Monthly sampling showed that the granules and small pebbles of the bay beaches can display pronounced longshore grading from time to time but that the overall picture is complicated by changing beach height and slope, local variations between minor headlands, and sorting parallel with, normal to, and vertically through, the beach, rather than longshore adjustment alone. Particle size is reflected in geological composition.
A short term intensive study of part of the area, designed to show relationships between surface particle size and the wave parameters, only produced significant correlations on Slapton beach. These were between mean phi (ø) size and the square root of the significant wave height (H31/2) and, to a lesser extent, between mean ø size and direction of wave approach (θ°)
Thereafter, two tracer experiments using polyurethane-coated shingle were carried out on Slapton beach. Where statistically valid results were obtained it was shown that: there was virtually no correlation between wave parameters and sediment transport; maximum longshore transport corresponded with smallest particle size; differing factors (ø weight and frequency, linear parameters, ratios and shape indexes) assumed importance on different occasions and in different beach zones; recoveries at high, mid or low tide levels were often atypical of both the overall recovered population for that tide, and for the injected population.
- Received February 25, 1974.
- Revision received June 6, 1974.
- © Geological Society of London 1975