Fig. 2. Variance of stream tube velocities, _vs² (red), and dispersivities that characterize: the spreading of an averaged breakthrough curve, equivalent dispersivity, _eq (black), the spreading of locally measured breakthrough curve, stream tube dispersivity, _s (blue), and the pore-scale dispersivity _d (green), in reference planes at different distances from the injection surface in an heterogeneous aquifer with _f² = 1, ₁ = ₂ = 5 m, ₃ = 1 m, _dL = 0.1 m, _dT = 0.01 m. Thick lines are first-order predictions; symbols refer to parameters derived from a numerical experiment in a realization of the conductivity field.