Daily to seasonal cross-shore behaviour of quasi-persistent intertidal beach morphology

摘要

In this study, an intertidal bar and trough system on the beach of Noordwkik, The Netherlands was monitored over a 15-month period in order to examine the daily to seasonal sequential cross-shore behaviour and to establish which conditions force or interrupt this cyclic bar behaviour. The beach morphology (bars and troughs) was classified from low-tide ARGUS video images based on surface composition. From the classified images, time series of the landward boundary of the bar and of the trough were extracted. The time series of the alongshore-averaged boundary positions described sawtooth motion with a period between 1 and 4 months, comprising gradual landward migration followed by abrupt seaward shifts. The abrupt seaward shift appeared to be a morphological reset induced by storm events, which lasted at least 30 h with a large average root-mean-square wave height ( t2 m) and offshore surge level (>= 0-5 m), and a small trough (<20 m wide) in the pre-storm beach morphology. The time series of the boundary positions exhibited very little longer (seasonal) scale variability, but somewhat larger smaller (daily) scale variability. The bar boundary was found to be more dynamic than the trough boundary. Copyright (c) 2007 John Wiley & Sons, Ltd.