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Off-contour swales

 
Posts: 16
Location: Hertfordshire & Devon, England
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(I originally bumped an old thread, now assigned to the organic forum since the new format came in, but nobody has replied, probably because it wasn't really the right place for that subject matter, so I'm putting it up here...)

We are looking to drain some of the excess water off our almost flat, heavy clay soil.

From everything that I have researched, it looks like off contour swales should help us do the job, but the only information I can find is about putting in swales on contour.

Brenda Goth mentioned here: https://permies.com/t/10983/organic/water-loged-soil about starting at the lowest point and putting in a pond, which sounds logical but will require more time, money and manpower than we currently have available. Although of course if that really is the way to go, I will wait until I can do the job properly.

We are planning to put in a pond in the future anyway, in the lowest part of the land, but I was intending to put the swales in first, encouraging the water down towards that area.

So, does anyone have any detailed instructions/advice on how to put in off-contour swales (Specifically any instructions/tips on actually digging out the swales off-contour, if relevant), or any conflicting advice or suggestions as to why this might not work or is not a good idea?

 
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I have wondered this myself recently. I am looking at an area where I can dig a small pond. What I would like to do, is dig a swale or trench leading down into the pond and channel all the rainwater coming off the hillside into the pond. This would not be a swale on contour. I have actually thought about directing multiple swales into this runoff ditch and taking everything down to the pond.
 
Iain Bagnall
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Location: Hertfordshire & Devon, England
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Glad I'm not the only one Jason, but whenever I look online or watch a video of Lawton (or whoever) putting in swales, it's always on contour.
I was hoping someone might have some experience of doing it the other way around and running water off the land rather than trying to capture it.
But so far, nothing.
Anyone....?




 
Posts: 151
Location: Madison, AL
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Maybe you'd have more luck looking at artificial creekbed designs/tutorials?
 
master pollinator
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The article "Dynamic Water Storage" on this page http://www.permaculture.org/nm/index.php/site/Beekeeping/ has some discussion of off-contour swales to divert water to ponds.

This chapter from "The Challenge of Landscape" by PA Yeomans discusses the construction of drains (swales) to fill dams: http://www.soilandhealth.org/01aglibrary/010126yeomansII/010126ch19.html The complete text and photographs: http://www.soilandhealth.org/01aglibrary/010126yeomansII/010126toc.html
 
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Location: North East Scotland
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It is so nice to see others with the same problem. We have major issues with waterlogged clay soil and erosion from the water taking the most direct route down the hill.
 
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I think this is what you are asking for. See especially section 6.9, although you may need to read some of the preceding sections to get familiar with some of the tools and techniques.
ftp://ftp.fao.org/fi/CDrom/FAO_Training/FAO_Training/General/x6707e/x6707e06.htm#117a

Obviously the specific answer for your site depends on topography, length of swale, etc, but once you decide on the slope you need to implement you can get as gradual as 0.1% slope using these methods. If you are really trying to move water away I would guess you would want at least a 1% slope, maybe more.
 
Iain Bagnall
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Location: Hertfordshire & Devon, England
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Thanks Robin, that's fantastic.
While some of the other links etc have been useful, what I have been looking for is something that goes into more detail on how to actually implement what I'm hoping to do. This site looks to do that, which is brilliant.
 
Robin Hones
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Happy it helped. I forgot to mention that Brad Lancaster's book "Rainwater Harvesting for Drylands and Beyond Vol 2" pp 208-210 also covers the topic. Basically run a countour line, measure off sections (eg 20'), then use a bunyip to offset from that whatever change in elevation you need for each section to get the desired grade. For example 2.5" per section of 20' would get you 1% grade, but of course you would need to add an extra 2.5" in each additional section to maintain that same 1% grade over the length of the swale.
 
gardener
Posts: 856
Location: South Puget Sound, Salish Sea, Cascadia, North America
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It seems like a question of scale. Most of the keyline work was done to figure out how to capture seasonal rain in the soil in sloping landscapes. You have the classic agricultural scenario, in that you want to increase drainage, commonly done using drainage ditches and drain tile... to the demise of many wetlands, and decline of many a summer stream. I don't know if this analysis suits your setting, but thought I'd put it on the table.

1. can you capture the water before it floods your site.
2. is you site a water receiving and storing part of the landscape, and by draining it are you degrading watershed hydrology?
3. is the saturation uniform, or is there variation that you can use to organize your planting.
4. can you grow plants adapted to winter wet?

It could be that "your" piece of land, is the part of the landscape that is wet... or that your upstream neighbors wanting their land dry, drained their land onto your land.

I just wanted to reintroduce the watershed hydrology viewpoint... maybe the problem is the solution...

Maybe you shift your viewpoint and trying to grown inundation intolerant communities is a Mollisonian 'type one error' and your place of abundance involves shifting to an aquaculture focussed development model. Ducks? Fish?

At a small scale, every ditch has a mound next to it that is drier then the surrounding land... and willow is a nitrogen fixer and a great producer of biomass and browse...

None of this may apply... but after all this is the permaculture forum.. and we really don't know much about your design situation
 
Iain Bagnall
Posts: 16
Location: Hertfordshire & Devon, England
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Very good point, Paul, I'll try to give more of a detailed description of the scenario:

The problem we have is that we are in an area of relatively high rainfall as we are near Dartmoor in Devon.
The soil is clay - we have about 2-3" of pretty decent clay-ish topsoil, then gradually becoming more clay. About a foot under the surface, we then hit solid grey clay. I've dug down about 3 feet and it's still the thick grey clay. How far down, I don't know yet.

We don't have much in the way of hills around us that run water down onto our land, or rivers, streams etc, it's just that the water that is there from that rainfall, just sort of sits there on the surface. It's a bit soggy in summer (soggier this year due to the rain we've had) and in winter, there is standing water on the surface. It's not underwater as such, but not far off.

We are planting up as many deep-rooted plants as possible, to try to break up that clay soil a bit.

Beyond that, my thinking was to create some off-contour swales to run some of that water down towards a pond, which will also provide a more diverse landscape, with mounds, swales, small ponds, hugelkultur beds, therefore lots more edge, and some different niches and microclimates to play with.

Willow is in my plans to soak up some of the water, as is bamboo.

This will all be done by hand, so we were going to put in one swale, and see how much of a difference all this makes to the area above the swale, with a view to putting in more if all goes well with the first one, only if we're putting in more, we'll hire a minidigger.

So, the quick answers to your questions would be:
1. No
2. No
3. Yes, although there is some slope so some areas are wetter than others
4. Yes, that's certainly a consideration.

One further problem (although also a lovely benefit in some ways) is that we are in an area of culm grassland, a local wetland habitat which is a depleting habitat for endangered butterflies and other creatures. We have consulted with our local Wildlife Trust, and on their advice, are going to leave around 1/4 - 1/3rd of the site (the wettest part that is slightly downslope and out of the way from the area we are looking to drain) as grassland for habitat.

Where the grassland has not been managed, though, we have very tall soft rush, which has totally dominated. Where we have started cutting this to encourage a more diverse mix of grasses, the ground is getting slightly less damp as the sun and wind get to the ground. We're doing all of this slowly and all with hand tools to begin with, in order to observe the changes and learn as much as possible about the land, rather than rushing in with the diggers and making possibly mistakes that can't be rectified.
 
Paul Cereghino
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Location: South Puget Sound, Salish Sea, Cascadia, North America
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Sounds like the London Clay rather than the Chalk Hills of Chiltern... thanks for the introduction--I like cultural geology. My am on a glacial plateau on a pocket of fine sandy silt, surrounded by compacted till, so I have winter wet soils, but no clay (much to the chagrin of my earthen plaster dreams! I am envious)

For spectators: http://en.wikipedia.org/wiki/London_Clay

Quick thoughts:
Clay has strong capilarity... your water level can be a foot below ground, but pore space is so tight, that you can have no oxygen a foot above water level. So you may have to drain more deeply then you suspect to achieve aerated soil over winter to grow your fava beans and kale.

I suspect ideas like hugelkultur might be very useful for disconnecting your surface soil from groundwater, while maintaining a summer moisture reserve (summer moisture might be more of a concern for me than for your... but climates change).

I suspect a really solid elevation surveys would be invaluable. If you don't know already, look into 'water levels'... more precise over distance than an A-frame.

Because of your sticky soil, both high angle of repose, and low erodability, you can move water with a pretty steep walled ditch. Rule of thumb is 2% slope to move water... or 2 inches drop over an 8' board.

Typically I have started at my end point elevation, and mapped my line up hill, measuring length and tracking elevation. over a 100 feet you'd want to drop 2 feet, and so you see having long drainage ditches involves deep trenches, and so managing lots of smaller wet and dry microclimates is more labor efficient for drainage, but gets in the way of broadscale cultivation.

It could be that you combine hugelkultur and drainage... such that along the ditch you have 'backwaters' by adding 'sills' to your drianage ditch, so that while you are lowering water level locally during rainy periods, you are recharging your wood, and the last light rains, don't leave the system. see attached.

All speculation, thanks for the opportunity

 
He baked a muffin that stole my car! And this tiny ad:
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https://permies.com/t/61704/Food-Forest-Card-Game-Game
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