The GWT:Groundwater Transport Process pane is used to activate the Groundwater Transport Process. It is on the MODFLOW Packages and Programs dialog box under Groundwater Transport| | GWT: Groundwater Transport. Activating it enables the other GWT packages to be activated.
The CSUB package can not be used with Groundwater Transport.
There are two options associated with the Groundwater Transport Process.
Use flow imbalance correction activates an option in the Flow Model Interface package that causes MODFLOW to correct for an imbalance in flows by assuming that any residual flow error comes in or leaves at the concentration of the cell. When this option is activated, the GWT Model budget written to the listing file will contain two additional entries: FLOW-ERROR and FLOW-CORRECTION. These two entries will be equal but opposite in sign. The FLOWCORRECTION term is a mass flow that is added to offset the error caused by an imprecise flow balance. If these terms are not relatively small, the flow model should be rerun with stricter convergence tolerances.
Use separate time discretization activates the Flow Model Interface package and causes the transport model to be run separately from the flow model. If this option is used, the time discretization for the transport model can be different from that of the flow model. However, for each stress period, the number of steps in the flow model must either be one or equal to the number of steps in the transport model.
Simulation choice provides options for how the groundwater transport simulations will be managed.
1.With the first choice, there will be only a single simulation that includes both flow and solute transport.
2.With the second choice, there will be a flow simulation and then a separate transport simulation for each solute.
If your time steps are short enough, a single, combined flow and transport simulation should suffice. However, the transport simulation often requires shorter time steps than the flow simulation. With separate flow and transport simulation, you can achieve this by specifying shorter time steps for the transport simulations on the GWT tab MODFLOW Time dialog box. If you think you need different time discretizations for different species, the third option can be helpful.
