scholarly journals Experimental Study on Uniform and Mixed Bed-Load Sediment Transport under Unsteady Flow

2020 ◽  
Vol 10 (6) ◽  
pp. 2002
Author(s):  
Zihao Duan ◽  
Jie Chen ◽  
Changbo Jiang ◽  
Xiaojian Liu ◽  
Bingbing Zhao
Keyword(s):  
Particle Size ◽  
Sediment Transport ◽  
Unsteady Flow ◽  
Steady Flow ◽  
Transport Rate ◽  
Bed Load ◽  
Sediment Transport Rate ◽  
Particle Size Ratio ◽  
Load Movement ◽  
Sediment Particles

The scouring and deposition of sediment caused by unsteady flows (e.g., storm waves and floods) produces many secondary disasters. The resultant bed-load movement exhibits different transport laws compared with that by steady flow. In this study, the flume experiments were performed to study the bed-load movement under unsteady flow with different velocity skewness. The movement of uniform and non-uniform non-cohesive sediment under unsteady flow as well as the influence of the steady and unsteady flow on sediment transport rate are compared. Additionally, the non-uniform sediment transport formula of fine-to-coarse particle diameter ratio was investigated. The results showed that the sediment transport rate between uniform and non-uniform sand under the same median diameter is different. The non-uniform sediment transport rate is 1.27-, 3.19-, and 0.68-times as large as that in uniform sediment under d50 = 0.664, 1.333, and 2.639 mm under unsteady flow, respectively. For non-uniform sand, the transport rate of non-uniform sand with a larger adjacent particle size ratio (δ = 0.29) was 1.31-times greater than that of the non-uniform sand with a smaller adjacent particle size ratio (δ = 0.50). Moreover, theoretical deduction was carried out and the incipient sediment motion was analyzed from the force mechanism. A new unsteadiness parameter based on the acceleration concept was proposed. The relationship between the travel distance and velocity skewness of sediment particles was set up. The experimental results and theoretical analysis showed that sediment under unsteady flow were easier to start and transport than those under steady flow in the same flow effect. The travel distance of sediment particles was longer under unsteady flow than that under steady flow.

Bed Load Transport under Complex Flow

2011 ◽  
Vol 255-260 ◽  
pp. 3589-3593
Author(s):  
Chun Rong Liu ◽  
Dao Lin Xu
Keyword(s):  
Sediment Transport ◽  
Time History ◽  
Shear Velocity ◽  
Transport Rate ◽  
Bed Load ◽  
Complex Flow ◽  
Sediment Transport Rate ◽  
Load Transport ◽  
History Of ◽  
Load Sediment

In this paper, the backward-facing step flow and the sediment transport downstream step were studied experimentally. The critical incipient bed shear velocity is obtained by the results of bed shear velocity and sediment incipient probability. It was found that the critical incipient bed shear velocity depends on the flow structures under the complex flow. By using the new critical incipient bed shear obtained in this paper and calculating the Shields parameter based on instantaneous bed shear velocity, the bed load sediment transport rate downstream step was given. The time history of the bed profile downstream step was calculated by bed load sediment transport rate and compared that obtained by the digital images. Good agreement was observed.

scholarly journals ON-OFFSHORE SEDIMENT TRANSPORT RATE IN THE SURF ZONE

1980 ◽  
Vol 1 (17) ◽  
pp. 72 ◽  
Author(s):  
Toru Sawaragi ◽  
Ichiro Deguchi
Keyword(s):  
Sediment Transport ◽  
Surf Zone ◽  
Suspended Load ◽  
Transport Rate ◽  
Bed Load ◽  
Relative Importance ◽  
Two Dimensional ◽  
Sediment Transport Rate

In this paper, models of the distribution of net on-offshore sediment transport based on two-dimensional equilibrium beach profiles and an equation of continuity of sediment transport are proposed. Various parameters of net on-offshore sediment transport in those models are discussed. Furhter, the relative importance of bed load and suspended load in the two-dimensional beach deformation are examined by measuring both of them on model beach experiments.

scholarly journals Morphodynamic model of the lower Yellow River: flux or entrainment form for sediment mass conservation?

2018 ◽  
Vol 6 (4) ◽  
pp. 989-1010 ◽  
Author(s):  
Chenge An ◽  
Andrew J. Moodie ◽  
Hongbo Ma ◽  
Xudong Fu ◽  
Yuanfeng Zhang ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Yellow River ◽  
Mass Conservation ◽  
Transport Rate ◽  
Entrainment Rate ◽  
Lower Yellow River ◽  
The Lower Yellow River ◽  
Fine Grained ◽  
Sediment Transport Rate ◽  
Sediment Mass

Abstract. Sediment mass conservation is a key factor that constrains river morphodynamic processes. In most models of river morphodynamics, sediment mass conservation is described by the Exner equation, which may take various forms depending on the problem in question. One of the most widely used forms of the Exner equation is the flux-based formulation, in which the conservation of bed material is related to the stream-wise gradient of the sediment transport rate. An alternative form of the Exner equation, however, is the entrainment-based formulation, in which the conservation of bed material is related to the difference between the entrainment rate of bed sediment into suspension and the deposition rate of suspended sediment onto the bed. Here we represent the flux form in terms of the local capacity sediment transport rate and the entrainment form in terms of the local capacity entrainment rate. In the flux form, sediment transport is a function of local hydraulic conditions. However, the entrainment form does not require this constraint: only the rate of entrainment into suspension is in local equilibrium with hydraulic conditions, and the sediment transport rate itself may lag in space and time behind the changing flow conditions. In modeling the fine-grained lower Yellow River, it is usual to treat sediment conservation in terms of an entrainment (nonequilibrium) form rather than a flux (equilibrium) form, in consideration of the condition that fine-grained sediment may be entrained at one place but deposited only at some distant location downstream. However, the differences in prediction between the two formulations have not been comprehensively studied to date. Here we study this problem by comparing the results predicted by both the flux form and the entrainment form of the Exner equation under conditions simplified from the lower Yellow River (i.e., a significant reduction of sediment supply after the closure of the Xiaolangdi Dam). We use a one-dimensional morphodynamic model and sediment transport equations specifically adapted for the lower Yellow River. We find that in a treatment of a 200 km reach using a single characteristic bed sediment size, there is little difference between the two forms since the corresponding adaptation length is relatively small. However, a consideration of sediment mixtures shows that the two forms give very different patterns of grain sorting: clear kinematic waves occur in the flux form but are diffused out in the entrainment form. Both numerical simulation and mathematical analysis show that the morphodynamic processes predicted by the entrainment form are sensitive to sediment fall velocity. We suggest that the entrainment form of the Exner equation might be required when the sorting process of fine-grained sediment is studied, especially when considering relatively short timescales.

scholarly journals Suspened sediment concentration and sediment transport rate under asymmetric waves.

1990 ◽  
pp. 295-296
Author(s):  
Shunsuke IKEDA ◽  
Makoto IFUKU ◽  
Tadao KAKINUMA ◽  
Hiromitsu GOTOH
Keyword(s):  
Sediment Transport ◽  
Sediment Concentration ◽  
Transport Rate ◽  
Sediment Transport Rate

scholarly journals APPLICATION OF A SEMI-EMPIRICAL LONGSHORE TRANSPORT FORMULATION

2012 ◽  
Vol 1 (33) ◽  
pp. 22
Author(s):  
Giuseppe Barbaro ◽  
Giuseppe Roberto Tomasicchio ◽  
Giovanni Malara ◽  
Felice D'Alessandro
Keyword(s):  
Sediment Transport ◽  
Transport Rate ◽  
Sediment Transport Rate ◽  
Longshore Sediment Transport ◽  
Longshore Transport ◽  
Semi Empirical

The present paper deals with the determination of longshore sediment transport rate. Specifically, case study of Saline Joniche (Reggio Calabria, Italy, is discussed. This case is of interest because, in this location, an artificial basin was built in the 70’s. After few years, port entrance experienced total obstruction by sand. Actually, the area is abandoned and several projects have been proposed for revitalising port activities. This paper discusses a method for estimating the longshore sediment transport rate at Saline Joniche and complements previous methodology.

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