Coastal retreat and/or advance adjacent to defences in England and Wales

Abstract

Retreat and advance of shoreline position occurs naturally, and also as a result of defences which are constructed to prevent erosion and flooding. Retreat more commonly manifests itself down-drift of defences due to a sediment deficit causing the coast to become ‘set-back’. Advance normally develops due to sediment accumulation up-drift of a barrier inhibiting longshore drift, resulting in the coast becoming ‘set-forward’. Many examples of set-backs and set-forwards are recorded, but their location, number and cause is not known on a national scale. Using the Futurecoast aerial photographs, approximately 200 localities were identified as set-back or set-forward in England and Wales, with half situated in the Eastern and South East regions of England. Half of the total set-backs or set-forwards were on cliffed coasts, and half on low-lying coasts. Without local knowledge it is difficult to distinguish between set-backs and set-forwards. Set-backs often indicate higher retreat rates, thus threatening cliff-top infrastructure which requires defence upgrade and extensions, as well as raising maintenance costs. Monitoring set-backs is important for shoreline management, because as retreat continues, set-backs evolve and artificial headlands form and grow. This is reinforced by the shift from hard defence policies towards softer engineering approaches, managed realignment and limited intervention.

Appendix

Table 2 Set-back and set-forward sites plotted for cliffed coasts in Fig. 5 and discussed throughout the text. No distinction is made between sites which are set-back or set-forward as this requires detailed case studies (see ‘Introduction’)

Table 3 Set-back and set-forward sites plotted for low-lying coasts in Fig. 6 and discussed throughout the text. No distinction is made between sites which are set-back or set-forward as this requires detailed case studies (see ‘Introduction’)