GGU-2D-TRANSIENT: Program concept

An initial steady-state condition is required for time-dependent modelling of groundwater flow. GGU-2D-TRANSIENT acquires this initial condition from a record (e.g. "Gwh1.da1" or "Gwv1.da1") generated during a previous analysis using the GGU-2D-SSFLOW application. It is therefore necessary to load this file first after opening the program. Beside the results, this file also contains the soil properties upon which the steady-state modelling is based. These steady-state soil properties (k, n_eff, etc.) cannot be altered from within the GGU-2D-TRANSIENT program. If amendment of these values were allowed, the soil properties would no longer correlate to the calculated potentials and discharges and the transient modelling would produce nonsensical results. However, additional soil properties, which are required for transient modelling, must be provided as a function of the type of groundwater system (vertical-plane, horizontal-plane, etc.).

Further to these additional soil properties, time-dependent boundary conditions can also be defined with GGU-2D-TRANSIENT. You must define boundary values (potential or discharge) as a function of time, by means of polygon courses. These polygon courses can then be assigned system nodes, either individually or in groups. Soil properties (transient) and polygon courses, as well as their allocations to system nodes, can be saved in a separate file as so-called boundary data, in order to make them available again for later modelling.

Boundary conditions defined in the course of steady-state modelling (GGU-2D-SSFLOW) are also contained in the file (e.g. "Gwh1.da1"). They are assumed by the program to be constant for the whole modelling duration, unless the so-called fixed boundary conditions are deleted in GGU-2D-TRANSIENT.

The GGU-2D-TRANSIENT program allows presentation of the steady-state file results (e.g. "Gwh1.da1") on the screen, facilitating quick and easy control. Transient data cannot be evaluated using the GGU-2D-TRANSIENT program. The GGU-PLGW program is available for this purpose; it is described in a separate user manual.

Generally, when modelling transient groundwater systems, a flood of result values is generated. Modelling results are saved by the GGU-2D-TRANSIENT program in a file "_t.plw". The file containing the base data (polygon courses, etc.) has the name "_ t.dat ". When modelling is complete, this file is automatically saved and then automatically reloaded when the GGU-2D-SSFLOW file (".da1") is reloaded.

The GGU-2D-TRANSIENT program is started using conventional WINDOWS operations. The program is equipped with a large number of error queries. Nonsensical input will usually be caught by the program and an error message displayed on the screen. Independently of this you should, for security reasons, intermittently save longer input.