Effect of Lateral Inflow of Branch on the Characteristics of Flow and Pollutant of the Mainstream in Tidal River

Based on the 2D hydrodynamic and water quality model of an open channel confluence at junction angle 90 with the oscillatory boundary layer, the characteristics of flow field and pollutant transport with different discharge ratios are numerically simulated. It is founded that during the period of ebb tide, a return flow separation zone and low velocity occur near the left side of releasing region downstream of the junction branch channel, and the high velocity occurs near the right side of the region. The condition during the period of flood tide is opposite, the high velocity occurs near the left side of the confluent region, and the low velocity occurs the other side. The size of the separate zone increases with the increase of the discharge ratio. The conclusion is that separation zone still exists even the zero discharge of tributary boundary is different from the situation of non tideway. There is an obvious pollution zone in the confluent region attribute to the sewage outlet in the branch. The area of pollution zone decreases with the increase of the discharge ratio. The effect of discharge ratio on the pollutant concentration at different cross sections differs by the distance of sections away from the junction.