Transport and Mixing at River Confluences

河流汇流-河流相互汇合的位置-是自然排水网络的基本组成部分。由于流域在地形、地质、土壤和土地利用方面的不同，导致河流流动的保守性和这些流动所输送的物质的不同。这些不同的水流和水流成分在汇流处汇聚在一起，导致河流混合。尽管在过去的几十年里，人们对汇流的河流动力学进行了深入的研究，但汇流在保守示踪剂、悬浮泥沙和底质泥沙的混合中所起的作用还没有得到全面的研究，而且仍然不完全了解。拟议的研究是由于这种认识的缺乏，旨在通过以下几个方面的组合来提供对河流汇流处及其下游横向混合的认识：旨在评估半控制条件下的混合的现场试验、从水文和地形变化的背景下评估混合的现场调查，以及基于流动和质量传输基本物理原理的三维数值模拟。拟议的研究将旨在结合控制因素对混合和传输过程进行直接评估，以便更好地了解沿流向的垂直单体和湍流相干结构在这些过程中的作用。所获得的数据集将促进定量理论模型的发展，该模型将描述这些单体的形成及其与大尺度河床形态的相互作用，包括河床不协调对沿河流方向的垂直单体的影响。通过对传统水动力模型的汇流动力学实验结果进行定量评估，探讨了河床粗糙度和空间不均匀对压力分布的影响，结果表明，混合率将直接与传统的水动力学特征，如湍流、涡粘性和体流参数有关。这项研究的实地研究将在国际实地考察站Tagliamento以及莱德拉河、奥德内塞河和施普雷河的汇合处进行。涡旋分辨数值模拟将扩大实验参数空间的范围和分辨率，并将提供关于混合和输送过程的精炼知识，然后将用于扩展河流过程的理论。拟议的研究结果将产生许多实际结果，因为它们将使人们能够更好地预测污染物、沉积物和生物物质在河流系统中的迁移和混合。

River confluences - locations where rivers join one another - are fundamental components of natural drainage networks.Differences in the topography, geology, soils, and land use of watersheds within a drainage network produce differences in conservative properties of river flows and in the materials transported by these flows. These different flows and flow constituents are brought together at confluences, leading to river mixing.Although the fluvial dynamics of confluences have been studied intensively over the past several decades, the role that confluences play in mixing of conservative tracers, suspended sediment, and bed-material sediment has not been examined comprehensively and is still incompletely understood.The proposed research is motivated by this lack of understanding and aims to provide a transformational improvement in knowledge of lateral mixing at and immediately downstream of river confluences through a combination of field experiments designed to evaluate mixing under semi-controlled conditions,field investigations undertaken to assess mixing in the context of hydrological and morphological variability, and three-dimensional numerical modeling based on fundamental physical principles of flow and mass transport.The proposed studies will aim at the direct assessment of mixing and transport processes concomitantly with the controlling factorsin order to better understand the role of streamwise oriented vertical cells and turbulent coherent structures in those processes. The obtained data sets will facilitate development of quantitative theoretical models which will describe formation of those cells and their interactions with the large-scale riverbed morphology including the effect of bed discordance on the streamwise oriented vertical cells. The effects of riverbed roughness and spatial inhomogeneity in pressure distribution will be also explored by carrying out the quantitative assessment of experimental results on confluence dynamics with conventional hydrodynamic models with the outcome that mixing rates will be directly linked to the conventional hydrodynamics characteristics such as turbulent eddy viscosity and bulk flow parameters. The field studies of this research will be performed at the international field research station Tagliamento and on the confluences of rivers Ledra and Oder-Neisse, and Spree. Eddy resolving numerical simulations will expand a range and resolution of the experimental parametric space and will deliver a refined knowledge on the mixing and transport processes which will then be used to expand theory of fluvial processes. The results of the proposed research will have numerous practical outcomes because they will allow better prediction of transport and mixing of pollutants, sediments, and biological substances in fluvial systems.