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6. Dispersivity under Partially-Saturated Conditions
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Moving from fully saturated conditions to unsaturated conditions, velocity variations
will increase due to the presence of drained pores which have smaller
velocities compared to velocities within saturated pores. However, at lower
saturations, when the fraction of percolating saturated pores is very low, the
velocity distributions will start to converge, resulting in a smaller value of dispersivity,
and a decrease in the fraction of the immobile water.
We have shown that saturation-relative permeability (k r − S w ) curve may be
utilized to get insight into the behavior of α − S w curve and to approximate
the critical saturation at which the maximum dispersivity, α max , occurs.
While these computations have been restricted to the transport of tracer solutes,
they demonstrate the significant potential of this formulation of porenetwork
model for investigating other transport properties such as mass transfer
coefficients for reactive/adsorptive solute and colloid transport, through
including limited mixing within the pore bodies.
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