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french drain pipe - not for water from above?

Posts: 5
Location: Knoxville TN
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Hey Paul

Sorry if this is redundant.

If your goal is to divert water coming downgrade around structures then it isn't a drain you want at all, and definitely not any kind of swale. What you need is a berm that is slightly longer than the width of what you are trying to divert around. Preferably this berm would be somewhat wedge shaped with the thin end of the wedge pointing uphill. The water coming down grade would "part" around the berm and continue down grade on either side of the structure you want to protect.

You might consider just digging a ditch at either end of the berm so that the increased water volume would have an easier excape route. This would be a good place for your "Paul drain" because an bare ditch might tend to erode (although if you seded it with some kind of ground cover this shouldn't be too much of an issue.

A swale behind anything you want to get water around is a bad idea because swales drive the water sub surface, which is why they are used to deliver water to the root zones of gardens. So the water would just end up under your structure.

I attached a picture of what I have in mind. If you could explain to me how you get the pics right in the message that would be helpful. I like drawings of things. BTW, what proftam are you using to draw?


[Thumbnail for berm-divert.jpg]
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I think the term "french drain" can mean several things in practice, whether or not there is a technical definition. For instance, I just put in what I would call a hybrid that is part dry well, part french drain.

Someone mentioned a solution as "find another building location" and that is very important. You will note that century homes virtually always are located on high ground / have good downward grading because in those days, they did things right ... and you pretty much can count on 1) gravity being there and 2) water will follow the path of least resistance.

I say this because nowadays I see homes being built in places where they simply should not be. Unless you have an array of pumps with a backup generator, don't build or buy your home in a depression / bowl. My development (like many) is stepped. Unfortunately, the steppes are between the sides of the houses, not at the back of the property. Worse, the steppes are clay - the water shoots right down them. I replaced the 1960's old, collapsed, plugged clay drain tile along side my house 20 years ago when we first had water problems. I replaced it with PVC and made two mistakes. I did not take the gravel all the way up (we are on a slab) and instead topped it with 4 inches of dirt; and I did not use any perforated meshing near the top of the gravel. 20 years and several flash floods later, I dug up the drain tile in late 2011 to find it was not plugged; However, the gravel around the PVC pipe was nearly 100% plugged with dirt. Major problem. (TIP: A snaking camera was about $250 to rent. I decided instead to dig up a small section of drain tile to check for problems - and the camera would have told me the pipe was fine, misleading me).

So in very late Fall 2012 I just finished replacing the PVC I did 20 years ago, and in addition to bringing the gravel up to the top of the foundation, I used the mesh on top the gravel and covered with rubber mulch. Probably every five years I will pull up the mesh and replace it. Now remember, I have a steppe next to the side of my house. I felt that while my new drain tile solution was good and even better than my first attempt, it wasn't enough due to the intermittent water problems over the last 20 years. So at the base of the steppe, I put in what I'll call a dry well / french drain. It is part dry well because I had to place the pipe high in the drain gravel because I piggybacked the outlet tile above my house drain tile system (ran it on top of one leg). It wasn't an ideal solution, but a pretty good one (and I can, with much more involvement dig up and place the pipe lower in the drain / run in a different direction if I had to). So if we have a deluge (which we have had in the past) it will take a good bit of water in the french drain for it to be effective, but all that matters is that it kicks in at some point. Right now the french drain is concavely topped with mesh and a small, small amount of topsoil, but I plan to put some (hopefully decorative and "walkable") rock on it in the Spring. Water would largely shoot right over it if I just leveled topsoil over it.

I learned the number one thing to remember is that foundation coatings and the like help a bit, and the solution is to get the water away from the home. I don't know how effective my solutions will be for the long run, but lets just say we got some good effect from Hurricane Sandy in what was already a very rainy Fall - my calculations were ~2 ft. of water between mid-October and mid-November 2012 - and we were ok. I actually had the drain tile around the house placed in the trench but not covered yet during Sandy, and the water level did not rise above the 4" PVC pipe. I'm pretty sure the french drain did not "kick in" either, but that was covered so I couldn't tell - thinking about some dye packets to test with someday, maybe.

I posted all this because I spent many, many hours surfing the web looking for french drain information, and found a lot of misinformation / sales pitch web sites. This forum has a lot of good info in it. You still have people out there advising that the holes in PVC pipe go up, believe it or not. And water proofers don't want to hear their products are only marginally effective.

So sorry if this got a bit off topic, but I hope it helps somebody somewhere, as I spent a LOT of time thinking about my solution. Like a waterproofing guy said (I didn't know where to start so called foundation sealer people at first), "At least you have an option [with the french drain you are thinking about], there are people further down in the housing development that have no options when we get hit with that amount rain. They are the lowest point, and they have to deal with it".

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This is what I did on the north end up hill side of my house. Building code called for 10 foot space sloped 3 inches in the 10 foot away from the house with a French drain below the fondation. that is what was built. I wanted to put a car port up against the hosi in that 10 foot space that would have water draining off both sides.

I dug a ditch just the width of the drain pipe that has two rows of holes on the top. I lined the ditch with plastic and pressed the pipe down to the bottom. I back filled the sides enough to bring the plastic to the sides of the holes. then I filled the rest of the ditch with round rock, that I have been digging out of my garden soil, to the surface level. This catches all the water running off the car port and any water coming down the slope. The two drains come together in a Y at the west slope and continue at the 10 foot spacing that was installed but without the liner and uling the flexible drain pipe with the slits all around and still has the rocks on top to catch any downpour that might flood down the cart path that goes up to the woodshed. The soil under my rock garden seems to wick up most of the drain water but any overflow can join the water from roof drains in the rain garden.

So that is my design that has worked for 2 1/2 winters.
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Part of this discussion should be "What are you trying to accomplish).  Are you draining standing surface water (shallow trench) or trying to prevent water seeping into your basement (deep trench).  Are you looking at moving a lot of water (may need a bigger trench, maybe more than 1 pipe).  As has been noted, a french drain is a lot better at moving standing water and isn't really designed to capture running water.  A big enough french drain could, I guess, stop a stream or sheet wash from moving further downhill, but it captures more by seepage than acting like a big hole the water pours into.  It might  be better to do some earthmoving.

The bottom of our back yard used to be unusable for weeks due to big puddles of standing water (lots of clay in the soil).  I dug a trench 1 shovel deep and 1 shovel wide running to our pond.  At the high end of the yard I had to dig deeper to keep the trench level or slanting slightly towards my pond (the yard slopes slightly away from the pond).  I bought some 1 1/2 inch (maybe 2 inch) pvc and drilled holes in it, and laid it in the trench on top of permeable landscaping cloth and poured gravel over  the mix, folded over the cloth and then finished covering everything with more gravel.  

All I was looking for was getting rid of the standing water.  Therefor I dug a shallow trench.  This small trench, a hundred feet long, took my son and I about 4 hours to complete with a couple of shovels and a wheelbarrow.  It has drained my yard very well for the last several years.  (May take a few hours to drain after a heavy rain, but I don't really know, I don't go down there then, everything's wet then anyway).  Since my drain is shallow I think the water ends up only about 4 to 6 inches below the surface.  I'm happy with that.

In my opinion the dirt covering the drain is mainly for cosmetics.  I didn't cap the drain with dirt because I wasn't sure how well it would drain and wanted to drain as quickly as possible.  Because it's so small, over the years the grass has kind of grown out sideways, so now it's hard to see the drain anyway.

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Years ago during a property inspection prior to purchasing a home, I was informed a french drain would have to be installed due to a small depression in the center of the 1/2 acre property.  Had that done by a professional.  Though on a slight hill, the house was barely above street level and the french drain did not function well, but code was satisfied.  Ha.

Not wanting a pool of mud or water in that particular area, and after watching trails of water travel through the yard during a downpour, I gathered sticks and put them along those paths.  

The next day I tinkered with a shovel and water hose.  Etched a small trench toward what was pretending to be a drainage ditch.  My sons and I cleared years of accumulated muck.  Then made a few small trenches about a foot deep and a foot wide along the stick paths laid during the aforementioned downpour, leading into the slightly wider first trench.  The soil was rather clayey, so I dragged a spade shovel up and down the bottom of each until they were solid gray along the bottoms and the lower part of the sides.  When I walked on the clay it was slippery so I called it 'done for now'.

Filled the trenches with 1" to 1 1/2" river rock slightly hilled about an inch above the ground, then added pebble sized river rock across the tops.  

Tested it with the hose.  Seemed ok.  The next downpour flowed nicely through the trenches into the cleared drainage ditch.

Later I added variegated lamium sprigs in the shady areas and creeping phlox in sunnier areas along the sides of the trenches.  The next year water still flowed well.  The rocks were low enough I mowed a little high over the lamium (potentially troublesome but lovely) and phlox to keep growth checked and the rock trenches clear.  I kind of helped the natural water waterways into a random shape of sorts.  At least the master gardener next door thought it was not an eyesore.

I asked a local builder why the french drain didn't work well.  He said the soil was dense with clay and water was forced to flow between and around it - path of least resistance - and that a couple more french drains might have kept that depression emptied during a heavy rain, however french drains were not ideal for that particular circumstance.  He added that open trenches were oftentimes more practical but most people don't want open trenches topped with rock in their yards.  He was surprised to see them in my yard.  Then I explained the experiment.

He also said moving a french drain is twice the cost of putting one in and that I had, in his opinion, been ill advised AND the so called professional who installed that single french drain in a mostly clay soil should have known better.

Not being an expert on the topic, I can only offer this personal experience.

It occurred while writing this, that nature leads best.  And nature doesn't have plastic holey pipes.  Going forward, I would avoid building where water wants to naturally gather in such a way as to affect the stability of an important structure.
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Location: Eastern Tennessee
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paul wheaton wrote:

Here are two pictures I just made up that attempt to express what is in my head.

Okay, not sure if I am replying to this correctly - I get lost in the intricacies  of html.....

What I'm replying about is the images you put here Paul - I was referred to this thread from another thread - my purpose being the planning of building my own home. It's on a hillside that is kinda steep, but not horribly so. We average 4" of rain per month (more or less depending on season) and I want something that will last without being soggy-fied.

So far this whole conversation has been pretty confusing - do it this way, no THIS way, and your way is wrong, my way is right, they work this way, but also that way.......

Your images here finally stuck in my head as a plausible explanation of what works and why. Light bulb moment, ding ding ding!

I love your images, Paul, and hope you continue using them to describe what's going on in your head. They really speak to me (most of the time).
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