We study how a coastal obstruction (peninsula or coastal island) aects the three-dimensional barotropic currents in an oblong rectangular basin with variable bathymetry across the basin width. The transverse depth pro®le is asymmetric and the peninsula or island lies in the middle of the long side of the rectangle. A semi-spectral model for the Boussinesq-approximated shallow water equations, developed in Haidvogel et al. and altered for semi-implicit numerical integration in time in Wang and

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... tter, is used to ®nd the steady barotropic state circulation pattern to external winds. The structural (qualitative) rearrangements and quan-ti2tative features of the current pattern are studied under four principal wind directions and dierent lengths of the peninsula and its inclination relative to the shore. The essentially non-linear relationships of the water¯ux between the two sub-basins (formed by the obstructing peninsula) and the corresponding crosssectional area left open are found and analysed. It is further analysed whether the depth-integrated model, usually adopted by others, is meaningful when applied to the water exchange problems. The¯ow through the channel narrowing is quantitatively estimated and compared with the three-dimensional results. The dynamics of the vortex structure and the identi®cation of the upwelling/down-welling zones around the obstruction are discussed in detail. The in¯uence of the transformation of the peninsula into a coastal island on the global basin circulation is considered as are the currents in the channel. The geometric and physical reasons for the anisotropy of the current structure which prevail through all obtained solutions are also discussed.