植被斑作用下生态河道水流结构及纵向混合机理研究

Currently, researches on ecological river mainly focus on the ecological restoration, engineering projects and its qualitative influences, while few are on the stability of river regime in the ecological river, capability of flood carrying and transport properties of pollutions. Our research will summarize ecological river into several classical types of open channel flow with vegetation patch. The hydrodynamics features and the shear stress distribution over the riverbed will be studied to explore temporal turbulence characteristics under the influences of vegetation patch and the secondary flow formed by the shape of the compound channel. By studying these, we are able to control the flow by the vegetation patch and riverbed boundaries, to stabilize river regime and to make sustainable development of the river possible. Based on the studies, we can construct 3D hydrodynamics model and 2D water depth averaged model of the river with vegetation patch, as well as the 1D unsteady flow model so as to describe the ecological river mathematically. At the same time, the momentum exchange between the region inside and outside the patches will be analyzed to show the effect of vegetation patch on longitudinal mixing. Analytical description is expected to be given on the longitudinal dispersion coefficient in the ecological river with vegetation patch. The research results will provide a base for design of ecological channel and environmental influences.

目前对生态河道的研究主要集中在河流生态恢复的研究，生态河道实践工程的研究和生态河道影响因素的定性研究上。而对生态河道水流结构特性是否有利于河势的稳定，行洪能力如何，污染物在生态河道中混合输移行为如何变化等研究的较少。本研究将生态河道水流概化为多个典型形式的植被斑明渠水流，研究植被斑的水动力学特性，揭示植被斑与河床断面形状形成二次流联合作用下水流时均与紊动特性，探究河床切应力的分布，以实现植被斑与河床边界对水流的控制，使得生态河道具有稳定的河势，以达到生态河道的可持续发展。进而建立描述植被斑水流的三维水动力学模型和水深平均二维模型，以及基于植被斑阻力模型的一维非恒定水流模型，以实现生态河道植被水流特性的数学描述。同时就植被斑内与斑间动量交换进行分析，揭示植被斑对纵向混合的影响。在试验与理论分析基础上给出植被斑作用下生态河道纵向离散系数的理论描述。该成果为生态河道设计和环境影响评估奠定基础。

生态河道对河流（网）水系的水环境保护与可持续发展起到重要作用，因此开展生态河道水流结构及其污染物混合输移特性的研究就显得更为迫切和重要。本项目研究的主要内容集中在三个方面，其一为生态河道植被、水流与河床边界耦合作用机理研究，其二生态河道阻力特性研究；其三为生态河道纵向离散系数研究，进而拓展为湿地泰勒弥散分析研究。最终获得了多种植被类型多种分布方式下生态河道水流流场结构特性，揭示了水流、植被和河床之间的相互作用机理，形成了一整套基于试验研究、理论分析、数值解法的勾勒三者作用与效应的生态河道水力学体系；在植被与水流相互作用形成的阻力特性方面，提出了新河床概念，给出植被水流过流能力计算新公式，统一了明渠水力学谢才公式；基于奇克维度（Chickwendu）的N区纵向离散模型，提出了生态河道纵向离散系数新公式；基于多孔介质流体动力学控制方程组，解析出湿地流动泰勒弥散分析解，完善了泰勒弥散理论。这些成果完善了生态环境水力学的理论，对当前生态河道环境影响评价和生态河道整治具有直接的应用前景。