【作者】 赵亮； 王学勇； 樊靖郁；

【Author】 Zhao Liang;Wang Xueyong;Fan Jingyu;School of Mechanics and Engineering Science, Shanghai University, Shanghai Institute of Applied Mathematics and Mechanics;

【机构】 上海大学力学与工程科学学院上海市应用数学和力学研究所；

【摘要】 潜流交换是河流水环境系统中,各种物质(水、溶质、污染物、胶体、细颗粒)在与地表水相邻的饱和沉积物层(潜流带)中发生的一种重要对流过程。潜流交换可由不同尺度和类型的水动力因子驱动,其中上覆水流与床面形态相互作用形成的不均匀床面压力变化,将会驱动各种物质产生进出底床的潜流交换过程。床面形态组成单元物理特性(渗透率、孔隙度、非均质性)是影响潜流交换通量的重要因素,其水动力影响机制和量化表征尚待深入研究。本文通过实验室环形水槽实验,采用概化的二维离散床面形态,主要研究床面形态组成单元物理特性与潜流交换通量之间的定量关联和变化特征,并分析床面形态组成单元渗透率变化对有效扩散系数的影响趋势。实验结果表明,床面形态组成单元的物理特性对潜流交换通量具有显著影响。在本文实验参数变化范围内,床面形态的存在引入了附加的泵吸交换,但泵吸交换对潜流交换通量的相对贡献与床面形态组成单元的渗透率变化密切相关,当其渗透率相对较低时,泵吸交换和湍流渗透均趋于减弱,与平整底床相比,有效扩散系数总体上呈不同程度的减小趋势。更多还原

【Abstract】 Hyporheic exchange is an important advective process in river water environment system,which occurs within saturated sediment layer adjacent to surface water(hyporheic zone) for a variety of substances, such as water, solutes, contaminants, colloids and fine particles. The hyporheic exchange can be driven by various hydrodynamic factors with different scales and forms, among which an inhomogeneous interfacial pressure variation formed by the interaction between overlying water flow and bedform can drive the substances into and out of sediment bed. The physical properties of the bedform composition elements(permeability, porosity and heterogeneity) are important influencing factors for hyporheic exchange flux, and their hydrodynamic mechanism and quantitative characterization have not been extensively investigated. In this paper, the quantitative correlation and variation feature between the physical properties of the bedform composition elements and the hyporheic exchange flux have been investigated by laboratory annular flume experiments and adopting conceptual 2D discrete bedforms, and the impact of the permeability variation of the bedform composition elements on effective diffusion coefficient has been analyzed. The experimental results indicate that the physical properties of the bedform composition elements have a significant effect on the hyporheic exchange flux. Within the variation range of the present experimental parameters, the presence of the bedforms introduces an additional bumping exchange, and yet the relative contribution of the pumping exchange to the hyporheic exchange flux is closely related with the permeability variation of the bedform composition elements. When the permeability of the bedform composition elements is relatively low, the bumping exchange and turbulence penetration tend to be attenuated, and the overall effective diffusion coefficient tends to decrease to a varying extent compared to that in the case of flat bed.更多还原