冰封河流的离散特性和水质变化规律研究

There is a long period with thick ice cover on water body of the rivers during the winter in Northeast China, the water quality in rivers is poorest due to slowed-down flow velocity, reduced tranportation rate as well as decreased decaying rate of pollutant. With the appearance of ice cover, flow resistance increases, and the distribution and velocity and turbulent intensity are obviously different from the open water body. As the result, the diffusion and dispersion of pollutant shows special characteristics with different conditions of ice cover due to climate change. Combining field observation, literature investigation, flume experiments, numerical simulation and theoretical analysis, the present proposal will observe the water movement and transportation of mass cloud under different regime of ice covers and investigate the effects of ice covers on distributions of flow velocities and mass concentrations. A useful numercial model for ice-covered river will be developed and tested by the observed data, the rate of diffusion and dispersion of polluant will be calculated and the corresponding cofficients will be determined. The change of water quality and environment effect with different conditions of ice cover will be described clearly. The study on this programme will be very helpful to development of the ice hydraulics and environmental hydraulics and will provide a powerful technical spports for recovery and protection of ice-coverd river environment.

我国东北地区大多数河流的冰封期漫长。冰封期间，水流速度减缓，污染物输移扩散能力减弱，水质污染最为严重。出现冰盖后，水流阻力加大，流速分布和紊动强度明显不同于畅流期，由于气候变化影响而冰封条件的不同，水流的离散特性和污染物的输移扩散呈现出独特的变化规律，河流水质随之发生变化。本项目将采用现场实地勘测、文献调研分析、室内水槽试验、精细数值模拟、严密理论推导等手段，研究不同冰封条件对水体运动的影响及冰封河道流动结构对离散特性的影响，建立高效实用的数学模型和计算方法，在得到实验与原型资料验证的基础上，精确模拟污染物在冰封河道中随流运动轨迹以及浓度分布，分析冰封期河道水流的紊动扩散和纵向离散特性，揭示不同冰封条件下水流水质变化规律与环境效应。项目的研究对于冰水力学和环境水力学的发展具有重要的学术价值，也将为冰封期河流水环境的修复与保护提供有力的技术支撑。

河道冰盖的形成改变了水流的阻力构成、流速分布和紊动特性，对冰封河流的水动力和水环境产生重大影响。课题以牡丹江干流为主要研究目标，提出了判别主要污染物的IAHP方法，揭示了北方河流冰封期以点源污染为主的污染特征。分析了冰盖对流速分布和水体紊动的影响，比较了流速垂向分布不均匀和横向分布不均匀对纵向离散的影响，得到了宽浅型河流的纵向离散以流速分布横向分布不均匀为为主的结论，并提出了宽浅河流纵向离散系数估算的简便方法。建立了冰封河流的纵向一维水流水质模型，分析了牡丹江城市江段主要污染物的沿程变化。基于紊动动能产生-耗散速率平衡理论，确定了适用于冰封河流的深度平均k-epsilon紊流模型的源项，并应用于北安河排污口污染混合区的模拟，分析了冰盖的出现对混合区流动特性和混合特性的影响。研究成果促进了对冰封河流物质输移扩散特性的认识，支撑了冰封期河流水环境的管理和保护。