CAREER: Integrated Experimental and Numerical Modeling Study of Non-uniform Sediment Transport in Meandering Channels

冲积河道输沙的科学知识来源于直槽试验。在弯曲河道中，泥沙与高度三维水流相互作用，形成点状沙洲和曲折的平面形态演变。到目前为止，还没有一种理论能够令人满意地解释和量化水流(平均和湍流)、粒度分数输沙、点坝动力学和弯道顺序迁移之间的相互作用。在许多适用于弯曲和曲折河道的数值模型中，泥沙输移的公式都是基于实验室直槽的数据，从未用弯曲的河道进行过检验。目前对曲折河道泥沙分选的认识限制了数值模型模拟河床物质级配、河床形态和弯曲平面形态演变的能力。为了全面了解河流中的泥沙运动，本项目旨在解决以下问题：水流如何影响泥沙运动？泥沙输移与近床面平均流量的偏差有多大？泥沙负荷的空间分布是什么？泥沙、水面和底质的级配是什么？它们如何通过粒度分数与泥沙输移速率相关联？空间变化的泥沙通量是如何构成点坝动力学的？曲流河运移对点沙坝的生长或抑制有何响应？实验将在曲度在1.25-3.7之间的几组自形成的曲流河中进行。在这些蜿蜒的河道中，将引入级配良好的泥沙混合物，以研究三维水动力流场、表层和底质的分布、不同粒级的泥沙在流向和横向的输移特性、顶点附近点状沙洲和水池的逐渐形成、发育和衰减，以及岸坡冲刷和点状沙洲演变过程中的平面形态演变。实验结果将被整合到一个数值模型中，以模拟实验水槽和一条天然河流中的蜿蜒迁移过程。研究成果将有助于对河流弯道的科学认识，为河流修复设计提供有价值的指导。其优点不仅在于基础研究，还在于工程实践。该项目将获得新课程所需的实验设施和计算机模型，让本科生参与研究，为女学生建立一个更长期的指导计划，为科学博物馆开发计算机动画展，并面向高中生。其目标是鼓励创造和创新，在工程教学中强调计算，提高女性在工程学领域的知名度，并吸引最有才华的高中毕业生进入土木工程专业。

AbstractThe scientific knowledge on sediment transport in alluvial channels stems from experiments in straight channels. In curved channels, sediment interacts with highly three-dimensional flow and induces point bars and meandering planform evolution. To date, no theory is able to satisfactorily explain and quantify the interactions among flow (mean and turbulence), sediment transport by size fractions, point bar dynamics and the sequential migration of bends. Among many numerical models applied to curved and meandering channels, formulations for sediment transport by size fractions have been based on data from straight laboratory flumes and never tested with sinuous channels. Current understanding of sediment sorting through meandering channels limits the capability of numerical models in simulating the evolution of bed material gradation, bed morphology, and bend planform. Towards a complete understanding of sediment transport in meanders, this project aims to address the following questions: How does flow influence sediment transport? How much does sediment transport deviate from the near-bed mean flow? What are the spatial distributions of sediment load? What are the size gradations of bed load, surface, and substrate material? How do they correlate to sediment transport rate by size fraction? How does spatially varied sediment flux constitute point bar dynamics? How does meandering migration response to the growth or dampening of point bars?Experiments will be conducted in several series of self-formed meandering channels with sinuosities ranging from 1.25 to 3.7. Well-graded sediment mixtures will be fed into these sinuous channels to enable investigation of three-dimensional hydrodynamic flow field, distributions of surface and substrate material, sediment transport characteristics for different size fractions at the streamwise and lateral directions, gradual formation, growth, and dampening of point bars and pools near the apex and channel crossing, planform evolution as bank erodes and point bar progresses. The experimental results will be integrated into a numerical model to simulate the processes of meandering migrations in both experimental flumes and a natural river. The results of this research will contribute to scientific understanding of river meanders and provide valuable guidance in river restoration design. The merit is not only in basic research but also in engineering practice. The project will acquire an experimental facility and a computer model needed for new courses, engage undergraduates in research, establish a longer-standing mentoring program for women students, develop a computer animation exhibition for science museums, and outreach to high school students. The objectives are to encourage creativity and innovation, stress computing in engineering teaching, increase the visibility of women in engineering, and attract most talented high school graduates to Civil Engineering.