Initial conditions, i.e., conditions throughout the transport domain at the beginning of simulation, need to be specified for each considered process. If one simulates water flow, then one needs to specify initial water contents or initial pressure heads throughout the entire transport domain. Similarly, if one simulates solute or heat transport, one needs to specify initial concentrations or initial temperatures.

Use this command to specify the initial conditions for water flow by defining the initial spatial distribution of the pressure head or water content over the flow domain. The decision whether to use the pressure head or the water content initial distribution is made in the main module in the "Iteration Criteria" dialog window. The initial conditions are specified in two steps. First, the spatial region (or parts thereof) is selected with the mouse; next, the value of the pressure head, h, assigned as initial condition to a selected region is specified in the pop-up window.

One can specify:

1. the same value to all selected nodes (Same value for all nodes),
2. a distribution versus depth that is in hydrostatic equilibrium with the pressure head of the lowest point in the selected region (Equilibrium from the lowest located nodal point),
3. a distribution versus depth that is in hydrostatic equilibrium with the pressure head at the soil surface (Hydrostatic Equilibrium from the domain top surface),
4. a Linear distribution with depth, and
5. equal to the Field Capacity (see below).

To simplify definition of the initial condition for problems that involve slopes, an option is provided to have pressure heads decrease in the x- and y- (the latter only for three dimensional problems) directions (Slope in X- direction and Slope in Y- direction).

The top right part of the dialog window (Values in selected nodes) provides information about the selected nodes, i.e., the number of selected nodes and the minimum and maximum values of the pressure head or water content.

Internal nodal sinks/sources: If a certain node is selected that is not located on the boundary, this node can be declared an Internal Pressure Head Sink/Source or Internal Flux Sink/Source, which can be either constant with time or time variable. For a constant internal pressure head sink/source, the specified pressure head at that node (indicated using the same color as the constant pressure head boundary condition) will then be kept constant during the simulation. For a time-variable internal pressure head or flux sink/source (node indicated using the same color as for the time-variable boundary conditions), the time series of specified pressure heads or fluxes needs to be specified in the "Time-Variable Boundary Conditions" dialog window in the 'Var. H4' or 'Var. Fl4' columns, respectively.

Hydrostatic Conditions:

One needs to do the following steps to specify hydrostatic conditions as the initial condition:

1. Select a part of the transport domain where you want to specify hydrostatic conditions,
2. When specifying the actual values, click the radio button “Equilibrium from the lowest located nodal point”.

The initial condition can be imported from the results of a previous calculation using the Import Initial Conditions command.

See also the following topics:

       Initial Conditions

       How to Edit Initial Conditions