Examples of Coastal Catch-up Including Barrier Roll-back, Marsh and Brick-earth Cliff Erosion in Southeast England

Coastal defences have been built in the past in locations where today there is no economic justification to rebuild or maintain them into the future. As these defences have usually been built in locations where coastline retreat through erosion or roll-back was seen as a threat, the underlying coastal processes are still operating and have over time increased the pressure on these defences. Removing defences or letting them fail is assumed to trigger the poorly understood process of coastal catch-up, a process of rapid change moving the coastline into a position it would have been in if defences had not halted natural evolution. Here we provide examples of this process at two open coast locations, one of which shows an annual rate of change measured over more than three years of more the 30 my^-1 or >20 times faster than historic rates. The topography over which the barrier rolls back appears to influence its speed. The results presented exceed those given in the literature and highlight the need for detailed monitoring of coastal catch-up in relation to a wide variety of defence structures under different conditions to reduce uncertainty in estimating future behaviour at sites where further investment in coastal defences is not possible.