The subtidal morphology of microtidal shore platforms and its implication for wave dynamics on rocky coasts

• Three types of subtidal morphology exist on microtidal platforms, (1) Steep cliffed edge, (2) terrace/reef, and (3) ramp.
• Vertical seaward cliffs are rare.
• Subtidal morphology is a key determinate of the impact of waves on the intertidal and subaerial portions of rock coasts.

The subtidal portions of shore platforms are important geomorphic features as they can modify deep-water wave energy before it impacts the intertidal platform edge. In this study an integrated marine and terrestrial aerial LiDAR dataset is used to analyse the morphology of the subtidal portion of shore platforms. Semi-horizontal intertidal platforms on an 85 km along stretch of microtidal, open-ocean, rocky coast in Victoria, Australia are investigated and described quantitatively. Three distinct types of subtidal morphology occur; (i) a steep cliff with a mean slope of 8–18°, (ii) a gently sloping ramp with a mean slope of < 3°, and (iii) a subtidal terrace/reef. It is inferred that the type of subtidal morphology present on a platform will determine the relative impact of marine and subaerial processes in the intertidal and supratidal zones.