Abstract
A validated numerical model of tidal flows and sediment transport around the Alderney South Banks was used to investigate the potential effects of large (300 MW) tidal turbine arrays at different locations in Alderney territorial waters. Two methods were used, firstly looking at hydrodynamic changes only and secondly modelling sediment transport over a non-erodible bed. The baseline hydrodynamic model was validated relative to ADCP velocity data collected in the immediate vicinity of the sandbank. Real-world sand transport rates were inferred from sand-wave migrations and agree favourably with sediment transport residuals calculated from model outputs. Outputs from the sediment model reproduced realistic morphological behaviours over the bank. Seventeen different locations were considered; most did not result in significant hydrodynamic changes over the South Banks; however, three array locations were singled out as requiring extra caution if development were to occur. The results provide a case for optimizing the array locations for twin objectives of maximizing array power and minimizing impacts on the sandbanks. This article is part of the theme issue 'New insights on tidal dynamics and tidal energy harvesting in the Alderney Race'.
Highlights
Fast tidal currents of interest for power generation often occur close to islands or headlands, where flow separation can occur and cause large areas of recirculation, extending over many kilometres
Many of the high energy locations within Alderney waters would be unlikely to significantly affect the flow velocities around the South Banks if a single large array were installed at that location
The hydrodynamic results indicate that the South Banks will experience relative flow deceleration from the modelled arrays on the ebb tide predominantly
Summary
Fast tidal currents of interest for power generation often occur close to islands or headlands, where flow separation can occur and cause large areas of recirculation, extending over many kilometres This is the case for a number of sites identified as having high. Potential for development, notably the Pentland Firth to the south of the island of Stroma [1,2,3]; at Portland [4] (a headland on the south coast of the UK) and Alderney [5] (an island in the Normandy-Brittany Gulf) In all these locations, large submerged sandbanks exist within a few hundred metres of flows that exceed 3 m s−1 at spring tides; flows that could remove the sand, if diverted onto the banks. In this way, localized changes in the flow regime could have a wider impact upon sand movement around sandbanks
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