An Investigation into the Morphodynamics of a Headland Rip Current at Bantham Beach, Devon, UK

Rip currents are offshore directed flows occurring in the surfzone. Rip mechanisms are driven by breaking waves, where a shoreward build-up of water returns seaward via the rip channel. Headland rip currents (HRCs) are topographically constrained mechanisms with a seaward flow, believed to cause significant offshore sediment transport. In this study, bed surface elevations and rip current flow velocities were collected and analysed, in addition to the collection of sediment samples from the rip channel and a downdrift beach. Comparisons were made between a theoretical depth of closure (DOC) and the observed depth of rip related morphology. The study area focussed specifically on Bantham beach, UK, with the overarching aim of improving the current limited knowledge on HRCs. The study found, that whilst the river located at Bantham was identified as the predominant sediment transportation mechanism, the HRC had a key influence on the morphodynamics, displaying a localised clockwise rotation of sediment. 100% of drifters were shown to exit straight through the surfzone, prior to travelling alongshore as the rip velocity attenuated. A maximum average velocity of 0.72m/s was observed at the rip neck, whilst the lowest average velocity of 0.37m/s was at the feeder currents. Velocity was found to significantly increase with an increased wave height (P<0.05). No depth threshold was identified to limit offshore flow, where drifters were transported by the HRC from the shoreline. Identified drifter tracks and rip induced morphology found DOC was not exceeded. Comparisons between sediment samples taken from Bantham beach and adjacent Thurlestone beach found a significant difference in median grain size (D50) (P