河流离岸排放污染物二维浓度分布特性分析

Analysis of the characteristics of the two-dimensional pollutant concentration distribution in river offshore discharge

从河流移流扩散二维简化方程的解析解出发,考虑两岸边界反射作用,通过离岸排放条件下的系列计算实验、浓度图谱绘制、数学归纳和分析整理,提出了以相对离岸距离a'(=排放口离近侧河岸的距离a/河宽B)为自变量的宽阔与中宽河段的分类线x'_(1.2)方程;提出了断面最大浓度轴线的定义、分段方程以及简化分段条件,给出了最大浓度轴线x轴段与弯曲段的分段线x'_e方程、弯曲段与靠岸段的临界线x'k方程以及断面最大相对浓度沿程分布的分段简化计算公式,提出了河流中心线和两岸线上相对浓度沿程分布的计算公式,为河流水环境影响预测与评价提供了理论支持。

It has been proved that analysis of the two-dimensional pollutant concentration distribution characteristics during the expansion of contaminated zone in river-offshore discharge,and prediction of the concentration on the environmental sensitive sites have aroused a considerable attention of the academic and engineering communities. Its boundary reflection being taken into consideration based on the analytical solution of the simplified two-dimensional advection-diffusion equation for rivers,the formula of x＇1. 2threshold,which categorizes the wide-and medium-wide rivers based on the relative offshore distance a＇（ defined as the ratio between the distance from the discharge outfall a and river width B）,has been proposed through series computational experiments on off-shore discharge,concentration distribution contouring,and mathematical induction and analysis. The definition of maximum concentration axis in river cross-sections has been proposed,along with its piecewise equations applying to each sub-situation classified by certain criterion. The thresholds x＇eand x＇kseparating the x-axis segment,curved segment and near-shore segment of the defined maximum concentration axis are given with a simplified calculation formula for cross-section maximum relative concentration,relative concentration along the centerline and banks of the rivers for each segment. The results afford a theoretical basis for the prediction and assessment of the river water environmental impact.