GMS

Risk Analysis for Well Groups

By aquaveo on August 3, 2022

In your groundwater model, do you need a way to capture multiple wells for risk analysis? For example, your project might have multiple pumping wells and you would like to see the probabilistic composite capture zone for all wells in the wellfield. GMS provides a way to access the Risk Analysis dialog for refining stochastic modeling results.

Example of the Risk Analysis Wizard in GMS
  1. First open your project in GMS, making sure to select the Plan View and 3D grid module, it will be more difficult to select wells otherwise.
  2. Using the Select Cells tool, drag a box around the entire grid to select all cells in the grid.
  3. Open the 3D Grid Cell Properties dialog and change the value for the MODPATH zone code to a number of your choice.
  4. Select the coverage of the well to make it active. Using the Select Points/Nodes tool, drag a box around the entire project to select all wells in the coverage.
  6. Select Intersecting Objects to open the Select Objects of Type dialog.
  7. Select 3D grid cells from the list and close the dialog. This will select all 3D grid cells that have a well in them.
  8. Open the 3D Grid Cell Properties dialog.
  9. Change the value for the MODPATH zone code to a different number than the one that was used before, close the dialog and save changes. From here, the probabilistic capture zone analysis should be able to run with the well groups setting turned on.

Please note that particles need to leave their original zone to be mapped on the risk analysis results. That is why nothing will show up when all cells were assigned to the same zone. The recommended solution is to change the zone code of just the cells with a well so that as many particles as possible can leave the assigned area.

GMS allows you to be as general or specific as you need when selecting wells for risk analysis. Try out using risk analysis for well groups using GMS today!

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Adding Multiple Screens to Well Points

By aquaveo on July 13, 2022

Do you have multiple screens to add to your MNW2 wells? Adding multiple well screens can be an important part of modeling what a well situation looks like in real life. But you might be frustrated trying to figure out how to get multiple screens on your well points. Today, we detail how to add multiple screens on MNW2 wells.

While wells with singular screens can be imported using the GMS import wizard, adding more than one screen to a well necessitates a different workflow.

To add multiple screens, add them one at a time to each well:

Example of setting multiple well screens
  1. Create a coverage with MNW2 wells enabled.
  2. Use your TXT or CSV file to add the well points to your coverage through the import wizard.
  3. Once the points are in GMS, right-click on that coverage and choose Attribute Table.
  4. Make sure that your Show dropdown is set to "all", so that each well point is visible.
  5. If needed, uncheck the checkbox in the Use screen column.
  6. In the column labeled Boreline, click on the ... to open up the z screen table for one of your points.
  7. In that table, you can list (or copy/paste) all of the well screen values applicable to that well point.
  8. Repeat steps 5–7 for each well.

Since adding multiple screens is a manual task, staying organized is an important part of it. Consider keeping track of which wells you have already added screens to. You could keep track in a spreadsheet or in a notes application of your choice. This is especially important with a large number of wells because it is not obvious in the Attribute Table which wells already have screens assigned to them.

Again, adding multiple screens is specifically for MNW2 wells. So, if you have multiple screens to add to your wells, then you might consider changing them to MNW2 wells. This would allow the wells to accommodate adding multiple screens.

If you have a project needing multiple well screens, use GMS today!

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GMS

Using the UPW Package for MODLFOW-NWT

By aquaveo on June 22, 2022

Do you have a groundwater model that might benefit from using the UPW package in GMS? The Upstream-Weighting (UPW) package is one of the four available options for flow packages for MODFLOW. It is used for calculating intercell conductances in a different manner than is done in the Block-Centered Flow (BCF), Layer Property Flow (LPF), or Hydrogeologic-Unit Flow (HUF) packages.Rather than the discrete approach of drying and rewetting that is used by the BCF, LPF, and HUF Packages, the UPW package treats nonlinearities of cell drying and rewetting by use of a continuous function of groundwater head.

Example of the UPW Package dialog

In order to use the UPW, you first need to have a MODFLOW-NWT simulation as part of your groundwater model in GMS. Once you have selected the MODFLOW-NWT version, you can use the Packages dialog to activate the UPW package.

The UPW flow package is based on the LPF package but differs in that the rewetting and vertical conductance correction options are not available. Otherwise, the UPW package allows you to work with both confined and convertible layers. It also has options for vertical hydraulic conductivity and interblock transmissivity. Array values can be set for the horizontal hydraulic conductivity, and vertical and horizontal anisotropy using the MODFLOW array editor in GMS.

Additional options are also included here. It is possible to remove vertical leakance correction or set a head value for dry cells. These options are in their own dialog accessible through the main UPW package dialog.

It should be noted that the UPW flow package is only available for use in the MODFLOW-NWT model and is not available with other versions of MODFLOW. The UPW is designed to work with the NWT linearization approach which generates an asymmetric matrix.

If you have a MODFLOW-NWT groundwater model that needs a different approach to calculating conductance, try out the UPW package in GMS today!

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GMS

Defining UGrids Layer Attributes in GMS

By aquaveo on June 1, 2022

In your groundwater model, do you need to define MODFLOW-USG attributes for a UGrid that vary by layer? For example, you might have multiple polygons that define your recharge zones for your model where the attributes on each polygon are only meant to be applied to specific layers on the UGrid. GMS provides tools for specifying how those attribute definitions get applied to UGrids.

First, you can always apply attributes directly to a UGrid using the grid approach. Doing this has the advantage of having direct control over the attributes assigned to each cell and element on each layer. However, doing this on a large UGrid or for more complex models, this can become tedious and time consuming. Using the conceptual model can aid in managing assigning attributes to layers in more complex models.

For the conceptual model approach, the Coverage Setup allows you to specify the layer range for sources, sinks, boundary conditions, and areal properties. The Layer range option must be turned on in order to specify the layer range for attributes applied to feature objects in the coverage. If Layer range option is not applied then the default layer range will be used when applying attributes on the coverage to the UGrid.

Example of Specified Layer Ranges in the Attribute Table

It should be noted that once you have chosen to assign attributes to specific layers, you will need to pay attention to which attributes are being assigned. It is recommended that you review the assigned MODFLOW attributes. Keep in mind that you cannot mix specified layer ranges with the default layer range. GMS does not give priority to the default layer range over the specified layer ranges and vice versa. For example, if you assign refinement attributes to a polygon to use a specific layer range, but leave other polygons on the same coverage to use the default layer range for refinement, this will likely cause issues in the model run or results.

GMS allows you to be as general or specific as you need when assigning MODFLOW attributes to UGrid layers. Try out defining the layer attributes for UGrids in GMS today!

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