Doctoral Dissertation Research: Flow Dynamics and Channel Morphology at Natural Confluent-Meander Bends

河流汇流几何形状是影响河道交界处水流结构、泥沙输移和河床形态的控制因素。以前的汇流动力学实验和理论模型的一个基本假设是，汇聚的河流具有具有角度构型的直槽。然而，天然河道，特别是那些蜿蜒曲折的河流，是弯曲的。这一性质导致了这样的假设，即自然溪流和河流的汇流优先发生在曲折弯曲的凹陷外岸。由此产生的汇流，被称为汇流-曲折弯曲，一个多世纪前就被观察到了，但几乎没有得到科学上的关注。本博士论文研究项目的目的是通过对天然汇流-曲流弯进行实地考察，促进对这一可能共同汇流的水流结构和形态的理解。将通过地图和数字正射四边形解译，生成选定流域汇流的系统清单，以确定汇流-曲折的规律性。在伊利诺伊州中东部和印第安纳州中西部不同大小和不同几何特征的汇流-曲流弯上收集的现场数据将包括测量时间平均的三维速度分量以辨别水流结构，测量河床和河道形态以记录地貌变化，并记录水温和电导率以揭示汇流之间混合的空间模式。将收集一系列流动条件的数据，以证明动量通量的变化对流动结构和流道形态的影响。研究还将对历史航片进行解释，以确定研究地点的汇流-曲折是否代表曲折水系中的准稳定河道形态。这项研究的结果将揭示汇流-曲折的水流和地貌结构特征，为管理决策提供依据，并有助于了解汇流和曲折动力学的基本知识。这种复杂的水动力环境对于工程师在评估渠道设计标准和通过排水网络进行洪水调度时具有实际意义，对于关心污染物扩散和水质的水资源管理人员也是如此。汇合处的水流结构和地貌变化也提供了破坏栖息地的局部多样性。地貌和生态之间的功能关系越来越重要，为河流生态学家提供更好的栖息地评估。这些河流和形态的考虑使得人们对这一可能是常见的、但迄今被忽视的汇合处的水流动力学和泥沙输送有了了解。对科学和渠道管理决策至关重要。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。

The geometry of river confluences is a controlling factor that influences flow structure, sediment transport and bed morphology at channel junctions. An underlying assumption of previous experimental and theoretical models of confluence dynamics has been that converging rivers have straight channels with angular configurations. However, natural channels, particularly those of meandering rivers, curve and bend. This property has led to the hypothesis that natural stream and river confluences preferentially occur on the concave outer bank of meander bends. The resulting confluence, referred to as a confluent-meander bend, was observed over a century ago but has received little scientific attention. The goal of this doctoral dissertation research project is to advance the understanding of the flow structure and morphology of this possibly common confluence by conducting a field investigation of natural confluent-meander bends. A systematic inventory of confluences throughout selected watersheds will be generated from map and digital ortho-quadrangle interpretation to determine the regularity of confluent-meander bends. Field data collection at confluent-meander bends of varying size and with differing geometric characteristics in east-central Illinois and west-central Indiana will include measuring time-averaged three-dimensional velocity components to discern flow structure, surveying bed and channel morphology to document geomorphic change and recording water temperature and conductivity to reveal spatial patterns of mixing between the confluent flows. Data for a range of flow conditions will be collected to document the effects that variation in momentum flux has on flow structure and channel morphology. Historical aerial photographs will also be interpreted to determine if the confluent-meander bends of the study sites represent a quasi-stable channel configuration in meandering drainage networks.The results of this study will reveal the characteristics of flow and geomorphic structures at confluent-meander bends to provide a basis for management decisions and a contribution to basic knowledge of confluence and meander bend dynamics. This complex hydrodynamic environment has practical ramifications for engineers when assessing channel design criteria and flood routing through drainage networks, as well as for water resource managers concerned about pollutant dispersal and water quality. Flow structure and geomorphic variability at confluences also provide local diversity that disrupts habitat. Functional relations between geomorphology and ecology are increasingly relevant to providing a better assessment of habitat for riverine ecologists. These fluvial and morphological considerations make knowledge of flow dynamics and sediment transport at this possibly common, yet heretofore overlooked, confluence. essential for science and channel management decisions. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.