Keywords: coastal modelling, environmental impacts, hydrodynamics, tidal energy.

Turbine arrays have the potential to significantly affect prevailing tidal currents and water levels. Current speeds will be reduced inside the array due to energy extraction and increased around the outsides of the array due to blockage effects and smaller tidal ranges may also result. These changes will have consequential impacts on the tidal regime and could result in the loss of habitat. It is imperative that the planning of tidal arrays takes account of these potential hydro-environmental impacts. The majority of tidal energy modelling studies to date have focussed solely on the hydrodynamic impacts of the turbines; this research investigates both the hydrodynamic and environmental impacts. The Shannon Estuary, a highly energetic estuary on the west coast of Ireland with significant potential for tidal current energy extraction, was simulated using a depth integrated two-dimensional hydro-environmental model. The numerical model was modified to incorporate the effects of energy extraction on the tidal regime and a multiple device array was simulated. In addition to changes in tidal flows, water levels are found to be affected by the inclusion of the array, with reductions in the tidal range upstream of the array. The prevailing tidal range upstream of the hypothetical turbine farm is 6m; significant expanses of mudflats are thus exposed at low tide and most of these are areas of environmental importance with environmental protection status. The research shows that large parts of these protected inter-tidal zones could be permanently inundated as a result of reductions in tidal range. By way of contrast, there are also potential benefits arising from reductions in tidal range such as reduced flood risk upstream of the farm.

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