In the study of transport and dispersion of pollutants in streams is usually used a unidimensional focus. The differential equation that describes the phenomenon is known as advection-dispersion equation and it is deduced from a mass balance in that the law of Fick is introduced. This equation contains two parameters that can be appraised of studies with tracer: the mean stream velocity, U, and the longitudinal dispersion coefficient, E L. Five different direct methods of determination of the coefficient of longitudinal dispersion are presented in this paper. These methods are conceived of the fundamental solution of the equation of the advecção-dispersion and they need the accomplishment of field tests with tracer: method of the moments, routing procedure, a graphic procedure due to Chatwin and two other simple methods based on the properties of the fundamental solution of the differential equation of the advection-dispersion.
longitudinal dispersion; tracer; water pollution
