Being relatively novice to SVN, I needed to backup a recent installation. I found a couple of great scripts that was described for Linux, however, will work for Windows with additional software that is described in this article.

Dump the repository to a file.

svnadmin dump d:\csvn\data\repositories\myrepository > reponame.svn_dump 

Or dump the repository to a compressed file. This requires gzip for Windows.

svnadmin dump d:\csvn\data\repositories\myrepository | gzip > reponame.svn_dump.gz 

Or dump the repository to a compressed file. This requires 7-zip for Windows.

svnadmin dump C:\csvn\data\repositories\myrepository | "%ProgramFiles%-Zipz.exe" a -si backup.7z

Alternately, instead of dump, use svnadmin hotcopy REPOS_PATH NEW_REPOS_PATH

svnadmin hotcopy /repos \\backupserver\svncopy

To decompress the dump.

gzip -d reponame.svn_dump.gz 

To import or restore your dump file.

svnadmin load d:\csvn\data\repositories\myrepository > reponame.svn_dump 

Sources
Moving a Subversion Repository to Another Server
How to backup svn server
Piping data on Windows command prompt
what is the best way to backup subversion repositories?
How to Mirror a Subversion Repository