under storms, where they contribute to extreme water levels and drive large morphological changes. Therefore, it is crucial to model accurately the propagation and dissipation of storm waves in the nearshore area. In this paper, field observations collected in contrasted environments and conditions are combined with predictions from a third-generation spectral wave model to evaluate four formulations of wave energy dissipation by depth-induced breaking.The results reveal a substantial over-dissipation of incident wave energy occurring over the continental shelf, resulting in a negative bias on significant wave height reaching up to 50%. To overcome this problem, a breaking coefficient dependent of the local bottom slope is introduced within depth-induced breaking models in order to account for the varying degrees of saturation naturally found in breaking and broken waves. This approach strongly reduces the negative bias observed in the shoreface compared to default parameterizations, yielding significant improvements in the prediction of storm waves. Among the implications of this study, our new parameterization of the breaking coefficient results in systematically increased predictions of the wave setup near the shoreline compared to the default parameterization. This increase reaches a factor 2 for gently sloping beaches.

Cross‐Shore Distribution of the Wave‐Induced Circulation Over a Dissipative Beach Under Storm Wave Conditions

“…The wave energy dissipation rate by depth-induced breaking is computed according to the model of Battjes and Janssen (1978) with an adaptive breaking coefficient (B) as proposed by Pezerat et al (2021). The local mean (phase-averaged) rate of energy dissipation per unit area 𝐴𝐴 𝐴𝐴𝑑𝑑𝑑𝑑 in (W/m 2 ) reads:…”

“…However, as pointed out by Pezerat et al. (2021), the introduction of the adaptive breaking coefficient requires a newly calibrated breaking index. Based on sensitivity tests performed with the model on $${H}_{m0}$$ results considering the entire data set (not shown), a constant value of $$\gamma $$ = 0.60 was considered for this study.…”

Wave Dissipation and Mean Circulation on a Shore Platform Under Storm Wave Conditions

“…Recently, Pezerat et al. (2021) reported that common parameterizations for depth‐induced breaking in spectral wave models yield significant over‐dissipation of storm waves propagating over gently sloping shorefaces, which can potentially lead to an underestimation of the wave setup at the shoreline. To overcome this problem, the authors proposed an adaptive parameterization of the breaking coefficient B based on the local bottom slope.…”

Storm surge hazard over Bengal delta: A probabilistic-deterministic modelling approach

“…We modelled the wave breaking using the formulation of Battjes and Janssen (1978). A low value of the coefficient of breaking, α = 0.1 (instead of α = 1), is adopted to avoid over-dissipation over a very mild slope region like the Bengal delta (Pezerat et al, 2020(Pezerat et al, , 2021Khan et al, 2021a). We have discretized our modelled spectra into 12 directional and 12 frequency bins.…”

“…The coupling between SCHISM and WWMIII allows accounting for the wave set-up induced by the radiation stress gradient of the waves (Longuet-Higgins and Stewart, 1964). breaking coefficient α is set to 0.1 (instead of the default parameter α = 1) to avoid over dissipation of the waves over the submarine part of the delta with mild slopes (Pezerat et al, 2021;Khan et al, 2021a). We also invoked the wetting and drying algorithm in SCHISM with a threshold of 10cm depth of water for an element to be registered as wet.…”