Pond Boss Forums INTRO Questions & Observations leaking siphon

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.