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linear stone heap soil building machine that will last centuries  RSS feed

 
Posts: 16
Location: Ithaca NY
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I have been reading the excellent book "The Hidden Life of Trees" by Peter Wohlleben. On page 87 he talks about how during a rain event if the soil becomes saturated, excess water runs off, taking tiny particles of soil with it. In this way large amounts of soil can be lost. Apparently as much as 2,900 tons per square mile per year, according to this book. If the soil is thin, he seems to indicate, then it will reach it's saturation point quickly, and erosion will happen with greater frequency and quantity in comparison to thicker soils.

I have a forest with gentle to moderate slopes with less than an inch of topsoil. If Wohlleben is right, it doesn't take much rain for this soil to reach it's saturation/erosion point. There are also huge piles of fieldstone all over this forest. (I imagine the stone piles give a clue as to why the soil is so thin, this area must have been farmland before it grew back up into forest).

So here is my idea, which is not really my idea at all because I have read about similar things elsewhere. Take the fieldstone, which is already onsite and accessible, and make heaps on contour, about a foot high and a foot wide. Wherever the heap meets a tree it can stop and then start again on the other side. After leaf fall the spaces between the stones will be filled with leaves. Then when water runs off, the linear heaps will hopefully slow it down and catch most of the soil particles that are in it, as well as small bits of other types organic matter. I would like to think that this system would build topsoil by at least an order of magnitude faster than simply doing nothing. (I do acknowledge that sometimes doing nothing is the best option).

If everything works as well as I hope, then I can use Stone Age technology to build a machine that will build soil depth for centuries to come. I don't yet know how far apart on slope one heap should be from the one above or below it, and I don't know if one foot is the optimal height and width.

Pros: no digging, all materials are already onsite, very little disturbance, should last for a very long time, might save literally tons of soil from washing into the creek. Can anyone think of some more?

Cons: stones are heavy, I don't know if this will really work. Can anyone think of some more?

I am interested in all suggestions, critiques, ideas, etc.
 
pollinator
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This is covered in a book. Rainwater harvesting in drylands and beyond volume 1

Even 1 layer of stones will collect. As it fills, add another layer.

They also have diagrams if you have a steep cliff.
 
steward
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Sounds good to me Carl. You might want to keep an eye on the water flows because you will be changing that by putting stones in the way of the normal flow. Over time the rock walls might become terraces so watch for small waterfalls to form over the walls which might cut out more soil. Try to keep the water in a sheet flow rather than causing it to become many small streams.  I like what Wayne said about one stone height. That means you can build more walls closer together.
If you run the wall up to a tree and let the trunk become part of the wall, keep an eye out for the water taking the path around the trunk and maybe exposing roots by eroding around the tree.
If you have dead branches or other cuttings you could add them uphill behind the walls too.

 
Posts: 1954
Location: Kent, UK - Zone 8
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Here is a video of just the system you describe.



Notice that even after fairly modest rains there is already a silt build up behind each of the small rock walls. These walls are going to slowly build soil in level terraces which will sink water, storing it in the landscape. Altering the landscape as a whole will mitigate against their cycle of devastating flashfloods followed by droughts. It is particularly effective in this setting because of their heavy seasonal rains and substantial surface water flows. It would not be effective at all for me - in our humid climate, and with our chalk geology, we don't have surface water - not even rivers or streams because it all sinks and recharges the aquifers.
 
carl gibson
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Thank you all for pointing the way to that book, that video, and pointers on making sure to avoid problems with rivulets around the trees or waterfalls off of the backside of the terrace. And thanks for the overall encouragement! Permies is really a blessing! Does anyone on this forum know anything about grant writing? I know that various water and soil conservation grants are available through the usda, I wonder if this would somehow qualify. I can do a small amount of these terraces by myself, but if I could somehow get a grant or funding some other way, I could do a lot more.

I am sure it would help with grant writing if someone did a scientific study to quantify exactly how much soil can be conserved in this way under various conditions. If anyone on this forum is a soil scientist in the Fingerlakes/Southern Tier region of New York, and you want to do this study, let me know. I can provide land and some labor.
 
Michael Cox
Posts: 1954
Location: Kent, UK - Zone 8
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Why not just get on and do that experiment yourself?

Some aspects to assess:

Impact of a single stone wall
Impact of a series of walls down a slope
Impact of height and thickness of wall (useful to know. If you get 90% of the benefits from a wall two rocks high you won't want to waste energy building walls 50cm high)
Steepness of slope on effectiveness

Importantly, you need controls to compare against. Areas with no alterations made to the land.

If you are doing the work anyway then all this really needs is a little mental effort before hand, and some data collection every 3 months or so.
 
gardener
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Location: Cache Valley, zone 4b, Irrigated, 9" rain in badlands.
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carl gibson wrote:I am sure it would help with grant writing if someone did a scientific study to quantify exactly how much soil can be conserved in this way under various conditions.



It was startling to me when I started paying attention to soil movement. Out in the desert, the whole mountain moves downhill when it rains... Anything laid on contour helps to slow that, and captures sediment. Anything laid on contour helps:: rocks, limbs, grasses, bones, etc...

 
pollinator
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When constructing a swale, there are a couple of key points to the design that, unless followed, will do more harm to your land than good.  I would imagine that these same design principles are generalizable to the stone wall system you are proposing.

1.  First, your swale needs to be level and on contour.  If it's not, the water will rush down the swale and not sink into the soil profile.  In the same way, if your wall moves down the slop, you'll just be creating a river bed behind the wall as soil accumulates against the rocks.  Within a couple of years, it will start to incise the soil behind the wall and move it laterally, toward a lower spot along the wall.  So I'd recommend that if you try this technique, you use an A-frame level to keep the wall on contour.

2.  I understand that you're not trying to capture the water but are trying to capture the soil.  But you've got to think about the water as well—particularly, how will you release that water in a non-destructive way?  On a swale, a key part of the design is the overflow sill where, once the swale if filled, the water flows down to the next swale.  It's usually "paved" with rocks.  Thus, water flows over the sill and makes its way downhill without picking up soil.  As with the concern in my first point, if not designed with a way to channel the water in a direction where you want it to go, it will find its own egress.  You may find that water masses behind your wall and then will erode through or under the wall at a point of weakness.

3.  I love the idea of using your stones to make check-dams and gabions, but these are normally built where there is already a water course of some sort --- usually in seasonal gullies -- not directly on the hillside.  My hunch is that just having a couple of widely spaced stone walls as you've described them, would be minimally effective.  However, if you were to combine on-contour stone walls with vetiver grass or bamboo, now you'd have a biological answer, not just a physical answer to the problem.  As you probably already understand, in permaculture design, we prioritize biological answers to the problems we face.  Combining grasses like vetiver with your wall would strengthen it exponentially, would create a finer filter to capture a higher percentage of the soil that is washing down, and would aid significantly in infiltration of the water.  Win, win, win.

Good luck.
 
carl gibson
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Location: Ithaca NY
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Why not just get on and do that experiment yourself?

Ideally a credentialed scientist would be involved, because when it comes to writing soil conservation grants or getting more people to do things like this, I would think that the data of a soil scientist would carry more weight with more people than the data of a guy with no degree or established credentials in anything. I am not saying that is right or wrong, just what I perceive to be the case. But I will certainly collect the data myself if need be, and post the results here.
 
carl gibson
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Marco thanks for the tip about why it is so important to keep the stone heap on contour. I plan to be very careful about that. I also see your point about how this work would have a bigger payoff if done in a watercourse or seasonal gully. Sadly I don't have any of those on the land that I "own." but I will look around to see if I can find a place where runoff seems to concentrate, and put the linear heaps there. I don't expect these stone heap "Swales" to ever fill with water because of the gaps between the stone, I can't imagine they would ever be waterproof, but the backs of them will be angled so that if water does ever flow over the top it will not turn into a waterfall on the backside.
 
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