Influence of hydrometeorological variation on saltwater intrusion in Changjiang River Estuary

Current situation of the study on the intrusion of saltwater and its influence factors,variation rules and temporal-spatial distribution in Changjiang River Estuary were discussed.3D numerical model(EFDC) was applied to the numerical calculation of hydrodynamic features and salinity of Changjiang River Estuary,Hangzhou Bay and their adjacent waters.The results were calibrated and verified with observed data.The results of the study show that the saltwater intrusion strength of the North Channel is higher than the North Passage,and the North Passage is higher than the South Passage;the outward diluting strength of the freshwater of the North Channel is also higher than the North and South Passages.Based on the simulation of the hydrodynamic features and salinity and through 15 groups of numerical experiments,the individual and integrated impacts of runoff,sea level rise,wind velocity and direction,different regulated flows of the Three Gorge Project and South-to-North Water Diversion Project(SNWDP) on the trend and effecting distance of the seawater intrusion were calculated,which shows that(1) the runoff change in dry season has a significant impact on the saltwater intrusion in Changjiang River Estuary,the less the runoff is,the stronger the saltwater intrusion becomes;(2) for the dry season flow of the SNWDP,and the dry season flow after the combined regulation of SNWDP and the Three-Gorge Project,the salinity in the South Branch is more than 0.5,and when the runoff reduced by 4 310 m3/s,the saltwater intrusion distance at the surface and bottom increased by 21.9 km and 25.6 km respectively,the effect on the surface is stronger than that on the bottom;(3) when the sea-level rises,the saltwater intrusion becomes stronger,and 0.3 m and 0.6 m of sea-level rise results in an increase of 4.0 km and 7.6 km of the saltwater intrusion distance at 1.5 salinity contours;(4) different wind velocity and direction have different influences on the saltwater intrusion,the intrusion distance resulted from 10 m/s north wind is 5.5 km and 24.0 km longer than that resulted from 10 m/s northeast wind and 5 m/s north wind or northeast wind separately.