Having a back up is very wise. if you go that route i'd split everything . one pump from the skimmer to it's own pump. where it has a pipe that splits one to the pipe that goes to the bog and has a branch that pushes water to a return in the water current / water movement is key.
Then the second pump that comes from a main drain or just close to the bottom. Have that split to a second return jet that blows toward the bottom. That way in winter you can shut down the main drain pump and the water current that will be moving water at the bottom of the pond that you want to avoid disturbing during colder months.
i would also entertain a intake bay
Sorry slow response, thanks for tips. Liner has finally floated its way across half the pacific and should be landed here next week.
In the interim I have managed to have 101 different ideas on how to wrap this thing up, but I think I settled.
On pump flow, I got a 5400 gph pump coming that will pull from bottom under drain rock that will push into a 600 gallonish bog that is partitioned within pond. It’s gravel will be about 6” below water line. The three clean out stub ups will have a t on each that will feed small returns that will barely pop out from gravel under the water to blow across top of bog. With aiming these and happy rock placement that may protrude surface , I can get the prevailing flow to a location.
The 2800 gph pump from old pond will move to this one to feed a barrel that will be clad in rock and also have so filtering capability, like sand gravel. Like dis
https://www.gardenpondforum.com/threads/sand-gravel-filter.21092/
But it would be within pond and flow over its rim like a pot with water hyacinth on top. The clean out pipe and air injection would be stubbed out the back over pond wall hidden by rock.
There should end up being an area that leaves naturally gather with combined flows and that is where I will put a skimmer that will be the intake for the waterfall.
Logic sound? Should I also have some bottom jets. No real winter here. Coldest water gets is 60 if shaded. I could add those if needed.
