The role of relative sea-level rise and changing sediment supply on Holocene gravel barrier development: The example of Porlock, Somerset, UK

The Holocene development of the coastal system at Porlock has been driven by variations in the rate of relative sea-level rise providing a long-term control on longshore sediment supply, which in turn has controlled gravel barrier beach dynamics. Relative sea-level rise rates of between approximately 8.5 mm yr^-1 and 2.0 mm yr^-1 define a critical range which allowed gravel barrier consolidation and back-barrier alder cart formation between c. 8500 to 6000 cal. yrs BP. A marked deceleration in rise rates around 7500 to 7000 cal. yrs BP caused a reduction in coarse clastic sediment supply, forcing the barrier into the breakdown domain, enhancing its vulnerability to storm events. Back-barrier sedimentation since c. 6000 cal. yrs BP has been exclusively inorganic, and probably included an important catchment-derived component resulting from anthropogenic disturbances.