Raised beds with french drains under the paths between?

I'm shortly moving to a new to me house in a new to me area (France) where there is about 1/3rd of a (flat) acre  I can put raised beds on, next to a reasonably sized outbuilding that currently has no gutters.

If I borrowed a digger and dug an 18" path, 12" deep, between 48" wide beds (approx), put that soil on the beds, lined the path trench with geotextile of some sort to keep weeds and fines out, laid something like a 3" perforated pipe along them all connected at the ends, backfilled about 8" with uniform sized stone to allow through flow, folded the geotextile over the top, covered that with barkchips then guttered the nearby roof diverting the rainwater into the french drains, would that be a total waste of time and money?

Covert in situ rainwater storage :)

But, would the veg in the raised beds benefit from water in the bottom of the path drain?

Would just a slightly dug out path topped with mulch do pretty much the same thing?

Would I destroy the geotextile if the beds needed tilling?

It does get a bit dry in the summer at the moment.

Thank you

Usually French drains are used for just that ... drain water from one point to another.

The explanation of how you plan to make the French drains sounds good, so I am confused at what you are wanting to do.

The explanation of what you are wanting sounds like water storage to feed plants.

Could you explain about the purpose you are wanting in more detail?

Currently rainwater is just lost into the ground around this particular outbuilding, and the 1/3rd of an acre next to it I could use for veggies on raised beds gets a bit dry.

So I thought I could use the pathways between the beds as a covered water store, with the french drain pipework to help the rainwater get from the end with the building to flow more evenly around the whole area, rather than just the building end getting most of it.

If I dig the paths out to the same level first then I think the water should spread fairly evenly around the pipe network.

The lowest corner can have a sump with an overflow.

What it might end up doing though is to lower the water table within the raised beds.

I could instead source a big catchment tank placed at the building and run that into drip feeder hose, but that's a big ugly lump of plastic most likely.

I'm no expert but I think you might of found the weakness to that plan. You could unintentionally wick away moisture when there isn't a lot of rain coming through.

Instead of trying to affect a large area of soil's moisture level, I am a fan of targeted introduction of moisture for the plants we like. Rain catchment is exactly what I was thinking. I however am not any help with the beautification of the vessel itself. Perhaps something can be built around it so that you don't have to see it if cleverly placed?

There are some Permies on here that know a lot about these systems so I hope to hear one of them give their opinion on the subject.

Oh, good luck on your move Jason!

Storing water in the soil is supposed to be very possible. But as you point out raised beds can dry out more, which can be problematical in a dry climate. I've seen several people have success however, where rainfall is intermittent but heavy, in using the paths to catch and store the water.

I'm thinking Rufaro's too little/too much rain



and Heather's community garden plot



I have a modification to suggest for you - I used sticks to make drains through my raised garden beds in my simple farming area



This was for the opposite reason, as you know we get quite a bit of rain here in NW Scotland (! ), so the drains were to help dry the beds out. I have heard that stick drains can remain functional for many hundreds of years - longer than stone drains, as the structure of the wood remains in the soil after it has rotted away and continues to allow water to flow through the wood/soil structure. Another benefit may be to create a hugelbed effect within the path , which Matthew explained here, which seemed to have been pretty successful.

Matthew Trotter's hugel path in construction

If you have access to any suitable wood it might be a way of reducing the cost of the project for you and making the drains return to enrich the soil, rather than be a problem in the future.

Thank you for the replies :)

I have some lazy beds here with ditches that I cleared out and the ground is now much firmer. I now sink 2" not 2' ;)

I was thinking that my proposed raised beds would actually not be very raised if I filled with bark almost up to the growing bed level. So although the water level may be a long way down compared to root depth, the moisture in the growing bed would be maintained to a greater height? And the path stays firm underfoot, not a stream.

It is possible I could put a water catchment tank inside the outbuilding even, and I do have some drip line already. I was thinking my french drain idea would be working all the time with no input. Then I could use drip line on newly planted growth or as required, rather than a full time daily maintained system.

I think this is such a good idea I have a post about doing something similar here:

https://permies.com/t/75626/Hugel-Chinampas-duckoponic-swales

If wildfire is a risk, gutters can be a major vector for building ignition. Covered ones are safer, but going gutter free is the safest.

If you can just grade the ground to provide the easiest possible path for water to your infiltration basins, the pipe may be largely unnecessary. At the property in the link above, I probably could have forgone the pipe between the beds and just filled with coarse woody debris then topped with wood chips. Roman era British Isle fortifications had such woody debris filled trenches that outlasted their occupation and rock or pipe based drainages. I would also skip the geotextile, as most are plastic based and bound to become forever trash mixed into your soil. Just wood would be a much less expensive, longer lasting, more effective and absorbent in my experience and research.

I used to live next to a field in SE UK which had wood filled drainage from many many years ago which gave a lovely undulation to the grazing. Maybe a 6' wide 1' dip every 18' running one side to the other.

I would rather not use plastic but I don't think putting branches in a relatively shallow trench and then stone or wood chip on top would give a good and safe path? It the trench was much deeper, much more depth of compacted branches with much more fill on top then maybe, but I'm not trying to drain, I'm trying to store where it's directly within reach, and undercover from the sun. A shallow fill would work away from a path, but I don't think directly under it would.

Unless I covered it with something solid like paving slabs but the cost of that would be silly. Although then they could be just covering a ditch with no plastic, no stone, no branches so maybe overall cost might not be silly, I'll have to look into that :)

Further away than the outbuilding is another building and a pond fed from next doors roof, so piping all that lot into the system might be on the cards too. The pond has no overflow, doesn't overflow but is 100% full at one point in the year normally I'm told, but almost dry about now so some work needed there as well. There's quite a bit of excess water soaking away somewhere I could make use of.

Paving slab cost would be huge unless I find some super cheap or free so that's a no no.

Maybe I could bury scaffold boards over a small ditch under the bark mulch though? How long does treated timber last if you bury it I wonder?

jason holdstock wrote:Paving slab cost would be huge unless I find some super cheap or free

If you have access to a company that fabricates stone countertops, the ones near me just throw the cut-out pieces (where sinks will go) into a dumpster and they're more than happy to have us pick through their trash.
(I don't really understand why shallow paths of woody debris aren't fine as-is, but this might be a free paver source if that's what you want.)

Shallow paths of woody debris have no means of storing a lot of excess water, and if there is excess the debris floats off and blocks outlets etc as other folks here have documented. If there is a small amount of surface water on the path then it becomes less useful as a path. I could build the paths to a fall but then even less will soak in where I want it.

I may be being daft but I like the idea of storing rainwater where it's needed and then used passively, with minimal evaporation, but I'd have to build the french drains before forming the raised beds.

The woody debris quickly (1-2yrs here) becomes fungally rich well drained but highly absorbent soil for the plants in surrounding beds to root into. It holds 1/3 its volume in water. If you are worried about the wood floating, then an overflow perforated pipe or sill would prevent that. The system I described in the post referred to above has handled 10” (25cm) days of rain with no such floating woody debris problems. The main risk anyhow would be in the first flush of rain hitting dry wood. Once it is waterlogged, it will not float off.  Topping up with more woodchips as the paths decompose and sink a bit is not much work.

Provide 1% gradient for water flow around any hugel bed and it will not float off. Of course, I would not recommend building dams with wood…leave that to beavers.

I'm bad at visualizing landscapes from text descriptions. Take this suggestion with a grain of salt, but it sounds to my rather novice brain that your situation is a pretty good one for setting up some swales? Geoff Lawton made the swales section of his PDC available for free I think. Something to look into if you haven't and it seems useful.

Ignore me if I'm way off base.

A rainwater catchment system can be buried:

Thank you for the replies.

If I leave the paths as just bark chip mulch then for any given rainfall the area closest to the inlet will always benefit first, maybe sucking up all the water delivered from the nearby roof.

A third of an acre would perhaps have twelve raised beds 50m long, (maybe subdivided).

I think I would need french drains laid to zero fall to try to get the water from the one or two delivery points to make its way as evenly and equally around the whole system as possible. I want it to stay under the beds, not get stuck at the beginning or pool at the outlet.

A filter at the outlet was in place in the examples I saw here a while back, but that got blocked with the chip, needed clearing, and then all that material needed putting back where it washed away from.

You could think of what I'm trying to do as put swales between the raised beds, I'm just putting a lid on them, topped with wood chip to keep the path usable when soaked and not too far below the working surface of the raised bed.