French Drain x French Mattress - Recommended trench dimensions

[Forest_Man]

Next project down the list: add some drainage in my parking area, which is downhill from a water spring that keeps the parking area wet almost all year round.

Here is how I would like to run this drainage:

I have two questions:

1. What is more appropriate for my condition: french drain or french mattress?
2. What should be a good trench dimension to capture the most of the underground water? Right now my foundation is taking a beating and I need to divert some of this water away from the parking and foundation.

Thanks in advance for any feedback!

 

[BravoXray]

I don't have an answer for you, but interestingly I just watched at video by Practical Engineering. You might give it a look.

 

[D&D]

Next project down the list: add some drainage in my parking area, which is downhill from a water spring that keeps the parking area wet almost all year round.

Here is how I would like to run this drainage:
View attachment 884004

I have two questions:

1. What is more appropriate for my condition: french drain or french mattress?
2. What should be a good trench dimension to capture the most of the underground water? Right now my foundation is taking a beating and I need to divert some of this water away from the parking and foundation.

Thanks in advance for any feedback!

Capturing the spring at its source and piping away isn’t an option?

 

[CaptPat]

I recommend getting an estimate/evaluation from a drainage professional. I had French drains installed by a firm experienced in design and installation, their proposed design was quite a bit different than what I had in mind. The results were better than expected. IIRC the trench was ~12" wide and 18-24" deep, sloped in the direction of desired water flow. The bottom of the trench was covered with crushed stone, up to about the top of the drain pipe. The drain pipes had slits in the sides and were encased in "nylon" fabric tubes to prevent dirt and debris from entering the pipe. I don't recall the diameter of the drain pipes, 8" seems right. The installation of ~300ft of pipe consumed a day, one mini-ex and 4 guys.

 

[Forest_Man]

I don't have an answer for you, but interestingly I just watched at video by Practical Engineering. You might give it a look.

Very interesting video, thanks for sharing it.

Capturing the spring at its source and piping away isn’t an option?

We looked into that and it opened another can of worms...

IIRC the trench was ~12" wide and 18-24" deep, sloped in the direction of desired water flow. The bottom of the trench was covered with crushed stone, up to about the top of the drain pipe. The drain pipes had slits in the sides and were encased in "nylon" fabric tubes to prevent dirt and debris from entering the pipe. I don't recall the diameter of the drain pipes, 8" seems right. The installation of ~300ft of pipe consumed a day, one mini-ex and 4 guys.

Thanks for the input. We tried getting different quotes but still have not found the right contractor, so highly considering doing the work ourselves.

 

[D&D]

Either way, I hope you at least hire a civil engineer to do the appropriate calculations and get the right permits. Cleaning up this type of job after the fact gets really expensive.

 

[DJ54]

I'm going to assume your house sets on somewhat of a hillside, and they cut a flat bench to build on.

That being said if that is the case, cutting that bench has gotten closer to the level the spring is perking out. Seeing what you have in mind to install, depending on how close to the surface the water is perking out may not solve the problem.

If you have a slope going uphill from the parking area, my thoughts would be to put in a horseshoe type french drain starting far left near the lateral you have, stepping into the slope maybe 18"-24", digging down to find the source of water above the parking area catching the water before it gets to the parking area. It'd be super helpful to dig down before and find the level of where water is at/perking off a hard surface.

I'm also going to assume there may be a layer of rock, or depending on your location a layer of fire clay, but that is usually only found in regions with coal. Water will soak down through dirt and coal until it hits the fire clay which is pretty much water proof, and perk out at that level. If no coal in your region, I'm guessing you have a layer of rock it is following out.

Catching the water before getting to the parking area, and long before the house will do what you want to do and dry things up. A 8" to 12" trench as deep as it requires with a fabric covered 4" plastic slotted pipe will carry away a lot of water. With seeing the trees alongside the drive and what may be out of the picture, just using gravel tree roots will go for the source of water and in 5 years or so may restrict/clog your drain.

Going with a trench 18"-24" deep will allow you to cover the pipe with around 12" of #8 gravel/pea gravel and catch any extra water that may perk out during the wet season. And you'll want to cover the gravel with some sort of fabric to keep dirt from sifting down through. On the job where we've installed drains on road slips we used surplus construction fabric contractors had left over, and gave back to us. Here at home, I've used the "better" 5 year landscape fabric used around tree's etc., folded over 2X. I dug into a drain I installed 15 years ago to connect more drainage, and the fabric I put in looked like new. Keeping the elements and air away from it will make it last a long time. Heck, years ago before fabric they used a layer of straw on leach beds to do the same thing. We did the same before using fabric. Some friends had an excavating business that installed septic systems. They would replace systems that people had planted trees and had clogged the laterals, and still found straw although somewhat deteriorated, still doing it's job.

You don't need a whole lot of fall 2% is a good amount of drop. That will flow water plus carry any sediment out that may get in the pipe. A lot of drop will let the water run fast and drop the sediment.

Once you get beyond the point of where you're picking up water, you'll want to go into solid pipe with no gravel only dirt. Do this right at the end of the perforated pipe and it will force water into the perforated pipe. Otherwise, you'll have water constantly seeping into the surrounding bank and possibly cover the outlet.

I'd definitely make some sort of splash pad or put larger stone in a trench at the outlet. You'll want that trench back a foot or so before the end of the pipe. Eventually, water will undercut the pipe when down to a trickle. Eventually you'll still have some erosion beyond where the splash pad/stone ends.

Whether you do it yourself, or contract it, having a good grade is most important. Having a belly in it somewhere along the line, water will lay there, and still perk out towards where you want to keep it out. And you'll want to check your outlet several times a year making sure you still have a flow, and check for erosion beyond the pipe outlet.

Another thought came to mind... If your County has a Soil Water Conservation office, contact them and have them have a look and maybe come up with a plan. The service should be at no cost. Your tax dollars pay for it, might as well get some benefit out of it. They will come out, assess the situation, shoot grade, etc. and come up with a plan, in blueprint form. Look it over then decide if you want to tackle it or let a contractor do it. If you do it yourself, a transit level and grade rod would be a must to keep proper grade. Just keep in mind a grade rod is in tenths of a foot, not 1/8" increments.

 

[EddieWalker]

I tried to look up what a "French Mattress Drain" is, but the results came back that it doesn't exist.

I am familiar with French Drains. As a Home Remodel Contractor, I have quite a few clients that have them. In my experience, all of them love it when they are first installed, and then it's just a matter of time until they stop working and they realize that they wasted their money. How long this takes to happen varies on where it's at, how long it is, and who installed it.

In my opinion, French Drains have become the magical fix to drainage that everyone knows about, but never performs over time.

There is only one sure fired, guaranteed to work method at removing water that is used by Commercial Contractors and Government Agencies. And that is a ditch. Only home owners, landscapers and the guys who mow your lawn, use French Drains. I'm sure there is an exception to this, but it's like saying you wont get cancer from smoking cigarettes'. It happens, but it's not worth the risk of failure.

Nobody wants to dig a ditch because it's a lot of work, and it's hard to make not look like a ditch. You have to go really wide to make it not look like a ditch. Or you have to fill it with gravel, or something to make it look better.

Since most people have to live with a wife that wont approve of a ditch, the only other option that might last is a pipe with a drain to catch the water and carry it away. An open drain can still plug up, but a lot of the time, you can clean it out, and if you are careful with what goes into it, you might get lucky and it never plugs up.

 

[Forest_Man]

I tried to look up what a "French Mattress Drain" is, but the results came back that it doesn't exist.

I had attached (2) Technical Bulletins PDF on the topic, under the first post.

 

[Fixastuff]

Around me a proper French drain lasts much, much longer than a ditch.(lasts as long as a septic drain field) If you don’t clean that ditch every other year it fills in with leaves/trees/bushes till it’s no longer a ditch. French drain make and forget.

 

[Forest_Man]

I'm going to assume your house sets on somewhat of a hillside, and they cut a flat bench to build on.

Very good post, thanks for sharing your feedback. And yes, the cabin is on the hillside.

 

[Forest_Man]

Around me a proper French drain lasts much, much longer than a ditch.(lasts as long as a septic drain field) If you don’t clean that ditch every other year it fills in with leaves/trees/bushes till it’s no longer a ditch. French drain make and forget.

We currently have a large ditch and it works only to contain the mountainside water: it is a pain in the a$$ to maintain it and it only catches the surface water.

We need something for the underground water as well..

 

[coldsteelva]

Could it potentially be more advantageous to simply elevate the parking area by bringing in some geo-grid/geo-cell and gravel? The mats would hold and lock the gravel while also supporting the base.

 

[Clayak]

If the ditch doesn't work, maybe it's not deep enough. My ditch is 4-5 deep. Across it I've put in a few bridges of railroad ties and 6 inch wide cedar strips to walk on and get to the garden. Looks decent to all, great IMHO, but then we live in the country where answers like that are understood.

 

[Streetcar]

I tried to look up what a "French Mattress Drain" is, but the results came back that it doesn't exist.

I am familiar with French Drains. As a Home Remodel Contractor, I have quite a few clients that have them. In my experience, all of them love it when they are first installed, and then it's just a matter of time until they stop working and they realize that they wasted their money. How long this takes to happen varies on where it's at, how long it is, and who installed it.

In my opinion, French Drains have become the magical fix to drainage that everyone knows about, but never performs over time.

There is only one sure fired, guaranteed to work method at removing water that is used by Commercial Contractors and Government Agencies. And that is a ditch. Only home owners, landscapers and the guys who mow your lawn, use French Drains. I'm sure there is an exception to this, but it's like saying you wont get cancer from smoking cigarettes'. It happens, but it's not worth the risk of failure.

Nobody wants to dig a ditch because it's a lot of work, and it's hard to make not look like a ditch. You have to go really wide to make it not look like a ditch. Or you have to fill it with gravel, or something to make it look better.

Since most people have to live with a wife that wont approve of a ditch, the only other option that might last is a pipe with a drain to catch the water and carry it away. An open drain can still plug up, but a lot of the time, you can clean it out, and if you are careful with what goes into it, you might get lucky and it never plugs up.

Eddie
I have worked on French drains that were still functioning after sixty years. Work was rerouted the portion damaged by road widening

 

[EddieWalker]

I believe you. Like anything, there are those rare occasion when something that is a very bad idea, actually works in certain cases. It would be interesting to figure out why it's still working. There are so many reasons for them to fail, finding one that lasted is really kind of amazing.

 

[Fixastuff]

Id guess installing them correctly had much to do with them lasting.