Characterisation of a tidal energy site: hydrodynamics and seabed structure

Tidal energy site characterisation typically concentrates on quantifying the extractable energy resource. For energetic sites such the Pentland Firth, the upper limit to this resource is likely to be determined by environmental or
economical constraints. However, the relationship between the flow and the wider environment is not well understood. Therefore site assessment should consider the whole environment including the relationship between the flow, seabed structure and morphology.

In this paper we construct an enhanced description of an important tidal stream energy site in the Pentland Firth. This is achieved via a multi-disciplinary approach that combines in situ acoustic field measurements and numerical modelling.

The results illustrate that the seabed is far from featureless. There is a clear relationship between the tidal streams and the seabed structure. Due to the fast current speeds the site exhibits large areas of exposed bedrock. Significant areas of sediment accumulation are also found at the margins, where current speeds are less and tidal eddies are formed. Most interesting is the presence of sand waves, which are attributed to the asymmetrical nature of the flood and ebb tidal currents.