Author(s): H. E. Power; T. E. Baldock
Linked Author(s):
Keywords: Swash; Inner surf zone; Bores; Saturation; Flow asymmetry; Surf-swash boundary
Abstract: Swash zone boundary conditions are investigated using field observations of the inner surf zone and the swash zone for a range of micro-tidal, predominantly swell-dominated, sandy beaches. The boundary conditions are characterized in terms of a terminal bore height and the asymmetry between uprush and backwash flows. Terminal bore heights are calculated by examining wave evolution across the surf zone. This is investigated in terms of wave height to water depth ratios (γ) and waves are shown to be unsaturated. These observations are used to approximate the terminal bore height at the surf swash boundary as Hb≈0.12H o, which is consistent with recent laboratory data sets. Wave transformation modelling is used to identify conditions where the surf zone is predicted to be unsaturated and this is found to occur for steep beaches and large wave periods. A normalised beach slope parameter is derived to separate these two regions. The asymmetry between uprush and backwash flows is investigated using remote sensing techniques. The time of flow reversal in the swash zone was found to occur at approximately 40-50% of the duration of the swash cycle, which is significantly different from previous theory.
Year: 2011