Sinking Depths of Sand Surface over an Intertidal Area Within a Tidal Inlet Channel


  • Shu Gao
  • Michael Collins


Sinking depth, tidal inlet channel sediment, depositional processes, threshold of motion, southern England


Observations from an intertidal area of a tidal inlet channel (during low water) show that, under a vertical pressure of around 2,500 kg m-2, the bed surface can descend by between 0 and 9 cm (caused by different sediment packing patterns). An analysis of the relevant sediment samples indicates that such a range of variations is not caused by differences in sediment characteristics i.e. grain size distribution, water content, mineral composition and shape. Hence, the observed variations are suggested to be hydrodynamically induced. The sinking depth is shown to be controlled by bed elevation, which is related to the tidal current speed and the rate of water-level changes immediately before the bed emerges during the ebb-tide phase. The presence of hydrodynamically induced variations in packing implies a difficulty in defining threshold of particle movement, on the basis of mechanics-based, semi-empirical approaches to sediment transport.