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Computer Session 9 Modeling Salinity Using the UnsatChem Module of HYDRUS-1D

Jirka Šimůnek and Tiago Ramos

Project Manager:

Button "New" Name: IAEA example II (note that if you have done the first “IAEA Example”, you can copy and modify it, rather than starting from the beginning) Description: IAEA Test Example II: Modeling salinity using the UnsatChem module of

HYDRUS-1D Button "OK" Button "Open"

Main Processes:

Heading: IAEA Test Example Check "Water Flow" Check "Solute Transport"

Check "Major Ion Chemistry"

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Check "Root Water Uptake " Button "Next"

Geometry Information:

Length Units: cm Number of Soil Materials: 3 Number of Layers for Mass Balances: 2 Decline from Vertical Axes: 1 Depth of the Soil Profile: 100 cm Button "Next"

Time Information:

Time Units: Days Final Time: 365 (d) Initial Time Step: 0.001 (d) Minimum Time Step: 0.000001 (d) Maximum Time Step: 0.5 (d) Time-Variable Boundary Conditions: 395 (intensive rainfalls are split in more records) Button "Next"

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Print Information:

Uncheck T-Level Information. Check Print at Regular Time Interval Number of Print Times: 12 Button "Select Print Times"

Print Times: 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 (d) Button "OK" Button "Next"

Water Flow – Iteration Criteria:

Leave the default values. Button "Next"

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Water Flow – Soil Hydraulic Model:

Select "van Genuchten - Mualem" model Button "Next"

Water Flow – Soil Hydraulic Parameters:

Copy the soil hydraulic parameters from the Excel file (units are cm and day) Button "Next"

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Water Flow – Boundary Conditions:

Upper Boundary Condition: Atmospheric BC with Surface Layer Lower Boundary Condition: Free Drainage Initial Condition: In Water Contents Max h at Soil Surface: 10 (cm) Button "Next"

Solute Transport - General Information:

Leave the default values, except Number of Solution Concentration Combinations: 6 Number of Adsorbed Concentration Combinations: 3 Number of Precipitated Concentration Combinations: 1 Button "Next"

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Solute Transport - Solution Compositions:

Enter the Solution Compositions and Adsorption Concentrations from the Excel File. Button "Next"

Solute Transport - Solution Compositions:

Leave default values. Button "Next"

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Solute Transport - Transport and Reaction Parameters:

Copy Bulk Densities, Dispersivities, Cation Exchange Capacities (CEC) and Gapon constants from the Excel File (1.49, 1.51, 1.61 (g/cm3), 25.8, 25.8, 12.2 (cm)) Diffusion Coefficient in liquid phase is 2 cm2/d Button "Next"

Solute Transport - Boundary Conditions

Upper Boundary Condition: Concentration Flux BC Lower Boundary Condition: Zero Concentration Gradient Button "Next"

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Root Water Uptake - Models

Water Uptake Reduction Model: Feddes Solute Stress Model: Multiplicative -> Threshold Model Maximum Allowed Concentration for Passive Root Solute Uptake: 0 Button "Next"

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Root Water Uptake - Water Stress Reduction

From the list box Database: Corn [Wesseling, 1991] Button "Next"

Root Water Uptake - Salinity Stress Reduction

From the list box Database: Corn Button "Next"

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Time Variable Boundary Conditions:

Copy time variable boundary conditions from the Excel file (units are cm and day) Button "Next"

HYDRUS-1D Guide:

Button "OK" Profile Information – Graphical Editor

Toolbar Button "Profile Discretization" ( ) Sidebar Button "Density"; with a "hand cursor" click on the top node of the profile and enter 0.5.

Toolbar Button "Material Distribution" ( )

Sidebar Button "Edit condition" Select with the Mouse: nodes from 39 to 81; specify Material 2 nodes from 82 to 101; specify Material 3

Toolbar Button "Root Distribution" ( ) Sidebar Button "Edit condition"

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Select with the Mouse: nodes from 1 to 71; specify Top value: 100, Bottom value: 0 and uncheck "Use top value for both".

Toolbar Button "Initial Conditions" ( )

Sidebar Button "Edit condition" Select with the Mouse the entire profile and set equal to 0.25.

Toolbar Button "Subregions" ( ) Sidebar Button "Edit condition" Select with the Mouse: nodes from 72 to 101; specify Subregion 2

Toolbar Button "Observation Nodes" ( )

Sidebar Button "Insert" Insert observation points to nodes 28, 50, and 69.

Save and Exit

Soil Profile Summary Assign Solution Composition (nConc) equal to 1 to nodes 1 through 38, 2 to nodes 39 through 81, and 3 to nodes 82 through 100. Assign Adsorbed Concentrations (nAds) equal to 1 to nodes 1 through 57, 2 to nodes 58 through 90, and 3 to nodes 91 through 100. Button "Next"

Execute HYDRUS-1D

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OUTPUT:

Observation Points

Profile Information

Water Flow - Boundary Fluxes

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