A bay in the republic of Korea has experienced significant reclamation and dredging works. Along with such artificial geomorphologic changes, a dam was built in the upstream river, which reduced the discharge of freshwater into the bay. Human induced changes in the coastal shape and freshwater supply have caused significant changes in the river environments, such as strong stratification, bottom salty water intrusion and oceanization downstream, etc. The present work investigated how such geomorphologic and hydrologic changes control the mixing and circulation in the bay and river using numerical modeling. The theoretical length of salt wedge has a relationship with the location, with 16 psu salinity observed as being ecologically important in that area. Coastline change can modified the estuarine circulation within bay but did not stronger effect on the salt wedge than other factors. The change of the interfacial shear can strengthen/weaken the salt wedge due to the discharge variation. Deepening the river channel can strengthen the stratification at the river mouth and elongates the salt wedge to river upstream. A rise in the sea level also enhances stratification and salt wedge.