Yard Drainage, Underground Downspout


Old 04-10-14, 07:37 AM
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Yard Drainage, Underground Downspout

Hello All,

I needed some advice on underground downspout drainage. I want to run all of my downspouts in the backyard (total of 2 downspouts) and 1 yard drain into a solid underground PVC pipe and then out to the front of my house where there would be a popup drain cap for the water to run out from.

The underground drain pipe would start at one corner of the back of my house run for about 30ft (while connecting to 2 downspouts and a yard drain) then run around the side of my house for about another 45ft.

My main concern is that by the time the drain pipe hits my front yard (keeping the proper slop of the PVC pipe) itís going to be buried too low in the yard for the water to then comeback up and out the popup drain cap.

How low can the PVC pipe be buried while still letting out water through the popup cap?


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Old 04-10-14, 08:49 AM
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It's all about the elevation of your yard and basic physics. If the water in the pipe is higher than your pop-up the water will flow regardless of how low it goes.

For best flow the pop-up should be as low as possible but as long as the piping is uphill of the pop-up it will work regardless of how long or low the pipe is in between. The long term problem will be keeping the pipe clear. Dirt and shingle grit from the roof will collect in any low spots only adding to the clogging problem of lighter stuff like leaves so low areas and sharp bends should be avoided. Best would be for all the pipes to slope downhill and emerge straight out to daylight. A vertical 90 degree bend at the end for the pop-up is guaranteed to collect sediment.

At the minimum make sure the pop-up is removable so you can clear any clogs right there at the end. Since you have long runs I would install clean outs so you are able to clean out the lines when they clog. Some way to access the piping where each downspout enters would be good as well as access before (upstream) of any 90 degree fittings.

Use smooth walled pipe PVC drain pipe. It's smooth walls are much less prone to clogging than corrugated black plastic pipe.
Old 04-10-14, 09:18 AM
Join Date: Oct 2008
Location: New England
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Hi Justin,
I didn't see mentioned your location, do you get a lot of frost?

Another option if your soil can take the extra water is to build a deep drainage pit. They are sometimes filled with stones and gravel and others are open chambers with a concrete lid. But, you need very good soils to drain that volume.

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