Water Abstraction Along The Yangtze River Downstream From Datong To Estuary And Its Impact On Water Discharge Into Estuary

The change of riverine water discharge into the estuary is one of the most important parameter in the estuary and the coastal zone, not only to the natural change, but also to the management policy. The Three Gorges Reservoir (TGR) on the Yangtze River began to adjust the river discharge in 2003, usually decreasing the water volumn in summer and increasing in the winter seasons. Theoretically, it will reduce the saltwater intrusion in the estuary in winter. But there are a large number of water extractions along the lower river stream from Datong to the estuary, in Anhui Province and Jiangsu Province. The water load extracted in winter seasons caused the hydrological records of Datong never correct when it means riverine discharge into the sea. This paper focuses on the water extractions and its temporal and spatial variability; want to explain the change and its impact on the fresh water supply in the estuary. Promote a method to control the Yangtze riverine discharge in winter seasons to ensure the fresh water supply and no saltwater intrusion anymore.By the end of 2014, the capacities of sluice and pumping station are 31234 m3/s. Through the analysis of the total water abstraction in the year from 2000 to 2014, it was found that the everage water abstraction was 279.52×108m3. The water abstraction of dry season accounted for 27.3% of the year from 2000 to 2014. The interannual water abstraction changes greatly, and the decrease of precipitation usually lead to an increase in water abstraction. The relative maximum values of water abstraction often occur in May, June, September and October. The water abstractions are small in December, January and February, but they account for a large proportion in Datong’s discharge, which have a more important impact on the estuary and the coastal zone.Water abstraction and drainage along the lower Yangtze River from Datong to the estuary are mainly influenced by the distribution of water projects, tide, topography and rainfall with great spatial differences in water abstraction. Water abstraction mainly occurs in Jiangsu portion. In spatial distribution of water projects, sluice density have great disparity. The density of sluice of Jiangsu Province is three times higher than that of Anhui Province and 85% of the water diversion project located in Jiangsu Province. These are the dominating reasons to the different spatial distribution of water abstraction. We carried out principal component analysis on each factors and executed multiple linear regression analysis futher on the two principal components, establishing the analytical math model between the water discharge and the two principal components.Analysis shows that the net water abstraction has a very significant impact on the saltwater intrusion in dry season:The net Datong-estuary abstraction reduces Datong’s discharge, which worsens saltwater intrusion. In dry year and a share turn from drought to flood, the net Datong-estuary abstraction strongly influences the balance between the estuary discharge and salt intrusion.This paper recommends that joint regulation mode should consider water abstraction and drainage along the river from Datong to the estuary to protect the freshwater resources in estuary area in dry season. The discharge into estuary (Qs) 16000 m3/s is regarded as the threshold value of the protection of safety of the estuary and the coastal zone’s freshwater supply, which is used to determine the mode of joint scheduling and dispatching water. Since 2000, higher frequency of dispatching often occur in December, January and February. It needs to schedule 10,14,13 times in December, January and February, respectively. Salt water intrusion usually occurs in December, January and February. And the average flow rate required to schedule are 1170 m3/s、3472 m3/s and 2728m3/s, respectively. The TGR needed to increase the release of water on the basis of the former river discharge adjusting, where 1200 m3/s、 3500 m3/s、2800 m3/s in December, January and February should be required to schedule to reach the threshold. Taking each factors’ comprehensive influence on the water abstraction into consideration to evaluate the discharge, it is predicted that the discharge adjusting, where 1600 m3/s、5100 m3/s、4400 m3/s in December, January and February should be required to schedule to reach the threshold in 2020.