Pond Boss Forums POND CONSTRUCTION Building a dam Question on the overflow

I have seen many plans for an overflow pipe that runs through the dam with baffles. Normally the pipe end that is in the pond has a tee with a valve on the horizontal end for pond draining, and the vertical run rises up to the desired height of the water in the pond, with a debris trap on top. The other end usually remains straight after it exits the rear of the dam and has rip rap around it to prevent erosion as water flows out of it.

I am wondering if a different scenario will work. What if the end of the pipe inside the pond still has a tee, with the horizontal run capped and the vertical run only rising a foot or so to keep it well above the mud? The other end that is on the outside of the pond also has a tee with the horizontal run capped with a screw on cap for pond draining, and the vertical run rising up to the desired water level in the pond? Then when the water in the pond rises above the desired level, water will flow out of the top of the pipe. Rip rap could be placed around the pipe so the water would fall down and splash off the rip rap.

Is there anything wrong with doing it this way?

Two things of concern, depending on the size and type of pipe you choose to use.
If you use PVC, a standpipe on the backside of the dam can freeze and break during a hard cold snap in east Texas.
The screw cap will be almost impossible to put back in place once you unscrew it and a big head of water streams out of the pipe. If you are able to put the screw cap in place, you'll probably have a "hammer" effect in the pipe as the force of water is immediately shut off. Plus, wear rain gear...you'll be soaked.
I'd spring for a valve and be sure to put the standpipe far enough back in the dam to keep it stable, surrounded by dirt. Riprap it well.

Good thought! I don't see anything wrong with it except:

There will be water all the time in the pipe. The inside of the pipe will have peressure against it at all times. If a small pin hole forms (and it will, given enough time) the water pressure will continually force water out of the pipe, eroding the soil and possibly the dam.

With pipes constructed the other way, you only have to worry about a leak at level that is under the water surface and a foot or 2 into the soil on the pond side of the dam.

Thanks for the input. I didn't think at all about freezing, but I have to wonder if there would be a problem anyway. Wouldn't the open ended pipe allow for any expansion if it did? Or do you think it would tend to bust the pipe regardless of that? FYI, for the size pond I am building, this would probably be 6 inch PVC pipe and the max depth of water will be about 8 feet. The pond will have an emergency spillway also, so this would be for normal overflow during non-flood conditions.

On the cap at the end of the pipe on the rear of the dam, yes, I would imagine that once you unscrewed the cap, it would fly off, possibly stripping the last few threads, and be impossible to replace until the pond is empty. But that would be the only reason I would want to ever remove it, is for draining. A valve would be a much better solution, and would allow partial draining. But the whole purpose of this was for Mr. Cheapo here to not have to purchase a valve in the first place.

I guess I'll just build it by the textbook, and rely on siphoning or a pump to drain it. I appreciate your replies.

Typically, the emergency overflow is for flood conditions, the overflow pipe is used for all other rain events.

For some reason last night the screw cap part didn't register in my brain, so I was thinking of corregated steel drainage pipe. Of course, plastic won't rust.

Bob is 100% correct about the freezing part, even with an open end, pipe could freeze and break.

Yeah, pop for the valve. I know it hurts, but when you consider the cost of the valve in relationship to the cost of the whole pond project, it really isn't that much. Shop around, don't skimp on quality. You really don't want to replace it a couple of years in the future. If the valve and any associated piping will be exposed to the sun, make sure you get plastic pipe that has UV inhibitors in it, or the pipe will get brittle and crack. It may take 3-5 years, but it will.

Thanks for the reply, esshup. On the spillway, I worded that where it could be misunderstood. I was just saying it would have an emergency spillway, and that the piping would be for normal overflow conditions, not the spillway. Sorry about that.

I hear ya on the freezing and the valve. I will go ahead and do it right, and will make sure the pvc is UV inhibited type. Thanks again for your time.

I'm having problems researching UV resistant PVC pipe. It appears some of the fittings are UV resistant, but I can't seem to find a place that offers the actual pipe in 4" or 6" diameters.

I also read that it is possible to paint the exposed parts of the pipe with a Krylon brand spray paint made for plastic after roughing it up with sandpaper or something similar, and that will block the UV. I shouldn't have hardly any of mine exposed to sunlight. The drain pipe in the pond will be almost completely underwater and will have a brush filter on the top of it. The output end will be covered by rip rap and larger rocks. So should I even be concerned?

I searched this website and couldn't find any posts about this subject, but then I never have much luck searching a forum for anything. Anyone got any pointers here?

You're right about the paint. Just something to keep the sun from getting to it. I've never seen UV pipe around here, I saw it all the time when I lived in Ca.