Short-term dynamics and maintenance processes of headland-associated sandbanks: Shambles Bank, English Channel, UK

Abstract

The short-term (over a spring tidal cycle) dynamics of a headland-associated sandbank (Shambles Bank, English Channel) are investigated, by means of field measurements (synchronous data, using an acoustic Doppler current profiler (ADCP) and repeated side-scan sonar imagery) and two-dimensional (2D) hydrodynamic and sediment transport models.

The dynamics of the bank are described in terms of along- and cross-bank velocity components, sand transport pathways and bedform asymmetries.The results showed the occurrence of a net bedload convergent zone along the crest of the bank as a result of anti-clockwise veering of sediment transport towards the crest.

This transport pattern is suggested to be the result of the dynamic interplay between two distinct tidally related processes acting over the sandbank, during each phase of the tidal cycle: (a) the formation and different stages of a transient tidal eddy that drives bedload movement during the flood phase of the tide and (b) the bottom-friction induced by the presence of the sandbank that governs the bedload transport dynamics during the ebb phase of the tidal cycle.