Salinity Response to the Runoff From Yangtze River Basin at Qingcaosha Reservoir Area in Yangtze Estuary

Qingcaosha Reservoir locates in the Yangtze Estuary of China is an estuary reservoir. As the third water source region of Shanghai city, about 717,000 m³/d raw water will be supplied from the Reservoir when the project is finished. In order to avoid salt water from saltwater intrusion, it is necessary to reveal the rule of salinity variation in the Qingcaosha Reservoir area. Saltwater intrusion in the Yangtze Estuary is mainly impacted by the fresh water discharge from the Yangtze River and the open sea tides. The salinity response of Qingcaosha Reservoir area to the runoff will be discussed. In the paper, the hydrodynamic and saltwater intrusion model of Yangtze Estuary is developed and calibrated with the TELEMAC model. The model domain covers the whole Yangtze Estuary and the Hangzhou Bay. Hydrological data of 9 tidal stations and 5 current measuring points during spring tide, middle tide and neap tide in March, 2002, are used to calibrate the salinity data. Comparisons of the calculated results and measurements show that the hydrodynamic model and the salinity model can reflect precisely the law of currents and the salt water intrusion in the Yangtze Estuary, and they can be used to forecast the salinity in Qingcaosha Reservoir region. According to the different characteristic discharges corresponding to the different cumulative frequencies, the salinity distributions in Yangtze Estuary are calculated under the conditions of different flow into the sea. The simulation results show that the salinity values will decrease with the increasing of discharge. When the upstream discharge is below 16,700 m³/s, the average value in dry season, the salinity response to the runoff is very sensitive. The salinity amplitude at the downstream gate area is inversely proportional to the upstream discharge, whereas, the parameter at upstream gate area is proportional to the upstream discharge if it isn’t up to the average value in dry seasons. The salinity at the downstream area of reservoir is obviously higher than that at the head region.