Dispersivity is a characteristic of the porous medium and is used to calculate the effects of mechanical mixing.
Source: Freeze, R. A., & Cherry, J. A.. 1979. Groundwater. Englewood Cliffs, New Jersey: Prentice-Hall, Inc.
How to use it:
Check the radio box next to ‘Local Dispersion L’ and/or ‘Local Dispersion T’ and input non-zero local dispersion coefficients (units: m2/day) to include lateral (L) and transverse (T) local dispersion in the solute transport simulations. Solute source concentrations and extents can be added using zones and the Sources and Sinks tabs in the Zone Attributes menu