4. Conclusion

3.4.2 Dimensionless shear stress (τ\*) vs. shear Reynolds number (Re\*) for the incipient

The relationship between the dimensionless shear Reynolds number and the dimensionless shear stress for the incipient motion of the coarsest sediment

(D<sup>50</sup> = 0.58 mm) and that of the finest sediment (D50 = 0.47 mm) under both open flow condition and rough ice-covered flow condition has been shown in Figure 12.

1. With increase in the dimensionless shear Reynolds number, the dimensionless shear stress increases correspondingly. For all three sands, the larger the dimensionless shear Reynolds number, the greater the dimensionless shear stress for the incipient motion of bed material. However, for the same

dimensionless shear stress, the finer sediment has a lower dimensionless shear

2. In terms of the impacts of ice cover on the incipient motion of bed material, for the same grain size of sediment, the rough ice cover requires an average lower

dimensionless shear stress for the incipient motion of bed material under rough ice-covered flow condition is lower than that under open flow conditions.

Of note, Wang et al. [24] also studied dimensionless shear stress (τ\*) against

ice-covered condition. Their result showed that for the same sediment grain size, larger values of the shear Reynolds number lead to the larger values of the dimensionless shear stress for incipient motion of bed material. It can also be said that, for the same dimensionless shear stress, the finer sediment particles need a lower value

Dimensionless shear stress (τ\*) vs. shear Reynolds number (Re\*) for the incipient motion of the finest sediment (D<sup>50</sup> = 0.47 mm) and the coarsest sediment (D<sup>50</sup> = 0.58 mm) under open and rough ice-covered flow

Reynolds number for the incipient motion of sediment particles.

dimensionless shear stress which implies that the threshold of the

shear Reynolds number (Re\*) for the incipient motion of sediment under

of shear Reynolds number for the incipient motion of sediment.

From Figure 12, the following observations can be noted:

Current Practice in Fluvial Geomorphology - Dynamics and Diversity

motion of sediment

Figure 12.

conditions.

24

In the current study, 108 experiments were done in a large-scale flume with nonuniform sediment to investigate the local scour process, velocity distribution, and incipient motion of sediment particles around four pairs of side-by-side cylindrical bridge piers under open-channel, smooth-covered, and rough-covered flow conditions. The following conclusions can be drawn from the current study:


Current Practice in Fluvial Geomorphology - Dynamics and Diversity

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