Abstract: The deceleration flow, called backwater in engineering, is a pattern of non-uniform flow. Research of bed sediment’s incipient motion under deceleration flow condition is of great application value in water conservancy project.In line with generalized flume experiment and field measured natural flow data, four classic formulae for incipient flow velocity are verified and compared. Results suggest that all the four classic formulae are suitable for deceleration flow condition in flume experiment, yet difference still exists in the selection of particle size. Representative particle size d₉₅ is of good accuracy. Moreover, the incipient motion of sediment under deceleration flow meets the Shields curve in general. According to verification of power incipient motion formula, the dimensionless incipient power is 0.0191, which can be used as the criterion of bed sediment initiation.

Key words: bed sediment, deceleration flow, flume experiment, incipient motion standard, experimental study