Field Observations of Step Dynamics on a Macrotidal Gravel Beach

A data set consisting of detailed measurements of the hydrodynamics, morphological and sedimentological change, and sediment transport, has been collected from the region of the beach step on a macrotidal gravel beach. The step is an accretionary feature which evolves with a different relaxation time to that of the berm. Initiation of the step requires relative tidal stationarity and is thought to be triggered by increasingly reflective conditions. Despite its location, the step has remarkably stable sedimentology, differentiated from the swash zone using sedimentary moments. Co-spectral analysis indicates that sediment transport in the region of the step is related to sub-incident wave frequencies. A reconstructed ensemble sediment transport event confirmed that sediment transport at the base of the step occurs as a negatively skewed wave, perhaps sensitive to wave groups. The transition matrix of the nearshore gravel bed motion data closely resembled that of a ‘memoryless' queuing process.