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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >An experimental study of discharge partitioning and flow structure at symmetrical bifurcations
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An experimental study of discharge partitioning and flow structure at symmetrical bifurcations

机译：对称分岔排出分配和流动结构的实验研究

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Recent research has examined the factors controlling the geometrical configuration of bifurcations, determined the range of stability conditions for a number of bifurcation types and assessed the impact of perturbations on bifurcation evolution. However, the flow division process and the parameters that influence flow and sediment partitioning are still poorly characterized. To identify and isolate these parameters, three-dimensional velocities were measured at 11 cross-sections in a fixed-walled experimental bifurcation. Water surface gradients were controlled, and systematically varied, using a weir in each distributary. As may be expected, the steepest distributary conveyed the most discharge (was dominant) while the mildest distributary conveyed the least discharge (was subordinate). A zone of water surface super-elevation was co-located with the bifurcation in symmetric cases or displaced into the subordinate branch in asymmetric cases. Downstream of a relatively acute-angled bifurcation, primary velocity cores were near to the water surface and against the inner banks, with near-bed zones of lower primary velocity at the outer banks. Downstream of an obtuse-angled bifurcation, velocity cores were initially at the outer banks, with near-bed zones of lower velocities at the inner banks, but patterns soon reverted to match the acute-angled case. A single secondary flow cell was generated in each distributary, with water flowing inwards at the water surface and outwards at the bed. Circulation was relatively enhanced within the subordinate branch, which may help explain why subordinate distributaries remain open, may play a role in determining the size of commonly-observed topographic features, and may thus exert some control on the stability of asymmetric bifurcations. Further, because larger values of circulation result from larger gradient disadvantages, the length of confluence-diffluence units in braided rivers or between diffluences within delta distributary networks may vary depending upon flow structures inherited from upstream and whether, and how, they are fed by dominant or subordinate distributaries.
机译：最近的研究已经研究了控制分叉几何配置的因素​​，确定了多种分叉类型的稳定性条件范围，并评估了扰动对分叉进化的影响。然而，流动分裂过程和影响流和沉积物分区的参数表征差。为了识别和分离这些参数，在固定壁实验分叉的11个横截面下测量三维速度。控制水面梯度，并在每个分销中使用堰系统地改变。尽可能预期的那样，最陡的分布式传送了最多排放量（占主导地位），而最温和的分布式输送了最少的放电（从属）。水面超高升高区域与对称案例的分叉共同定位，或者在不对称案件中移入下属分支。在相对急性角度的分叉的下游，初级速度芯靠近水面和靠在内部的内部，在外部存储器处具有较低初级速度的近床区域。在钝角分叉的下游，速度芯最初在外部堤处，内部存储器处具有较低速度的近床区域，但是很快恢复以匹配锐角壳体。在每个分配器中产生单个次级流动池，水在水面向内流动并在床上向外流动。在下级分支内循环相对增强，这可能有助于解释为什么下属分布仍然是开放的，可以在确定公共观察到的地形特征的尺寸方面发挥作用，并且因此可以对不对称分叉的稳定性发挥一些控制。此外，因为循环的循环值较大的梯度缺点，编织河流中的汇合 - 扩散单元的长度或三角洲分配网络内的差异之间的长度可以根据从上游遗传的流动结构而变化，以及是否以及如何通过主导地供给它们或从属分布。

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