The Advection Package is used to simulate transport by advective flow. The ADV: GWE Advection Package pane is on the MODFLOW Packages and Programs dialog box under Groundwater Transport| | GWE: Groundwater Energy Transport Process.
Advection Scheme: 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."
ATS_PERCEL is the fractional cell distance submitted by the ADV Package to the adaptive time stepping (ATS) package. If ATS_PERCEL is specified and the ATS Package is active, a time step calculation will be made for each cell based on flow through the cell and cell properties. The largest time step will be calculated such that the advective fractional cell distance (ATS_PERCEL) is not exceeded for any active cell in the grid. This time-step constraint will be submitted to the ATS Package, perhaps with constraints submitted by other packages, in the calculation of the time step. ATS_PERCEL must be greater than zero. If a value of zero is specified for ATS_PERCEL the program will automatically reset it to an internal no data value to indicate that time steps should not be subject to this constraint.
