Transient Retention of Floating Particles Captured by Emergent Vegetation Through Capillarity

This work presents and discusses a series of experiments focusing on the transport of floating particles, mimicking seeds and propagules, within an array of randomly arranged cylinders mimicking emergent vegetation stems. The focus is on the temporary capture process by which particles colliding with a cylinder are trapped by surface tension for finite but relatively long retention times, thus promoting a large mechanical dispersion. Video analysis of the particle paths within the array shows that the probability of particles being captured, either temporarily or permanently, as well as the mean retention time, vary with flow velocity while being weakly affected by stem density. On the contrary, stem density plays a significant role in determining the frequency of the temporary captures; in particular, the probability of having temporary, rather than permanent, captures increases with vegetation density. We also propose some relationships to predict the probability of having temporary capture events and their mean duration based on experimental results.