Tutorial 3.03

Tutorial 3.03

Furrow infiltration with a solute pulse

Video for Version 1.0 (46 MB) - Download

Download Project Furrowx.zip (0,6 MB)

Download the PDF file with detailed description accompanied with figures.

The third example considers alternate furrow irrigation into a soil profile with a subsurface drain. Water infiltration is evaluated for 100 days, with a solute pulse being added to the irrigation water during the first 50 days. The soil profile is 1 m deep with furrows 3 m apart; the drain is located in the middle between the two furrows at a depth of 75 cm. Alternate furrow irrigation is initiated by ponding the left furrow; mathematically this is accomplished using a time-variable pressure head boundary condition. The drain is represented by a circle to which a seepage face boundary condition is applied. Users become in this example more familiar with the basic concepts of transport domain design in the graphical environment of HYDRUS, including how to numerically define boundary objects, and again with boundaries and domain discretization. Initial and boundary conditions are specified, and graphical displays of the results using contour and spectrum maps, including animation, are provided, for a more complex transport domain than in the previous example.

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

• New Project (or File->New Project)
  Name: Furrow
  Description: Furrow irrigation with solute pulse
  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
  Make sure that "Edit domain properties, initial and boundary conditions on geometric objects" is checked.
  Initial Workspace: Xmin=-50 cm, Xmax=350 cm, Zmin=-50 cm, Zmax=150 cm (to accommodate the transport domain)
  Button “Next”

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

• Time Information (Edit->Flow and Transport Parameters->Time Information)
  Time Units: days
  Final Time: 100
  Initial Time Step: 0.01
  Minimum Time Step: 0.001
  Maximum Time Step: 5
  Check "Time-Variable Boundary Conditions" and set the "Number of Time-Variable Boundary Records" equal to 2.
  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: 18
  Print Times: 0.5, 1, 2.5, 5 10, 20, 30, 40, 50, 50.5, 51, 52.5, 55, 60, 70, 80, 90, 100
  Update
  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)
  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)
  Select Silt from Soil Catalog
  Button “Next”

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

• Solute Transport - Solute Transport Parameters
  Leave default values except
  Bulk Density = 1.5 cm3/g
  Longitudinal Dispersivity, Disp.L = 5 cm
  Transverse Dispersivity, Disp.T = 0.5 cm
  Molecular Diffusion Coefficient for Liquid Phase, Diffus.W.=2 cm2/d
  Button “Next”

• Solute Transport - Transport Parameters
  Leave default values for tracer
  Set cBnd in Boundary Conditions equal to 1 (this is boundary concentration)
  Button “Next”

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

Button “Next”

• FE-Mesh - FE-Mesh Parameters (Edit->FE-Mesh->FE-Mesh Parameters)
  Targeted FE – Size – Unselect Automatic and specify TS = 10 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 = 20 cm, Distance h = 20 cm
  Make sure that Snap to Grid is checked
  
  a) Outer Boundary
  Select the Line-Polyline command from the Edit Bar (or Insert->Domain Geometry->Lines->Polylines->Graphically)
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  b) Drain
  Select the Circle via Center and Radius command from the Edit Bar (or Insert->Domain Geometry->Lines->Circle->Graphically)
  Specify Coordinates of the Center X=150 cm, Z = 25 cm numerically on the Edit Bar
  Click Apply
  Specify Parameter R = 5 cm
  Click Apply
  Click Stop
• 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.
  Select the Opening via Boundaries command at the Edit Bar and click on the circle. This will specify that the inside of the circle is not part of the transport domain.

• Define FE-Mesh
  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=2.5 cm.
  After clicking OK, select two nodes at the bottom of the furrow at the left side.
  Small green circles should appear around these nodes indicating the size of finite elements.
  
  Click Generate FE-Mesh from the Edit Bar (or Edit->FE-Mesh->Generate FE-Mesh)
  
  Click on View All at the Toolbar (or View->View All)

• Initial Conditions:
  Click on the Initial Conditions Tab under the View Window.
  Make sure that you are in the mode of specifying properties on Geo Objects.
  On the Edit Bar click on New Initial Condition and in the window that appears check Equilibrium from the lowest located point, and set the Bottom Pressure Head IC to 50 cm. Click the button OK.
  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) Click on Zoom by Rectangle at the Toolbar (or View-> Zoom by Rectangle) and zoom on the left furrow.
  On the Edit Bar click on New Boundary Condition and in the window New Water Flow Boundary Condition check Variable Head 1,
  Select Variable Head 1 from the Edit Bar, and select the bottom and the side of the left furrow.
  b) Click on View All at the Toolbar (or View->View All).
  Click on Zoom by Rectangle at the Toolbar (or View-> Zoom by Rectangle) and zoom on the drain.
  On the Edit Bar click on New Boundary Condition and in the window New Water Flow Boundary Condition check Seepage face.
  Select Seepage face from the Edit Bar and assign it to the circle representing the drain.
  Click on View All at the toolbar (or View->View All).
  
  c) On the Edit Bar click on Boundary Condition Options and in the window check the option Switch the boundary condition from time-variable pressure head to zero flux when the specified nodal pressure head is negative.
  
   

• 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 furrow and drain.
  
   

• 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 – 61 s)

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