Abstract
Flood-ebb asymmetry of a tidal flow has important implications for net sediment transport and the potential extractable resource. The asymmetry of the tide in U.K. waters may be understood through the interaction of the M2 (principal lunar) and M4 (first even overtide of the M2) tidal constituents. 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. In this chapter the impact of a row of tidal-stream turbines on the overtides of the M2 has been investigated through a numerical modelling study. Further, the way that additional turbines alter the way the turbines impact the shallow-water tides individually is explored. The results of the modelling show that when deployed in a row, on average, the peak velocity deficit and change to the current magnitude asymmetry (CMA) per turbine was less than were it deployed alone. The difference between the per turbine impact of turbines in a row and that of an individual turbine grew as the number of turbines in the row, and therefore the row blockage, increased. Additionally, the total area of the model domain experiencing a change to the M2 current and CMA > 1% increased with the addition of turbines to the row, for a row blockage >~10%, but remained similar to the single turbine case for lower blockage values. The implication of the change to the CMA by a turbine in a row for the asymmetry in energy conversion for its lateral neighbours was small as the turbines do not lie within the area of effect of their neighbours. However, the per turbine energy conversion increased as the number of turbines and row blockage increased, in line with theory.
Keywords
- Tidal-Stream turbines
- Tidal asymmetry
- Tidal-Stream array
- Physical environment impact
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When simulating a real-world site, better representation of the harmonic generation within the model domain will be obtained by supplying the harmonic tides at the boundaries of the model (Le Provost and Fornerino 1985). As only an idealised case is considered in this work any choice of harmonics supplied at the boundaries would be somewhat arbitrary. Therefore, the simplest case was considered. The case of undistorted tides at either boundary, i.e. M2 tide with negligible harmonics.
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Acknowledgements
This work was funded by a Natural Environment Research Council studentship, part of the ENVISON Doctoral Training Program, awarded to the lead author. Thanks also goes to DHI UK for providing a student licence for MIKE, allowing this work to be undertaken.
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Potter, D., Ilić, S., Folkard, A. (2020). Assessing the Impact of Rows of Tidal-Stream Turbines on the Overtides of the M2. In: Nguyen, K., Guillou, S., Gourbesville, P., Thiébot, J. (eds) Estuaries and Coastal Zones in Times of Global Change. Springer Water. Springer, Singapore. https://doi.org/10.1007/978-981-15-2081-5_13
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