1 IMPACTS OF TIDAL ENERGY EXTRACTION ON SEA BED MORPHOLOGY Antonia Chatzirodou 1 and Harshinie Karunarathna 1 In this paper, the application of a 3D numerical model covering the area of Pentland Firth channel (Scotland, UK) to investigate the hydrodynamics related to tidal energy extraction is presented in detail. A full validation analysis is carried out so that the fully operational 3D hydrodynamic model could be applied with confidence in order to explore possible impacts of tidal devices on the ambient marine environment. Following that, a higher resolution hydrodynamic and morphodynamic model covering the area of Inner Sound channel, between the Island of Stroma and Scottish Mainland, favoured for tidal energy extraction inside Pentland Firth, is set up. Preliminary results indicate that the existing morphodynamics of the observed sandbank areas inside Inner Sound Channel are very dynamic. In such a dynamic environment, results imply that possible alterations in tidal currents due to energy extraction may have some implications on the existing morphodynamic regime. Keywords: tidal hydrodynamics; morphodynamics; Delft3D; renewable energy; Pentland Firth; numerical modelling; tidal energy extraction INTRODUCTION UK is ideally located to exploit marine renewable energy resources. Tidal energy generation is an option favoured by the UK Government (Bryden, 2006). Since industry is now moving to large array installations, it is vital that the local and regional environmental impacts of tidal energy extraction are well understood (Robins, 2013). Particular concerns are the extent to which the altered tidal environment as a result of energy extraction will change the natural sediment transport regime and hence the sea bottom morphodynamics, which may have some implications on beach stability, coastal ecology and flooding (Neill, Jordan & Couch, 2012). Prior to exploring the environmental effects of tidal energy extraction it is essential that the natural environment is modelled in detail and understood. In consistence with the above statement a 3D hydrodynamic and morphodynamic model is set up and validated in the present work. The validated model will afterwards provide a powerful tool to investigate possible impacts of tidal stream turbines in the sediment transport regime. Pentland Firth (PF) channel between Scottish Mainland (UK) and Orkney Islands, joining Atlantic Ocean with the Northern Sea, is used as the test site. Due to different tidal ranges and phases at the ends of the channel, hydraulic tidal currents of up to 8 m/s are generated in places in response to 2.5 m head drop (Bowyer & Marchi, 2011), providing a substantial energy resource for turbines deployment (Baston & Harris, 2011) (Figure 1). Figure 1. Field Site 1 College of Engineering, Swansea University, Singleton Park, Swansea SA2 8PP, UK