I guess it would help if I provided a little explanation. If you look at a normal automatic bottom draw siphon system the vent is above ground allowing the bottom draw to act as a normal overflow pipe until the water level covers the vent hole. Once this happens your bottom draw goes into siphon mode until the water level drops below the vent opening breaking the siphon mode. It then returns to normal overflow. Northern climates have to contend with freezing conditions in winter and Southern climates have to make sure their vent doesn�t get blocked. If the vent gets either frozen or blocked, there is a risk of entirely siphoning your pond. The only difference with the idea that I have would be that the entire system would be completely buried below the frost line in your location. This idea would eliminate both possibilities if it will work. The downward open end of the vent that will reach the water in a siphon control would extend inside a larger piece of pipe that is higher than the apex of the main siphon pipe. An adapter (example 2� pipe to 4� pipe adapter) is also higher than the apex of the siphon pipe would allow you to have the smaller pipe inside a larger pipe with hole(s) drilled in the smaller pipe up to the point it reaches the apex level of the siphon pipe. The solid larger pipe would extend underneath the face of the dam before coming out into the water side face of the dam (trash rack on the end of the larger pipe???) that would then be covered with rock to allow water not debris to rise and fall in the larger pipe as the water level rises and falls. The hole(s) in the smaller pipe inside the larger solid pipe would control when the water siphons and stops. I was thinking this might be a possible solution for those in northern and southern climates. Comments?
Thanks,
Heppy