Protection and Evaluation of Ecological Security of Source Areas of Drinking Water along Yangtze River in Jiangsu Province

Yangtze River is the drinking water source of regions along the river and the water source of the South-to-North water transfer of China, so protecting its water quality is very important. In 2003, we made an investigation in the source areas of drinking water along Yangtze River in Jiangsu province, it indicates that the majority of them had been polluted and the water quality didn't satisfy the prescribed standard. Water quality of the source areas of drinking water was affected by many factors such as the land use around every water intake, the location of mouth of tributary and sewage discharge outlet, the quantity of waste water, the treatment rate for discharged waste water, flow velocity near water intake and so on. The exploitation along Yangtze River in Jiangsu province will change land use types, land use intensity around every water intake and enhance the quantity of waste water, so it must be reasonable, otherwise it may be likely to deteriorate water quality of the source areas of drinking water. This paper mainly discusses the relationship between land use around every water intake and water quality of the source areas of drinking water. A new method is tried to do this. First, land around every water intake is divided into four units, which includes: 1) river bank from 1km upward from the water intake to 1km downward from the water intake; 2) river bank within 1km～5 km upward from the water intake; 3) river bank within 1km～5 km downward from water intake; 4) hinterland of the source area of drinking water. Generally speaking, the land use of each unit from (1) to (4) has decreasing influence in turn on water quality of the source area of drinking water. Second, the land use of each unit is subdivided into several tiers on the basis of land use types, land use intensity and sewage discharge outlets. Third, Delphi is employed to weight factors. Thus the index system for evaluating ecological security of every source area of drinking water is built. Fourth, the needed data are obtained both by method of image fusion between high-resolution satellite images and lower resolution images and by investigating on the spot. In the end, in terms of the evaluating system, the ecological security of 26 source areas of drinking water is evaluated. The results indicate that 27% of them are secure, 46% are less secure, 27% are no secure, which is consistent with current water quality by and large, so it is verified that our evaluation is accurate on the whole. Then we propose such effective means for protecting the source areas of drinking water as adjusting riverbank's function, protecting and utilizing wetland in reason etc.