Sediment Transport by Tidal Currents and Waves: Observations from a Sandy Intertidal Zone (Burry Inlet, South Wales)

  1. S.-D. Nio,
  2. R. T. E. Shüttenhelm and
  3. Tj. C. E. Van Weering
  1. P. A. Carling

Published Online: 29 JUN 2009

DOI: 10.1002/9781444303759.ch5

Holocene Marine Sedimentation in the North Sea Basin

Holocene Marine Sedimentation in the North Sea Basin

How to Cite

Carling, P. A. (1981) Sediment Transport by Tidal Currents and Waves: Observations from a Sandy Intertidal Zone (Burry Inlet, South Wales), in Holocene Marine Sedimentation in the North Sea Basin (eds S.-D. Nio, R. T. E. Shüttenhelm and Tj. C. E. Van Weering), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303759.ch5

Author Information

  1. Department of Oceanography, University College of Swansea, Singleton Park, Swansea, UK

  1. Freshwater Biological Association, The Ferry House, Far Sawrey, Ambleside, Cumbria, UK

Publication History

  1. Published Online: 29 JUN 2009
  2. Published Print: 23 DEC 1981

ISBN Information

Print ISBN: 9780632008582

Online ISBN: 9781444303759

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Keywords:

  • sediment transport by tidal currents;
  • boundary-layer flow measurements;
  • tidal circulation pattern;
  • circulation of tidal waters and sediments over channelled intertidal zone complex;
  • low-amplitude wind wave action

Summary

Measurements of tidal current velocities and suspended sediment concentrations have been made at fifteen stations on a sandy intertidal zone in South Wales, UK These data have been interpreted in terms of tidal circulation and sediment transport.

Self-recording current meters yielded continuous data on tidal current velocities at 0·50 m above the bed, for periods of up to one month. In particular, measurements of tidal current speed made simultaneously at a series of points in a vertical plane, provided information on the structure of the boundary layer.

In general, velocity data fit a logarithmic distribution of current speed with height above the bed. Coefficients of determination better than 0·80 are achieved for 81% of the time during flooding tides and 75% of the time during ebbing tides. Deviations from the model occur primarily, close to the beginning and the end of a tidal half-cycle.

Throughout most of a tidal cycle, variations in suspended sediment concentration and grain-size distributions within the water column are related to the first-order fluctuations in tidal current velocity and the shear stress exerted at the sediment–water interface. Generally, average sediment concentrations are reduced exponentially as a function of height above the sediment–water interface. However, an exponential relationship is inadequate for limited periods. Close to low water, wind–wave-induced resuspension, producing reversed concentration gradients, is a more influential factor when compared with tidal current scour. Conversely, gravitational settling dominates close to high water, producing ‘bulges’ in the instantaneous vertical concentration gradient.

For those periods dominated by tidal current resuspension, close agreement exists between observed sediment transport rates and transport estimated from time-integrated stream-power values. At stations where no suspended sediment concentration data are available, sediment transport may be estimated from stream-power relationships.

Conclusions drawn from this investigation should be capable of extrapolation to other similar intertidal zones.