The differential equation of the bed sediment movement in clear water was used and the method for computing equilibrium time of scour was elaborated. New hydraulic criterion is proposed to find equilibrium time of scour near elliptical guide banks. According to the method presented the equilibrium time of scour is depending on: Froude number, contraction rate of the flow, bed layering, grain size diameter, local flow velocity, and ratio of local velocity to critical one. The test results of scour evaluation in time with duration of 7 hours were prolonged till the equilibrium stage of scour [1] and compared with equilibrium time of scour calculated by the method presented, and they were in good agreement.