Tidal and residual currents around a Norfolk Sandbank |
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| Authors: | MJ Howarth JM Huthnance |
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| Institution: | Institute of Oceanographic Sciences, Bidston Observatory, Birkenhead L43 7RA, U.K. |
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| Abstract: | Currents on either side of Well Bank were recorded for 41 days in May–June 1981, in order to distinguish locally tidally-generated asymmetries (pertinent to maintenance of the bank) from larger-scale and wind-driven flows.Semi-diurnal currents were dominant, nearly rectilinear and slightly inclined to the bank axis.Fourth-diurnal currents were consistent with previously observed and computed fourth-diurnal tides for the area overall; amplitudes varied as the square of the semi-diurnal amplitude. Hence they appear to be generated by tides, but only a small part locally.Residual currents (average over a tidal cycle) were always in the sense of clock-wise circulation around the bank, consistent with simple models and giving strong evidence of local generation by tides. This circulation combines with the semidiurnal currents to maintain the bank. The slow increase of the residuals with the semi-diurnal amplitude is interpreted as an effect of strong semi-diurnal currents. A persistent component onto the bank 7 m above the bottom at one position may indicate distortion of the frictional layer by the sloping bottom or by bank curvature. |
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| Keywords: | Sand-bank tidal currents non-tidal circulations current measurements North Sea |
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