Question about pitch of underground drainage pipe 1

[hardcor80]

I hired a contractor to fix some water issues in our backyard. We're on a hill and he went about 120 ft around two sides of our house with this drainage pipe. It's the perforated black piping, tied into our down spouts of our gutters, with a pop top at the end of the pipe to keep rodents out. It has some reservoirs with covers in it for cleanup of debris.

My problem with it was I was under the impression it needed a constant pitch of 1/4 inch a foot or more for proper water drainage. I know that is not the case and in some places may actually go uphill, but at the end is the low point and all the water drains out that end. I'm guessing some water is remaining in the piping. He said it's not a concern, and that no bugs or anything will reside in it. Then I got to thinking about water possibly freezing (we're in MN), or trees or something starting to grow in it (we have maple trees with the helicopters). Any thoughts? Am I just being paranoid?

 

[fattdad]

Usually perforated pipes are bedded in gravel. When water accumulates in the gravel it'll bubble up in the perforated pipe and at some point it'll discharge out the end. Perforated pipes do not need to be placed on a design slope like a gravity pipe. If there's no water in the pipe bedding the water will drain from the pipe into the bedding (or the underlying soil).

It's likely just fine.

f-d

¡papá gordo ain’t no madre flaca!

 

[hardcor80]

***UPDATE*** Thanks fat-dad for the reply. Unfortunately it is not perforated pipe, it's only flexible 4 inch pipe. I mis-represented the product. It does not have perforated holes in the pipe that water can leak out of, so it will sit indefinitely in there until it dries. But the question remains, is this a concern?

 

[bencraddock]

hardcor80,

I would agree that a slope of at least 1/4" per foot would give proper drainage, however my guess is that your pipes will be fine even if it freezes. Unless the pipe is standing full of water, there will be space above the water for it to expand as it freezes so the pipes shouldn't burst. Again, your situation is not ideal, but I would wager that it will function OK.

The thing that I would watch out for is that a large amount of ice will reduce the capacity of the drain pipe - so if you have a large roof area going into the pipe and the pipe is half full of ice, then the rain water could back up and leak out where the downspout is connected to the undergound pipe. This could be a problem if a large amount of water leaks out near your house and finds its way into the basement.

Ben

PS. I doubt that trees will grow in it since they won't have any sunlight.

 

[MiketheEngineer]

I would usually want some kind of slope - any is better than none. But having small areas of stagnation - 1'-2'' deep is usually not a concern.

BUT ice could be a problem - sudden warm up causing ice/snow melt off the roof.

Ask him to guarantee it for five years and see what happens.

 

[cvg]

the low spots in the pipe are ineffective to drain water by gravity, regardless if they are full of water, ice or empty. The only way you will get fully effective flow through your pipe is under pressure flow conditions. If you have pressure flow with ice in the line, your pipe will have reduced capacity.

 

[fattdad]

tight lines should drain. it's a typical specification that most contractors should recognize (I'd hope).

f-d

¡papá gordo ain’t no madre flaca!

 

[VulcanExcavating]

How deep are the "low spots?" Are you talking an inch, or a foot deeper than the rest? How deep in the ground is the pipe on average? If the pipe isnt perforated, try pouring a 5 gallon pail of water down the pipe at one of the downspouts. If you dont get at least 4 gallons draining out of the termination point, I'd be getting it fixed.. Plugged or frozen downspouts as a result of improper discharge lead to all sorts of other issues like ice damming and damage to your roof etc. I'd be worried about having paid for shoddy craftsmanship if nothing else.

 

[hardcor80]

***UPDATE*** Thanks for all the replies***

The big 120 ft drain with 3 gutter spouts in it remains almost flat (maybe 4-6 inches of downward pitch - tops) for the first 85 ft or so. The last section is where it starts to pitch downward (another foot or so). I can't tell exactly how it flows (it was covered before I saw the complete layout), but it may rise a couple inches in a few long stretches is my best guess. It's about a foot under the ground across the whole section.

The termination point is actually a popup that jumps vertically up and the water comes out the top. So at a minimum, water at least resides by the popup. It could have been dug 5 ft farther to come out the side of the hill (where the steep incline is, and we could have made up the pitch from the flat ground). A shorter drain he put in the front I poured a couple gallons of water in last week and nothing came out. It's got a similar slope/popup on a smaller scale. It's shaped similarly to an elongated fishing hook, when taking the gutter attachment into account.

 

[civilperson]

Water will flow in a flat pipe, (or ditch). Minimum pitch is required for velocity requirements.

 

[cvg]

water will flow in a flat pipe only if there is a hydraulic gradient to drive it. That is, the hydraulic grade line at one end must be deeper than at the other. With a foot of cover and another 4 - 6 inches of fall, you could have about 16 inches of head to work with. that head must be sufficient to overcome frictional resistance in the pipe.

 

[dicksewerrat]

Have the contractor put the pipe in properly. And yes it will freeze. The pipe should be empty in the spring becaue you get rain sometimes before the frost is gone. Lived there 60 plus years.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[beej67]

"The termination point is actually a popup that jumps vertically up and the water comes out the top. So at a minimum, water at least resides by the popup."

**

Are you saying the pipe has a 90 degree bend, and comes up out of the ground, and that's the low point where the pipe discharges?

If so, then your pipe is probably mostly full of water most of the time, and is going to burst in about 6 months, knowing Minnesota.



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