Confluence mixing: near-field hydrodynamic controls of the intermodal behavior and their implications for fish ecology

河流汇流是河流网络的重要节点，也是淡水生态系统中生物多样性的热点。交汇处的流动结构是不均匀的，在混合界面内产生了以多态行为为特征的复杂模式。汇合处的总体混合速率与界面模式有关，界面模式对有害污染物、水温、沉积物和生物群的扩散有相当大的影响。这项拟议的研究旨在通过对射流、水流停滞和河流治理对混合界面的多式联运行为的影响及其对鱼类生态的影响提供基于基本理论的见解，以提高对汇流混合的认识。在该项目中，将利用遥感和仪器测量，在广泛的水文条件下，在实地直接评估在浅水、粗糙河床环境中产生的复杂混合界面。混合动力学将通过将现场观测与跨模式行为理论进行比较来进一步分析，该理论将利用基于现场的实验和数值模拟的结果进行扩展和验证。这些实验还将提供有关混合界面内鱼类轨迹和鱼类行为的信息。从这些关于混合的不同信息来源中，我们将开发一个基于代理的模型来模拟鱼类在有害毒素通过期间的生存。模拟将使用一条受管制的河流的鱼类调查结果进行验证，该河流的生态系统最近遭受了大量鱼类死亡。本研究的理论和实证结果将被用于发展基于遥感的河流混合预测方法。

River confluences are vital nodal points of fluvial networks and are hotspots of biodiversity in freshwaters ecosystems. Flow structure at confluences is non-uniform and produces complex patterns within mixing interfaces that are characterized by intermodal behavior. The overall mixing rate at confluences is related to the interface pattern, which has a considerable impact on the spread of harmful pollutants, water temperature, sediments and biota. The proposed research aims to improve knowledge of confluence mixing by providing fundamental theory-based insights into the effects of jetting, flow stagnation and river regulation on the intermodal behavior of mixing interfaces and their implications for fish ecology. In this project, complex mixing interfaces generated in shallow, rough-bedded river environments will be assessed directly in the field at a wide range of hydrological conditions using remote sensing and instrumental measurements. Mixing dynamics will be further analyzed by comparing field observations with the theory of intermodal behavior, which will be expanded and validated using results from field-based experiments and numerical simulations. These experiments will also provide information on fish trajectories and fish behavior within mixing interfaces. From these diverse sources of information on mixing, we will develop an agent-based model to simulate fish survival during a passage of harmful toxins. Simulations will be validated using results of a fish survey in a regulated river which ecosystem has recently suffered a mass kill of fish. Theoretical and empirical results of our study will be used to advance predictive methods based on remote sensing of mixing in rivers.