@Beercan31 the cistern is right around 3000 gallons and on average it can keep the pond toped off without adding water. mother nature rained enough even after this past year to keep it full. I have half the back side of my house collecting rain water where it is piped directly to the pond, there is only a fine wire screen that filters out small granules and twigs from the gutter.
The -pond was built first , I then added the expansion with the negative edge and cistern.
I had hoped that I could just move the intake from the skimmer "which was abandoned". To the cistern , however what I quickly found out was that external pumps are poor at pulling water. The bottom of the cistern is about 5 feet lower and a good 12 feet away. The external pump just could not draw the water on it's own no matter what I did. Even adding a hose bib" outdoor garden faucet " to the pvc pipe and had the hose running on full to supplement the flow getting the pump started. FAILED
So the solution was to add a small submersible circulating pump at 500 gph that is on a float switch. This pushes from the cistern up to the stream above the main and upper pond.
An 2" intake pipe was added in the small catch pool below the negative edge which is about 2 feet lower and 8 feet away from the external pump.
So the water in the pond has the two main drains and a negative edge for suction pipes. The water that goes over the negative edge is pulled in 90% by the 2" intake that is within a aqua block and is buried under 2" rock. the remaining 10% over flows this catch pool and drops into the cistern.
This can be seen in this video at 1:40 i show the overflow into the cistern which is the small lower fall and the larger at the top is the negative edge and the catch pool.
The cistern is stacked 2 rows high and is 12x12 . if you scan down the showcase you'll see the cistern being built, AND IN A OLD BUILDING TRASH DUMP WHEN THEY BUILT THE HOME BACK IN THE 20'S
