When the flow parameters, such as celerity and hydrodynamic dispersion coefficient, are allowed to vary spatially within a basin, three mechanisms, namely, geomorphologic, kinematic, and hydrodynamic dispersion, contribute to the variance of the instantaneous response function. The relative contributions of the three dispersion mechanisms as a function of scale, or Strahler order of the basin, are studied. This analysis is performed for two study basins, the Vermilion and the Mackinaw river basins, in central Illinois. Log linear trends for all the dispersion coefficients as a function of scale are observed. These trends can be cast in the form of Horton law type of relations. The asymptotic behavior of the dispersion coefficients of basins with self-similar network structure is consistent with the observations.