I started this thread a few months ago and yesterday the water in my pond got high enough to start the syphon. In previous times this much rain would have gone over the emergency spillway and would have damaged it as originally constructed (since the original construction I have had the spillway reworked at a cost of several thousand dollars). This time, the 10 inch sypon started as the vent pipe went under water and when the pond level reached the top of the sypon pipe at the level where the syphon pipe went through the top of the dam. I have a 45 degree elbow at the bottom of the syphon and when I first viewed the sypon flow it was a full pipe and was ejecting water 4 to 5 feet in the air and throwing it 8 to 10 feet away from the syphon outlet. I went to the vent pipe and it was clear from the sound that the water was passing through the sypon pipe under pressure. There was no whirlpool around the vent pipe but I assume it was full of water. Likewise, there was no whirlpool over the intake which is 10 feet deep.
Most impressive was the fact that the emergency spillway did not get used even though water was coming into the pond from approximately 70 acres of grassland and was coming in in large volume. As I observed the pond level, I could see that the pond level was declining and after about an hour it was down about 6 inches and continuing.
The design of the syphon follows the pond dam piping specifications and I am very pleased with how it is working.
Rockcreek
