Long-term evolution of a sand spit, physical forcing and links to coastal flooding

Abstract

Aerial photographs, topographic field data and environmental forcing agents were used to assess historic and annual sand spit changes at Ginst Spit, Pendine Sands, West Wales. Aerial photographs highlighted that the spit shoreline facing the dominant wave direction had accreted steadily throughout the assessment timeframe (1947–2010). Stabilisation works in the form of rubble mounds aided recovery of the dune system thought to have been damaged due to training exercises carried out during the Second World War. Annual topographic surveys (1995–2010) showed a terminal end eastward migration extending into the channel of the 3 estuary complex. Dominant waves emanate from south southwest, and wave models suggest that longshore sediment drift is from west toward east. Sub-dominant southeast waves create a counter drift back toward the west forming the customary northward hook. Model results showed significant wave transformation from offshore model boundaries to the nearshore zone for both wave height and direction, which found agreement with qualitative assessment. Annually averaged wave components showed varying correlations with sand spit rates of shoreline change. Precipitation and spit growth were associated with flood events, which suggested that a combination of fluvial and coastal processes contribute to lowland inundation. By showing the major role the spit plays in protecting the town in its lee, this work provides a new understanding of sand spit evolution to inform coastal management.