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Water Resources Research

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Critical shear stress and unit discharge flow competence models were tested against coarse bed load data from Dupuyer Creek, Montana, United States. Maximum particle sizes sampled (Dmax) and D-50 to D-90 percentiles in the bed load grain size distribution were well correlated with both shear stress and unit discharge. Bed load grain sizes became coarser with increasing flow strength. For the D-max curve, Shields dimensionless parameter for the surface D-50 was estimated at 0.044, and the exponent for relative particle size (D-i/ D-50) was - 0.59. In the unit discharge criterion the critical flow to entrain the surface D50 was poorly predicted. Flow competence relationships based on D-max are prone to the influence of outliers and sample mass variability. The mean of the three largest particles, D-max ( 3), is more sensitive to changes in flow strength than the D-50 to D-90 bed load grain sizes, and may represent a good compromise.




© 2007, American Geophysical Union.