Waves are a primary erosive agent on intertidal shore platforms. In microtidal environments, as waves cross a shore platform the energy transforms from gravity to infragravity frequencies. The morphology of the intertidal zone is a key boundary condition for this energy transformation. Waves approaching the shore however often interact with the seabed at some distance from the intertidal platform. In this study we explore this wave interaction over a gently sloping subtidal ramp (1 km wide) down to 11 m water depth fronting a semi-horizontal intertidal platform (180 m wide). Five non-directional pressure sensors were installed on the sea floor from 5 to 11 m depth for one week with a further four placed on the intertidal platform for two tidal cycles during the offshore deployment. It is found that a shift in wave frequency starts to occur at the base of the seaward ramp at 7 m water depth, with the primary development of infragravity waves occurring at less than 5 m depth. The offshore energy signal was also tidally modulated with infragravity frequency waves hypothesised to be able to escape seaward across the platform edge at high tide. This new exploration of nearshore wave energy shows that wave dynamics over the entire platform surface should be considered rather than just focussing on the intertidal zone.

波浪是潮间带海岸平台上的主要侵蚀剂。在微潮环境中，当波浪穿过海岸平台时，能量从重力转换为次重力频率。潮间带的形态是这种能量转换的关键边界条件。然而，接近海岸的波浪经常与距潮间带平台一定距离的海床相互作用。在这项研究中，我们在半水平潮间带平台（180 m 宽）前面的缓坡潮下坡道（1 km 宽）下到 11 m 水深探索了这种波浪相互作用。五个非定向压力传感器安装在 5 至 11 m 深度的海底一周，另外四个安装在潮间带平台上，用于海上部署期间的两个潮汐周期。发现在 7 m 水深的向海斜坡底部开始发生波频率的变化，在小于 5 m 深度发生次重力波的主要发展。近海能量信号还用超重力频率波进行潮汐调制，假设能够在涨潮时穿过平台边缘向海逃逸。这种对近岸波浪能的新探索表明，应该考虑整个平台表面的波浪动力学，而不仅仅是关注潮间带。