Requirements for a french drain used for surface runoff ?

18 years ago

I have been reading that for a true french drain the pipe has to be buried deep enough that it reaches the water table, otherwuse groundwater wont rise through the bottom facing holes. Is this true ?

Can I use a french drain kind of thing with holes all round to catch surface water from my large expansive driveway ? I plan to edge my driveway with lots of gravel and lay the pipe underneath it. This should work right ? Ideally I'd like to have a linear drain to catch surface runoff but I cant afford to pay anyone just yet!

I've also been reading that there can be too much of a good thing and that french drains can dry out the soil around so much that it can cause the foundation to settle ? Is this a common occurence around the pacific northwest ? Is there anyway I can check for it ?

BTW I am in the Seattle Washington area.

Thanks for reading my rather long post

Anita

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Comments (5)

laag
18 years ago
I have heard the term "French Drain" used so many different ways that I am no longer sure what the real definition is.

If you want to remove water from saturated soils using perforated pipe, the pipe has to be where it is saturated (in ground water) for it to enter the holes.

If you want to leach water into the soil to get rid of it, the pipe must be in unsaturated soil (the larger the particle size - the larger the voids - the more water holding capacity and the more the water will drain by gravity).

If you want to drain water before it saturates the soil, you have to catch it on the surface as it runs off. That is what you are essentially doing wuth your gravel strip. But if you want to get it in a perforated pipe and carry it away, you need to place the pipe at the bottom of the trench. If you use white PVC with two parallel rows of holes (recommended), put the narrow part between the holes on the bottom. This allows the water to rise in the trench and fill the narrow vally between the rows and slope away without leaking out. You could line the bottom and sides of the trench with something impervious to force the water to rise and enter the pipe. But, the pipe has to have a place to give up the water (drain to daylight in a lower area or a drywell or a leaching trench).

A leaching trench will be a trench with gravel under and around the pipe where it will flow out of the holes and drain into the gravel.
ani_t
Original Author
18 years ago
Laag, Thankyou for your reply. It is indeed very confusing to me- all this
I thought I had posted a sketch of my yard and what I'm going to do with it.
As you can see from the picture areas with the red lines (fench drain) are both not a place which drains water well. Its right next to the foundation and all the water currently dumps into it. I want to remove water coming into both areas from the surface as well as remove ground water because this area does saturate.
From what I understand of your advice this is what I should do.

1. Dig a trench - a foot wide, how deep ?
2. Buy PVC pipe with 2 rows of holes- how big ? Are the holes premade ? If Ihave to make them how far apart ?
3. Place filter fabric along sides and bottom of trench
4. place pvc pipe with holes down, on the bottom of trench with no gravel below it
5. Fill up trench with gravel (how big pieces ?)

Can I connect this pvc pipe to the catch basin which I already have ?

Thankyou
anita

Here is a link that might be useful: My yard sketch.
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It sounds as though you tried diplomacy and it failed. A second attempt might be to ask the neighbor to attach the two ends of the pipe to another buried pipe that would divert the water to the street just inside his property line. You may present YOUR alternative plan of cutting his trees brancehes back to the property line and trenching just inside your property, if that is not done (you have that right). This would be a major threat to his screening trees that he could simply avoid by adding a few feet of pipe. (personally, I think your neighbor is a jerk and that the people in your town hall are completely wrong about him being able to dump water a few feet from your property). If you see that as a confrontation and you don't want to deal with it, you could build a berm with a sloped swale to divert the water toward the street. My concern from your other pictures is that once it gets to the street it will drain back onto your property because it appears that your proprty is lower than the street. You could also dig a big deep trench and fill it with drain rock to try to get it into the ground.
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It's too hard to figure out your explanation without pictures. Please add some so we can see what's happening. Show where water stands (though it doesn't need to be in the picture; you can describe it,) where it should go and the path it should take. So far, the only soil I've seen in is Florida is well-draining sand; is yours different?
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It's difficult to tell where the water flows after it leaves your property, but looks like another road or drive where the police car sits.? It looks like you have negative grade in the area closest to your house. If this was done by a landscaper or contractor, then this is a poor job. As far as I know you have the right to have water flow from your property. Is the water flow from the right coming from your neighbors property? It's really tough to give advise without knowing all of the entire story. But, I think that I would put in a french drain, as you indicated in pink, that extends under the standing water on the far side of your property. This would take care of that problem, too. I would get a small excavating company do the job. Do any of your neighbors downspouts connect to anything? I see that yours just spills out onto the concrete. If you could tie in your downspouts to a drain this would probably take care of it. Is there a storm sewer at the street? I have more questions than answers. You just have to help gravity do its job. Luke
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I agree with where yardvaark is going with the conversation: look at the root of the problem. I may be misunderstanding something here because like yaardvark said we could use some more details, but I'll try to read in to what I think you are describing: From what I can tell from your description, there are two problems: 1) water can't get out from behind the neighbors side of the wall in a "normal" way. 2) your yard can't deal with the water, especially when it comes "forcefully" out of the sinkhole in that location. I'd be worried about silt clogging your proposed french drain, and/or the "inlet" of the sinkhole to your propsed drain system moving/collapsing. If it's currently a dirt tunnel, it will continue to change in size and direction as the water carves it. BTW: I'd put money on it that this was happening before you bought the house too- holes like this don't arrive in a year (unless the wall was put in within the year). More on #1: By "normal" I mean that a sinkhole is not normal, and as you've said it concentrates the water from both left and right sides of their lawn into this one hole. Walls that have this much water from other yard areas draining into the back of them should not be a solid "dam" of concrete: Do a google images search of "drainage behind retaining wall" and you'll see lots of photos showing a clear rock layer behind the wall, and tubing in the rock layer to have water come out the face of the wall or thru a tube to an appropriate exit location. The city may be right that you can't enforce a rule that says "water can't drain downhill"' because gravity will always move water downhill. But you should be allowed to prevent concentrated outpourings of water from sinkholes in your yard that are flooding your basement. Who pays for it may be an issue, but here's a proposed improvement: I see two options for drainage behind the wall: add drainage behind the full width (or nearly full width) of the wall and have the tubes connect to either a) multiple spaced face drains cut in the wall. This should distribute the water to have it come out more evenly and on the property line instead of so close to your house, then you stand a chance of managing it on your side. And/or b). Put drainage behind the wall and route a tube to the side/front of your property where it won't cause problems (and put small rock bed and/or distribute the water at the exit to spread out the water and to slow erosion at the exit). Even with drainage behind the wall, you should correct grade problems on your yard: surface grade away from your house and make sure the swale drains to the side/front as you mentioned. Good luck with your project.
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inkognito
18 years ago
Anita, go to http://www.pavingexpert.com/drain03.htm for an explanation of land drainage.
Incidentally a true French drain does not have a pipe in it.
ani_t
Original Author
18 years ago
Thankyou very much for the very useful link!

I discovered today that the "catch basin " and pipe combination has perforations on the top! I first thought my digging had made a hole but the slits are regular and spaced every alternative ridge. I have to figure out what the original intention was.
I am afraid to connect my french drain to it if the current pipe is connected to the sewer system. Do you think I should try and dig all the way around it to find out if it is so ? What is the danger of connecting my french drain to the current pipe ?

Thankyou, I have lots to read
Anita
Caroline
17 years ago
Hi All,
I just got a quote of about 13K to install a French drain behind my house, and re-do the perimter drains which are old, made of clay, and clogged with roots and rocks.

You have a mind like mine if your response to this is...how much is a Ditch-Witch? I'm in the wrong line of work.

How can it possibly cost so much to do such a low-tech project? Are these contractors really cleaning up, or am I missing something?

Thanks--and apologies in advance to hardworking ditchdiggers everywhere.

Requirements for a french drain used for surface runoff ?

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laag

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Requirements for a french drain used for surface runoff ?

Comments (5)

laag

ani_tOriginal Author

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inkognito

ani_tOriginal Author

Caroline

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ani_t
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