Question for you guys...

[kris77]

I have a drainage problem. I have access to a walk behind ditch witch that cuts almost a 5" trench. I've used it before and a 4" french drain barely fits in. My problem is have too much water for a 4" pipe. I need at least a 6", possibly 8".

2 questions.

1. Use the ditch witch, install 2-4in drains.
2. Use toothbar, dig a wider ditch, make a bigger mess, install 1-8" bigger drain.

Two 4" PVC sch 40 10' pipes are about $24. One 8" pipe is WAY more expensive.

 

[Jchonline]

It will probably take you less time to dig 2 separate 5” trenches a foot apart than to dig 1 wider (no ditch witch). As long as you have drop in both I would Y into 2 separate lines.

 

[SRG]

Cross sectional area, is the info you need to pay attention too, when it comes to pipe sizing and flow rates.

A single 6" pipe will flow slightly more than 2-4" pipes.....

https://www.engineeringtoolbox.com/pipe-formulas-d_1335.html

Scroll down about half way for a chart of pipe sizing, circumference and cross sectional area of certain sizes.

 

[skeets]

SRG beat me to it

 

[D2Cat]

You can get spacers for the teeth on a trencher which widen the cut of the trench. Typically there would be 6 pieces, three pairs of two. Bolt them behind the teeth and you're done.

If you're renting the trencher they may have the spacers. If not you can easily make them. Simply widen the tooth a bit and you can use 6" pipe.

My trencher cuts a 6" wide trench without spacers. I have several sets of spacers. Can cut an 8", 10" 12" width just by changing the spacers. The 8" is used around here for required width of frost footings. The 10" & 12" I don't think I've ever installed.

 

[kris77]

Thanks for the link. I think I will do one 6" or even one 8" just to be on the safe side. But man, the price difference between a 4" pipe and a 8 or even 6 is insane.

 

[winesalot]

Look at small culvert pipe instead of pvc. It's less expensive when you get in to larger sizes. Schedule 40 and schedule 80 pvc has thick walls because for pressurized systems. Culvert pipe (S&D pipe as well) is designed for water not under pressure and, therefore, is less expensive.

 

[BravoXray]

An eight inch line will carry twice as much as two four inch lines will. If you are getting too much water for a four inch line you may have too much for two four inch lines. I think I would bite the bullet and go with the eight inch.

 

[North Idaho Wolfman]

One major question
With this drain:
Are the ends exposed and is that where the water needs to enter?
Or is it a perforated drainage pipe that is used to pull water out of the ground?

You said french drain, so I'm not thinking culvert.

If it's the first (culvert) then 8" or even larger, and get culvert pipe not drain pipe, way cheaper!

If it's the second one 4" will do the job, and yes 2, 4" will do better just space them out about 2 feet apart.
Also look at the type with the foam peanuts or just the sock version and cover with gravel as they both work very well!

And with a french drain it's very very uncommon for it to flow anywhere near the pipe capacity, even on long runs!

 

[kris77]

So to answer your question, I have both needs. I dug back into the hillside to make a spot to park a camper and trailer. That spot has a lot of water drainage above it from a strip mine up on the ridge. So I need to french drain around the edge of the parking spot before I put gravel down. I am draining that into a 24" culvert buried in the yard that handles the small creek from above the property.

It's very hard to explain. But above the parking spot I just dug, there is an old fire road that is now used to carry water down to the small creek. I need to put a drain line in there and tie it into the main 24" line as well. I was thinking if i just tied that drain, into the french drain, i could kill 2 birds with one stone. Sort of like how people tie the 2nd floor gutters into the 1st floor gutters and then into a drain on the ground.

Hope all that makes sense.

 

[Flienlow]

Are you specing your pipe based on the machine used for the ditch? Don't- Rent a mini and put in the correct sided pipe.