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To Swale or Not to Swale

 
pollinator
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I came across this video today and thought it might promote some interesting discussion. It'd David Holmgren, Darren Doherty, and Dan Palmer talking about a variety of interesting subjects.



And adding my own 2 cents, Sepp's big lakes in Portugal and Spain did end up working although it took some time, see the Desert or Paradise Projects
 
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Location: Thunder Bay, Ontario, Canada
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Interesting video, thanks!

I agree that every technique and tool has a time and place. Swales are one of the more general tools that I think can be applied to the majority of cases. Darren made a great point that before applying a tool, it's best to first think about what you are intending to achieve by using that tool.

With a swale, you are doing one of the following things:
  • Getting water into the ground in situations where it would otherwise run over the surface.
  • Lifting tree growing zones above the water table where there is a lot of water.
  • Creating deeper fertility zones where the topsoil is very thin.



  • David mentioned that swales on his property is currently inappropriate because he gets only winter rain and the soil soaks it all in. It got me thinking about this. I would expect that under these conditions, a swale would collect some water as it percolated through the top layer of soil, concentrate it, and provide a pathway for this collected water to infiltrate deeper layers. Come the dry summer months, wouldn't that mean less evaporation due to the reduced surface area, and increased depth the water is now at?

    He mentioned that his soil never saturates. If that is the case then is he getting no movement of water through his land? If that is the case then it also means he is getting no movement of nutrients either...
     
    steward
    Posts: 809
    Location: Italy, Siena, Gaiole in Chianti zone 9
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    Zach I think this video I'll watch it over and over again I'm taking my PDC now but this video is really great and inspiring, thanks I'll share
     
    Zach Weiss
    pollinator
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    Nick Kitchener wrote:Come the dry summer months, wouldn't that mean less evaporation due to the reduced surface area



    Swales increase the surface area of soil exposed to air, so all other conditions being equal this would actually increase evaporation during summer months.

    Nick Kitchener wrote:He mentioned that his soil never saturates. If that is the case then is he getting no movement of water through his land?



    My understanding of this is that he that he means his soil never saturates to the point where there is surface runoff; water is still moving through the soil, just not over the surface. In a very specific situation where there is an impermeable clay layer right at swale depth or a bit above, the swales would act in the way you described even without surface runoff. Without this very specific geological condition though there would be nothing I can see keeping the water high enough in the soil to actually enter the swale system.
     
    Posts: 113
    Location: PNW
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    Really great stuff! Thanks!

    I am taking a PDC as well (Hi there, Lorenzo!) and can totally identify with the 'urgency/momentum' part of the discussion.
    This is defiantly one I need to hear again. Thanks for sharing.
     
    Lorenzo Costa
    steward
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    Hi Zenais, yep we're in the same class!
     
    Posts: 7
    Location: Dandenong Ranges - Oz
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    Hi all,

    I live in the same state as these guys and have quizzed both David (at one of his house and garden tours) and more extensively Darren at one of his Joel Salatin events a year or so ago. (So lucky to have these guys in the same state)

    Apologies to Darren if he reads this, I really bugged him but I had to know the answers to my questions. Sorry Darren.

    I was curious how in the state we live, Victoria, where we get winter rain and very hot dry summers, how does one cope with it from a grazing perspective and annual plant growth perspective and access to on farm trapped water.

    The winter rain can be endless drizzle or actual rain and then in summer it can go weeks and weeks and weeks without rain.

    I remember Darren saying that swales can act as drainage systems and from that I understood it to mean when used in the wrong environment they could actually interfere with the water flows as water would collect in bands where the swales were but little or substantially less elsewhere.

    Darren's thought was that rather than widely space swales, closer space smaller earth mounds would suit our environment. (maybe the raised lines of keyline would be enough then in combination with the ripping would do more than swales.

    Just on what David said about swales and winter rain, the wet in our state in winter is constant and the ground can be saturated all winter long and holding rain in swales in my opinion would stop the spread of water to the sub soil rather than spread it. Solution? Not too sure but holding it in dams (ponds) may be the answer or keyline to soak it more where it fell than in widely spaced swales.


    The takeaway point would be that in summer, swales around here would be little more than hot, bone dry ditches that held the water up in winter when it was wet and do nothing in summer as it it bone dry.

    Anyway, just my 2cents

    Cheers
     
    pollinator
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    Bede - swales are not really pasture systems. They are designed to collect and concentrate moisture in the deeper soil where tree roots can access it in the dry season. From what I have studies Savory style rotational grazing is one of the best way to improve pasture; over time the concentration of soil organic matter increases, so the water retention capacity of the soil increases over huge areas so grass growth improves.

    If you want to integrate tree crops in your pastures then swales are very helpful - this might be to provide shade, windbrakes, tree fodder for droughts, fruit and nuts etc...


    [caveat - they may be appropriate in pasture systems if you have torrential rainfall and substantial surface run-off, but my experience of pasture land is that surface run off is unusual as the grass slows and helps infiltrate surface water]
     
    Bede Carroll
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    Location: Dandenong Ranges - Oz
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    Michael Cox wrote:Bede - swales are not really pasture systems. They are designed to collect and concentrate moisture in the deeper soil where tree roots can access it in the dry season. From what I have studies Savory style rotational grazing is one of the best way to improve pasture; over time the concentration of soil organic matter increases, so the water retention capacity of the soil increases over huge areas so grass growth improves.

    If you want to integrate tree crops in your pastures then swales are very helpful - this might be to provide shade, windbrakes, tree fodder for droughts, fruit and nuts etc...


    [caveat - they may be appropriate in pasture systems if you have torrential rainfall and substantial surface run-off, but my experience of pasture land is that surface run off is unusual as the grass slows and helps infiltrate surface water]



    Hi Michael,

    Thanks so much for the reply and good advice.

    I have to admit that although having purchased and read the designer manual many years ago and understanding that permaculture covers many topics including legal structures and even finance/banking systems, I had indeed fallen into the trap of thinking that swales were more than a permaculture tool and were obligatory

    I've since stumbled onto the very person you mention in Alan Savoury and then further into Greg Judy and his books.

    Great reading btw for anyone interested in pasture systems and now I've heard online that Greg is using Keyline to further his pasture.

    Interesting stuff.

    Cheers Michael.
     
    Posts: 88
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    Hi guys,

    i live in the south of Portugal, with mediterranean climate caratheristics ( rainy autumn/winter and dry late spring/summer).

    Nick Kitchener said an important thing about swale systems ( "Creating deeper fertility zones where the topsoil is very thin.") On the ridges of my property i have sometimes 20 cm of soil before hitting the bedrock so the added soil is definitely a plus.

    And like Bede Carrol remarked about D. Doherty idea ("...closer space smaller earth mounds would suit our environment") an orchard installed in earth mounds with 6 meters distance in between plus the annual inter mound ripping looks effective in spreading water through the farm.

    Take care

     
    Posts: 1444
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    Bede, i have to admit to confusion at the suggestion that swales would interfere with water soaking into subsoils but ponds would help water soak in.

    Either one is preventing surface runoff from, well, running off Which means holding the water on the given piece of land, where it can either evaporate or soak in to the ground. The other options would be animals drinking it or people diverting it someplace else. Left alone, in either case, the wate only has two choices.

    So both will lose some to evaporation and some will soak in. A deep pond with relatively low surface to volume ratio may lose less to evaporation than a swale, but that pond also has less soil to water contact area, so it won't infiltrate into the soil as fast either.

    Ponds are, essentially, point sources. Their area of effect is going to be a distorted outline of the pond, elongated downhill.
    Swales being lines on contour, their area of effect is going to be along the length of the line, and again elongated on the downhill side.

    In both cases, if the ground is allowing water to percolate, water will soak in. It will soak as far as the soil conditions and the volume of water permit, in either case.

    In an environment with wet winters and dry summers, the winter effects of the two systems will be indistinguishable, I think.

    The difference comes with summer dry times, where the swale system has contributed its water and is now dry. Not that the water did not soak in, but it went into the ground and evaporated into the air, and that is all it had to contribute. The pond, with larger volume and less surface area, still has water to infiltrate after the swales have gone dry. I think that is due to the pond being less efficient at getting water into the soil - but it is more efficient at reserving water above the ground later into the dry season.

    That has up and down sides. Holding water above ground means more exposure to evaporation than if it were held in the ground. Depending on your soil hydrology, holding water in your soil And available for your plants may be a problem. I know my sand runs really deep and nothing holds water from just dropping down and down, so holding above ground, even with evaporation losses, works better than losing it down beyond the reach of any roots.
     
    Posts: 119
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    I believe it was Darren who said, in sites where both swales and keyline plowing are appropriate, the swale will have a more immediate affect on soil hydration.

    Swales are planning for run off, but really, we don't necessarily want run off, we want water infiltration on 100% of our soil. So as we improve our soil, hopefully our swales will eventually become obsolete.

    Another thought: Once installed swales will exist on a landscape for a long time. (100s of years? forever?) How long will the effects of keyline plowing exist?
     
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    Thank you for posting this great video Zach Weiss!
     
    He's my best friend. Not yours. Mine. You can have this tiny ad:
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