Numerical modeling of hyper-concentrated sediment transport in the lower Yellow River

2008 ◽  
Vol 46 (5) ◽  
pp. 659-667 ◽  
Author(s):  
Qingchao Guo ◽  
Chunhong Hu ◽  
Koniyoshi Takeuchi ◽  
Hiroshi Ishidaira ◽  
Wenhong Cao ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Sediment Transport ◽  
Yellow River ◽  
Lower Yellow River ◽  
The Lower Yellow River

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 Morphodynamic model of Lower Yellow River: flux or entrainment form for sediment mass conservation?

2018 ◽  
Author(s):  
Chenge An ◽  
Andrew J. Moodie ◽  
Hongbo Ma ◽  
Xudong Fu ◽  
Yuanfeng Zhang ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Yellow River ◽  
Mass Conservation ◽  
Transport Rate ◽  
Lower Yellow River ◽  
The Lower Yellow River ◽  
Fine Grained ◽  
Sediment Transport Rate ◽  
Sediment Mass ◽  
Bed Material

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 streamwise gradient of the sediment transport rate. An alternate 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. In the flux form, sediment transport is regarded to be in local equilibrium (i.e., sediment transport rate locally equals sediment transport capacity). However, the entrainment form does not require this constraint: the sediment transport rate 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 of flux-based and entrainment-based morphodynamics under conditions typical of the Lower Yellow River, but simplified for clarity of comparison. We used sediment transport equations specifically designed 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.

The High Efficient Sediment-Transport Water Volume in the Lower Yellow River

2011 ◽  
Vol 403-408 ◽  
pp. 228-234
Author(s):  
Jun Yan ◽  
Biao Liang ◽  
Yu Hua Zhang ◽  
Hui Cao
Keyword(s):  
Sediment Transport ◽  
Transport Process ◽  
Yellow River ◽  
Water Volume ◽  
Lower Yellow River ◽  
The Lower Yellow River ◽  
Calculating Method ◽  
High Efficient ◽  
Xiaolangdi Reservoir ◽  
High Sediment

Analyzed the sediment-transport process in high sediment-laden river, the new concept and calculating method for sediment-transport water volume are proposed. Based on field data of sediment and water volume in the Lower Yellow River from 1950 to 2000, the sediment-transport water volume and unit sediment-transport water volume in LYR are calculated. Meanwhile, relations between them and influencing factors are confirmed to calculate efficient sediment-transport water volume after construction of the Xiaolangdi reservoir. Results gained from these functions are consistent well with the facts of real water-sediment regulation in LYR.

Channel geometry adjustments in response to hyperconcentrated floods in a braided reach of the Lower Yellow River

2018 ◽  
Vol 42 (3) ◽  
pp. 352-368 ◽  
Author(s):  
Jie Li ◽  
Junqiang Xia ◽  
Meirong Zhou ◽  
Shanshan Deng ◽  
Zenghui Wang
Keyword(s):  
Sediment Transport ◽  
Yellow River ◽  
Empirical Relation ◽  
Characteristic Parameter ◽  
Transport Rate ◽  
Channel Geometry ◽  
Lower Yellow River ◽  
The Lower Yellow River ◽  
Sediment Transport Rate ◽  
Braided Reach

Hyperconcentrated floods with more than 200–300 kg/m3 sediment concentrations often occur in the Lower Yellow River (LYR) during flood seasons, which leads to unique fluvial processes in the braided reach of the LYR. The investigation of channel geometry adjustments in response to hyperconcentrated floods can not only help to gain a better understanding of associated fluvial processes, but also is significant for making flood control strategies in the braided reach. In this study, pre- and post-flood bankfull channel dimensions in the braided reach were calculated based on the observed cross-sectional profiles in 15 years with the occurrence of hyperconcentrated flood events. Adjustments in channel geometry at section- and reach-scales were investigated, with several factors influencing adjustments in reach-scale channel geometry being analyzed. It indicates that the mean sediment transport rate was a key factor influencing the adjustment index, although pre-flood channel geometry and sediment deposition can also affect the index to some extent. An empirical relationship was developed between the characteristic parameter representing the pre- and post-flood channel geometries and mean sediment transport rate in hyperconcentrated floods. Eleven datasets were used to calibrate the parameters in the empirical relation, with the datasets in 1973, 1988, 1995, and 2002 verifying the relation. The calculated post-flood characteristic parameter of channel geometry using the empirical relation agreed well with observed data, and the proposed method can be used to predict the reach-scale adjustment of channel geometry during hyperconcentrated floods in alluvial rivers.

BP Model Used for Calculating the High Efficient Sediment-Transport Water Volume in the Lower Yellow River

2011 ◽  
Vol 225-226 ◽  
pp. 1345-1349
Author(s):  
Jun Yan ◽  
Biao Liang ◽  
Hui Cao ◽  
Yu Hua Zhang
Keyword(s):  
Sediment Transport ◽  
Transport Process ◽  
Yellow River ◽  
Water Volume ◽  
Lower Yellow River ◽  
The Lower Yellow River ◽  
Calculating Method ◽  
High Efficient ◽  
Set Up ◽  
Bp Model

Analyzed the sediment-transport process in the Lower Yellow river, the concept and normal calculating method for sediment-transport water volume are proposed. Based on field data of sediment and water volume in the Lower Yellow River from 1950 to 2000, the sediment-transport water volume and unit sediment-transport water volume in LYR are calculated. Furthermore, BP model is set up to calculate the high efficient sediment-transport water volume in the Lower Yellow River. Compared the results of BP model with normal calculating method, BP model is confirmed for calculating the high efficient sediment-transport water volume in the Lower Yellow river.

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