Ridge and Runnel Beach Morphodynamics: An Example from the Central East Coast of Ireland


  • Monica E. Mulrennan


Morphodynamic response, equilibrium swash bars, ebb-tidal delta


Variations in the morphodynamic response of a ridge and runnel beach system, on the central east coast of Ireland" were measured over twelve months. The ridge and runnel system complies with the general criteria of true ridge and runnel forms, as defined by KING and WILLIAMS (1949), in that it occurs under conditions of limited fetch, low beach gradient, large tidal range and medium to fine sediment size. The ridges represent semi-permanent mid- to low-energy equilibrium forms which are destroyed under high energy conditions. Relatively minor changes in the morphological expression of the ridge and runnel beach were superimposed upon large scale volumetric changes to the beach. The beach surface aggraded during a year characterised by a significantly higher incidence of storm conditions than average. This response is largely dependent on the availability of sediment and the prevailing wind direction. The changes in the morphology of the ridges and runnels were also controlled by the meso tidal conditions which operate along the study area but showed no relation to spring/neap tidal movements. The findings suggest that definitions of 'ridge and runnel' may have been too rigorous with regard to conditions of permanency, mobility and sediment availability.