SIZE, SHAPE AND DENSITY SORTING OF BEACH MATERIAL ALONG THE HOLDERNESS COAST, YORKSHIRE

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Abstract
SUMMARY: The results of investigations on the size, shape and density distribution in samples collected from the boulder clays, beach and offshore zone of Holderness are presented. None of the data indicate the existence of major north—south drift along the coast as previously thought. Many beach and offshore samples have a bi- or tri-modal size distribution whilst the shape density data show that most sands consist of different truncated populations which must have undergone a very complex history. The beach sands have a distinctly lag character compared to the boulder clays, their main source material, so that most selection processes must have occurred in the offshore area in zones parallel to the beach. It is postulated that erosion of the cliffs and subsequent withdrawal of the material from the beach are achieved mainly during storms from the east. The strong undertow transports the mobilised material towards the shallow and somewhat deeper offshore waters but only a fraction of it re-enters the beach as prograding bars during moderate conditions. The inability of westerly winds to produce sufficiently large waves causes the sediment balance to be strongly negative. Material reaching the deeper offshore zone may be removed by tidal currents, probably with a net component to the north. The properties of the Spurn Head sands are best explained in terms of the continuous withdrawal of the spit over its own sediment, in which wind action also plays a part.

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