The economic viability of tidal turbines will require the deployment of multiple devices in array formations in a manner analogous to wind farms. This research investigates the effects of the configuration of a tidal turbine array, specifically the turbine spacing and capacity, on the hydro-environmental impacts of the array. The hydrodynamic regime of the Shannon Estuary, a highly energetic estuary on the west coast of Ireland, was simulated using a depth integrated 2D hydro-environmental model. The numerical model was modified to incorporate the mechanics of energy extraction using linear momentum actuator disc theory and the impacts of a multiple device array were simulated. Three different array configurations were examined with turbine spacings of 0.5, 2 and 5 rotor diameters. The model results demonstrate that flows are attenuated inside the array and accelerated around the array. Water levels are also affected with a reduction in tidal range within, and upstream of, the array and a delay in high and low tides upstream of the array. The magnitude and extent of the observed impacts are found to reduce as the density and capacity are increased and that the impacts of large-scale arrays can be acceptable if deployed using a low density spacing of 5 rotor diameters. (C) 2013 Elsevier Ltd. All rights reserved.