Abstract:

There are many rivers and lakes in China, which are widely distributed with abundant water quantity. They are the important drinking water sources for nearby towns. But rivers and lakes have the characteristics of open water. Apart from providing drinking water, they have other functions such as blowdown, shipping, irrigation, which are potential threats to water quality. In Taihu Lake Basin, the rapid population growth, the acceleration of urbanization and rapid industrial development, and the increasing demand for water generated a lot of sewage and wastewater. How to protect the lake water environment has become a focus of public concern. Understanding hydrodynamic characteristics and contaminants transport and diffusion processes in Taihu Lake is helpful for people to use water resources carrying capacity rationally, and optimize water pollution control measures. It can also provide a strong scientific and technological support for develop a reasonable plan of water resources protection and engineering decision making along the lake. Based on the practice of clean water diversion from the Wangyu River to the Taihu Lake and a large amount of investigation and monitoring data, a 2D model of water quantity and quality in Taihu Lake was established. The hydrodynamic model preferably reflected the dynamic characteristics of the study lake region. On the impact of the flow direction, clean water transport process distribution of the study lake region was zonal, and distribution relied on the shore, the lower water concentration of the distance is near the outfall of the Wangyu River. The spatial variations of each water quality index concentration before and after the water diversion were obtained. The results indicated that the water diversion could improve the lake water quality. The concentrations of CODMn, NH3N and TN were decreased by 60%, 160% and 92% respectively, but the concentration of TP rose by 44%. The quality of 37% of the total area of the Taihu Lake was improved. These areas were concentrated in the Gonghu Lake,the Meiliang Bay and east regions of the Taihu Lake which were all across by water transfer route. The transport processes were closely related to diverted water quality,the tide type, flow rate, flow, and underwater topography. Under the same conditions, the higher the tidal water level, the stronger the dilution of lake water capacity was, and the increase of pollutant concentration was relatively small; the greater the flow rate, the stronger of the effect of lake water migration was. The water diversion project was very important to the improvement of the water quality in part of the area and to secure water supply in Taihu Lake. This study may provide scientific bases for water pollution control in other similar water bodies.