69. Backward Particle Tracking, Quad-Refined Grid, Steady-State Flow
This example demonstrates a MODFLOW 6 particle tracking (PRT) model by reproducing example problem 2 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.
69.1. Example description
PRT/MP7 Example 2 modifies the flow system from PRT/MP7 Example 1 with a quad-refined unstructured grid. The region near the well is refined three levels. This example also employs a backwards tracking analysis, in which groundwater flows are reversed with FloPy before providing them to PRT to track particle trajectories in reverse. The system includes the same well and river boundary conditions as in example 1. Model parameters for this example are summarized in Table 69.1.
Parameter |
Value |
|---|---|
Number of periods |
1 |
Number of layers (base grid) |
3 |
Number of rows (base grid) |
21 |
Number of columns (base grid) |
20 |
Column width (\(ft\)) |
500.0 |
Row width (\(ft\)) |
500.0 |
Top of the model (\(ft\)) |
400.0 |
Layer bottom elevations (\(ft\)) |
220.0, 200.0, 0.0 |
Soil porosity (unitless) |
0.1 |
Recharge rate (\(ft/d\)) |
0.005 |
Horizontal hydraulic conductivity (\(ft/d\)) |
50.0, 0.01, 200.0 |
Vertical hydraulic conductivity (\(ft/d\)) |
10.0, 0.01, 20.0 |
Well pumping rate (\(ft^3/d\)) |
–150000.0 |
River stage (\(ft\)) |
320.0 |
River bottom (\(ft\)) |
317.0 |
River conductance (\(ft^2/d\)) |
1.0e5 |
69.2. 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.
Subproblem 2A configures 16 particles for release on the horizontal faces of the cell that contains the well. Subproblem 2B configures 100 particles for release on the horizontal faces of the cell that contains the well, with another 16 particles released from the top of the cell.
Subproblem 2A pathlines and points on a 1000-day time interval are visualized in plan view in fig Figure 69.1. Subproblem 2A pathlines and 2B recharge points are shown in 3D in fig Figure 69.2. Subproblem 2B recharge points are colored by travel time in fig Figure 69.3.
Figure 69.1 Particle pathlines and 1000-day points for subproblem 2A. Points are colored by layer.
Figure 69.2 Three-dimensional perspective of pathlines and 1000-day points for subproblem 2A, and recharge points for subproblem 2B. Points are colored by layer.
Figure 69.3 Particle recharge points for subproblem 2B, colored by travel time.
69.3. 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
69.4. Jupyter Notebook
The Jupyter notebook used to create the MODFLOW 6 input files for this example and post-process the results is: