SGF, given those figures, a WAG is that you have to move around 712,799 gallons per hour. I would call Pond Dam Piping and see what they recommend. They will probably need a bit more information such as length of pipe, etc.
Taken from the resource guide:

Contact:Keith JohnsonAddress:398 Eighth Street
Macon, GA 31201Phone:(478) 742-0003 Toll Free:(800) 333-2611 Email:[email protected]
Website:ponddampiping.com

Or, if you want to plug in the numbers yourself, go here: http://www.ercp.com/catalog/design/hydraulicdesign_culvertdesign.htm

Last edited by esshup; 08/15/11 12:30 AM. Reason: added link
www.hoosierpondpros.com

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).