Effects of Concentration Distribution Upstream of the Diverging Area on the Characteristics of Pollutant Allocation in Branching Structures

In branching structures, the concentration distribution observed upstream of the diverging area is strongly correlated with pollutant allocation, which is crucial for developing more accurate predictive models for pollutant distribution in complex water systems. This study conducted a series of physical model experiments in branching structures. The findings revealed that the concentration distribution—characterized by two key parameters: the peak position and the standard deviation width—is a pivotal factor in determining pollutant allocation. Specifically, the more the peak position deviated from the upstream longitudinal centerline, the greater the deviation of the pollutant flux ratio from the corresponding discharge ratio; moreover, a small degree of mixing exacerbated this deviation. An exponential-type relationship was identified between the dimensionless peak position and the dimensionless deviation of the pollutant flux ratio. Based on these findings, new comprehensive equations have been proposed for predicting pollutant allocation within branching structures, utilizing the concentration distribution as a basis. These results deepen our understanding of pollutant transport and allocation mechanisms in branching structures and offer a new approach for predicting pollutant allocation.