Influence of Dunes on Channel-Scale Flow and Sediment Transport in a Sand Bed Braided River
Influence of Dunes on Channel-Scale Flow and Sediment Transport in a Sand Bed Braided River
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沙丘对沙床辫状河河道尺度水流和输沙的影响
DOI：
10.1029/2020jf005571
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Unsworth C
中科院分区：
文献类型：
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作者：
Unsworth C
目前对沙丘在控制沙坝和河道尺度过程以及河流形态动力学方面所起作用的理解还不完整。我们提出了一个综合的数值模拟和现场监测研究的结果，隔离沙丘的深度平均和近床流结构的影响，与形态动力学建模的影响。使用三维计算流体动力学代码OpenFOAM进行数值模拟，使用数字高程模型（DEM）量化400 m × 100 m航道内的时间平均水流结构，其中（i）模型中存在沙丘和沙洲，（ii）仅解析沙洲尺度地形特征（沙丘被移除）。这两个模拟结果的比较表明，沙丘增强横向流动，并减少酒吧顶部的速度高达30%。沙丘在比单个底形更大的空间尺度上影响模拟泥沙输运的方向，这是因为沙丘对近床水流结构的地形转向有影响。我们发现，沙丘可以放大，抑制，甚至逆转沉积物的偏转下横向酒吧斜坡，这是密切相关的三维和倾斜定向沙丘。使用深度平均形态动力学模型中实施的理论计算的沉积物输运模式表明，即使存在沙丘，沉积物的重力偏转仍受条形地形的控制。然而，需要改进深度平均形态动力学模型中水流和泥沙输运的参数化，以考虑沙丘和沙洲尺度形态对近床水流和泥沙输运的影响。
Current understanding of the role that dunes play in controlling bar and channel‐scale processes and river morphodynamics is incomplete. We present results from a combined numerical modeling and field monitoring study that isolates the impact of dunes on depth‐averaged and near‐bed flow structure, with implications for morphodynamic modeling. Numerical simulations were conducted using the three‐dimensional computational fluid dynamics code OpenFOAM to quantify the time‐averaged flow structure within a 400 m × 100 m channel using digital elevation models (DEMs) for which (i) dunes and bars were present within the model and (ii) only bar‐scale topographic features were resolved (dunes were removed). Comparison of these two simulations shows that dunes enhance lateral flows and reduce velocities over bar tops by as much as 30%. Dunes influence the direction of modeled sediment transport at spatial scales larger than individual bedforms due to their effect on topographic steering of the near‐bed flow structure. We show that dunes can amplify, dampen, or even reverse the deflection of sediment down lateral bar slopes, and this is closely associated with 3‐D and obliquely orientated dunes. Sediment transport patterns calculated using theory implemented in depth‐averaged morphodynamic models suggest that gravitational deflection of sediment is still controlled by bar‐scale topography, even in the presence of dunes. However, improved parameterizations of flow and sediment transport in depth‐averaged morphodynamic models are needed that account for the effects of both dune‐ and bar‐scale morphology on near‐bed flow and sediment transport.