Mike, you're right, 60 gal an hour is a lot of water and it should show up somewhere.
Your lower pond is a liner too, right?
Poke at the liner in the lower pond and see if the water from your stream is running under that liner. If it is, the lower liner might be raised up in places.

Other than that, I had about the same thing one time. Waterfall/stream. Ended up just taking it all apart and re-doing it all. Nothing else worked. When I re-did it, I didn't use a liner, used concrete.

Corrie

Watch the current in the pond with the leak and determine where it is hitting the sides. At that point where the current hits the side of the pond raise the pond liner.

I have three pools in my pond, The water is pumped into the top pool through a pipe that is about 14" below the surface of the pool. The discharge from the pipe cause the water level on the opposite side of the pond to raise and go over the liner.

People assume that the water level in a pool will be constant. While this is somewhat true for a pool where there is no circulation, once the water starts to circulate there can be variance in the water level in various parts of the pool.

You can see the effect around a rock in a stream. The water on the upstream side of the rock will be slightly higher than the water on the downstream side of the rock. Same effect in a pool where the current hits the side of the pond.

The original owner of our pond did not understand fluid dynamics, and thought if every thing was on the same level he had it correct.

Thank you both for the interesting and helpful responses. I feel now that the problem is in my upper pond. It is about 4x8 feet and close to 2.5' deep. Initially I had a low spillway and the pond never filled with water. A lot of very large flat stones overhang the surface to hide the liner a bit.

Last year I raised the spillway for a more dramatic fall from the pond and to raise the pond water to further hide the liner. A huge amount of water flows into the pond and as you suggest no doubt goes over the liner under the large stones--and I bet they have settled to lower the liner. There doesn't appear to be a problem from outside the pond, and the stones are far too heavy and settled to move. Tomorrow I will run a very heavy flow, get in the pond and poke under the stones.

The hydrology is a bit complicated. I have dense soils underlain by an impervious layer over which I believe the lost pond water runs down a short but steep slope. I am thinking now that it does end up under my pond liner. The pond was put in an area of very high ground water and has drainage structure under it to prevent ballooning. The drainage pipes send water to my subsurface storm drains and ultimately into the municipal storm sewer.

My plan is to auger some holes in the likely drainage course from the upper pond. I will run lots of water, let the level in the system drop, and see what is revealed in the holes. Later I will check for discharge into the storm water system.

Ultimately I am going to lower the spillway from the upper pond and hope that will solve the problem.

knuttle, your lesson on fluid dynamics is spot-on and much appreciated--new to me and no douobt germane. corrie22, concrete has more than once entered my desperate mind, but it is not an option with a large stream.

I will report back after tomorrow's work, hopefully with positive results. Again, thanks for the invaluable help.
Mike

I ran a level line from the top of my spillway in the upper pond and noted that at a couple of locations the liner top was not too much above the spillway. When I turned on the water I saw that the water over the spillway was about .5" deep and the water level along the edge of the pond, in places, was right up to the top of the liner. Fluid dynamics.

I removed the top spillstone, lowering the water about 3" and the possibility of overflow over the liner was gone. I then let the whole thing run for a while and the water level in the pond dropped rapidly again.

I ran one pipe feeding the pond and stream to see what would happen. The water dropped. I turned that off and ran the other feed. The water dropped. I doubt a pipe is leaking, unless both are leaking, somewhat improbable.

The leak has to be in the pond (the water level is stable when the pipes are off), in the spillway area which will take some doing to disasemble, or in the stream where I pulled rocks and saw only dry liner on the stream sides and banks. One last try at opening a valve I have forgotten and feeding the stream from below the spillway and see what happens. If the water loss continues, it is the stream. If the loss doesn't continue, it is the pond-spillway.

Does anyone have an idea of how big a tear there must be to lose 60 gallons (or maybe more now) an hour? I would think there should be a tear rather than just a small hole.

When I run one stream with lots of water, the pond level is completely stable, not the slightest water loss over a 2-3 week period. Might as well just enjoy and leave the other area until spring.

There is another post about a leaking stream--perhaps that ponder will discover something I am overlooking. Wishing luck to that person.
Mike