Gravel beach swash zone dynamics

A swash flow transducer was constructed to record wave energies and swash velocities measured via a system of marker poles. Long (4m) metal poles were installed on a gravel beach located at Nash Point, South Wales, UK, a rugged, high energy, coastal environment. These were secured to three 30kg concrete anchoring legs per pole buried in the beach. A Rustrak Event recorder with manual trip pen device recorded the time taken by a series of swash edges to pass each marker pole. Twenty such consecutive swashes were monitored over various tidal stages. The event recorder also obtained wave period, swash period and run up. Profiles and surface sediments were also recorded both before and after each experiment. Non-parametric testing of the sediment samples pre and post experiments were carried out in order to identify any significant differences in gravel size. No specific point of peak velocity was found. A scatter of velocity value points, which increased up beach, correlated with the swash tip. Swash values were an order of magnitude higher than those produced by other workers. Average swash velocity was > 4m/sec. A correlation (0.7) was found between t/T-b (swash period/breaker period) - the 'phase difference' and H-b (breaker height), reflecting the association between wave height and the amount of water brought onto the beach surface. For a given wave period, an increase in height induced an increase in phase difference. No such relationship was found between swash velocity and H-0 (deep-water wave height) or H-b (breaker height).