Changes in Sediment Transport Rates Caused by Wave Action and Tidal Flow Time-Asymmetry

Abstract

Net and directionally-related mean sediment transport rates have been calculated for two stations within an estuarine system, using self-recording current meter and wave data. Analysis of the data set shows that: (1) because the relationship between sediment transport rate and near-bed current velocity is non-linear, the direction of net sediment transport may differ significantly from, or oppose, that of the near-bed residual current velocity; (2) in response to rotatory tidal currents and increasing wave action, net transport rates may remain unchanged-hence, it is the directionally-related mean transport rates (rather than the net transport rate itself) which should be used to describe the mobility of seabed sediments (such an observation implies that the time-scale on which the net sediment transport rate is meaningful is controlled by the time-scale on which changes in seabed morphology take place); and (3) under the influence of a combination of wave action and time-asymmetry of the tidal currents, changes in the direction of net transport rates may occur, implying that net transport during calm periods may reverse during storm periods.