The beach slope is a key component characterizing the coastal response to wave forcing. Here we investigate the rapid adaptation of the upper beach slope to a given wave forcing, for the case of a lower flat platform. Such types of morphology are found on coral and rocky reef beaches and low tide terrace environments. The influence of the lower platform on this rapid equilibrium beach state is shown to be significant depending on the breaking wave regime. In particular, the width of the platform and its water level can affect the wave dissipation along the inner surf and thus the wave structure entering the swash. This paper provides a classification of the beach slope equilibrium values as a function of the Dean number on a short time scale (individual wave action), based on both offshore and swash wave conditions. A decreasing trend of the beach slope with increasing offshore Dean number () is found for . For it is observed that the beach slope gradient is strongly controlled by the surf zone dissipation and it becomes necessary to define the swash Dean number () to classify the slope. Finally, a semi-empirical formula for the beach slope evolution in the case of a low tide platform is introduced and tested on two natural low-tide terrace beaches.

中文翻译：

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平坦低平台海滩坡度的半经验公式

海滩坡度是表征海岸对波浪强迫响应的关键组成部分。在这里，我们研究了在下部平坦平台的情况下上部海滩坡度对给定波浪力的快速适应。这种形态常见于珊瑚和岩礁海滩以及低潮阶地环境中。根据破碎波状况，下部平台对这种快速平衡海滩状态的影响是显着的。特别是，平台的宽度及其水位会影响沿内海浪的波浪消散，从而影响进入斜盘的波浪结构。本文根据近海和斜波条件，提供了海滩坡度平衡值的分类，作为短时间尺度上迪恩数（单个波浪作用）的函数。发现海滩坡度随着离岸 Dean 数 () 的增加而减小。因为据观察，海滩坡度梯度受到冲浪区耗散的强烈控制，因此有必要定义斜盘迪安数（）来对坡度进行分类。最后，引入了低潮平台情况下海滩坡度演化的半经验公式，并在两个天然低潮阶地海滩上进行了测试。