Domain Properties

Domain Properties are variables or parameters that may vary in space and are therefore defined either on Geometrical Objects or Finite Element Mesh. The table below lists Domain Properties recognized by HYDRUS.

Materials	Subsurface is usually composed of various material layers (horizons) that may have similar or dramatically different properties. Users must first define the Number of Materials needed to fully describe the subsurface in their project, then provide various parameters characterizing this material (e.g., Water Flow Parameters and Solute Transport and Reaction Parameters), and finally describe the Spatial Distribution of Materials.
Roots	Roots, and correspondingly the root water uptake, are spatially distributed. There is usually more roots closer to the soil surface and their number then decreases with depth. There is more roots closer to the trunk of the tree or a shrub and less further away. Users can either manually specify Spatial Distribution of Root Water Uptake or use predefined Root Distribution Analytical Functions.
Nodal Recharge	Nodes in the finite element mesh can be assigned either positive or negative Nodal Recharge, which may represent either sink or source of water in a particular node, respectively. These nodes can represent, for example, pumping or injecting wells.
Scaling Factors	The spatial distribution of soil hydraulic properties can also be described using the so called Scaling Factors. These Scaling Factors, which can be specified for Pressure Head, Hydraulic Conductivity, and Water Content, then linearly transform the basic soil hydraulic functions. The spatial distribution of scaling factors can be defined either manually, or they can be generated Stochastically.
Anisotropy	Hydraulic conductivity can have different values in different directions. For example, hydraulic conductivity may be significantly larger in the horizontal direction than in the vertical direction (likely due to organization of soil particles). The Anisotropy is fully described by the Tensor of Anisotropy (angles between directions of anisotropy and spatial coordinates; and individual components of anisotropy).
Subregions	Subregions are parts of the transport domain, for which mass balances (for water, solutes, etc) are evaluated and printed to the Balance.out output file. Their spatial distribution can correspond with the spatial distribution of Material Layers, but can also be different. One can, for example, request separate mass balances for the root zone and the rest of the transport domain (even when the domain is homogeneous, or there are multiple soil horizons in the root zone).
Observation Nodes	Observation Nodes are selected finite elements nodes for which various output variables, such as pressure heads, water contents, temperatures and concentrations are reported at specified time intervals. Such information can then be used, for example, to compare HYDRUS predictions with measured data (e.g., pressure heads measured by tensiometers, water contents measured by TDR, etc) or to calibrate the model against measured data.
Drains	A simplified way of representing Tile Drain.
Particles	Users can specify the initial positions of a set of hypothetical Particles (currently available only in two-dimensional applications) and the program then calculates trajectories and positions of these particles with time.

Parameters characterizing the flow domain (e.g., material distribution) are defined in a similar way as initial conditions (Section 6.2). Users must first select that part of the transport domain to which he/she wants to assign a particular value of the selected variable. It is possible to select the entire transport domain, part of it, or only individual nodes or elements. A particular part of the transport domain can be selected as follows: first move the mouse to a selected position. The beginning and end of the selection operation is framed by clicking the left mouse button. The selected area is the rectangle defined by the two mouse positions when the left mouse button was clicked. Selection can alternatively (instead of using the rectangular selection) be made using a rhomboid (with the Edit->Select->Select by Rhomboid command), circle (Edit->Select->Select by Circle) or polygon (Edit->Select->Select by Polygon). When the selection is completed, users must click the Set values button and specify the value of a particular variable. The given value will then be assigned to the selected area. When material numbers are to be specified, users can do this directly by clicking on the color representing a particular material (at the Edit Bar). All variables are assigned to nodal points, except for those defining anisotropy angles, the first and second components of anisotropy, and subregion numbers, which are all assigned to elements.

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