In this paper, we investigate the effects of stem density and flow velocity on interaction processes between two types of floating particles and rigid emergent vegetation in open channel flow. A new definition of the probability that a floating particle interacts with a stem is proposed and validated, and particle–stem interaction processes (including collision and capture mechanisms) are further explored, including a collision model proposed and validated to predict the probability of collision with a correction parameter. We also establish an appropriate length scale to analyse the particle–stem mechanism (for the vegetation characteristics and arrangement used in this study). A more accurate statistical model based on Gamma function is proposed to describe floating particle dispersal from unvegetated section to vegetated section, which is verified compared with exponential model, and two empirical formulas are …