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Hydrus-2D Tutorials

Jirka Simunek and Rien van Genuchten

The purpose of this tutorial is to give Hydrus-2D users hands-on experience with the software package (version 2.0). Four examples are given to familiarize users with the major parts and modules of Hydrus-2D (e.g., the project manager, Meshgen-2D, Boundary and Graphics modules), and with the main concepts and procedures of pre- and post-processing (e.g., domain design, boundary and domain discretization, initial and boundary conditions specification, and graphical display of results).

We encourage Hydrus-2D users to provide us with additional examples (e.g., helpful classroom exercises) that they believe could be included in later versions of this tutorial, or could be discusses in more detail in one of our short courses. The following four examples are presented here

1. Infiltration into a one-dimensional soil profile

The first example represents infiltration into a one-meter deep loamy soil profile. In this example we use the internal structural mesh generator to construct a one-dimensional profile using two vertical columns each discretized into 51 nodes. Infiltration is run for one day. Ponded infiltration is initiated with a zero pressure head at the soil surface, while free drainage is used at the bottom of the soil profile. The example is divided into two parts: (A) first, only water flow is considered, after which solute transport is added. Solute transport is evaluated for both (B) Dirichlet and (C) Cauchy upper boundary conditions. Users in this example become familiar with most dialog windows of the main module, and with the use of the internal structural mesh generator.

2. Infiltration from a subsurface source in a vertical plane

The second example considers a subsurface line source of water and/or solute (drip irrigation) in a vertical cross-section. The (x, z) transport domain is 2 x 5 m2, with the source located 1.5 m below the soil surface at the left boundary of the transport domain. Infiltration is initiated with a constant head boundary condition and is maintained for 25 days, with the duration of the solute pulse being 10 days. The unstructured finite element mesh is generated using the external Meshgen-2D program. Example is, again, divided into two parts: (A) first, only water flow is considered, after which (B) solute transport is added. This example will familiarize users with the basic concepts of transport domain design in the graphical environment of Meshgen-2D, with boundaries and domain discretization, and with the graphical display of results using contour and spectrum maps.

3. Furrow infiltration with a solute pulse

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 constant 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 Meshgen-2D, 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.

Furrow infiltration with a solute pulse

4. Flow and transport in a transect to a stream

The most complicated fourth example considers water flow and solute transport in a vertical transect with a stream. The transport domain is relatively complex and consists of objects formed by polylines and splines. The problem, divided into four parts, also demonstrates how results of a previous simulation can be used in follow-up calculations with different boundary conditions or having additional features. At first (A), steady state water flow in the transect towards the stream is calculated. Second (B), a source (e.g., simulating water drainage from waste disposal site) is added to the soil surface about 30 m to the left of the stream for a duration of 100 d. Third (C), a contaminant is added to the source of water of simulation run (B). Finally (D), the contaminant source is assumed to be removed after 100 days. Transport of the 100-day solute pulse through the unsaturated zone into groundwater and to the stream is subsequently followed for 1100 days.

We believe that by carrying out these four examples, Hydrus-2D users will obtain the basic skills necessary to solve their own problems. We wish you all the luck and patience needed in this endeavor.