Transverse dispersion of non-reactive tracers in porous media: A new nonlinear relationship to predict dispersion coefficients

Laboratory experiments were carried out using a 2-dimensional acrylic glass tank filled with glass beads, quartz sand and field site material as porous media. Flow velocities and grain sizes were varied in order to cover a large range of Peclet numbers including typical field scenarios. The laboratory study was extended by a comprehensive literature search to compare the new results with earlier work. As a result we propose a new empirical relationship for prediction of transverse dispersion coefficients (Dt) which is based on the Peclet number (Pe). This new relationship indicates a nonlinear dependency on the flow velocity (νa) and grain size (d), namely a relative decrease of the dispersion coefficient with increasing flow velocity in relatively fast flowing water: Dt / Daq = Dp / Daq + 0.28(Pe)0.72 (with Pe = νad / Daq; Daq and Dp denote the aqueous and pore diffusion coefficients, resp.).