Local and regional interactions between tidal stream turbines and coastal environment.

An extended three-dimensional unstructured ocean model for simulating impacts of tidal stream turbines on tidal current, turbulence and surface waves has been applied to study the interactions between a tidal turbine farm and its surrounding environment. The present study aims to reveal three-dimensional local and regional changes due to the operation of a proposed turbine farm in natural coastal environment. Fine mesh size is assigned at the turbine farm location to capture the details of local wake dynamics, hydrodynamics and suspended sediment transport. Large geographic coverage of the model provides details of changes in regional features. Results showed that the proposed turbine farm comprised of 18 turbines (15–20 m in diameter) with approximately 20% power extraction from the average available power (averaged over five and half tidal cycles) led to local variation of surface elevation within the range of −10 to 3 mm, flow acceleration on both sides of the turbine farm, flow acceleration of ∼ 0.4 m/s near the bed in the vicinity of the turbine farm which caused bed shear stress to rise up to 2.5 N/m2 (corresponding to the critical stress of a range of fine gravel and finer sediment particles), locally increased TKE of 0.09 m2/s2, reduced wave height of 0.01–0.05 m, and upward sediment transport in the water column. On a regional scale, most of the changes on amplitude and phase of M 2 constituent were observed within 10 km (∼ 15 times the array width) from the centre of the turbine farm, and the wake in terms of 95% flow rate recovery was found to be 9 km long (∼ 14 times the array width). Noticeable changes were also found in surface waves, bed shear stress and suspended sediment transport on regional scale as result of moderation in tidal and flow dynamics, although much less prominent than the local effects. It is recommended that consideration during the Environmental Impact Assessment stage of tidal stream energy projects should be given to an area that extends beyond the immediate vicinity of the planned turbine farm. • Detailed study of hydrodynamic and sedimentary impacts of tidal stream energy extraction. • A three-dimensional ocean model with additional terms for tidal turbine simulation is used. • Both local and regional scale impacts are revealed. • Regional scale impacts are less prominent than local scale impacts. • Environmental Impact Assessment of tidal stream energy projects should consider an area beyond the immediate vicinity of the turbine farm. [ABSTRACT FROM AUTHOR]