Tutorial 3.02

Tutorial 3.02

Subsurface Line Source

The example in this computer session considers a subsurface line source (e.g. drip irrigation) of water (first without and then with a solute) in a vertical cross-section. The (x, z) transport domain is 75 x 100 cm2, with the source located 20 cm below the soil surface on the left boundary of the transport domain. Infiltration is initiated with a variable flux boundary condition and is maintained for 1 day, with the duration of the solute pulse being 0.1 days; with 2 cycles per week. An unstructured finite element mesh is generated using the Meshgen-2D program. The example is again divided into two parts: first only water flow is considered, after which solute transport is added. This example will familiarize users with the basic concepts of transport domain design in the graphical environment of HYDRUS, with boundaries and domain discretization, and with the graphical display of results using contour and spectral maps.

Download the PDF file with detailed description accompanied with figures.

A. Infiltration of Water From a Subsurface Source

Video for Version 1.0 (60 MB) - Download
Download Project Source1x.zip (0,4 MB)

• Project Manager (File->Project Manager)
  Button “New”

• New Project (or File->New Project)
  Name: Source1
  Description: Infiltration of Water from a Subsurface Source
  Working Directory: Temporary – exists only when the project is open
  Button “Next”

• Domain Type and Units (Edit->Domain Geometry->Domain Type and Units)
  Type of Geometry: 2D - General
  2D-Domain Options: 2D - Vertical Plane XZ
  Units: cm
  Check "'Edit domain properties, initial and boundary conditions on geometric objects'"
  Initial Workspace: Xmin=-25 cm, Xmax=100 cm, Zmin=-25 cm, Zmax=125 cm (to accommodate the transport domain)
  Button “Next”

• Main Processes (Edit->Flow and Transport Parameters->Main Processes)
  Check Box: Water Flow Button “Next”

• Time Information (Edit->Flow and Transport Parameters->Time Information)
  Time Units: days
  Final Time: 7
  Initial Time Step: 0.0001
  Minimum Time Step: 0.000001
  Maximum Time Step: 5
  Time Variable BC: Check
  Number of Time-Variable BC: 4
  Number of times to repeat the same set of BC records: 1
  Button “Next”

• Output Information (Edit->Flow and Transport Parameters->Output Information)
  Print Options:
  Check T-Level Information
  Check Screen Output
  Check Press Enter at the End
  Print Times: Count: 14
  Update
  Print Times: 0.1, 0.25, 0.5, 0.75, 1, 1.5, 2, 3.5, 3.6, 3.75, 4, 4.5, 5.5, 7 d
  Button “Next”

• Water Flow - Iteration Criteria (Edit->Flow and Transport Parameters->Water Flow Parameters->Iteration Criteria)
  Leave default values as follows:
  Maximum Number of Iterations: 10
  Water Content Tolerance: 0.001
  Pressure Head Tolerance: 1
  Lower Optimal Iteration Range: 3
  Upper Optimal Iteration Range: 7
  Lower Time Step Multiplication Factor: 1.3
  Upper Time Step Multiplication Factor: 0.7
  Lower Limit of the Tension Interval: 0.0001
  Upper Limit of the Tension Interval: 10000
  Initial Condition: In Pressure Heads
  Button “Next”

• Water Flow - Soil Hydraulic Model (Edit->Flow and Transport Parameters->Water Flow Parameters ->Hydraulic Properties Model)
  Leave default values as follows:
  Radio button - van Genuchten-Mualem
  Radio button - No hysteresis
  Button “Next”

• Water Flow - Soil Hydraulic Parameters (Edit->Flow and Transport Parameters->Water Flow Parameters ->Soil Hydraulic Parameters)
  Leave default values for loam
  Button “Next”

• Variable Boundary Conditions (Edit->Flow and Transport Parameters->Variable Boundary Conditions)

Time	Transp	Var.Fl1 (variable flux)
1.0	0	-60 (drip discharge distributed over the circumference of the drip)
3.5	0	0
4.5	0	-60
7	0	0

See how to calculate the Drip Tape Recharge from the applied flux (-60 cm/d).
Button “Next”

• FE-Mesh - FE-Mesh Parameters (Edit->FE-Mesh->FE-Mesh Parameters)
  Targeted FE – Size – Unselect Automatic and specify TS = 5 cm
  Button “OK”

• Definition of the Transport Geometry
  Click on Grid and Work Plane Setting at the toolbar (or Tools->Grid and Work Plane)
  Grid Point Spacing – Distance w = 1 cm, Distance h = 1 cm
  Make sure that Snap to Grid is checked
  
  a) Outer Boundary
  Select the Line->Connected Abscissae command from the Edit Bar (or Insert->Domain Geometry->Curves->Lines->Graphically)
  Nodes coordinates: (0,79), (0,0), (75,0), (75,100), (0,100),(0,81)
  
  b) Drip
  Click on Zoom by Rectangle at the Toolbar (or View-> Zoom by Rectangle) and zoom at the source.
  Select the Arc via Three Points command from the Edit Bar (or Insert->Domain Geometry->Lines->Arc->Graphically->Three Points) and specify coordinates of three points: (0,81), (1,80), (0,79)
  Click on View All at the Toolbar (or View->View All).

• Define the Planar Surface
  Select the Planar Surface via Boundaries command from the Edit Bar (or Insert->Domain Geometry->Surfaces->Planar->Graphically) and click at the outer boundary.
  Alternatively, you can use the Planar Surfaces - Generate command from the Edit Bar to generate the Planar Surface automatically.

• Define FE-Mesh
  Click on the FE-Mesh Tab under the View Window.
  Select the Insert Mesh Refinement command from the Edit Bar (or Insert->FE-Mesh Refinement->Graphically): a dialog New FE Mesh Refinement appears, in which specify Finite Element Size S=0.5 cm.
  After clicking OK, select three nodes defining the drip (arc) at the left side of the domain. Small green circles should appear around these nodes indicating the size of finite elements.
  
  Click again on the Insert Mesh Refinement at the Edit Bar, then click New, and in the dialog specify Finite Element Size S = 2 cm. Assign this refinement to the node at the top left corner. A larger green circle should appear there.
  
  Click Generate FE-Mesh from the Edit Bar (or Edit->FE-Mesh->Generate FE-Mesh)

• Initial Conditions:
  Click on the Initial Conditions Tab under the View Window.
  On the Edit Bar click on New Initial Condition and in the window "New Pressure Head Initial Condition" specify Pressure Head IC = -400.
  Click on the newly defined initial condition at the Edit Bar and then click at the transport domain to assign it.

• Water Flow Boundary Conditions:
  Click on the Boundary Conditions Tab under the View Window.
  a) On the Edit Bar click on New Boundary Condition and in the window "New Water Flow Boundary Condition" check Variable Flux 1 and type Dripper for Name.
  Click on Zoom by Rectangle at the Toolbar (or View-> Zoom by Rectangle) and zoom on source: (0,80).
  Click on the newly defined boundary condition at the Edit Bar ( ) and then assign it by clicking on the arc representing the dripper.
  
  b) Click on View All at the Toolbar (or View->View All)
  On the Edit Bar click on New Boundary Condition and in the window "New Water Flow Boundary Condition" check Free Drainage (No need to change the name here).
  Click on the newly defined Free Drainage boundary condition at the Edit Bar and then assign it by clicking on the bottom line of the transport domain.

• Observation Nodes
  Click on the Domain Properties Tab under the View Window.++ On the Navigator Bar click on Domain Properties – Observation Nodes (or Insert->Domain Properties->Observation Nodes).
  Since we do not have any Points inside of the transport domain, which we could define as Observation Nodes, we will define Observation Nodes directly using FE-Mesh Nodes.
  To do that, click on the Edit Properties on FE-Mesh command on the Edit Bar, then on the Insert Observation Node command, and specify 5 points arbitrarily in the transport domain between the dripper and the bottom of the domain.

• Save
  Save the project using the Save command on the Toolbar (or File->Save).

• Run Calculations
  Click the Calculate Current Project command on the Toolbar (or Calculation->Calculate Current Project)
  (Execution time on 3 GHz PC – 18 s)

• OUTPUT:

Results – Other Information: Observation Points (from the Navigator Bar, or Results->Observation Points from menu)
Click on the Results Tab under the View Window.

Pressure Heads
Water Contents

Results – Other Information: Boundary Fluxes (from the Navigator Bar, or Results->Boundary Information->Boundary Fluxes from menu)
Variable Boundary Flux
Free Drainage Boundary Flux

Results – Other Information: Cumulative Fluxes (from the Navigator Bar, or Results->Boundary Information->Cumulative Fluxes from menu)
Variable Boundary Flux

Results – Other Information: Mass Balance Information (from the Navigator Bar, or Results->Mass Balance Information from menu)

Results – Graphical Display: Pressure Heads (from the Navigator Bar, or Results->Display Quantity->Pressure Heads from menu)
Use Listbox Time Layer or Slidebar on the Edit Bar to view results for different print times
Check Flow Animation
Select Boundary Line Chart from the Edit Bar and draw pressure heads for one vertical column
Select Cross Section Chart and draw pressure heads through the middle of the column
Select different display modes using Options->Graph Type

Results – Graphical Display: Water Contents (from the Navigator Bar, or Results->Display Quantity->Water Contents from menu)

Results – Graphical Display: Velocity Vectors (from the Navigator Bar, or Results->Display Quantity->Velocity Vectors from menu)

B. Infiltration of Water and Solute From a Subsurface Source

Video for Version 1.0 (40 MB) - Download
Download Project Source2x.zip (0,6 MB)

Close the Source1 Project (click Save Project at the Toolbar or File->Save)

• Project Manager (File->Project Manager)
  Select the Source1 project
  Button “Copy”
  Name: Source 2
  Description: Infiltration of Water and Solute from a Subsurface Source
  Button “OK”

• Main Processes (Edit->Flow and Transport Parameters->Main Processes)
  Check Box: Solute Transport
  You will be warned that this action will lead to deleting results. Click Yes.
  Button “OK”

• Solute Transport – General Info (Edit->Flow and Transport Parameters->Solute Transport Parameters->General Information)
  Leave default values
  Button “Next”

• Solute Transport - Solute Transport Parameters (Edit->Flow and Transport Parameters->Solute Transport Parameters->Solute Transport Parameters)
  Leave default values
  Bulk Density = 1.5 cm3/g
  Longitudinal Dispersivity, Disp.L = 2 cm
  Transverse Dispersivity, Disp.T = 0.2 cm
  Molecular Diffusion Coefficient for Liquid Phase, Diffus.W.=0
  Button “Next”

• Solute Transport - Transport Parameters (Edit->Flow and Transport Parameters->Solute Transport Parameters->Solute Reaction Parameters)
  Leave default values for tracer (all values are zero except for the Freundlich exponent Beta)
  Button “Next”

• Variable Boundary Conditions (Edit->Flow and Transport Parameters->Variable Boundary Conditions)
  Click on Time 1 and click add line
  Click on Time 4.5 and click add line

Time	Transp	Var.Fl.1	cValue1
0.1	0	-60	1
1.0	0	-60	0
3.5	0	0	0
3.6	0	-60	1
4.5	0	-60	0
7	0	0	0

Button “Next”

• Initial Condition:
  Import the final pressure head profile from Source1 as the initial condition for Source2 (Edit->Initial Conditions->Import)
  Find the project Source1
  Select Pressure Head and click OK
  If you do not see important values, click on the Navigator Bar Initial Condition->Pressure Head and the Edit Conditions on FE-mesh command on the Edit Bar.
   

• Run Calculations
  Click the Calculate Current Project command on the Toolbar (or Calculation->Calculate Current Project)
  You will get a warning that the Pressure Head Initial Conditions on Geo Objects are different than those on FE-Mesh. That is correct since the imported pressure head initial conditions are defined only on FE-Mesh. Click Yes to start calculations.
  (Execution time on 3 GHz PC – 50 s)

• OUTPUT: Click on the Results Tab under the View Window.

Results – Other Information: Solute Fluxes (from the Navigator Bar, or Results->Boundary Information->Solute Fluxes from menu)
Variable Boundary Flux
Free Drainage Boundary Flux

Results – Graphical Display: Concentrations (from the Navigator Bar, or Results->Display Quantity->Concentrations from menu)
Click with the right mouse button on the color scale and from the pop-up menu click on Min/Max Global in Time. See how the display changed.

C. Infiltration of Water and Solute From a Subsurface Source - Additional Root Water Uptake

Download Project Source3x.zip (0,6 MB)

Close the Source2 Project (click Save Project at the Toolbar or File->Save)

• Project Manager (File->Project Manager)
  Select the Source2 project
  Button “Copy”
  Name: Source3
  Description: Infiltration of Water and Solute from a Subsurface Source, Root Water Uptake
  Button “OK”

• Main Processes (Edit->Flow and Transport Parameters->Main Processes)
  Check Box: Root Water Uptake
  You will be warned that this action will lead to deleting results. Click Yes.
  Button “OK”

• Root Water and Solute Uptake – Models
  (Edit->Flow and Transport Parameters->Root Water and Solute Uptake->Root Water/Solute Uptake Models)
  Leave default values
  Button “Next”

• Root Water and Solute Uptake – Pressure Head Reduction++ (Edit->Flow and Transport Parameters->Root Water and Solute Uptake->Pressure Head Reduction)
  Leave default values
  Button “Next”

• Variable Boundary Conditions (Edit->Flow and Transport Parameters->Variable Boundary Conditions)
  Add Transpiration in the table as follows:

Time	Transp	Var.Fl.1	cValue1
0.1	1	-60	1
1.0	1	-60	0
3.5	1	0	0
3.6	1	-60	1
4.5	1	-60	0
7	1	0	0

Surface area associated with transpiration: 75 cm (length of the soil surface)
Button “OK”

• Initial Condition:
  Import the final pressure head profile from Source2 as the initial condition for Source3 (Edit->Initial Conditions->Import)
  Find the project Source2
  Select Pressure Head and Concentration and click OK
  If you do not see imported values, click on the Navigator Bar Initial Condition->Pressure Head and the Edit Conditions on FE-mesh command on the Edit Bar.

• Spatial Root Distribution (Edit->Domain Properties->Parameters for Root Distribution)
  Maximum Rooting Depth: 60
  Depth of Maximum Intensity: 15
  Parameter Pz: 1
  Check "Specify Parameters for Horizontal Distribution"
  Maximum Rooting Radius: 60
  Depth of Maximum Intensity: 0
  Parameter Py: 1

• Run Calculations
  Click the Calculate Current Project command on the Toolbar (or Calculation->Calculate Current Project)
  You will get a warning that the Pressure Head and Concentration Initial Conditions on Geo Objects are different than those on FE-Mesh. That is correct since the imported pressure head and concentration initial conditions are defined only on FE-Mesh. The same warning is issued also for root water uptake, which was also defined on FE-Mesh. Click Yes to start calculations.
   

D. Infiltration of Water and Solute From a Subsurface Source - Triggered Irrigation

Download Project Source4x.zip (0.8 MB)

Close the Source3 Project (click Save Project at the Toolbar or File->Save)

• Project Manager (File->Project Manager)
  Select the Source3 project
  Button “Copy”
  Name: Source4
  Description: Infiltration of Water and Solute from a Subsurface Source, Root Water Uptake and Triggered Irrigation
  Button “OK”

• Variable Boundary Conditions (Edit->Flow and Transport Parameters->Variable Boundary Conditions)
  Delete lines 4 though 6 and change the time on line 3 to 7 d as follows:

Time	Transp	Var.Fl.1	cValue1
0.1	1	-60	1
1.0	1	-60	0
7	1	0	0

Surface area associated with transpiration: 75 cm (length of the soil surface)
Button “OK”

• Boundary Condition:
  On the Edit Bar select the command Boundary Condition Options (Edit->Boundary Conditions->Boundary Condition Options)
  Select the third tab "Triggered Irrigation":
  Check "Triggered Irrigation" check box
  "Observation Node Triggering Irrigation": 1.
  "Pressure Head Triggering Irrigation: -150 cm
  Select "Variable Flux Boundary"
  Irrigation Rate: 60 cm/d
  Irrigation Duration: 1 d.++

• Run Calculations
  Click the Calculate Current Project command on the Toolbar (or Calculation->Calculate Current Project)
  You will get a warning that the Pressure Head and Concentration Initial Conditions on Geo Objects are different than those on FE-Mesh. That is correct since the imported pressure head and concentration initial conditions are defined only on FE-Mesh. The same warning is issued also for root water uptake, which was also defined on FE-Mesh. Click Yes to start calculations.