A Froude‐scaled model of a bedrock‐alluvial channel reach: 2. Sediment cover
A Froude‐scaled model of a bedrock‐alluvial channel reach: 2. Sediment cover
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基岩冲积河道河段的弗劳德比例模型：2.沉积物覆盖
DOI：
10.1002/2015jf003709
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
T. Hoey
中科院分区：
文献类型：
--
作者：
R. Hodge;T. Hoey
前人对基岩-冲积河道泥沙盖度的研究主要集中在泥沙总盖度上，而不是河道内盖度的空间分布。后者很重要，因为它决定了防止侵蚀的基岩区域以及泥沙输送路径的起点和终点。我们使用1：10弗劳德比例尺模型对基岩-冲积河道18×9 m的河段进行研究，以研究沉积物斑块的产生和侵蚀，从而研究水流、河床地形和沉积物动力学之间的空间关系。文中给出了该床层的水力数据。在这些试验中，在模型河段的上游边缘提供一定数量的泥沙，作为单输入，在一系列排放中的每一种。这些沉积物形成了斑块，一旦这些斑块稳定下来，水流就会稳步增加，以侵蚀这些斑块。总而言之：(1)斑块倾向于在河床的最低处开始形成，但地形诱导的高流速区域会抑制斑块的发展；(2)在低泥沙输入时，沉积物斑块的范围由河床地形决定，可能对确切的泥沙供应量不敏感；(3)在较高的泥沙输入时，会产生更广泛的斑块，由颗粒-颗粒和颗粒-水流相互作用稳定，受河床地形的影响较小。因此，基岩地形可能是沉积物斑块动态的一个重要制约因素，因此要求地形度量纳入其可及范围内的可变性。泥沙输入事件的大小和时间控制着河流尺度的泥沙复盖。
Previous research into sediment cover in bedrock‐alluvial channels has focussed on total sediment cover, rather than the spatial distribution of cover within the channel. The latter is important because it determines the bedrock areas that are protected from erosion and the start and end of sediment transport pathways. We use a 1:10 Froude‐scaled model of an 18 by 9 m reach of a bedrock‐alluvial channel to study the production and erosion of sediment patches and hence the spatial relationships between flow, bed topography, and sediment dynamics. The hydraulic data from this bed are presented in the companion paper. In these experiments specified volumes of sediment were supplied at the upstream edge of the model reach as single inputs, at each of a range of discharges. This sediment formed patches, and once these stabilized, flow was steadily increased to erode the patches. In summary: (1) patches tend to initiate in the lowest areas of the bed, but areas of topographically induced high flow velocity can inhibit patch development; (2) at low sediment inputs the extent of sediment patches is determined by the bed topography and can be insensitive to the exact volume of sediment supplied; and (3) at higher sediment inputs more extensive patches are produced, stabilized by grain‐grain and grain‐flow interactions and less influenced by the bed topography. Bedrock topography can therefore be an important constraint on sediment patch dynamics, and topographic metrics are required that incorporate its within‐reach variability. The magnitude and timing of sediment input events controls reach‐scale sediment cover.