I'm afraid the procedure here only works for access.admin members. I can check out the repo, but can't create a new branch with the command you've used as I get:
svn: E000013: Can't open file '/g/data/access/access-svn/cmip5/db/txn-current-lock': Permission denied
It looks like there is a script that can be run to give individuals access to a repository, but it would have to be run by the repo owner. Might have to add in something about requesting that the script be run? Not sure what the procedure is there.