66. Backward Particle Tracking, Refined Grid, Lateral Flow Boundaries
This example demonstrates a MODFLOW 6 particle tracking (PRT) model by reproducing example problem 4 from the MODPATH 7 (D. W. Pollock, 2016) example problems document (D. Pollock, 2017). An equivalent MODPATH 7 model is constructed for comparison, though only PRT results are shown.
66.1. Example description
PRT/MP7 Example 4 involves steady-state flow on an unstructured quad-refined grid. The grid has a large, irregular inactive region around its boundary. The left side of the active region is lined with injection wells to represent boundary flows. There is a quad-refined region in the upper left quadrant of the grid, in which two pumping wells are located. Particles are released from two areas: around the horizontal faces of both pumping well cells, and from the left faces of a constant-head boundary along the active region on the right border of the grid. Particles are then tracked backwards to terminating locations along the left border of the grid. Like PRT/MP7 Example 2, groundwater flows are reversed with FloPy before providing them to PRT for backwards tracking. Model parameters for this example are summarized in Table 66.1.
Parameter |
Value |
|---|---|
Number of periods |
1 |
Numer of layers |
1 |
Number of rows |
21 |
Number of columns |
26 |
Column width (\(ft\)) |
500.0 |
Row width (\(ft\)) |
500.0 |
Top of the model (\(ft\)) |
100.0 |
Layer bottom elevations (\(ft\)) |
0.0 |
Horizontal hydraulic conductivity (\(ft/d\)) |
50.0 |
Porosity (unitless) |
0.1 |
66.2. Example Results
In this example a MODFLOW 6 particle tracking (PRT) model runs in a separate simulation from the groundwater flow (GWF) model. Intercell flows are read by the PRT model from the binary budget file written by the GWF model. The model grid and boundary conditions are shown in fig Figure 66.1.
Figure 66.1 Model grid and boundary conditions, with close-up view of the refined region and the pumping wells.
Heads and pathlines are shown in fig Figure 66.2.
Figure 66.2 Heads from the flow model, with particle tracking pathlines superimposed.
66.3. References Cited
Pollock, D. (2017). MODPATH version 7: Example problems.
Pollock, D. W. (2016). User guide for MODPATH Version 7—A particle-tracking model for MODFLOW. https://doi.org/10.3133/ofr20161086
66.4. Jupyter Notebook
The Jupyter notebook used to create the MODFLOW 6 input files for this example and post-process the results is: