Regression model of saltwater intrusion for the Baogang reservoir in the Changjiang Estuary

The saltwater intrusion at the Baogang reservoir comes from the saltwater spilling over from the North Branch in the Changjiang Estuary, and its intensity is determined mainly by the river discharge and tide. Based on the origin and dynamic mechanism of saltwater intrusion, the tidal range at Qinglonggang gauging station 3.5 days in advance and mean river discharge at Datong station during the period from the previous 5^th to 12^th day were used in the establishment of the daily mean salinity regression model for Baogang reservoir. The regression model, which was composed of a salinity-tidal range relation and a salinity-river discharge relation, was set up by stepwise regression method. The relation between salinity and tidal range was specified through the least square fitting firstly. Then a remanent salinity could be obtained by the subtraction of the calculated tide-induced salinity from observed salinity, and was standardized to further eliminate the tide influence. The standardized remanent salinity was fitted with river discharge to derive the salinity-river discharge relation. Adding together the two fitted relations produced the pre-estimated salinity regression model. Based on the pre-estimated model, the revised salinity regression model was achieved in a similar way. Error analysis suggested that the revised salinity regression model has higher accuracy than the pre-estimated one. The salinity predicted by the regression model is generally in good agreement with the observed data. As long as tidal range at Qinglonggang and river discharge at Datong are known, it is convenient to predict the daily mean salinity for the Baogang reservoir using the salinity regression model.