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Help.... working on slopes over 50% gradient.!!!

 
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Hi.. I would appreciate any help or advice.

I am currently in Southern Ecuador introducing permaculture to families here. They live in the mountains and many work on lands over 50% slope.
Currently many of the families are only planting corn here so I want to introduce them to the three sisters...

However on the steep slopes there is a large problem with water retention and run off.
At first I wanted to introduce swales but have read that on steep slopes they are not a viable option.... We are a team of two working by hand so large scale works are not an option. (impossible for machinery to reach some of the land we are working with. )

Any help or suggestions would be appreciated....THANK YOU!

attached are some images to show...
IMG_20200204_152354.jpg
Maize field on top of mountain
Maize field on top of mountain
IMG_20200206_092031.jpg
Idea of slopes we are working with
Idea of slopes we are working with
IMG_20200206_095630.jpg
herbs
herbs
 
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    Swales are viable options on steep slopes. Just don’t make them bigger than maybe about a foot deep, but have many of them. The advantage you have here is that if stuff is arranged properly, you can let gravity do your work for you. For example, the Polynesians planted candleberry trees right next to the streams that flowed down the volcanic slopes into their villages, so they would drop the berries, which were used as fuel, into the stream.
    I suggest food forest (and just forest) to stabilize the slopes.
    Using three sisters is a good start, sunflowers and amaranth are reportedly good companion plants for all of the sisters, as well as being awesome chop-and-drop chicken feed and bird attractors. You can stabilize the corners and right, left and downhill sides of the garden beds with perennials.
 
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Myron Platte wrote: I suggest food forest (and just forest) to stabilize the slopes.



The issue of slope stability is a true issue in these slopes! You indicate 50% slope, which translates to around 45° hillslopes. This is way above the stability angle of unconsolidated material, which is usually around 35°. Such areas are usually very prone to landslides, which can be deadly for people living there. I would think well abouth Swales, since what they do is get water into the ground, further weakening their cohesion and thus might increase the probability of a landslide ...
 
pollinator
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Water retention on such steep slopes is a big NO-NO. Mostly these slopes found a balance between runoff and infiltration which makes them sort of stable as long as the weather stays within "normal" fluctuations for that area. If you would get an exceptionally wet rainy season the risk of landslides goes up A LOT. Please ask the people living there about these stories, I'm pretty sure they saw a slope or two come down somewhere in the past decades.

General rule of thumb for swales is: only on slopes less steep that 1:3 / 18° / 33% (I hope I got those figures right, I always use the 1:X method when measuring, because that's fast and easy and fool proof :-) ) with as main reason stability. On steeper slopes you can use terracing with retaining walls. Those are a lot of work, more so when the slopes get steeper. On slopes 1:1 you cannot really do much (for every meter horizontal you need to build a meter high retaining wall), except for hoping that you don't get killed in a massive landslide. The pictures below show one on a 1:1 slope. And I have seen WAY worse :-( ...

Since you're dealing with a reality of "this is where poor people live", there might be an option you could try: slopes are seldom totally the same everywhere. Look for areas that are less steep than average, with nobody living right below them (so that if there would be a landslide it won't kill anyone). Generally landslides occur when excess water cannot drain away quickly enough. That builds pressure by weight while weakening the stability of the soil at the same time until the whole or part of the slope gives way, relieving this pressure. To avoid things getting to that point make sure you have an exit channel for excess water. This channel needs to go to an even more uninhabited area! Normally you could use the natural occuring gullies (super eroded in these landscapes) for this. I think people tend to stay clear of those. Like this you can try to build some terraces.

Good luck! People in your area don't have a lot of options so hopefully you can help them improve, even if just a little!
A_landslide1.jpg
[Thumbnail for A_landslide1.jpg]
C_wall_of_mud.jpg
[Thumbnail for C_wall_of_mud.jpg]
 
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I'll be watching this thread carefully. I've got 4 acres and more than half of it is hill at similar grades. I've finally started in on working on plantings on a specific hill behind the house after staring at it for a year or so. I started here because of all of the California Bays looming over the house both blocking light and threatening to fall on it, as they do often enough. I understand there's a lot of dangers in altering the landscape too much, either in grade or capturing too much water in the soil. I'm taking a light approach and am following established animal trails, establishing them further with timber from trees I've cleared and rock from the area. Then creating small uphill retaining walls for planting dwarf fruit trees, and filling in here and there with interesting native bushes and other plantings like yerba buena, salal, alpine strawberry, huckleberry, creeping manzanita.

The idea is that not only will the hill stability not be compromised, but there'll be a lot of low maintenance fruits berries and herbs growing--the other big issue with hills is just getting up there to tend to things. We'll see if it pays off.


 
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terrace farming

 
pollinator
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Indeed you have an interesting situation ahead of you.
Can I ask what the # sisters are please?
As I think about your situtation I realise many communities have experience and I can see some ideas are coming along already.
What is the rainfall there ? Because that seems to be one of the causes of land slides.
But when you look at those terraces built in Japan in the photos it will be interesting to see how they are stabalised.
 
John C Daley
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Building rice terraces
Building terraces

This group may be able to help with knowledge
History of work
 
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I don’t know if you’ve figured out solutions, but I came across this and thought of you. What I found is a very helpful diagram of working on a slope, which apparently comes from a chapter in a soils book about working on slopes.

https://media.springernature.com/lw785/springer-static/image/chp%3A10.1007%2F978-3-319-75527-4_8/MediaObjects/334329_1_En_8_Fig18_HTML.gif

Here’s a link to the chapter, in case you are able to source it somehow: https://link.springer.com/chapter/10.1007/978-3-319-75527-4_8
 
pollinator
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I'm farming on a similar slope right now. I'm still working on getting things set up, but the plan eventually is to divide the field into horizontal sections about 50 feet wide for annual crops like corn, potatoes, and squash, with a 10-20 foot wide section of perennial crops in between. The perennial crops will include small fruit trees, berry bushes, and vining crops on trellises, as well as things like herbs and clover. The combination of trees, bushes, trellises, and ground covers should help trap the soil runoff as well as stabilizing the slope. Eventually I may add short rock walls to act as terraces to help hold the soil as well. Lord knows I've got enough rocks.

From the air it might look like a topo map, with the horizontal bands following the curve of the hill.

If soil erosion is a serious problem, you may want to adjust the widths of those sections, making the annual sections a little narrower and the perennial sections a little wider, but it should still work.
 
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My friend, forget about swales on those slopes. Many people have died in landslides on slopes like that please be very very careful what advice you give others. The key to working those steep heavy clay slopes is contour hedgerows. With inga or other early and mid succession trees to get started. They will stop erosion, give you mulch for the corn to cycle nutrients and over time if you also plant vetiver or lemongrass start to form terraces. In the tropics in swales are very delicate because in large rainstorms we can get 8 or 10 inches of rain and it will either wash out the earthworks or cause a landslide that can take lives. You can plant out contour lines at 5 or 6 m and have plenty of room for annual crops and along the tree lines plant out banana and other fruit trees that will add income and food security. Again please be very very careful when you give advice to someone else especially if you have not done it first
 
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Russ Cann wrote:Again please be very very careful when you give advice to someone else especially if you have not done it first



This is sage advice.

Be careful, people.  Once a hillside begins to give way, there's no way to stop it.  Long term, I think that creating a food forest with minimal soil disturbance would be best.  An interlocking web of tree roots will not only hold the hillside in place, but will also help infiltrate water quickly.

Take a few years and stand out on that hillside during a few heavy storms --- see what actually happens to all that water that falls.  Get to know your land intimately.  Perhaps there may be some small areas where you could use water capture strategies, but I'd be really cautious about taking an A-frame and a shovel out there and digging swales.  
 
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Ecuador is tropical I think, so vetiver would thrive there.

Vetiver is an amazing grass for planting in contour rows on steep land. It’s roots anchor the soil, extending incredibly deep. It slows surface runoff, increasing water infiltration, reducing soil erosion, and building sediment on the upslope side, forming natural terraces for planting. The grass itself can be cut twice per year for mulch. The plant is sterile, so won’t spread by seed and will stay where planted.
 
Myron Platte
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My comment about swales was based on the fact that spread and soak systems were used with good results by Polynesians on volcanic islands, which have very, very, steep slopes. I suppose that these might not have been swales specifically, perhaps shallow cut and fill terraces, but I know that they brought water out on contour from streams and it worked out fine for them, so it’s pretty clear that one can indeed do water retention on steep slopes. The Polynesians used the water soak systems to grow trees. Trees do help stabilize slopes. I’m sorry that I assumed that swales specifically were used.
 
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Hello all, my first post on this forum.

I am glad that someone is talking about steep slopes. Have been researching on swales but have not yet seen convincing results from working on very steep slopes.

I have just acquired 18 hectares (45 acres) of land with 35 acres on slopes between 20% and 70% above the house. Much of those 35 acres is covered in gorse and I intend to mulch strips in between the gorse (allowing the rest to continue to hold ground and act as nursing shelter) to create some form of swales and/or terraces to retain water and to plant native trees and incorporating an edible forest.

Elevation from the house to the top of the boundary is about 395m (1304 ft) and 660m (2178 ft). Beyond my property boundary, the elevation goes up to the hill top at 835m (2755 ft).


[See attached photo of the slope behind the house]

Location: Oxford, New Zealand (South Island, temperate climate)

Rainfall: around 800mm average annually

Main fresh water source: stream and creek on land.

Sunlight: north-facing all-day sun (Southern Hemisphere)

Has anyone any experience in working on such steep slopes? I intend to get a mini excavator (maybe 5-tonne) to get it going. I'm trying to get as much experienced advice as I can before starting the project, if it is feasible in anyway at all.

Any help in any direction would be appreciated. Thanks.
House-angle-and-water-tanks-NE.jpg
One angle of the slope behind the house
One angle of the slope behind the house
 
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Personally I would not be using swales at all. I would be creating terraces for growing annuals and for access, and growing trees between the terraces to hold the hillside in place.

Sepp Holzer also puts in a series of drainage pipes and cisterns along the base of each terrace cut, and connects them with a pipe which he runs to the bottom of the hill which can be tapped for pressurized irrigation water.
 
Dan Sheng
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Nick Kitchener wrote:Personally I would not be using swales at all. I would be creating terraces for growing annuals and for access, and growing trees between the terraces to hold the hillside in place.

Sepp Holzer also puts in a series of drainage pipes and cisterns along the base of each terrace cut, and connects them with a pipe which he runs to the bottom of the hill which can be tapped for pressurized irrigation water.



I am also concerned as the soil type on my property is known to be Perch-gley Pallic. which is of weak structure and may not hold too well when saturated with water.

Where can I find out more info on terrace building and specifics in dimensions pertaining to slope and soil attributes?
 
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I echo all of the concerns about landslides and mud flows.  I would think that best use for unterraced steep land would be to plant perennial crops and fruits like orchard fruits and bramble fruits.  Maybe other types of plants that you would minimally disturb the soil - i.e., plant corn singly without disturbing more than needed to get the seed in, then do not pull out the stalk when harvested, cut it off and leave the root in the ground, plant next for the next crop. But I still believe you'd better served using such land for perennial fruits production where you would actually improve the ground with the tree roots.
 
Myron Platte
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The three sisters garden has been used as an early succession soil building plan on the way to a food forest. Annuals slowly give way to bushes, then understory trees, then canopy trees.
 
Dan Sheng
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Given that my hill slope gets over 70% steep at places, I am considering terracing.

Any suggestions for how to get going? Anyone has experience working with excavators on slopes 70% or more for terracing? I tried looking at earthworks for terracing but haven't found many that I could use to understand better. I am totally new to this.

Would a 5-tonne excavator do?

Any input would be appreciated.

Cheers.
 
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Dan:

I'm sorry I can't answer your questions directly - issues of steep slope, soil and water rapidly become soil engineering problems and most folks have neither the experience or knowledge to address it.  Its sort of like - I dunno - trying to find a how-to-homeowner book on heart surgery.

A few thoughts in lieu of answers:
1) I had to go and find where Oxford is ... I'm suspecting that you are on a formerly forested plot - and without tree root systems you are right to wonder what's keeping the soil there!
2) Steep slope work, done wrong, can be a disaster.  The general principle on these things is to observe the land for a year before making decisions.  Since you indicate that this is a recent acquisition, you may find that a longer observation period gives you a better plan. ( I know I was ready to do all sorts of things right away ... and in hindsight I'm glad I didn't because they were all bad ideas).
3) I think you're on to something with plantings... trees once held that slope together, I'd think more root systems is the key.
4) I'd be very wary of operating an excavator on those slopes.   An excavator can make a real mess of the plants that are there (see #2 above), and presents a real tipping hazard as well.  If you must, consider one of the "walking" or "spider" excavators that can level itself (although I have never seen one for rent in my area).
5) The very first thing to do might be cutting test trenches so you can see the actual makeup of the soil layers.  These can be done by hand (ugh) or give you an excuse to rent a small excavator.  Understanding the actual, on your property, soil seems critical to developing a viable plan.

Edit - thanks to all opinions above.  Sorry if I don't reference them... its late and I'm tired.  
I hope you can stick around here and give us some updates as your plan and work progresses!
 
Dan Sheng
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Thank you, Eliot for your advice.

From what I could see on New Zealand soil map (https://soils-maps.landcareresearch.co.nz) that the soil on the property is likely to be Perch-Gley Pallic, which is said to be "susceptible to erosion because of high potential for slaking and dispersion".

Since the arrival of European settlers 200 years ago, much of New Zealand native forest has been cleared for conventional farmland and I am guessing that this property has also endured similar fate. Not sure if the most recent large-scale effect on the land had been for pine forestry or not. However, gorse is one of the most efficient first-colonizers of open land, thanks to the British for bringing them in for hedge planting.

I would say that the deep-rooted nitrogen-fixing gorse which feature significantly on the slopes are the current ones holding the ground.

If I were to create terraces, they would be between strips of gorse to be left standing, also as nursery shelter strips. My plan is still to re-generate native forest and incorporate it with an edible forest as well. I am not sure how it will turn out but am open to ideas.

It is very tempting to dive right into it upon arrival, eager to get on the excavator to shape the land but I know it is good to observe for a while, like you suggest. I will definitely do smaller-scale trenching and see how it goes.

I would still like to hear more inputs about terracing on such a gradient from others, thanks.
 
Dan Sheng
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Myron Platte wrote:The three sisters garden has been used as an early succession soil building plan on the way to a food forest. Annuals slowly give way to bushes, then understory trees, then canopy trees.



I will look into the Three Sisters Gardening as part of the plan, thank you, Myron :)
 
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