4" or 6" Pipe for frech drain

[MMH]

I'm putting in a french drain that will catch water from a spring, a big hillside, and gutters from two buildings (my house and a 40x60 pole barn). There will be two curtain drains each going around the back of the buildings that will have 4" HDPE perforated pipe. These two curtains and the pipes whre the gutters from the two buildings will tee to solid 4" HDPE pipe which will run the pipe out to a creak where it will daylight drain. There will be quite a bit of drop, so gravity will help the water flow. The distance from where the curtains & gutters connect to the solid pipe down to the creak is 200' and the drop is 30'. Will a 4" pipe be able to handle this volume of water? If I go with 6" the pipe will be corregated which I don't like as much as the solid smooth pipe. It will also will be more expensive.

[sdkubota]

With that kind of drop, a 4" pipe is capable of handling a lot of water. A 4" does seem undersized for that building though. I assume you are not catching the water directly from the downspouts? If you give the runoff an area to pool during large rainfall events and then having your pipes drain the water away the 4" all the way will be fine. If you are expecting to drain the water immediately, I would say you are undersized on all of them.

[Redneck in training]

I just did something similar. The french drain is made of 4" pipe and about 150 ft long. It catches weak spring coming from a slope behind my house and water from my house. The water pools for short time above the drain during heavy rain but disappears withing minutes after rain stops. The pipe never got completely full of water. The gravel above the pipe has more resistance than the pipe. Therefore I think 4" will be fine. If you don't want water pooling at all then french drain is not the solution.

[Travelover]

It is not clear if you are planning to allow the gutters to directly flow into the French drain. I would advice against it as you will be introducing debris into the pipes and also distributing water into an area where you want to get rid of it.

When I put in my French drain, the hard part was digging the trench. So I laid the gravel and perforated pipe on the bottom and laid a 4" solid pipe over it, which was connected to the gutters. That way the lower pipe collects ground water and the top pipe directly discharges the roof runoff. I also installed a clean out at the surface so I can run a snake through it if I ever need to. It was only a few bucks for the extra pipe.

You can buy 6" PVC pipe with a smooth wall. It costs more than 4" but is more resistant to plugging.

[radioman]

If I was in your shoes - I would use 4 inch from each new starting point and when you connect them all with a T, I would upgrade the size of pipe. with two 4 inch pipes connecting to a 6 inch flows better then all 4 inch . This way , you will have a air pocket on top of the pipes and it wont slow down and gurgle. Anytime you slow down water, you increase the chance of debris filling up in the pipes.

[wrooster]

When I put in my French drain, the hard part was digging the trench. So I laid the gravel and perforated pipe on the bottom and laid a 4" solid pipe over it, which was connected to the gutters. That way the lower pipe collects ground water and the top pipe directly discharges the roof runoff. I also installed a clean out at the surface so I can run a snake through it if I ever need to. It was only a few bucks for the extra pipe.

^^^ This is the best approach.

Wrooster

[MMH]

It is not clear if you are planning to allow the gutters to directly flow into the French drain. I would advice against it as you will be introducing debris into the pipes and also distributing water into an area where you want to get rid of it.

When I put in my French drain, the hard part was digging the trench. So I laid the gravel and perforated pipe on the bottom and laid a 4" solid pipe over it, which was connected to the gutters. That way the lower pipe collects ground water and the top pipe directly discharges the roof runoff. I also installed a clean out at the surface so I can run a snake through it if I ever need to. It was only a few bucks for the extra pipe.

You can buy 6" PVC pipe with a smooth wall. It costs more than 4" but is more resistant to plugging.

The gutters will be piped directlu to the solid pipe and not the french drain. I was intending to do a cleanout.

[MMH]

It is not clear if you are planning to allow the gutters to directly flow into the French drain. I would advice against it as you will be introducing debris into the pipes and also distributing water into an area where you want to get rid of it.

When I put in my French drain, the hard part was digging the trench. So I laid the gravel and perforated pipe on the bottom and laid a 4" solid pipe over it, which was connected to the gutters. That way the lower pipe collects ground water and the top pipe directly discharges the roof runoff. I also installed a clean out at the surface so I can run a snake through it if I ever need to. It was only a few bucks for the extra pipe.

You can buy 6" PVC pipe with a smooth wall. It costs more than 4" but is more resistant to plugging.

This is more or less what I will be doing except the solid pipe & the perforated pipe will be in separate trenches due to where they need to run.

[Travelover]

This is more or less what I will be doing except the solid pipe & the perforated pipe will be in separate trenches due to where they need to run.

Sounds good. Like I said, you can buy smooth wall 6" PVC. I had to go to a commercial supply place to get it - not Home Depot.

[czechsonofagun]

I used 6" black corrugated pipe in a sleewe and gravel. It was several years ago and the difference it made to our place is amazing.