| The Loess Plateau which is situated on the middle reaches of the Yellow River in Northwest China,suffers from soil erosion and wind-sand damage due to loose soil,scarce vegetation and fragile ecological environment.As it serves as the main source of sediment in the Yellow River,studying on soil erosion in this area has become increasingly important.Water erosion is the most primary means of soil erosion.The hydrodynamic characteristics of sediment-laden flow and calculation methods of sediment transport capacity are of great value to explore mechanisms of soil water erosion.The major conclusions are as follows:(1)Reynolds number ranged from 296.6 to 1249.4,meaning that the sediment-laden flow is in laminar and transitional flow zones.It indicates that the sediment-laden flow could "control the turbulence" to a certain extent and transform turbulent flow into laminar or transitional flow.The range of Froude number varied from 2.032 to 2.874,which represents that the sediment-laden flow is in a state of jet flow.The Froude number kept relatively stable in the clear water test,and the sediment content had a significant influence on it.Moreover,the relationship between resistance coefficient and sediment content is complex.In the initial stage,the resistance coefficient decreased with sediment content,and then the resistance coefficient rose with when sediment concentration increased.The mean velocity of sediment-laden flow had a certain relationship with discharge and sediment content,and the effect of discharge on mean velocity was more significant than sediment content on that.(2)By choosing two particle size of sediment experiment results proved that sediment transport capacity showed an increasing trend with the increase of slope and unit discharge,and had a power function relationship with them.In addition,unit discharge had a more significant impact on sediment transport capacity than slope.The mean velocity of sediment-laden flow was sensitive to slope and unit discharge,and also had a power function with them.The relationship between mean velocity and sediment transport capacity was mainly affected by mean particle size.The sediment transport capacity of slope flow could be expressed by the power function of shear force,which was affected by soil types.Among the power indexes,the relationship between stream power,effective stream power and sediment transport capacity are not affected by the change of mean particle size.The relationship between unit stream power and sediment transport capacity is seriously affected by the change of mean particle size,and their index of power function are different.After considering the critical flow power W0,the relationships between stream power and sediment transport capacity are same under two mean particle size,and the effective flow power should still be investigated in future research.(3)According to the test for cohesive soil and other kinds of non-cohesive sediment,it could be seen that when calculating sediment transport capacity of non-cohesive sediment flow on slopes,the applicability of velocity index is poor among the existing intensity indexes of three schools.Power indexes could be seen as a composite factor to predict sediment transport capacity of different median particle sizes,especially the effective flow power.Therefore,the flow intensity index and volume sediment concentration of dimensionless effective flow power were regarded as influence factors of sediment transport capacity.As for the formula of total sediment,it was given by calibration in the form of power function.And it is more accurate in calculating the sediment transport capacity of soils with different grain sizes,showing that the sediment transport capacity of slope flow is obviously different from that of river flow. |
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