Future Energy by Trevor Letcher

Author:Trevor Letcher
Language: eng
Format: epub
ISBN: 9780080994222
Publisher: Elsevier Science
Published: 2013-11-13T16:00:00+00:00

16.2.2 Creation of Tidal Currents

Tidal currents can be defined as the periodic movement of water driven principally, though not necessarily exclusively, by a head difference created by out-of-phase ocean tides at each end of a restriction. Other external and, frequently, non-periodic forces are applied to tidal currents and these will often depend on the local weather patterns (radiational tides), ocean characteristics (internal tides) and geography. The rotation of the Earth is important in that the Coriolis forces modify the flow away from the equator. The flow characteristics are also dependent on the local topography and the bathymetry at any particular location, as these will affect the bottom friction energy losses as well as the intensity of turbulent mixing.

Tidal current frequencies and amplitudes can be analysed and predicted using the same mathematical techniques as tidal heights. The process of obtaining the initial data from tidal currents is more difficult than that of reading tidal heights, but the introduction of advanced subsea digital electronics has made acquisition of substantial quantities of high-quality tidal current velocity data relatively straightforward and inexpensive. Beyond the relatively simplistic velocities given in tidal atlases, all tidal currents will behave in their own idiosyncratic way, sometimes with large temporal and spatial variations in the flow behaviour throughout the 18.6-year cycle. Metre length-scale vortices and turbulence within the system render many highly energetic areas unusable for energy extraction.

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