Aquaveo & Water Resources Engineering News

MODFLOW-USG Complex Stratigraphy

MODFLOW–USG (for UnStructured Grid), was developed to support a wide variety of structured and unstructured grid types, including nested grids and grids based on prismatic triangles, rectangles, hexagons, and other cell shapes. Flexibility in grid design can be used to focus resolution along rivers and around wells, for example, or to subdiscretize individual layers to better represent hydrostratigraphic units.

MODFLOW-USG’s subdiscretization capability to better represent hydrostratigraphic units is an extremely powerful feature. Traditional MODFLOW requires that grid layers be continuous throughout the model domain even if the particular stratigraphic unit ends or pinches out.

Complex unstructured grids can be created in GMS by using the horizons approach.

There is a new video on the aquaveo youtube channel that highlights this feature. There is also a new tutorial that explains the various options associated with this feature.

Traditional MODFLOW Layering
MODFLOW-USG Layer that pinches out
3D Unstructured Grid generated using the horizons approach

MODFLOW Native Text Format

GMS uses a modified version of MODFLOW that can read data from HDF5 files. HDF5 is a binary, cross-platform file format for storing data. Large portions of the MODFLOW inputs are stored in an HDF5 file when creating a MODFLOW model in GMS. Large MODFLOW models are stored much more efficiently using HDF5 (compression ratios of 95% when compared to text files are common). Also, the read/write times are much faster with the binary HDF5 file when compared to text files.

Even though it has been shown that HDF5 with MODFLOW is extremely efficient, many users would also like to have their MODFLOW simulations in the native MODFLOW format. This is particularly true when completing a modeling project and the user needs to archive the project.

Native MODFLOW text files can be saved from GMS. Beginning with version 10.0, these text files also contain documentation comments that more clearly identify the contents of each line in the MODFLOW input file. Further, parameter definitions are also included in the text files.

There is a new video on the aquaveo youtube channel that highlights this feature. There is also a new tutorial that explains the various options associated with this feature.

GMS Sprint March 2014

  • Fixed four bugs
  • Finished advanced Run MODFLOW dialog
  • Finished improvements to MODFLOW native text
  • Created tutorial on converting existing models to MODFLOW-USG
  • Created MODFLOW-USG tutorial on quad tree refinement around rivers, wells
  • GMS asks user for local or online help preference on first-time help
  • vtu file saved with MODFLOW files
  • Some work on modflow.org
  • New plot axes finished
  • "Ortho" view for UGrids done. Symbols drawn on top when faces are filled
  • Arc and poly refinement attributes added for quadtree refinement
  • Arc and poly refinement works for quadtree UGrids
  • Added command to extrude 2D UGrid to a 3D UGrid
  • Ctrl-click to select UGrid cells now works
  • Disabled dragging UGrid nodes or editing coordinates
  • Cell size now displayed for selected UGrid cell
  • MODFLOW symbols in other layers not displayed when doing single layer
  • MODFLOW-USG arrays work like data sets - show contours
  • F2 edits selected name in Project Explorer
  • CTRL+U unselects all
  • Octree UGrid creation added
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