The coefficients of the dimensionless partial differential equation of convection-diffusion-dispersion of flood waves are shown to be functions of the Froude and Vedernikov numbers only. The Froude number is the ratio of mean velocity to relative dynamic wave celerity. The Vedernikov number is the ratio of relative kinematic wave celerity to relative dynamic wave celerity. The third-order convection-diffusion-dispersion equation can be used to analyze flood propagation problems where both diffusion and dispersion are deemed to be significant. ¿ American Geophysical Union 1994