Flume study of the effect of relative depth on the incipient motion of coarse uniform sediments

An experimental study of the incipient motion of coarse uniform sediments w as undertaken in an 8 m long by 0.3 m wide tilting flume. The concept of cr itical shear stress for the initial motion of streambeds has been linked to the probability of sediment entrainment through the intensity of sediment transport. The experiments have revealed that critical flow conditions for uniform sediment motion are dependent not only on the grain size but also o n the ratio of flow depth to grain diameter. A revised Shields diagram rela ting critical stress, grain Reynolds number, and depth to grain size ratio has been derived. This has implications for the calculation of sediment tra nsport rates, design of stable alluvial channels, and physical hydraulic mo deling.