LPF: Layer Property Flow Package Pane

The Layer Property Flow (LPF) 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. There are several options

The first two options are most often used if a layer that is really unconfined will be treated as confined to help make convergence easier.

Interpret variable Ss and SS parameters as storage coefficient rather than specific storage (STORAGECOEFFICIENT)

The specific storage is treated as if it were specific yield. Note that this applies all layers not just convertible layers.

In designated confined layers; starting heads will be used to compute cell thickness (THICKSTRT)

THICKSTRT indicates that in designated confined layers, the cell thickness for conductance calculations will be computed as [starting head-cell bottom] rather than [cell top-cell bottom]. This is normally done because the layer is really an unconfined layer being treated as confined layer to promote model stability. To designate a layer for this option select the Compute saturated thickness using starting head check box in the MODFLOW Layer Groups dialog box.

The remaining options are used to promote model convergence by disabling or simplifying some calculations regarding vertical flow.

Use cell thickness to compute vertical conductance in unconfined cells (CONSTANTCV)

CONSTANTCV indicates that vertical conductance for an unconfined cell is computed from the cell thickness rather than the saturated thickness.

Use vertical flow correction (inverse of NOCVCORRECTION)

NOCVCORRECTION indicates that vertical conductance is not corrected when the vertical flow correction is applied. The NOCVCORRECTION option is used when the checkbox is NOT checked.

Use vertical flow correction under dewatered conditions (inverse of NOVFC)

The NOVFC option turns off the vertical flow calculation described on p. 5-8 of USGS Techniques and Methods Report 6-A16 and the vertical conductance correction described on p. 5-18 of that report. The NOVFC option is used when the checkbox is NOT checked.

Skip checking that a value is defined for all cells when parameters are used to define layer data (NOPARCHECK)

Normally, when parameters are used to define a data set, MODFLOW checks that every active cell has a value defined. The NOPARCHECK option may be used to skip that check. The NOPARCHECK option can be useful to speed up automated parameter estimation once it is clear that valid input files will always be created.

Further discussion of the first 4 options may be found on pages 5-18 and 5-19 of the MODFLOW-2005 documentation. The NOVFC and NOPARCHECK optionS were added later.

Parameters used in the Layer Property Flow 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.

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.