Pond Boss Forums POND CONSTRUCTION Building a dam Critique My Overflow Stand Pipe Design

This is what I currently have. It is a 6" Sch40 PVC Pipe, 40' Long that goes through my berm. At full pool it will be about 3' under water. I have a "T" on the end with a female clean out adapter, which I will put the plug in when the water gets high enough to run out the pipe. Currently water is flowing into the pond through the pipe, helping it fill.



Here is what I am planning on doing. Coming off the top of the "T" will be a 6 to 8 reducer. The standpipe will be 8" SCH40. Over that I will slide a section of 12" Irrigation pipe so that water overflowing into the pipe will come from lower in the water column instead of off the surface. It hold the 12" inplace, I will use 3/8" stainless bolts through the 12", double nutted in place holding a bind against the 8" at the bottom (so no holes are in the 8" under water). At the top the 3/8" bolts will go into the side wall of the 8" to hold the 12" in place. The 12" pipe will be 2" taller that the 8" so that if the water rises enough it will bypass 12". 2" from the top of the 8" will be two 2" holes that will handle the water flow from normal rain events. The top of the 12" will be capped with a brass trash screen I am making from some scrap 1/4" brass rod and brass plate.




This setup should give me a 4 stage overflow system along with the arability to pull the 6" clean out cap and drop 3-4' of water.
Normal rain event, water will go between the 8 and 12" and through the two 2" holes.

Heavy rain event the water will go between the 8 and 12" and through the two 2" holes, while spilling over the top of the 8" pipe.

Severe rain event, water will spill over 12" pipe, through the trash rack, and directly into the 8" pipe.

Extreme rain event, emergency spillway will see water.

The pond is 1.5 acres with about a 1:3 to 1:4 watershed.

Any comments? suggestions? My main concerns are if the 2" difference in pipe height is enough or should it be greater and about the two 2" holes, are they the correct size?

I think you have the right idea. I don't know if the 2" holes are necessary, and I'm unsure whether the 8" to 12" pipe will leave enough water thru before it starts going over the top (you are close on matching volume)s. But, it would be easy enough to bump up the 12" pipe after the fact. Just make sure that the emergency spillwas will handle the amount of water that is expected in a major hurricane/rain event and won't wash out.

Going by cross section, it looks like it should work. I did not go by flow rate.

Cross section area of a 6" is 28.27sqin and 8" pipe is 50.27sqin.
The cross section area between the walls of the 8" and 12" inch is 45.44sqin, which is 90% of the 8" and 160% of the 6" cross area.

Take the outer pipe on the lower portion to go deep into the water, and cut a comb-shaped pattern in it where each notch is maybe 3/4" wide, 3-6" along the pipe (I'm not sure how to describe it). You could alternately put a bunch of large holes in the pipe on the low end also.

Then install coarse screen over the entire end to prevent fish and debris from getting into the pipe. I would guesstimate 1/4" hole screen or so. The goal is to reduce water pressure at the screen so that you don't vacuum up debris and get a clog so more surface area will reduce the pressure difference.

In its current form I would worry about getting clogs with old leaves and other things like dead fish getting caught in there and then you have a problem.

I have a spring in the front field that I ran a 3/4 water pipe to and then used the elevation change to give me water pressure to make an ice castle by spraying water.

https://picasaweb.google.com/wymanfamily3/20101218?authuser=0&feat=directlink
Yeah I'm weird that way...

Anyhow that spring is helping keep the pond topped off right now, but I kept getting plugs when I used various pipe ends like you have here. Crayfish would oddly show up and plug themselves into the pipe. Leaves, frogs, etc. My dad came up with a method where there was a pipe within a pipe like you have here, but drilled the inner with a bunch of holes, and the outer with larger holes, then ran window screen around the otter pipe with the larger holes and glued the works together. The inner pipe mated with the water line. It has never plugged since, and has moved a LOT of water over the past 5 years.

I added the blue horizontal line to show where the normal water level will be.

I see what you are doing with it, (taking water from way below the pond surface first, then only taking water off the top during a high water event) and I think it's a great idea.

Have you checked with NRCS to see what amount of rainfall (in gallons) your pond could see for every of inch of rain that fell?

If you did that, you could calculate to see if the primiary pipe was big enough in diameter. I have a feeling that the 6" pipe might be a bit undersized and you might see more water going over the emergency spillway than you realize. NRCS should be able to tell you what the correct sized primiary pipe should be too.

My local NRCS agent was not the best of help. He did help determine if the soil was suitable, but that was about it. By going going off my rain gauge and measuring the rise in water level in the pond, I have roughly determined that for every 1" of rain I receive when the ground is saturated and all run off makes it to the pond, I get a 3" rise in water level. Being that it is a 1.5 acre pond, take 1" from the 3" (what fell directly into the pond) leaving 2" which would mean an additional 3 acre of water shed is hitting the pond.

Our land is very flat (compared to you guys up north) and we average 55" of rain per year. We have received over 15" so far this year and are expecting several more inches this weekend.

Behind my berm, about 7' from where my overflow pipe comes out, there is an 8" pipe that goes under my driveway. Roughly 75% of the water that used to drain through it now goes into the pond. When full, it will go through the 6" pipe and back to the 8", under the driveway, and into the gully.

Since I have been here, through 2 hurricanes and several very wet winters, I have only seen the 8" pipe fill up to full flow twice, but never enough to go over the driveway (the top of the pipe is about 12" from the top of the DW).

I plan on having the normal pool level at least 12" from my emergency spill way level. If that is not enough I can lower it by lowering the height of my inner pipe. I may add an additional 6" drain pipe set up as a siphon system at a later point.

Your county agent is like mine. 'nuf said.

I'd have at least 12" of freeboard before the emergency spillway, not less.

I think the extra siphon would be a good idea, and have it pick up water from the bottom of the pond too.

I did some work with the transit yesterday. Let me start off by saying this is a roughly 75% excavated pond with all watershed coming in from the south and the drain in the north west corner. I have two main inlets that the majority of my run off enters the pond on the south side, both bulk headed. The lowest one is currently 22" above the water and the other is 29". The top of my 'levee' which is more of a berm, is a little over 4' over the current water level and my emergency spillway is about 35" above the water.

With all that being said, I have decided to have my full pool level even with the top of my lowest inlet bulkhead, the one that is currently at 22" above water. that will give me 12"+ of free board to the emergency spillway and over 2' to the lowest point anywhere on the downhill side of the pond. If the water backs up over the bulkhead while it drains, it will not cause any issues since it is a wet area to begin with.

Sounds like a plan. A little more leeway as a buffer than the 12" before.

Thanks for all the help. I will be cutting my 6 to 8 reducer will be in today. I brought my 8 and 12" pipes to work to cut in the wellsaw so I can get everything in place before our next round of rain. Here is what the 3.6" of rain from last Saturday did.



It was dry just to the bottom of the socket, talk about cutting it close.

I have also changed the design a little. I did away with the hole in the side of the 8" pipe and changed the outer pipe from 12" to 15". This will have a bigger gap between the 8-6 reducer and the inner wall of the outer pipe to better match the area of the 8" pipe. The will allow me to put more SS hold off bolts around the bottom (probably every 1.5") which will create a screen or grate effect to help keep fish from getting between the two pipes.

Is some SCUBA diving in your future?

Chest waders have sufficed thus far. What you see sticking up in the photo is the top socket of the Tee fitting. The water is about 3' deep under it.

Oh. I thought I was looking at the top of the 8" pipe.....

If it is not too late I would replace the clean-out plug with a slide gate valve. Trying to take a clean-out plug off with 3 ft of water over it can be very difficult and dangerous.

-HH

I was wanting to use a butterfly or slide gate valve and figured I could thread on on at a later date since I have a NPT connection at the end of the pipe. Do you know of a good source to get one?

Here is an updated view of the plan. I added antivortex baffles and the bolts that hold the outer tube centered will double as a coarse fish screen with openings 1.5" X 2.5" between the bolts.

Here is the finished standpipe structure in place. The line of SS bolts running vertical are on 1" centers and will give me water level below full at a quick glance. The ring of bolts at the bottom act as a coarse screen to keep large fish or debris from getting between the walls.

Ya did a heck of a job! That looks great. No worries about the nuts loosening up either.

good catch, nylocks on everything.

great design......ever think of producing for sale?