french drain pipe - not for water from above?

I must be an ignorant boob.

In the last six months, whenever there is an excess of water, the first solution that appears to come to everybody's mind is to put in a french drain. 

For those that don't know what that is, you dig a trench, put in some river rock, put in a pipe full of holes, more river rock, then a layer of soil fabric then fill the trench with soil.  The pipe needs to have a slight downhill slope for the water to run out.

But here is my concern. The pipe has holes in it.  It's as if you have a leak in your boat, so you drill a hole in the bottom to let the water out. 

Further, the pipe doesn't have many holes in it - so it seems like some water that wants to get in the pipe might not find its way in. 

So, I'm now getting a bit obsessed with asking this question ...

I have made two pics.  One, is the french drain.  The pipe (the circle in the pic) has lots of holes in it.  I'll assume that you can line up the holes in such a way that you have zero holes along the very bottom edge.  I tried to make little holes in blue.  The black line in the pic shows soil fabric (water can go through, but soil and roots should not be able to).  It seems that if there is a lot of water, it should take most of the water out.  But if there is a little water, it will take hardly any out.

In the next pic, there is my idea for an alternative.  There is just a slice of solid pipe at the bottom.  The blue line is an optional layer of sheet plastic (visqueen or the like).  Let's start by assuming that there is no sheet plastic and that the soil fabric goes all the down to wrap the underside of the pipe.  I suspect that in a situation with a lot of water, it will probably do just as well as the french drain.  And if there is a little water, it would do way better than the french drain. 

But since this is not the way things are currently done (that I'm aware of) I kinda figure that my idea is stupid and I just don't yet understand why. 

So, maybe somebody can tell me why?

The 2nd picture (and the 1st, to a degree) looks like a dry creek bed underground.  The typical french drain would move water faster (not having to go through rock).

I like the addition of the fabric around the rocks making a "virtual tube" that is at least dirtless and rootless.  I think the typical french drain would work a lot like your paul drain for small amounts of water:  it would be handled primarly via the rock path.

I'm not quite sure I understand the need for the solid pipe bottom to the paul drain though.  I wouldn't have a problem with an open bottom, or even holes on the bottom of the french drain tube.  If water wants to go down, go ahead.  If it doesn't soak in, it'll go further down the tube.  If you're worried about a high water table, nothing's going to help save a pump...

And of course I speak not from any expertise in french drains... just physics.

I've been corrected.  Apparently this picture is a more accurate representation of a french drain:

I guess it does help to discuss what is the problem being solved.

In the last six months, I guess the things where I've thought a french drain is possibly not the best solution: 

1)  People thinking about french drains around underground structures.  I think the real solution is to shape the earth around the structure to properly deal with this.  But some people seem intent on french drains.  In which case, it would seem that you would want to remove nearly all of the water - not just most of the water.  And the fact that the french drain has holes in the bottom of the pipe seems to me to make it so that a little bit of water is still going to end up in the ground.

2)  Existing structures that are getting flooded during heavy rains.  Again, I think the land should be reshaped instead.

3)  Earthen pond dams on steep slopes.  The idea is that the french drain would help to insure that the dam would stay dry on the inside rather than turning to a squishy mud and failing.  I have to admit that I have all sorts of concerns and questions around this one. 

I guess I keep hearing lots and lots of people suggesting french drains for lots of stuff and I keep thinking that they are expensive and ... well ... why wouldn't this "paul drain" work better (even though it would still be expensive).

So here is part of my concern.  The drain pipe doesn't have a lot of holes.  The holes are about a quarter of an inch in size (sometimes a little bigger) and about every 4 to 6 inches.  So as you travel the pipe, there will be about 4 inches of pipe that has no holes.  And when water encounters that section of pipe, I kind think it does something like this:

Now I've learned that the holes for a french drain pipe have to be on the bottom. 

And here is my concern on that:  If I do manage to get water into the pipe, I want to get the water out of the area.  But with holes in the bottom, it just seems like I'm gonna end up with the water going right back into the area where I don't want it.

As an example ....

Folks seem to want to put a french drain in uphill of a shed to keep the water from flooding the shed.

I think a better example would be to make a bit of a swale/ditch around the shed and divert the water that way.

a french drain could be thought of as an underground swale. but you don't have the problems of securing the soil, fencing through a valley etc.... and the water can move faster without damaging things. the holes go on the bottom so that as the trench fills with water a fast path out is provided. if there is so little water that it is leaking back out those little holes then it is not  a moment when the french drain is needed and regular percolation into the soil will suffice. does that make sense? it is not there to carry away ALL the water just any excess.

french drain I put in for my parents.

All I know about French drains I learned in Brad Lancaster's book Rainwater Harvesting for Drylands series.

I can't see any reason AT ALL for use of a French drain on the high side of a structure, unless (possibly) the drain is carefully lined with a heavy plastic or something, so the water can't permeate into the soil and damage the building foundation.  I can't think what they're called, but I read about a better type of drain for that use.

Paul, what is the large dark brown thing that is sitting on the top of the drain.  Is that supposed to be soil?  I've never heard of soil being put on top of a French drain, as it's begging for trouble.

The way I understand French drains are used is mainly to collect water that would ordinarily pool in an inappropriate place.  For instance, if your neighbor's yard is slightly higher than yours, and the water falling on his property flows onto your driveway and lawn. 

Permaculturally speaking, in this case you would probably want the water to percolate into the soil, with any excess flowing into a holding area where it could soak into the soil at a pace the soil could accept. As a last resort, it could be diverted to the street gutter.  What you DON'T want is soil to move with the water.

You would probably need to line the trench with landscaping fabric and design it so any loose soil wouldn't have access to the trench.  Having a very low groundcover planted right alongside the drain might filter the water well enough.  Any soil entering the drain would eventually fill the drain and clog it.  The top of the trench is leveled with rock so it can be walked on.

Maybe I'm all wrong with this.

Sue

I think that generally you are right sue, a french drain is for pooling water but I can see where it can help divert water that is perking down a hill.  often a foundation wall such as the idea suggested will have gravel all the way up from the bottom to the top with a french drain pipe at the bottom and moisture proof barrier against the wall. we looked at a home that was partially built into a hill and had water problems, and this was the suggested fix for it. right or wrong it was being referred to as a french drain also.

My impression is that a french drain is an attempt to keep the water table from rising above the ground. 

So once the water table gets so high that it touches the inside of the pipe, the pipe begins to move all of that water right on out of the area. 

I guess you could look at it that way. its more sensical. as the water percolates in and raises the water table it flows out. I know it worked well for one of my parents standing water problem.

In areas of high rainfall and heavy soil saturation, it would need someplace lower to drain to, and I can visualize that being a problem in some places.  My sister bought a place in a hole. Unless she had a lower spot dug as a retention pond (or whatever they call them here), there would be no place for the water to drain if the soil couldn't absorb it fast enough.

In areas of drought, with just occasional, relatively short periods of heavy rainfall, I can see them being extremely useful for catching surface flow and allowing the water to percolate into the water table.

Sue

we created a slight fall in the pipe and had an outlet at the ditch. a dry well is also an excellent idea if you just want to give it more time to drain without creating a standing puddle. that is just a hole lined with weed barrier and filled with rock.

We're putting in some French drains on the property where we live this summer. 
It's to divert surface groundwater away from buildings and sodden soil, to reverse an ongoing problem of basement flooding. (The area has been heavily developed, both uphill and down, since the owner's family originally moved here in the 1950's; and some of the natural creek beds have been backfilled.)

Reasons we don't want a swale instead:
1) We are already creating a 0.4 acre wetland on the property, which the drains will feed.  We don't need more swale habitat.
2) We use the space: there are paths along and across the intended drainage lines, and we also have yard parties in summer.  We want to be able to walk there, and walking in a ditch is not good for you or the ditch. 
3) In some areas, the clearance between buildings and retaining-walls is too narrow. Even if we were willing to give up the option of walking around the building, a deep-enough swale with properly sloped sides would destabilize one or the other foundation.
3) We don't want the kind of soil erosion that a deep, narrow ditch would create.

French drains are essentially a way to create tiny, deep ditches wherever you need them, and then stabilize them with mesh and gravel so the sides don't slump down and fill them up.

The pipe is not to "catch" the water.  It's to create a space where the water can flow freely.  Like a tunnel, culvert, or bridge.  It holds the gravel up out of the way and makes an easy path for the water.

If you don't have a pipe, the gravel still allows water to flow out as long as your grades are right, but it can't move as much water as quickly.  Your "Paul" drain would probably work; just not as well as the conventional drain.

Problems I've heard about with French drains include:
1) using impermeable fabrics or plastic instead of proper mesh cloth (careless contractors in a hurry to pass inspection; these "drains" don't work AT ALL.)

2) wrapping the entire structure instead of leaving a gap/overlap for water to leak in (even permeable cloth can clog over time with the particles it traps.)

3) failure to cover the gravel bed and prevent soil from filtering down and filling in the gaps in the gravel.

4) putting the pipes in upside-down (with holes at the top instead of the bottom), so that soil falls in, blocks the holes and/or the pipe.

If you really want to see how this works, find some folks with existing French drains, ask how they did it, and visit their land now (while it's still wet) to see how it's working.

French drains don't last forever, though Ernie says the Romans made some similar field drains that worked pretty well for centuries.  (They capped them with flagstone, not cloth.) 
French drains do allow you to adjust the drainage of a property, without creating ankle-twisting holes or gullies, and with minimal erosion.

Yes, you do want groundwater to percolate down. 
Impermeable surfaces prevent groundwater from replenishing soil reserves and aquifers, and contribute to surface water problems like we're having here. 
Percolated groundwater is not as much of an erosive force as surface water.

French drains are not designed to prevent saturated subsoils and landslides; if that's your problem you need engineered solutions, or a better choice of building site. 

French drains are designed to move surface water in desirable directions, mitigate erosive effects of surface groundwater, and drain soggy surface soils that hinder activities like gardening, farming, or yard play.

Just a little tip.  The recommended slope for drainage pipe and septic too is 1/4 inch per foot.  If you cap the end of the pipe with a screen or porous cap made for it that will keep the rodents from going up the pipe ands clogging it with a nest and debris.
  1 inch to 1.5 inch stone is the recommended size for the stone.  Washed stone is best and the 1" stone is the easiest to move with a rake or shovel.

French drains really can be anything that allows water to move.  A log underground can achieve this although the water will move slowly along the log.  The same thing occurs with underground piping, water moves along the pipe until it is inhibited from moving for whatever reason (change in grade, etc.).
In the Kittitas County area where ground water is a problem, french drains are used to divert water from around drain fields for septic systems and they work very well in diverting the water so the system can function.  I don't know if that is allowed over there any more or not, but it did work well, the drain is installed below the leach field grade by a couple of feet to drain that area sufficiently. 
Since water will move on a flat surface if it has somewhere to go, your french drain can be flat, and, so long as there is an outlet, it will allow water to move to where you want it to go.  Any rock that has no fines in it will work well for moving water, obviously, the larger the rock, the faster the water will move through it.  Some sort of geofabric does work well in keeping fines from accumulating in the rock and clogging the system, typically the bottom and sides of the ditch are draped with fabric, the rock added, and then the fabric is draped over the top of the rock and topsoil or other material is placed on that.
French drains work well to prevent build up against retaining walls of water and pressure from the soils themselves.  Most retaining walls I have built had pea gravel (about 1/4 inch size rock) placed against the wall, (about 18 inches deep) which kept the soils from loading up against it and pushing the wall out. Water would thereby also drain down to the bottom of the footing where it would collect in the pipe system much like is shown in Paul's picture.  The pipe merely acts as a hole in the rock to allow the water to move faster to an outlet.  In the case of footings or a retaining wall built without footings, this helps to prevent saturation of the soils under the concrete or rock structure, which could result in the soils washing out from under the structure and cause cracks or a failure of the structure.
In my opinion, any structure built that has any components underground should have some sort of french drain to carry of any water that could collect at the bottom of it.
It takes a long time for soils to migrate very far into a french drain, but it does happen.
In the "old days" we used to use newspaper around the pipe and no rock at all in some drain fields.  This allowed the effluent to eventually leach out of the pipe, but kept the dirt from entering into the pipe until the ground on the top and side of the pipe had packed sufficiently so that it would not enter into the pipe, after the newspaper had deteriorated. 
You could use straw or similar material for a filtering layer to keep out soils also, although generally it only works well on the top of the drain.

French drains are mostly for diverting and catching underground water.  The only way for them to be effective for diverting surface water is to bring the crushed stone right to the surface and not bury it.  In this scenario the system works to catch underground water and surface water.

FYI.  The stone carries most of the water.  The pipe is there just to catch water in extreme events when the water table rises up to the level of the pipe.  That's why the holes are on the bottom.  That way the crap doesn't get into the pipe from above.  Just the water.  The ditch and the pipe need to slope 1/4" per foot and there should be a minimum of 6" of crushed stone under the pipe and that much over it and around it too.  1' is better but most people skimp on the stone to save money... at their peril down the road.

French drains are also used underground to divert water found there.  I have used them many times for this, especially in the Kittitas county area I mentioned.  They can be buried, a footing drain is nothing more than a french drain, and they are buried at the bottom of a footing.
I agree with you that in order to divert surface water they need to somehow be designed to intercept the water as it moves along the surface of the ground.  A catch basin of any type can do this just as well as constructing it so that the drain itself does the intercepting, however, in that instance, the drain is subject to clogging from the movement of surface debris.  A catch basin of some sort allows for silt and other debris to settle out below the drain, or pipe that leads into the drain, if someone designed it that way, so that infiltration does not incur.

As I said, even a log can act as a french drain, it conducts water along its surface even underground.  Of course, it is not very efficient and I only used it as an example of how most anything can be used as a french drain.

The pipe is better located at the bottom of the ditch so that it provides a better conduit for the water to move.  The rock does indeed carry water but the pipe provides a better conduit for water movement.  Footing drains require that the pipe be located at the bottom of the footing trench for this reason.  There is really no reason to locate the pipe in the higher areas of the trench, it would be useless unless the trench filled with water to that point and so would be pretty much pointless.

I have seen and used a variety of stone that works well.  Yes, larger stone does drain better, but pea gravel, crushed rock with no fines, and similar material all work fine.

We used to use 3/4 inch drain rock for septic leach fields, but infiltrators are pretty much the norm around here now. 

French drains come in a variety of configurations that can be modified to suit the needs and almost any situation that requires some sort of drainage.  In over 30 years of working in the excavation industry I have seen many, many different uses for this type of drain.

It really doesn't matter, this is one of those things that can be built to suit the need and does not have to conform to any one design.

We built our house on a slope and we've used French drains to take away the water falling towards the house to our ponds. We often get flash floods here and as dirtworks says, the black pipes are there in the extreme case where the water's flowing really fast.


We used large round river stones because the water runs through them easily and covered them with a geo-textile to keep out smaller stones and dirt to keep the drains working efficiently.


The main house pond always has water and the house is bone dry. This new pond from the water in front of the extension hasn't been empty since we dug the drains.


After the geo-textile has covered the stones they're weighed down by more smaller stones and the drain is invisible. This part of our roof has no gutter which allowed us to finish it in the traditional French style "genoise" and the water runs down into the drain. The larger back roofs are fed into water collectors.

having run thousands of feet of french drain on this property and having it work beautifully, all i can say is it works well for out situation..which is very wet land in the spring and fall and very dry land in late summer.

when our son's house went in we put french drain all around his basement..it takes the water away to another system of french drains that are under the back yard..these run "across" the grade at intervals ..and pick up the water that is running down hill and drains it off into a ditch area..thus stops all the flooding of the property..these drains come together with a Y where needed to channel the water to the ditch...we don't want ALL the water to run off..as the soil needs some water..but it runs off the excess "running" water that would cause flooding and overflow..

there is a pond at the bottom of the slop..and the rest of the excess water collects into the pond..however..the pond is not large enough to hold all of the excess water we get on the property, esp in the spring.

the pond is 140 x 75 ' and the shallower parts go dry about the end of July or the first part of August in most years..the deeper parts never go dry.

however the ditch is nearly always running some type of water away from the property to the marshes in the rear..they never really ever go dry completey.

if it wasn't for the french drains ..and the pond..a large part of our property would be uninhabitable..but do we want all the water to drain..of course not..just the over abundance.

This picture illustrates the function of a french drain in a slight rain. You can see there is a little bit of surface water and it has soaked into the soil some. There is also a little bit in the french drain itself but not in the pipe because there isn't enough water to have risen to that point. The gray is the gravel that surrounds the pipe within the french drain.

This illustrates the function of a french drain in a moderate rain. Notice the further saturation of soil and there is more surface water. As a result there is water that would naturally be in the french drain due to rainfall and then additional water that is there from rain that has flowed there from the surrounding area. Also note that even in this scenario there isn't any water in the drain pipe itself. The water is strictly located in the gravel area and it flows through the gravel to a point of lower elevation.

Yes! 

Pictures really do help!

And, yes, this is exactly my point.    90% of the time, the french drain does nothing.  The soil will still be freaky soggy and not a drop moves out of the french drain.    And this is great for a garden where the mission is to have the soil be soggy, but not flooded.  But next to a house, the mission is .....  different:  soggy is better than flooded, and slightly damp is better than soggy, and bone dry is better than slightly damp.  In fact, if it can be bone dry all the time, that would be optimal.

This illustration shows what happens in a heavy rain involving a french drain. Notice the severe saturation of soil and as a result more severe puddling of water on the surface. What happens to that water? A lot of it flows into the french drain where it travels through the gravel. However, it has now reached the point that it can flow through the pipe as well. The holes on the bottom allow water to seep up into the perforated pipe and because it is empty on the inside it allows a more rapid removal of water rather than through all of the stone. The red area shows where the water is able to move faster on the inside of the pipe because of least resistance.

And in what situation will it be bone dry? Do you plan to live where it doesn't rain? Or do you plan to cover your entire area and keep all water from falling on your ground?

These are quotes taken from an off-topic discussion in the thread titled "Wofati Eco Building".

Paul Wheaton:
"What is your source?  I just googled a chunck of what you say and google could not find anything."

My definition was my own that took me 30 seconds to type up. If you want a different definition then you can use wikipedia. If you don't care for wikipedia then you can do some research on your own and find similar definitions.

http://en.wikipedia.org/wiki/French_drain

From wikipedia: "A French drain, drain tile, perimeter drain or land drain is a ditch covered with gravel or rock that redirects surface and ground water away from an area. A French drain can have hollow pipes along the bottom to quickly vent water that seeps down through the upper gravel or rock. French drains are common drainage systems, primarily used to prevent ground and surface water from penetrating or damaging building foundations."

It states in there that in addition to "surface" water it also deals with "ground" water. They are referring to ground water that has come from above and not necessarily from below. If you have ground water coming from below(the water table) then you more than likely are in a low spot and can not send the french drain anywhere else since water can't flow uphill.



Paul Wheaton:
"The design of the french drain is designed to work only when there is sufficient puddling.  And it does not create puddling - in fact, it's mission is to allow water from above to pass through - hence the holes in the bottom.  "

I think that this might be the source of your confusion. You seem to think that the main component of a french drain is the pipe. It seems that you think the pipe IS the french drain. You can have just a trench of crushed stone and THAT would be a french drain. The pipe merely helps in high volume situations when you need to move the water away quickly. The crushed stone allows water to flow through but it is relatively resistant to water flow compared to an open pipe.

I skipped your analogy of someone pouring a 500 gallons of water on a french drain pipe "in the open" because it wasn't very applicable since that isn't the purpose of a french drain pipe.

Now we're cookin!

The red area shows where the water is able to move faster on the inside of the pipe because of least resistance.

Yes!  During a severe event, the water will puddle under the french drain pipe.  Eventually, the puddle will get so deep that it will reach the pipe (deep puddle is like the water table coming up higher - which, in a way, it is) and then the water starts to move out.

And in what situation will it be bone dry?

That's my point.  With a french drain, the idea is to remove water only during severe events - and then, only when the subsoil is so water logged that it starts to puddle inside the french drain trench.

So if you wish to have things closer to the bone-dry side year round, a french drain is not a good choice.    Imagine for a moment a steep hill and your structure is at the tippy top of that steep hill - all sides of the structure go downhill.  So in any kind of rain event, how wet is the sub soil around the structure?    I want to say "pretty damn dry".

Of course, it is rare to have that situation, but we can try to create something that is closer to that situation.  We can build a packed trench around our structure with a gentle grade drop that will take any water away from the structure and downhill.  Still not perfect, but far better than the french drain solution. 

I'm going to pontificate that a french drain might take away 10% to 20% of the water throughout the year, and for 20 days of the year, the subsoil surrounding the structure is 90% or more saturated. 

With the packed trench, it takes away 30% to 40% of the water and the subsoil surrounding the structure is never more than 90% saturated.

But this is just what my brain tells me based on my understanding of these things at this time.  There can be all sorts of circumstances that can monkey with these thoughts.

I think that this might be the source of your confusion.

Again, I'm flattered that you want to talk about me, and how addled my brain is.  But when you switch the conversation to me, it makes me think that your position is terribly weak.

Perhaps what you really intend to talk about is your position.

You seem to think that the main component of a french drain is the pipe. It seems that you think the pipe IS the french drain. You can have just a trench of crushed stone and THAT would be a french drain. The pipe merely helps in high volume situations when you need to move the water away quickly.

I can tell you that what I think is the same as what you appear to think in this regard:  you can make a french drain without the pipe, but few people do.

Take a look at the "paul drain" at the top of this thread.  That will take far more surface water away than a french drain.  And you could put a french drain pipe in that if you wanted to.

paul wheaton wrote:
We can build a packed trench around our structure with a gentle grade drop that will take any water away from the structure and downhill.  Still not perfect, but far better than the french drain solution. 

I'm going to pontificate that a french drain might take away 10% to 20% of the water throughout the year, and for 20 days of the year, the subsoil surrounding the structure is 90% or more saturated. 

With the packed trench, it takes away 30% to 40% of the water and the subsoil surrounding the structure is never more than 90% saturated.

But this is just what my brain tells me based on my understanding of these things at this time.  There can be all sorts of circumstances that can monkey with these thoughts.

Again, I'm flattered that you want to talk about me, and how addled my brain is.  But when you switch the conversation to me, it makes me think that your position is terribly weak.

Perhaps what you really intend to talk about is your position.

I can tell you that what I think is the same as what you appear to think in this regard:  you can make a french drain without the pipe, but few people do.

Take a look at the "paul drain" at the top of this thread.  That will take far more surface water away than a french drain.  And you could put a french drain pipe in that if you wanted to.

Can you send me some links to where you are getting your percentages?

Actually, what you have described as a "paul drain" is actually a french drain just without a pipe. And your "paul drain" wouldn't take away far more surface rain than a french drain would. Your diagram is pretty much exactly what I would draw of a pipeless french drain. This form of french drain has more internal resistance to water flow because it doesn't have a pipe and thus it can't remove as much surface water.

Also, your ground is going to become 90% saturated with water regardless of the fact that you have a "paul drain"(aka pipeless french drain) or a piped french drain. Rain will fall on your ground and it will soak into the soil and thus saturate it. The only way to prevent this is to cover the area and prevent water from falling on it completely and to provide a way for water to flow around that area if you have drainage issues like that(a french drain would work well here).

Also, I believe that I am not going after you. I am going after your mis conceptualizations of water flow. If it comes across as an attack against you then I am sorry. That is not my intent.

How many "paul drains" have you made? Have you compared their feasability against a french drain in side by side comparison? In fact, how many french drains have you made? I haven't made terribly many compared to some people but I have probably done at least a dozen ranging in length from 10 to 60 feet in length. I have used a pipeless french drain("paul drain") and it works fine. In fact, it worked just as good as a french drain but that's because I didn't need a piped french drain in that situation. I needed a controlled way to move some surface water away from a site but the volume of water wasn't that great so the pipe wasn't needed.

Can you send me some links to where you are getting your percentages?

Please take a very close look at what I said.  It started with the qualification "I'm going to pontificate ..." - therefore, these percentages are what is commonly known as "pulling numbers out of your ass."

Actually, what you have described as a "paul drain" is actually a french drain just without a pipe.

Actually, it is actually, not.  Actually.  To actually be a french drain, it would actually need to let water actually bleed out the actual bottom.  Actually.  The "paul drain" is actually lined with impermeable plastic and a section of impermeable pipe.  Actually.

I'm using the word "actually" in a feeble attempt to out-actually your "actually" statement.  Ta da!  I win!

Also, your ground is going to become 90% saturated with water regardless of the fact that you have a "paul drain"

For water coming from above, the paul drain is gonna kick ass over the french drain at moving more water out of the area.  But for water coming from below, the paul drain is loaded with serious problems.  And for areas where you want some moisture, but not too much, the paul drain is stupid. 

But if your mission is get as close to bone dry as you can,  the paul drain comes in second place to the shaping the land around the structure, including the packed trench concept.

Also, I believe that I am not going after you. I am going after your mis conceptualizations of water flow. If it comes across as an attack against you then I am sorry. That is not my intent.

I appreciate that you mean well.  At the same time, I hope to gently guide you away from talking about me and focus on the issues.  Mostly because I think this works well for all of these forums:  to talk about the issues and not the participants.  To never suggest that anybody on this site is less than perfect.  That way, we can all have excellent conversations without people feeling .... icky. 

So, when you say "your confusion" or "your mis conceptualizations", then you are suggesting that I may be confused or that my conceptualizations may be a bit off.  For me, I am happy to admit that this is, indeed, the case.  At the same time, I know that other people might read it and decide that won't be comfortable participating here because someone might take the time to point out that they are less than perfect.  So we have less of a community. 

Therefore, if a person suggests that another person here is less than perfect, it seems that I would be wise to delete that.  And then the person who posted that would be mad at me for deleting it.  So mad, that they might move on and not share any more.

I rather like the idea that you stick around and everybody loves the things that you say and I never have to bother deleting your stuff.  Easy on me.  Easy on others.  And others are happy to share too. 

Hearts, flowers and rainbows. 

This is certainly a bit awkward to try to convey and I hope you will respond with something like "I see where you are coming from, and I hope to follow the path that you suggest." and as frosting on the cake "I like these forums and I hope to be around a long time." 

And then I'll feel like an excellent community steward! 

How many "paul drains" have you made?

Zero.  I cannot think of a case where they would be wise. 

In fact, how many french drains have you made?

I dunno .... six?

I needed a controlled way to move some surface water away from a site but the volume of water wasn't that great so the pipe wasn't needed.

French drains have other problems.  The wikipedia page talks about those. 

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

I have never made a french drain without tamping the bottom. That's part of the process.


EDIT: Actually, i didn't tamp a couple of times on one site. That's because the clay subsoil was such that tamping wouldn't have improved anything.

Also, unless you use some sort of impermeable clay you are still going to have just as much infiltration from your "packed trench" as you would from a paul/french drain. Plus, you still have the issue of the surrounding soil being soak naturally from the rain.


Quote
How many "paul drains" have you made?

"Zero.  I cannot think of a case where they would be wise.  "

Then why are you espousing the benefits of a paul/french drain and trying to prove that a french drain is useless? If that's not your case then that is what it appears from reading these posts.

This would be a more accurate representation of a packed trench if it didn't have an impermeable layer. Even then, if you have plants growing on it their roots would eventually pierce the impermeable layer unless that layer was something like concrete etc.

Kabir424 wrote:

Quote
How many "paul drains" have you made?

"Zero.  I cannot think of a case where they would be wise.  "

Then why are you espousing the benefits of a paul/french drain and trying to prove that a french drain is useless? If that's not your case then that is what it appears from reading these posts.

Well, first of all, I am not trying to prove that a french drain is useless.  I am trying to express my opinion that when your desire is to have things as bone dry as you can get, a french drain is not as good as a packed trench (which can be a shallow trench).

A french drain is excellent for areas where you like moisture, but you don't want too much moisture.

paul wheaton wrote:
So here is part of my concern.  The drain pipe doesn't have a lot of holes.  The holes are about a quarter of an inch in size (sometimes a little bigger) and about every 4 to 6 inches.  So as you travel the pipe, there will be about 4 inches of pipe that has no holes.  And when water encounters that section of pipe, I kind think it does something like this:

In the example above, we need to have a 3-D vision of what is happening. If your hypothetical drop of water hits the pipe where it is solid, it might flow down and around like you show. But since water is flowing into the pipe via holes not shown, it might flow 1/2" or 2" along the pipe into another hole. Gravity is still important, but the pressure gradient and flow of water is not straight down when such a pipe is in place.  The flow is different in soil than in air - there is much more adhesion/cohesion and potential for lateral movement towards the drain holes.

Also, it may not matter that there are holes in the bottom of the pipe - equally or more important is the slope of the pipe and the water content of the soil.  When the soil is wet, downward flow in the soil is rather slow compared to lateral movement in the pipe.... the french drain will effectively remove water.  If the soil is not above field capacity, then little water is moving downwards.  The holes in the bottom of the pipe will quickly saturate the soil below the pipe when there is water flowing, and this reduces loss of water out of the pipe.

I think a key point to all of the math is:  less than 1% of the surface is holes.  Therefore, if water is poured all over the pipe, then no more than 1% can get in that way.  Further, the holes are aligned perfectly with the bottom.  So 100% of the water that makes it into the pipe is very likely to get out of the pipe. 

Unless!  The water level in the trench that the pipe is in is higher than the bottom of the pipe.

the french drain will effectively remove water.

.... when there is so much water that it can start to puddle in the french drain. 

If the subsoil below or around the french drain can absorb the water, it will do that first.  Only when that is saturated, and the water begins to puddle in the french drain trench, does the french drain start to remove water.  And pipe doesn't come into play at all until the puddling reaches the bottom of the pipe.

(I think I am saying what you said, in different words - correct me if I'm wrong)

You are exactly right. And the same is true for your packed trench or for your paul/french drain. It's just that the french drain with a pipe can handle greater loads of water than either of those in a more controlled fashion(with the exception, in certain situations, of a well built packed trench with good vegetation). But, with that same packed trench you would actually have more water infiltration because of the fact that the plants would create lots and lots of little holes in your packed trench for water to infiltrate down. The french drain does not have this vegetation and thus is superior.

Edit: Please look at my modification of your "packed trench" diagram, about 4 posts up, to show you where the water will infiltrate.

This thread is awesome!  We're talking with pictures!  So cool.

Okay, I'm looking at your enhancement of my packed trench drawing.  My opinion is that the amount of water that might be soaking in would be ten to twenty times less than the unpacked stuff off to the right.  If any. It really depends on the soil type and how well it is packed.

As for the "paul drain" vs. the "french drain":  I just wanna say that I think these are two rather different things.  A proper french drain will let water soak down, below the drain.  The "paul drain" is lined with plastic. 

And yet another obnoxious opinion from me:  If you are building a trench for a french drain, and you pack the bottom, you don't pack the sides.  Therefore, water can still seep to the edges - although it will be slower.  And clay soils will make a difference in that there will be a near zero soaking into the soils - although they are more likely to plug.

As for vegetation in the packed trench:  it depends on how well it is packed.  If you use a freaky big trac hoe with a little bucket to do the packing, I think hardly anything will be able to grow there and poke holes in it.  Further, the packed-ness will go mighty deep.

If you want any vegetation to grow there then you will have their little roots growing through your packed trench. If you don't want any vegetation growing there then you will be constantly fighting a losing battle of water erosion. You can't have both. Either way the packed drain fails as an impermeable form to transfer water.

The seeping from the edges of the drain would be negligible unless you have extremely permeable soil. If that is the case though then you have bigger problems than water seeping in.

If you want any vegetation to grow there then you will have their little roots growing through your packed trench. If you don't want any vegetation growing there then you will be constantly fighting a losing battle of water erosion. You can't have both.

Is that a challenge?

What if I put four inches of top soil on top of the packed stuff?