Three-dimensional hydrodynamic model of the Rance estuary (France) influenced by the world's second largest tidal power plant

The Rance estuary is a small steep-sided ria, located in the Brittany coast of northern France, with a maximum spring tidal range of 13.5m and an average river discharge of 7m(3)/s. Taking advantage of this significant tidal range, the Rance tidal power station (RTPS) was built in the 1960s as the world's first and largest tidal power plant, with peak output capacity of 240 Megawatts. It is currently the second world's largest tidal power installation after the Sihwa-Lake tidal barrage. The RTPS has two active parts: a barrage of 6 sluice gates and a structure of 24 turbines. Despite a well-known effect of the plant on damping estuarine water levels, little attention has been given to currents vertical distribution and the plant's impact on the dynamics of freshwater-saltwater interface. Therefore, a three-dimensional model of the Rance estuary was developed. Moreover, currents and salinity measurements were carried out to validate the numerical model. Simulated and measured currents showed that (i)the RTPS induces an acceleration of flood currents directly upstream of the sluice gates and (ii)ebb currents are strengthened by the narrowness of the Saint-Hubert-Port. Finally, salinity analyses assessed the dynamics of the freshwater-saltwater interface which is pushed further upstream during summer.