Sea-bed noises reveal role of turbulent bursting phenomenon in sediment transport by tidal currents

Abstract

In many engineering and sedimentological applications, it is usual to relate sediment movement to the time-averaged bed shear stress. However, the shear stress exerted on the sea bed by tidal currents is intermittent in nature due to the turbulent bursting phenomenon^1,2. Sediment movement at the sea bed also occurs in bursts^3,4. However, attempts to link these two processes have failed because of the poor temporal resolution of existing sediment-transport measurement techniques. Recent experimental advances now make this possible and we describe here the first detailed observations of sediment movement and fluid turbulence in tidal currents flowing over sandy gravels. These results show that high stress values are a necessary, but not sufficient, condition for bed-load sediment movement and that form drag on individual particles may have greater dynamical significance than the stress. This work also suggests that it may now be possible to describe sediment movement at a level which is deterministic in terms of the turbulence and at very much shorter timescales than have been used previously.