The suspended sediment transport equation and its near-bed sediment flux

Abstract

The suspended sediment transport equation and its near-bed sediment flux are one of the key problems of sediment transport research under nonequilibrium condition. Based on the three-dimensional primitive suspended transport equation, the two-dimensional suspended sediment transport equation is deduced. The derived process indicates that the physical essence of the near-bed sediment flux is right the bottom boundary condition for the suspended sediment transport equation. This paper analyzes the internal relations between the two methods of sediment carrying capacity and shear stress in common use, points out the consistency of these two methods in terms of form and physical meaning, and unifies these two methods theoretically. Furthermore, based on the analysis and comparison of the expressions of the near-bed sediment flux, this paper summarizes some problems to which attention should be paid, thus offering a novel approach to the study and the solution of the problems of suspended sediment transport and exchange flux of near-bed water sediment.suspended sediment transport equation, near-bed sediment flux, sediment carrying capacity, shear stress Domestic sediment study starts from the time of the construction of the Dujiang Dam Water Diversion Project (BC 256) and through the efforts made by the older generation of sediment experts it has already established its own status worldwide, with its research system combined with east and west [1][2][3][4][5][6][7][8] .When studying river, estuary and coast suspended sediment movement, different researchers often employ different methods to determine the exchange flux between suspended load and bed load near bed (near-bed sediment flux). The method of sediment carrying capacity and the method of shear stress are usually used to deal with the near-bed sediment flux, both of which result in a lot of expressions of near-bed sediment flux mostly done on the basis of empirical relations. However, all these expressions lack universality, and also have points of irrationality. For the diversiform expressions and different applications of near-bed sediment flux, there are many different kinds of interpretations in terms of theories and methods of sediment movement. This has positive effect on sediment study, but on the other hand, it would also bring some chaos to the further research of sediment. This paper starts, firstly, from the brief derivation of two-dimensional suspended sediment transport equation due to the three-dimensional suspended sediment transport equation, and then searches for the real physical meanings and the internal relations between the method of sediment carrying capacity and the method of shear stress, analyzes the consistency in the sense of form and physical meaning, and unifies theoretically the mathematic expressions of the two methods. Finally, two kinds of expressions usually used to represent the near-bed sediment flux are compared and summarized,

A new technology for suspended sediment simulation in Lake Taihu, China: Combination of hydrodynamic modeling and remote sensing

“…There are mainly two types of criterions for calculating the sediment erosion flux at the bed: critical shear stress and sediment carrying capacity. Although they have different forms, their essence is identical (Li et al, 2008). Here we chose the critical stress method (Gailani et al, 1991 to judge erosion flux:…”

The Influence of Vertical Velocity Distribution on the Calculation of Suspended Sediment Concentration

“…In addition, the distribution of suspended sediment in (21) is slightly diferent for diferent values of the vertical time-averaged velocity coefcient. [17,[38][39][40]. Te velocity range is 0.072 ∼ 3.12 m/s, the sediment concentration range is 0.002 ∼ 2.27 kg/m 3 , the water depth is 5 ∼ 30 m, and the median particle size is 0.01 ∼ 0.2 mm.…”

Challenges to the representation of suspended sediment transfer using a depth‐averaged flux

“…The former method is adopted in Deflt3D (Deltares, 2014), which is a physicsbased morphodynamic model extensively used for various hydrodynamic and sediment transport studies (Lesser et al, 2004;van Maren, 2007;Hu et al, 2009;Caldwell and Edmonds, 2014). Li et al (2009) argued that there was a consistency of these two methods in form, but not in their physical mechanisms. Li et al (2009) argued that there was a consistency of these two methods in form, but not in their physical mechanisms.…”

“…The latter method is mainly used in onedimensional (1D) (Zhou and Lin, 1998;Guo and Jin, 1999;Wu et al, 2004) or two-dimensional (2D) (Wu, 2004;Yang et al, 2014) depth-integrated SST models. Li et al (2009) argued that there was a consistency of these two methods in form, but not in their physical mechanisms. Intrinsically, the latter corresponds to the sediment saturation recovery process within a certain length or timescale, as mentioned earlier, rather than an instantaneous transition; while the former represents the rapid reaction to the variation of bed shear stress like bedload by means of algebraic relationships, excluding the effects of the sediment saturation recovery process.…”