Channel confluences happen commonly in water transport networks and natural rivers. Utilizing a 3D CFD code, a series of numerical simulations were performed using a large eddy simulation turbulence model to investigate the effect of the variations in tributary channel width and the transverse geometrical shape of the main channel on the flow parameters and vertical structure in a T-shape confluence. The code was calibrated using the experimental data from the literature. Flow parameters were considered in ratios of tributary width to the main channel width in trapezoidal and rectangular channels. Results indicate that decreasing the width ratio of the tributary channel to the main channel significantly affects the flow structure in the confluence. Generally, it increases the width and length of the main recirculation zone. It also increases the maximum velocity near the bed, especially in cases with a trapezoidal shape. Besides, it highly affects the structure and formation of the recirculation zone in trapezoidal channels.

Channel confluences are of the common structures in fluid transport channels. In this study, a series of numerical simulations were performed, utilizing a 3D code to investigate the reaction of the flow parameters and vortical structure to the variations in flow discharge and its Froude number from both main channel and tributary branch in a T-shape junction. The code was calibrated with the experimental data. Parameters, including the velocity, the turbulence energy, stream surface profile, head losses, and the transverse flow motions, were considered in different situations. It was concluded that increasing the ratio of discharge of flow from side-channel to the main channel (Q*) increased the area and power of the recirculation zone, as well as the width of separation plate downstream of the confluence, while it reduced the area of the stagnation zone (or the wake vortex) within the side-channel. It was also indicated that increasing the discharge ratio from side-channel resulted in an increase in the upstream water level in the main channels, which was dependent on the upstream discharge.

Groundwater is an important source of water in Beijing. Hydrochemical composition and water quality are the key factors to determine the availability of groundwater. Therefore, an improved integrated weight water quality index approach (IWQI) combining the entropy weight method and the stochastic simulation method is proposed. Through systematic investigation of groundwater chemical composition in different periods, using a hydrogeochemical diagram, multivariate statistics and spatial interpolation analysis, the spatial evolution characteristics and genetic mechanism of groundwater chemistry are discussed. The results show that the groundwater in the study area is weakly alkaline and low mineralized water. The south part of the study area showed higher concentrations of total dissolved solids, total hardness and ${\mathrm{NO}}_3^{-}$-N in the dry season and wet season, and the main hydrochemical types are ${\mathrm{HCO}}_3^{-}$-Ca and ${\mathrm{HCO}}_3^{-}$-Ca-Mg. The natural source mechanism of the groundwater chemical components in Chaoyang District includes rock weathering, dissolution and cation exchange, while the human-made sources are mainly residents and industrial activities. Improved IWQI evaluation results indicate that water quality decreases from southwest to northeast along groundwater flow path. The water quality index (WQI) method cannot reflect the trend of groundwater. Sensitivity analysis indicated that the improved IWQI method could describe the overall water quality reliably, accurately and stably.