The Upstream Weighting package is one of several packages in MODFLOW that can be used to simulate flow in the saturated zone. The pane for this package is on the MODFLOW Packages and Programs dialog box under Flow Packages.
When the Upstream Weighting package is used, the Newton Solver (NWT) package must also be used. It will be selected automatically if the Upstream Weighting package is used. The Upstream Weighting package is only available in MODFLOW-NWT.
There is a single option in the UPW package: IPHDRY. If the IPHDRY checkbox is checked, HDRY will be printed for the convertible cells in which the simulated head is lower than the aquifer bottom. Otherwise, the simulated head will be printed even if that cell is below the bottom of the cell. If the head solution from one simulation will be used as starting heads for a subsequent simulation, or if the Observation Process is used then HDRY should not be printed to the output file for dry cells
Parameters used in the Upstream Weighting package are defined in this pane. The types of parameters that can be defined are:
•HK—horizontal hydraulic conductivity
•HANI—horizontal anisotropy (ratio of hydraulic conductivity along columns to hydraulic conductivity along rows)
•VK—vertical hydraulic conductivity in those layers that use vertical hydraulic conductivity
•VANI—vertical anisotropy in those layers that use vertical anisotropy
•SS—specific storage for models that have transient stress periods
•SY—specific yield for models that have transient stress periods and convertible layers.
•VKCB—vertical hydraulic conductivity of a quasi-three-dimensional confining layer.
These are the same parameter types defined in the LPF package.
Each parameter must have a unique Name. Only ASCII characters are allowed in parameter names.
The Value of the parameter is used to determine the input to MODFLOW.
If Use Zone is checked in the MODFLOW Packages and Programs or Manage Parameters dialog boxes, a boolean data set will be created that can be used to determine where the parameter applies. The parameter will apply everywhere where the data set is true. The name of the data set will be the name of the parameter followed by "_Zone.." If Use Zone is not checked, the parameter will apply everywhere.
If Use Multiplier is checked in the MODFLOW Packages and Programs or Manage Parameters dialog boxes, a real-number data set will be created that can be used to determine how the parameter Value is related to the input. The name of the data set will be the name of the parameter followed by "_Multiplier." The parameter value will be multiplied by the values in the multiplier data set for each cell to determine the input value for MODFLOW at that cell.
If more than one parameter of the same type applies to the same cell, the input value for MODFLOW will be the sum of the input values determined for that cell for all the parameters that apply to the cell. For example, suppose that there are two HK parameters defined: HK1 and HK2. They have Values of 10 and 20 respectively. If they both apply to the cell in column 1, row 1, layer 1 and neither has multiplier data sets, the hydraulic conductivity for that cell would be 10 + 20 = 30. Now suppose that the multiplier for HK1 was 5 at that cell. The hydraulic conductivity for that cell would be 10*5 + 20 = 70.
Parameters can also be edited in the Manage Parameters dialog box.
