In the following window the input parameters for the flow are defined:
Calculation method
The choice of the calculation modules will remain until the module SITRA is adapted as described above. Until then, for a horizontal model with a partially 3D model and for the stream- and path line calculation the module INSTAT has to be selected (the modul XTRA will be available in the near future).
Equation solver and termination criteria
The equation solver and the termination criteria have been described in the calculation of steady-state flow.
Storage coefficient
The following parameters can be changed here:
The specific storage coefficient in horizontal models (confined aquifer) or the fluid and matrix compressibility in 3D models (saturated/unsaturated calculation).
Calculation of the storage term
The storage term calculation is based on the van Genuchten parameters.
Boundary conditions at intermediate points in time
If it is calculated with a fixed time step size or smaller time steps of the transient input file, it is possible for the intermediate time steps, which are not regulated by the transient input file to interpolate the transient boundary conditions! In principle he following is assumed:
Transient terrain settings are always linear interpolated!
Is a point of time listed in the transient input file (without data as well), the boundary conditions (except BERG) from that date are not interpolated, i.e. only the data that are listed below are changed. All other conditions remain those of the previous time step! The following example explains this:
Example 1:
The model file contains: POTE 10.0 1,….
The transient input file contains:
ZEITEINHEIT ZEIT TAG
ZEIT (first date)
2.0
POTE
1 12.0
In case a constant time step of 1 day is defined the fixed potential heads are:
a) with interpolation of the boundary conditions:
10.0 for the 0th time step (not interpreted)
11.0 for the 1st time step (i.e. after 1 day)
12.0 for the 2nd time step (i.e. after 2 days)
b) without interpolation of the boundary conditions:
10.0 for the 0th time step (not interpreted)
10.0 for the 1st time step (i.e. after 1 day)
12.0 for the 2nd time step (i.e. after 2 days)
Example 2:
The model file contains: POTE 10.0 1,…
The transient input file contains:
ZEITEINHEIT ZEIT TAG
ZEIT (first time step)
1.0 (without data)
ZEIT (2nd time step)
2.0
POTE
1 12.0
So, the boundary conditions for node 1 do not change on the first day. The potential head is fixed at 10.0 m on the first day. A requested change must be defined explicitly! The fixed potential head for node 1 is:
for the case in which a constant time step of 1 day is defined or the time steps defined in the transient input file are used with and without interpolation of boundary conditions:
10.
10.
12.
For the case in which a constant time step of 0.5 day is defined or the time steps defined in the transient input file are multiplied by 0.5:
10.
10.
10.
11.
12.
10.
10.
10.
10.
12.
Remark: Volume boundary conditions are always handled explicitly:
For the calculation of the state at the point in time tn+1 the boundary conditions of the point in time tn are used.
Initial conditions
Here is defined with which initial potential heads the transient flow computation is started.
Initialization with initial potentials (EICH): The in the steady state flow computation calculated resulting potentials are used as the initial potential. This requires that the resulting potentials are assigned to the attribute EICH via the menu item Attributes 
Import data/computation results Potentials.
The transient calculation can be continued, if the corresponding null-file from the previous calculation exists (warm start). If the user wants to continue the actual calculation, the program has to create the corresponding file called out66. This is specified in the choice of output parameters (Save for continuing (out66) ).
No initial potentials: The iteration is started with initial potentials = 0.0.