Theory 40/Transport & flow/Sediment transport
Movement Starts at a Shields Threshold
The claim
Sediment begins to move above a threshold in the ratio of bed shear to particle submerged weight, so the critical velocity depends on grain density.
01Mechanism
Lift and drag must exceed the weight holding the grain.
02Prediction
Entrainment should track the ratio.
03Refutation
Entrainment tracking velocity alone would remove grain weight.