Page 297 - Fundamentals of Ocean Renewable Energy Generating Electricity From The Sea

Other Aspects of Ocean Renewable Energy Chapter | 10 283

of Fundy is in resonance at the semidiurnal frequency, and so the water depth
(in comparison to the channel length) is expected to be sensitive to changes in
mean sea level—see Section 3.5. Pelling and Green [20] simulated the response
in tidal dynamics that a 1 m SLR would have in this region. This 1 m SLR led
to an increase in the M2 tidal amplitude of around 0.1 m throughout the Bay of
Fundy, and this is attributed to the basin approaching true resonance as sea level
(i.e. the mean water depth in the basin) increases. In a study of the northwest
European shelf seas, 1 m of SLR led to significant changes in the tidal dynamics
[21]. Again, in regions that are in resonance such as the northern Irish Sea,
tidal amplitude increased (by around 0.05 m), but there were many regions that
reduced in amplitude, and one important region is the Bristol Channel (which
hosts Swansea Bay—proposed location of a tidal lagoon power plant), where
the M2 amplitude reduced by around 0.05 m. The M2 amplitude in Swansea Bay
is around 3 m (Fig. 3.6). Since theoretical tidal range power is related to tidal
range squared (e.g. Section 3.14), a reduction of 0.05 m in the M2 amplitude
would therefore represent a 3% reduction in the mean tidal range resource.
Finally, although the IPCC AR5 is a highly respected source of projected
SLR, there are other studies that consider the possibility of even greater SLR
by the end of the century. It is useful to consider more extreme future scenarios
since, although they are highly unlikely to occur, they are associated with very
high levels of impact. The UK Met Office UKCP09 includes a high-plus-plus
(H++) scenario, that is associated with SLR of up to 1.9 m by 2100. The
response of the M2 amplitude across the world’s oceans to an SLR of such
magnitude is plotted in Fig. 10.8 [22], demonstrating a complex pattern of
significant regional increases/decreases in the tidal range resource. For example,
the changes in the Irish Sea discussed earlier are further amplified under such
a scenario, and there is a significant reduction in the tidal range resource in
the Gulf of St Malo (where La Rance barrage is situated)—see Pickering et al.
[22] (which is open access) for more details, including a consideration of the
additional tidal constituents S2, K1, and O1.

Tidal Stream
There are surprisingly few published studies that investigate how the tidal stream
resource is likely to vary in the future. In an appendix included in Pickering
et al. [22], it is noted that Manning’s equation expresses the depth-averaged
velocity as a function of the square root of the hydraulic slope, and so a 10%
change in elevation amplitude would result in ∼3% change in current amplitude.
Under a scenario of 1 m SLR, a typical change in M2 elevation amplitude of
0.1 m was reported in the previous section for the Bay of Fundy (where the
typical M2 elevation amplitude is in the range 2–5 m [20]), and this equates to a
2–5% change in tidal elevation. Therefore, currents in the Bay of Fundy would
change by 1.4–2.2% which, for a typical M2 current amplitude of 1 m/s would
lead to an increase in current speed of 1.4–2.2 cm/s. This change is likely to be
within the bounds of natural variability (e.g. consideration of nonastronomical