The river discharged flow behavior in the ROFI (Regions of Freshwater Influence; Simpson, 1997) is studied using FVCOM (Chen et al, 2006), an unstructured grid primitive equation model. In the present study we can resolve detailed motion near the river mouth and consider the effect of an obstacle (a sea mount or an island) placed in front of the river mouth. The unstructured grid zooms up the behavior of a bulge which was widely observed in earlier estuarine model studies and we could investigate the separation of the bulge by the anti-cyclonic motion due to the river discharge. A sea mount seems to play a similar role as the core of a bulge, but in a case with an island, totally different flow patterns were observed, since island can affect the surface motions. Under the same geometrical conditions, we also considered tide, which could enhance vertical mixing and change flow patterns induced by the river discharge.