Abstract: The minimun flow rate which can keep the open channel without siltation is called the critical velocity.It is significant to the design of trailing hydro-transport.According to the assumption of the minimum energy loss of the muddy water under the critical condition,a formula is obtained by using the differential method in maths.Based on both theory and experiments,the derivation process of this formula is clear and correct.Many factors such as the characteristic parameters of the open channel and the two-p...