Theoretical approach to the investigation of ridge and runnel topography of a macrotidal beach: Dundrum Bay, Northern Ireland

Abstract

Ridge and runnel beach topographies have been extensively studied in the literature of beach dynamics. Empirical and numerical approaches have attempted to explain the formation and evolution of such morphological features. This paper reports on an investigation conducted at Dundrum Bay, Northern Ireland, to study the morphodynamics of a ridge and runnel topography set in a low energy fetch limited macrotidal coastal environment of the Irish Sea. The study focussed on the potential effects of wave action as interpreted from deep water records and numerical modelling of shoaling across the extensive surf zone. Extensive wave propagation simulations were conducted over a highly detailed topographic representation of the ridge and runnel system acquired by Differential Global Position System survey (accuracy sub-centimetre). Simulations showed that energy levels on incoming waves decreased progressively as water depth decreased and slopes increased. The first (most seaward) bar acts as a buffer for incoming waves and the patterns of wave energy dissipation suggest that onshore sediment transport may occur from the seaward face of the bar towards the top of the feature. Wave energy is subsequently lower on more landward bars. A conceptual behavioural model for the morphodynamics of ridge and runnel topography is presented based on the wave analyses.