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首页> 外文期刊>Journal of geophysical research. Earth Surface: JGR >Entrainment, motion, and deposition of coarse particles transported by water over a sloping mobile bed
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Entrainment, motion, and deposition of coarse particles transported by water over a sloping mobile bed

机译：水在倾斜的移动床上带走的粗颗粒的夹带，运动和沉积

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In gravel bed rivers, bed load transport exhibits considerable variability in time and space. Recently, stochastic bed load transport theories have been developed to address the mechanisms and effects of bed load transport fluctuations. Stochastic models involve parameters such as particle diffusivity, entrainment, and deposition rates. The lack of hard information on how these parameters vary with flow conditions is a clear impediment to their application to real-world scenarios. In this paper, we determined the closure equations for the above parameters from laboratory experiments. We focused on shallow supercritical flow on a sloping mobile bed in straight channels, a setting that was representative of flow conditions in mountain rivers. Experiments were run at low sediment transport rates under steady nonuniform flow conditions (i.e., the water discharge was kept constant, but bed forms developed and migrated upstream, making flow nonuniform). Using image processing, we reconstructed particle paths to deduce the particle velocity and its probability distribution, particle diffusivity, and rates of deposition and entrainment. We found that on average, particle acceleration, velocity, and deposition rate were responsive to local flow conditions, whereas entrainment rate depended strongly on local bed activity. Particle diffusivity varied linearly with the depth-averaged flow velocity. The empirical probability distribution of particle velocity was well approximated by a Gaussian distribution when all particle positions were considered together. In contrast, the particles located in close vicinity to the bed had exponentially distributed velocities. Our experimental results provide closure equations for stochastic or deterministic bed load transport models.
机译：在砾石河床中，河床荷载运输在时间和空间上表现出很大的可变性。近来，已经开发了随机的床载运输理论来解决床载运输波动的机理和影响。随机模型涉及诸如粒子扩散率，夹带和沉积速率等参数。缺乏有关这些参数如何随流动条件变化的硬信息，显然阻碍了它们在现实世界中的应用。在本文中，我们通过实验室实验确定了上述参数的闭合方程。我们将重点放在直通道的倾斜移动床上的浅超临界流上，该设置代表了山区河流的流动状况。在稳定的非均匀流动条件下（即排水量保持恒定，但床形发育并向上游迁移，使流动不均匀），在低泥沙输送速率下进行了实验。使用图像处理，我们重构了粒子路径，以推断出粒子速度及其概率分布，粒子扩散率以及沉积和夹带速率。我们发现，平均而言，粒子的加速度，速度和沉积速率对局部流动条件有响应，而夹带速率则强烈取决于局部的床层活动。颗粒扩散率随深度平均流速呈线性变化。当一起考虑所有粒子位置时，粒子速度的经验概率分布可以很好地近似于高斯分布。相反，位于床附近的颗粒具有指数分布的速度。我们的实验结果为随机或确定性的床载运输模型提供了闭合方程。

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