Flood-ebb asymmetry of a tidal flow has important implications for net sediment transport (e.g. Wang 1999) and the potential extractable resource (Neill et al. 2014, Robins et al. 2015). The asymmetry of the tide may be understood through the interaction of the M2 (principal lunar) and M4 (first even overtide of the M2) tidal constituents in UK waters (Pingree & Griffiths, 1979). The interaction of the M2 tide with a tidal-stream turbine will alter the M4 tide, both augmenting and reducing the M4 amplitude, leading to an alteration of flood-ebb asymmetry (Potter et al., 2017). In this paper, through numerical modelling, the impact of multiple turbines, deployed in a row aligned normal to the tidal flow direction, on the overtides of the M2 have been investigated, along with the way that additional turbines change the way the turbines impact shallow-water tides individually. The results of the modelling show that in rows of turbines, each individual turbine has less impact on the asymmetry than it would individually. In rows with spacings of 1D and 2D, where D is the turbine diameter, despite the smaller impact of the turbines individually, the footprint of the row on the asymmetry (defined as the area where the change to the asymmetry is ≥ 2%) grows with additional turbines and therefore reduced spacing. For a more sparsely packed row, with a spacing of 3D, the footprint of the row is the same as that of an individual turbine. This suggests that for N ≥ 2, where N is the number of turbines in the row, and spacings > 3D a row of turbines may have a smaller footprint than an individual turbine. This requires further testing to confirm.
More information about the EIMR 2018 Conference is available here.