I saw a chart a while back that compared the flow of a conventional standpipe system to a siphon. If I recall, a 12" siphon would do as much or more than a 36" standpipe. I don't remember where I saw this chart. Can anyone help?

My watershed is about 320 acres, so I am thinking about two 12" siphons. Any suggestions on this?

Thanks.

How big is your pond? Do you have any other spill-way and does/would your pond have any retaining buffer before it would start going out the drain?

I can tell you from experience that a siphon of the same size will move more water. My watershed is 150 but I also usaully have a buffer to play with in my pond to hold atleast 25ac feet just in case one of those hurricanes hit. This give me some reaction time to plan what I am going to do on weather forcasts.

Pond will be about 7-8 acres. 6 - 12 feet deep. It will have a spillway on top. The top of the dam is a driveway, too. 600' long x 14' high.

I'm thinking about not putting in a drain. I would be counting on the siphon to drain it if I had to.

Jersy,

I would consider a drain optional. I dont understand the logic behind having 2? How many times would you ever actually need 2?

I think a second pipe makes sense with
320 acres of water shed. I have a 12"
siphon pipe on a creek pond with 165
acres of water shed and it could not
handle the inflow during heavy rains
last winter. If there had not been 70
feet of emergency spillway, water would
have went over the dam.

Squeeky,

I agree that having a drain is good, however, I am asking why 2 vs. 1? If your drain is too small to handle the required capacity, why not go larger on that drain vs. installing a second one? I am also assuming a riser on the dam (1 - 1.5 feet?) which will handle the excess water until the lake can drain. Excessive flooding could be handled with the emergency spillway.

Jersey, does this mean that you got the go-ahead to build your pond?

If so, I'm truly happy for you.

Jersey,

Depends on the head. If you have a very low head, you may need to go to a 16" pipe or 2 of the 12 inchers. However, if you have anything more than 5 or 6 feet of head, a 12" siphon will move a *tremendous* amount of water. Even a 6' head will produce a very powerful and destructive flow of water. (better have some big rocks at the outlet!)

I have only a 4" siphon on my 1.5 acre pond, with 10 acres of catchment. It would have to rain very hard and steady to catch up with the siphon. That's partly because the deeper the water gets, the faster the siphon flows.

Beware of back water, which effectively reduces the head.

bobad,

Can you help me understand what you are refering to by head? (i'm a rookie)

It's a sexual slang. Bwa Ha Haaaaaaaa
Sorry bobad I had to do it.

I haven't the calculation for water flow. I think there is discussion about it in past threads. It seems like the area of a pipe is pie x radius (which is half the diameter) squared. The area seems to grow exponentially. For example...

Pie Diameter Radius Radius Squared Area
3.14 2 1 1 3.14
3.14 4 2 4 12.56
3.14 6 3 9 28.26
3.14 8 4 16 50.24
3.14 10 5 25 78.5
3.14 12 6 36 113.04
3.14 14 7 49 153.86
3.14 16 8 64 200.96

Even though an 8" diameter pipe sounds just twice as large as a 4", it is actual over 4 times as large. I'm getting 14" pipe and plan for much to go over emergency spillways and such, but Illinois USED TO have more rain than Texas.

Even though an 8" diameter pipe sounds just twice as large as a 4", it is actual over 4 times as large. Splain that theory.

Well... According to the formula a 4" circle (pipe) would have an area of 12.56". An 8" circle would have an area of 50.24". Now you may say, "Whoa! How can that be?"

Maybe it can't be. Maybe I have the formula wrong. I'm just going from memory, but before you assume the formula is wrong... Do this... Go out and see if you can eat half a 16" diameter pizza faster than a friend can eat a full 8" diameter pizza. I think it will become more clear. Besides it will give you a good excuse to go out for supper!

Well... According to the formula a 4" circle (pipe) would have an area of 12.56". An 8" circle would have an area of 50.24".

A 4 " circle is 12.56".
Then a 8" is 25.12".
Where did the 50.24 come from?

Just Joe: I'm not a mathematician, but I don't think so. Try the pizza test! Jeff

A 16" pipe would do you. Now lets go eat Pizza.
Miller Lite here and you.

pie isn't half, pie are squared !

He won't pay for the Pizza.
I'll take a lemon or apple pie round or square.Later.

I want to go with the 12" because pipe gets real pricey above that. I am thinking it would be good to have 2 of them because 1) 320+ acres of watershed - in Georgia, and 2) Two is beter than one. You know, just in case. I remember my spring last year when the 4 hurricanes came by here. I would rather not ever have to use the spillway.

I will have about 3 feet of dam below the spillway x 7 acres = 21 acre-feet.

Sunil, I think I will soon have a great story to tell. But you'll just have to wait for now.

If you don't understand why one 8" pipe is a lot bigger than two 4" pipes look HERE

The "hole" secret of a round hole is in the "squared". The formula for the area of a circle is pie(3.14)times the radius squared, or 3.14 times radius times radius. This is why a 3/4" pipe will carry about twice as much water as a 1/2" pipe before you run out of pressure in the shower when your spouse flushes the toilet...

It's simply the difference between the height of the water intake and the height of the outlet.

If you have a head greater than 6-8 feet, and a 12" or larger siphon pipe, you get into astronomical flow rates.

It's interesting that a 1" diameter pipe 10 feet tall and a 12' pipe 10' tall have the same water pressure measured at the bottom.

Is this what you are looking for?
pipe flow calculator

Bob, I never really understood water pressure until a city engineer told me "If the water tower were 100' taller, it would bust every pipe in town".

Nice calculator Bonanza_Peak & welcome to the site!

It's been so long I'd have to look up the physics but the same pressure in a 1" pipe that would lift say a 1# weight in a 10" pipe it could lift a car.
Just an example why it's so important to compact dirt & use anti-seep collars. The pressure is tremdous along the bottom of a dam.

That's what I was looking for, Bonanza. Thanks.

The water pressure is about 7 1/2 psi at 15 feet deep. How many square inches is your dam? Yep, that's a lot of pressure!