To create a new user-defined subbasin, first select the desired objects on the workspace. In the subbasin manager, make sure you are in the User Defined tab. Next select Subbasin, then Append New Subbasin. A new subbasin is created that contains the selected objects on the workspace. The name of the subbasin can be modified by selecting the name and entering a new name (or using the right-click Edit Subbasin Name menu). Alternately, you do not need to select the objects before creating the subbasin. Instead, create an empty subbasin and then add objects to it using the selector; see Adding and Removing Subbasin Members for details. Additional subbasins can be created or removed using the menu options in the Subbasin menu to append or insert a new subbasin.

An additional menu option, Append Typed Subbasin allows the user to add a subbasin that has a special classification. These include

The first four types are used in optimization. A Computational Subbasin can also be added using the Subbasin, then Append Computational Subbasin menu. See Computational Subbasin for details.