Prospective of development of large-scale tidal current turbine array: An example numerical investigation of Zhejiang, China

Despite the rapid development of tidal current energy, understanding of its potential environmental impacts is still far from complete, especially for the region with considerable input of freshwater and sediment. As the large-scale tidal energy stations were deployed in Canada, the UK, China, Netherlands, France, and the US, concerns about its harm to the environment are growing. To address such issues, the Zhejiang area, one of the top tidal sites in the world, is taken as an example and a three-dimensional two-way-nested model was constructed. The embedded array of 5 turbines, 50 turbines, and 200 turbines are estimated to produce an average power of 0.9 MW, 7.8 MW, and 22.1 MW, respectively. The results show that currents are decelerated significantly downstream of the array, while accelerations are observed in the neighboring channel. Moreover, significant increases in tidal elevation are found in the small basins characterized by both deep water and great velocity deficits. Modifications to sediment transport are predicted through changes in the bed shear stress. Notably, disturbance from the turbines unlikely changes the locations of sediment erosion and deposition. However, considerable reductions in bed shear stress extending over 10 km downstream could potentially slow down the sediment transport rates. The presence of the turbine array also induces a more noticeable effect in the areas with more benign hydrodynamic conditions. Especially in the coastal waters, the relatively small bed shear stresses decrease greatly in percentage, reaching up to 40%.