TO BREACH OR NOT TO BREACH? SPIT DYNAMICS AND COASTAL MANAGEMENT

摘要

The breaching of spits can have important consequences for subsequent spit evolution as well as flooding and siltation within estuaries. This paper describes an investigation into spit evolution and breach formation at East Head, Hampshire, UK. A multi-disciplinary approach was adopted which considered past coastal changes, sediment transport, geomorphological regime relationships and numerical modelling of sediment transport. Synthesising these results shows that East Head spit has had a long history of erosion (since at least 1842). This has arisen from decreasing longshore sediment supply following the development of a stable crenulate bay system between Selsey and Portsmouth. Spit recession has been closely associated with increases in the cross sectional area of the estuary mouth, which also has been brought about by the decreasing longshore sediment supply. In the future, erosion is likely to continue leading to the potential formation of a breach at the neck of the spit. Modelling indicates that a breach of 1.0m ODN depth could be kept open by tidal and wave action and that, if this breach deepened to 0.5m ODN, it would produce increases in siltation within the Harbour mouth. In the short term, the presence of rock armouring and gabions is likely to retard breach formation. The long term evolution of East Head is dependant on the sea defence strategy for the updrift frontage of West Wittering.