The dominant mechanism for morphodynamic modelling of the surf zone

Measurements of rip current trajectories at Woolamai Beach, Phillip Island, were used to determine the dominant mechanism for the formation and evolution of rhythmic morphology in surf zones. A total of eleven rip trajectories were mapped from two adjacent rip channels in what was the most extensive data of its type recorded from a high energy surf zone. Woolamai was found to give a good representation of hydrodynamics and morphodynamics for other beaches around the world. The results were analysed using a novel method, which found that feedback is the dominant mechanism and that free (or instability) models best describe morphodynamics in the surf zone. It is hypothesised that scales of morphodynamic instability and hydrodynamic instability are operating separately throughout the tide cycle and that the two types of instability are linked to separate mechanisms