Morphological development of the Sandettie-South Falls gap: a degeneration ebb dominated tidal passage in the Southern North Sea
Smith, D.B. (1988). Morphological development of the Sandettie-South Falls gap: a degeneration ebb dominated tidal passage in the Southern North Sea, in: de Boer, P.L. et al. (Ed.) Tide-influenced sedimentary environments and facies. Extended versions of papers presented at the Symposium on Classic Tidal Deposits, held August 1985 in Utrecht, Netherlands. pp. 51-64 In: de Boer, P.L. et al. (Ed.) (1988). Tide-influenced sedimentary environments and facies. Extended versions of papers presented at the Symposium on Classic Tidal Deposits, held August 1985 in Utrecht, Netherlands. D. Reidel Publishing: Dordrecht. ISBN 90-277-2622-1. ix, 530 pp., more |
| Abstract | Northeast of Dover Strait the tails of both Sandettie and South Falls bank converge to confine a narrow ebb dominated passage flanked by fields of large sand waves. Two thirds of the channel floor is barred by a transverse ridge of gravel that forms an erosion resistant sill behind which a tapering lobe of sediment has accumulated. The morphology of this unique setting is described from recent hydrographic and sidescan sonar data. A comparison of repeated hydrographic surveys made of the sand waves comprising the tail to Sandettie Bank reveals that these have changed little in form or position between 1970 and 1978. Over the same period the volume of sand held in the bank's tail above the 35 m. Isobath appears to have decreased. A similar comparison of sand waves comprising the tail to South Falls Bank reveals that these, like their opposite counterparts, have also decreased in volume. The hydrographic comparison also reveals, that the Tail of the Falls is in fact comprised of two not entirely autonomous echelons of sand waves that have rotated slightly clockwise. It is proposed that the observed changes in the tail of South Falls Bank result from a decrease in the quantity of sand supplied to the end of the bank from along the bank itself and, more importantly, brought in across the seafloor along the regional south - southwesterly sand transport pathway. The latter is of particular importance because sand reserves held within the basin between Sandettie and South Falls banks and further north appear to approaching or have effectively reached a state of depletion. The Tail of the Falls appears to be an example of a sandbank adjusting to a hydraulic regime in which it's supply of sand has been reduced to a level below that needed to maintain itself. |
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