Incipient flow velocity of non-uniform sediment particles by considering the additional mass force

Experimental study of sediment transport processes and size selectivity of eroded sediment on steep Pisha sandstone slopes

10.5194/egusphere-egu2020-2269 ◽

2020 ◽

Author(s):

Pan Zhang ◽

Pingqing Xiao ◽

Chunxia Yang

Keyword(s):

Sediment Transport ◽

Flow Velocity ◽

Overland Flow ◽

Yellow River ◽

Transport Processes ◽

The Yellow River ◽

Size Selectivity ◽

Coarse Sediment ◽

Sediment Particles ◽

Slope Flow

The Pisha sandstone area on the Ordos Plateau of China is the primary source of coarse sediment of the Yellow River. Sediment size distribution and selectivity greatly affect sediment transport and deposition. Hence, sediment transport processes and size selectivity by overland flow on Pisha sandstone slopes were investigated in this study. Experiments were run with Pisha sandstone soil (bulk density of 1.35 g/cm3) under rainfall intensities of 87 and 133 mm/h with a 25&#176; slope gradient, and the duration of simulated rainfall is 1 h. Sediment and runoff were sampled at 2-min intervals to examine the size distribution change of the eroded sediment. The particle composition, enrichment rate, fractal dimension, and time distribution characteristics of median grain size (d50) of eroded sediment were comprehensively analyzed. Statistical analyses showed that the erosion process of Pisha sandstone slope mainly transported coarse sediment. More than 40% of eroded sediment particles were coarse sediment, which will become the main sediment in the lower reaches of the Yellow River bed. The particle size of eroded sediment tended to gradually decrease with the continuous rainfall but remained larger than the background value of Pisha sandstone soil after refinement. The fractal dimension was positively correlated with the slope flow velocity, while the d50 was negatively correlated with the slope flow velocity. Overall, these findings show a strong relationship between the sediment transport and flow velocity, which indicates that the selectivity and transportation of sediment particles on the Pisha sand slopes is mainly influenced by the hydrodynamic parameters of overland flow. This study provides a methodology and data references for studying the particle selectivity characteristics of eroded sediment and provides a scientific basis for revealing the mechanism of erosion and sediment yield in the Pisha sandstone area of China.

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Experiments on particle—turbulence interactions in the near–wall region of an open channel flow: implications for sediment transport

Journal of Fluid Mechanics ◽

10.1017/s0022112096008324 ◽

1996 ◽

Vol 326 ◽

pp. 285-319 ◽

Cited By ~ 204

Author(s):

Y. Ninto ◽

M. H. Garcia

Keyword(s):

Flow Velocity ◽

Channel Flow ◽

Open Channel ◽

Vertical Component ◽

Open Channel Flow ◽

Viscous Sublayer ◽

Wall Region ◽

Mean Flow ◽

Sediment Particles ◽

Near Wall

A high-speed video system was used to study the interaction between sediment particles and turbulence in the wall region of an open channel flow with both smooth and transitionally rough beds. In smooth flows, particles immersed within the viscous sublayer were seen to accumulate along low-speed wall streaks; apparently due to the presence of quasi-streamwise vortices in the wall region. Larger particles did not tend to group along streaks, however their velocity was observed to respond to the streaky structure of the flow velocity in the wall region. In transitionally rough flows particle sorting was not observed. Coherent flow structures in the form of shear layers typically observed in the near-wall region interacted with sediment particles lying on the channel bottom, resulting in the particles being entrained into suspension. Although there has been some speculation that this process would not be effective in entraining particles totally immersed in the viscous sublayer, the results obtained demonstrate the opposite. The entrainment mechanism appears to be the same independent of the roughness condition of the bottom wall, smooth or transitionally rough. In the latter case, however, hiding effects tend to preclude the entrainment of particles with sizes finer than that of the roughness elements. The analysis of particle velocity during entrainment shows that the streamwise component tends to be much smaller than the local mean flow velocity, while the vertical component tends to be much larger than the local standard deviation of the vertical flow velocity fluctuations, which would indicate that such particles are responding to rather extreme flow ejection events.

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Balance Adjustment of the Gravel-Sand River Downstream Reservoir

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.444-445.1218 ◽

2013 ◽

Vol 444-445 ◽

pp. 1218-1221

Author(s):

Ling Ling Zhu ◽

Hua Ge

Keyword(s):

Flow Velocity ◽

Surface Resistance ◽

Experiment Data ◽

River Bed ◽

The Reformation ◽

Sediment Particles

In this article, the typical phenomenon of bed armoring was firstly summarized based on both the field and experiment data, and then followed by the analysis on its internal influence on the reformation process to the balance status for the gravel-sand rivers. It was pointed out that this phenomenon is caused by the chosen of the flow, that the finer sediment particles are washed away and the coarser ones are left on the river bed surface. This phenomenon firstly restricts the start of the sediment particles on the bed surface, secondly increases the river bed surface resistance and reduces the flow velocity. The comprehensive effect of these two aspects leads to the final balance status for the gravel-sand river.

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