A Drawdown Line is used to define the drawdown level of the water table if you are using the rapid drawdown analysis option for dams or embankments. The Add Drawdown Line option is only enabled if you have selected the Rapid Drawdown option in the Advanced Groundwater section of the Project Settings dialog.
To add a Drawdown Line to your model:
Select Add Drawdown Line from the Boundaries menu.
Enter the vertices of the Drawdown Line as described in Entering Coordinates.
NOTE: the Drawdown Line MUST BE DEFINED ACROSS ALL MATERIALS to which the water table has been assigned. If it is not, then the analysis will not be able to calculate the safety factor for slip surfaces where the water table is not defined.
When all vertices are entered, right-click and select Done, or press Enter with nothing in the prompt line.
The Drawdown Line will appear on the model as a dotted blue line, labeled W (Final) to indicate that this is the final water level for the drawdown analysis.
Only one Drawdown Line can be defined for a model.
For a rapid drawdown analysis you must define the initial water level with the Add Water Table option. The initial water table is labeled W (Initial).
A Drawdown line is optional. If you are modeling a full drawdown scenario, then you do not necessarily have to define a drawdown line. If no drawdown line is defined then complete drawdown is assumed.
For additional details about the properties of a drawdown line, see the Add Water Table topic. For example, pore pressure calculation, ponded water, etc.
For tutorials illustrating rapid drawdown analysis see the Slide Tutorials page.