Pond Boss Forums POND CONSTRUCTION Building a dam Surface vs Bottom Withdrawal Spillway

Happy Monday!

Originally, I was planning on installing a primary surface withdrawal spillway. However, I've been researching and the state of MO has an "aqua guide" discussing the benefits of a bottom withdrawal spillway. The bottom withdrawal spillway is apparently superior to the surface withdrawal spillway as it removes unwanted stagnant water from the bottom rather than siphoning good quality water from the surface.

It seems like an easy decision to go with the bottom withdrawal spillway but I'm not sure. It'd be great to get some input from the Pond Boss Community regarding this choice.

Thanks in advance.

Hi PJB! I am a huge proponent of bottom draw systems! I prefer an automatic start siphon system. A standpipe with an outer sleeve that draws from below will offer high water event top drawing also...that arguably has some added safety against blockage/malfunction. No matter what system you choose, you should always include an emergency spillway that is way oversized for your watershed.

An emergency spillway is planned in addition to the primary spillway. I haven't read about the automatic start siphon system. How does that differ from a manual start system?

Another vote for the auto start bottom siphon system.

Grate it so a turtle can't get stuck.

Good idea to get this squared away before construction. Once it gets going, it's pretty difficult to make changes, decisions, etc.. The guys I had working on the pond had a lot of different things going on, besides my pond. Juggling in between storms, getting their crops in and out, getting the NRCS rep in there. I felt lucky to get it done. I found out about the siphon drain too late in the process, to try and make changes. I'm planning on aeration in the near future, hoping that will offset some of the gains of the siphon system.
Where in Missouri are you? I'm up near Hannibal. (My pond is)

I haven't finalized all of the details yet and won't be starting until the end of July or even August so I have time to square this away with the builder.

We are moving to the Labadie, MO area from IA at the beginning of July. We purchased 10 acres down there...you can't get 10 acres of timber in IA for the price you can down there without being completely cutoff from all amenities.

SetterGuy - We passed through the Hannibal area a couple weeks ago and passed by the Mark Twain Lake. Saw a lot of fishing boats. Do you know what kind of fishing that lake is good for?

It's known as a crappie lake. Not sure if they catch that many bass up there. Lots of crappie!
Also, we love Labadie! My primary residence is only a few miles from there. Have had many meals at the Hawthorn Inn! Great lunches! Welcome to Missouri! There are beautiful rolling hills all around Labidie. I've seen some very nice small lakes and ponds out that way also.



My place is about 2 miles from the dam.

Wow...that is a great catch of Crappie. Next to Bass, Crappie fishing is my second choice and Mark Twain isn't too far away so I hope to be spending some time there now.

The property we purchased is closer to Washington. We have to rent (in Labadie) while we wait to build a house. The whole area is pretty beautiful with the MO river valley being right there.

The Purina dealer at T and old 100 always has Aquamax in stock.
Let me know if you go thru the Hannibal Mo area again. I'll show you our "work in process" pond. We were just starting test holes etc at this time last year.
Finding this forum has been extremely helpful. Lots and lots of friendly, and well informed members.

RE: Auto Start Siphon description

Is the auto-start feature simply that the spillway will begin siphoning water from the bottom when the air vent at the apex is submerged in water and will stop once the water level is below the air vent at the apex?

Not exactly, PJB. The air vent must be submerged AND the water level inside the siphon has to rise to, or somewhat above, the bottom of the siphon pipe at the apex for the siphon to start. Once water begins to flow, and the vent tube has all entering air blocked, gravity and atmospheric pressure take over and the siphon effect begins.

The vent tube is set to determine what the water level must reach for the siphon to STOP by allowing air to enter as a "vacuum break". If you set the entrance of the vent tube a couple inches below the pipe apex (and no whirlpool allows air to enter) the siphon would stop when the pond is 2" below the bottom of the apex....and no water would flow out at all.

If you set the vent tube a couple inches ABOVE the apex of the siphon pipe, the pipe will act like any normal drain pipe UNTIL the pond rises a couple inches higher and blocks the air entering the siphon pipe. Gravity will make the pipe drain slightly faster once the pond is above the top of the apex, but until air is blocked, it will not siphon.

I like setting the vent a little above the Apex.

You can also incorporate a "normal" drain into a siphon by adding 2 wye's and a valve. You connect a pipe straight through the bottom of the dam, wye'd into the riser pipes that will siphon, and a valve in the straight pipe on the back side of the dam using an frost valve access similar to the old water meter pipes.

Nice area PJB....I live in Maryland Heights.

The siphon questions seem to come up a lot. Has anybody ever posted a sketch of one?

Yes but there can be adaptations.

See this link

http://www.ponddampiping.com/syphon1.html

Rainman,

Question 1
With the top of the vent tube a couple inches above the apex, water will drain from the bottom of the pond when water in the tube reaches the downstream side of the apex. I assume that this type of drainage is not that significant. Is that correct?

Question 2
Most diagrams that I've reviewed have an adjustable vent tube. Can the vent tube be fixed with the top a couple inches above the apex? Also, can some type of "vent hose" be attached to the fixed vent tube if you needed to lower the water level?

These are just the very basic principles of a siphon. You will also want to make some sort of "trash rack" on the inlet of the main pipe and vent opening to ensure they never plug up.

If the main inlet plugs, or worse, a stick or turtle gets trapped in a curve, then water will not flow properly and could lead to a dam breach and difficult repairs. If the vent plugs, the siphon will not stop till the pond drains completely, or the lift is too high to overcome and water either vaporizes or the tubing itself collapses from the vacuum pressure.

Rainman,

I don't know what your occupation is so forgive me with this question; have you installed bottom withdrawal systems? The reason I ask is because you live in the area and I could use a "consultant" on my pond build since my pond builder doesn't have experience installing a BWS.

I REALLY wish I'd known about the bottom siphon solution when I had my big pond built...as stated above it's a far superior solution. If I ever build another pond it'll have one, no doubt about it.

Nothing to forgive, PJB...I kind of chuckled reading your question, since your request is certainly within the realm of my "occupation:.

I'll send you a Private message.

I just had a pond built on my farm. The gentlemen who did the excavation discussed surface vs bottom withdrawal spillway concepts with me when I asked about pond turnover avoidance. He had never installed one but said he didn't mind trying a bottom draw system if I wanted to. He finished levee construction just prior to all of the rains this late fall/winter 2015. I have gone out daily to observe the water level anticipating the flow of water through the 6" spillway pipe for the past two days. It began overnight last night apparently. When I observed the pond late yesterday afternoon, it was nearly to my estimated apex point on the levee (water level about 15 feet). We received a couple more inches of rain overnight. This afternoon when I arrived, the water level had dropped approximately 6 feet. Immediately, I thought the levee had failed in some place. Finding no evidence of this I next thought seepage was occurring in some other way (new pond, still unknowns). Then it occurred to me that perhaps a siphon had occurred when the spilling began through the pipe. The pipe is not vented. This appears to be what occurred. I hate to oversimplify the fix but does tapping into the pond side of the pipe before the apex with a two inch pipe saddled around the six inch pipe sound reasonable?

Installing a vacuum breaker should be ok...would be a better option over dropping the pond level everytime a sufficent rain occurs.

Here's the basic idea. Right?

http://www.bing.com/images/search?q=auto...&ajaxhist=0

Just to state what has already been said, but perhaps from a different angle.

1. The name, "siphon bottom drain system" starts the confusion in the name itself.

2. Under normal pond overflow conditions, the "siphon effect" does not come into play. As Rainman explained well pressure from the pond water level forces water from the bottom of the pond over the bottom of the overflow pipe and out of the pond. Thus the "bottom drain". But there is no siphon involved. Only regular bottom drain taking stale water from the bottom of the pond instead of the good water from the top of the pond. No siphon effect at all. You could have a bottom drain overflow pipe with no siphon effect, and in fact if there is insufficient drop behind the dam for the pipe to slant downward that is exactly what a person will have.

3. The "siphon" only comes into play when the water depth of the pond becomes high enough to cover the air vent at the apex of the system. The advantage to a siphon over a comparable size regular overflow pipe is that a siphon takes advantage of gravitational pull of water exiting the pond. So one of the main reasons to have a "siphon" overflow as compared to a conventional is that for a given size pipe it will flow significantly more water.

4. A regular overflow pipe that is angled downward towards the bottom of the dam can go into "siphon" mode even though it is not a bottom draw system. My pond,for example in it s design, has two different flow rates for the 8" overflow pipe. One flow rate at regular flow, and a higher rate once the top of the pipe gets completely covered and goes into "siphon" mode. So either a bottom draw system OR a regular overflow pipe can be designed to have increased flow in "siphon" mode.

5. The air vent at the top of the bottom drain siphon system is to "break" the siphon and reduce flow rates down to normal rates (as opposed to siphon rate flow) until the water reaches normal pond level - the bottom of the highest point of the overflow pipe. Without this "air break", the siphon would continue to drain the pond down to the level possible as Rainman explained. Therefore unless you want to drain your pond, MAKE SURE NOTHING BLOCKS THE AIR VENT ACCIDENTALLY.

6. In summary, to understand the system, in my opinion it is best to separate the functions of a bottom draw siphon system into two distinct, different, functions. 1.Bottom draw and 2. siphon system. A regular type overflow pipe angled down can go into "siphon mode" and a bottom draw system can either be a regular type or "siphon" type, depending on the design. Siphon only comes into play when the pond level is high enough to expel all air from the pipe and gravity becomes a "turbocharger" so to speak for flow rates only applicable if the pipe angles downward behind the pond dam.

Clear as mud?

Great explanation and break down snrub

JD, Snrub, and For the Family,

Thanks for the great information and for verifying my suspicions and further explaining my situation. Will be tapping into existing pipe to install vent pipe on Thursday.

My best to you all.

David