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Swales, terraces or neither on 45 deg. slope?

 
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Hey all. Got a real challenge: What to do with a 40 - 45 degree slope where the client wants trees, etc.? Basically, a food forest? All my research is crying out for very sturdy terracing, but the client wants natural and, to make matters worse, wants to plant all the trees with a 3 ft. diameter hole for each because of a technique he came across that seems to grow young trees very rapidly.

Swales on a 40 - 45 degree slope?

Just to be clear, those planting holes, whether individual or carried across as swales, mean basically 3 ft terraces with very steep backs and no way I can see to keep soil in place without stone or wood terraces.

The other option is to keep it as is and only make a spot for each tree, but the problems with runoff and erosion as water gathers at the trees or comes down or across slope and hits one of those trees... lordy. This is a semi-arid area of about 16 in rain, but like anywhere we do get heavy rains. The slope hasn't eroded that badly given it's been there for @ 20 years. Still... When gathering water on that pitch...

I am thinking trying to connect the trees on contour with small swales and use them as pools with as many little dinky swales as I can get on the slope BETWEEN tree lines and only one connector swale at the tree lines.

Thoughts?
IMG_20130802_102247.jpg
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Yard and slope 1
IMG_20130802_102242.jpg
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yard and slope on west end, no retaining wall
 
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Without knowing how densely he wants them planted out it's hard to say and being no expert i hope others will continue adding to this thread
If it was me doing it i would leave the slope as is , planting trees in rows , and the second row offset in a diamond grid pattern , and place a small berm on the lower side of each planting
Thus allowing for the tree berms to slow the water down , and retain it for a period , allowing it time to soak to the roots , while keeping the existing soil structure in place , undamaged as it has already been capable of holding the erosion for 20+ years as you say..... Just my two cents
Peace and Love Dave oxoxoxo
 
Killian O'Brien
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David Williams wrote:Without knowing how densely he wants them planted out it's hard to say and being no expert i hope others will continue adding to this thread
If it was me doing it i would leave the slope as is , planting trees in rows , and the second row offset in a diamond grid pattern , and place a small berm on the lower side of each planting
Thus allowing for the tree berms to slow the water down , and retain it for a period , allowing it time to soak to the roots , while keeping the existing soil structure in place , undamaged as it has already been capable of holding the erosion for 20+ years as you say..... Just my two cents
Peace and Love Dave oxoxoxo



Except he wants the holes for the trees to be 3ft. That's a significant dig into the slope of, what, 1.5 ft., no matter what? That's not a small berm, unfortunately.
IMG_20130802_102617.jpg
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The slope, on contour.
 
David Williams
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How many trees are we talking ? are they advanced in growth (potted) 1-2 year olds? and what spacing are you guys planning? Are you digging manually or mechanically?
 
pollinator
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I would say neither. I'm basing this on my drives up and down I-15 through the Fallbrook, CA area, noting that they just popped the avocado trees right into the hillside, and don't do much in the way of swales and terraces. If you go to Google maps and use the street view feature, you can see what I'm talking about without ever having to burn any gas.

Here's a reference that discusses erosion control when putting in an avocado orchard.

 
David Williams
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I Tree planted for 2 years on roadsides and non arable farm areas with "Landcare" groups , we planted in everything from rich deep black loams to rock infested clays, and we rarely made any attempt at swale making admittedly since the trees planted were endemic to the area, On hilly area's and planting tube stock plant (not really advanced) would use the excavated soil to make a small berm around the dig site , might have only been 2-3 inches deep on the down side of the hill , and planting area's was anything from 10 inches to 100 inches annual rainfall...
 
Killian O'Brien
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John Elliott wrote:I would say neither. I'm basing this on my drives up and down I-15 through the Fallbrook, CA area, noting that they just popped the avocado trees right into the hillside, and don't do much in the way of swales and terraces. If you go to Google maps and use the street view feature, you can see what I'm talking about without ever having to burn any gas.

Here's a reference that discusses erosion control when putting in an avocado orchard.



The client is adamant about using this planting procedure. I can try to keep the slope and use ground cover for erosion control, I suppose, but he seems to want the root syste4m in this 3 ft. circle. Ground cover is an option. However, the owner is elderly and the slope needs to be more easily accessible for management/harvesting. #of trees is up to me. No # set yet.

Cheers
 
Killian O'Brien
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David Williams wrote:I Tree planted for 2 years on roadsides and non arable farm areas with "Landcare" groups , we planted in everything from rich deep black loams to rock infested clays, and we rarely made any attempt at swale making admittedly since the trees planted were endemic to the area, On hilly area's and planting tube stock plant (not really advanced) would use the excavated soil to make a small berm around the dig site , might have only been 2-3 inches deep on the down side of the hill , and planting area's was anything from 10 inches to 100 inches annual rainfall...



I'm trying to think long-term. With rainfalls getting heavier even with our low overall rainfall, catastrophic rains are becoming more common anywhere rain falls. This slope with features that drive water to specific areas (the tree plantings) seems like an invitation to getting gulleys started and needing repair.

Cheers
 
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net and pan earthworks work well for steep slopes. basically each tree gets it's own catch basin and water is overflowed down to the next tree catch basin. you wouldn't want the overflows to go straight down hill to the next tree, but across the slope and down slightly. It forms a sort of diamond pattern with the basins. hope that helps.

yes you will have to reinforce the back wall of the basins if you are going to cut in the hillside 1.5 ft. are there large rocks on the property? you may be able to stack them as a retaining wall. This should also give you some condensation which will drip into the soil, as well as some thermal mass for extra heat which you may or may not want.
 
pollinator
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I'd ask him for more information about the technique he wants to try, maybe he's got something there. I'm guessing it's based on the African fellow who puts mini-swales around his trees to hold water - they also have to water them, I think. Something like that could be very dependent on the type of soil - how easily it washes away or stays in place. I think that man used rocks to hold the soil in place. I've thought of using logs to make temporary retaining walls, hoping plants/roots would grow to replace them as they rotted.

As for access, I just saw on Pinterest some steps up a steep slope made by putting cinder blocks hole-side-up to make stairs, filling the holes with soil and planting herbs that can be walked on like thyme. Very cool!
 
David Williams
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Killian O'Brien wrote:I'm trying to think long-term. With rainfalls getting heavier even with our low overall rainfall, catastrophic rains are becoming more common anywhere rain falls. This slope with features that drive water to specific areas (the tree plantings) seems like an invitation to getting gulleys started and needing repair.



Your tree roots will increase quicker than your rainfall, one counters the other

Dave Keck wrote:net and pan earthworks work well for steep slopes. basically each tree gets it's own catch basin and water is overflowed down to the next tree catch basin. you wouldn't want the overflows to go straight down hill to the next tree, but across the slope and down slightly. It forms a sort of diamond pattern with the basins. hope that helps.



This is the method i am referring to... but being an Australian my english is poor lol

Killian O'Brien wrote:He seems to want the root system in this 3 ft. circle.



He's 100% right in compacted soils , tho makes no measurable difference in non compacted soil
 
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