Advec ve – Dispersive Equa on with Spa al Frac onal Deriva ves Evaluated with Tracer Transport Data

242 A dispersion are considered to be the dominant mechanisms of solute transport in the vadose zone, i.e., the variably saturated layer of soils and sediments between the soil surface and groundwater table (Jury and Flühler, 1992). Advection is associated with the average water fl ux or velocity, whereas hydrodynamic dispersion is modeled using an analog of Fick’s law corresponding to the Brownian motion of solute particles relative to the average advective fl ow (Bhattacharya and Gupta, 1990). Under these assumptions, the parabolic one-dimensional ADE is the mass conservation equation for the transport of an inert (conservative) solute in a homogeneous rigid porous medium with steady-state water fl ow: ∂ ∂ ∂ − ∂ ∂ ∂ 2