Disc with radial transport Ṁ_A = 10⁻⁸ M_⊙ yr⁻¹ generated in the active layer with Σ(z) ≤ 0.1 g cm⁻². Top panel: radial velocity normalised with respect to the sound speed; bottom panel: total mass flow as a function of the distance from the star. The flow transported by the active layer is 75% of the nominal flow M_A = 10⁻⁸ M_⊙ yr⁻¹ (see text); the flow due to viscosity is clearly negligible with respect to Ṁ_A, so that the total flow is transported by the active layer and the green and red curve are superposed (the minus sign in the plot indicates inflow).