Tracer dispersion study: Diffusion coefficient and modeling results

This work compared the outcome of tracer dispersion experiments with the results of a far field numerical modeling. The studies were carried out on two different locations from Rio de Janeiro coast: the first near the city of Maricá, approximately 30 km east from the Guanabara Bay, and the second inside the bay, at São Gonçalo. For the tracer experiment, it was used a Rhodamine, Amidorhodamine G®. The experiment released approximately 50 liters of the compound into the water. The release was made by an instantaneous injection into the system. Three ships were used during the operation to release the compound, to monitor the movement and the dilution of the Rhodamine on the water and to collect environmental data. To measures the concentration of the tracer on the field, the boats has done line measures along the movement axis of the plume. The results from the tracer experiment were used to estimate the vertical and horizontal diffusion coefficient. These coefficients were used in the far field model and the results of the modeling were compared with what was measured. The far-field model used was CHEMMAP, a model that can simulate the dispersion and distribution of chemical products on the surface and water column. It was considered the same meteorological and oceanographic conditions found by the field team. The results were similar, with little difference on the dispersion cloud. In the experiment inside Guanabara Bay, the linear correlation coefficient was 0.84 while in Maricá region it was 0.73.