Abstract
Huthnance [Estuarine Coastal Mar. Sci. 1973, 1, 89–99] is reviewed, whereby an oscillating tide over bathymetric features induces a mean flow generally along isobaths. The effect is a superposition of Coriolis and frictional processes. These are discussed with the intention of elucidating the processes for a more general readership. Induced velocities of order several are expected around the UK shelf seas. The effect is dynamically significant over bathymetric scales of order a few kilometres and has previously been of most interest to dynamicists studying processes on this scale. However, with the increase in computing power, appropriate scales can be simulated in shelf-wide regional models and in next generation operational models. It is demonstrated that this small-scale effect is likely to be important for shelf-wide regional models and that a spatial resolution of at least 1.8 km is recommended for shelf sea simulations.
Highlights
Huthnance (1973), “Tidal current asymmetries over the Norfolk Sandbanks”, was motivated by some unexplained observations of mean flows along sandbanks (Caston and Stride 1970)
The interpretation attributes the net circulation to two processes: (1) Coriolis effects and (2) inertia or frictional effects
Though equation (4) does not capture the potential for neighbouring locations to connect via a residual current, nor does it has a dynamic representation of the frictional effects that may enhance or diminish the induced mean currents, it does give a first-order estimate of the tidally induced persistent currents
Summary
Huthnance (1973), “Tidal current asymmetries over the Norfolk Sandbanks”, was motivated by some unexplained observations of mean flows along sandbanks (Caston and Stride 1970) These sandbanks were typically 40 km long by 2 km wide, of height 30 m in the shallow water of depth of 40 m and critically were present in the tidally active waters in the southern North Sea. The major axes of the tidal ellipses are not aligned with the long axis of the bathymetric features (figure 1) such that over a tidal period, water columns are forced up and down the bathymetric slopes. The net effect is additive and interestingly, under appropriate conditions, the induced circulations can be in opposite directions This piece of work appears to have been largely picked up by sediment dynamicists (Dyer 1986), and presents contemporary challenges for wide-area shelf sea models.
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