How do I delete a branch in TortoiseSVN?
The SVN book ("Version Control with Subversion") explains how to delete and restore branches.
Although it suggests remote deletion like
$ svn delete http://svn.example.com/repos/calc/branches/my-calc-branch \
-m "Removing obsolete branch of calc project."
you could also do it locally (with the TortoiseSVN > Delete command).
As mentioned in the book, you can always restore branches, so you won't get any unexpected consequences.