I am installing the pond dam piping syphon system. Is it necessary for the level in the pond to rise above the level of the pipe through the top of the pond dam? Also, does the level of the pond have to rise over the small vent pipe in order to start the syphon? Any advice will be appreciated.

The way I understand it, Not really and yes. In a basic setup water will flow out through the pipe as long as the water level is higher than the bottom of the highest point of the pipe. This can be just a trickle without actually creating a siphon. A true siphon action will not start until the pipe is filled enough that the weight of the water on the downhill side is enough to pull water up the intake. If there was enough water flowing to actually start a true siphon then the water would continue to be drawn through the system until until either the water drops below the intake pipe or siphon break vent pipe. Whichever is the highest will break the siphon. It is possible that your siphon system would never truly siphon but you'd still get the benefit of pulling "dead" water off the bottom of the pond if your intake pipe went deep enough.

Ryan: Thanks for the info. My syphon pipe intake on the pond side (water side of the dam) is about ten feet below the normal surface level of the pond. The bottom of the syphon pipe running thru the top of the dam is about 3 inches above normal pond level. The bottom of the vent pipe is about 2 inches above normal pond level

If I understand your post correctly, the syphon pipe will begin to run (but not syphon) if the pond level rises above the bottom of the syphon pipe running thru the top of the dam. The syphon action will probably not start unless the water level rises pretty much over the top of the syphon pipe going thru the top of the dam. If the syphon action starts, it will stop when the vent pipe is above the level of the pond.

I am probably going to raise the elevation of my emergency spillway to ensure the level of the pond will engage the syphon action before running off thru the emergency spillway.

If I have understood your advice please confirm that I have.

Thanks very much for your input.

You can always call the folks at PDPiping as well. The pipe going through the dam sets you lake level. I think this is the same but stated differently. It is gravity feed system everyday. When the lake is full and water running it simply goes through the pipe and out the back. Siphon stats when pipe level is full and vent tube under water, once the vent tube catches air it will shutoff. The emergency spillway should be halfway between lake level and top of dam height ( quite a bit above the air vent if you have enough freeboard. good luck!

Your vent line needs to be high enough to let all the air out of the pipe system in the dam. Otherwise the trapped air stays in there. The pipe will still let water overflow through it, but will not run a full pipe or really move water during a high water event as long as there is air in the system.

Kent: Thanks for your input. There seems to be several views on the elevation to use for when the vent pipe is under water for the syphon action to start. The Pondampiping diagram shows the elevation of the vent pipe to be at the elevation of bottom of the pipe running thru the top of the dam. I admit that your explanation makes sense -ie. the air must be out of the pipe for the syphon action to start; but, if I could get the syphon action to start at a lower level, say at the elevation of the bottom of the pipe running thru the top of the dam, it would allow the syphon action to run longer and obtain a lower water level.

Does anyone else have a comment on the elevation of the vent pipe with respect to how it allows the syphon action to commence?

It sounds like you've got the idea. You could experiment with a large paper cup and one of those straws that bend at the top or a piece of clear hose. The red dot in my illustration shows where you could locate a vent hole for further experimentation. Once the vent hole is added the water should only siphon down to the height of the vent hole. Keep in mind that once siphoning has begun, should the vent hole become plugged the water will drop until air enters the system at the intake. Basically emptying your pond if the intake goes all the way to the bottom.

ryan nice diagram. I have alwyas been told the siphon will not "kick in" until there is a full pipe of water. Vent tubes on clietns lakes vary from below the top of pipe to 4 inches above the pipe.

I think that is the best advice. Make sure you have a trash rack around the vent. One of the ponds at my deer lease had the vent hole get plugged up and it almost drained the entire pond.

Ryan,
In your second pic how did the air get out the top?
The air won't go out the ends because they are lower.

The air that is trapped will be pushed out of the outflow end once the weight of the water has overcome it either due to the pressure from the weight of the water above or the suction developed from the weight of the water below once the lower part of the pipe is filled. It will work as long as there isn't significantly more air trapped in the high section of the pipe than there is water filling the lower section of the pipe. Try the experiment.

To further demonstrate that water can be sucked/pushed down try this. Take a clear piece of aquarium air tubing or any clear tubing a few feet long and completely submerse it in a bucket of water. While under water let all the air escape from the tubing and cap off one end with your thumb. Pull out the capped end and lower it below water level while leaving the other end in the water. Remove your thumb and allow the siphoning action to start. While the water is flowing, very quickly pull the end in the bucket out of the water and put it back in. You should see a pocket of air travel through the tubing and out the lower end.

Ryan,
I disagree that the air is shoved out the end of larger pipes.
The suction part won't start until the air is out so that is a catch 22.
The 2" vent pipe on my ponds 12" pipe was set to low. The 12" pipe ran an awesome amount of water, but never a full pipe during a flood event where we had 20" of rain in 48 hrs or so. The pipe ran about 2/3 - 5/8 full on the discharge end while the pond was at spillway elevation. The 12" pipe had over 4' of head at that point. (about 8 psi)

Kent: I have set my 2 inch vent pipe at the level of the bottom of my 10 inch sypon pipe going thru the top of the dam. Based on your experience is this too low to allow the sypon action to start? It will not be difficult to raise the 2 inch vent pipe if I need to, but I would like to allow the sypon to reduce the pond level to the bottom of the syphon 10 inch pipe and shut off automatically at that level as the 2 inch allows air into the 10 inch pipe. Your thoughts are appreciated.

Rock Creek

Rock Creek,
My experience is that the draw down will not start a true siphon unless the vent pipe is the high enough to let out all the air.
The siphon will stop at this point as the water comes down.
The 10" pipe will continue to flow a lot of water without any siphon effect.
The next big rain will retest my system. It hasn't ran any water since repairing it.

I have two 12" siphons with 4" vents. I have seen the vents a good 6" below the surface with a lot of water coming out the 12" pipes, but have never seen it actually siphon. I took to cap off of the tee in the vent so I could see straight down to the 12" pipe, and it had about 6-8" of water flowing over the bend. I am not sure why it didn't siphon.

If the vent is mounted near the highest point of the pipe, as the mainline fills, air will be pushed out the vent tube as long as the pressure at the open end isn't greater than it is on the inside opening...following the path of least resistance. Once the downhill side is completely filled with enough water on the downside that the weight of is greater than the weight of water it has to lift on the intake side, the siphoning starts, some remaining air left in the vent will be sucked back into the pipe (If the air volume inside the vent pipe is too much than it could potentially defeat the siphon) Assuming the vent is appropriately sized, during the siphoning, water should be getting pulled up through the vent. It will be part of the intake. The water filling the outlet pipe works like a plunger sliding down the pipe pulling water up the intake side. Once the water level drops below the vent intake, it will be easier to suck in air than water (again if the air vent is properly sized) The length and angle of the pipe on outlet side are going to have a major impact on the power and effectiveness of the system. The steeper and longer the downside of the pipe the more suction will be developed.

Water level has to be (1 1/2 the pipe diameter) higher than normal water level to run a full pipe of water with a conventional pond pipe that includes a canopy inlet.
This is optimum conditions to start suction and a pipe has to be submerged 1 and 1/2 times its dia. to start sucking and run a full pipe.
I wouldn't expect the siphon system to start running a full pipe as quickly, because of the incoming water having to pulled through piping and being less available.
I don't think air will be pushed anywhere out of the system. The pressure is on the pond side trying to push into both the vent and system. If the air can't go up it is trapped. The pressure on the pond side is not great enough to force a full pipe of water and purge the system on larger pipes.

zhkent & Jersey, do you have a trap on the outlet side of your systems? This is a key component if you want your siphon to start naturally, especially on the larger systems you have described. It traps water in the elbow at the bottom of the outlet side, allowing water to fill the downhill side of the pipe aiding in starting a siphon. Basically the same way your toilet works.

Dear Rock Creek:
The answer to both your questions is yes. The water must go over the pipe and over the small vent pipe to start the syphon.

Ryan: I am not sure what you refer to as a "trap" I have a 45 degree elbow at the bottom of my 10 inch pipe on the backside of the dam. I have approx 20 feet elevation difference between the intake in the pond and the end of the 10 inch on the backside of the dam. Assuming that the 2 inch vent pipe is set at the bottom of the 10 inch pipe, do you think this arrangement will be sufficient to start the syphon action when the water level of the pond is above the 10 inch pipe?

Rock Creek

You are correct that the elbow at the bottom forms your trap. It sounds likely you'll start to siphon when the water reaches above the pipe and could possibly even start a siphon when the pipe is half full. One of the siphon system manufacturers could tell you for sure at what point a siphon would start if you give them the full specs of your system.

Keep in mind it really isn't all that important to start a siphon unless you absolutely need the added capacity to remove excess water from your pond. You will still get the benefits of removing water from the bottom of the pond in contrast to a conventional overflow even if water is only trickling out.

Ryan: Thank you for your thoughful and concise posts. It gives me confidence that, when needed, the syphon will prevent a big release down the emergency spillway. I also like the early ordinary flow but the real reason for the installation of the syphon is to protect the spillway and the pond from those huge rains we get here in eastern Kansas from time to time. When we have the right conditions to test the syphon, I will post and bring you and all the other posters on this thread with a "real time" update.

Rock Creek

Since you're in Kansas, is freezing water in the trap something to be concerned about?

Ryan,
I just got off the phone with EasyWay Plastics of Georgia in regards to the Syphon Piping and the potential of it freezing in the winter. I was informed the only reason for the trap is to prevent the water discharge from washing out the back of the dam.
They said you can use what ever angle pipe I prefer 45 Deg or 22.5 Deg. My concern was the pipe freezing if flow stops since there will always be water in the trap.

Ryan: I had considered the freezing issue and decided to wait and see exactly what water remains in the pipe with the 45 degree elbow. If I think it will have the potential to crack the elbow I will probably drill a small drip hole in the elbow to allow most of the water to drain slowly out of the elbow. In theory that should take care of the possibility of freezing water damaging the elbow.

Rock Creek

Then why is it called a trap?

"Outlet elbow
The elbow on the outlet end of the pipe serves three purposes. It acts as an aerator so the anoxic bottom water is aerated before it enters the stream, as an energy dissipator so a deep plunge pool doesn't develop and as an air lock so siphoning will begin at lower water levels (low flows) and will continue until air enters the upstream air vent."

See http://extension.missouri.edu/explore/agguides/agengin/g01530.htm for reference

I think their adjustable intake vent is pretty neat too.

The article also brings up a good point about the intake freezing. What if just water in the air vent freezes, forming a plug? Couldn't that potentially drain the pond if a siphon started?. It seems as though it would be better that the vent was above the bottom of the high point in the overflow pipe.

All this siphon theory has helped me understand something. I'm not bright, at least about this stuff anyways.

I want to ask you siphon brained folks for help. Construction will start soon on Cindy's pond. The contractor has bid on a dual level pond with about a 3 foot difference in the levels. When I first talked to the contractor about two levels I said I was thinking in terms of having two siphons, on at each elevation. What I just realized is that I'm not certain that both siphons can function at different elevations. To maintain the pond at the higher level would require closing off the lower siphon. In that case we lose that volume of drainage. Right? IIRC the contractor included two different sized pipes, perhaps with the smaller one at the lower level with the higher siphon being adequate for the entire pond.

Without rambling on more here's my basic question; how best can we design drainage for a dual level pond?

I really like the idea of a siphon system if feasible.

Determine what size pipe you need along with your emergency spillway. Use 2 pipes that size one at each level with the ability to close off the lower one with a valve and cap on the pipe.

I have a 22 1/2 degree trap at the bottom of both siphons.

Chris brings up a good point about the vent tube. The piping system that is being referred to is not actually a syphon, but is a bottom water drain system, UNLESS the vent tube gets blocked. The pupose of the vent is to prevent a syphon from beggining. Ryans drawing is great and is a true syphon. If you use the Pond Dam System, make sureyou use a trash guard on the vent tube so you DON'T ever create a syphon. You can always create a syphon system by blocking off the vent and then opening it when you get to the point were you want to draw the water down to. BTW, this is the easiest and least expensive way to retrofit a drain into a pond 20' deep or less and if 100% sealed there is no chance of leakage causing a dam failure, like a conventional "through the dam" drain.

For GW. If you want a dual level pond, setup your syphon for the highest pool level, you can add an extension to the vent tube to lower it to your desired "low" level by creating the syphon action at any time. There would be no need for two seperate systems. To maintain the "low" pool level, you would need to restart the syphon each time the pool level raised, because the syphon will not self-start until the "high" level is reached.

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

Cool. That'd make a good video.

I'm happy with my siphon since adding a trap to the outlet. I'm still confused as to why it has started two different times when the pond wasn't receiving much water at all. Both times this happened during a period where no rain had fallen for several days.

OK I have read though all of the siphon threads and still have a couple of questions.

Did anyone ever get an answer to does the trap freeze and ways to avoid this? Prevent damage?

I am still confused a bit on starting the siphon manually to lower the pond level or drain it. From what I could gather the first step is to block the vent pipe with either a cap over the end or value. Then the outlet side needs to be closed off. Has anyone considered using a threaded coupling at the end and a threaded plug to do this? Any issues with this? After closing off the outlet pipe fill it with water via the vent tee. Since the pond is at or below normal pool the pipe will not completely fill with water, how to get the rest of the air out of the pipe or is there enough pull with the water in the downslope side? The downslope side will be 6' to 15' lower than the pond side.

Rock Creek mentioned drilling a hole in the bottom of the elbow to let it drain so it won't freeze.
I would doubt 6' would start a siphon with some air in the system but would be optimistic about 15'.
lassig,
To get the rest of the air out of the intake pipe you either have to:
put a check valve in it
put a valve you can close in it
vacuum out the air, vacuum pump or the vacuum of a gas motor
suck the water into the pipe with a water pump with the suction hooked to the vent
wait for a flood
If you use a threaded coupling you will get very wet getting it unscrewed and it will be pretty tight with the pressure on it. Should work several times, last couple threads might get damaged with repeat usage.

Thanks for the suggestions. Based on where we are building the pond I think I will have the 15' difference (if not more). Should I add something to assist in the vacuum or after filling with water I coujld put the shop vac over the vent tube to get the air out of the tube and use a value in the vent tube to seal it off.

I thought I posted this this afternoon. For some reason it isn't here. This is my plan for the siphon systemm, any commnets



FYI does anyone know how to post pdfs so they could be used enstead of this jpg, or do someone have a conversion tool for jpgs that don't add a watermark.

Lassig,
Your drawing is exactly what I have. Two 12" siphons with 4" vents. One is about 2" higher than the other, and I don't think the higher one has ever been used. It is absolutely amazing how much water a siphon can move. I am now keeping the vent cap off of the higher siphon just to keep the pond about 2" deeper.

Since my pond is spring fed, there is always at least a good trickle of water flowing through the pipe. Since this water comes off the pond bottom, it would never let the discharge elbow freeze. But living in Ga helps too.

If the bottom of your trap elbow was exposed, or buried in pervious rip-rap, a small hole could be drilled in the bottom of the elbow...say 1/4" to allow it to drain during non-siphoning flow. The elbow should still function as a trap once there enough water to overcome the 1/4" hole.

To manually start the siphon, cap water level vent or extend underwater. Cap discharge (a valve that's easy to open that doesn't create a place for a clog to develop is ideal). Use a shop vac to remove air from the system through the vertical vent pipe and cap off (a check valve would be handy on the vertical vent pipe to assist in this). Carefull open discharge and stand back.

Rip rap over geotextile fabric would be good for the immediate discharge area. If there is a ditch or swale leading from the discharge, there are turf reinforcing geotextiles, TRF, that can be installed that allow vegetation (grass usually) to grow through it and can handle a lot of water while preventing erosion. TRFs are pretty inexpensive and require no more than seasonal mowing of the vegetation.

THanks for the comments guys. I like the idea of the 1/4" hole, doesn't require any maintenance. I had the following ideas today before seeing this post, I may still implement this

Possibly add a check valve in the vertical pipe and a shutoff valve in the horizontal pipe in Detail A for manual starting. In detail B, you could drill a weep hole in a spare 6" threaded cap in the cleanout Y and exchange it seasonally with a non drilled cap. Consider a lesser angle elbow (maybe a 22.5 or 45 depending on slope) on the horizontal siphon break vent. This would allow you to easily extend it deeper along the slope if a drawdown is desired. It would be less vulnerable than extending the horizontal pipe to reach deeper water and probably look nicer too.

Ryan,

Again thanks for the suggestions. I really like the suggestion on changing the vent pipe elbow and will consider this. As for the check value do they make them for 4" pipe? Figure that I will have to make an adaptor that screws on to the top of the vent and reduces the pipe size down to 1 1/2". Then my shop vac would fit over it and I can get a check value for that size of pipe. Not sure how many times I will manually siphon the pond down, just nice to konw this can be done.

I didn't catch that you had a 4" vent pipe. A 2" vent/siphon break will be plenty for for a 6" siphon and will make it easier to begin siphoning. 2" check valves are about $10. Check valves aren't 100% reliable so you'll want the check valve capped off and only remove the cap to attach a vac to manually start.

Ryan,

Thanks again, So the vertical piece (coming up from the 6" pipe) could be 2"? I haven't seen a 6" to 2" Tee?

That's what I was thinking. Maybe a 2" saddle? http://www.plumbingsupply.com/saddle.html

A pluming store will be able to get you from 6inch to 2inch maybe not in one conection, but it is done all the time

I am currently planning on using a couple of pieces to get me down to 1.5" (6x6x4 tee and then a 4x4x2 tee followed by a 4 to 2 reducer and then a 2 to 1 1/2 reducer). Trying to get to 1 1/2" in the vertical part of the vent so the shop vac can be used to vacuum out the air to start the siphon. The horizontal part will be 2" and have a value in it to asist in the manual siphon. Just was trying to see if I can get by will less parts and a more direct route? See drawing here

Ilove it