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iMOD User Manual version 4.4 (html)


7.14Start Pathline Simulation

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)

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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.

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Open File
Click this button to search for a folder on disk.

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.

Alias

Subfolder

Flow Lower Face [z] (m\(^3\)/d)

BDGFLF\BDGFLF_L*.IDF

Flow Right Face [x] (m\(^3\)/d)

BDGFRF\BDGFRF_L*.IDF

Flow Front Face [y] (m\(^3\)/d)

BDGFFF\BDGFFF_L*.IDF


Displays the status of the selected model. Whenever data is missing the other tabs are greyed out.

Help…

Click this button to start the HELP functionality.

Close

Click this button to close the Pathlines Simulation window.

Pathlines Simulation window, Input tab:

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Open
Click this button to open an *.IPS (iMOD Pathlines Settings) file.


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SaveAs
Click this button to save the current input settings to an *.IPS file.


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Properties
Click this button to open the Input Properties window.

Input Properties

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Generate List of Files (below) associated with Flow Boundaries
Enter the folder name to be used to construct filenames, e.g. D:\MODEL.


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Click this button to select a folder from the file selector.

Using the keyword
Enter the keyword that need to be added to the foldername, e.g. IB_L.

Fill List Below
Click this button to construct filenames for all modellayers. The above mentioned example yield the filenames D:\MODEL\IB_L1.IDF, up to modellayer 7.

List of files …
Display the filenames and/or constant values to be used in the pathline simulation. It is possible to modify these afterwards.

Apply
Click this button to use the filenames from the list.

Help …
Click this button to start the Help functionality.

Cancel
Click this button to cancel any modification to the existing list of files.

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.


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Open
Click this button to select an *.ISD (iMOD Startpoint Definition File).

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.

Example of an IPF file for startpoint definition

6
3
XCRD
YCRD
ZCRD
0,TXT
409303.493700,6017187.81200,902.4000
400622.804100,6016278.02000,922.5000
399755.548000,6017384.92100,916.2000
399765.786900,6017395.04500,918.0000
399765.786900,6017395.04500,918.0000
399351.346300,6018221.23500,897.4000


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Open
Click this button to open an *.IPF (iMOD Point File).

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)

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Transient
Simulation

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 Particle after end date:
Stop the particle simulation whenever the elapsed time of the particle exceeds the given To date.
Repeat period until particle stops:
Repeat the period selection (From-To) until the elapsed time of the particle exceeds the increased To date.
Continue with last period until particle stops:
Use the last solution within the From-To period, to simulate all particles until they are captured.

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.

Pathlines Simulation window, Weak Sinks tab:

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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
stopped …

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
stopped when
they enter …

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.

Example of Strong sink (left) and a Weak sink (right):

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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

Pathlines Simulation window, Result tab:

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Trace Direction

Select one of the following options:
Forward:
This option will compute pathlines in the direction of flow
Backward:
This option will compute pathlines against the direction of flow

Result Save as:

Select one the following options:
Save Entire Flowpath (*.iff):
Select this option to save the entire flowpath in an *.IFF file (see section Section 9.8 for more details). The IFF has the following attributes:
PARTICLE_NUMBER – number of the released particle;
ILAY – modellayer of the current particle position;
XCRD. – X coordinate of the current particle position;
YCRD. – Y coordinate of the current particle position;
ZCRD. – Z coordinate of the current particle position;
TIME(YEARS) – elapsed time on the current particle since moment of release;
VELOCITY(M/DAY) – current velocity of the particle;
IROW – row index of current location;
ICOL – column index of current location.

Example of flowpaths (IFF) plotted by the 3D Tool.

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Save End- and Startpoints (*.ipf):
Select this option to save the entire flowpath in an *.IPF file (see section Section 9.7). The IPF has the following attributes:
SP_XCRD – X coordinate of starting location of particle;
SP_YCRD – Y coordinate of starting location of particle;
SP_ZCRD – Z coordinate of starting location of particle;
SP_ILAY – modellayer of starting location of particle;
SP_IROW – row index of starting location;
SP_ICOL – column index of starting location;
EP_XCRD – X coordinate of end location of particle;
EP_YCRD – Y coordinate of end location of particle;
EP_ZCRD – Z coordinate of end location of particle;
EP_ILAY – modellayer of end location of particle;
EP_IROW – row index of end location;
EP_ICOL – column index of end location;
TIME(YEARS) – elapsed time of particle at end location;
MAXLAYER – deepest model layer that a particles passed;
DISTANCE – traveled distance of particle from begin to end location;
IDENT.NO. – number of particle;
CAPTURED_BY – code identification of capture:
-1 – error occurred
0 – initial value
1 – inactive cell
2 – velocity is zero
3 – strong sink (no outflow)
4 – weak sink (regardless of flow)
5 – weak sink outflow greater than fraction
6 – modelboundary reached
7 – elapsed time greater that maximum time allowed.

Browse:
Select this radio button to specify a result folder from a different location
Click the Open file button ( pictures/h5/image878.png) to search for this folder location or type your foldername in the text field.

Default Folder
Same folder as selected on the Model Tab referring to the chosen folder with MODFLOW fluxes available.

List of existing IFF or IPF file in the chosen folder.
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Select an existing IFF or IPF file (e.g. ISLAND.IFF) to overwrite or type a new name in the text field.

The file IMODPATH.RUN is saved in the same folder. This IMODPATH.RUN contains al settings needed to run iMODPATH and can be re-used for pathline simulation in iMOD Batch (see section Section 8.6.6)

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 Section 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.

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 Section 8.6.6). A log-file will be saved there as well, that gives information about the used files.

Example of the results of a particle tracking (black) and starting points (red dots)

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