Pond with waterfall

[Neil Cheney]

We have a large pond with a waterfall into a smaller pond. The pump takes water from the small pond (reservoir?) and discharges it into the large pond (header tank?). Normally the large pond is completely full and the water level in the small pond gradually reduces until I top it up. What has recently happened is that the process has been reversed in that after turning off the pump water travels back to the small pond which becomes completely full and of course the large pond now has a lower water level.

I can’t understand what’s going on and any comments welcomed please.

 

[Lisak1]

It would seem to me that ANY time you turn off the pump the small pond would overflow - that's just how water flow works. You should always have the larger pond at the end of the system. Your design seems backwards. What would stop it from continuing to flow?

Can you post some photos of your set up?

 

[Neil Cheney]

It’s only just started happening. Maybe a coincidence that it occurred after adding blanket weed killer to the water. Please see photo

 

[poconojoe]

Nice setup! I'm not totally sure of your problem. Water will always seek it's level. Obviously, if you turn off the pump, the larger pond will always empty to the level of the waterfall. The waterfall is the lowest point which the water can escape. It just can't, empty any further unless there's a leak somewhere.

 

[Jhn]

Where does the pump hose/pipe feed into the upper pond? Is it underwater and is there a check valve in the pump hose?

Assuming you had a check valve in line to prevent backflow from the upper pond to the lower pond through the pump and hose. If the check valve failed which they can do after awhile, it can back siphon from the top pond when the pump is shut off until the hose is exposed and sucks air, breaking the siphon.

 

[Neil Cheney]

Thank you. It’s something which was here when we arrived and up to now which is 2 years the lowest/smallest pond was always lower than the upper pond so something has occurred. Maybe the way it is now is right as you say but I really don’t know what would cause such a shift. It occurred to me that there could be a one way valve in the outlet pipe of the small pond to prevent water from flowing back and it’s no longer working? The normal operation is that once the pump starts water is taken from the small pond and discharged into the upper one which of course then returns via the waterfall. Once the pump stops no water is therefore pumped into the upper pond and the waterfall continues to release water into the lower pond until the water level drops to the lowest part of the blade. What happens now is that the lower pond continues to rise and the water level in the upper pond drops to below the lowest level of the blade by several inches so the water presumably is being returned to the smaller pond via the pipe.

 

[Neil Cheney]

Where does the pump hose/pipe feed into the upper pond? Is it underwater and is there a check valve in the pump hose?

Assuming you had a check valve in line to prevent backflow from the upper pond to the lower pond through the pump and hose. If the check valve failed which they can do after awhile, it can back siphon from the top pond when the pump is shut off until the hose is exposed and sucks air, breaking the siphon.

The pump hose pipe feeds into the upper pond well below the surface of the water in the upper pond. Your theory that the check valve is stuck open probably is the answer. I suppose that I shall have to drain the lower pond and remove the inlet pipe which comes out of the side. It’s about two feet long with holes and see if the check valve can be released. Thanks for that!

 

[poconojoe]

I think jhn hit the nail on the head. If your upper pond water is dropping lower than the waterfall, there is either a leak, as I suggested, or the water is flowing back to the lower pond through the plumbing. And a check valve would stop that.

 

[poconojoe]

If you can't find a check valve, and it's basically buried somewhere, pull your pump. disconnect the outlet pipe (or hose), add a check valve and reconnect it to the pump.

 

[Neil Cheney]

The pump hose pipe feeds into the upper pond well below the surface of the water in the upper pond. Your theory that the check valve is stuck open probably is the answer. I suppose that I shall have to drain the lower pond and remove the inlet pipe which comes out of the side. It’s about two feet long with holes and see if the check valve can be released. Thanks for that!

I’ve been trying to locate the check valve and was wondering where you would suggest? The small/lower pond has a long perforated plastic pipe installed which exports water to the pond plant area emerging under the filter unit where there is a valve I operate to shut off water flow to the pump for cleaning the strainer basket. Once again, thanks for your comments.

 

[poconojoe]

I'm not sure, but from looking at your pictures, that white coupling thing on the outlet hose (on the ground) looks like a check valve. It may have an arrow embossed on it for water direction.
Can you take a closer picture of that?

 

[Neil Cheney]

I'm not sure, but from looking at your pictures, that white coupling thing on the outlet hose (on the ground) looks like a check valve. It may have an arrow embossed on it for water direction.
Can you take a closer picture of that?

Please see attached. The white coupling has a silver hose which runs to a pipe with a tap and is used to drain the small pond. The yellow thingy turns off and on water running to the pump. The black plastic pipe passes under the filter so that the piece of bamboo can turn the yellow thingy without removing the filter. Btw what would you say is the purpose of the three foot or so long perforated black plastic pipe (the far end is covered with a membrane so that water can only pass through the perforation) that comes out of the side of the small pond and is located six inches or so from the bottom of the pond? I pulled it out today and it was full of blanket weed?

 

[poconojoe]

I was referring to the big white plastic coupling looking thing towards the bottom of the second picture. Does it look like just a coupling or is it a tee? It might be a check valve. Can't really tell from the picture.
The perforated pipe with the "membrane " may be the intake for the pump. The membrane would possibly be to prevent fish or large particles from getting to the pump.

 

[Neil Cheney]

It does look like one of these so you may be on the right track. Very interesting. The perforated pipe looks like it’s the initial filter from the lower pond before reaching the pump and strainer. Also stops fish entering the plumbing as you say.https://www.screwfix.com/p/mcalpine-t28m-nrv-non-return-valve-white-40mm/61561

 

[Neil Cheney]

I’ve been having a closer look at the white coupling in the close up photo attached. One end has a metal turn screw to allow water to enter the silver pipe/tube in the centre which allows the lower pond to drain so I’m not totally sure that it’s a check valve unless it’s a modified one. Would appreciate your thoughts....