Mike ther has been a lot of information posted on this subject but right now archival search is very unkind to me to say the least.
My preference, and in use on our ponds, is a siphon spillway system that has peformed very well the past year when we finally got some rain in Texas.
Others will chime in I know, but you might start your search with
http://www.ponddampiping.com , a PB advertiser.
Good luck...
