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Mechanisms for linear sandbank formation and maintenance in relation to dynamical oceanographic observations

1987; Elsevier BV; Volume: 19; Issue: 2 Linguagem: Inglês

10.1016/0079-6611(87)90006-1

1873-4472

Charitha Pattiaratchi, Michael B. Collins,

Oceanographic and Atmospheric Processes

Theories associated with flow in the vicinity of headlands and sandbanks, together with proposed mechanisms for sandbank formation and maintenance, are reviewed. To exemplify water and sand movement around a sandbank on a tidally-dominated shelf, tidal currents in the vicinity of a headland-associated linear sandbank are described. These data are integrated with sedimentological information on bedforms and grain size distributions. The sandbank under detailed investigation, the Scarweather Sands, is located along the northern coastline of the Bristol Channel (UK) which is an area susceptible to high energy inputs. The maximum spring tidal range here is around 10m and a 6000km fetch is available for storm wave approach from the Atlantic Ocean, but the area is 460km from the shelf break. Detailed observations are presented from 11 long-term current meter stations located within 10km of the sandbank. Currents are described in terms of residual water circulation, shallow water harmonics and tidal ellipse characteristics. Bedload transport paths are inferred from the distribution of bedforms, grain size and M2/M4 tidal current interactions. Transport vectors are predicted from near-bed current meter observations combined with empirically-derived formulae. It is demonstrated that water circulation and sand transport paths form part of a clockwise eddy system around the sandbank. Mechanisms controlling the location and the characteristics of this particular sandbank are shown to be explicable in terms of a combination of models for sandbank formation and maintenance. The results of the present study are thought to be applicable directly to headland-associated sandbanks elsewhere. It is shown, on the basis of theoretical considerations, that the pattern of residual water movement and, possibly, sand transport around this sandbank could be extended to continental shelves on a global basis.