GMS

Using the Drawing Grid in GMS

By aquaveo on September 22, 2021

Have you needed to create precise drawing on your map coverage for your groundwater modeling project in GMS? Using the Drawing Grid display options can help with this. This post will review what these are and how they can be used in your GMS project.

When the drawing grid is turned on, you will have a grid which can be used to reference and measure positions in the project.

To access the GMS Drawing Grid display options:

Open up the Display Options dialog, either by going to the Display | Display Options command or clicking on the Display Options macro.
Once the dialog has opened up, select Drawing Grid from the list on the left, and the dialog will populate with the relevant options.

The following is a list of the GMS Drawing Grid display options and what they do.

This Spacing option allows the user to specify by how many units each grid point is separated. This will determine how dense or scattered out the points are, so it is useful to set a value that won’t either be too cluttered or too open.

When the Snap option is selected, all new (not previously existing) vertices, nodes, points, etc., will snap to the nearest grid point when they are being created, or will interactively snap to grid points if they are being dragged. When this is not selected, the drawn grid will have no impact on where they will be placed. Turning this on can be useful when constructing certain features that are meant to conform to the more rigid structure of a grid.

When the Display Grid Lines option is selected, grid lines will be displayed, using the Line spacing increment to determine how many grid points are passed over before another line is drawn. There are also two buttons to the right of this option which will allow the user to customize the look of the lines. Using grid lines can help complement grid points by giving more of a structure to the drawing grid rather than it being just a set of points, especially when the lines are separated at a good distance.

When the Display Grid Points option is selected, grid points will be displayed similar to how the grid lines are displayed, except using the Point spacing increment instead of the Line spacing increment. Grid points not displayed are still functioning as intended within GMS, they just aren’t visible. There are also two buttons to the right of this option which will allow the user to customize the look of the points. Using grid points can help quantify in the Graphics Window where everything is placed and give it orientation, especially when the points are separated at a good distance.

Try experimenting with Drawing Grid display options in GMS 10.5 today!

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GMS

Using the Equal Color Segment Height Legend Option

By aquaveo on September 1, 2021

Have you wanted the legend to better represent the scale of your contours in your GMS projects, especially if your intervals are logarithmic? Having a well-configured legend can be very helpful in interpreting the contours of your project in the Graphics Window. And a logarithmic scale for your legend can be useful when you have wide-ranging values in your model that you want to represent in a compact and nuanced way. This post will review how to modify your contour legend options and how your legend is scaled.

To access the GMS Contour Legend Options:

First, contour options can be accessed either through relevant parts of the Display Options dialog (accessed from the Display Options macro) or through clicking on the Contour Options macro directly.
Look to the bottom-left of the dialog and turn on the Legend checkbox.
Click the Options button to bring up the Contour Legend Options dialog where all the contour legend options will be. This post won’t go into most of these options, but they include such options as setting the legend’s height and width, setting where in the graphics window it will be situated, and customizing its font.

Countour legend using an equal height option

The focus of this post will be the option to turn on Equal Color Segment Height. If the Contour Interval has been set to Number or Specified Interval, this option might not seem so useful, as the values for the contours should already be equally separated. But if the Contour Interval has been set to Specified Values, the Populate Values button will be clickable. This brings up the Value Population Method dialog, where different methods can be used to populate the values of the contours, including a Log Scale Method that will create a logarithmic rather than linear scale to the contours and their legend.

Normally, when a logarithmic scale is used for the contours, the legend will be as well, leading to a lot of the space on the legend being taken up by the higher values and a small amount of space being taken up by the more crowded lower values. Turning on Equal color segment height in the Contour Legend Options dialog can correct this, if that is how you want the legend to be displayed. This option will make the legend display logarithmically, with each logarithmic value displaying equally distant from each other. This means that the legend is no longer a linear gradient, but it better reflects the spread of a logarithmic scale when one is used.

Try experimenting with logarithmic contour intervals and other contour options in GMS 10.5 today!

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GMS

Using A Well Pumping Rate to Calibrate a Model

By aquaveo on August 11, 2021

Have you needed to know how to use a well pumping rate as a calibration parameter in a PEST run? For example, this might be useful in estimating a probabilistic capture zone. We have a workflow that can help with this, utilizing an extraction well and the WEL package for model calibration. This post will review how you can set your MODFLOW parameters in GMS to incorporate well information to be used for parameter estimation.

To do so, use the following steps:

In a well coverage, create a well and give it a constant pumping rate (negative for extraction).
Go to MODFLOW | Parameters... to bring up the Parameters dialog and click the New button to create a new parameter.
Turn on the Show all columns checkbox at the top of the dialog and change the Type value to WELL.
Enter the value that was used for step 1 as the Key, and enter its inverse as the Value.
Enter values for Min and Max that are greater than 0.0. These values and Value will be multiplied by the Q factor later on, which will be -1.0, so positive values listed here will actually become negative.
Turn on the Log Xform checkbox and close the dialog.
Go to MODFLOW | Optional Packages | WEL - Well… to bring up the MODFLOW Well Package dialog.
Enter a Q factor of -1.0 and close the dialog.
Go to MODFLOW | Global Options… to bring up the MODFLOW Global/Basic Package dialog.
Under the Run options section, select Parameter Estimation and close the dialog.
Create a new Observed Flow coverage with Observation Points set to Head in the Coverage Setup dialog, and create a head observation with the Map module active.
Save the project and then click Run MODFLOW to run the PEST Parameter Estimation. When the run is complete, make sure to read the solution into your GMS project.

Example of PEST running using pumping rate as a parameter

Following the above steps will generate solution data where you can use any of the post-processing tools in GMS to review and adjust your model. Try out using well pumping rates in model calibration in GMS 10.5 today!

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GMS

Mapping Multiple Coverages in GMS

By aquaveo on July 21, 2021

Do you have a conceptual model project in GMS where you have multiple map coverages with values for the same MODFLOW package? Are you wondering how GMS maps values from multiple coverages over to the MODFLOW packages?

It's not unusual for some projects to require the same attributes to be in separate coverages rather than having all the attributes in a single coverage. For example you might want to use recharge attributes from different sources and have placed the values on different coverages. But how exactly does GMS handle this? This post should hopefully give you a better sense of what GMS is doing behind the scenes.

Normally, the values for a particular MODFLOW package, such as recharge, are placed on one coverage that uses multiple polygons. In this case, a single value can be calculated, taken only from the predominant polygon, as it is expected that the polygons will all be within the same coverage. Also in this case, the methodology is designed to accommodate polygons being used to calibrate recharge zones in PEST, as opposed to calibrating with pilot points. If using gradient recharges, it is recommended to use scatter points to interpolate recharge values to MODFLOW layers.

You may have a case where you have the values for a package, such as recharge, on polygons on different map coverages. This could be because you imported the values from different sources. In cases where the polygons on different map coverage overlap, the attribute types with different values will have those values summed up when they are applied all at once if you map all of the coverages at the same time. If you don’t want them summed up, make sure that rather than applying them all at once, the value you want is the last value mapped over. This is because when multiple coverages are applied at once, GMS sum the values cumulatively, but when done individually, GMS overwrites the value with the most recently mapped coverage.

It is important to note that hydraulic conductivity is not cumulative, though the sources may be. Hydraulic conductivity is overwritten every time, so the values MODFLOW receives are the values of the last polygon that intersected an individual cell.

Items in the Project Explorer are mapped in descending order, so changing the order of the coverages can change the end results.

You can also find more information on how objects are mapped to MODFLOW at the Aquaveo XMS Wiki.

Try mapping multiple coverages in GMS 10.5 today!

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GMS