  If a body in a stream is provided with small ridges aligned in the local flow
direction, a remarkable drag reduction can be reached under turbulent flow
conditions. This surprising phenomenon is called the 'shark skin effect'. We
demonstrate, that a reduction of resistance can also be reached in creeping
flows if the ridges are aligned perpendicular to the flow direction. We
especially consider in gravity-driven film flows the effect of the bottom
topography on the mean transport velocity.
