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Swale Depth

 
Author
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Location: Frederick, Maryland
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I have been hand digging swales for raised garden beds and food forest plantings using an A frame to find contour. Generally I have been digging the basin part about 12" deep by 24" wide for 40+ feet in length. I was told to maintain the depth all along but when I move across the hill I notice that one end of the basin sits much lower than the other. I know I am missing something here. Can anyone please clue me in.

Muchas Gracias.

Michael
 
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Location: Reno, NV
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Several things could be happening.

1. do you flip-flop your a-frame when measuring contour. if not and you haven't calibrated exactly, you'll get progressive error as you go along. flip flopping is the simplest way to manage for this.

2. it may look off contour. test with water if you have the means. if you end up with a deep puddle at one end you know that's lower. water always finds a level.

3. if your water test shows you have it off level, I recommend using a 4 ft. builders level to do finishing work on a hand dug swale

4. if your already dug swales are way off contour, install some check dams across the cross section of the swale. this will create several smaller swales nested in one ditch and berm system.

when deciding how to size your swales, you want to take into account your soil type, your rainfall patterns and intensity, the slope, the proposed plantings you want to grow, and the methods used to build it.

I'd be happy to share more details about various choices based on specific contexts.
 
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neilbertrando McCoy wrote:this will create several smaller swales nested in one ditch and berm system.



Could you expand on this?
This really looks like what I'm about to do. I'm unable to find the contour, and the slope is quite slight anyway. I was thinking of scalloping and connecting the dips with trenches.

I know that when I tilled, the rain all puddled diagonally from the top right corner into the bottom left corner, so I'm planning on trying to move water diagonally from top left to bottom right and then back again, ziz-zag fashion.

Should I compact the ditches? I only have hand tools and my feet.

Know of any resources on this?

thanks.
-william
 
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As I understand it, the bottoms of swales are never compacted, because you want the water to infiltrate into the soil. The berm part of the swale can be compacted to keep it from sliding back down into the ditch.

There's tons of information about constructing water-harvesting earthworks in "Rainwater Harvesting for Drylands and Beyond" Volume 2, by Brad Lancaster.
 
Michael Judd
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Neil.

Great reply. What I was hoping for, thank you. Few questions on your reply. Also like to ask what tool/machine you would recommend as the next scale up from hand digging, taking tight spacing into mind.

1. I don't flip flop the A frame as I noticed it changes level when on a perfectly level slab. But you're saying that is part of the design? Think I'm going to work with a bunyip from here on.


3. Are you saying dig out the difference in the basin using the 4' level? That could up make a very deep end.
 
neil bertrando
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"Could you expand on this?"
I second the vote for Brad Lancaster's books. Vol. 1 has a picture of this. ? is it reasonable to post a scanned image of this diagram and reference it?

basically, what I was visioninpg was different from your following description. rather, if you have already dug a swale off contour, you can 1) remeasure and dig a new channel, or 2) pile rocks or other structures perpendicular to the cross-section of the swale (basically running in the same direction as the hill-slope) to slow the water in the higher sections and eventually these will level out as sediment settles. There are probably an unlimited number of creative ways to alter these systems for benefit, I'm just listing an option i think might be a 'least effort for greatest effect' option.

"This really looks like what I'm about to do. I'm unable to find the contour, and the slope is quite slight anyway."

I recommend getting a tool that is accurate enough to find the contour before you move soil if you want to do swales. the flatter the land, the longer distance the tool can be (needs to be?) to get resolution. An a-frame works great on steep land or for small sections (you will get the most edge from this tool), a bunyip/water level is usually a bit longer giving resolution over longer distance (at any resolution you choose up to the max distance of the tool) and you can accurately measure differences in elevation, a transit or laser gives you longer distance accuracy and may be the tool you want, again any distance to the max is your resolution and you can measure fall and rise.

depending on your slope you have lots of options...

"I was thinking of scalloping and connecting the dips with trenches.
I know that when I tilled, the rain all puddled diagonally from the top right corner into the bottom left corner, so I'm planning on trying to move water diagonally from top left to bottom right and then back again, ziz-zag fashion. "

this sounds like a great idea if you have the energy to build all the scallops. I would still find contour with a tool to decide on my preferred layout. The pattern you describe sounds like a net and pan system. check in the big black book for some figures of this.

an awesome article with some examples
http://permaculture.org.au/2010/05/10/thinking-outside-the-square-in-wagga-wagga-thoughts-on-contour/

an in practice example
http://greenfriendsfarm.org/wp-content/uploads/2011/03/net-and-pan-plantings-large.jpg

I recommend you do what makes the most sense for you when you consider, style, maintenance, microclimate, harvest, water, and whatever else you consider important when you imagine interacting with the system. Also, I always get started so I can see the response of the system to my meddlings.

Should I compact the ditches? I only have hand tools and my feet.

in general, a swale is used as an infiltrating, tree growing system to establish a food forest or other multifunction forest systems. I think of it as a stop-gap and trajectory changing structure.

If your goal is to pond the water on the surface to create wetlands or other surface water features, then compact it.

Know of any resources on this?

here's a few links
http://www.harvestingrainwater.com/
http://permaculture-and-sanity.com/pcarticles/permaculture-earthworks-and-swales.php
http://appleseedpermaculture.com/permaculture-earthworks-in-the-hudson-valley/
http://permaculture.tv/tag/swale/
http://www.youtube.com/watch?v=UFeylOa_S4c

hope this helps
 
neil bertrando
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Michael Judd wrote:Great reply. What I was hoping for, thank you. Few questions on your reply. Also like to ask what tool/machine you would recommend as the next scale up from hand digging, taking tight spacing into mind.



tight spacing can be tough with a machine, if you don't want to use a shovel and have tight turns (how tight? sharp turns in 3'? i.e what is the a-frame width?) then you can use a small track-hoe aka excavator, depending on the size you would like to build. the track-hoe, with a skilled operator, should be able to make turns in the earthworks about as tight as the width of the bucket as long as you have space for the tracks.

Michael Judd wrote:1. I don't flip flop the A frame as I noticed it changes level when on a perfectly level slab. But you're saying that is part of the design? Think I'm going to work with a bunyip from here on.


to calibrate your a-frame,
1. take two small, sharp sticks and your a-frame to slightly uneven ground (a noticable slope will give you confidence in this method).
2. place one stick in the ground and place one leg of the a-frame touching the stick
3. place the other leg as close to level as you can with your eyes then put the other stick in the ground at that location.
4. mark the location of the string at this point after it stops moving
5. take the a-frame and switch the positions of the legs, touching the sticks in the same locations as the first time
6. mark the location of the string at this point after it stops moving
7. level is the line that falls in the center of those two lines. Mark this location as your level line.

I calibrate an a-frame each time i use it because some warp in my experience. I still flop flop it to account for human error.

Michael Judd wrote:3. Are you saying dig out the difference in the basin using the 4' level? That could up make a very deep end.



If you have measured contour well the first time, it will not have a very deep end, the level will just even out any microdepressions that occur during digging. if you have substantial rainfall or catchment area this won't matter as much or at all (as long as your first measurement is good and your spillway is large enough).

if you will have a really deep end, you may want to alter you earthworks. you could do as I described, or check the links from my last post, another option would be to measure a contour line off various points from the top of the current swale and dig those out. then your current swale can act as a spillway to link them.

what is the best way to post a picture? just add as an attachment? can you post one that will give us a reference point for conversation?



ps. just figured how to quote transfer. yay!

and attach photos...

here's a street runoff harvesting swale, unplanted, mulched, spillway is original earth drain with a small checkdam added to divert water into the swale.
swale-harvesting-streetwater.jpg
[Thumbnail for swale-harvesting-streetwater.jpg]
 
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Michael Judd wrote:... Generally I have been digging the basin part about 12" deep by 24" wide for 40+ feet in length. I was told to maintain the depth all along but when I move across the hill I notice that one end of the basin sits much lower than the other.



I did a test swale this summer 12" w x 8" deep about 30' long. I had to use a pick ax, mostly. It's not totally level but it did the job! It was about 6' past the pig paddock, a little down slope. The runoff from the pigs did an incredible job of fertilizing the paddock with the swale and the swale capture that fertilized water. Frogs & other small creatures moved in. I'll be added many more small swales. Who cares if their not level!
 
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