Study On Effects Of The South-to-north Water Diversion Project On Nansi Lake’s Water Environmental Safety

Nansi Lake is the only canal to transport water for the south-to-north water diversion project, and it is also a very important regulation and storing lake in North China, it also has a considerable degree of effect on configuration of scheduling for water resources. In this paper, a research is conducted to survay the present situation of international and domestic water diversion projects, analyze the impact of the south-to-north water diversion project to Nansi Lake’s water environmental factors, and Nansi Lake water environment is evaluated by the way of BP neural network, MIKE21 model of Nansi Lake is established. The following aspects are the main parts included in the research.Examine the development of domestic and international water transfer projects, and then extend to the impact of the south-to-north water diversion project on Nansi Lake. Analyze the impact of the south-to-north water diversion project on Nansi Lake’s water environmental safety from 3 aspects of water environmental factors, dry and wet season and surrounding tributaries.Study on the common methods of water environmental assessment and decide to set up the Nansi Lake’s grid of water environmental assessment using BP neural network. For the relatively complex multi-factor water environmental system of Nansi Lake, use MATLAB to compute and make the monitoring data poblished by the environmental protection agency of Shan Dong province to be the training target, evaluate the water environment of Nansi Lake, then get the conclusion that the Nansi Lake’s water environment could almost reach the national standard and meet the requirements of the south-to-north water diversion project.Study on the common species of water environmental model and decide to set up the Nansi Lake’s model of water environmental assessment using the software of MIKE published by DHI after considering the need of Nansi Lake. Then analyze the impact of the south-to-north water diversion project on Nansi Lake’s water environmental safety from 4 aspects of water level, water flow field, velocity of water flow and water quality.After setting up the Nansi Lake’s MIKE21 model of water environmental, respectively monitor the water level of Nansi Lake on the condition of the water diversion project working and not working, and then obtain the outputs that on the condition of the water diversion project not working, Nansi Lake’s high water level position is in the narrow segment of Zhaoyang Lake, which is in a unfavorable hydraulic condition.However, on the condition of the water diversion project working,Water level of the vast Weishan Lake rise and the water level of Zhaoyang Lake slowly go down, which is in a favorable hydraulic condition. Respectively monitor the water flow field of Nansi Lake on the condition of the water diversion project working and not working, and then obtain the outputs that on the condition of the water diversion project not working, around the islands in the in the downstream of Erji Dam, the east and west side of the junction of Zhaoyang Lake and Weishan Lake and the north part of Weishan Island, which 3 area get low rad values. It shows that these 3 area’s have less liquid that in a unfavorable hydraulic condition. However, on the condition of the water diversion project working, devising water’s high flow velocity and large flow make these area get more liquid and higher rad values. Respectively monitor the velocity of water flow of Nansi Lake on the condition of the water diversion project working and not working, and then obtain the outputs that the estuary on the north of Pei County, southwest of the junction of Zhaoyang Lake and Weishan Lake and around Weishan Lake, which 3 area get low water flow velocity, which comes to under 0.04m/s. This tends to form dead water zones, water districts and other low flow area, which is in a unfavorable hydraulic condition.However, on the condition of the water diversion project working, most of waters of the lake have better larger liquidity, faster switching speed of flow and diffusion.Water of the south-to-north water diversion project which has better quality brings Nansi Lake better water quality after water mixing, therefore the representative pollutants such as TN,NH3-N and PO4 are reduced. Analyze from aspects of water level, water flow field, velocity of water flow and water quality, the south-to-north water diversion project improves the water environment of Nansi Lake.