So it turns out that I was ‘delightfully wrong’ again, with my thought that lowering the intake would lower the pond level. (In my defense I would say that Jon convinced me that the height of the ‘suction’ determines how much water is drained), but Mike Callahan gave this explanation, echoing Dave Scola’s summary of what Skip Lisle told him.
When a beaver dam pipe is installed through a beaver dam to control the pond level the primary factor that determines the pond level is the highest part of the pipe. With most beaver dam pipes the highest part of the pipe is where the pipe goes through the dam (e.g Flexible Pond Leveler™ or Castor Mastor™ with a Round Filter). See diagram below. The Clemson Pond Leveler has a standpipe positioned behind the beaver dam. The height of the stand pipe determines the pond level with that flow device.
In all these examples, gravity drives water through the pipe. Since water seeks it’s own level, the water level inside the pipe is always equal to the pond height. When the pond level rises above the high point in the pipe, water will flow through the pipe. If the pond level drops below the high point of the pipe during a dry period, then the pipe will stop flowing until the pond level rises enough for it to flow again. There should be no siphoning. The pond level determines if water flows through the pipe.
The diameter of the beaver dam pipe(s) need to be large enough to carry the flow of the entire stream most of the time. Beavers only raise the height of their dams in response to water flowing over the top of the dam. When the pipes are properly sized the beavers are unable to raise the height of their dam because the pipe(s) have created a permanent leak, keeping the water level down at a safe level. Very large storm events will flow over the top of the dam and the pond will only temporarily rise a little bit before the pipe(s) return the pond to the goal level. The pipe(s) should be set at a height in the dam to account for these minor pond level fluctuations of 6 – 12 inches.
So there you have it, the highest point of the pipe (and not the lowest) determines pond height. Which wasn’t changed during this recent re-filtering episode. As long as they rebuild the secondary dam everything should be fine and we shouldn’t worry. And since we’re on the topic I thought I’d post the graphic about flow devices I made for Sunday’s meeting.
