Pond - New Culvert Project

[tractordk]

Hi everyone,

I just returned to Maine for the summer after a nice long winter away to find a few new projects have turned up in the yard. Looks like the first will have to be the culvert for the back pond. Here are the details:

It is a small pond in one of the back fields with a very old culvert made from welded barrels. Somewhere along the run the culvert has collapsed and is causing the dirt to erode. Looks like a simple project.

My plan is to dig up the old culvert and replace it with a new black plastic 12" or 15" culvert and standpipe. The culvert run is about 150'. I have never set a culvert before and wanted to know if there is anything in particular I should keep in mind. Our soil is primarily hard clay.

Additional questions:

any thoughts on 12" or 15" culvert size? looks like about $1200 worth of 15"
is there a less expensive alternitive to the black culvert pipe?
should i set the culvert directly in the clay or something else?

I have attached a few pictures so you all can get a look at the problem / project.

Thank you very much in advance for any ideas and advice.

Stay tuned for additional projects.

 

[Toiyabe]

The most important thing when laying culvert is getting good compaction underneath and around the pipe. Having support under the bottom quarters of the pipe is especially important. Think of the pipe as holding the shape, and the compacted soil as taking the loads. If you have portions of the run which aren't going to be driven over, that's maybe less important for those portions.

It sounds like you will be downsizing the pipe diameter (and therefore flow capacity) by a good bit. Without knowing more about the situation it's hard to tell if that will be a problem.

Is it possible to convert part of the run to a suface channel?

 

[tractordk]

Thanks Toiyabe,

The diameter of the original culvert is about 22" so we will likely be downsizing a bit.

I think part of the run could be converted to a surface channel.

Only the first 30' will ever be driven over.

Let me know what further info would be useful and Ill provide it.

Thanks again,
Ben

 

[Toiyabe]

A 15" pipe has only 46% of the area as a 22" pipe. Corrugated plastic (if that's what you are getting - there's also smoothwall plastic but that's more expensive) also has more friction than smooth steel. Friction is an important factor on a long run. My seat of the pants guess is that you'll only have about 25% of the capacity that you used to have. To run the actual numbers, you would need to know the slope of the pipe, and the inlet and outlet conditions.

Is that a problem? Do you have a sense of how full the old pipe used to flow? What are the consequences if the pond overflows?

 

[tractordk]

Toiyabe,

I will do a little research and get back to you. Its raining hard here today so I don't know if I will go out and measure the slope.

What do you mean by inlet and outlet conditions? The outlet feeds in to a rather large ditch. The inlet will likely be a standpipe - though i haven't been hearing great things about stand pipes. Any thoughts?

We have a much larger - 7.5 acre - pond in our front yard and it has a 3' daimeter stand pipe feeding a 24" steel culvert. It has worked well for the 10 or so years it has been in. That particular pond also has a large spill way incase of overflow, but I have only seen the water rise that high twice in 10 years.

Thanks again,
Ben

 

[Toiyabe]

To run the numbers properly, you'd need to know the maximum head on the inlet side (how high can the water get above the bottom of the pipe before you have problems) and the tailwater depth on the outlet side (how high the water is above bottom of the pipe at the outlet, although this can be flow dependent). Then you can calculate your capacity.

And then you need to break out the topo maps and define the watershed, figure out your runoff coefficient, and look up the precipitation charts for your areas to calculate amount of water you need to deal with.

I'm not saying you need to run the numbers. The safe thing to do is to replace the culvert with the same size or larger one.

If, having lived on the property for a while, you have reason to belive that the existing culvert is oversized, then maybe you could save some bucks by going with a smaller one. I'd feel more comfortable doing this if the consequences of a flood are minor (i.e. not going to wash out anything important).