ABSTRACT
Beach accretion is taking place rapidly in the area between Skegness and Gibraltar Point in south Lincolnshire, England. The processes involved are generating dune ridges, saltings, new salt marsh in the shelter of a spit, foredunes with intervening marsh strips, and ridges and runnels on the wide foreshore. The formation of these features is related to the pattern of offshore tidal channels and banks. The source of material lies to the north and it is brought into the area by tidal streams and wave drifting. A source in mixed glacial and fluvioglacial deposits, which crop out on the foreshore and cliffs to the north, is supported by a study of the sediment size distribution and electron microscopy. The reason for accretion at this point is probably related to the offshore morphology. Sediment reaches this particular area on account of the nature of the tidal streams and their residual flow, which allow sediment to move with the south-flowing flood stream onto the lower foreshore in the zones of maximum accretion. Trend analysis reveals the marked regularity and magnitude of the accretion in terms of beach ridge size and movement, accretion of sediment on the foreshore and in trends of spit growth. The sediment builds up convex-seaward elongated foredunes on a foundation of stabilized beach ridges on the upper foreshore, while salt marsh accumulates in the sheltered runnels to landward. The relationship between ridge height and accretion confirms the hypothesis that ridges develop where there is a surfeit of sand on the beach, producing a gradient lower than the equilibrium swash slope gradient. In this process waves build the coast out seawards on a broad front, by the creation of “nesses” of accumulation, the position of which is related to the pattern of offshore banks and channels. Thus tidal processes are of fundamental significance on this coast in determining the location of maximum accretion, which changes with time as the offshore morphology is modified by the tidal streams.
