This study aims to provide further understanding about the effects that tidal turbines arranged in block farms could have over the water levels when they are deployed in estuaries with shallow bathymetry. As an application of the methodology presented for this purpose, a real case study, the Solway Firth estuary in the UK, has been modelled by means of MIKE21. An idealised model of the estuary has been used to identify the trends in extractable energy and impacts on tidal range for different farm densities and contrasted with a fully detailed model. A spring tide and a coastal flooding scenario have been considered for the detailed model as well as different densities and configurations of the tidal farms. For the densest arrays the extractable energy tends to a limit and the impacts on tidal range become relevant, although they are still lower than the ones resulting from tidal range schemes with similar installed capacities. It has been found that the effects on water levels are not linearly proportional to the increase of the farm density but they seem more closely related to the energy dissipated by the farms. The results of the changes on high and low tide levels over the estuary and time-series at specific locations have been analysed for the detailed models. When comparing between different layouts, changes during low tide levels are slightly higher for the parallel arrays. It can also be concluded that flood risk levels could be potentially reduced in the shoreline whereas some of the intertidal areas and their habitats could disappear as a consequence of significant water level rise at low tides.