Characterisation of a Highly Energetic Tidal Energy Site with Specific Reference to Hydrodynamics and Bathymetry

Abstract — Characterisation of a tidal energy site must include the interrelationships between flow and bathymetry so that impacts can be anticipated with a high level of detail and confidence. This paper presents high-spatial resolution velocity data of tidal flow, which was measured using a vessel-mounted acoustic Doppler current profiler (ADCP) within Ramsey Sound, Wales. This is a high energy environment where peak mean current speeds during spring tides are in excess of 4ms -1 . The spatial variability of the flow, both transversely and vertically, in this area is high, with the flood and ebb tides displaying markedly different regimes. The vertical shear across the swept width of a 15m diameter TST has revealed that the shear at lower velocities (namely during the ebb tide) is relatively low, however, the vertical shear increases with increasing velocity and in many locations along the deeper channel where designthe velocity magnitude is high enough for energy extraction, the vertical shear is very high. A selection of locations are identified where the average velocity across the turbine is high and the vertical shear is relatively low, however, these areas are adjacent to areas of high vertical shear in the deep channel. Vertical shear during peak flood conditions is greatest immediately upstream and downstream of a prominent pinnacle. This paper demonstrates that small-scale and large-scale bathymetric features have a major influence on velocity structure, and can significantly alter the principal flow direction.