Author(s): Reza Ahmadian; Ceri Morris; Roger Falconer
Keywords: No Keywords
Abstract: The climate change challenge has increased the importance of all forms of renewable energy. In the UK interest in tidal renewable energy, in particular, has increased due to its vast potential. Offshore and coastally attached tidal impoundments are one of the types of schemes proposed for different locations around the UK, including the Severn Estuary and along the North Wales coast. Tidal impoundments produce a tidal phase difference by impounding water inside the basin and realising the impounded water, either into or out of the impoundment, through turbines to generate electricity. This study focuses on the hydro-environmental modelling of offshore and coastally attached impoundments proposed along the North Wales coast, and includes investigating the far-and near-field impacts of such impoundments on the tidal water levels, velocities and flood risk, and flushing characteristics of the impoundments. A two-dimensional depth integrated model was set up over a 65×37. 5 km2 region along the North Wales coast and Irish Sea, and then modified to conserve momentum as well as mass passing through the turbines. Various offshore and coastally attached impoundments, including different turbine formations and using ebb only and flood-ebb generation, were modelled in this study. It was found that an impoundment located a few kilometres offshore would not significantly affect the shoreline tidal water levels. In contrast, the coastally attached impoundments were capable of offering some degree of reduced flood risk. The velocities around both the offshore and coastally attached impoundments were generally reduced on one side of the impoundment and increased on the other side of the structure, dependent upon the direction of flow through the impoundment. Although during the generation phase the velocities inside the domain decreased and were low; during the filling phase, they were increased locally in the proximity of the turbines and two large eddies occurred in the middle of the impoundment, while the velocities close embankment furthest away from the turbines were decreased. These velocity patterns indicated that there is a high chance of deposition arising inside the impoundments, away from the turbines and in areas where lower velocities occurred, namely at the centre of the eddies and also in regions outside of the impoundments and where the velocities were decreased. Spreading the turbines more around the periphery of the embankments reduced the impact of the impoundment on velocities, both inside and outside the domain, and was likely to lead to reduced the risk of sedimentation and improved tidal flushing efficiency.