Numerical model simulations for optimisation of tidal lagoon schemes

This study considers environmental impacts and the power production potential of a number of coastally attached tidal lagoons, proposed along the North Wales coast, UK. Initially, the impoundment shape, turbine and sluice gate locations were modified according to the regional bathymetric data. A refined 0-Dimensional approach was implemented to optimise the lagoon operation, based on given turbine and sluice gate specifications. In turn, a two-dimensional numerical model, based on an unstructured triangular mesh, has been refined to simulate the hydrodynamic processes, initially without and subsequently in the presence of the lagoons. The hydrodynamic model adopts a TVD finite volume method to solve the 2D shallow water equations, based on a second-order accurate spatial and temporal numerical scheme. An encouraging performance is apparent in reproducing the established conditions encountered in the region through comparisons against available data. The incorporation of tidal lagoons in the model appears to have a considerable effect on the flow structure in the region, by inducing high velocity accelerations near the sluices and turbines, depending on the stage of the tidal cycle. Considering a two-way generation regime, it is outlined that the loss of intertidal regions can be minimised, which is a major source of concern with regards to the environmental impact of such schemes through an ebb-generation operation. Particular focus is directed towards the comparisons between the 0-D and 2-D modelling results, an aspect which has not been reported previously. Predictions of the models diverge as the scale of the lagoon project increases, but it is highlighted that the 0-D methodology can be utilised for the optimisation of the processes in the initial stages of design before proceeding to more sophisticated numerical model simulations.