I wanted to split an SVN repository into pieces:

svnadmin dump repository > dumpfile_2007-09-17

cat dumpfile_2007-09-17 | svndumpfilter include blahablh > newdumpfile_2007-09-17

svnadmin create blahablh

svnadmin load blahablh < dumpfile_2007-09-17

trac-admin resync