Don't acorns float so they'd be picked up by a skimmer?
I don't have any info but I'd imagine it'd better if you could remain level all the way to the first filter although
realistically I don't think it's often possible in most ponds. I think a good compromise is to add a clean-out at
a lower level but iirc your swimming pond is planned to be 8' deep so rising 3' you'd still be entering the first
gravity fed filter at ~5' below water level? If so that's plenty deep and if I was concerned about clogging I'd just
add a clean out via a wye fitting straight to waste at the lowest level on the BD pipe, so it would be possible to
open a valve and have an enormous amount of flow to waste and it'd clear any debris that might have stuck in
the pipe. I used 2 45* fittings as opposed to a single 90* on my BD plumbing to keep clogging down to a minimum
and it seems to have worked on mine.