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FIG. 10.15 Mechanism for headland sand bank formation. (Reproduced from S.P. Neill, The role
of coriolis in sandbank formation due to a headland/island system, Estuar. Coast. Shelf Sci. 79 (3)
(2008) 419–428, with permission from Elsevier.)

(e.g. [62]). It is therefore useful to examine the influence that tidal energy
conversion in the vicinity of headlands would have on the evolution (and
maintenance) of headland sand banks.
Neill et al. [38] initially developed an idealized model to demonstrate that
a ∼300 MW TEC array sited in the vicinity of a headland could have a
significant influence on headland sand bank formation (Fig. 10.16). Subsequent
application to a case study—flow past the island of Alderney in the Alderney
Race—showed how tidal energy conversion influenced the evolution of a
neighbouring headland sand bank. They also found that siting the array close
to a headland significantly increased flow between the array and the coastline,
hence potentially increasing coastal erosion. A modest offset in the array
position, siting it to one side of the headland, led to a significant reduction
on the hydrodynamic and sedimentary impact. A similar study of the same
region, although focussed more on the French side of the Alderney Race,
again demonstrated the significant impact of a 300 MW array on sediment
dynamics, and how careful and localized siting of the array can minimize such
impacts [63]. However, offshore sand banks are characterized by interannual
and intraannual variabilities [61]. To determine the influence of tidal energy
extraction, it is therefore necessary to compare the magnitude of this impact
to natural variability. Robins et al. [37] attempted to do so for a modest sand
bank known as Langdon sand bank that is located in the vicinity of Anglesey
Skerries—a leased tidal energy site that was once under active development by
Marine Current Turbines. By combining outputs from tidal and wave models,
they showed that energy extraction had little influence on the evolution of
Langdon sand bank, perhaps because its maintenance is not strongly controlled
by flow through the Skerries where the hypothetical array is located. However,
their study did lead to one interesting finding. Local change in bed shear stress
due to energy extraction was greater than natural variability when the TEC
array exceeded 87 MW (Fig. 10.17). However, this result was valid only for