The Advection Package is used to simulate transport by advective flow. The ADV: GWT Advection Package pane is on the MODFLOW Packages and Programs dialog box under Groundwater Transport| | GWT: Groundwater Transport.
The user can choose among three options for advection: Upstream, Central, or Total Variation Diminishing (TVD).
The documentation for the advection package notes that "central-in-space weighting is not often used because it can result in spurious oscillations in the simulated concentrations. It is included as an option in the ADV Package, however, because it may be useful for model testing and comparison purposes."
