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In slow open channel flow that features emergent vegetation, the dispersal of floating particles is affected by hydrodynamic characteristics at the free surface (e.g., surface tension), fluid drag, and inertial impaction. We investigated the interaction mechanism between floating particles and emergent stems. A mechanical model that considers the combined effect of fluid drag and inertial impaction has been presented to predict the probability that a particle collides with emergent stems. This model correctly captures the expected positive correlation between collision probability and vegetation density for dense emergent canopies. Furthermore, a new definition of the probability that a floating particle interacts with a stem is proposed. A statistical model to predict the probability that particles are permanently captured by stems is also proposed where the physical characteristics of particles (such as density and shape) are explicitly treated. Flume experiments have been conducted to explore the simultaneous effects of stem density and flow velocity on the approach and retention of slow-moving inertial particles. These experiments are used to evaluate the scaling assumptions and the proposed model performance.

Plain Language Summary We are interested about this topic because seed dispersal can play an important role in the distribution and abundance of aquatic species, and we believe it may be a hot topic in the future years. Based on former work, we have investigated the effects of stem density and flow velocity on the interaction processes between two types of floating particles and rigid emergent vegetation in open channel flow with small velocity, and many improvements have been made. In this paper, the probability that a floating particle interacts with a stem is redefined based on stem density and independent on stem arrangement pattern, which is more statistically reasonable compared with former works (e.g., Shimeta & Jumars, 1991; Peruzzo & Defina, 2012, https://doi.org/10.1029/2012WR011944). A mechanical model that considers the combined effect of capillary force and inertial force has been developed to predict the probability that a particle collides with emergent stems. We also conducted experiments to validate its reliability. Further, we develop a statistical model to predict the probability that particles are permanently captured by stems, where the physical characteristics of particles (such as density and shape) are also considered in the model.