Intertidal flat development in response to controlled embankment retreat: Freiston Shore, The Wash, UK

Changes in Coastal Sediment Dynamics Due to Managed Realignment

“…The sediment is transported seawards by the dominant ebb 8 tides and deposited in the low intertidal flats creating a concave profile in the mid-flats and a convex profile in the lower areas; (2) once the drainage channels are able to deal with the tidal discharge, the sheet flow and associated erosion ceases, the mid-intertidal stabilise; the flood tide is enhanced and the lower intertidal area starts to erode, with sediments potentially moving landward to accrete the upper areas and the realignment site; and (3) after decades, the drainage channels reach morphologic equilibrium and the intertidal profile regain characteristics similar to pre-breaching. Field measurements between October 2003 and October 2004 at Freiston Shore indicate a temporal variation in mean grain size along the intertidal profile seaward of the realignment site, which seems to be greater at the lower intertidal areas, where higher proportion of sand correlate with increased rates of erosion (Ni et al 2014). …”

“…Vertical accretion within the site (at decreasing rates with time) and short-term erosion due to drainage creek development at the breaches are often observed (e.g. van Proosdij et al 2010;Vandenbruwaene et al 2012), corresponding to the rapid adjustment phase after breaching described by Ni et al (2014). Following tidal restoration, mudflats will develop within the site (Figure 1b), dominating through time if site elevation is low and unfavourable for the development of saltmarshes ( Figure 1c).…”

“…French 2006;Pye and Blott 2014), others describe changes in drainage channels and adjacent intertidal area following seawall breaching (e.g. Freiss et al 2014;Ni et al 2014), while modelling approaches have been used to predict long-term (>50 years) evolution of realigned sites (Spearman 2011;Ni et al 2014). An increasing number of publications discuss the functional equivalency of recreated sites compared with natural ecosystems (e.g.…”

“…Based on a combination of field measurements and modelling for the Freiston realignment, Ni et al (2014) suggest a conceptual model for the evolution of intertidal areas seaward of realignment sites. The authors identify three phases: (1) after breaching, rapid erosion occurs in the mid-intertidal area due to headward erosion of drainage channels and the development of new channels due to sheet flow.…”

“…The understanding of the long-term evolution of managed realignment sites is still deficient (e.g. French 2006;Rotman et al 2008;Esteves and Thomas 2014;Ni et al 2014). TO MANAGED REALIGNMENT.…”