By “complex water feature” I mean a water feature consisting of at least a main pond, a header pond and a waterfall. The complex one I will now describe is the one in the picture and in the Youtube video.
It consists of the main pond where the submersible pump is and a header pond about 1 meter higher and 4 meters away. The header pond has a waterfall of its own, from where the water cascades down at 7000 liters per hour into this pond. From there it cascades over a weir onto a “bed” of natural rock, with a slope of about 25 degrees into a little intermediate pool. 
Two little streams join the main stream in this pool. (In the video these two streams have been closed). From there the stream continues further down onto another natural “rock bed”, underneath a bridge, and over the final spillway of natural rock into the main pond.
Phases: The system was developed in phases. The original water feature consisted only of the intermediate pool (+ small waterfall), with a 1750 liters per hour submersible pump. In the second phase the main pond was built and connected to this pool and the pump replaced by a 4500 liters per hour pump. In the final stage the header pond + waterfall was built and connected to the little pool.
The rocky “beds” connecting the header pond with the intermediate pool and the intermediate pool with the main pool: Since the header pond was considerably higher than the intermediate pool, I had to add some filling to create a natural slope, which I stamped down to have it as firm possible. 
I then covered this with underlayment and liner, to make absolutely sure that no water finds its way into the soil. I then filled the whole slope with concrete and arranged the rocks in a natural way, but making sure that the water will cascade over them. I then raised the edges (also natural rock) to make sure that the water stays in the waterfall and not spill over the edge.
The rocky bed from the intermediate pool to the main pond was done in the same way, with one difference: I Used small round rocks to imitate a riverbed.
The spillway over the edge of the main pond:
I used a piece of natural slate to create a proper spillway which hangs over the edge by at least 30 centimeters. (Please ignore the ugly liner! I removed some stones so that you can claerly see what I’ve done.) This is to make absolutely sure that all the cascading water ends up in the main pond and some does not find a way over the edge and out of the pond.
The spillway over the edge of the header pond:
I struggled to prevent leaks and spillages, but eventually got it right. I made my own weir from 1 cm thick plastic and sealed it properly in its place. Now every single drop of water finds its way through this weir onto the rocky bed. (I exposed the weir so that you can see it. Normally it is concealed.)
The waterfall of the header pond:
The header pond is more than merely a header pond; I’ve made it is just as big as the main pond for two reasons: Firstly, to have enough space to accommodate the “feeder” waterfall I intended; secondly, to have enough space to create a natural wetland system as a natural filter, filling half of the space with certain reeds.
Building this waterfall was the hardest past of the whole project, so learn from my experience and do not make the same mistakes!
The main challenge was to make sure that no spillages occur and with a stream of 7000 liters per hour that was quite a challenge. Anyway, in the end I got it right and this is what I did. I created a “shelve” over the one corner of the header pond onto which the waterfall could be built. I did that by simply putting a few supporting aluminium pipes (inserted into PVC pipes) across the one corner of the pond. You can clearly see two of the two pipes in this picture. Then I built the waterfall with natural rock on that and cemented everything at the back to make sure no water finds its way over the edge and out of the pond.
This was the hard way (but very rewarding). An easier way would have been to build the header pond with a black plastic skimmer/weir , of which a variety is available at Amazon.
Future plans: The header pond + waterfall being placed next to the driveway supporting wall gives me more opportunities, which I intend exploiting some time. I could use the height supplied by this wall to raise the waterfall by another 4 feet, but then I will have to use faux rock, since natural rock will simply be too heavy for the “shelve” below the existing waterfall.
The impact of this water feature:
This water feature has been a huge success. My wife and I, my children and grandchildren as well as many friends have spent many hours looking down at this water feature looking down from the deck. The sound of cascading water has had a mesmerizing effect on everyone. Our grandchildren love sitting on the bridge and watching leaves and other things drift down into the main pond. The ecosystem it has created has been a joy to insects, birds and frogs. Many birds like taking a bath in the “pebble bed” leading to the main pond. Some of the wild deer which stay in the ravine where our property is located, enjoy drinking water here as well. Unfortunately a local porcupine pays a visit as well from time to time and then destroys the many arums growing around the system. But we take that with a smile and just watch how they grow back again. This water feature has been a very rewarding DIY project!