感潮河口突发水污染事故的径流调控效应研究

On the runoff-regulation effects of sudden water pollution accidents in tidal estuaries

感潮河口多为我国人口密集、经济发达地区,突发水污染事故将对河口水环境、社会生产生活产生重要影响。研究事故污染团在径流和潮汐动力作用下的迁移、扩散规律及上游下泄流量的水力调控效应具有重要意义。以钱塘江河口为例,构建钱江四桥突发Cd污染事故的水流水质数学模型,模拟了富春江电站下泄流量50～4 000m3/s条件下事故污染团质量浓度场的时空变化过程,分析了不同下泄流量对污染团迁移扩散特征及对重要敏感点超标时间、超标倍数的调控效应。结果表明,加大上游径流量可明显加快污染团的迁移、扩散和稀释速度,减轻对杭州闸口站正常取水的影响及缩短污染物在河口的滞留时间。

This paper is aiming to present our study on the runoff-regulation effects of sudden water pollution accidents in tidal estuaries. As we know, it is of great importance to study the migration and diffusion law of the unexpected pollution mass caused by the runoff and tidal power along with the water-regulation influence of the upstream runoff. Here we should like to take the runoff of Qiantangjiang Estuary （Shejiang） as our case study sample. To present the water-regulation influence of the upstream runoff more clearly, we have built a water flow and quality mathematical model of sudden Cd water-contamination accidents with the fourth Qianjiang River Bridge as an example, which could serve as a water quality simulation on the sudden Cd pollution accidents. The source power of the pollution accident was estimated to contain 20 tons of heavy metal Cd and the leakage time lasted about 30 minutes. The discharged water volume by the Fuchunjiang power plant was estimated at about 50 m3/s, 400 m3/s, 700 m3/s, 1 000 m3/s, 1 600 m3/s, 2 000 m3/s, 2 500 m3/s, 3 000 m3/s, 3 500 m3/s and 4 000 m3/s, respectively. Based on the simulation model, we have also worked out and analyzed the migration and diffusion characteristics of the pollution mass and its regulation effect on the accident lasting time and spreading to the important sensitive points by different runoffs. The results of our study show that when the upstream runoff is 50-3 000 m3/s, the highest concentration is 0.59-0.01 mg/L of the gates, with the lasting time of 0.8 to 125.8 hours. When the runoff is greater than 3 000 m3/s, the accident would hardly have any effect on the water intake of the gates, where the runoff power is beyond the tidal power. However, if the upstream runoff were less powerful （less than 700 m3/s）, the time affecting the normal water intake of the gates should be able to last about 2.5 to 7 days. The tide containing pollutants would then be able to reciprocate with the vicinity of the water intake. However, if the upstream runoff exceeded 1 000 m3/s, the time affecting the water intake should be able to last no more than 3 days. Therefore, it has become clear that with the increase of upstream runoff, runoff/tide ratio should be able to increase, too, which should be able to give significant push to accelerate the water-pushing force migration, diffusion as well as the dilution speed of pollution mass and in turn have an obvious regulation effect on the reduction of the pollutants＇ lasting time, and in turn, to speed up the downstream migration of the pollution mass and the diminution of the retention time of pollutants in the estuary.