DIFFERENTIAL MOVEMENT OF COARSE SEDIMENT PARTICLES

Abstract

This paper mainly describes experiments that have been carried out on two shingle beaches on the south coast of England. The results for the higher energy environment of Chesil Beach showed that largest tracer material travelled farthest, and best correlations tended to be with the short axis. At Slapton, however, different sediment parameters appeared significant at various times. Where linear parameters were relevant correlations were again best with the short axis, but smaller material travelled farthest. This may reflect different wave regime, a less efficient sediment rejection mechanism, finer grades of sediment or better adjustment of tracer to indigenous background material at Slapton. There was a marked degree of selectivity at both sites between material recovered along a particular zone of the beach as compared with the overall recovery on the same day, and between the overall recovery for a particular day as compared with the originally injected tracer. Attempts have been made to correlate wave data from f.m.pressure recorders with longshore transport of the coarse grades of sediment in the inter-tidal zone. While at Chesil wave direction, frequency and height were all important there were no obvious relationships at Slapton. The results have relevance in respect of beach stability and in the conclusions drawn from tracer studies using coarse grades of sediment.