Over the past decade, renewable energy initiatives have been widely adopted and integrated into national electricity grids, with solar and wind technologies experiencing exponential growth. To sustainably transition to a carbon-free energy system, nations must build resilient and robust electricity grids from diverse sources of renewable energy. In the UK, tidal range energy holds the potential to predictably and reliably supply an estimated 12% of annual electricity demand. However, converting tidal range energy involves constructing and operating large-scale coastal structures (tidal lagoons or barrages), these structures will redefine near and far-field hydrodynamics and morphodynamics. The relationship between these impacts and the physical characteristics of tidal lagoons (e.g. impoundment surface area) is not trivial, nor is it well understood. To address this, we establish a fully-validated two-dimensional (depth-averaged) shelf-scale TELEMAC tidal model. Six potential lagoon scenarios were simulated, each involving a North Wales-based lagoon design of varying impoundment area (25 - 150 km2). Far-field modifications to the amplitude of the semi-diurnal constituents exhibited a strong linear relationship with impoundment area and volume (correlation coefficient R = 0.95 and R = 0.96, respectively). In the case of the largest tidal lagoon (150 km2), these changes produced a maximum water level increase in the far-field (2 < ηmax < 3 cm, in the western Irish Sea) and a reduction in the near-field (ηmax > −3 cm, in the eastern Irish Sea and Bristol Channel). Tidal current speeds (and bed shear stresses) were reduced to the west of the structure (resulting in trivial changes to the tidal stream resource), owing to the structures ability to impede on the eastward progression of the tidal wave. We found that the 125 km2 tidal lagoon uniquely interacts with the diurnal and
overtide constituents (O1, K1 and M4), and resulted in a reduction in far-field maximum water levels (but amplifying local levels) – a consideration for future tidal range developments in the region. Reflecting on the correlation between impounded water volume and far-field hydrodynamic changes, our results suggest that, through strategic site selection and embankment placement, future tidal range scheme impact studies should seek to minimise the impounded water volume in order to reduce far-field hydrodynamic impacts, at no cost to power generation.