NUMERICAL MODELLING OF SALTWATER AND FRESHWATER FLOW DYNAMICS AT THE CONFLUENCE OF TIDAL RIVERS

The interaction between saltwater and freshwater related to complex topography at the confluence of Arakawa and Sumida River estuaries were studied using a 3D hydrodynamic model Fantom Refined and analyzed the flow characteristics using particle tracking. The analysis results showed that the saltwater distribution in the Arakawa River was well-mixed during spring tide and partially mixed during neap tide. The results of the particle tracking revealed that most of the river water flowing from the upstream to downstream of Arakawa River flows into the mainstream Arakawa River itself instead of splitting into Sumida River. In other words, it flows into a wide river with wide and straight channel. When the particles are released from the Sumida River at downstream of the confluence during the flood tide, all the particles in the surface layer pass through the Iwabuchi gate and flow into the Arakawa, while about 80% of the particles in the bottom layer flow into the upstream of the Sumida River (known as Shingashi River). In addition, the surface layer is more affected by freshwater inflow in spring tide. Furthermore, the impact of freshwater inflow at neap tide was greater than at spring tide.