# iMOD User Manual version 4.4 (html)

#### 11.10Tutorial 10: Multi-Node Well- and HFB Package

This tutorial gives an introduction to the Multi-Node Well Package (MNW, see Section 12.30) by using it in an unconfined quasi 3-D transient model. It also compares the MNW package with the conventional WEL package. We also add to this tutorial the HFB package, developed to block the horizontal flow from a particular direction.

Outline This is what you will do:

• • Load an existing model project and display the model in 3-D;

• • Construct a quick and simple model project with the WEL package;

• • Define the model as an unconfined model and simulate the model;

• Modify the model project with the MNW package and simulate the model;

• Inspect both results;

• • Change some parameters in the MNW package to simulate well losses;

• • Include the horizontal barrier flow package (HFB) and simulate the results for that configuration.

Required Data For this tutorial you need the following iMOD Data Files/folders:

• • The entire folder (and subfolders) in {path of tutorialfolder} \TUT_MNW \DBASE, containing:

• – BND \BND.IDF – boundary conditions of the model;

• – TOP \TOP.IDF – top elevation of each model layer;

• – BOT \BOT.IDF – bottom elevation of each model layer;

– HFB \SHEET_PILE.GEN – location of the sheet piling (to be created);

– WEL \WEL.IPF – location of the extraction well;

• – WEL \WEL.TXT – time series of the extraction rate of the well;

• – MNW \WEL_THIEM.IPF – location of the extraction well configured for a well loss based on Thiem equation;

– MNW \WEL.TXT – time series of the extraction rate of the well;

• • MODEL_WEL.PRJ – initial model project file;

• • MODEL_MNW.PRJ – model project file with the MNW package (to be created);

• MODEL_HFB.PRJ – model project file with the HFB package (to be created);

Getting Started

• 1. Start iMOD.

• 2. Select the option Create a New iMOD Project.

• 3. Click the Start button;

4. Activate the iMOD Manager (short-cut is Ctrl+M)

Load the Modelling Project in 3-D

We will load the modelling project and generate a 3-D image of our model.

• 5. Select the option View and then select Project Manager to start the iMOD Project Manager window;

• 6. Click the Open Projectfile button (   ) and select the file {path of tutorialfolder} \TUT_MNW \MODEL_WEL.PRJ;

• 7. Click the Open button;

• 8. Select the option (WEL) in the tree view Project Definition;

• 9. Click the Draw button (   ) to add the well file to the iMOD Manager;

• 10. Click the Zoom All button (   ) to view the location of the well.

We want to display the well in 3-D together with the modellayers, so we need to configure the Z-settings of the well via IPF Configure, let’s do that.

• 11. Right click your mouse button and select the option IPF Options and than IPF Configure to start the IPF Configure window;

• 12. Select “Z1” at the dropdown menu at Z-coordinate. (top elevation of the screen);

• 13. Check the option Sec.Z-Crd to define the secondary Z-coordinate. (botom elevation of the screen);

14. Select “Z2” at the dropdown menu at Sec.Z-Crd;

• 15. Click the button Pick Colour;

• 16. Select a red colour from the Colour window;

17. Click the Ok button to leave the Colour window;

• 18. Click the Close button to leave the IPF Configure window.

We will now load the upper- and lower elevations per model layer, we use the Special Open option from the Project Manager. This option allows you to quickly read a selection of IDF files in a particular order from the current model project to the iMOD Manager. In that way, it is easy to port the files in the right order to the Profile Tool and/or 3-D Tool.

• 19. In the Project Manager window click the Special Open button (   ) to start the Special Open window.

• 20. Click the OK button to load the selected files to the Project Manger and leave the Special Open window;

• 21. Click the Zoom All button (   ) to set the graphical display to the extent of the IDF files loaded in the iMOD Manager;

• 22. Select in the iMOD Manager all IDF-files together with the WEL.IPF;

• 23. Click the 3-D button (   ) from the iMOD Main window;

You’ll notice that prior to the 3D tool the 3D IDF Settings dialog appears. In this dialog the appearance of the IDF-files can be configured. For example, an IDF can be represented by planes (quads between mids of gridcells giving a smooth surface) and/or cubes (representing the grid cells as flat surfaces, like Lego-blocks). To visualize aquitards as solids we will combine each bottom of an aquifer with the top of the aquifer lying underneath it.

• 24. Select the option “Quasi 3D Model (aquitard)” from the Configuration dropdown menu;

• 25. Click the Apply button.

To show the well we need to instruct iMOD to ignore the associated txt file temporarily and use the Z and Sec.Z-Crd as set previously. Therefore do the following:

• 26. Select the tab IPF’s from the 3-D Tool window;

• 27. Select the option Deact. Associated Files.

Now we see our well.

• 28. Select the tab IDFs from the 3-D Tool window;

• 29. Select the option Transparancy to create translucent blocks in order to see the well clearly;

• 30. Rotate the image with your left mouse button.

The image might look like this:

The 3D-image allows you to observe that the well is penetrating all model layers; in fact the well screen is for a length of 1.0 meter in model layer 1, model layer 2 is fully penetrated and layer 3 contains 5 meters (half of the thickness of that aquifer) of the well screen. The well extracts from all three model layers, proportional to the respective length of the well screen in each layer; this will be computed by iMOD when the model definition is translated to the MF2005 WEL package. The total strength of the well is 10,000.0 m$^3$/d from December 1$^{\rm st}$ 2016 up to December 1$^{\rm st}$ 2040. Starting from December 1$^{\rm st}$ 2040 the well is turned off (0.0 m$^3$/d). This is specified in the WEL.TXT file associated to the WEL.IPF. Below is the content of that file.

2
2
DATE , -9999.0
Q , -9999.0
20161201,-10000.0
20401201, 0.0

• 31. Quit the 3-D Tool window by clicking the option File and then Quit 3-D Tool;

Run the Model

Because we want to be able to simulate layers falling dry we apply a model with unconfined model layers. In that way the areas that fall dry are no part of the simulation until these model cells are re-wetted again. When unconfined model layers are applied in iMOD, iMOD includes the wetting option of MF2005 automatically.

• 32. Whenever the Project Manager may have disappeared, pop-it-up by selecting the menu option View and than Project Manager;

• 33. Click the Save Model button (   ) to start the Define Simulation Configuration window;

• 34. Click on the button Define 3 Layer Types to start the Layer Types window.

• 35. Select the option Convertible (HNEW-BOT) for model layer 1, 2 and 3. In this way all model layers will be unconfined and the transmissivity is a function of the computed head (HNEW) minus the bottom of each model layer (BOT).

It is important to know that MF2005 includes the option to simulate model cells becoming dry when the hydraulic head of that cell drops below the bottom of that model cell. To ensure that dry cells can become part of the simulation again, iMOD includes the wetdry-option in the LPF-package automatically: it is not needed to specify extra input for this option. iMOD defines the wetdry-option to all active model cells that are part of an unconfined model layer. Whenever the head underneath the dry cell ($h_n$) is higher than 0.1 meter above the bottom of the model layer (BOT), it becomes wet again. Using this option, is more stable than using all four adjacent model cells as well. In the iteration, the head at that cell is than initially set to by following equation:

$$h = {\rm BOT} + {\rm WETFCT} \left ( h_n - {\rm BOT} \right ),$$

whereby WETFCT=0.1. These are programmed internally in iMOD as they give the most robust approach. However, whenever it is still needed to modify this, the (advanced) model user can modify the exported MF2005-files outside iMOD themselves.

• 36. Click the OK button;

From the PRJ-file iMOD has read the transient characteristics of your model; it starts at 1$^{\rm st}$ of December 2017 00:00:00 and ends at the same date. More input was not yet given to the model, but we can extent the simulation period of the model by simply defining another end date, let’s do that.

• 37. Enter the year “2050” at the Enddate;

• 38. Enter “Monthly” at the TimeSteps;

• 39. Select the option Export/Simulate Standard MODFLOW 2005.

After step Item 39. the Define Simulation Configuration window should look like in Figure 11.140.

The model will generate results on a monthly time step which is based on the definition of the input data, we can inspect this.

• 40. Enter “TUT_WEL”  at the entry field Output Folder. iMOD creates this sub folder in {installfolder}\IMOD_USER\MODELS and exports the model to MODFLOW 2005 files.

• 41. Click the Simulate on Foreground … button to start the simulation.

iMOD will now first create the necessary MODFLOW2005 files; as the model is tiny this will be will finished quickly. Immediately thereafter the simulation starts. You’ll see that the model starts in a separate DOS-command window and it will echo the simulation progress. It is a transient simulation of 396 stress periods, it probably will take something like 20 seconds of runtime (e.g. on a computer with a 2.6 GHz processor).

Note: {installfolder} refers to the full path of the directory you installed iMOD in (e.g. D:\iMOD).

Inspect the result of simulation

Let’s inspect the hydraulic head of the first model layer and the well rates and generate time series.

• 42. Select the option Map and then the option Quick Open to start the Quick Open window, see Section 6.2. With this window it is easy to open and view results from a model simulation.

• 44. Select the option “20171201” from the Time: dropdown menu.

45. Select the options “1”, “2” and “3” from the Layer dropdown menu. Tip: drag your mouse to select multiply entries of the menu field.

• 46. Click the Open button; the specified head maps are added to the iMOD Manager;

• 47. Repeat the above mentioned steps to open the results for BDGWEL as well;

48. Click the Close button to leave the Quick Open window.

iMOD will load all selected result files into the iMOD Manager and displays the result on the graphical canvas. Use your experience learned from the previous Tutorials to display the computed heads (HEAD) and the extraction rate (BDGWEL) as time series as shown in the following figure. Be aware that it can take a few seconds, as iMOD needs to open 2049 files.

Note: The extraction in model layer 1 is inactive as soon as the layer becomes dry. Also observe that the layer is re-wetted and the extraction of layer 1 is re-activated again as a result of deactivation of the extractions in the other model layers.

The total extraction for the entire duration of the model is less than was assigned to the model. So, instead of taking out 87.8E$^6$ m$^3$/d, the amount of extracted water was 86.8E$^6$ m$^3$/d. One of the advantages of the MNW package is that the total extracted amount remains intact once a model layer falls dry. Another improvement is that the extraction rate declines gradually as a model layers tends to dry, instead of abrupt as with the WEL package. The other layers will get an increased extraction for those case. Let’s observe that in the coming part of this tutorial.

Creating the Multi-Node Well (MNW) input

• 49. Select the option View and then select Project Manager to start the iMOD Project Manager window;

• 50. Click the Open Projectfile button (   ) and select the file {path of tutorialfolder} \TUT_MNW \IMOD_USER \RUNFILE \MODEL_MNW.PRJ;

• 51. Click the Open button;

This will clean the entire Project Manager first before loading in the selected PRJ file.

• 52. Select the option (MNW) in the tree view Project Definition;

• 53. Click the Draw button (   ) to add the well file to the iMOD Manager;

• 54. Select the option Map, IPF Options and than IPF Analyse ... to start the IPF Analyse window.

• 55. Click your right mouse button on the graphical canvas and select the option Select the Entire Domain.

Now we have selected our MNW-well and the values for the different attributes are presented in the table. We can see that that screens of the well starts at 96.0 m+MSL and ends at 70.0 m+MSL. This is similar to our previous well modelled by the conventional WEL package. You can also see that the methodology of computing well loss is given by the keyword THIEM and the appropriate parameter relevant to that is the RADUIS ($r_w=0.25$ m), see section Section 12.30 for more detailed information about the MNW package.

MNW computes a hydraulic head in the cell $h_n$ such that it equals the computed hydraulic head at the well minus a head loss term (e.g. the Thiem equation, see (Konikow2009)). Here we neglect head loss due to skin and local turbulence effects for that particular cell, so:

$$h_{\rm WELL}-h_n = \frac {Q_n}{2 \pi T}\rm {ln}\frac {r_0}{r_w},$$

where $Q_n$ is the well rate (m$^3$/d), $T$ is transmissivity of the aquifer (m$^2$/d) at the well, $r_0$ is the effective radius of a finite-difference cell (m), this is assumed for isotropic conditions as $r_0=0.14\sqrt {\Delta x^2+\Delta y^2}$; and $r_w$ is the actual radius of the well.

Note: Because $r_0$ is typically much larger than $r_w$, the head in a pumping well will be lower than the model-computed head. The head in the pumping well is not equal to the hydraulic head saved by the model.

Okay, let’s run the model with the MNW package.

• 56. Apply steps Item 32. and further;

• 57. Enter “TUT_MNW”  at the entry field Output Folder. iMOD creates this sub folder in {installfolder}\IMOD_USER\MODELS and exports the model to MODFLOW 2005 files.

• 58. Click the Simulate on Foreground … button to start the simulation.

Again, iMOD will first create the necessary MODFLOW2005 files and start the simulation immediately. Similar to the model using the WEL package, this model including the MNW package will also probably take no more than something like 20 seconds to run.

Compare the result of WEL and MNW simulation

Let’s inspect the hydraulic head of the first model layer and the computed distribution of extraction rates and generate time series.

• 59. Select the option Map and then the option Quick Open to start the Quick Open window, see Section 6.2. With this window it is easy to open and view results from a model simulation.

• 60. Select the option “TUT_MNW” from the Variant dropdown menu.

62. Select the option “20171201” from the Time: dropdown menu.

• 63. Select the options “1”, “2” and “3” from the Layer dropdown menu. Tip: drag your mouse to select multiply entries of the menu field.

• 64. Click the Open button;

65. Repeat the above mentioned steps to open the results for BDGMNW as well;

• 66. Click the Close button to leave the Quick Open window.

iMOD will load all selected result files into the iMOD Manager and displays the result on the graphical canvas.

• 67. Use your experience learned from the previous Tutorials to display the extraction rate (BDGMNW) as time series as shown in the following figure. Be aware that it can take a few seconds, as iMOD needs to open 1224 files.

As expected, you might observe that the total extraction rate varies and that the extraction rate for the first model layer slowly decrease to zero. At the same time the extraction of the deeper aquifers, increases to sum up to 10,000 m$^3$/d. If we look at the zoomed in image (bottom) for the period after 2040, where we turned off the well, we observe that the well rates vary although there is no external rate specified.

So, what is happening?

Well, one of the features of the MNW package is the capability of simulating intra borehole flow, actually water can move from one aquifer - through the borehole - to another aquifer. Due to the stopping of the pumping, the deeper aquifers recover quicker from the computed draw down than the unconfined aquifer, mainly due to the low storage coefficient. This causes an overpressure from the deep aquifers to the shallow one and generates a groundwater flow that migrates directly through the borehole into the first aquifer.

• 68. Use your experience learned from the previous Tutorials to display the hydraulic head (HEAD) for our model with the WEL- and MNW package as time series as shown in the following figure. Be aware that it can take a few seconds, as iMOD need to open 1632 files.

The figure of timeseries of computer hydraulic heads at the location of the well clearly shows that there is an overpressure that causes this intra borehole flow. Moreover, when comparing the hydraulic heads in layer 1 cells at the well location, in the model with the MNW package the cell remains wet for a longer period of time compared to the model with the WEL package. This is caused by the MNW package decreasing the extraction amount gradually and therefore decreases the draw down rate of the ground water head. Due to the early mentioned intra borehole flow, the heads in the model with an MNW package recover more quickly than in the model with the WEL package.

So the MNW package can really add some extra features concerning the behaviour of a well in your model. Speaking of more detail, it seems that there is a horizontal barrier (sheet pile wall) blocking the flow to our well. Let’s see how to incorporate this with iMOD into our model.

Enhancing the model with a Horizontal Flow Barrier (HFB) input

Let’s create our sheet pile wall.

• 69. Select from the main menu the option Edit, Create Features and then GENs ... to start the Create GENs window.

• 70. Click the Draw button (   ), this will start the Select window;

• 71. Select the option Line from the Shape types;

• 72. Click the Ok button.

• 73. Start drawing a line at the west side of the well. Click your left mouse button to position the first point of the line. Each left mouse click will insert another point.

• 74. Click your right mouse button to finish the drawing.

Let’s save the sheet pile wall.

• 75. Click the Save As button (   ) and save the sheet pile at{installfolder} \IMOD_USER \DBASE \TUT_MNW \SHEET_PILE.GEN.

• 76. Click the Save button.

• 77. Click the Close button to close the Create GENs window.

Now we have to add this sheet pile to our modelling project.

• 78. Select the option View and then select Project Manager to start the iMOD Project Manager window;

• 79. Select the option (HFB) in the tree view Project Definition;

• 80. Click Properties button (   ) to start the Define Characteristics for window.

• 81. Enter a value of “2”at the Assign Parameter to model layer ..., our pile sheet wall will act as barrier for the second model layer only;

• 82. Enter a value of “1000.0”at the Assign Parameter Addition Value, our pile sheet wall will have a resistance of 1000.0 days;

• 83. Click the Add File button (   ) and select the file we just created:{installfolder} \IMOD_USER \DBASE \TUT_MNW \SHEET_PILE.GEN.

• 84. Click the Add New System button to add the parameter to the modeling project; the Define Characteristics for window will be closed.

• 85. Click the Draw button (   ) to open the sheet pile to the iMOD Manager;

• 86. Click the Save As button (   ) and save a new modeling project file at{installfolder} \IMOD_USER \RUNFILES \MODEL_HFB.PRJ.

So, we’re ready to run this model.

• 87. Apply steps Item 32. and further;

• 88. Enter “TUT_HFB”  at the entry field Output Folder. iMOD creates this sub folder in {installfolder}\IMOD_USER\MODELS and exports the model to MODFLOW 2005 files.

• 89. Click the Simulate on Foreground … button to start the simulation.

Also here again iMOD will first create the necessary MODFLOW2005 files and starts the simulation. Similar to the previous 2 models, this model including the MNW + HFB package will also probably take no more than something like 20 seconds to run.

Compare the results of the MNW and HFB simulation

Let’s inspect the hydraulic head of the first model layer and generate time series.

• 90. Click the Close button to leave the Define Simulation Configuration window;

• 91. Select the option Map and then the option Quick Open to start the Quick Open window, see Section 6.2. With this window it is easy to open and view results from a model simulation.

• 92. Select the option “TUT_HFB” from the Variant dropdown menu.

• 94. Select the option “20171201” from the Time: dropdown menu.

• 95. Select the options “2” from the Layer dropdown menu.

96. Click the Open button;

• 97. Click the Close button to leave the Quick Open window.

iMOD will load all selected result files into the iMOD Manager and displays the result on the graphical canvas.
During the simulation iMOD translates the manually drawn sheet pile wall - which we saved earlier as SHEET_PILE.GEN - to a continuous (kinked) line coinciding exactly with the lateral cell faces it intersects; when utilizing the HFB package the specified resistance is assigned to these cell faces. It is always a good idea to examine the result of such a translation, e.g. to check whether the discretization has resulted in a sheet pile wall that is fully continuous and thus behaving like a true barrier. Let’s open that file.

• 98. Click the Add File button (   ) from the main toolbar and select the file{installfolder} \IMOD_USER \MODELS \TUT_HFB\MODELINPPUT \TUT_HFB_L2.GEN.

• 99. Select the file SHEET_PILE.GEN and HEAD_20171201_L2.IDF from the iMOD Manager window.

• 100. Click the Redraw button (   ).

• 101. Use your experience to change the colour of the lines.

You should see, more-or-less, the following image. In white is the actual position of the sheet pile in the model. Due to the chosen grid size, it is a little bit shifted and crenelated due to the rectangular simulation network.

You could try to experiment with more complex shapes for the HFB and/or modify the resistance of the sheet pile.