Sediment dynamics of saltmarshes and intertidal flats, Southern and Eastern England.
University of Southampton, Dept. of Oceanography,
Saltmarshes and intertidal flats at Freiston Shore (The Wash) and from Lymington to
Keyhaven (West Solent) in eastern and southern England, respectively, are studied in terms
of water and sediment movement and their interactions.
Based upon tidal current measurements, wave monitoring, suspended sediment
concentration and seabed sediment sampling/analyses, the sediment dynamics over the
saltmarshes and intertidal flats of The Wash are identified as accretional. The area is
characterised by a standing tidal wave, flood-tidal dominance, and suspended sediment
supply from offshore. In contrast, the West Solent is erosional; it is characterised by a
progressive tidal wave, ebb-tidal dominance, and the net suspended sediment offshore
export. In the accretional intertidal and saltmarsh environments: (i) maximum tidal
current speeds and suspended sediment concentrations occur at the beginning of the flood
and end of ebb phases; and (ii) there is always a net landward sediment transport, due to
the tidal asymmetry (flood dominant) throughout each tidal cycle.
Velocity gradient rigs were deployed over the saltmarshes and intertidal flats of the two
regions. Boundary layer flow parameters were obtained and their patterns established
throughout tidal cycles. This part of the study illustrate the distinctive differences in the
boundary layer flows between saltmarshes and intertidal flats, and sandflats and mudflats
of the intertidal zone. These differences are due mainly to: the different roughness
elements; and the inter-relationship between the directions of the tidal currents and the
orientation of the bedforms.
Comparing with the 'traditional' model elsewhere, wave action is generally effective over
the intertidal flat environments in the U.K.. Interaction between the wave- and tidallyinduced
currents is an essential condition for transport over the intertidal flats and sediment
supply to (and deposition over) the saltmarshes of The Wash. Likewise, waves are the
dominant process causing erosion along the edge of the saltmarshes in the West Solent.
Based upon the results of the present study, a new dynamic classification of saltmarshes
and intertidal flats is proposed: (i) tidally-dominated; (ii) wave-influenced/tidallydominated;
(iii) tidally-influenced/wave-dominated; and (iv) wave- and tidally-
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