钱塘江感潮河段污染物迁移扩散数值分析

感潮河流由于受到潮汐的作用,污染物会因潮汐的涨落作用沿河道往复运动,影响用水安全.以高锰酸盐指数作为主要水环境指标,分析了钱塘江感潮河段上游富阳水文站监测到的持续高锰酸盐污染物输入情况下对下游河段的影响,旨在得到不同水期情况下之江站污染物出现的时间,作为取水安全预警指标参考.同时,基于潮流连续性方程、动量方程和污染物扩散方程,模拟计算了9种流况下污染物的迁移扩散过程.结果显示,径流处于平水月份时,之江站最早受到上游污染物影响,其次是枯季,最后是洪季,说明径流作用有利于污染物向下游迁移扩散.在大潮作用下,之江站一般最晚受到上游污染物影响,中潮次之,最早受到影响的是在小潮情况下.说明在感潮河段,由于受到下游潮流的影响,对污染物往下迁移有一个阻滞作用,且潮流越强阻滞作用越明显.本文构建的潮流水质模型可作为污染物在感潮河段迁移扩散机理研究的模型基础,对于制定降低污染物迁移扩散对地表水环境质量影响措施具有现实意义.

Numerical analysis of pollutant transport and diffusion in the tidal reach of Qiantang River

Due to the effect of tide fluctuation, pollutants transport back and forth along the river course, posing threat on the water safety. This paper takes the permanganate index as the main water environmental indicator to investigate the effect of the permanganate pollutant continuously imported from upstream Fuyang on the downstream water. The pollutant peaking time at Zhijiang station in different water phases is obtained and used as a reference index for early warning of water safety. Based on current continuity equation, momentum equation and pollutants diffusion equation, the pollutant transport and diffusion process under nine flow conditions are simulated and analyzed. The results show that the peaking time at Zhijiang station is the earliest in the normal condition, followed by the low-flow season and the flood season. It indicates that the runoff facilitates transport and diffusion of pollutants to the downstream area. The peaking time at Zhijiang station appeared the latest under the action of spring tide, the earliest under neap tide, and in between for middle tide. This illustrates that the downstream tide has blocking effect to the downward transport of pollutant, and the greater the tide, the more obvious the blocking effect. The tidal water quality model can be used as the base model for studying pollutant migration and diffusion mechanism in the tidal river. It is practically meaningful for the development of measures for reducing the influence of the pollutant migration and diffusion on the surface water quality.