Production of topographic vorticity by vortex stretching and bottom friction in circularly rotating currents in shallow tidal areas is studied as a function of topographic length scale. It is shown that vorticity is transferred from the oscillating field to the mean (residual) field and to higher harmonics (the overtides). For a given slope in the bottom topography the transfer is largest for a topographic wave length of the order of the tidal displacement amplitude....