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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Bar dynamics and bifurcation evolution in a modelled braided sand-bed river
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Bar dynamics and bifurcation evolution in a modelled braided sand-bed river

机译：模拟的辫状沙床河中的坝动力学和分叉演化

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Morphodynamics in sand-bed braided rivers are associated with simultaneous evolution of mid-channel bars and channels on the braidplain. Bifurcations around mid-channel bars are key elements that divide discharge and sediment. This, in turn, may control the evolution of connected branches, with effects propagating to both upstream and downstream bifurcations. Recent works on bifurcation stability and development hypothesize major roles of secondary flow and gradient advantage. However, this has not been tested for channel networks within a fully developed dynamic braided river. A reason for this is a lack of detailed measurements with sufficient temporal and spatial length, covering multiple bifurcations. Therefore we used a physics-based numerical model to generate a dataset of bathymetry, flow and sediment transport of an 80 km river reach with self-formed braid bars and bifurcations. The study shows that bar dissection due to local transverse water surface gradients is the dominant bifurcation initiation mechanism, although conversion of unit bars into compound bars dominates in the initial stage of a braided river. Several bifurcation closure mechanisms are equally important. Furthermore, the study showed that nodal point relations for bifurcations are unable to predict short-term bifurcation evolution in a braided river. This is explained by occurrence of nonlinear processes and non-uniformity within the branches, in particular migrating bars and larger-scale backwater-effects, which are not included in the nodal point relations. Planform morphology, on the other hand, has predictive capacity: bifurcation angle asymmetry and bar-tail limb shape are indicators for near-future bifurcation evolution. Remote sensing data has predictive value, for which we developed a conceptual model for interactions between bars, bifurcations and channels in the network. We conducted a preliminary test of the conceptual model on satellite images of the Brahmaputra. Copyright (c) 2015John Wiley & Sons, Ltd.
机译：沙床辫状河的形态动力学与辫状平原上的中河道和河道同时演化有关。中通道横梁周围的分叉是划分排放和沉积物的关键因素。继而，这可以控制连接的分支的演变，其影响传播到上游和下游分支。关于分叉稳定性和发展的最新研究假设了次要流动和梯度优势的主要作用。但是，这尚未在完全发达的动态辫状河中进行过渠道网络测试。其原因是缺乏具有足够的时间和空间长度的，覆盖多个分支的详细测量。因此，我们使用了基于物理的数值模型来生成一个80 km的测深，水流和泥沙输送数据集，该数据集具有自编成的编织条和分叉。研究表明，尽管在辫状河的初始阶段，单位棒向复合棒的转化仍占主导地位，但由于局部横向水面梯度引起的棒剥离是主要的分叉引发机制。几种分叉闭合机制同样重要。此外，研究表明，分叉的节点关系不能预测辫状河的短期分叉演变。这可以通过在分支内发生非线性过程和不均匀性来解释，特别是在迁移点和更大范围的回水效应中，这不包括在节点关系中。另一方面，平面形态具有预测能力：分叉角不对称和尾巴四肢形状是近期分叉演化的指标。遥感数据具有预测价值，为此，我们开发了一个概念模型，用于网络中条形，分叉和通道之间的交互。我们对雅鲁藏布江的卫星图像进行了概念模型的初步测试。版权所有（c）2015 John Wiley＆Sons，Ltd.

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