Sound knowledge of the local distribution and diversity of freshwater snail intermediate hosts and the factors driving the occurrence and abundance of them is crucial to understanding snail-borne parasitic disease transmission and to setting up effective interventions in endemic areas. In this study, we investigated the freshwater snails, water quality parameters, physical characteristics of habitats, predators and competitors, and human activity variables at 102 sites during December 2018 and August 2019 in Shenzhen and adjacent areas in China. We used decision tree models and canonical correspondence analysis to identify the main environmental and biotic factors affecting the occurrence and abundance of snail species. A total of nine species of snail were collected throughout the study area, with Biomphalaria straminea, Sinotaia quadrata, and Physella acuta being the most predominant species. Our study showed that the most important variables affecting the abundance and occurrence of snail species were the presence of predators and competitors, macrophyte cover, chlorophyll-a, substrate type, river depth, and water velocity. In terms of human activities, snail species occurred more frequently and in larger numbers in water bodies affected by human disturbances, especially for sewage discharge, which may reduce the occurrence and abundance of snail predators and competitors. These findings suggest that proper management of water bodies to reduce water pollution may increase the abundance of snail predators and competitors, and should be considered in integrated snail control strategies in the study area.

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.