床面粗糙度和底床渗透率对泥-水界面物质交换特性的影响

泥-水界面物质交换过程对自然水体中污染物的迁移转化起重要作用,粗糙底床界面物质交换过程涉及到床面粗糙度和底床渗透率的影响。通过实验室环形水槽实验测量得到水力粗糙砂质底床条件下界面物质交换通量的定量数据和变化特征,采用参数化方法分析有效扩散系数与其主要影响参数之间的依赖关系。实验结果表明,在实验参数变化范围内,受上覆水平均流速、床面粗糙度和底床渗透率的共同作用,有效扩散系数从水力光滑区、过渡粗糙区至完全粗糙区呈现较为明显的分段变化特征,采用渗透率雷诺数可将有效扩散系数与其主要影响参数的依赖关系进行较为一致的描述。基于双参数(粗糙雷诺数和渗透率雷诺数)分析,确定了不同流动区域的相应阈值以合理表征床面粗糙度和底床渗透率对界面物质交换特性的综合影响。

Impact of bed roughness and sediment permeability on mass exchange across sediment-water interface

The mass exchange process across sediment-water interface (SWI) plays an important role in contaminant migration and transformation in natural waters. The mass exchange across the SWI for rough bed depends on both bed roughness and sediment permeability. By means of laboratory annular flume experiment, quantitative measurements of interfacial mass exchange flux at the SWI and its variations have been performed under the rough bed condition. A parameterization method has been adopted to analyze the dependence of effective diffusion coefficient on its main controlling parameters. The experimental results indicate that within the variation range of the present flow and sediment conditions, the effective diffusion coefficient shows an obvious piecewise variation feature from hydraulically smooth, transitional up to fully rough regimes due to the joint effect of mean flow velocity, bed roughness and sediment permeability. The dependence of the effective diffusion coefficient on its main controlling parameters can be described consistently by adopting the permeability Reynolds number. Based on an analysis of dual parameters (i.e. the roughness and permeability Reynolds numbers), the corresponding threshold values for different flow regimes have been determined to reasonably characterize the comprehensive impact of the bed roughness and sediment permeability on the interfacial mass exchange characteristics.