From the Site Management section select Departments
The current departments for that site will be listed.
To copy the members from one department to another, select the copy icon to the right of the department in the list.
Use the drop down to select the destination department you wish to copy the member list to and press Copy.
The members from the source department will be replicated in the destination department. If the member already exists in the destination then they will not be repeated.
To copy all departments to another site select the Copy Departments button top right on the page.
In this situation use the drop down to select the destination site you wish to copy the departments to and press Copy.
The department names will be created in the destination site but no members will be added. These will need to be added by modifying the copy in the destination site.