GMS

Using Advanced Data Services Options

In the current versions of GMS, SMS, and WMS, the data service options for importing online maps has changed. It was noted by some of our users that the Advanced option for the Data Services Options dialog was removed.

We are happy to say that the advanced options for the Data Services Options dialog has been restored. The new advanced options are only available when using the Import from Web command in the release of GMS, SMS, and WMS that went out at the beginning of May 2019.

To access the Advanced options from the Data Services Options dialog, click the Advanced button, just as before, to bring up the Select Online Source dialog. This dialog allows users to bring in new data sources for downloading data.

Select Online Source Dialog

Adding new data sources to the Select Online Source dialog can be done in any of three ways:

    Add New Source Dialog
  1. The Select Online Source dialog contains a list of all of the data sources currently available. You can select one of these sources and click the Duplicate Source button to create a copy of the data source. Then, with the copy selected, click the Edit Source button to reach a dialog where you can make modifications to the source such as limiting the layers downloaded from the source or changing the image format downloaded from the source.
  2. You can click the Add New Source button to reach a dialog where you can specify the url of a new data source along with any modifications.
  3. Finally, if you have an Online Source File with the information needed to reach a source, you can click the Add Sources from File to add the source to the available list.

Sources can be deleted from the available list by selecting a source in the list and clicking the Remove Source button. Only sources that have been manually added can be removed or edited.

To get access to the new advanced options for the Data Services Options dialog, visit our downloads page today.

Blog tags: 

Splitting UGrid Layers

Have you been working with a project in GMS only to discover that the project’s 3D unstructured grid (UGrid) needs to include another layer? Fortunately, it’s rare that a UGrid needs to have another layer, but every once in a while a layer needs to be added to an existing UGrid. GMS provides a way to divide UGrid layers quickly.

One thing to note: whenever a UGrid is changed—such as with adding a new layer—the existing MODFLOW simulation attached to the UGrid will be removed. It is therefore best to make certain the UGrid is correct—including having the necessary number of layers—before building the MODFLOW simulation.

In order to add a new layer to an existing Ugrid, do the following:

  1. Using the Select Cell tool, select a cell on the layer you want to split.
  2. Right-click on the selected cell and select the Split Layer command to start the process of dividing the UGrid layer.
UGrid layer before and after being split

When GMS finishes processing, it creates a new UGrid with the additional layer, leaving the original UGrid intact. The layer to which the selected cell belonged is divided into two layers on the new UGrid. GMS averages the distance between the top and bottom of the layer, then divides the layer equally to create the two new layers. It is recommended to carefully review the new UGrid to check for any unintended anomalies.

As mentioned above, any MODFLOW simulations contained in the original UGrid are not copied to the new UGrid. A new MODFLOW simulation must be created for the new UGrid.

Another option is to create a new UGrid with the additional layer and leave the existing UGrid as is. This option is best if you need to finely control the layer elevations.

For adding layers to complicated UGrids, you may want to consider using Aquaveo’s consulting services.

Now that you’ve seen the basics of splitting a UGrid layer, try it out in GMS today!

Blog tags: 

Tips for Working with PEST

Parameter estimation using PEST can assist in data interpretation, model calibration, and predictive analysis. PEST can do a lot for your project.

Because PEST offers so much, it can be a little overwhelming to use at first. We provide tutorials and articles on our wiki to help guide you in using PEST with GMS.

In addition to the resources available in the tutorials and wiki, this post covers some useful tips that have helped some of our users.

General PEST Tips
Model calibrated using PEST

Here are some general tips for troubleshooting PEST in GMS:

  • Verify that the parameter key values have been successfully initialized under MODFLOW | Parameters. The key values should match the parameters names. For example, if the key value for hydraulic conductivity is “-30”, the parameter name should be “HK_30”. No key value should be used twice, even across different packages. To continue the example, if you have an “HK_30”, there should not be a “RCH_30”.
  • Key values are needed for both zones and pilot points.
  • Key values are expected to be negative integers. Non-integers will not be automatically recognized as key values.
  • If the key value is not a negative integer, or is a parameter from the WEL package, they will have to be manually added. If you’re missing a value, check that it initialized in the first place.
  • Parameters included in the run will be written to the *.param file. Once PEST runs, the optimal values are written to the *.par file.
  • If the iterations are giving identical values for the same parameter, check if the value is either the minimum or the maximum of the range assigned to the parameter, then evaluate if that range needs adjusting.
  • Adjusting the starting values or the PEST options may help.
Pilot Point Tips
PEST with pilot points

When using PEST and pilot points, consider the following:

  • Follow the recommended guidelines found here.
  • You can get a quick 2D Scatter set to use for pilot points with the MODFLOW Layers → 2D Scatter Points tool. This is particularly useful for areal parameters, such as HK or RCH.
  • If you’re running Null Space Monte Carlo, you must use pilot points and your interpolation method must be set to kriging.
  • If running with SVD-Assist, you can point to the Jacobian file so it doesn’t re-solve for every iteration.
  • Depending on the parameter, pilot points often should not start with zero values. This especially applies to log transforms.

We hope these tips help and that your project are improved by using PEST with GMS.

Blog tags: 

Troubleshooting MODFLOW, Part 2

A while back on this blog, we discussed troubleshooting MODFLOW errors. That blog post specifically discussed making use of the Model Checker, the MODFLOW command line output, and the output file. It also gave a few tips on how to fix your model when an error is encountered.

We wanted to expand on this, and specifically discuss what to do when you model doesn’t converge. When the model does not converge, an error message should appear in the MODFLOW command line output.

MODFLOW Not Converging

Essentially, when a model doesn’t converge component of the model has not been setup correctly. This inaccurate component may only cause the model to not converge when certain conditions have been met, but otherwise the model will converge when those conditions are not present.

As for why your model converges sometimes and not others, there are a wide range of possible causes for instability. Here are a few general suggestions for helping MODFLOW converge:

  • Check model inputs for reasonableness.
  • Try running the model with different solvers. There are several solvers to choose from, and each of them have their own strengths and weaknesses. To switch solvers, select MODFLOW | Global Options | Packages and then select a different solver in the lower left area of the MODFLOW Packages dialog.
  • Try changing the solver parameters.
  • Check the troubleshooting items for a model that is not converging can be found under item K of the Frequently Asked Questions section of the Online Guide to MODFLOW.
  • Deselecting the "Enable saving of computed flows for all source/sink objects" option in the MODFLOW Output Control dialog.
  • Reduce the time step length for the model run.

It can take some time to review the model to discover why it is not converging, but the effort it worth it for an accurate result. For more in-depth assistance with model troubleshooting, please consider reaching out to Aquaveo’s consulting team.

Blog tags: 

Pages