French Drain Question

[jrdepew]

All,

I have a french drain on my property which was done by the previous owner. It seems to be working fine, although I don't like where the water is being put currently. I plan to re-do it X years down the road when I get around to it or if it stops working correctly. Anyway, the previous owners lined the top of the drain with large field stone, some pieces are dinner plate sized and stick up out of the soil (lots of clay here). I pulled all the big rocks out as they kept getting whacked by the lawn mower blades and didn't look that great. Where I pulled the large stones out I made sure to remove any sod, then I put down some large drainage rock to about 4-5" from the surface. Following that I put down a layer of pea gravel. The drain is still working properly, but I am wondering if I can put some top soil over the pea gravel and seed it. Most of the french drain is current covered with top soil and grass, except for the sections with the large rocks.

Would this be an okay situation to put topsoil and grass over the top of the french drain?

Let me know if I left anything out.

Thanks,
Joe

 

[dave1949]

Joe, I would want to, or try at least, to figure out the original purpose of the flat rocks, and why just are they in that one part of the drain. Of course, there is no guarantee of a logical reason.

Is there a drainage pipe down lower in the drain?

 

[Fossil Farm]

Depending on how much work you want to do and money you want to spend, it would be a good idea to put a layer of landscape fabric between the pea gravel and the soil. The further you can get it down between the existing rock and soil would help keep the drain from plugging with soil for a longer period of time. If you think you will redo the drain within a year or two, just wait until then to use the landscape fabric. Use the tougher fabric, not the cheap, flimsy stuff. It holds up to rock much better.

 

[jrdepew]

Joe, I would want to, or try at least, to figure out the original purpose of the flat rocks, and why just are they in that one part of the drain. Of course, there is no guarantee of a logical reason.

Is there a drainage pipe down lower in the drain?

Dave, there is a black corrugated pipe down lower in the drain, surrounded by crushed stone on all sides. The large rocks sat on top of the crushed stone along most of the length of the pipe from what I can tell. I am not sure if they were heaved in two spots, or the topsoil layer wasn't as thick at the two spots I removed, but the stones were making mowing near the drain a pain. All in all I removed enough field stone to fill my bucket heaping once, so I didn't remove a ton of stone.

The problem with the drain, in my opinion, is that it was stopped short. The drain goes to daylight (which is why I know there is black pipe in there) in my back yard. This is the last place to dry out on my property as the french drain collects a lot of run off, and directs it there. I think the drain should have been extended another 100' or so to get to the steeper, less used part of the yard. However, I don't know the money situation or the tool situation of the people who dug this drain. My plan in the future is to re-dig this drain, and extend it to where I think it should exit. Would a ditch-witch be out as this is already an existing french drain? I am wondering how it would handle the large field stones thrown in the mix. Is a 200' french drain a bad idea because of the amount of runoff it can collect? When I get closer to the project I will post pictures and look for help with pipe layout.

For right now, I just need to figure out what to top the french drain with. I am probably past the use of landscape fabric, and it would only be in a few small sections of the ditch, so I am betting the benefit would be minimal. My options are: more pea gravel to bring the level up a little so we can mow, or add a coarse sand on top of the pea gravel, or cover the pea with top soil and seed it.

Fossil Farm, I learned my lesson using the cheap landscape fabric....wondering why I have weeds growing up between rocks at the back of my garden where I made a small crushed stone walkway!!

Thanks for the info all.

Joe

 

[dave1949]

It sounds like the stones you picked up were there "just because."

If a french drain is correctly built with good filter fabric covering the washed gravel completely surrounding the pipe, top, bottom and sides, it can be covered with enough soil to grow grass and you wouldn't even know the drain is there. I think the best method is to put the fabric in first, all the way to the bottom of the trench, but leave enough fabric slack on each side to fold over the completed drain stone and pipe. Basically, it ends up like a fabric tube with stone and a drain pipe in it.

The open spaces in the washed gravel collects the water, the pipe transports it. So, a narrow ditch witch trench is going to have a limited collection ability as there would be little room in the trench for stone around the pipe. The more water there is to collect from the surrounding soil, the wider the collection trench needs to be.

If you plan on eventually re-digging to extend the drain to a better outlet location, I would leave what is there alone as long as it is working, then redo the whole thing at the same time. Then you would know exactly what you have end-to-end. I don't think 200' would be a problem as long as you make the drain trench big enough.

I have a french drain that runs underneath a shallow surface drainage swale. The drain dries out a perennially wet area in my driveway primarily, but of course collects ground water all along the way. The surface swale handles the quick run-off from heavy downpours. That has been working well for me. No problems keeping everything dry enough to mow over without ruts.

 

[vtsnowedin]

I wouldn't call what you discribe a French drain at all but instead a homemade catchbasin and drainage pipe. The pipe is why as a french drain usually doesn't have one and just lets the water it collects soak into a sandy layer of soil in the bottom. To me "French drain" translates to "dosen't work when you need it." As yours is in clay soil and works yours must be English.
You can extend the drain pipe to outlet anywhere you want with a pipe the same size or larger. What you need on the top is a frame and grate for highway drainage structures. Just remove the top eight inches of dry laid stone and mortar on the frame to the grade that works and drop the grate in, then backfill around it. Most highway grates are two feet square and will take in all the water you need.
Here is a link to a standard. I'd use a type B in a mow area.
http://www.nh.gov/dot/org/projectdevelopment/highwaydesign/standardplans/documents/2010_dr-1.pdf

 

[Egon]

Pictures would be nice.

Your method of change to make mowing easy sounds perfectly feasible.

From what I can understand all works well but the exit is not where you want it. Consider just extending an ordinary pipe to the area you wish or digging a well back sloped ditch out to where the water should go.

 

[Qapla]

As far as extending the drain goes, as long as the existing portion is collecting the water from the needed area and all you want ti to dump that water to a different spot you can extent with "solid" pipe - pipe without all those holes in it - corrugated is fine - and that way you probably could use a trenching machine since you only need a ditch a bit wider than the pipe .... just make sure it runs downhill.

If you decide to "replace" the entire drain, you will want to dig with a backhoe or excavator since you need a ditch wide enough for the pipe and rock. 200' is no problem as long as it runs downhill. We have installed some much longer and they work fine.

Another alternative to a "French Drain" is to reshape the land to create "low spots" where water can gather. In those spots you install a drain box like this one and use pipe without holes to run the water anywhere you want it to go. You can "Y" several boxes into a main run and direct that run to your outlet area like this

 

[dave1949]

I wouldn't call what you discribe a French drain at all but instead a homemade catchbasin and drainage pipe. The pipe is why as a french drain usually doesn't have one and just lets the water it collects soak into a sandy layer of soil in the bottom. To me "French drain" translates to "dosen't work when you need it." As yours is in clay soil and works yours must be English.
You can extend the drain pipe to outlet anywhere you want with a pipe the same size or larger. What you need on the top is a frame and grate for highway drainage structures. Just remove the top eight inches of dry laid stone and mortar on the frame to the grade that works and drop the grate in, then backfill around it. Most highway grates are two feet square and will take in all the water you need.
Here is a link to a standard. I'd use a type B in a mow area.
http://www.nh.gov/dot/org/projectdevelopment/highwaydesign/standardplans/documents/2010_dr-1.pdf

My french drain, or whatever you want to call it, and my surface swale work independently of each other. The french drain is installed below the frost line. You would never know it existed unless you found the daylight outlet.

I think of a french drain as something that collects ground water, not surface water, and certainly not running surface water. The only way a (my) french drain will remove surface water is by drying the soil below, and that will draw the surface water/moisture down to the drain.

My yard would look a bit funny with a 100+' long catch basin.

I've never heard of someone digging a trench and putting only stone in it and expecting good results. On that we agree, if not on the name of my drain. :laughing: Whatever you wish to call it, what I have is basically a form of a standard foundation drain adapted to a dirt trench, if that helps visualize it.

Joe's sentence: "This is the last place to dry out on my property as the french drain collects a lot of run off, and directs it there" leads me to think he is dealing with excess ground water at that location and surface drainage too.

 

[vtsnowedin]

I need to eat a little crow here. When I goggle "French drains" several pop up that are as the OP described.
I call those side drains or just under drains though most shown on Wiki have more elaborate top dressing then anything I've installed. They all appear to be quite functional as long as the bottom of the ditch is graded properly. I would think that loam and grass sod over the top of one would work but at a slower rate as long as the loam was more sand then clay.