One of possible solutions is:
1. create a Session Parameter of Department catalog reference type, for example UserDepartment
2. create a Role for users who will have restrictions
3. doubleclick it and navigate to documents (or whatever) which you need to restrict
4. in rights list mark and highlight Read right
5. over rights in Data Access Restrictions list add a new restriction
6. leave Margins column empty (value "Other Fields") this means that your restriction will be applied to all fields of your document
7. in Access Restrictions column click the select ("...") button
8. in Restrict Access click Query Builder button
9. on the Conditions tab navigate to and doubleclick the document's Department field and see on the right side a new condition appears
10. in the last column (after the equal sign in previous column) type the name of your session parameter
11. you will have something like that: WHERE Department = &UserDepartment
