Pond Boss Forums Thread Like Summary - Overflow pipe size

Hello everyone,

First off, I'm not only new to the site, I'm completely green when it comes to ponds. I am in the middle of having an old over grown beaver pond dredged and an overflow added since there wasn't one; don't know why the beavers didn't put one in. Anyway, my contractor originally requested an 50' x 18" thick wall steel pipe system; 40' stretching under the dam, and 8' standpipe/riser for the pond overflow. After discussing the $13k cost for just the materials and fabrication, we went back and forth and agreed on 12" thick wall steel pipe under the dam (which I picked up new on Facebook for over $11k less), with whatever size I chose for the standpipe/riser. Now, his original idea was to install the 18" pipe with an earthen emergency spillway on one end of the dam. What we are doing instead is a smaller standpipe/riser, with a 12" plastic culvert slightly higher than the standpipe/riser, and an emergency earthen spillway off on one end of the dam. I think this will work, the question I now have is 8" or 10" standpipe/riser? The 8" is readily available and very cheap. The 10" has been hard to find; retailers want nearly what I paid for the 40' of 12" for just 10'. However, I've found some used 10", just not very convenient to get to and transfer. So, would the 8" be enough?

Some background here, the pond is approx 1/3 acre, with the deepest area just over 8'. And I'm not sure about rainfall/heavy rain periods, but there has always been a spring feeding into the pond with a constant flowing trickle, and a foundation drain around the house, also dumping a trickle of ground water. Before the dredging, a notch in the dam was created to lower the water level to rid of the beavers. That was done 20 years ago and it worked; water level dropped approx 3' and beavers were gone. So, for 20 years, the only spillway for water was an 18" wide dug notch into the dam itself; no pipe, rock, nothing. Nothing ever eroded, and water never has reached anywhere near the top. The contractor suggested 18" not because of the volume of water, but because he knows it's overkill and will work, plus that's just what he's always done. I think the 8" standpipe/riser with a 12" culvert should take care of it all, with the earthen spillway likely never being used, but I would like to know the thoughts of those experienced. Will 8" plug up far easier than 10" or any other problems with the smaller pipe I'm oblivious to? Are my three methods of discharging overflow a great idea that will work, or a flop that will lead to several headaches?

And lastly, what about escaping fish. From what I've read, it's best to not screen overflows with anything to prevent fish from escaping during heavy rain periods. Sounds like losing some fish is normal from time to time, most important thing is to have the water flow; fish are far more cheaper and easier to replace than an eroded or blown out dam. Thoughts?

The one that I installed myself was only 6", and I used ratchet straps to pull them together (using the proper casket grease). With 2 ratchet straps, it was easy. I added an elbow on the pond side a year later to raise the water level and needed to make a wooden jig so the ratchet straps would pull it on evenly. I have 15" and 12" on my other 2 ponds and they used machines to push them together.

It's a combination of the size of the pond, the type of vegetation on the watershed, the type of soil in the area and how much rain can fall in a 50 to 100 year rain event. Earthen spillways tend to erode and wash out, that is why they are only used for emergencies. Go to your counties NRCS office and talk to their pond guru. They can pull up the watershed around the pond and properly size the overflow pipe. If the 18" pipe was spec'd out and you dropped the size to 12", I'd be concerned that it is too small and would put in two pipes both 12" dia.

https://www.nrcs.usda.gov/wps/portal/nrcs/main/national/contact/local/

Machines are our friend, Fishinrod, a block of wood and a good helping of lube, (pipe layers KY jelly) and they go together pretty smoothly.

Bigger pipes you can use cable come-alongs too. There is glue that has a slower set time also - gives you more working time.