Mapping currents at tidal turbine sites using VHF high resolution ocean radar

A pair of VHF high resolution radar stations is equivalent to deploying several hundred moorings for surface current measurements. Mapping of currents is a basic requirement in planning and operating a production area for tidal energy. This paper addresses the challenge to use surface current measurements to estimate currents lower in the water column where the turbines will be deployed. A logarithmic boundary layer model is used for the vertical profile of current in a turbulent flow, with validation from published measurements. Considerations of potential and turbulent kinetic energy for a stratified water column show that the modeled vertical velocity profile can be used within limits of flow velocity at the surface, and degree of bottom roughness. The bottom roughness required to fit the logarithmic boundary layer to observed velocity profiles in this energetic flow was about 10 times larger than would normally be expected in coastal oceans. The conclusion drawn is that VHF radar surface measurements are quite well conditioned for planning and monitoring tidal energy sites.