Destabilisation and Accelerated Roll-Back of a Mixed Sediment Barrier in Response to a Managed Breach

Sea level rise increases the pressure on many coastlines to retreat landwards which will lead previously held in position through management, being allowed where this is no longer affordable or sustainable. Barrier beaches have historically rolled back response different hydrodynamic events and sea rise, but very little known as how quickly far roll-back going occur once management has ceased. Data from more than 40 topographical surveys collected over 7 years along 1.5 km long, almost swash-aligned shingle barrier at Medmerry (southern England) are used together with data a wide-ranging assessment of roll-back. This study shows that progressing time downdrift direction gradual reduction cross-sectional area longshore transport. The Inertia concept provides practical means assess stability/instability for experienced, also tool short- medium term risk coast immediate flood still needs be managed. Roll-back influenced particularly by creation an artificial tidal breach removal its sediment, elevation underlying marsh clay sediments, number severity storms experienced presence legacy groynes; exceeded modelled predictions expert judgement order magnitude.