Abstract/Summary

Managed realignment describes the breaching of coastal flood defence such as sea walls, embankments, and barrier beaches for habitat restoration and flood defence purposes. These sites are deliberately breached at pre-determined locations, often with extensive engineering works carried out to encourage a mosaic of habitat types. However, landscaping and engineering works typically alter the site's morphology, resulting in a more simplified creek and drainage network with lower topographic variability than natural saltmarshes. As a result, drainage might be restricted, impacting the plant communities that can colonise and preventing widespread sedimentation and seed dispersal. In contrast, unmanaged realignment (uMR) is the natural breaching of flood defences without any of these costly engineering or landscaping works performed prior to site breaching. uMR sites provide an opportunity to assess the ‘natural’ morphological evolution of realignment sites without the influence of extensive site design, engineering, or landscaping features, yet there remains little analysis of the evolution of ‘recent’ uMR sites. To address this gap in knowledge, this paper describes ten recent occurrences of uMR on the coast of England since 1996. From these sites, five were selected for analysis of the pre-breach morphology in comparison to areas of natural saltmarsh and the subsequent morphological evolution. In general, lower topographic variability, although a higher density of creeks, was found within the sites before breaching in comparison to the adjacent areas of natural marsh. Following site breaching, results suggest that uMR sites become less topographically diverse, with some evidence of subsequent increases in topographic variability at the two oldest uMR sites. Findings are discussed in terms of the potential benefits of uMR for shoreline management planning. It is recommended that further consideration of the wider impact of uMR on coastal and estuarine systems is required within the shoreline management process to ensure uMR sites have a positive impact on the strategic delivery of shoreline management planning.