Pond Boss Magazine
Newest Members
FrankleyScarlet, AndrewT, Cchristopher, jschmid19, 7hjd2
15740 Registered Users
Forum Stats
15741 Members
36 Forums
36217 Topics
493353 Posts

Max Online: 1210 @ 08/23/18 11:01 PM
Top Posters
esshup 24029
Cecil Baird1 20043
ewest 19656
Dave Davidson1 13660
Bill Cody 12631
Who's Online
9 registered (TGW1, bigpullerman, Bill D., FireIsHot, Flame, dreams of ponds, corgi, Dave Davidson1, RAH), 94 Guests and 460 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
#481530 - 10/23/17 08:23 PM 8" siphon, normal vs siphon mode
roundy Offline

Registered: 09/10/16
Posts: 51
Loc: Central Illinois
My pond has an 8" siphon installed. How much water will it move in normal vs siphon mode.
2 acres, still filling. FHM, GSH, PSC, RES, HBG, BG, LMB and YP

#481534 - 10/23/17 09:00 PM Re: 8" siphon, normal vs siphon mode [Re: roundy]
KapHn8d Offline

Registered: 10/02/17
Posts: 160
Loc: TX
I don't know the answer to this... but, I would suspect you could use a gravity flow calculator for a rough estimate. I Googled up this one... maybe it will get you close?

96.85840735 percent clayton... the rest is just pi.

We become what we think about.

#481535 - 10/23/17 09:13 PM Re: 8" siphon, normal vs siphon mode [Re: roundy]
snrub Offline

Registered: 10/05/13
Posts: 5326
Loc: SE Kansas
You should be able to do a search and find a calculator. It mostly depends on the amount of vertical drop vs the horizontal distance the water travels and the size of the pipe. The "steeper" the pipe is the more differential in pressure is created by the weight of the water.

I do not have a siphon system (bottom draw) and mine is just a surface draw pipe. But it does have several feet drop and when my NRCS guy designed the pond he did calculate its flow when it goes into siphon mode (inlet fully covered and all air expelled from pipe). It would flow lots more than just a horizontal pipe. And if it gets covered with water you can tell it is drawing water and exiting like it was under pressure.

Good luck with the calculations. An on line calculator should be out there. You will need to know the figures to plug in. Pipe diameter, vertical fall and pipe length or horizontal distance.

Edited by snrub (10/23/17 09:17 PM)

I subscribe to Pond Boss Magazine

#481536 - 10/23/17 09:22 PM Re: 8" siphon, normal vs siphon mode [Re: snrub]
snrub Offline

Registered: 10/05/13
Posts: 5326
Loc: SE Kansas
Here is a link to an engineering download that should help. If not I got lots of hits with a search.

web page to a site that has a pdf siphon download

Edit: oops. Pipe size starts at 12". Better look further.

The top tool on this page should come close.
water flow calc through a pipe using gravity

I used the calculator and guessed my pond at 40ft of 8" pipe with a 6' drop and came up with about 448 cu ft per minute times 7.5 gal. per cu ft equals 3360 gpm as an example.

Edited by snrub (10/23/17 09:38 PM)

I subscribe to Pond Boss Magazine

#486065 - 02/11/18 10:15 PM Re: 8" siphon, normal vs siphon mode [Re: snrub]
ronl Offline

Registered: 07/16/17
Posts: 4
Loc: georgia
I'm a civil engineer and I can tell that the Hazen Williams calculator applies to pipes flowing under pressure, and it grossly overstates gravity flow situations such as culverts and pond outlets.....the correct answer could be as little as 10% of what the calculator shows. Also, your question cannot be answered without a sketch of the pipe with pertinent dimensions and info as to allowable water depth at the inlet to the pipe, etc. Sorry to rain on the parade, but it's better to know the truth than to be making decisions with bad info.

#486085 - 02/12/18 12:10 PM Re: 8" siphon, normal vs siphon mode [Re: roundy]
Rainman Offline
Field Correspondent
Hall of Fame


Registered: 06/06/07
Posts: 6986
Loc: St Louis, MO area
Roundy, a lot of information is needed to estimate the flow of your siphon.

In "normal" mode, the pipe acts like any normal, gravity drain pipe, but when in siphon mode, the weight of the water, head pressure, pressurizes your pipe and flow increases dramatically.

Contrary to what was said about where the inlet is, the inlet location has no bearing on flow. Head pressure, (and pipe pressure) is determined by total height of the water level to the outlet, vertically.

With a 50 foot long pipe, and a 10 foot drop using smooth bore PVC and a minimal roughness coefficient, I'd conservatively estimate typical discharge flow around a minimum of 5000 GPM in "full siphon" mode, and about 500 GPM, maximum, in normal gravity drain mode....a 100 foot long pipe, but with 5 feet more of drop (15'), your flow would drop about 10% due to friction.

Edited by Rainman (02/12/18 10:15 PM)
Edit Reason: correct mistake on head pressure calculation..TY Highflyer!


#486099 - 02/13/18 10:17 AM Re: 8" siphon, normal vs siphon mode [Re: roundy]
highflyer Offline

Registered: 07/09/11
Posts: 1875
Loc: East Texas
Here is what our eight inch syphon pipe looks like running full. The flow is able to add about a foot and a half to the little pond before it flow out its emergency outflow. Little pond is a half acre pond.


The one thing is the one thing
A dry fly catches no fish
Try not to be THAT 10%

#486106 - 02/13/18 04:17 PM Re: 8" siphon, normal vs siphon mode [Re: roundy]
Redonthehead Offline

Registered: 04/03/07
Posts: 198
Loc: Missouri
I have an 8" Sch 40 PVC pipe the NRCS calculated a "peak outflow" of 4.72 cfs (2,118 GPM) at an effective height of 19 feet and 113 foot long pipe. I assumed that is in siphon mode but not sure.

This reminds me I need to haul in more broken concrete to dump in the discharge area before it eats out a big hole this spring.


Today's Birthdays
No Birthdays
Recent Posts
by Bill D.
16 minutes 34 seconds ago
Pros and cons of gas powered golf carts
by TGW1
44 minutes 48 seconds ago
Selecting male lmb not so easy
by TGW1
Today at 07:09 AM
building floating islands for their ponds
by Bill Cody
Yesterday at 10:24 PM
New to the site and building a pond in Indiana
by wannapond0001
Yesterday at 07:55 PM
flathead catfish
by wannapond0001
Yesterday at 07:51 PM
What did you do at your pond today?
by wannapond0001
Yesterday at 07:29 PM
Got my Jan. 2019 Pond Boss Mag today!!
by ewest
Yesterday at 06:46 PM
My front yard cow pond
by Augie
Yesterday at 06:38 PM
Love The Pond
by gully washer
Yesterday at 05:52 PM
Newly Uploaded Images
Pond site
Pond dig
My recent haul
Hello From Lufkin Texas!
Cant seem to Identify what this is.  Any thoughts?
Evaluating and adjusting Fish populations and ID

2014 POND BOSS INC. all rights reserved USA and Worldwide