Modelling hydrodynamics of fast tidal stream around a promontory headland

Abstract

Areas around headlands often have higher tidal flow, making them important foraging locations for seabirds and marine mammals, as well as of interest for tidal energy extraction. Using in situ field measurements and hydrodynamic modelling, this study investigated tidal features around the most northerly promontory headland on the United Kingdom mainland. An acoustic wave and current (AWAC) instrument and an acoustic Doppler current profiler (ADCP) were deployed for 109 days in upward-facing configurations. These data were used to calibrate a hydrodynamic model developed using the TELEMAC-MASCARET modelling suite. This study used a non-hydrostatic model with a vertical layer configuration to reproduce upwelling present in field data. Data showed complex hydrodynamics with occurrences of vertical water velocities of up to 0.219 m/s. Modelling suggests upwelling begins in association with headland eddy formation as a result of secondary circulation due to flow curvature, which occurs off the tip of the headland. Upwelling continues to develop as the eddy dissipates and forms an upwelling front which moves away from the headland as the tide starts to turn. The modelling work successfully reproduces upwelling recorded by field instruments. Models of sufficient complexity are required to resolve fine-scale hydrodynamics associated with such features, which is important for tidal stream renewable energy developments in these environments, as well as understanding foraging activity of seabirds and marine mammals.