Deleting old WAL-files

Hi,

I am looking for a good method of determining what WAL-segments can be deleted from our backup-archive.

We are using Postgresql 9.3 and do nightly basebackups along with archiving of WAL-segments.

We would like to prevent our backup-archive from growing forever, and thus delete basebackups and WAL-segments older
thansay 1 year. 

Is there a good way of finding the oldest WAL-segment needed for a given basebackup? (If not, what is the typical
methodfor deleting old WAL-segments?) 


(We are aware that Barman is offering this functionality, and might migrate to using it, but would still like to know
themethod used) 


Regards,
Gustav Karlsson