By default the manager for a Department may manage departments through the web portal under
Responsibilities:

In Web Designer this is defined under
Edit | Configure project | Web project...- Expand
Role Management then select
Responsibility for objects of type Department.
Here the default query can be changed accordingly by clicking the blue plus symbol:

Then click the edit button to open the
SQL expression window:

Save the change and compile the web project. Test using the Web Designer preview.