Modelling the response of subtidal sandbank dynamics to tidal energy extraction

Antonia Chatzirodou, Harshinie Karunarathna, Dominic E. Reeve

Tuesday 30 june 2015

9:45 - 10:00h at Antarctica (level 0)

Themes: (T) Special session, (ST) Marine renewable energy

Parallel session: 4D. Special session: Marine Renewable Energy

The UK holds a leading position in the emerging marine renewable energy road-map. Marine renewable energy industry is now moving towards deployment of arrays of tidal devices. Prior to consider large scale installations, it is important to investigate environmental impacts associated with tidal energy extraction (Shields et al., 2009). The main objective of the present study is to investigate the morphodynamic response of sub tidal sandbanks to tidal energy extraction. The Inner Sound strait inside Pentland Firth (PF) Channel (Scotland, UK), between Scottish Mainland (UK) and the island of Stroma, is used as the test site. Concerning sea bed morphology, a large sandbank located eastwards and a smaller scale shelf bank area located westwards in the lee of the Island of Stroma, in Inner Sound channel are of particular interest. Open source Delft3D flow model is used. Hydrodynamics of a regional (PF) model provided the boundary conditions for a high resolution local scale model in the Inner Sound sub channel, an area favoured for tidal turbines deployment (Goddijn-Murphy et al., 2013). Investigation of the sandbank dynamics during two spring-neap tidal cycles, at ‘no-energy’ extraction scenario, showed that they are highly dynamic. It is found that the observed tidal asymmetry along with the less significant secondary flows due to the curvature of the flow mainly contribute to the maintenance mechanisms of the sandbanks. Following that, the current model set up was used to investigate the impacts of tidal current turbines on sea bed dynamics. A range of energy extraction scenarios and array configurations was selected and modelled to map notable relationships between the altered currents and seabed changes. References 1. Goddijn-Murphy, L. M., Woolf, D. K. & Easton, M. 2013: Current patterns in the Inner Sound (Pentland Firth) from underway ADCP data. J. Atmos. Oceanic Technol., 30, 96–111. 2. Shields, M.A., Dillon, L.J., Woolf, D.K., & Ford, A.T. (2009). Strategic priorities for assessing ecological impacts of marine renewable energy devices in the Pentland Firth (Scotland, UK). Marine Policy, 33(4), 635–642.