We are just finishing up construction on a two acre levee pond in southern Louisiana. It was planned with NRCS guidance who recommended a 12 inch siphon spillway. We used a standard siphon kit from Pond Dam Piping Ltd. No problem with these guys. They had reasonable prices and provided prompt delivery.
The issue I have is with the Brain Surgeon/"Pond Guy" who installed the siphon. Luckily, I spotted him getting ready to lay the inlet and outlet at the same level. So, I stopped him, telling him that the inlet needs to be 4-5 feet higher than the outlet. Well, he argues with me saying that's nonsense, that the sole determining siphoning factor is the difference in height between the high water level in the pond and the outlet, that I want the inlet to be at the bottom of the pond to draw the "dead water" but goes on to say "no problem, I'll do whatever you ask".
So I go back later that afternoon and find The inlet on the absolute bottom of the pond. The horizontal pipe through the dam was laid in correctly, but something looks funky on the outlet side. The outlet appears to be at the same exact level as the inlet???!!??. I go look inside the outlet (which is at the same level as the inlet)and look down the pipe and he has it going about 6 feet underground before it elbows back up.
"I put the outlet 6 feet below the inlet, just like you said!"
Anyone have any advice? I doubt the guy has the basic competency to fix the problem. What I'm thinking is going out there after he's, gone, and cut out about a 6-7 foot length of the pond side slope pipe and then re-attach with a coupling to bring the intake up to an appropriate level.
I wonder if this may be a common problem with construction. Certainly, my dirt guy didn't get an "A" in high school science. I've read a few posts on here from people noticing that their siphons never seem to move much water. In fact, I might have been authoring a post like that a year from now if I hadn't spotted this construction error.
My first thought was to get the guy to fix the problem, but after today's problems and his inability to comprehend what he did wrong, I just want him off my property.
I'm planning to leave that 6 foot underground "V" alone but remove enough length of pipe on the pond side to bring the intake structure about 5-6 feet above the true outflow level.
If it were me, I would raise the inlet. Obviously your dam is level front and back and that's your only option is to raise the inlet unless you can dig down and somehow change the grade behind the dam. That "Vee" has me a little worried in restricting flow due to turbulence thats not needed, what size pipe did you use?
Lets say you used 8" pipe and have a 100' run, a 1' drop in the back will pull 777 Gallons per minute and a very safe velocity
2'=1130 GPM with velocity @ 7.21 Feet Per Second 3'=1407 GPM 9 FPS 4'=1643 GPM 10.5 FPS with a "V" 6' under ground that does nothing hope he glued it well and compacted underneath......personally at what ever grade is on outlet I would use the double 22.5 or double 45 fittings depending on the slope of the dam
A 6' drop is 2046 GPM with a velocity of 13 feet per second
The way it's set up right now once the siphon starts, it will drain the whole pond.
If you "T" in an air break, that will allow you to keep the sipon like it stands. Plumb that in so the opening of the air gap is at the level that you want the pond to be when the siphon stops. http://www.ponddampiping.com/syphon1.html
I'd dig out the funky fittings at the backside of the pond and use 2 45° sweeps to get the outlet away from the bottom of the dam.
It's good to take the bad water off the bottom of the pond.
Last edited by esshup; 10/24/1308:24 AM. Reason: added link
It's 12 inch PVC. The siphon does have a standard type air vent, the attached drawing doesn't show it.
In my view, a pond siphon spillway is a tool to ensure the levee is never overrun with water and the emergency spillway is rarely, if ever utilized. I can appreciate having the inlet as low as reasonably possible to draw brackish water but not at the expense of greatly compromised siphon flow. Am I off base with this assumption?
That 6 foot underground "V" on the downslope was the pond guy's idea. I don't see any positive about doing that. :-(
In my view, a pond siphon spillway is a tool to ensure the levee is never overrun with water and the emergency spillway is rarely, if ever utilized. I can appreciate having the inlet as low as reasonably possible to draw brackish water but not at the expense of greatly compromised siphon flow. Am I off base with this assumption?
I think you might be.....
The way I have come to understand it, is that when the inlet pipe is deeper there is more weight of the water itself at that inlet. This weight adds to the force that pushes the water thru the pipe, thus increasing the volume that goes thru the pipe giving better siphon flow.
I think the funky "V" at the outlet side is more of a flow reducer and something to be concerned about.
If all else fails, you could use a collar or coupling to glue on another length of 12 inch PVC in order to extend the outlet to the level that you want the pond water to be. The result would be an unsightly passive system and the riser would probably have to be braced against breakage. You could paint it green or brown and tell people to use their imaginations as to what it might represent.
Alternatively, you could cut off the outlet at ground level and install a valve, but that would require you to manually allow or disallow water flow, and certainly not as great a flow as you had hoped for. Yes, I know, but just overlook that preposition business. You could cut off the outlet below ground level and trench in additional pipe to get the outflow away from the dam, installing the valve anywhere along the discharge line.
If it's 12" PVC just raise the inlet above the outlet
Inlet 1' above above outlet is 2258 Gallons per minute in siphon @ 6.41 Feet per second
2' above = 3284 GPM @ 9.31 FPS ( this would worry me on that outlet thing he put in if it wasn't glued and compacted extremely well) if it were me and I was in your position it seems raising the inlet would retain your siphon even if its only 1' above the outlet but if that thing he built 6' underground breaks that fitting loose under those volumes traveling @ those velocities ..........yowsers.
He should have just looked at the diagram of the siphon system and easily understood the simplicity of it and known how to properly build the outlet and I think even a second grader understand for a siphon the inlet needs to be higher elevation without introducing air
I will add that I really wanted a siphoning spillway but as I started calculating cost of 8", 10" and 12" pipe and was astounded at the price of fittings above 8" and all I could think was just one fitting not glued and compacted well on the back side of the dam and it would be game over
Why is it that the higher the inlet pipe is the more gallons you get to flow thru?
The company "dam piping" says they recommend the inlet 4' higher than the outlet, which is what Gus referred to originally. I can understand this concept because you can't siphon water to a higher area, and you want to make sure the siphon works at the point of inlet( that is if you ever want the water level to go down to that point), so the outlet has to be lower, even by a small amount. But to go higher than that recommended point (of 4') seems to be counterproductive to the amount of flow.
I would take both siphon inlets to the deepest points possible for two reasons...First, to remove the worst water in the pond every time there is a draining event and second, when going into siphon mode, 11,12,20 feet of head pressure will push water out far faster than 10 feet of head pressure and with 500+ acres of watershed, volume will matter!!!
Its pretty simple, this is really a gravity pipe plain and simple once the siphon starts. The more weight below the input, the harder and faster it pulls.
Length has everything to do with this as well and since you bought 200' of pipe I will assume you have 200' in the dam, my other calculations were for 100' of pipe. I'm not figuring the friction loss for fittings but 22.5 and 45s are minimal
12" pipe with a 10' drop in siphon mode is 5385 Gallons per minute @ 15.3 feet per second. Now velocity is always figured for a pipe that has valves and a means of pushing the water and the feet per second has an effect called Water Hammer. Lets say I put a valve on the outlet and close it, water doesn't compress so that massive amount of water flowing @ 15 fps sends a " Hammer" all the way to the source. Schedule 40 PVCs safe zone is 5 feet per second with out blowing apart fittings, check valves, pumps, valves, etc in a "Shut Off" situation.
The reason I mention velocity is I'm not sure what that "vee" is buried under ground and you should have continuos flow which should mean you would never see a "hammer" but if its raining in say a 100 year event and the wind is blowing causing waves which may or may not effect the vent ( basically a valve of sorts) of the siphon. I'm probably waaaayyyy over thinking this scenario but say you have a nice steady flow and on the verge of siphon and waves are opening and closing the vent somehow it would be like turning a valve on and off. My guess is this wouldn't happen because you're vent is at water level which is 12" below where the water will be when it starts its siphon therefore needing a 12" wave to create the situation of a possible "hammer"
heres a gravity calculator, http://www.calctool.org/CALC/eng/civil/hazen-williams_g use them all the time we have a pretty complex irrigation system and gravity feed from one pond to another, to another using 2" rain bird valves to start and stop the flow via a "Dig" solar controller and we see hammer because we have drop as much as 40'
The reason the "dam piping place" recommends 4'-5' drop is they are suggesting 8" pipe and they are wanting maximum pull in a rain event without to high of velocities which for 200' of pipe 8" with a 4' drop has the velocities @ 7 FPS which doesn't sound too bad.
Also think of that siphon as a giant vacuum on the inlet side, run it wide open and fish are taking a journey, put a screen on it and fish, debris and silt are obviously getting sucked into the screen if it were a 12" pipe with a 10' drop traveling at 15feet per second. This is why I would raise the inlet to say 3'-4' off the bottom and you will still be pulling off the bottom regardless. Take a wet dry vac and a pile of shredded paper and see that the paper is gone well before the tube gets close to "bottom"
This is actually another reason I opted out of a siphoning spillway because when it's in siphon mode I didn't want all my fish plugging the screen or getting sucked to the vent screen and plugging it and walking out to an empty pond in the morning, We have rather large Bass
Thank you Huskerduck for your informative response. I am only an interested third party to this thread, and have been trying to collect information on siphons for future reference. You have added a lot to that.
I wonder which adds/subtracts more from water flow: 1) the height of the inlet compared to the outlet, or 2) the amount of head pressure from the inlet being deeper under the normal water level...... As the height of the inlet goes up, the head pressure has to be considered as it would get less. Seems like you would have to consider both aspects if someone was after the strongest flow (and not considering the level at which poor quality water is at, along with if the pipe can withstand that pressure). Possibly one value always trumps the other as far as a gain?
In reality, I don't think head pressure would even play a role, the water is already there thanks to gravity. The only factor that would have a highly measurable effect would be the drop of the outlet because that water is not there at least until the siphon starts. Theres only one way to effect the flow in his circumstance and that's raise the inlet, or lower the outlet.
The ultimate in his scenario would be to lower behind the pond if he has the grade to do this, my guess is this might not be an option unless he travels a long way from the dam and even then maybe his grade just won't allow for the "easy fix"?
Im curious though Gus......did you guys throw a laser level or Transit and see just how equal the inlet and outlet are? A dozer can move 3' of dirt in minutes.
This whole thing about the weight of the water in the pond actually pushing the water out of the pipe because of its pressure doesn't even register unless the pipe goes straight through the dam and even then.........the pressure is virtually nothing, I think I remember something like .433 or .344 per foot of water regardless if its a watering hole or an ocean, it's nothing unless he's like 50' deep and maybe he is, but even if he is, his horizontal pipe is at the waterline with 0 P.S.I until the siphon starts
Yep, the inlet and outlet of the siphon spillway are at the same elevation. I know this, from one nice side benefit I got with the construction of the levee. The dirt guy installed a level straight pipe of 6 inch schedule 40 through the bottom of the levee as he didn't want the pond to fill as he was brining the levee up to grade. The siphon inlet/outlets are even with this pipe.
Better re-think that siphon stuff unless you have a way to turn off the flow when you need to or you'll drain your pond.
Siphons are great for maintaining the same water level in adjacent ponds, but if you only want to get rid of water that exceeds a certain level in one pond with the system you have, you'll have to raise the discharge port to the water level that you want to maintain in your pond.
Better re-think that siphon stuff unless you have a way to turn off the flow when you need to or you'll drain your pond.
Siphons are great for maintaining the same water level in adjacent ponds, but if you only want to get rid of water that exceeds a certain level in one pond with the system you have, you'll have to raise the discharge port to the water level that you want to maintain in your pond.
He should have a vent where he wants his water level and that vent breaks the siphon
Huskerduck- what you have all said makes sense to me. I never had considered that the pressure from the water is only relevant if the pipe was going thru the bottom.
Now, what would happen if the inlet pipe was place high enough to get the amount of drop/flow needed to the outlet, and that makes it near the water surface level. You get the flow rate that way, but you end up taking the quality water. Put a larger diameter pipe over that inlet back down to near the bottom. The top of that pipe would be seal off, forcing the water to be sucked up from the bottom. I have seen designs like this to remove the bottom water, just can't find an image right now to include here. Hope this make enough sense by description.
Do you think this scenario effects flow rate? Seems like you end up with the best of both worlds: high flow rate and rid of bad water.
Fish n chips, Gus said his guy put the inlet on the bottom and the outlet on the bottom, If Gus moves his inlet up just several feet it will still suck water from the bottom if his pond is say 15' deep. Water is molecularly connected in a way that the suction isn't in a straight line, its conical. In fact if he leaves the inlet say 3' out from the dam and 3' up from the bottom there will be a pull along the dam and bottom, mid and actually probably more so than the water up top.
I miss read and thought Gus used 12" pipe but that was someone else. I'm guessing here that Gus used 8" or maybe 10" but either of those are small enough to move up very little and still get good suction and siphon.
If Gus doesn't think he will be sucking the water off the bottom he can always run a 4" or 6" siphon system and leave the inlet 2' off the bottom and lay the outlet as low as possible and then he will know he's pulling off the bottom and 4" and 6" is fairly cheap
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