Here's a video showing a couple of low-profile sheet falls like what I am hoping to achieve. Guy says to plan for 500 GPH/inch of width in the falls for a typical sheet falls.
That seems crazy to me, though. I calculated it more like 150-200 gph/inch based on this pump flow comparison video:
Those sheet falls are all 14" wide. The 2000 gph flow looks good to me, which is about 150 gph/inch. The 3000 looks really good, and that's about 200 gph/inch. All the bigger pumps look like too much for me. The 5,000 gph pump (350 gph/inch) looks like way more flow than what they're pushing over their falls, so I don't know what is driving that guy's rule of thumb of 500 gph/inch. It looks like he's pushing more like 200.
Maybe he means 500 gph/inch spec'd on the pump and he's losing half of it to head pressure. Don't know. Either way, that's kind of what I'm going for. A wide, low profile sheet falls. The main one in that video looks like about 8" and it looks amazing.