  This paper discusses the effect of rotation on the boundary layer in high
Reynolds number flow over a ridge using a numerical method based on stabilised
finite elements that captures steady solutions up to Reynolds number of order
$10^6$. The results are validated against boundary layer computations in
shallow flows and for deep flows against experimental observations reported in
Machicoane et al. (Phys. Rev. Fluids, 2018). In all cases considered the
boundary layer remains attached, even at large Reynolds numbers, provided the
Rossby number of the flow is sufficiently small. At any fixed Rossby number the
flow detaches at sufficiently high Reynolds number to form a steady
recirculating region in the lee of the ridge. At even higher Reynolds numbers
no steady flow is found. This disappearance of steady solutions closely
reproduces the transition to unsteadiness seen in the laboratory.
