Tidal range energy comprises a vast theoretical resource of 9,220 TWh per year, globally, with advantageous characteristics of predictability, generation flexibility and reliability. Approximately 13% of this resource lies within the United Kingdom’s (UK) coastal waters, where it could supply up to 12% of annual electricity demand. Tidal range energy conversion traditionally involves constructing and operating large-scale coastal or offshore impoundments (10-100 km), which will redefine near and far-field water levels and flow patterns. The relationship between the scale of the impoundment area and hydrodynamic impact has not been investigated for UK sites. To address this, we develop a two-dimensional (depth-averaged) TELEMAC model of the Irish Sea, and simulate six scenarios involving tidal range schemes of increasing basin area, from 25 to 150 km, located on the North Wales coast in an open coastal basin setting. Results indicate that far-field ( km) changes to the amplitude of the semi-diurnal () tidal constituent exhibit a linear relationship with impoundment area and volume (correlation coefficient and , respectively). The largest impoundment (150 km) caused far-field changes in maximum surface elevation ( cm); near-field surface elevation was reduced ( cm).