Spatial and temporal patterns of sediment activation depth on a high-energy beach

Abstract

Sediment activation depth, by means of continuous temporal high-resolution sampling (Sediment Activity Meter-SAM) and tide-to-tide (DOD rods), field data were collected during six low tide conditions on a high-energy micro-tidal sandy beach. A large swell event also occurred during the experiment with offshore wave heights of 6 m. Waves at the intertidal zone reached heights of 0.30 m and periods 5 s during the pre-and post-storm scenarios; whereas waves heights of up to 0.60 m and periods of 6 s during the swell event. Sediment activation previous to the swell event reached values of 0.035 m, whilst during the storm increased to 0.24 m, and finally once the beach had recovered and the tidal range increased, the sediment-moving layer was 0.062 m in depth. The use of DOD rod data reveals a spatial gradient in sediment activation depth where the maximum activation depths are recorded at mean high water position at each high tide giving unimodal-like distribution of activity across the beach width. Use of the SAM method reveals a complex variability in beach surface position during each high-tide level. As the daily tidal range increased during the experiment, the location of the highest activation depth also advanced landward with this increase. ADDITIONAL INDEX WORDS: sediment activation depth, sediment activation meter, spatial patterns