Predicting the runup heights from the offshore waves and beach characteristics has been one of the most important issues in coastal engineering. Various parameters are considered potential contributing factors, but some of them have not been verified in the field. This study discusses the characteristics of infragravity (IG) swash and its relationship with the offshore wave parameters by analyzing the nine-month field observation data of waves and their runup at a sandy beach in Japan. In particular, the contribution of the frequency spread and directional spread was investigated using field data. IG waves developed as bound waves in a shoaling zone, while they caused frequency-dependent dissipation in the surf and swash zone, which affected the IG swash. The lower frequency components of incoming IG waves generated a larger swash than the higher frequency components when IG wave dissipation was not negligible, but the latter was higher without the dissipation. The integrated IG swash was roughly proportional to $\sqrt{H_0{L}_0}$, where $H_0$ is offshore wave height and $L_0$ is offshore wavelength. Furthermore, the inclusion of the frequency spread and directional spread improved the IG swash prediction. An increase in the frequency spread and decrease in the directional spread tended to increase the IG swash, which is in qualitative agreement with the bound wave characteristics. The contribution of the directional spread becomes prominent under energetic conditions. The definition of the offshore wave period also affected the swash prediction, and the spectral mean period gave better performance than the peak period during multimodal wave conditions.

根据近海波浪和海滩特征预测爬升高度一直是沿海工程中最重要的问题之一。各种参数被认为是潜在的影响因素，但其中一些参数尚未在现场得到验证。本研究通过分析日本某沙滩长达 9 个月的海浪及其爬升的现场观测数据，讨论了次重力 (IG) 冲刷的特征及其与近海波浪参数的关系。特别是，使用现场数据研究了频率扩展和定向扩展的贡献。IG 波在浅滩区以束缚波的形式发展，而它们在冲浪区和倾斜区引起频率相关的耗散，从而影响了 IG 倾斜区。当 IG 波耗散不可忽略时，传入 IG 波的低频分量比高频分量产生更大的斜度，但后者在没有耗散的情况下更高。集成的 IG 斜盘大致与$\sqrt{H_0{升}_0}$， 在哪里 $H_0$ 是离岸波高和 ${升}_0$是离岸波长。此外，包含频率扩展和定向扩展改进了 IG 斜盘预测。频率扩展的增加和方向扩展的减小往往会增加 IG 斜度，这与束缚波特性定性一致。定向传播的贡献在能量条件下变得突出。海上波浪周期的定义也影响了倾斜预测，在多峰波条件下，频谱平均周期比峰值周期具有更好的性能。