Estimation of Abrasion Loss on Flint Shingle Beaches in East Sussex, Uk

The results are described of ongoing field and laboratory experiments to estimate losses from shingle beaches due to abrasion. Field abrasion experiments of two exotic lithologies (quartzite and limestone) used as tracers on two flint shingle beaches at Telscombe and Saltdean in East Sussex, UK, have been carried out over 23 months, resulting in 985 weight loss measurements. Relationships between the abrasion rate, offshore wave height, tracer lithology, weight and time the tracer has been on the beach and the beach on which the tracer was placed are demonstrated. Laboratory abrasion experiments in rock tumblers using 52 tracer pebbles and flint shingle collected from one of the beaches have been used to provide a calibration between the abrasion rates of the tracers and that of natural flint shingle. This produces a first estimate for the mean annual abrasion rate for flint in the beach volume that is moved annually on the two beaches of ~1.5%. The annually active beach volume has been calculated from twice weekly profile surveys of the two beaches carried out between January and December 2002. Using this volume and the flint abrasion rates the annual loss of beach material has been calculated as being 90m3 and 15m3 or 0.3% and 0.05% of the present beach volume at Telscombe and Saltdean respectively. INTRODUCTION Volume changes of shingle beaches are usually attributed to variations in longshore or crossshore transport with the possibility of volume loss from in situ abrasion of shingle acknowledged (e.g. Simm et al. 1996) but seldom measured (Salminen 1935, Zhdanov 1958). Dornbusch et al. (2002) have demonstrated that abrasion of shingle on beaches can be measured by seeding a beach with marked exotic pebbles. This paper reports further results of this continuing study using exotic tracer pebbles and describes laboratory tumbling experiments designed to establish a calibration between the field abrasion of the tracers and the field abrasion of the natural flint that constitutes the beaches of East Sussex. Changes in the profiles of the beaches used for the field abrasion experiments have been measured regularly in order to estimate the beach volume to which the average abrasion rate of shingle applies. Combining the data enables the shingle volume that is lost annually through in situ abrasion of the beach material to be estimated. LOCATION AND ENVIRONMENTAL CONDITIONS Both beaches used in this study are located along the cliffed chalk coastline of East Sussex, in the southeast of England, UK (Figure 1). The beaches face south-southwest into the English Channel and are shaped mainly by waves formed in the Atlantic travelling up the English Channel or by waves generated locally within the Channel by southerly winds. 1 Centre for Environmental Research, University of Sussex, Brighton, BN1 9QJ, UK. [email protected] 2 " [email protected] 3 " [email protected] 4 " [email protected]