I like the layout and would use layout # 2.
I think BigJim and CaptainAhab are right about the flow rates however. The table from flex PVC
seemed very optimistic to me. The length of pipe, fittings, and bends all affect the flow rate. Also, any build up on the inside of the pipe will reduce the flow rate.
Your 1" PVC
will flow about 510 gph
(8.5 gpm) at a velocity of 3.5 ft/sec. The chart you were using assumed a 6.0 ft/sec flow rate which I believe to be overly optimistic. (BTW a 4 ft/sec flow rate gives the approximate 600 gph
) everyone quotes.)
A 1-1/4" pipe would allow about 920 gph
at 4.0 ft/sec and about 800 gph
at 3.5 ft/sec which I believe is a more realistic number. 1-1/2" would give you 1150 gph
at 3.5 ft/sec.
I think a real world test of your overflow box ( say 2 - 5 gal
. buckets of water timed through the overflow) would be a good idea to make sure it will perform as you want.