THE BEACH MORPHODYNAMIC PERSPECTIVE AND GRAVEL BARRIER EVOLUTION

In spatial terms, coarse clastic sediments comprising gravels to boulders, form substantial barriers in mid-to high latitudes to an extent that they are the majority sediment element of barriers at latitude >N45^o (and probably >S45^o as well). On that basis, understanding the controls on barrier evolution are seen as essential to the future planning of coastal societies where these barriers are major components of coastal defence. Recent research on gravel barrier beaches has developed the models of reflective morphodynamic regime by which understanding of swash flows and morpho-sedimentary responses on steep gravel beach slopes have been advanced. The links between the timescales appropriate for these analyses and those appropriate for barrier behaviour at century-scale and beyond have not yet been established. Consideration is made of both i) morpho-sedimentary responses (Buscombe and Masselink, 2006) and ii) extreme event analysis through barrier resilience and barrier rebuilding during storms and afterwards, by which morphodynamics may provide link with longer-term barrier behaviour. The existing paradigms for millennium barrier evolution and behaviour identified as sea-level change, sediment supply, wave climate and basement context are difficult, possibly impractical, variables to reconcile within a morphodynamics framework. This paper considers this difficulty to see whether there is continuity between morphodynamics and the various time and space scale dependent mechanisms of barrier change, which can be used for forecasting / planning purposes into the next century. These issues are considered using examples drawn from Canada, France and the UK.