The effects of tidal stream turbines on hydrodynamics and flushing properties

Many of the environmental issues associated with the deployment of tidal stream turbines will be due to changes in hydrodynamic flowfields due to the turbines. The deployment of arrays of turbines within a tidally dynamic area will have a number of impacts on the waterbody; in particular, the turbines extract energy from the water and hence alter flowfields during both ebb and flood tides. This paper describes research undertaken by the Authors who have developed a two-dimensional hydrodynamic model to predict changes to tidal dynamics and flushing characteristics caused by tidal turbines. The momentum term of the Navier Stokes equation was adapted to reflect the energy extracted by turbines and consequential effects on flowfields. The model was applied to the Shannon Estuary, a highly dynamic estuary in Ireland with significant capacity to produce tidal stream energy. Flushing parameters were calculated for the cases with and without turbines. The residence time is shown to increase when turbines are included; this illustrates likely changes in pollutant transport of the region due to the deployment of tidal turbines.