Collaborative Research: A Field and Numerical Study of the Morphology, Flow, Sedimentary Processes, and Stability of Sand-Bed Fluvial Bifurcations

河道分叉是指一条河道分成两条，是辫状河道、闭合河道和分流河道网络的组成部分。最近的工作表明，最常见的流量分配在分叉是不对称的，这种不对称似乎促进稳定性。为什么以及在什么样的水文学和沉积学条件下会这样，仍然是一个谜。在这里，我们提出了一个综合的领域和理论研究的形态，流动和沉积过程的较高的剪切应力，天然河流分叉，理解和预测其动力学行为的目标。现场研究将包括两个具有不同沉积特征的分叉系统：i）萨斯喀彻温河Mossy三角洲的分流河道分叉，我们在那里进行了关于分叉形态动力学的试点研究，ii）路易斯安那州Wax Lake三角洲系统内的分叉，活跃的沉积导致分流河道快速生长。将在每个部位选择几个分叉，以跨越一系列形态类型。床形态，水面地形，流速和泥沙输移率将在每个分叉处测量一个紧密间隔的网格在几个流动阶段。现场数据将提供边界和初始条件的数值实验，旨在定义的过程和形态条件，导致固有的不稳定的分叉，并详细控制稳定的边界条件。早期的数值模型将通过使用Delft 3D-FLOW进行改进，Delft 3D-FLOW是一种形态动力学模型，可考虑：（1）三维湍流非稳定、非均匀流，（2）河床地形、水流、推移质和悬移质之间的相互作用，以及（3）形态动力学相互作用的可侵蚀河岸和河床。数值实验将使我们能够确定的反馈过程，促进稳定的分叉和预测的通道配置是稳定的，在面对扰动。我们的目标是产生一个稳定图的通道分叉和评估的影响，条形动力学和下游通道的变化，影响分叉稳定性。更好地理解和预测能力的渠道分叉行为将改善洪水预报，规划和洪泛区和渠道结构的发展，渠道设计，以及河流恢复工作的成功。这项研究的结果也将推进我们的知识，何时何地河流撕脱将采取。尽管它是变革性的，它将解决相互竞争的稳定性理论之间的差异，并产生一个模型，由最好的现场数据，可用于预测这些无处不在的水文和地貌节点的稳定性和行为的约束。研究结果：本研究构成了一位博士学位论文的选题和资助。候选人，并将支持一名博士后研究员。来自萨斯喀彻温省坎伯兰众议院克里族的两名美国土著高中生将接受科学方法的培训。所有的学生将受益于接触到一个问题，需要整合地貌，泥沙输运，流体动力学和形态动力学建模。

Channel bifurcations, wherein one channel splits into two, are the building blocks of braided, anastomosed, and distributary channel networks. Recent work has shown that the most common flow partitioning at bifurcations is asymmetric, and that this asymmetry seems to promote stability. Why and under what hydrographic and sedimentologic conditions this should be so, remain a puzzle. Here we propose an integrated field and theoretical investigation of the morphology, flow, and sedimentary processes of higher shear-stress, natural river bifurcations, with the objective of understanding and predicting their dynamical behavior. The field studies will be conducted to encompass two bifurcating systems with different sedimentation characteristics: i) distributary channel bifurcations of the Mossy Delta of the Saskatchewan River, where we have conducted pilot studies concerning bifurcation morphodynamics, and ii) bifurcations within the Wax Lake delta system, Louisiana, where active sedimentation is leading to rapid distributary channel growth. Several bifurcations at each site will be chosen to span a range of morphologic types. Bed morphology, water surface topography, flow velocity, and sediment transport rate will be measured at each bifurcation on a closely spaced grid at several flow stages. The field data will provide boundary and initial conditions for numerical experiments designed to define the processes and morphological conditions that lead to inherently unstable bifurcations, and detail the controlling boundary conditions for stability. Earlier numerical models will be improved by using Delft3D-FLOW, a morphodynamic model that accounts for: (1) three-dimensional turbulent unsteady, nonuniform flow, (2) interaction between bed topography, flow, and both bedload and suspended load, and (3) morphodynamically interacting erodible banks and bed. Numerical experiments will allow us to determine the feedback processes that promote stable bifurcations and predict which channel configurations are stable in the face of perturbations. We aim to yield a stability diagram for channel bifurcations and assess the influence of barform dynamics and downstream channel change in influencing bifurcation stability. A better understanding and predictive capability of channel bifurcation behavior would improve flood forecasting, planning and development of floodplain and channel structures, channel designs, and the success of stream restoration efforts. The results of this study also will advance our knowledge of when and where river avulsions will take. Insofar as it is transformative, it will resolve the differences among competing stability theories, and produce a model, constrained by the best-available field data, which can be used to predict the stability and behavior of these ubiquitous hydrologic and geomorphic nodes. Resulting from This Study: This work constitutes the dissertation topic and financial support for one Ph. D. candidate and will support one post-doctoral researcher. Two Native American high school students from the Cumberland House Cree Nation, Saskatchewan will be trained in its scientific methods. All students will benefit from exposure to a problem requiring the integration of geomorphology, sediment transport, hydrodynamics, and morphodynamic modeling.