The swash zone is the most dynamic part of the upper beach. Here breaking waves interact with sediments, leading to beach morphodynamics, and eventually to coastal erosion and flooding. An understanding of swash characteristics such as the vertical excursion and mean swash period is of vital importance to identify and predict the possible impact of storms in coastal areas. The prediction of these swash parameters is commonly based on bulk offshore spectral wave parameters and the beach slope, the latter being expensive to monitor. In this study, a dataset from an intermediate beach on the south-west coast of Sylt, Germany was derived to analyze swash characteristics. Field observations show high variability in swash excursion even for similar incident wave conditions if expressed by bulk parameters. Here, the role of frequency spread was further investigated. An inverse relationship between swash frequency spread and swash characteristics (excursion and mean period) was identified. A parameterization for the swash frequency spread based on incident wave parameters is proposed, and a new approach to obtain total swash excursion and mean swash period is developed. The parameterization is validated using two independent swash datasets (Duck 1982 and Duck 1994) and compared to the predictive ability of other parameterizations. It is highlighted that common parameterizations based on peak period do not perform well in characterizing incident conditions when bi-modal spectra are present. The choice of the right descriptor for wave periods may have a more pronounced influence on the predictive skill than the inclusion of the beach slope.

中文翻译：

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频率扩展对斜盘动力学的作用

冲刷区是上海滩最具活力的部分。在这里，碎波与沉积物相互作用，导致海滩形态动力学，最终导致海岸侵蚀和洪水。了解倾斜特征（例如垂直偏移和平均倾斜周期）对于识别和预测沿海地区风暴的可能影响至关重要。这些倾斜参数的预测通常基于大量离岸波谱参数和海滩坡度，后者的监测成本很高。在这项研究中，来自德国叙尔特岛西南海岸中间海滩的数据集被派生用于分析花体特征。如果用体参数表示，即使在类似的入射波条件下，现场观察也显示了斜角偏移的高度可变性。这里，进一步研究了频率扩展的作用。确定了斜盘频率扩展和斜盘特性（偏移和平均周期）之间的反比关系。提出了基于入射波参数的斜盘频率扩展的参数化，并开发了一种获得总斜盘偏移和平均斜盘周期的新方法。参数化使用两个独立的 swash 数据集（Duck 1982 和 Duck 1994）进行验证，并与其他参数化的预测能力进行比较。需要强调的是，当存在双峰谱时，基于峰值周期的常见参数化在表征事件条件方面表现不佳。为波浪周期选择正确的描述符可能比包含海滩坡度对预测技能有更明显的影响。确定了斜盘频率扩展和斜盘特性（偏移和平均周期）之间的反比关系。提出了基于入射波参数的斜盘频率扩展的参数化，并开发了一种获得总斜盘偏移和平均斜盘周期的新方法。参数化使用两个独立的 swash 数据集（Duck 1982 和 Duck 1994）进行验证，并与其他参数化的预测能力进行比较。需要强调的是，当存在双峰谱时，基于峰值周期的常见参数化在表征事件条件方面表现不佳。为波浪周期选择正确的描述符可能比包含海滩坡度对预测技能有更明显的影响。确定了斜盘频率扩展和斜盘特性（偏移和平均周期）之间的反比关系。提出了基于入射波参数的斜盘频率扩展的参数化，并开发了一种获得总斜盘偏移和平均斜盘周期的新方法。参数化使用两个独立的 swash 数据集（Duck 1982 和 Duck 1994）进行验证，并与其他参数化的预测能力进行比较。需要强调的是，当存在双峰谱时，基于峰值周期的常见参数化在表征事件条件方面表现不佳。为波浪周期选择正确的描述符可能比包含海滩坡度对预测技能有更明显的影响。