Important in erosion and transport. Froude Number Role of gravity forces in flow, especially where gravity instead of stream head determine flow. If F r is less than 1 then flow is tranquil and the velocity that surface waves move is greater than flow velocity, thus waves can move upstream. F r greater than 1 results in rapid flow. Both rapid and tranquil flows can be turbulent.
Froude number determines the type of bedform that occurs under given flow conditions.
Particle Transport By Fluids Higher flow needed for initial entrainment than transport. Generalized case shown on Hjulstrom or Shields Diagrams. Only well sorted spheres shown but typical sand populations show only moderate scatter about plotted curve. Impact Threshold generally once grains begin to move, they continue do move even when the flow slows slightly. Thus impact threshold is always less than entrainment threshold.