When you install a new version of Mac OS X, git svn breaks. This happened with Mountain Lion and Mavericks, it happened with Yosemite. It happens again with El Capitan.
Unfortunately, the old solutions no longer work due to El Capitan’s System Integrity Protection:
$ sudo ln -s /Applications/Xcode.app/Contents/Developer/Library/Perl/5.18/darwin-thread-multi-2level/SVN /System/Library/Perl/Extras/5.18/SVN
ln: /System/Library/Perl/Extras/5.18/SVN: Operation not permitted
While you can disable SIP, that’s unnecessary in this case.
Here’s how you get git-svn working:
sudo mkdir /Library/Perl/5.18/auto
sudo ln -s /Applications/Xcode.app/Contents/Developer/Library/Perl/5.18/darwin-thread-multi-2level/SVN /Library/Perl/5.18/darwin-thread-multi-2level
sudo ln -s /Applications/Xcode.app/Contents/Developer/Library/Perl/5.18/darwin-thread-multi-2level/auto/SVN /Library/Perl/5.18/auto/
You can’t write to /System, but you can still write to /Library.