Dimensionless critical shear stress in gravel-bed rivers

作者：Petit Francois^*; Houbrechts Geoffrey; Peeters Alexandre; Hallot Eric; Van Campenhout Jean; Denis Anne Cecile

来源：Geomorphology, 2015, 250: 308-320.

DOI：10.1016/j.geomorph.2015.09.008

• Critical shear stress
• Shields criterion
• Grain shear stress
• Shear velocity
• Gravel-bed rivers
• Meuse basin

This paper first compiles critical shear stress values from 26 studies of gravel-bed rivers (GBRs) worldwide. The most frequently proposed value of the Shields criterion (theta(c)) is 0.045, but three major groups with theta(c) values ranging from <0.030 to >0.100 were identified.
Second, dimensionless critical shear stresses (the Shields criterion) were evaluated for 14 GBRs (18 sites) with watershed areas ranging from 12 to 3000 km(2). Different approaches were used to identify the initial movement of the bed material: painted and PIT-tag pebbles, sediment traps, and bedload samplers. The Shields criterion (theta(c)) was estimated using the total shear stress (tau) and the grain shear stress (tau'). Several shear stresses were also estimated using shear velocities. For bedload transport, we obtained an average Shields criterion (theta(c)) of 0.040. The values were higher in small rivers (>0.050) than larger rivers (<0.030) because of more significant bedform shear stresses. The Shields criterion (theta'(c)) was lower when the grain shear stress (tau') was used and only reached 0.019. Different values are also proposed in relation to the type of mobilization: the theta(c), value for partial transport was similar to 0.025 and exceeded 0.040 for full transport (usually reached in association with discharges with a 10-year return period). The values based on the results of sediment traps and a bedload sampler were greater than those obtained using tracers, but these differences are smaller than those usually reported in the literature.

• 出版日期2015-12-1