Well, I'm not a builder but I'll tell you what I know:
First, be sure you have as sharp an edge as possible on the pool side to allow the water to pull away from the surface as it goes over.
Second, you need about 1/4" of lift for every 3' of drop from the edge to the trough. The further the water has to drop the more likely it is to start coming apart, so the more water has to be pushed over. For every 1/4" of lift you need 10 gpm per foot of edge. So...
30' is a BIG edge. That will require 300 GPM just for a 3' drop, 600 for 6', 900 for 9', etc.
Now to size the trough:
First, I'll assume at your size that your surface area is about 16 x 32, or roughly 500 sq ft. And we know you need at least 1/4" of lift in the whole pool to push over the edge. Since there are 7.48 gallons in a cubic foot, we can divide by 48 to get down to 1/4". So 1/4" of water is .156 gallons per square foot. You have 500 square feet, so that means you need to add 78 gallons of water per 3' of drop. This is called your "water in transit", or the water that will still be moving once you turn the pump for the edge off.
Next, you need to consider bather surge (max amount of water displaced from swimmers), which as a rule is 2" which through the above calculations works out to 620 gallons.
If you have a spa attached to the pool it is a good idea to add the gallons for it as well, just as a precaution. I'll assume no spa here.
You'll need your trough to be about 1' wider than the edge itself to compensate for water spreading out from the wind, so 31' total, and you need it to extend far enough to catch the water. Size this based on your drop. 3' drop will fall 1' from the wall, 6' will fall 2', 12' will fall slightly less than 3' away. This is all based on the 1/4" of water per 3' of drop rule.
So let's just say we've now got a 31' long by 2' wide trough, and a 3' drop from the pool to the trough. That gives us 62' square feet. We need to compensate for:
Water in transit = 78 gallons
Bather surge = 620
Spa volume = 0 (i assume)
So that total is about 700 gallons. Divide that by 7.48 to get the necessary cubic feet (~94). Divide that by your square footage (94/62 = ~1.5). That's the depth required to compensate for all the water that could spill over. You want to add an extra foot to this to be sure that when running the trough does not start to create a vortex and draw air through the drains. So your total trough depth should be 2.5'. Call it 3' since you probably won't be full to the top.
To get your 300 GPM you'll need multiple pumps. Theoretically 2 3hp pumps could do it, but you'd probably need three. You'll also have multiple main drains since they should only operate at 1.5 FPS max. That's only 20 GPM in 2" pipe, so you'll want to think about some larger diameter plumbing (3 or 4").
Hope this helps!
