Longitudinal Dispersion from Cylinders to Realistic Plant Forms

Many studies on the hydrodynamics and mixing processes due to vegetation have significantly simplified the physical characteristics of plants by representing the stem distribution, e.g. for reeds, as an array of cylinders.These studies often use single diameter cylinders, placed in regular arrays, producing unrealistic preferential flow paths.New solute tracing studies (Machibya 2024) were performed using realistic plant forms, with leaves, stems and branches.Experiments were conducted in a 12.5 m long, 300 mm wide flume and longitudinal dispersion coefficients (Dx) were determined over a range of discharges.The results confirm the linear relationship between Dx and the mean velocity, u observed in cylinder arrays.The longitudinal dispersion coefficients for the realistic plant forms were found to be an order of magnitude greater than those from studies conducted using cylinders.This illustrates and quantifies the effect of plant structure on solute mixing processes.