Had to run to work for a bit...
OK, in your drawing above you have a brown hatched area like a steep water-fall/white water stream.
That can work, but is very tricky for a first time pond builder to do it right.
Design a small pool at the top. Water from the pump enters through this. It can be a preformed filter/pool/overflow such as the box on the left in this link:
This spills into the top of the stream.
See the box (same link) on the right? That is a skimmer box, and acts like a swimming pool skimmer. Floating debris is picked up, and your pump can hide in there. You can build this into your lower pond.
I do not do it that way, I just have the pump in the pond itself.
And yes, I did a different sort of write up at APC. More details on how I made my pond and stream.