WHY?
Particle tracking analyses are particularly useful for delineating capture zones or areas of influence for wells.
WHAT?
iMOD is equipped with iMODPATH that is a modified version of MODPATH version 3 ([Pollock(1994)]). iMODPATH is a particle tracking code that is used in conjunction with iMODFLOW. After running a iMODFLOW simulation, the user can designate the location of a set of particles. The particles are then tracked through time assuming they are transported by advection using the flow field computed by iMODFLOW. Particles can be tracked either forward in time or backward in time.
HOW?
Select the option Toolbox from the main menu and then choose the option Start Pathline Simulation to open the Pathlines Simulation window.
Pathlines Simulation window, Model tab for a steady-state model (left) and transient model (right)
Browse |
Select this radio button to specify a result folder from a different location. This folder need to contain subfolder that contain following subfolders BDGFLF, BDGFFF and BDGFRF. | |
Open File Click this button to search for a folder on disk. |
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Existing folder with Results available in the Models Folder |
Select one of the folders that appear in this listbox. These are folders with model results in the folder {IMOD_USER}\MODELS. | |
Existing Budget Terms |
iMOD will check those results that are available and includes the number of modellayers. |
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Alias |
Subfolder |
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Flow Lower Face [z] (m\(^3\)/d) |
BDGFLF\BDGFLF_L*.IDF |
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Flow Right Face [x] (m\(^3\)/d) |
BDGFRF\BDGFRF_L*.IDF |
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Flow Front Face [y] (m\(^3\)/d) |
BDGFFF\BDGFFF_L*.IDF |
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Displays the status of the selected model. Whenever data is missing the other tabs are greyed out. |
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Help… |
Click this button to start the HELP functionality. | |
Close |
Click this button to close the Pathlines Simulation window. | |
Pathlines Simulation window, Input tab:
Open |
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SaveAs |
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Properties |
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Generate List of Files (below) associated with Flow Boundaries |
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Using the keyword |
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Fill List Below |
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List of files … |
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Apply |
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Help … |
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Cancel |
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Boundary Settings |
Click the dropdown menu to view the current files and/or values to be used as boundary settings. Any value greater than zero determines the active flow extent in which particle tracking is allowed. As a default the boundary of the flow simulation can be used (see section 7.9), however, it is not obligatory to use that particular file. |
Top- and bottom |
Click the dropdown menu to view the current files and/or values to be used as top- and bottom elevations of the model layers. |
Porosity |
Click the dropdown menu to view the current files and/or values to be used as porosity. |
Defined via a Startpoint Definition File (ISD) |
Select this option to use an *.ISD files that configures the starting location of particles. Those *.ISD can be created by the Startpoint Tool (section 7.13) and are located in the {IMOD_USER}\STARTPOINTS folder. It is also possible to gather those files from another location using the file-selector functionalities. |
Open |
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Defined via an 3-D Point File (IPF) |
Select this option to use an *.IPF files that configures the starting location of particles. An IPF file need to have at least three columns for x,y and z. |
Open |
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Help… |
Click this button to start the Help functionality. |
Close |
Click this button to close the Pathlines Simulation window. |
Pathlines Simulation window, Time tab for a steady-state model (left) and transient model (right)
Transient |
This checkbox is selected automatically for transient solutions and deselected for steady-state solutions. |
From, to |
Specify the start- and end period whenever a transient solution is used. The input fields are filled in automatically and defined by the content of the selected result folder on the Model tab. |
Stop criteria |
Select one out of three options to specify how particles are to be treated whenever they are not captured before the end of the existing solution files (only for transient simulations). |
Stop tracing after |
Enter the number of years for which particles need to be traced. |
Help… |
Click this button to start the HELP functionality. |
Close |
Click this button to close the Pathlines Simulation window. |
Particles pass … |
Select this option to let particles pass any cell with a weak sink, no matter how “weak” they are. Be aware of the consequences of this option, since particles tend to trace over long distances until they are captured by a strong sink. This option could be wise to use whenever Forward Tracing option is selected on the Result tab. |
Particles are |
Select this option to stop particles at any cell with a weak sink, no matter how “weak” they are. Use this option whenever Backward Tracing is selected on the Result tab. |
Particles are |
Select this option to let particles stop whenever they enter a cell where the discharge is larger than a fraction of the total inflow. Whenever the fraction=1.0, particles stop at a strong sink only, as fraction=0.0, they will always stop, no matter the size of the total outflow. |
Help… |
Click this button to start the HELP functionality. |
Close |
Click this button to close the Pathlines Simulation window. |
Note: The final representation of flowpaths and/or endpoints of particles is influenced significantly by the treatment of weak sinks. A strong sink is defined as a model cell in which all flowterms are directed into the model cell. Weak sinks are those that have at least one flow component that directs outside the model cell.
There is no way that the particle tracking algorithm itself can decide correctly whether a particle should stop or not. Moreover, it is an essential scale issue, since strong or weak sinks do not exist in reality. As the scale size (rastersize) increases, the occurrences of weak sinks in the model, will increase. This is simply caused by the phenomenon that a single coarse modelcell should represent more than one internal boundary condition and represents a larger area than the area taken by the boundary condition. So, the flowterms of these coarse cells represent an average flowfield that represent on average particles that should stop and particles that should continue. Unfortunately, that particular particles can not be simulated with the coarse model, so one should decide whether the particles should stop, continue of stop/continue depending on the ratio between the total inflow and the outflow component. These three options can be chosen in iMOD
Trace Direction |
Select one of the following options: |
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Result Save as: |
Select one the following options: |
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Example of flowpaths (IFF) plotted by the 3D Tool.![]() |
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List of existing IFF or IPF file in the chosen folder. |
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Example of startpoints plotted by their age (upper figure) and their captured_by code (lower figure):![]() |
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Start IPS … |
Click this button to start the Interactive Pathline Simulation (IPS), see 7.15. iMOD will start the 3-D Tool directly and opens the IPS tab in the 3-D Tool in which pathlines might be computed interactively. The output of those simulation go straight into OpenGL and will be rendered, no results will be saved to disc, use the Start … option for that instead. Any selected SDF file will be neglected whenever the IPS is started as the starting points for the pathlines will be defined in the IPS-Tool. |
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Start … |
Click this button to start the pathline simulation. iMOD will start directly, or asks for confirmation in the situation that the output file exists already. The iMODPATH runfile will be saved in the Model folder as given on tab Model. This runfile can be re-used easily by the iMODBatch function IMODPATH (see 8.7.6). A log-file will be saved there as well, that gives information about the used files. |
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