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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Experimental study on transient and steady-state dynamics of bedforms in supply limited configuration
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Experimental study on transient and steady-state dynamics of bedforms in supply limited configuration

机译：有限供应条件下床架瞬态和稳态动力学的实验研究

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The purpose of the present study is to investigate experimentally the development of bedforms in a configuration where the sediment supply is limited. The experimental setup is a rectangular closed duct combining an innovative system to control the rate of sediment supply Q_(in), and a digitizing system to measure in real time the 3D bedform topography. We carried out different sets of experiments with two sediment sizes (100-μm and 500-μm) varying both the sediment supply and the water flow rate to obtain a total of 46 different configurations. After a transient phase, steady sub-centimeter bedforms of various shapes have been observed: barchans dunes, straight transverse dune, linguoid transverse dunes and bedload sheets. Height, spacing, migration speed, and mean bed elevation of the equilibrium bedforms were measured. For a given flow rate, two regimes were identified with fine sediment: (i) a monotonic increasing regime where the equilibrium bedform height and velocity increase with the sediment supply rate Q_(in) and (ii) an invariant regime for which both parameters are almost independent of Q_(in). For coarse sediment, only the first regime is observed. We interpret the saturation of height and velocity for fine sediment bedforms as the transition from a supply-limited regime to a transport-limited regime in which the bedload flux has reached its maximum value under the prevailing flow conditions. We also demonstrate that all experiments can be rescaled if the migration speed and height of the bedforms are, respectively, divided and multiplied by the cube of the shear velocity. This normalization is independent of grain size and of bedform morphology. These experimental results provide a new quantification of the factors controlling equilibrium height and migration speed of bedforms in supply-limited conditions against which theoretical and numerical models can be tested.
机译：本研究的目的是通过实验研究沉积物供应受限的构造中床形的发育。实验装置是矩形封闭管道，结合了创新的系统以控制沉积物的供应速度Q_（in）和数字化系统以实时测量3D床形地形。我们用两种沉积物大小（100-μm和500-μm）改变了沉积物的供给量和水的流速进行了不同的实验，总共获得了46种不同的配置。在过渡阶段之后，已观察到各种形状的稳定的亚厘米床形：巴汉斯沙丘，笔直的横向沙丘，舌状横向沙丘和床单。测量了平衡床形的高度，间距，迁移速度和平均床高。对于给定的流速，确定了两种含细沉积物的状态：（i）单调增加的状态，其中平衡床形高度和速度随沉积物供应速率Q_（in）的增加而增加;（ii）不变的状态，两个参数均为几乎独立于Q_（in）。对于较粗的沉积物，仅观察到第一种状态。我们将精细沉积物床形的高度和速度的饱和解释为从供给受限状态到运输受限状态的过渡，在这种过渡中，基础负荷通量在主要流动条件下已达到最大值。我们还证明，如果将床形的迁移速度和高度分别除以并乘以剪切速度的立方，则可以重新缩放所有实验。该归一化与晶粒尺寸和床形形态无关。这些实验结果提供了一种新的量化方法，用于量化在供应受限的条件下控制床形平衡高度和迁移速度的因素，从而可以对理论和数值模型进行测试。

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