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Another Swale Hillside Question

 
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Recently moved to a new home and have been evaluating my site for permaculture purposes.  My home is situated on a hillside about half way up.  That means directly behind my home the ground continues to slope up.  I've noticed the ground directly behind my house feels water logged even when we haven't had rain in days.  My guess is water is flowing down the hillside and just getting trapped by my house.  Naturally I am worried about what this means for water getting into my basement as well as the foundation of my home.  I plan to install a french drain around the house and hopefully catch that water or divert it somewhere useful.

My question is will building swale(s) behind my house up the hillside also serve to alleviate this problem and better hydrate the hillside behind my house?  Or could it actually make it worse?  Is there any danger building a swale like this behind my house?  I've read figures on this site suggesting what is considered too steep to implement a swale.  I think I fall in a safe range.  I'm actually unsure how to calculate this but just taking the rise and run given by google maps I get a percent slope of about 23%.  There are of course sections that are steeper and section that are more gentle.  I actually live in a pretty arid region which is why I was surprised that the area directly behind the house was seemingly so water logged but I think I now understand better.  Any advice would be appreciate.  

Site info:
Southeast Idaho
5 Acres
Elevation: 5,029 - 5,170
13 in annual precipitation





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Location: Australia, New South Wales. Köppen: Cfa (Humid Subtropical), USDA: 10/11
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Hello Earl,

I assume the hillside is dry but near the house is wet?

At a guess it seems when they excavated the house/basement it probably cut through an impermeable layer like clay or stone, so subterranean water is now emerging at the house - a man made spring.

To keep the foundation/basement dry means some substantial excavation and drainage works to catch the discharge and move it downhill.

Swales are meant to improve the infiltration of water, so it may be counterproductive unless the drainage works are designed for extra inflows.

Also, Swales shouldn't be constructed on slopes exceeding 15 degrees because of the risk of land slip.

 
Earl Ironside
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Yes the hill above is much drier.  To be clear I've estimated the slope to be about 23 percent which I believe is actually slightly less than 15 degrees.
 
gardener
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You might look into a terrace. In simple terms it is a swale that gradually slopes downhill, moving the water away. When they did mine the drop was something like 1ft every 50ft. The water moves slowly.
 
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Thinking laterally, can you put this water to good use?
Vegetable garden, orchard etc or simply trees that may love that situation.
I have seen trees planted on farms to absorb water
 
Earl Ironside
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wayne fajkus wrote:You might look into a terrace. In simple terms it is a swale that gradually slopes downhill, moving the water away. When they did mine the drop was something like 1ft every 50ft. The water moves slowly.



Thanks I'm assuming this always involves heavy equipment.  I might have access issues with this.

John C Daley wrote:
Thinking laterally, can you put this water to good use?
Vegetable garden, orchard etc or simply trees that may love that situation.
I have seen trees planted on farms to absorb water



Like diverting water with the french drain and running it to an orchard or garden area?  That is definitely the plan when we install the french drain or at the very worst to some sort of catchment that can be pumped elsewhere.


Similarly, instead of a swale uphill could I run more of a diversion trench that runs away from the house but towards an area that could use water like an orchard?
 
John C Daley
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No, not diverting any water, planting into the moist ground
 
Earl Ironside
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John C Daley wrote:No, not diverting any water, planting into the moist ground



Oh I see that makes sense.  Unfortunately the area is actually only about 10 feet wide strip behind my house.  After the 10 feet there is a retaining wall and behind that a rather steep section of hill.
 
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Earl Ironside wrote:

wayne fajkus wrote:You might look into a terrace. In simple terms it is a swale that gradually slopes downhill, moving the water away. When they did mine the drop was something like 1ft every 50ft. The water moves slowly.


Thanks I'm assuming this always involves heavy equipment.  I might have access issues with this.


One way to build a terrace slowly over time, apparently, without heavy equipment is to live stake trees and bushes like willow into that wet ground along contour into a pretty thick living hedgerow, then let flowing rainwater accumulate brush, soil, sediment, seeds, etc. behind this hedgerow. I read about this technique as used traditionally in Sonora, Mexico, in Gary Paul Nabhan's Food from the Radical Center, published last year, and posted about it here. That linked thread, if you go back to the first page, contains a running list of plants that can be root cut like that and could potentially be used in this way.

I haven't tried either of these techniques yet, but another way to build a terrace without heavy equipment has been used in Oaxaca, Mexico, since before Europeans arrived. I posted about it here and quoted an anthropologist:

"Farmers described a process in which green and dry brush is cut and piled in mountain drainages in a cross-channel direction to retain soil and sediments washed down from the hills during the rainy season. Called bordos, these brush barriers are lined in the front with stones found nearby to create a permeable retention wall. The stones are carefully fitted like a jigsaw puzzle, but they are not cut or bound with mortar. The placement of stones is progressive and begins after the brush bordos have already begun to collect sediment. Low, vertical rows of stone are positioned in front of the brush bordos to create the base of a terrace wall. As the rains continue to transport more sediment, additional stone rows are placed slightly upslope and at a tilt, increasing terrace height. The result is a sloping, porous wall that allows excess water to filter through. This mode of construction protects crops from oversaturation and prevents wall collapse, since strong currents of water are filtered through the walls. Terrace maintenance is a continuous, yearly process."


I'm not sure how well this would work behind/upslope from your house and would have to think on that some more!
 
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