# iMOD User Manual version 5.2 (html)

#### 11.12Tutorial 11: Unsaturated Zone Package

This tutorial gives an introduction to a transient implementation of the Unsaturated Zone package (UZF), see section 12.31.

Outline

This is what you will do:

• • Create a transient PRJ file with TOP, BOT, KHV, RCH and EVT package;

• • Simulate the RCH and EVT package for an unconfined model and examine the results;

• • Modify the PRJ file with the UZF package;

• • Simulate the UZF package and examine the results and compare it with the conventional RCH and EVT model;

• • Modify the parameters of the UZF package to see the impact of parameters;

Required Data

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

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

• – . \TOP \TOP_L*.IDF – IDF files with top of model layers (3);

• – . \BOT \BOT_l*.IDF – IDF files with bottom of model layers (3);

• – . \PREC \PREC_*.IDF – IDF files with precipitation on a daily base;

• • MODEL_RCH_EVT.PRJ – model project file with RCH and EVT package (to be created);

• • MODEL_UZF.PRJ – model project file with UZF package (to be created);

Getting Started

• 1. Start iMOD.

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

• 3. Click the Start button;

Create a PRJ file

We will quickly generate a PRJ file using the auto fill option of the Project Manager.

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

• 5. Select the option (TOP) in the tree view Project Definition;

• 6. Click Define Characteristics Automatically button (   ) to start the Define Characteristics for window.

• 7. Add the following string to the second column in the table “{path of tutorialfolder} \TUT_UZF \DBASE \TOP \TOP_L*.IDF”;

• 8. Select the option Select files within Given Layer Range and enter “1” and“3” in the input fields to the right.

In this manner we tell iMOD to add the given files for model layer 1,2 and 3 automatically. Let’s see how that works.

• 9. Click the Allocate Files ... button.

iMOD will pop-up a window with the files found in the Automatic Package Allocation window.

Here we can inspect the results, or even modify this. We leave it like this as it is correct and continue.

• 10. Click the Add System button, this will add the files to our modelling project and closes the Automatic Package Allocation window.

• 11. Repeat the steps 5 up to 10 for the bottom of the model layers (keyword is BOT), these are stored in “{path of tutorialfolder} \TUT_UZF \DBASE \BOT \BOT_L*.IDF”.

Also constant values for a package or modules can be inserted in this manner, as the boundary conditions of our three-layered model are all equal one, we insert this information as follows:

• 12. Select the option (BND) in the tree view Project Definition;

• 13. Click Define Characteristics Automatically button (   ) to start the Define Characteristics for window.

• 14. Add the following string to the second column in the table “1”;

• 15. Select the option Select files within Given Layer Range and enter “1” and“3” in the input fields to the right.

• 16. Click the Allocate Files ... button.

• 17. Click the Add System button, this will add the files to our modelling project and closes the Automatic Package Allocation window.

That’s convenient, right? Let’s add the constant information for the other packages repeating the steps 12 up to 17.

• 18. Add a constant starting head of “95.0” m+MSL for the SHD package (starting heads) for the model layers 1,2 and 3;

• 19. Add a constant starting head of “10.0” m/d for the KHV package (horizontal permeability) for the model layers 1,2 and 3;

• 20. Add a constant starting head of “1.0” for the KVA package (vertical anisotropy) for the model layers 1,2 and 3;

• 21. Add a constant starting head of “0.3” for the SPY package (specific yield) for the model layers 1,2 and 3.

Next thing is to add the confined storage coefficients (STO).

• 22. Select the option (STO) in the tree view Project Definition;

• 23. Click Define Characteristics Automatically button (   ) to start the Define Characteristics for window.

• 24. Add the following string to the second column in the table “0.2E-03”;

• 25. Select the option Select files within Given Layer Range and enter “1” and“3” in the input fields to the right.

• 26. Click the Allocate Files ... button.

• 27. Modify the value “0.2E-03” for model layer 1 into “1.0”;

• 28. Click the Add System button, this will add the files to our modelling project and closes the Automatic Package Allocation window.

Almost done, we will add the Evaporation package (EVT) on the conventional way as it will be defined for our first stress period only.

• 29. Select the option (EVT) in the tree view Project Definition.

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

• 31. Select the option Transient, start from and enter the date “6 October 2013” in the date entry fields.

• 32. Select the option Assign a Single Value to all Cells.

We will enter the 3 following values for the different input parameters by selecting the appropriate parameter from the Parameter dropdown list sequentially.

• 33. First select (EVA) Evapotranspiration Rate (IDF) and assign the value 10.0 (mm/day).

• 34. Than select (SUR) Surface Level (IDF) and make it 100.0 (m+MSL)

• 35. Finally select (EXD) Extinction Depth (IDF) and assign value 8.0 (m).

• 36. Click the Add System button to add the parameter to the modelling project and close the Define Characteristics for window.

Note: By defining a surface level (SUR) of 100.0 m+MSL and an extinction depth (EXD) of 8.0, there will be a linear reduction of evaporation with depth. At a depth of 8 m+MSL (2 meter above the bottom of model layer 1), the evaporation is 0.0.

Precipitation is the input parameter that varies per stress period. We will add that parameter with the automatic package allocation.

• 37. Select the option (RCH) in the tree view Project Definition.

• 38. Click Define Characteristics Automatically button (   ) to start the Define Characteristics for window.

• 39. Add the following string to the second column in the table (without quotes) {root of your Tutorial folder} \TUT_UZF \DBASE \PREC \PREC_*.IDF.

• 40. Select the option iMOD will look for unique TIME STEPS ...

• 41. Click the Allocate Files ... button.

• 42. Click the Add System button, this will add the files to our modelling project and closes the Automatic Package Allocation window.

We have add now 459 definitions for precipitation in a single mouse click, that’s awesome isn’t it. Final thing to do is to add the configuration for the PCG solver.

• 43. Select the option (PCG) in the tree view Project Definition.

• 44. Click Properties button (   ) to start the PCG settings window.

• 45. Click the Apply button to add the parameter to the modelling project and close the PCG settings window.

Okay, we’re done, let’s save the modelling project.

• 46. Click the Save As button (   ) and save a new modeling project file at{installfolder} \IMOD_USER \RUNFILE \MODEL_RCH_EVT.PRJ.

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

Simulate the model

With this project file we generate a standard MODFLOW2005 model, let’s do that.

• 47. Click the Start Simulation Manager button (   ) to start the Simulation Manger window;

• 48. On the tab Main select the option Standard MODFLOW 2005.

• 49. Select the tab Layers/Packages.

• 50. 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).

• 51. Go to the tab Time dim. to define the time dimensions.

iMOD has found out what the transient content of your model is, it starts at 6$^{\rm st}$ of October 2013 00:00:00 and ends at the 7$^{\rm st}$ of January 2015 00:00:00. based on the entered precipitation (RCH) and evaporation (EVT) data.

• 52. Be sure that the option “Packages ”  is selected from the TimeSteps: dropdown menu field.

• 53. Click the option Fill In Actual Stress Periods.

iMOD will generate 459 stress periods in the section Actual Stress Perios Configuration. For each timestep the model results are saved, this is indicated as value 1 in the column Save.

We will leave the definition of the stress-periods for now.

• 54. Go to the Tab Output to organize the output of RCH flux files.

• 55. Select (RCH) Recharge from the field Result Variable:.

• 56. Select Layer 1 from the field Selected Modellayers:.

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

• 59. Click the Start … button to start the simulation.

• 60. Clik the YES button to confirm the simulation.

iMOD will now create the necessary MODFLOW2005 file and runs the model, as the model is tiny, this will be finished rapidly. It will start the simulation directly thereafter. You’ll see that the model start in a separate DOS-command window and it will echo the simulation progress. As it is a transient simulation with 458 stress periods, it will consume probably 10 seconds to accomplish.

Inspect the result of simulation

Let’s inspect the hydraulic head of the first model layer and the computed recharge (equal to the input in fact) and generate time series.

• 61. 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.

• 63. Select the option “20131006” from the Time: dropdown menu.

• 64. Select the option “1” from the Layer menu.

• 65. Click the Open button.

• 66. Repeat the above mentioned steps to open the results for BDGRCH as well.

iMOD will load all selected results 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 as time series as shown in the following figure.

Note: Modify the settings of the time series to assign the recharge from the BDGRCH on the second y-axes and use “BlockLines” as LineStyle.

As you may have noticed, the groundwater levels respond directly to the net-recharge. This is often, especially by these deep groundwater levels (> 2 meter depth) unrealistic. A delay of recharge through the unsaturated zone is a process that is taken care of by the UZF package.

Creating the UZF input

So, this tutorial is called UZF Package, but up to now we didn’t do anything with that. Well, most of the preparation we have done and running the model with the RCH and EVT packages, gives us a nice comparison of two different commonly used concepts. First we will delete the RCH and EVT packages.

• 67. Select the option (RCH) in the tree view Project Definition;

• 68. Click the Delete option and confirm that you really want to remove the package content;

• 69. Select the option (EVT) in the tree view Project Definition;

• 70. Click the Delete option and confirm that you really want to remove the package content;

Now we will add the input for the UZF package which is more-or-less a combination of the RCH and EVT package input.

• 71. Select the option (UZF) in the tree view Project Definition;

• 72. Click Define Characteristics Automatically button (   ) to start the Define Characteristics for window.

• 73. Add the following strings to the second column in the table:

• (AEA) Areal Extent of Active Model (IDF) = “1”;

• (BCE) Brooks-Corey Epsilon (IDF) = “4”;

• (SWC) Saturated Water Content of Unsat. Zone (IDF) = “0.3”;

• (IWC) Initial Water Content (IDF) = “0.05”;

• (INF) Infiltration Rates at Land Surface (IDF) = “{path of tutorialfolder} \TUT_UZF \DBASE \PREC \PREC_*.IDF”;

• (EVA) Evaporation Demands (IDF) = “10.0”;

• (EXD) Extinction Depth (IDF) = “8”

• (EWC) Extinction Water Content (IDF) = “0.01”;

Below is an example of your current window.

Let’s gather the appropriate files.

• 74. Select the option iMOD will look for unique TIME STEPS ...;

• 75. Click the Allocate Files ... button.

iMOD will combine the constant given values with the wild cards. At those location where the “inherent” is mentioned, iMOD will use the previous mentioned value/file.

We will leave it like it is.

• 76. Click the Add System button, this will add the files to our modelling project and closes the Automatic Package Allocation window.

It can take a little bit longer to refill the Project Manager. But once it is finished, we’re ready to save the PRJ file and start the model.

• 77. Click the Save As button (   ) and save a new modeling project file at{installfolder} \IMOD_USER \RUNFILE \MODEL_UZF.PRJ.

Model Simulation

• 78. Click the Start Simulation Manager button (   ) to start the Simulation Manager window;

• 79. Select the Tab Layers/Packages.

• 80. 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).

• 81. Go to the Tab Output to organize the output of UZF flux files.

• 82. Select (UZF) Unsaturated Zone Flow Package from the field Result Variable:.

• 83. Select Layer 1 from the field Selected Modellayers:.

• 84. Return to Tab Main and select the Model Type Standard MODFLOW 2005.

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

• 86. Click the Start … button to start the simulation.

• 87. Click the YES button to confirm the simulation.

iMOD will now create the necessary MODFLOW2005 file and runs the model, it will consume probably a little bit longer than our previous model to accomplish.

Inspect the result of simulation

Let’s inspect the hydraulic head of the first model layer, the computed groundwater recharge, the precipitation and evaporation and generate time series.

• 88. 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.

• 89. Select the option “TUT_UZF” from the Varient dropdown menu.

• 91. Select the option “20131006” from the Time: dropdown menu.

• 92. Select the options “1” from the Layer menu.

• 93. Click the Open button.

• 94. Repeat the above mentioned steps up to to open the results for:

• BDGGET = the amount of computed evapotranspiration (m$^3$/d);

• BDGGRC = the amount of computed groundwater recharge (m$^3$/d);

• UZFET = the amount of computed evapotranspiration in the unsaturated zone (m$^3$/d);

• UZFINF = the amount of precipitation (infiltration) in the unsaturated zone (m$^3$/d).

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

• 95. Select the files HEAD_20131006_L1.IDF for both the model TUT_RCH_EVT and TUT_UZF from the iMOD Manager window;

• 96. Add to the current selection of files the files BDGGET, BDGGRC, UZFINF and UZFET;

• 97. Use your experience learned from the previous Tutorials to display the selected files as time series as shown in the following figure.

Modify the parameters of the UZF package

As you may have noticed, the UZF package generates some ground water recharge whenever multiply rainfall events appear on a short notice (dark green line). Short, heavy rainfall events, may not even feed the groundwater due to the strong evaporation or instant surface runoff. The evaporation has been modelled with an extinction depth of 8 meter, this may be a bit unrealistic and deplete the groundwater more than it should; let us change some parameters to see the effect of this.

First we should know what the Brooks-Corey Exponent ($\epsilon$) represents. The Brooks-Corey Exponent is used to compute the unsaturated hydraulic conductivity $K(\theta )$ as a function of the moisture content $\theta$.

$$K \left ( \theta \right ) = K_s \left [ \frac {\theta - \theta _r}{\theta _s - \theta _r} \right ]^\epsilon ,$$

whereby $K_s$ is the saturated hydraulic conductivity; $\theta _r$ is the residual water content; $\theta _s$ is the saturated water content; and $\epsilon$ is the Brooks-Corey exponent. This function describes how the hydraulic conductivity approaches the saturated conductivity as the water content $\theta$ increases. This can be a linear relation ship ($\epsilon =1.0$), or a non-linear whereby the hydraulic conductivity increases more slow than the water content increases ($\epsilon > 1.0$) or faster than the water content increases ($\epsilon < 1.0$). The next figure shows the relation ship for different values of $\epsilon$ and the effect on the hydraulic conductivity $K(\epsilon )$.

In our case, it seems that our model has too less amount of recharge. In order to increase the recharge we need to decrease the Brooks-Corey Exponent ($\epsilon$). The hydraulic conductivity will increase more rapid for a slight increase of the water content, allowing precipitation seeps through the subsoil more quicker.

The easiest way to modify the parameters for the UZF package is to re-read the input, let’s do that:

• 98. Repeat the steps 67. up to 73., but use the value 2.0 for the Brooks-Corey Exponent;

• 99. Repeat the steps 78. up to 86. to run the adjusted model, save the results in the folder {installfolder}\IMOD_USER \MODELS \TUT_UZF2;

• 100. Repeat the steps starting from 88. to load the results into iMOD and generate time series;

If you have successfully carried out the above mentioned steps, the time series should like the figure below.

With a Brooks-Corey ($\epsilon$=2.0) the computed hydraulic head is significantly different and almost align (though more smooth) with the RCH-EVT combination. If you examine the water balance in the output files (*.LST-files), the following tables can be derived to clearly show the influence of the UZF package on the net recharge of the aquifer.

The UZF package is able to reduce the net recharge significantly, the Brooks-Corey Exponent ($\epsilon$) is very sensitive in the amount of ground water recharge that seeps through the unsaturated zone and influences the behaviour of the groundwater level. Feel free to experiment more with the UZF parameters and observe how the influence the model outcomes. If you decrease the (SWC) Saturated Water Content of Unsat. Zone (IDF), the yielding hydraulic heads will be almost similar to the RCH-EVT combination. It is also interesting to start with a very wet subsoil (IWC) Initial Water Content (IDF), and see how the model responds on that.

Note: It is possible to examine per cell the moisture content in more detail, especially during the model building phase this could be desirable. This functionality is not steered via iMOD, but can be easily added to the MF2005 file directly, please visit the website of the USGS for this adjustments.

Note: It is possible to examine per cell the moisture content in more detail, especially during the model building phase this could be desirable. This functionality is not steered via iMOD, but can be easily added to the MF2005 file directly, please visit the website of the USGS for this adjustments.