Influence of the Salinity Intrusion on Island Water Source Safety: A Case Study of the Chongming Island, China

The estuary is a junction of river and sea and is also where freshwater and saltwater meet together. Salinity intrusion may happen when the runoff is relatively weaker or the tidal dynamic is relatively stronger. The Yangtze Estuary is the largest estuary in China. There are some water sources in the estuary to store and provide freshwater. The Dongfengxisha Reservoir is one of these water sources and is constructed in 2014 to provide drinking water for the islanders in the Chongming Island. The water source safety of major islands is most often suffer from the high salinity content of water. For The Dongfengxisha Reservoir, saltwater spilling over from the North Branch is a major threat under natural conditions. To research into how salinity intrusion influence on the water source safety, A two-dimensional tidal-salinity numerical model of the Yangtze Estuary is established to study the relationship between the salinity and the runoff process of the water intake in Dongfengxisha Reservoir. Salinity intrusion in the Yangtze Estuary is the most severe in January and because of its short duration, the water sources safety can be guaranteed. The northeast and northerly wind would increase the salinity of the water intake and northeast wind has a greater influence. The northwest wind would reduce the salinity of the water intake. The sustained north wind would aggravate the intrusion below the South Branch, but it would not affect the water source area. This research can provide reference for the construction of water sources in other islands.