# iMOD User Manual version 4.4 (html)

#### 11.8Tutorial 8: Surface Flow Routing (SFR) and Flow Head Boundary (FHB) Package

This tutorial gives an introduction to a steady-state, surface water routing package (see Section 12.28, and (Prudic2004)). See for more detailed references regarding ISG-Edit (see Section 6.10.3) and the ISG-file format regarding the SFR package (Section 9.9). The tutorial also outlines the use of the FHB package (Section 12.26) which facilitates a combination of constant head- and constant flux boundaries.

Outline

This is what you will do:

• • Define a simple, single-layer, steady-state model and head- and flux boundaries using the FHB package;

• • Define the outline of the stream network;

• • Set the characteristics of each stream and define the connections within the stream network;

• Start the SFR simulation and examine the outcome.

Required Data

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

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

• – .\DBASE\TOP.IDF – the uppermost elevation of the model;

• – .\DBASE\BND.IDF – boundary conditions of the model (to be created in tutorial);

• – .\DBASE\FHB.IDF – constant head and constant flow boundary of the model (to be created in tutorial);

– .\DBASE\SFR.ISG – ISG with surface flow routing information (to be created in tutorial);

– .\DBASE\CROSSSECTION.CSV – CSV file with a complex cross-section;

• – .\MODEL.PRJ – model project file;

Getting Started

• 1. Start iMOD.

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

• 3. Click the Start button.

• 4. Go to View in the menu bar and select the iMOD Manager (or use the shortcut Ctrl+M), or click the iMOD Manager button (   ) from the main window to start the iMOD Manager window.

• 5. Click the Open IDF button (   ) from the Maps tabs on the iMOD Manager and open {path of tutorialfolder}\TUT_SFR\DBASE\TOP.IDF.

This IDF describes the upper most elevation of the model, the top of our single layered aquifer that declines from 512 m+MSL in the west towards 505 m+MSL in the east. We use this IDF to create the boundary IDF.

Creating the Boundary File BND.IDF

• 6. Click the Calculator ) on the iMOD Manager in the iMOD Manager window to start the Map Operations window.

• 7. Enter the output name “{installfolder}\IMOD_USER\DBASE\TUT_SFR\BND.IDF” at Map C.

• 8. Make sure the Formulae is “C=0*A”.

• 9. Select the option Map A at the section Select the extent for which the computation applies.

• 10. Click the Compute ... button.

Note: {installfolder} refers to the full path of the directory you installed iMOD in (e.g. D:\iMOD).
Note: If you are a left-handed person and you converted your mouse button settings, ’left mouse button’ should be ’right mouse button’ and vice versa in these tutorials.

We will use this BND.IDF file to specify how the boundary conditions need to be. On the west we apply an open boundary condition with constant heads (511 m+MSL, that is 1 meter below the surface level TOP.IDF). On the east we apply an open boundary condition with a constant outflow flux boundary (-950 m$^3$/d; a negative number will be used to take water out of the groundwater system, use a positive number to insert water to the groundwater system instead). We will modify the BND.IDF via IDF-Edit, which has been part of Tutorial 2, make sure you have applied this tutorial already.

• 11. Click the menu option View, Show IDF features and then IDF Raster Lines to display the gridlines of the IDF files.

• 12. Click the right mouse button and the select from the dropfown menu, the option IDF Options and then the option IDF Edit ... to start the IDF-Edit window.

• 13. In the ’Selection’-tab click the Draw ...-button to start the IDF Edit Draw window.

14. Move your mouse in the graphical canvas (note that the cursor symbol changes) and drag, while holding your left-mouse button, all model cells in the left column of our model.

You can release the left mouse button to position the mouse on a different location without selecting the underlying cells. To continue selecting cells, you need to press the left mouse button again. If you need to remove some of the selected cells, click the Remove Cells from the IDF Edit Draw window. Restart selecting cells, click the Add Cells again from the IDF Edit Draw window. Below is an image of the final selected cells.

Now we are going to change the values for those cells.

• 15. Click the Close button on the IDF Edit Draw window to leave the mode to select cells.

• 16. Click the Calculate option from the IDF Edit window to start the IDF Edit Calculation window.

• 17. Selection the option New Value and enter the value “-2” in the input field next the the “=” sign.

18. Click the Calculate button to assign those values to the BND.IDF file.

• 19. Click the Close button.

• 20. Click Yes to leave the editing mode.

A constant head boundary is specified by a negative number, so all values less than zero are appropriate. However, whenever the FHB package is used and a constant head boundary needs to be combined with a constant flux boundary, it is necessary to specify a -2 for constant head cells. For constant flux boundaries we need to specify a +2. Let’s do that for the right boundary.

• 21. Click the Clear button and agree to the question whether you are sure to delete the current selection.

• 22. Click the option Draw to start the IDF Edit Draw window.

• 23. Move your mouse in the graphical canvas and drag, while holding your left-mouse button, all model cells in the right column of our model.

24. Click the Close button on the IDF Edit Draw window to leave the mode to select cells.

• 25. Click the Calculate option from the IDF Edit window to start the IDF Edit Calculation window.

• 26. Selection the option New Value and enter the value “2” in the input field next the the “=” sign.

27. Click the Calculate button to assign those values to the BND.IDF file.

• 28. Click the Close button.

• 29. Click Yes to leave the editing mode.

We’re almost done, we only need to change all the zero values in the BND.IDF to be 1.

• 30. Click the Clear button and agree to the question whether you are sure to delete the current selection.

• 31. Click the option Select to start the IDF Edit Select window.

• 32. Select “BND.IDF” at IDF-File:; select “=” at Logic: and select “0.0” at Value:.

33. Click the Get Selection button and notice all rows are selected for column 2 up 14.

• 34. Click the Close button.

• 35. Click the Calculate option from the IDF Edit window to start the IDF Edit Calculation window.

36. Selection the option New Value and enter the value “1.0” in the input field next the the “=” sign.

• 37. Click the Calculate button to assign those values to the BND.IDF file.

• 38. Click the Close button to leave the IDF Edit Calculation window..

39. Click Yes to leave the editing mode.

• 40. Click the Close button to leave the IDF Edit window.

We’re finished !

Specify the characteristic of the boundary

We need two other files that specify the actual constant head values and the constant flux rates. For this we need to copy the BND.IDF into a file called FHB_H.IDF, give the values that are -2 (in BND.IDF that represent a constant head boundary) the value 511 m+MSL.

Note: To estimate the flux over the edge of model, apply Darcy’s Law. In our case we have a head gradient of $\Delta h=$ 7 m over distance $d=$ 1500 m, a permeability of $k=$ 60 m/d and an average thickness of $T=$ 34 m, so the horizontal conductance $c=k \times T=$ 2040 m$^2$/d. Filling these in in Darcy’s Law we come up with:

$$\begin {array}{ll} q & =k \times T\frac {\Delta h}{d} \\ \\ & =60 \times 34 \times \frac {7}{1500} \\ \\ & =9.52 \rm {m}^2/\rm {d} \end {array}$$

The cell width is $100$ m, so the total volume of water is $Q=952$ m$^3$/d.

Secondly, we need to copy the BND.IDF to a file called FHB_Q.IDF and give the values that are +2 (in BND.IDF that represent a constant flux boundary) a value of -950 m$^3$/d (constant flux boundary). It is more-or-less a repetition of the previous steps, but let’s dot that together.

• 41. Click the Calculator ) on the iMOD Managerin the iMOD Manager window to start the Map Operations window. Make sure you have selected the BND.IDF in the iMOD Manager.

• 42. Enter the output name “{installfolder}\IMOD_USER\DBASE\TUT_SFR\FHB_H.IDF” at Map C.

• 43. Make sure the Formulae is “C=A”.

• 44. Select the option Map A at the section Select the extent for which the computation applies.

• 45. Click the Compute ... button.

Let’s create the IDF file for the constant flux boundary as well.

• 46. Click the Calculator ) on the iMOD Manager in the iMOD Manager window to start the Map Operations window. Make sure you have selected the BND.IDF in the iMOD Manager.

• 47. Enter the output name “{installfolder}\IMOD_USER\DBASE\TUT_SFR\FHB_Q.IDF” at Map C.

• 48. Make sure the Formulae is “C=A”.

• 49. Select the option Map A at the section Select the extent for which the computation applies.

• 50. Click the Compute ... button.

Enter the IDF Edit to change the values.

• 51. Click the right mouse button and the select from the dropfown menu, the option IDF Options and then the option IDF Edit ... to start the IDF-Edit window.

• 52. Click the option Select to start the IDF Edit Select window.

• 53. Select “BND.IDF” at IDF-File:; select “=” at Logic: and select “-2.0” at Value:.

54. Click the Get Selection button and notice all rows are selected for column 1.

• 55. Click the Close button.

• 56. Click the Calculate option from the IDF Edit window to start the IDF Edit Calculation window.

57. Selection the option New Value and enter the value “511.0” in the input field next the the “=” sign.

• 58. Make sure the FHB_H.IDF is selected in the Available IDF Files at the Assign Value to section.

• 59. Click the Calculate button to assign those values to the FHB_H.IDF file.

60. Click Yes to leave the editing mode.

• 61. Click the Close button to leave the IDF Edit Calculation window.

Now for the constant flux boundary on the right.

• 62. Click the option Select to start the IDF Edit Select window.

• 63. Select “BND.IDF” at IDF-File:; select “=” at Logic: and select “2.0” at Value:.

• 64. Click the Get Selection button and notice all rows are selected for column 15.

65. Click the Close button.

• 66. Click the Calculate option from the IDF Edit window to start the IDF Edit Calculation window.

• 67. Selection the option New Value and enter the value “-950.0” in the input field next the the “=” sign.

68. Make sure the FHB_Q.IDF is selected in the Available IDF Files at the Assign Value to section.

• 69. Click the Calculate button to assign those values to the FHB_Q.IDF file.

• 70. Click the Close button to leave the IDF Edit Calculation window.

71. Click Yes to leave the editing mode.

• 72. Click the Close button to leave the IDF Edit window.

Done regarding the boundary definition. We need to add this to the model via the iMOD Project Manager. For the Tutorial we have done already a small amount of work to fill in an iMOD Model Project file (*.PRJ). We need to add the BND.IDF, FHB_H.IDF and FHB_Q.IDF to the current PRJ file. We will do this after we have created the input for the SFR package.

Creating the SFR Package

In our model a stream flows from the west towards the east and splits halfway into two separate streams (see Figure 11.112). We will model this stream in iMOD. First we need to create an ISG file that is capable of generating the SFR input.

• 73. Select from the main window, the option Edit, Create Feature, ISGs and then SFR Applicable ....

• 74. Enter the ISG file name “{installfolder}\IMOD_USER\DBASE\TUT_SFR\SFR.ISG” in the Save window.

The entered ISG file will be added to your iMOD Manager, but since it will be completely empty, you’ll not see anything appearing on the screen. So, let us create the stream network and the corresponding characteristics.

• 75. In the iMOD Manager select and draw ( ) the file FHB_H.IDF.

• 76. Select the Legend button (   ) from the iMOD Manager to start the Legend window.

• 77. Deselect the option (   ) to ignore the colouring of the FHB_H.IDF file.

• 78. Click the Apply button to leave the Legend window.

• 79. Select from the main window the option View, Show IDF Features and then the option IDF Indices to display the cell indices (row-column numbers) of the IDF file FHB_H.IDF. This is handy to produce the ISG file in the next steps.

• 80. Add the created SFR.ISG file in the iMOD Manager to the current selection of files: use the key “Ctrl” and click your left mouse button on the SFR.ISG file to this file to the selection. So both SFR.ISG and FHB_H.IDF should be selected now.

• 81. Select from the main window, the option Map, ISG options and then ISG Edit ... to start the ISG Edit window.

So because we cannot visualize the file SFR.IDF yet (it is still completely empty) we also selected the FHB_H.IDF in the iMOD Manager to use it as a guide to draw the stream network in the next steps.

Drawing the Stream Network

We are ready now to start drawing our stream network.

• 82. Select the Draw option (   ) from the ISG Edit window.

• 83. Start drawing the first stream from west to east, we start by clicking the left mouse button at the cell (8-1) (row are numbered from top to bottom); and then make a straight line and click the left mouse button at cell (8-7).

• 84. Right mouse click to stop drawing.

You’ll notice that a stream has been created in the menu field on the ISG Edit window called “Segment_1”. This was our first stream, let’s create another one.

• 85. Select the Draw option (   ) from the ISG Edit window.

• 86. Start drawing the second stream by clicking your left mouse button at cell (8-7), towards the north and click the left mouse button at cell (4-7), further up north-east click at cell (3-10) and finally towards the east, mouse click at cell (3-15).

• 87. Right mouse click to stop drawing.

and the final one:

• 88. Select the Draw option (   ) from the ISG Edit window.

• 89. Start drawing the second stream from cell and click the left mouse button at cell (8-7), towards the south and click at cell (12-7 , further down south-east click at cell (13-10) and finally towards the east click at cell (13-15).

• 90. Right mouse click to stop drawing.

• 91. Select all stream from the menu field, i.e. “Segment_1”; “Segment_2” and “Segment_3”.

• 92. Check the options Nodes; C.Section; Seg.Nodes; Clc.Pnts. and Direction in the Show section at the bottom of the ISG edit window.

• 93. Click the Update button.

When you did it right (I’m sure you did), the following stream network should be displayed on your graphical canvas.

So, what do we see?

First of all, each stream consists of segment nodes (red dots, Seg.Nodes). Each stream contains a single cross-section (green polygons, C.Section), and a calculation point at the beginning and end of a stream (blue rectangle with a cross, Clc.Pnts. and the start and end of a stream (blue dot, Nodes). Furthermore, as we draw the stream, the order in which the coordinates of each stream are entered by clicking the left mouse button, determines the direction of the flow (black arrow, Direction). In our case, the order of the coordinates is such that water is flowing from the west to the east and splits at the bifurcation in a north- and south branch. Finally, all segments are selected and therefore those are highlighted in cyan.

Characterizing the Stream Network

The next thing to do is to characterise the stream with appropriate water levels, bottom height, cross-sections and so on.

• 94. Select “Segment_1”  in the ’Segment’-TAB of the ’ISG EDit: SFR.ISG’ window.

• 95. Click the Attributes button (   ) to open the ISG Attributes window, stretch the window a bit such that the entire table is visible.

We will enter some data in the table. First of all, we will apply this SFR to a steady-state model, so the date and time are irrelevant in this case. We will leave it as it is.

• 96. Enter “511” for the Water Level (column 3).

• 97. Enter “510” for the Bottom level (column 4).

• 98. Enter “20” for the Stream width (column 5).

99. Enter “1” for the Bed thickness (column 6).

• 100. Enter “1” for the Bed Permeability (column 7).

• 101. We will define a rectangular cross-section: select “1” from the drop down menu for Calc Opt. (column 10).

102. There is a flow rate entering from the west into the stream of 1.2 million m$^3$/day. It is necessary to enter this in m$^3$/s, so $\frac {1.2E10^6}{86400}=13.9$, so enter “13.9” m$^3$/s for the Q flow (column 12).

We accept the default values for the remaining columns; the table should look similar to the figure below.

The next thing is to enter data for the downstream node.

• 103. Select the “CalcPnt TO” from the drop down menu Calculation Point:.

• 104. Enter “508” for the Water Level (column 3).

• 105. Enter “507” for the Bottom level (column 4).

106. Enter “20” for the Stream width (column 5).

• 107. Enter “1” for the Bed thickness (column 6).

• 108. Enter “1” for the Bed Permeability (column 7).

We accept the default values for the remaining columns.

Even though we specified the width and depth of the stream already on the tab Waterlevels, we need to specify the Manning’s Resistance Coefficient MRC for the cross-section. In case you need to use a more sophisticated cross-section, you can specify that in the table on the tab Crosssections. We modify the table such that it will align with our entered width ($w=$ 20 m) and maximal depth ($d=$ 2 m), and assign a Manning’s Resistance Coefficient $n=$ 0.03.

Note: Manning’s Resistance Coefficients $n$ range roughly from $n$=0.01-0.06; some important values are given in table Table 11.5.

• 109. Select the tab Crosssections from the ISG Attributes window.

• 110. Enter “-20” in column=1 and row=1 and 2 (Distance).

• 111. Enter “+20” in column=1 and row=3 and 4 (Distance).

• 112. Enter “2.0” in column=2 and row=1 and 4 (Z).

• 113. Enter “0.0” in column=2 and row=2 and 3 (Z).

• 114. Enter “0.03” in column=3 for all rows (MRC).

• 115. Click the Redraw button (   ) to update the display with your modified cross-section.

After you did it correctly, the ISG Attributes window should look like the figure below.

Bear in mind that iMOD stores all modifications in memory. To actually save your modification on disk, you need to save your data explicitly, let’s do that.

• 116. Click the Save button to store our adjusted stream data and return to the ISG Edit window.

• 117. Click the Save button on the ISG Edit window to save your adjusted SFR.ISG to disk.

• 118. Click the Yes button to accept overwriting the existing SFR.ISG file.

Okay, one third done! You need to apply the modifications to the other segments by applying the previous steps (76 to 91) using the data from Table 11.6.

Note: To compute the total steady-state influx of 13.9 m$^3$/s, we apply the simplified Manning’s Equation for a rectangular stream. The gradient of Segment_1 is $S=\Delta h=$ 7 m over $d=1500$ m; its width is $w=$ 20 m, its depth is $d=$ 1 m and its roughness is $n=$ 0.03. Filling these in in the simplified Mannings’ Equation:

$$\begin {array}{ll} Q & =\frac {1.0}{n} \times w \times y^\frac {5}{3} \times S^\frac {1}{2} \\ \\ & =45.5 \times 20.0 \times 1.0^\frac {5}{3} \times \left ( \frac {7.0}{1500.0}\right )^\frac {1}{2} \\ \\ & =1239393~\rm {m}^3/\rm {d} \\ \\ & =13.9~\rm {m}^3/\rm {s} \end {array}$$

Note: A nice functionality to check whether you didn’t make any typo’s entering the data is the profile option; this functionality is also very handy when you need to inspect the result of the simulation (more on that later). Let’s do that.

• 119. Click the Profile button (   ) on the ISG Edit window (not the same icon on the main iMOD window) to start the ISG Profile window.

• 120. Select “Segment_1” and “Segment_2” from the menu field at Profile Along Selected Segments.

• 121. Select “Bottom Level” from the drop down menu Parameter A: window.

• 122. Check the checkbox at Parameter B: and select “Water Level” from the drop down menu Parameter B: window.

• 123. Click the Close button to return to the ISG Edit window.

• 124. Click the Save button in the ISG Edit window to save your adjusted stream data to disk.

• 125. Click the Yes button to accept overwriting the existing SFR.ISG file.

Connecting the Stream Network

Now that we have given all streams their appropriate characteristics, the streams need to be connected. This can be done manually or automatically. When many streams are to be connected, this automatic option is very handy, it connects streams within a certain distance automatically. To give an idea of how easy streams can be connected manually, we will practice that right now.

• 126. Select the stream “Segment_1” on the graphical canvas by clicking your left mouse button near a node or in between two nodes. If the stream is selected it turns into a cyan-coloured line.

• 127. Click the option Show Selected to draw features on the selected stream only, just for reasons of simplification of the image on the graphical canvas.

• 128. Click the Connect To button (   ) and move your mouse toward “Segment_2” until it becomes a red line.

• 129. Click the left mouse button to indicate that this stream “Segment_1” will be connected to “Segment_2”. If you click next to a line (so no segment is selected), the connection will be removed.

• 130. Click the right mouse button to stop this selection process and return to the ISG Edit window.

• 131. Click the option Connections on the ISG Edit window to display the connection as a grey arrow.

• 132. Click the Update button to refresh the graphical canvas.

When you did it right (I’m sure you did), the your display should look similar to the figure below.

So, “Segment_1” flow into “Segment_2” , but in fact it also flows towards “Segment_3”. We call this a diversion. In order to achieve this, we need to define for “Segment_3” that its inflow is diverted from “Segment_1”. We can do that interactively using the Connect From button (   ), or specifying this explicitly in ISG Attributed window.

• 133. Select “Segment_3” from the menu field on the ISG Edit window.

• 134. Click the Attributes button (   ) to start the ISG Attribute window.

• 135. Make sure the “ClcPnt FROM” from the menu field Attributes for:.

• 136. Enter the stream number “1” in column Iup Seg. This specifies the model to divert from segment Segment_1 (first in the segment list).

• 137. Select the option “-2” in column Div. Opt. This specifies the model to divert from Segment_1 as a fraction of the total inflow.

• 138. Enter the value “0.30” in column Q Flow. This specifies that the fraction of diversion is 0.30 of the outflow of Segment_1.

• 139. Click the Save button to store your modification in memory and return to the ISG Edit window.

It is not necessary to specify a diversion for Segment_2 as it automatically receives 100-30=70% of the outflow of Segment_1.

I think we’re done with this ISG, let’s quit the ISG Edit window.

• 140. Click the Save button in the ISG Edit window to save your adjusted stream data to disk.

• 141. Click the Yes button to accept overwriting the existing SFR.ISG file.

Defining the Model Project Now that we have created all necessary packages for our model, let’s get them together in a Model Project.

• 142. Select from the main menu the option View and then Project Manager to start the Project Manager window.

• 143. Click the Open Projectfile button (   ) and select the file {path of tutorialfolder} \TUT_SFR\MODEL.PRJ.

• 144. Click OK.

For a detailed exercise on how to create a Project-file from scratch, see Tutorial 4: Create your First Groundwater Flow Model, we will not exercise that here. The opened project file MODEL.PRJ contains all necessary parameter definitions.

The Project Manager will look as follows:

We have a permeability of KHV=60 m/d, a bottom height of our aquifer of BOT=470 m+MSL, a uniform starting head of SHD=510 m+MSL, a uniform recharge of RCH=1 mm/d. Notice that we filled in the FHB- and SFR package for you.

Running the Model

Let’s run this model.

• 145. Click the Save As Run button (   ) to start the Define Simulation Configuration window.

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

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

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

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

Note: There is an option to start a model simulation in the background so that you can continue working with iMOD once the model has been started. As this model is very, very small, we will run the model in the foreground and we have to wait until it has finished before we can continue working with iMOD - probably, reading this sentence was enough time for the model to be finished.

Once iMOD converts your model to MF2005 files, it creates a conventional ISG-file that can be used to transfer the results of the SFR package into iMOD. In this way we can use the existing functionalities in ISG-Edit (such as displaying time series, profiles) for the output of the model. Four items are converted to iMOD after the simulation has finished using the iMOD Batch function SFRTOISG (see Section 8.3.10). This iMOD Batch function is part of the run-script (. \TUT_SFR \run.bat) and has been carried out already, so let’s see some results.

• 150. Click the OK button once the simulation has been finished.

• 151. Click the Close button on the iMOD Project Manager window to close it.

• 152. Select from the main menu the option Map, Add Map ... and select the ISG file{installfolder} \MOD_USER \MODELS \TUT_SFR \BDGSFR \ISG \SFR.ISG.

153. Select from the main menu the option Map, ISG Options and than ISG Edit ... to start the ISG Edit window.

You probably notice that instead of three segments, we have now 35 segments.

• 154. Check Seg. Nodes whenever it has not been checked yet.

• 155. Click on the Update button.

The names of the individual segments still contain the original segment name, so it is easy to select all streams that belong to the same original stream.

• 156. In the ’ISG Edit’ window select all items from the menu field that belong to the original Segment_1 and Segment_2.

Now we want to see the decline of the water level, or change in discharge per segment.

• 157. Click the Profile button (   ) to start the Profile window.

In this picture we observe that the computed surface water level is declining from west to east. We can see how the discharge distribution aligns with our predefined diversion fractions.

• 158. Select the option “Stream Discharge“ from the drop down menu Parameter A:.

• 159. In the ’ISG Profile’ window (not the ’ISG Edit’ window) select all segments from the menu field.

• 160. Try the other options from the drop down menu Parameter A:.

In the graph we see that the inflow volume in “Segment_1” is 14 m$^3$/s, and the volumes for the “Segment_2” and “Segment_3” are 10 m$^3$/s ($\approx$ 70%) and 4.25 m$^3$/s ($\approx$ 30%), respectively.

Another (fancy) way to look at your results is to use a legend to colour the lines for a selected output item, such as water levels, discharges.

• 161. Click the Close button to return to the ISG Edit window.

• 162. Select the Legend button (   ) to start the ISG Colouring window.

• 163. Select the option Current window to colour all segments within the current graphical window.

• 164. Increase the line-thickness to 5.

In this visual we observe that the surface water is indeed declining from west to east.

It is easy to visualize the other model outcomes as well:

• 165. Select “StreamDepth” ,“StreamWidth”  and “StreamDischarge” as well.

The legend is computed automatically based on the data of the ISG file. Each stream characteristic in the ISG file has its own legend. This can be modified by using the default Legend window that starts whenever you select the option Legend ) from the ISG Colouring window. For any transient simulation you might do in future, you can drag the slider in the ’Period’ part of the of the ’ISG colouring’-window to visualise stream characteristics for different periods.

Now it’s time to visualise the total exchange flux between the surface water and groundwater.

• 166. Click the Close button on the ISG Edit window to close the ISG Edit window and ISG Colouring window, accept the question upon closing.

• 167. Select from the main menu the option Map, Add Map ... and select the ISG file{installfolder} \IMOD_USER \MODELS \TUT_SFR \BDGSFR \BDGSFR_STEADY-STATE_L1.IDF.

• 168. Click the Adjust Legend button (   ) from the iMOD Manager to start the Legend window. If the iMOD Manager is not visible, display it again by selecting the iMOD Manager button (   ) from the main iMOD window.

• 169. Use your skills to create the legend as displayed in the next figure. If you find difficulties reproducing this legend, have a look again at Tutorial 1: Map Display.

Regarding practising the visualisation of ISG’s it’s OK for now.

• 170. Click the Close button to stop ISG Edit window.

It would be nice if you try experimenting with different parameters of the SFR package, such as stream width, Manning’s Resistant Coefficients and/or implement an extraction in the model to see whether that effects the surface water level. To estimate the extraction rate, such that the surface water level might change with 0.10 m, use the following equation of the re-organised Manning’s Equation:

$$y=\left [ \frac {Q \times n}{C \times w \times S^\frac {1}{2}} \right ]^\frac {3}{5}$$

If you apply this for stream “Segment_2” , the extraction need to be at least 3.3 m$^3$/s=285,000 m$^3$/d.

Enhance the model by an Eight Point Cross-Section

In the coming few steps we will enhance the model a bit more, adding a more complex cross-section and apply a q-width/depth relationship for a segment.

• 171. Select the option ISG Options and then ISG Edit to start the ISG Edit window.

• 172. Select “Segment_1” from the menu list of segment names.

• 173. Click the Attributes button (   ) to start the ISG Attributes window.

• 174. Select the tab Cross-sections from the ISG Attributes window.

• 175. Select the Open button (   ) and select the file {path of tutorialfolder} \TUT_SFR \DBASE \CROSSSECTION.CSV.

• 176. Click OK to read the selected file.

iMOD will open the Read CSV file window. Here you can specify what column from the CSV-file you want to use for each of the columns of the cross-section, such as “Distance” , “BottomLevel” and “MRC”. We leave the default values as shown below.

• 177. Click Ok to accept the column definitions and return to tab Cross-sections on the ISG Attributes window.

• 178. Click the checkbox Simplified to observe a simplified cross-section.

The SFR Package has the limitation that only eight-point cross section geometries can be assumed. Eight values each for the horizontal and vertical distances are specified for the segment. Vertical walls are assumed at the end of each cross section. Stream depth, width, and wetted perimeter (hydraulic radius) are computed from the cross section for a given flow using Manning’s equation and by dividing the cross section into three parts, one part for the points 1-2-3, a second part for the points 3-4-5-6 and a third part for the points 6-7-8. All those together form the total wetted perimeter and the area. As this can be rather complex, the SFR package uses an iterative procedure to estimate the total discharge (sum of the three parts) until the computed flow is more-or-less equal to the stream flow. This method may not solve for all geometries, especially wide, flat bottom geometries might cause problems, in those case an other option is advised to be used for computing the stream depth.

From the figure above, it seems that the simplified cross-section has a more-or-less similar wetted area (108.46 m$^2$) compared to the original one (109.80 m$^2$). Actually, this simplification is done once the model is exported to the SFR package of MODFLOW2005, automatically.

Next thing is to modify the ISG file a little bit more such that it knowns to use this eight-point cross-section.

• 179. Select the tab Water Levels on the ISG Attributes window.

• 180. Select the option “2 Eight Point” from column 10 with label Calc Opt..

• 181. Click the Save button to save the modification in memory and return to the ISG Edit window.

182. Click the Save As button to save the modification on disk in another name, enter the file name{installfolder} \IMOD_USER\DBASE\TUT_SFR\SFR2.ISG.

• 183. Click the Close button to leave to the ISG Edit window.

• 184. Accept the question by clicking the Yes button.