复杂岸坡河库岸边排放浓度分布规律及侧向与垂向扩散系数的实验研究

Most research on the concentration distribution characters of rivers and reservoirs by now relies on the calculation of the concentration distribution and pollutant mixing zone for planer two-dimensional, vertical-bank and sloped-bank three-dimensional cases. The effects of complex bank shape on the distribution and diffusion coefficient are rarely studied. In this project we will focus on five typical bank shapes commonly seen in rivers and reservoirs, including compound step bank, compound trapezoidal bank, sloped step bank, sloped wavy bank and sloped wavy step bank. The objective is to study the concentration distribution of side discharge and its application. Our vertical 2-D sloped-bank diffusion tank and variable-frequency vibrating-grid system will be employed in the experiments to simulate these banks and the situation that the lateral and vertical diffusion coefficients are different. Side discharge condition will be chosen. At least 4 groups of compound scales for the compound part of the bank, 4 inclination angles θ=2π/β (corner field mapping coefficient β=8,9,10,11…) for the sloped part, as well as various wavy shapes or step heights, will be studied to explore concentration distribution orderliness in complex bank side discharging situation, the changing pattern of lateral and vertical diffusion coefficients and the calculation method of the pollutant mixing zone's shape and characteristic parameters for variable-coefficient longitudinal uniform flow. The results of this project will have great theoretical and practical value for the calculation of the side pollutant mixing zone in rivers and reservoirs and of water area pollution capacity, and also for the development of environmental hydraulics.

以往对河库浓度分布特性的研究，多集中在平面二维、垂直岸和倾斜岸三维条件下的浓度分布和污染混合区计算，很少考虑复杂岸坡形态对浓度分布和扩散系数的影响。针对天然河流和水库普遍存在的复式阶梯岸坡、复式梯形岸坡、倾斜阶梯岸坡、倾斜波状岸坡、倾斜波状阶梯岸坡等5种岸坡形态，以研究岸边排放浓度分布规律和应用为目标。采用立面二维扩散水槽实验装置和变频格栅振荡系统，模拟不同岸坡形态以及侧向与垂向扩散系数不相等的实验环境，选择岸边排放方式，对复式岸坡各选4组以上几何尺度，对倾斜岸坡各选4个以上角形域角度θ=2π/β(角域映射系数β=8,9,10,11…)以及不同的波状或阶梯高度，研究复杂岸坡岸边排放浓度分布规律、侧向与垂向扩散系数的变化规律和纵向均匀流动中变扩散系数条件下污染混合区形态与各特征值的计算方法。对江河水库岸边污染混合区和水域纳污能力的计算，推动环境水力学的学科发展，具有重要的理论价值和实际意义。

河流和水库等天然水体的岸坡地形大都不规则，基于岸边排污扩散理论，研制了一种槽中槽岸坡模型污染扩散实验装置。采用变频格栅振荡系统，模拟了4组侧向与垂向扩散系数不相等的水环境条件；通过调整内水槽的坡度或几何尺寸，模拟和采集了复式阶梯、复式梯形、倾斜阶梯、倾斜波状和倾斜波状阶梯共5种岸坡形态20多个实验工况扩散过程的浓度场RGB图像；通过开发数字图像处理技术得到二维浓度分布数据。再依据瞬时线源二维扩散与恒定点源移流扩散的转换关系式得到稳态条件下，复杂岸坡岸边排放的三维浓度分布。分析了断面浓度分布、水面与深度平均浓度分布规律，提出了采用深度累积浓度矩来估算横向扩散系数的方法，给出了侧向与垂向扩散系数以及深度平均侧向扩散系数随岸坡倾角、漫滩宽度、水深和震荡频率等参数的变化规律。.在理论方面：①推导了倾斜岸水体中深度平均浓度分布方程，给出了倾斜岸深度平均污染混合区几何特征参数的计算公式和外边界标准曲线方程；提出了岸坡倾角分区的简化条件和相应的平面二维、深度平均和三维铅垂岸污染混合区计算公式。②以无量纲坐标、参数和分类曲线方程，全面给出了河流离岸排放的污染物二维浓度分布特性以及断面最大浓度、“三线”（中心线和两岸线）浓度沿程分布的计算公式。③基于大涡对“污染云”扩散的主导作用，提出了横向扩散系数随“污染云”范围的扩大而增大的变横向扩散系数概念和处理方法，并推导了变扩散系数污染混合区几何特征尺度、面积公式和外边界标准曲线方程，与长江黄沙溪排污混合区深度平均NH3-N现场观测等值线吻合良好。④基于河流污染混合区理论，提出了水环境影响预测中背景浓度和各计算参数的确定方法。.本项目的研究成果对环境影响评价技术导则（地表水环境）和建设项目环境风险评价技术导则水质模型部分的制定、岸边污染混合区和水域纳污能力的计算以及地表水环境影响评价，推动环境保护事业和环境水力学的学科发展，具有重要的理论价值和实际意义。