I posted a while back about an elusive pond leak and it remains elusive. I have isolated it to one part of my system which is an upper filter pond and a stream. There are two pipes that provide water to the upper pond and each comes from a different pump. One pipe makes a small cascade that looks like a spring feeding the pond. The other pipe provides water to the bottom of the pond. Each pipe alone provides sufficient water to allow the pond to feed the stream.
When water to the upper pond is shut off, the pond level is stable. Last week I ran water heavy in the stream, removed rocks and found no location where water was overflowing the liner, and saw no tears. Yet, when I run that part of the system with a good flow, I lose water. If I run one pipe alone, I lose water. If I run the other pipe alone, I lose water. If I run it at low volume I do not.
Reliable calculation of water loss is about 60 gallons per hour--which I consider a lot of water. Yesterday the pond ran for about 10 hours while I was away, the level in the main pond was way down--theoretically and by visual estimate 600 gallons lost!
I cannot imagine how 600 gallons of water can just disappear like that. One of the pipes to the upper pond is mostly above ground and dry. The other is buried maybe 4-6 inches in dense silt clay loam with a high water table. It is so wet and cohesive that when I built the stream next to the pipe's location there was so much soil creep I had to build a concrete retaining wall to hold it back. The point is that with that very slow permeability 600 gallons can't just diappear into the ground--and there is no wet, muddy area along the pipe's course. Or anywhere else I can find.
I welcome any and all thoughts, guesses, wild ideas and guidance to help solve the problem. Since the water flows fine and nothing leaks when the flow is reduced, perhaps the answer is to just run at low volume. But shouldn't any leak that swallows up 60 gallons per hour show in some way as long as water is present in any amount?
Winterizing the pond soon will only postpone the inevitable next spring, and a winter of frustrated pondering does not appeal. Help!