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View Maps


Following a successful model simulation, outputs are generated and Outputs branch in the Model Explorer tree for the active run.

Flow Engine Outputs

oHeads and Drawdown



oWater Table

oFlooded Cells





Transport Engine Outputs


oConcentration Residuals


Flow Engine Outputs

Upon successful completion of a flow engine simulation, heads and related outputs can be visualized at the View Maps step as discussed below.


Heads and Drawdown

At the View Maps step, you can view contours and color shading of the flow engine results.


By default, you will see color shading and contours of the calculated heads, in layer view. You can display heads along a row, and along a column, and in 3D, using the same tools as you used earlier.

If your model is transient, use the time controls above the Flex Viewer to change the output time; as you do this, all active viewers (layer, row, column, 3D), will refresh to show the heads for the new output time.



The display settings (color classes, contour line intervals, etc.) for the Layer, Cross-section, or 3D views can be adjusted in the Style settings. To load these settings, right click on Heads or Drawdown in the Outputs section of the Model Explorer, and select "Settings".  For more details about these settings, see the section on 3D Gridded Data Settings.



At the View Maps step, you can view cell-by-cell flows (read from the MODFLOW .BGT file). Once displayed in the viewer, load the Style settings for Budget, and choose the desired display type (Cells is turned on by default). Under the Colors panel (shown below), you can select from various Budget attributes:

XRate: lateral flow into the cell from the right and left face (adjacent columns)

YRate: lateral flow into the cell from the front and rear face (adjacent rows)

ZRate: vertical flow into the cell from cells in the upper and lower layer face (adjacent layers)

InFlowRate: total flow into the cell from all adjacent cells

OutFlowRate: total flow out of the cell from all adjacent cells

NetFlowRate: InFlowRate - OutFlowRate

One term will be also added for each active boundary condition type with external flows in the model simulation (e.g. Wells, Drains, Recharge, Constant Heads, Rivers, etc.).


Calculation Cell Flow–in/ Flow–out Based on Inter–Cell Flow Terms

Inter–cell flow terms are saved in the output budget file (.BGT) for three neighbors of a given cell(j,i,k):

RIGHT FACE (j+½,i,k)

FRONT FACE (j,i+½,k)

LOWER FACE (j,i,k+½)


 Indices for the six adjacent cell faces surrounding cell j,i,k.

The inter-cell flows for the remaining three faces are given by:

LEFT FACE(j-½,i,k) = RIGHT FACE([j-1]+½,i,k)

FRONT FACE(j,i+½,k) =  REAR FACE(j,[i-1]+½,k)

UPPER FACE(j,i,k+½) = LOWER FACE(j,i,[k-1]+½)


 Indices for the six adjacent cells surrounding cell j,i,k.
 Adapted from MODFLOW-2005 Users Manual, USGS Publication TM6-A16


InFlowRate (Flow In): total amount of flux into that cell. Calculated as follows:

InFlowRate =

 FLOW RIGHT FACE[i,j–1,k] * H(FLOW RIGHT FACE[i,j–1,k])

+ FLOW FRONT FACE[i–1, j, k] * H(FLOW FRONT FACE[i–1, j, k])

+ FLOW LOWER FACE[i,j,k–1] * H(FLOW LOWER FACE[i,j,k–1])


- FLOW FRONT FACE[i, j, k] * H(–FLOW FRONT FACE[i, j, k])



OutFlowRate (Flow Out): total amount of flux out of that cell. Calculated as follows:

OutFlowRate =


+ FLOW FRONT FACE[i, j, k] * H(FLOW FRONT FACE[i,j,k])


- FLOW RIGHT FACE[i,j–1,k] * H(–FLOW RIGHT FACE[i,j–1,k])

- FLOW FRONT FACE[i–1,j,k] * H(–FLOW FRONT FACE[i–1,j,k])

- FLOW LOWER FACE[i,j,k–1] * H(–FLOW LOWER FACE[i,j,k–1])


Where H(x) is the Heaviside Step Function; for more details on this function, see:

NetFlowRate = InFlowRate - OutFlowRate



At the View Maps step, you can view groundwater velocities in a variety of ways as described in the section on 3D Gridded Data Settings. By default, velocity vectors are shown as vectors.



Calculation of Velocities in Visual MODFLOW Flex for Finite Difference Grids

Model velocities are estimated in Visual MODFLOW Flex using a two-step process:

1.Estimate inter-cell velocities at each cell face in each component direction (X, Y, and Z)

2.Interpolate component velocities to the cell centroid


Inter-cell Darcy Velocity and Average Linear Velocity

Inter-cell Darcy velocities (also known as Fluxes) are calculated in Visual MODFLOW Flex using the following equations:


Inter-cell average linear velocities () are estimated from the Darcy velocities ():



is the calculated value from the model


Component velocities interpolated to the cell centroid

Component velocities are interpolated to the cell centroid by the following equations:




Water Table

The water table is the surface represented by the calculated head in the uppermost active cell in the simulation.  In 2D (Layer) and 3D views, the Water Table is displayed as a surface object, and as such has style settings similar to Surfaces (for more details on these options, see Style Settings: Surfaces.   In 2D cross-sectional view (by row or column), the water table is drawn as a solid line.  On the toolbar above the view, you have an option to control how the line is calculated and displayed.


Smooth WTL (Water Table Line): the line is smoothed (interpolated) between each grid cell. Since the line is interpolated, this is an approximation.



Discrete WTL (Water Table Line): the line is drawn as piecewise constant, with a flat line drawn across each grid cell at the elevation corresponding to the water table. This option better reflects the actual output data and the MODFLOW grid cell geometry.



If your model is Transient, you can adjust the output time as explained above, and the Water table display will update to reflect the new values for that output time.


 The Water Table is only calculated for MODFLOW-2000, -2005, -NWT, -SURFACT, and SEAWAT model runs; it is not calculated for MODFLOW-LGR.


Export Water Table

The water table data can also be exported to .CSV file for further post-processing. Right-click on Water Table from the Model Explorer and select "Export..."


The format of this file is as follows:

x (x-coordinate at center of cell)

y (y-coordinate at center of cell)

ztop (elevation of the top of layer 1; this can be used to calculate depth to water table)




wt_"time": water table value at the defined MODFLOW time step; for transient models, you will see additional columns for each saved MODFLOW time step.




Flooded Cells

Flooded cells are the collection of model cells in the uppermost active layer (i.e. water table cells) with simulated head values greater than the top of the model. These can be visualized as points or cell polygons in 2D and 3D views as a solid color (default is light blue ), or using a color ramp based on the depth of flooding (i.e. the difference between the simulated head and the top of the model).  Flooded cells have the vertices and time style settings in both the 2D and 3D views at the View Maps workflow step.  The 3D view also supports the cells style settings.



If your model included observations, you can view residuals relative to a target residual as error bars with various settings at the View Maps step, as described in the section on 3D Gridded Data.


Calculation of Residuals

In Visual MODFLOW Flex, residuals are expressed as the difference between the simulated value and the observed value. For example, the heads residuals are calculated as follows:



is the residual value

is the model-calculated value

is the observed value


Give that simulated results rarely coincide exactly with the location and time of given observations, Visual MODFLOW Flex interpolates model-calculated results. The interpolation is a two step process - the simulated values are interpolated spatially based on results from the surrounding grid cells. If the model is transient, the spatial values will be interpolated for the output time step before and after the observation and these two values are linearly interpolated in time. Using observations outside of the simulation time is generally not recommended.

When displayed in Visual MODFLOW Flex, residuals are compared to target residual values which can be set per observation or globally. For more information, please refer to the sections discussing calibration statistics and view settings.


Transport Engine Outputs

Upon successful completion of a transportation engine simulation concentrations and concentration residuals can be visualized at the View Maps step as discussed below.



If you ran a transport simulation (e.g. MT3D-MS, RT3D, or SEAWAT), you will also see output nodes for Concentration (one for each species).



The settings allow you to clip the upper and/or lower levels - for example if we use the Lower Cutoff of 20:



This would result in the following rendering of the concentrations:




The option to use lower and upper cutoffs are available both for Colormap and ThreeSlices display options.


Concentration Residuals

If the transport simulation included concentration observations, you will also output nodes for Concentration residuals (one for each observed species).  Similar to residuals for heads, you can view concentration residuals relative to a target residual as error bars with various settings, as described in the section on 3D Gridded Data.


Adjusting Style Settings

The style settings of either the 2D or 3D views can be adjusted (note, each one must be defined independently)

First make the desired property group selected and visible in the Flex Viewer.

Next make the desired 2D viewer active

Then right-click on the desired property group in the tree as shown below and select `Settings`




The 2D Colors and Contour line settings can be adjusted. For more details, see Color and Contour settings


Exporting Outputs.

Outputs can also be exported in a variety of formats. Please see the section on Exporting Files for more details.



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