GMS

Tips for Importing Wells to the Conceptual Model

In many MODFLOW projects, having the correct placement and settings for wells is important for getting correct results. GMS facilitates the implementation of wells by allowing well data to be imported directly into the conceptual model. This article gives an overview of importing well data directly into the conceptual model along with some tips.

Importing wells directly into the conceptual model first requires that the wells be in a file with the correct format. Typically this is a text file. Please refer to our wiki article for the correct format that GMS will use.

Other file formats, such as shapefiles, are also common, but often cannot be imported directly into the conceptual model. These other formats will import the wells into a different module, such as the GIS module, and will need to be converted over to the conceptual model.

Before importing well data into the conceptual model, make certain you have an existing map coverage with the well option turned on. Without this, the well data cannot be imported directly to the conceptual model.

When importing well data in a text file, you will use the Open command then the Import File Wizard. In the second step of the File Import Wizard, you must select "Well data" for the GMS data type. Also in the second step, make certain all the data columns are correctly assigned. Failing to assign the data columns correctly can result in errors.

Importing a well file into GMS

It should be noted that you are not limited to the number of data columns you have in the file. Therefore, you can import multiple wells at the same time. You can also import multiple time series or other data applicable to the wells using this method. Please note that while the wells and time series can be defined in the same text file, it is necessary to import the file twice: once to create the wells, and once to assign the time series to the wells. Constant flow rates can be imported at the time of well creation.

Review the well data after it has been imported. That can be done quickly by bringing up the coverage attribute table dialog for the wells. If the data was not imported correctly, minor changes can be made in using the tools in GMS.

Try out importing well data directly into the conceptual model using GMS today!

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Using the SAMG Solver for MODFLOW

Are you needing to use multiple processors to run your MODFLOW or MODFLOW-USG model? Using multiple processors can speed up the model processing time. In order to use multiple processors for MODFLOW in GMS, the SAMG solver provides the means to do this.

The SAMG solver is developed by the Fraunhofer Institute for Algorithms and Scientific Computing (SCAI). It contains a library of subroutines for the highly efficient solution of large linear systems of equations with sparse matrices. SAMG has an advantage in being almost unconditionally numerically scalable. This means that the computational cost using SAMG depends linearly on the number of unknowns.

Before using the SAMG solver, check to see if you have it added to your license. Do this by going to the Register command in the Help menu. Look through the list of components to make certain the SAMG parallel interface / solver has been enabled.

The SAMG solver works with the LMG solver package in MODFLOW. The LMG solver needs to be selected to access the SAMG solver. The LMG solver links the MODFLOW project to the SAMG solver.

SAMG warning message

To activate the SAMG solver do the following:

  1. Open the MODLOW Global/Basic Package dialog.
  2. Then open the MODFLOW Packages dialog.
  3. Turn on the LMG – Link-AMG option.
  4. A warning may appear discussing the SAMG solver. This warning can be turned off if desired.
  5. Once the LMG solver has been turned on, the Link-AMG (LMG) Package dialog can be accessed through the MODFLOW menu in order to set the solver parameters.

Using the SAMG solver is not ideal for all MODFLOW projects. It is generally meant for large linear problems and simulations which use several time steps. For the right project, SAMG can help significantly accelerate the model run time.

Contact Aquaveo’s licensing team to see about using the SAMG solver with your GMS projects.

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The HDF5 File Format and MODFLOW

The HDF5 file format is a cross platform binary format for storing scientific data. HDF5 allows you to reduce the size of the file data by compressing repeated values. This allows your data to be read and written much faster than if you stored the data as ASCII (plain text) files. GMS can read and write to HDF5 files, and stores its own HDF5 files with the other MODFLOW data files.

Exporting an HDF5 file

There are no hard file size limits. The number of objects within an HDF5 file is not limited, and the format supports complex relationships through grouping and linking. In addition to support for common metadata types, you can create user-defined metadata to accommodate whatever needs you have in your project. The only limits with these are the capabilities of your computer.

HDF5 was designed to be extensible and to allow for future changes to the platform. GMS takes advantage of this by checking HDF5 data for key values in order to substitute them into your arrays or lists. This allows you to better use transient parameters and very large pilot point sets. GMS handles the pilot point interpolation through an external routine that helps speed up the processing.

There are external HDF5 file viewers and editors, such as HDFView. However, it is very easy for you to modify the data in such a way that it makes the HDF5 unreadable by GMS. Because of this, we recommend only viewing the files using these tools. You should only manually edit the file if given explicit directions by a developer. If modifications need to be made to the HDF5 file, we recommend you make the changes to your project in GMS which will re-export the HDF5 file.

Learn more about the HDF5 file format from the HDF Group, a consortium of scientists worldwide that works on the HDF5 format. You can also read the article on the XMSWiki about using the HDF5 format with MODFLOW. This article goes into more details about multiple specific uses for the file format.

Make use of HDF5 files with MODFLOW in GMS today!

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Using the CLN Package to Model Faults and Fractures

Needing to model features or faults in your MODFLOW-USG model? The CLN Package is used in conjunction with MODFLOW-USG to model features that are significantly smaller than the individual cells in a 3D groundwater flow model. This tool allows you to model one-dimensional linear features within a three-dimensional simulation domain when the flow connections are separate from those of the aquifer. This makes it ideal for modeling fractures and faults.

CLN network map

There are a number of requirements to use the CLN package:

  1. The MODFLOW version must be set to MODFLOW-USG in the MODFLOW Global/Basic Package dialog.
  2. There must be a coverage with Wells and Wells (CLN) turned on in the Coverage Setup dialog.
  3. The coverage must have a default layer range of at least two layers, and it must be active on the layers where the CLN features will be.

The CLN package works with unstructured and 3D grids. It allows connections to be set up between the CLN cells to regular groundwater cells. You can connect a CLN cell to one or more groundwater flow cell, and CLN cells do not have to be ordered upstream to downstream. These features allow you to scale the conceptualization of the flow as needed.

For example, a single cylindrical CLN cell (representing a long fracture or fault within the ground) connected to multiple groundwater flow cells may be pumped to simulate multi-node well connections. The CLN cell extracts water from the groundwater flow cells as part of the solution to the coupled CLN and groundwater flow equations.

You can treat a CLN cell as a well by using the WEL Package to assign a source or sink to the cell. This can also be done using multiple CLN cells. Multiple fractures can be connected together to form one larger network. To make things easier, you can also use shapefiles to map the features of the CLN cells and connections.

CLN network map examples

By using this method, you can create a more complete picture of the domain you are modeling. Try using the CLN package to model faults and features in GMS today!

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