Pond Boss
Posted By: Cliff76169 leaking siphon - 03/22/20 01:20 AM
After being away from my BOW for three weeks, I came to find the pond has leaked half of its water. This is a ten acre lake up to 17 feet deep. The water level is now at the level of the bottom of the siphon. I am wondering if the siphon could have malfunctioned?


Cliff
Posted By: jpsdad Re: leaking siphon - 03/22/20 01:54 AM
Cliff,

Do you mean the siphon took the pond down further than anticipated? or maybe it leaked around it?

If the former, the lowest a siphon could lower the pond is its depth on the pond side. But it could only do so if the siphon outlet is at or below the elevation of the pond side siphon entrance. Otherwise ... the lowest the siphon could lower the pond is the elevation of the outlet.

If the level of the pond is below the level of the outlet ... then there must be some other problem.
Posted By: Cliff76169 Re: leaking siphon - 03/22/20 02:15 AM
The pond level has been perfect for the last three years. Now the water has drain to the level of the siphon intake. It was about 8 feet under water
Posted By: Bobbss Re: leaking siphon - 03/22/20 02:27 AM
Isn't there a vent? Did it get clogged?
Posted By: Cliff76169 Re: leaking siphon - 03/22/20 02:31 AM
There is a vent. Will check first thing in morning
Posted By: Cliff76169 Re: leaking siphon - 03/22/20 03:28 PM
The vent seems to be clear. I do think there is water coming into the siphon. Not sure what to look at next.
Posted By: nehunter Re: leaking siphon - 03/22/20 03:35 PM
There has to be a wasp nest or maybe a mouse nest in the vent. If water is come up 8 feet to exit out the drain there has to be suction. IMO
Posted By: Cliff76169 Re: leaking siphon - 03/22/20 06:55 PM
Ive doubled check the vent and there is no blockage. Is there some other type of problem the siphon could have?

It is possible the siphon is not the problem, I just cant figure out where millions of gallons of water has gone. Ive got a call into Mike Otto to see if he can help.
Posted By: jpsdad Re: leaking siphon - 03/22/20 07:24 PM
One possibility is that the vent was on sufficient vacuum to trap a bird or squirrel perhaps? In such case, the siphon could empty the lake until the vacuum was lost (air sucked in from inlet of siphon).

I guess the advantage of having the siphon outlet at lower elevation than the inlet would be faster draining and discharge away from the dam but things like this can happen when the discharge is below the siphon inlet. Probably won't happen again though if that is what happened.

Hope all is well and Otto gives it a clean bill of health.
Posted By: Cliff76169 Re: leaking siphon - 03/22/20 08:14 PM
It is possible, the BOW did come up about 6 in last night from the rain
Posted By: nehunter Re: leaking siphon - 03/22/20 09:57 PM
Maybe a pipe extension with holes in it would eliminate the possibility of something plunging the vent.
Posted By: Cliff76169 Re: leaking siphon - 03/30/20 01:37 AM
Update

With the recent rains the BOW has come up about 2 feet with no water coming out of the siphon. Hoping it has self healed
Posted By: Cliff76169 Re: leaking siphon - 04/20/20 12:56 AM
Update 2


The BOW is now at full pool and the siphon is running. Now I have to hope it will not drain the BOW again

Cliff
Posted By: jpsdad Re: leaking siphon - 04/20/20 02:18 AM
Its great to hear that all is well.

Was there any vacuum at the vent? At some point you should see that and the air should stop the siphon.
Posted By: Cliff76169 Re: leaking siphon - 04/24/20 12:20 AM
update 3

As feared once suction was created, it would not stop until it emptied the lake again. That is exactly what happened.

Meeting with Otto in the morning

We will see what happens......


Cliff


Posted By: nehunter Re: leaking siphon - 04/24/20 12:48 PM
What is the size of the air tube? If to small compared to the main pipe could be it does not suck in enough air to break the siphon. Is there any way a wasp nest could have plug the air vent? Run water threw it if you can.
Posted By: Cliff76169 Re: leaking siphon - 04/24/20 05:56 PM
The drain pipe is 12 inch PVC and the vent is 1 or 1.5 inch.

Met with Mike Otto this morning. We removed the entire vent tube and there was no clog. Mike was unable to identify the cause of the problem. We left the vent tube off and Mike wants to monitor the drain during the next rain fall

Cliff
Posted By: nehunter Re: leaking siphon - 04/24/20 07:25 PM
I do not have a system like yours but what I have read. People use a 2 inch vent on 4 inch and 6 inch drain pipes. Your 12 inch pipe could need a 4 inch vent. It may create so much suction your small vent pipe won't let in enough air to break it. You may be able to buy a saddle fitting to put a larger vet pipe on your 12 inch drain?
Posted By: Cliff76169 Re: leaking siphon - 04/24/20 07:45 PM
Nehunter

I could see that the vent could be larger, but I cant get past the fact that it worked for three years. Something has happened. Its like a detective case


Cliff

Posted By: jpsdad Re: leaking siphon - 04/25/20 03:39 AM
Has there been any change like extending the outlet to a lower elevation? What is the height of the water when the siphon initiates? Has the recent flows been higher than in the past? For example, has there been significant flow over the spillway where before the siphon kept up with lake inflows and prevented flow over the spill way. The reason I ask is that it may be that in the past the siphon may not have worked even though it may have appeared to. I mean it may have flowed through the works while drawing too much air to initiate the siphon vacuum in which case the siphon may have worked more like an overflow pipe. A difference of a foot or so of pond elevation could be difference between the siphon piping working like a siphon or working like an overflow pipe.
Posted By: Cliff76169 Re: leaking siphon - 04/25/20 01:55 PM
Jp


Thanks for the response, I appreciate the PB family helping me with this issue. There has been no changes or modifications to the siphon since it was installed ( about 4 years ago). As far as I can tell water has never run over the emergency spillway. While it is definitely possible the siphon has acted as an overflow pipe over the years, I am still at a loss as to what changed to cause the BOW to drain down to the siphon intake, refill and repeat.


Cliff
Posted By: jpsdad Re: leaking siphon - 04/25/20 07:58 PM
You're welcome of course. Cliff, that you have not seen evidence of overflow at the spillway tells me that the peak pond elevation during previous rain events has been variable with all water flowing through the siphon piping. So what will happen as the water rises above the highest elevation of the siphon piping is that water will flow through the siphon. Once sufficient water is passing to create slugs on the downstream stretch there will be a vacuum develop. Air will be sucked in through vent in combination with the water. In this early stage of siphoning the air prevents the siphon from really taking off. But if the level in the pond gets high enough ... water will rise into the vent tube and the siphon's capacity to carry water will be maximized and flow is a raging torrent through the siphon. If there is a enough drop on the outlet side, the siphon may not suck enough air through the vent to break the siphon until it begins sucking air from siphon inlet.

I am pretty sure that until this year, the rain events have not be sufficient to get your siphon fully charged. In part this may be because the pond was lower during prior rain events, or that there was more filtration back then, or possibly just because the rain events provided less runoff. Whatever the case, we now know this will be an ongoing issue if you do not change something.

It is my impression that you have a fairly tall dam and that the elevation difference between the top of siphon and the outlet is also a fair distance. There is a couple of ways to solve it and so I will discuss them.

1. Reduce the flow potential of siphon. The best way to do this is probably to raise the height of the outlet. This could be done by extending the outlet with an elbow and additional piping. Or the siphon could be directed to the spillway with the outlet at a higher elevation.

2. Increase the flow potential of the vent. This would allow a greater amount of air to break the siphon. This may be cheapest and easiest route to take but it will depend on your installation. Ask Otto for his recommendation.
Posted By: Cliff76169 Re: leaking siphon - 04/28/20 08:47 PM
Here is a look at the siphon.

Attached picture 20200321_185245.jpg
Posted By: Cliff76169 Re: leaking siphon - 06/08/20 02:55 PM
Jpsdad

Option #2 seems to be the winner. I had a new pond builder come out and he replaced the one inch vent with a 2 inch. The siphon has gone through multiple cycles and is working properly.

Still no explanation of why this became a problem 4 years after the pond filled. But I am very happy the problem is fixed and the pond seems to have recovered.

Nehunter you were also right on target

Thanks for all the input of forum posters.

[Linked Image from forums.pondboss.com]

Cliff

Attached picture 20200529_204242.jpg
Posted By: jpsdad Re: leaking siphon - 06/09/20 03:03 AM
That's great news Cliff. Thanks for the update.
© Pond Boss Forum