Wave-Swash Interactions and Saturation in the Swash Zone.

Brief description

This study draws on 4 existing and 5 new sets of swash zone data acquired on swell dominated, sandy beaches of the east Australian coastline, and constitutes one of the most comprehensive sets of swash zone data currently available. Previous studies of swash have loosely identified a lower and upper swash zone characterised by different hydrodynamic processes. By integrating data acquired simultaneously in Eulerian and Lagrangian reference frames a new method has been developed that identifies this critical process boundary on the basis of uniform hydrokinematics. For the wide range of beaches investigated in this study the lower or "transition zone" is 0.53 ± 0.21 of the swash zone length. Wave-swash interactions are therefore ubiquitous and spatially extensive. This study indicates that vertical swash excursion lengths conform to a Normal distribution on most beaches. The presence of wave-swash interaction within the lower swash zone provides a plausible explanation for the transformation from Rayleigh distributed wave heights within the surf zone to Normally distributed vertical swash excursions. This study highlights the need for further investigation of the causes and physical meaning of rolloff in shoreline spectra.

Lineage

Statement: Shore-normal pressure sensor arrays and resistance wires were used to simultaneously log wave and shoreline motion within the swash zone of beach states ranging from dissipative through to reflective. All shoreline spectra calculated from the current dataset exhibit a universal form, S(f)=af-x where the spectral rolloff, f-x , varies between f-3 and f-4. Within the literature, the bandwidth of spectral rolloff is widely referred to as the "saturation bandwidth". The two different concepts of swash saturation discussed in the literature, referred to here as "energy saturation" and "wave-swash interaction", are expected from theory to coincide with (or equate to) spectral rolloff at f-4. Data were tested for swash saturation using methods sympathetic to the premise underlying each saturation concept and, although wave-swash interactions were identified within the sea-swell band at all beaches, energy saturation was entirely absent within the f-4 rolloff band at 1 out of 9 beaches.

Notes

Purpose
Investigating aspects of swash zone data, utilising both existing and new data sets.