NPF: Node Property Flow Package Pane

  • Scroll to top of this topic Scroll to Top of Page

  • Print the current topic Print Topic

  • No expanding elements on this page Show/Hide Expanders

The Node Property Flow package is the package used to calculate flow between cells in MODFLOW 6. The NPF: Node Property Flow Package pane is on the MODFLOW Packages and Programs dialog box under Flow Packages.

In the Node Property Flow package, there are four methods of calculating the transmissivity between blocks in the horizontal direction. These are:

•(default)—Harmonic mean (This is most appropriate for confined and unconfined aquifers with abrupt boundaries in transmissivity at the cell boundaries or for confined aquifers with uniform hydraulic conductivity.)

•LOGARITHMIC—Logarithmic mean (This is most appropriate for confined aquifers with gradually varying transmissivities.)

•AMT-LMK—Arithmetic mean of saturated thickness and logarithmic-mean hydraulic conductivity. (This is most appropriate for unconfined aquifers with gradually varying transmissivities.)

•AMT-HMK—Arithmetic mean of saturated thickness and harmonic-mean hydraulic conductivity.

The Node Property Flow package also has a number of options. The user can select an option by checking the appropriate checkboxes.

XT3D indicates that the XT3D formulation will be used. If the RHS keyword is also included, then the XT3D additional terms will be added to the right-hand side. If the RHS keyword is excluded, then the XT3D terms will be put into the coefficient matrix. Use of XT3D will substantially increase the computational effort, but will result in improved accuracy for anisotropic conductivity fields and for unstructured grids in which the Control Volume Finite Difference (CVFD) requirement is violated. The XT3D option can not be used with the Ghost-Node Correction package.

Numerical models, such as the GWF Model, formulate a nonlinear system of equations of the form

Ax “ b,

where A is the coefficient matrix, x is the vector of dependent variables (for example, head, stage, and concentration), and b is the right-hand-side vector. If the RHS keyword is also included, then the XT3D additional terms will be added to the righthand side. If the RHS keyword is excluded, then the XT3D terms will be put into the coefficient matrix. This has the effect of causing certain values in the equation to be evaluated using values from the previous iteration or time step rather than from the current iteration of the time step. When the RHS option is used, the simulation will require less memory and computational effort  per iteration than if it is not used but may require more iterations.

The THICKSTRT option indicates that cells having a negative ICELLTYPE are confined, and their cell thickness for conductance calculations will be computed as the initial head minus the cell bottom  rather than the cell top minus the cell bottom.

VARIABLECV indicates that the vertical conductance will be calculated using the saturated thickness and properties of the overlying cell and the thickness and properties of the underlying cell. If the DEWATERED keyword is also specified, then the vertical conductance is calculated using only the saturated thickness and properties of the overlying cell if the head in the underlying cell is below its top. If these keywords are not specified, then the default condition is to calculate the vertical conductance at the start of the simulation using the initial head and the cell properties. The vertical conductance remains constant for the entire simulation.

If the DEWATERED keyword is specified, then the vertical conductance is calculated using only the saturated thickness and properties of the overlying cell if the head in the underlying cell is below its top.

PERCHED indicates that when a cell is overlying a dewatered convertible cell, the head difference used in Darcy’s Law is equal to the head in the overlying cell minus the bottom elevation of the overlying cell. If not specified, then the default is to use the head difference between the two cells.

SAVE_SPECIFIC_DISCHARGE indicates that x, y, and z components of specific discharge will be calculated at cell centers and written to the cell-by-cell flow file, which is specified with “BUDGET SAVE FILE” in Output Control.

Use horizontal anisotropy (K22OVERK) indicates that horizontal anisotropy will be defined in the data set Ky_Over_Kx. That data set will be exported as the K22 data set in MODFLOW 6. MODFLOW 6 will multiply the values in the input file by the corresponding value of K to determine the final Ky values.

Use vertical anisotropy (K33OVERK) indicates that vertical anisotropy will be defined in the data set Kz_Over_Kx That data set will be exported as the K33 data set in MODFLOW 6. MODFLOW 6 will multiply the values in the input file by the corresponding value of K to determine the final Kz values.

Some of the NPF options can not be used together or with the Newton formulation specified on the Wetting Tab of the MODFLOW Options dialog box. ModelMuse prevents the user from selecting incompatible options by disabling some options that are incompatible with the selected options.