'Heavy Clay and the French Drain'...

More than just a catchy name for a new biligual R&B band celebrating Franco-American relations..... :-) ........ the excessive water in the yard around our animal shelters has me focused on that issue and wondering "What would YOU do?..."

Although our yard and our region in general is flatter than a pancake, we are fortunate enough to have a slow drop of about 6-8 ft across ~200 ft of yard.  As we are in a glacial lake bed south of the Canadian border, the heavy clay soil is several feet thick, so I'm not assuming our problems can be solved for decades into the future, but for several years until we vacate the property I'm hoping we can come up with some solutions.  I'm satisfied with the plans from YouTube sources for using a geotextile divider between the clay and some aggregate and gravel for the walk spaces, but it's the drainage I'm still stuck on.  I hope to use some version of the image below to trench the problem areas with the backhoe, but also have become convinced NOT to not wrap the pipe with porous geotextile fabric since the clay silt will clog the fabric pronto.  But in that light, should I not even line the trench with geotextile in any way?  

Our worst time for battling the mud is spring, when frost is still coming out of the ground and all of that clay is holding into the water near the surface.  But even in mid-summer a heavy rain can take many days to dry out and the water moves slowly.  I'm prepared to go up in cost a bit to use 8" or possibly even 12" culverting into which I manually drill the drain holes on one side in order to mimic the typical perforated drainage pipe....would that help at all assuming that it will be surrounded by coarse aggregate?  Or will the larger diameter not make enough difference in flow rate and system longevity to justify the added expense?  Thanks for stories, examples, suggestions and opinions.

Photo source:  https://waterprotoronto.ca/wp-content/uploads/2021/08/french-drain-toronto-850x500.jpg

Our property where our daughter lives has a problem when it rains because all the water runs downhill on a gentle slope and stops on my neighbor's property.  This starts about ten houses before ours.

I don't know what the neighbor did when my property was a vacant lot and he didn't have anyone to yell at.

We fixed the problem by creating a ditch along the driveway so some of the water flowed into the ditch.

Where water came off the house we did french drains without any landscape fabric, just rock top and bottom.

It would look similar to the picture you posted except not as deep and the rock is level with the ground since that is part of our driveway, like a parking area.

Since it nearly flat you should be able to direct the water around any places you don't want it.  No French drain needed.  

On roads long low directional water chanel's are called a roll out. Only 6" high maybe 20' across.

Here's a presentation by Brad Lancaster. Rollout is at 11:00 minute mark.
https://m.youtube.com/watch?v=D6_WZ789lpM

I recently learned in agriculture these are called a Mangum terrace.   Almost on contour wide 1% drop 6" tall ditch like a keyline water delivery trench but shallow.  Every 6' of fall.  It lets you direct water along the contour and still plow straight across the field.  

https://archive.org/details/mangumterraceini94cate/page/n3/mode/1up

Since it is clay direct it into a large bowl and keep the water as long as you can.  As you have noted I fear if you install a French drain in a year or 2 you will just have rocky strip across the yard when the clay fills in between the gravel.

Generally I think French drains are for subterranean water issues or where you don't have room for above ground control.    Tom

I love French drains. The one I am proudest of has made a huge difference in how wet my mother's yard and basement is in the spring and after a heavy rain. It's about 8' out from the house on one side, and 3' on the other side. 6' would be better, but it's at the edge of the property line.  

Design considerations:

1) Make sure the ground slopes towards the French drain ( sounds obvious, but it's a reminder.).
2) try to end it well beyond where you need it
3) Ideally put a bit of a slope in the drain towards where you want the water to go.


Do you need filter cloth?

Yes. You need geotextile between the native soil and the gravel - the cleaner the gravel you can get the better. Why?

Imagine a plastic bucket with a hole in the bottom. Fill the bottom with a few inches of clean, washed gravel, then a scoop of your native soil. Drag out your hose and fill the bucket. What colour is the water that comes out the hole in the bottom? Muddy, because the native soil washes in. Now put a layer of filter cloth in first. The water should run more or less clear. But in real life, in a frnehc drain, the mud that enters with the water never leaves, it just settles into the gravel, reducing permeability with every rainfall. So, unless you have the kind of soil that doesn't need a French drain, for longevity, line the trench with filter cloth.

You have two main options for design:
- Yes, the perforated pipe works well.
- So does digging a bigger hole and putting in more clean gravel, and no pipe.  

Personally, I tend to chose no plastic thingy that may break with holes that may clog, and just go with bigger hole and more gravel. If your space is more limited, the pipe makes more sense.

- I like to also cover the top of the drain with landscape fabric, and then put a few inches of mulch  or even soil or grass on top, making sure the drian is still a slight depression. This keeps soil from washing in to the gravel, increasing longevity, and, IMO looks better. You can do this under gravel driveways too.  It does make it slightly slower to begin working in the spring, but I have not seen this being an issue in our yard or in practice, the snow above the French drain tends to be the first spot to melt.

- You can put a filter sock around the drainage pipe - or not. If you use a less clean gravel or don't wrap the top of the gravel with filter cloth, it's probably a good idea. If you use a clean gravel and burrito wrap the landscape fabric around the gravel,  (purpose made geotextile intended for filtration is better!)  It might not be necessary. They make purpose made filter socks and those definitly shouldn't clog up and reduce flow.  I probably wouldn't use a thick layer of landscape fabric.


Anyway, sorry for how disjointed this is. But that's my experience with french drains.

Thanks for all responses so far.  With rain coming down and frost still in the ground, the situation is still acute.  As noted above, *most* of the problems will go away with the disappearance of the frost below ground, the change in the weather to late spring and early summer during which the trees and vegetation begin to transpire water more, and the drying effects of summer heat.  Nevertheless, the situation merits some serious landscaping with stone and drainage and I'm grateful for the responses.

Catie George, thanks for providing your experience and pointers with french drains in clay soil.  With the added photos below, hopefully the situation is better illustrated.  For sure we can provide the sloping and pits/trenching towards which the water can flow.  It's the way the clay holds on to water and prevents percolation that really is the problem (but of course is equally a benefit for growing our crops in moisture-deficient years).  I can see the advantage of using only the geotextile fabric to line the trench which then would be back-filled with coarse rock.  When compared to the same with a good sized perforated pipe running down the middle, however, would one silt-up more quickly than another?  Also, it would seem that we have to choose the barrier textile sheet carefully......too small a pore size and it will clog quickly, but too large a pore size and the clay silt will infiltrate the rock and clog the whole channel too early, thereby reducing the lifespan of the drain.  Thoughts or recommendations on this from anyone?  The high traffic areas in the photos below are slated for complete overhaul this summer....removal of topsoil, base cover with geotextile, then coarse rock and then finer gravel-sand mix with drain tiling below leading into the french drain trenches.  I realize many Permie situations have the opposite problem....that of trying to encourage water arrival and retention, but this just isn't one of those areas at this point and ultimately it will be interesting to see to what exent all of this solves the problem and for how long.  Thanks for continued input!.....

Oh that looks pleasant...

So I live in clay too. Right before I bought my place they put in a 250ft long, 2-4 foot deep french drain just like the one you outlined above and it failed completely the first season. Clay and "normal" french drains are incompatible, What I did in the interim was just trench down 4-6" on top of the drain, just down to the top of the aggregate, Like has been said above, it worked well but I can see that your situation is different. I had much more slope to work with.

Now for the good advice:

Sand! I found this reddit thread:  https://www.reddit.com/r/HomeImprovement/comments/85m7x2/has_anyone_installed_a_french_drain_in_clay_soil/

Basically use concrete sand instead of rock for the material of the drain. This fine sand won't let the silt in like rock will. Also mentioned is that landscape fabric is not the right stuff. This is literally the most practical thing I have learned on the internet.

Dan Fish wrote:Oh that looks pleasant...

So I live in clay too. Right before I bought my place they put in a 250ft long, 2-4 foot deep french drain just like the one you outlined above and it failed completely the first season. Clay and "normal" french drains are incompatible, What I did in the interim was just trench down 4-6" on top of the drain, just down to the top of the aggregate, Like has been said above, it worked well but I can see that your situation is different. I had much more slope to work with.

A good last post within this thread to provide an update.  Below is a photo from the same vantage point as my muddy photo #4 above.  But it's not really a fair comparison since we were in a drought year this summer whereas all photos in the OP were from spring melt.  But to echo Dan F's comments, we were only moderately successful at controlling or redirecting water in this heavy clay with the very shallow slopes available to us.  My best efforts (most arduous) yielded drainage only slightly better than the shallow depression used before.  That effort was a pretty solidly replicated 'burrito' of trench coated with rock at the bottom, then porous geotextile fabric onto which was laid drainpipe (6" diameter, perforated on underside). The trench/fabric/pipe then received more of a rock-sand mix after which the outer uncovered edges of fabric were laid over the top of the pipe.  More rock followed and then a bit of driveway composite (called class #5 here...used on the gravel roads in the region) to make it a bit smoother.  

The whole set up worked okay with a few storms that followed, but that drainage depression is surrounded on all sides by bare topsoil/clay (no grass, shrubs, landscaping) to hold back run-off of this sediment.  So within a few weeks and a new spring season, there was not much improvement to the saturation and mudiness of the yard.  Oddly, I'm not sure to what extent slope would necessarily help us here without a wholesale changeover to a much more porous surface of about 1-2 ft. thickness.  I suspect some of the farmyards locally that have had the equpment and budget have done this in the parking areas of their homesteads.  At any rate, that is our experience so far.  As an aside, the buidling off to the right was constructed on an elevated 4 ft compressed pile of the class #5 composite noted above.  Even with this height and composition, water *still* pools even here for about a day before finally percolating downward and providing a firm walking surface.

Hello John,

I read your posts via the Permies daily-ish email.
We too are on clay soil.

1. About the French drain; you say you put it with the holes downwards. I'd think it might work better with the holes up (and with geotextile on top, filtering away any soil particles), allowing the water to seep into the drain and flow away on the 'floor' of the drain? I haven't tried it, nor do I have any theoretical knowledge about correct use of it, it's just what pops into my mind now.

2. We thought about putting in a French drain, but I was lucky to have a conversation about the here on Permies, and went for wood chips instead. It has worked really well! You can read about it, and see a couple of photos here .