This paper describes research undertaken by the authors to investigate the effects of tidal turbine installations using an amended numerical model. The study considers an idealised turbine installation in Orkney in the North of Scotland. The potential of the Orkney for marine renewable energy has led to the formation of the European Marine Energy Centre (EMEC) and provides a test site for wave and tidal renewable energy devices. An amended three-dimensional hydrodynamic model was used to incorporate the effects of tidal turbine farms using a multiple layer approach. This technique allowed tidal turbines to occupy multiple vertical water layers enabling a better representation of tidal turbine devices. The model incorporates a technique that allows the conservation of energy due to power generation and the dissipation of kinetic energy through the conversion of electric power generated to heat. A tidal turbine farm was simulated and velocities in the region of the tidal turbine farms were shown to have been affected by the inclusion of tidal turbine farms. The resolution of the model in the vertical was also shown to have a significant affect on the simulation of the changes to the hydrodynamics with the inclusion of tidal turbine farms.