  The observed temporary dark streaks on some dune slopes on Mars may be due to
thin sheets of water (or some other liquid) trickling downhill. This note
corrects conceptual errors in a previous paper (M\"{o}hlmann and Kereszturi
2010, Icarus 207, 654-658) which affect the velocity profile of such flows, and
produce over-estimates of their depths and mass fluxes by factors of almost
two.
