Evaluating river water quality to ensure human health and the environment is one of the most important goals of physical pollutant models. In this study, the transport of dissolved substances was simulated with tracer experiments. The experiments were conducted in a flume with a length, width, and depth of 12, 0.5, and 0.7 meters, whose bed consists of fine sand with 88% of particles between 4.75 and 19 mm and an average diameter of 11.85 mm. A longitudinal slope of 0.006 was considered to simulate the bed of coarse-grained rivers. In each experiment, sodium chloride solution was injected instantaneously upstream and the penetration curves were extracted based on electrical conductivity. After calibration, the data were converted to pollutant concentrations, and the peak concentration and time to peak were extracted from the curves, and the percentage of peak concentration reduction compared to the control condition was calculated. Then, the transport of contamination was investigated in the presence of three gabion dams with fine and coarse aggregates (dimensions 75×48×40 cm). The pollutant concentration was measured by three sensors at distances of 1.5, 4.5, and 7.5 meters downstream and the curves were compared with the control sample. The results showed that fine-grained dams, due to their lower porosity and greater trapping capability, caused a greater reduction in peak concentration and increased the retention time of pollutants. The highest relative reduction in peak concentration (42.4%) was observed in the case of three fine-grained dams and low discharge. The results are at a laboratory scale and generalization to field conditions requires long-term studies and validation in real rivers.