Laboratory investigation of near-resonance stem motion and lateral dispersion in flexible aquatic canopy under surface wave action

Aquatic plants have significant effects on wave dynamics and contaminant transport. Using a laboratory canopy model, we investigated the interaction of a surface wave with flexible stems with a focus on the case when the wave frequency is close to natural frequency of stems. The experiments were conducted at various wave frequencies and heights at canopy densities of 0.8 and 1.2%. The oscillation amplitude of stems and the lateral dispersion coefficient were measured. Image processing techniques were employed to analyze the experiments. The results indicate that the oscillation amplitude of the stems is larger than the orbital displacement of fluid particles when the surface wave frequency approaches the stem natural frequency. However, the intensified longitudinal oscillation of stems does not lead to rapid cloud expansion beyond the effect of turbulence and vortex shedding represented by Reynolds and Keulegan-Carpenter numbers, respectively. The results confirm that a denser vegetation results in a higher transverse dispersion coefficient. By comparing to the available results for dispersion coefficient under current, we found that the lateral dispersion under wave action is much smaller than that by current.