Prevention of salt-tide down-draught from north branch of Yangtze River Estuary to support South-to-North Water Transfer

There are two drinking water sources in Shanghai, i.e. the Songpu Bridge water source on the upper Huangpu River, and the Chenhang Reservoir water source at the Yangtze River Estuary. The former supplies 80% of the total volume of raw water, being the grade IV surface water, and the latter supplies 20%, being the grade II surface water. To increase the total volume of water supply and improve the quality of raw water, it is necessary to strengthen the development and utilization of fresh water resources at the Yangtze River Estuary. However, in the dry season, the water quality at the Yangtze River Estuary is prone to be polluted by direct salt tide encroachment from the south branch and indirect salt tide down draught from the north branch, and hydrological tests show that the impacts of the latter is more serious. Furthermore, after the completion of the South to North Water Transfer Project, especially the west route project, the operation of the project will decrease the runoff through the Yangtze River Estuary, and lower the water level at the estuary, further aggravating the salt water encroachment to the Yangtze River Estuary. For protection of the fresh water resources of the south branch of the Yangtze River Estuary and promotion of the South to North Water Transfer Project, Shanghai Water Authority has granted a special project to search for engineering measures to prevent the salt tide down draught from the north branch and non engineering measures for reasonable dispatch and allocation of water resources of the Yangtze River.