INFLUENCE OF FLEXIBLE SUBMERGED VEGETATION ON POLLUTANT TRANSPORT IN FREE-SURFACE FLOW UNDER CONTINUOUS INJECTION

Understanding pollutant transport and dispersion mechanisms in free-surface flows is a key issue for water quality management in rivers, irrigation canals, and drainage networks. Among the factors that can significantly influence these processes, aquatic vegetation plays a crucial role by modifying the hydraulic structure of the flow, velocity profiles, and turbulent mixing mechanisms. The present study experimentally investigates the effect of flexible submerged vegetation on tracer transport in a free-surface flow under continuous injection conditions. Experiments were conducted in a 10 m long glass-sided laboratory flume installed at the laboratory of the National Agronomic Institute of Tunisia. Two flow regimes corresponding to discharges of 5 L/s and 8 L/s were examined under two bed configurations: a smooth bed and a bed covered with artificial submerged vegetation composed of flexible stems with a height of 4 cm. The tracer used was a colored saline solution continuously injected to simulate a progressive pollution input. Concentration measurements were performed at several downstream sections to analyze the temporal evolution of the tracer. Results indicate that the presence of vegetation significantly reduces concentration peaks and increases the temporal spreading of concentration curves. This behavior reflects a slowdown in pollutant propagation caused by hydraulic resistance and temporary retention effects within the vegetated canopy.