It has been argued in recent papers that the nature of headland and coastal island wakes can be highly dependent on the level of turbulence caused by complicated coastal geometry and bottom topography, as well as on the loss of energy and momentum to the seabed due to friction. A series of field experiments was conducted around Bass Point (a 4‐km‐long headland near Sydney, Australia) using moored current meters and an acoustic Doppler current profiler. The offshore component of currents, measured offshore of the point, showed a high degree of spectral energy at about the 7‐day cycle, with a small amount at the diurnal frequency, but the reverse was found in the lee of the headland, where most of the recirculation was at the diurnal frequency. Numerical experiments resulted in similar spectra being obtained from locations behind the headland when the numerical model was forced with a spectrum of frequencies resembling the spectrum of the offshore free stream current, which was derived from the field results. The size and frequency of eddyshedding in the lee of the headland depended on the degree of variability of the inflowing free stream, with a diurnal component in the free stream appearing to cause the oscillations in the wake also of diurnal frequency. The numerical experiments also show that the size of the recirculating wake was affected by the complexity of the headland's geometry.

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This paper presents the application of phase averaging to experimental data obtained during scale model testing of a forward facing bent duct oscillating water column (OWC). Phase averaging is applied to both wave probe data and a two dimensional velocity field at the centreline plane of the OWC model obtained using PIV. Results are presented for one monochromatic wave condition. The influence of varied wave frequency is briefly discussed.

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A recent set of coastal experiments (Pattiaratchi et al., 1987), found that the horizontal eddy Reynolds number did not adequately describe the wakes found in the lee of coastal islands. Other flow parameters formulated on bottom friction were found to be much better at describing these wakes. In this paper it is suggested that these findings are caused by the extraction of energy from the flow due to bottom friction, which is the net result of the vertical viscous transfer of momentum through the water column to the seabed. This is in contrast to the horizontal viscous transfer of momentum which results in negligible energy loss to the coast, because of the far larger horizontal scales. It is hypothesized that this difference results in fundamentally different flow regimes and this hypothesis is investigated both analytically and numerically. Conditions for the existence of steady zones of barotropic recirculation under the influence of both horizontal viscosity and bottom friction in the wake behind a bluff body are examined analytically. It is found that such steady recirculation requires the presence of horizontal viscosity and is hindered by the loss of energy due to bottom friction. A numerical model is used to verify and quantify this analytical result for the case of two‐dimensional flow around a circular cylinder, and it is concluded that an appropriate bottom friction number, based on the ratio of scales of the nonlinear and bottom friction terms, may often govern the nature of the recirculation in the lee of coastal islands, instead of the eddy Reynolds number based on horizontal eddy viscosity, as is sometimes assumed.