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

合作研究：沙床河流分叉形态、流动、沉积过程和稳定性的现场和数值研究

• 批准号: 0809775
• 负责人: James Best
• 金额: $ 13.55万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-09-15 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0809775&HistoricalAwards=false
• 关键词: Collaborative; Research; Field; Numerical; Study

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.

河道分叉，即一条河道一分为二，是辫状、网状和分流河道网络的组成部分。最近的研究表明，分叉处最常见的流动分配是不对称的，并且这种不对称似乎可以促进稳定性。为什么以及在什么水文学和沉积学条件下会出现这种情况，仍然是一个谜。在这里，我们提出对高剪切应力、天然河流分叉的形态、流动和沉积过程进行综合的现场和理论研究，目的是理解和预测它们的动态行为。实地研究将涵盖两个具有不同沉积特征的分叉系统：i）萨斯喀彻温河莫西三角洲的分流河道分叉，我们在那里进行了有关分叉形态动力学的试点研究；ii）路易斯安那州蜡湖三角洲系统内的分叉，其中活跃的沉积导致分流河道快速增长。每个位点的几个分叉将被选择以跨越一系列形态类型。将在多个流动阶段的紧密间隔的网格上的每个分叉处测量床形态、水面地形、流速和沉积物输送速率。现场数据将为数值实验提供边界和初始条件，数值实验旨在定义导致固有不稳定分岔的过程和形态条件，并详细说明稳定性的控制边界条件。早期的数值模型将通过使用 Delft3D-FLOW 进行改进，Delft3D-FLOW 是一种形态动力学模型，它考虑了：(1) 三维湍流非定常、非均匀流动，(2) 河床地形、流动以及河床荷载和悬浮荷载之间的相互作用，以及 (3) 形态动力学相互作用的侵蚀河岸和河床。数值实验将使我们能够确定促进稳定分叉的反馈过程，并预测哪些通道配置在面对扰动时是稳定的。我们的目标是生成通道分叉的稳定性图，并评估条形动力学和下游通道变化对分叉稳定性的影响。更好地理解和预测河道分叉行为将改善洪水预报、洪泛区和河道结构的规划和开发、河道设计以及河流恢复工作的成功。这项研究的结果还将增进我们对河流撕扯何时何地发生的了解。就其变革性而言，它将解决相互竞争的稳定性理论之间的差异，并产生一个受最佳可用现场数据约束的模型，该模型可用于预测这些普遍存在的水文和地貌节点的稳定性和行为。这项研究的结果：这项工作构成了一名博士候选人的论文主题和财政支持，并将支持一名博士后研究员。来自萨斯喀彻温省坎伯兰克里族部落的两名美国原住民高中生将接受其科学方法的培训。所有学生都将受益于需要整合地貌学、沉积物迁移、流体动力学和形态动力学建模的问题。