Posted by & filed under Dams, Food Forests, Irrigation, Land, Swales, Water Conservation, Water Harvesting.

by Rob Avis

Michelle, Rowen and I were driving home from a vacation in the mountains when we passed by a swale on a farmer’s field in the middle of Alberta cattle country. Naturally, it piqued my curiosity and I had to stop the car to investigate. It was such a great example of how this simple technique can catch and store water on a large scale, we decided to make a short video about it….

What’s a Swale?


Rob walking along a swale after a huge rain
event at the Permaculture Research Institute
of Australia

Simply put, swales are water-harvesting ditches, built on the contour of a landscape. Most ditches are designed to move water away from an area, so the bottom of the ditch is built on a modest slope, usually between 200:1 to 400:1.

Swales, however, are flat on the bottom because they’re designed to do the opposite; they slow water down to a standstill, eliminate erosion, infiltrate the surrounding area with water, and recharge the groundwater table. When water moves along the flat bottom of a swale, it fills it up like a bathtub — that is, all parts of the bath tub fill at the same rate. The water in a swale is therefore passive; it doesn’t flow the way it would on a slope.

To install a swale, we have to find a contour line. A contour is a horizontal line (with a constant elevation), along a landscape.

To better understand contour, imagine walking on a hill. If you are walking up the hill you will be putting most of your weight on your toes, if you are walking down a hill you will be putting most of your weight on your heels and if you are walking along the contour of the hill, you will be placing an even amount of weight on your heels and your toes. It is this contour line that we need to find when designing and building swales. A variety of survey tools such as transits, laser levels, water levels or A-frame levels are used to find contour lines.

Dam Filling Devices

The swale you saw in the video was being used to carry water across the landscape — from the ditch by the road to the dam far in the distance. But how?

Well, we know water always goes to the lowest possible point. So the swale is built lower than the ditch. When water flows from the ditch, it moves across the swale and fills up the dam. Once the dam is full, the extra water will sit in the swale, or get pushed back into the ditch if it gets high enough. In this way, the swale system is self-regulating. Once the available water has reached an equilibrium, meaning it has filled the lowest point and has no where else to go, it just sits there, unmoving. And as it sits, it slowly seeps into the surrounding landscape, hydrating the soil and recharging the water table below.


Rob explaining a mini-swale to students — looks like he could use
some of his own swales to help revegetate his head!

In this way, the swale fulfills three important functions: it carries water from the ditch to fill the dam, it rehydrates the landscape, and it prevents the dam from overflowing by acting as a channel back to the ditch.

Swales are great for filling dams anywhere except for arid or hyper-arid environments, where they would dry up too quickly.

Establishing Trees — No Watering Required

In my video, I showed how wet the top of the swale is. This was due to capillary action pulling water from the back side of the swale into the soft mound. (Capillary action is the phenomenon where liquid flows upward through narrow spaces against gravity — you can see this phenomenon when you dip the end of a paper towel in water and watch the water climb up it).


Diagram by: Adrian Buckley of
Big Sky Permaculture – thanks, Adrian!

Because the capillary action is so effective in the soil, these mounds along the swale can provide enough water to establish a tree system with little to no additional irrigation. Melt water that would normally be lost to the ground is captured and stored. Trees established on top of a swale at the right time of year (when the swale wall is wet) have a much higher chance of success than trees in the middle of a field. Once one row of trees is established, you can start to revegetate lower parts of the field.

Conventional wisdom says that you need more than 15” or 381 mm of annual rainfall to establish trees. This is not necessary when you design a swale system to aid with water catchment, because it effectively concentrates and holds the available water in that area.

Plant a Tree, Grow a … Farm!

In the example in my video, this farmer would be wise to establish trees along the swale that could act as a windbreak, provide lumber, or double as fodder for chickens, pigs, cows and other animals, especially in times of drought. This sort of mixed modality farming leads to increased productivity and more resilient income streams, as well as happier animals and healthier ecologies. The implications of using swales to rehydrate farmland and establish trees are huge. Joel Salatin, a successful farmer and respected author, grosses 2 million dollars a year on only 1400 acres using this system of mixed farming. When he spoke recently in Calgary, he showed how, if every cattle farmer in North America farmed the way he did, we could sequester all of the CO2 produced since the beginning of the Industrial Revolution!

Even permaculture founder Bill Mollison demonstrates that farms can be placed under 25% forest cover without a reduction in output. This is due to the increase in yields from the farm as well as the creation of additional habitat for predatory birds, insects and mammals that keep the the “pests” in balance.

So now you can see why we had to pull over — swales, though simple, can open up the floodgates to healthier landscapes and food systems!

18 Responses to “Swales: The Permaculture Element That Really “Holds Water””

  1. narf7

    I LOVE swales…the only thing about our property is that we live in Tasmania and our entire 4 acre property is covered in rocks. We live on a very steep slope and could really benefit from the use of swales to slow the decent of water down to the river and out to sea but have no idea of how to circumvent the rock problem. Love the post however :)

    Reply
  2. Nicollas

    Swale are great but on my 1:3 slope it is not the good otion, too bad.

    @narf7 : try planting pioner species on contour (like sea buckthon), it helps infiltration (some numbers here)

    Reply
  3. Cheryl

    @ narf7, are they the kind of rocks you can use or just really big “look-at-me, I’m stunning!” landscape rocks?

    We have between 3 and 8 inches of sandy loam (or straight sand, depending where you dig) then another 8 inches of river pebbles, then clay, so I can kind of sympathise. I’m sure if I was keen enough I could pave my garden paths with pebbles – I have started filling in the holes in the driveway.

    Maybe there are some spaces between the rocks? Under the rocks? If you can move them – I’ve always adored the views around Tilba in NSW, with the big (house sized in some cases) pieces of rock visible in the hills, but actually doing anything with it would be a challenge.

    Reply
  4. Geoff Lawton

    Small rocks that can be piled on contour will form stone walled earth backed swales and there are examples that are 1000′s of years old in the Middle East. If you back fill with soil and mulch you will speed up the process of growing trees on contour rapidly. Large rocks that cannot be moved are 100% run off and effectively roofs and can be swaled around to great effect for rapid tree growth because of the major increase volume of rainfall infiltration. Steep slopes can be net and pan earth worked with small catch pan basin mini earth worked for trees connected by diversion drains as net to trap and infiltrate water to each tree planted for steep slope recovery and stability. Swales work perfectly fine in all mixtures of soil media sands, sandy loam, pebbles, clay even volcanic ash has now proven to be fine, the pioneer plant and tree growth successional planting changes thats all.

    Reply
  5. Carolyn Payne

    If anyone wants to talk about swales in clay that hold water for three months please head over to Mudlark Permaculture on the Permaculture global site and feel free to contact me. I have fine powder silt over quartz gravel over clay. Thanks for putting this up Rob, I can’t believe that Alberta countryside is so devoid of trees.

    Reply
  6. Cheryl

    I’ve been sitting in the sun on my tank the last few mornings, looking at the slope around it and trying to work out where and how you’d put swales.

    I haven’t come across the net and pan idea before and it helps – the whole block slopes gradually south to the creek but below the tank it drops more sharply from the east and west as well. I think that comes from the earthworks when the tank went in, but we bought as is so I’m just guessing.

    I couldn’t see how a single swale would work but linking catch pans makes lots of sense.

    Now I just need to read some more and wait for the frost so I can see where it flows too.

    Reply
  7. C

    narf7, your property sounds a lot like Sepp Holzer’s. Like Geoff said large rocks are great hard surfaces for capturing runoff but Sepp Holzer also uses them as thermal mass to store heat. That way you can create warm microclimates and grow cold sensitive plants that might not normally grow in Tasmania.

    I recommend you have a look at some of the Sepp Holzer videos on youtube. They’re really good.

    Reply
  8. Angelo Eliades

    Carolyn, since you’re in Victoria, Australia, and you have swales in clay that hold water for three months, have you considered growing any water loving aquatic marginal edibles? You could grow taro really well with that much water, I’m in Melbourne and can grow taro in my regular garden beds.

    Reply
  9. Joshua

    My favorite article yet and the comments are great. I have only installed one small 9m long swale on the front of my urban property and the results are amazing.. In fact, I killed two trees by not trusting that it was working and the drowned. Feedback – the swale works. It is the first step of any of my designs now…. Thanks Rob!

    Reply
  10. lisa

    These seem awesome. Does anyone use them in regular suburban blocks? Would they be a water hazard for young children? Or do they only remain full briefly after rain?

    Reply
    • mujeeb ur Rehman

      i got many thing from this page but i want to learn about concrete Swale. if you can tell me please reply me

      Reply
  11. Carmen

    Hi, great info!! Now, what are the particulars about having the swales in the pasture with the cattle? How can that be made to work?

    Reply
  12. Louie

    Can anyone reply to Lisa’s post I really would like to install a swale in my suburban block too. How deep and wide would they need to be? Are the bottom of the swales roughed after construction to improve infiltration and are they heavily mulched?

    Reply
  13. Stan

    Yes Lisa, you can make use of PC principles in designs anywhere. Just make the best of what recourses you have.
    We just cut swales on my property & have been impressed with amount of water they capture! Lots more to do of course. Ck out book by Toby Hemenway called Gaia’s Garden.

    Reply
  14. Stan

    Posted comment re: Lisa. About size & spacing depends on your site specifics. But in general swales can be 1-3 ft wide and usually 1/3rd of width for depth. (If 3ft wide by 1 ft deep) Although they can be smaller or way bigger – it just depends. About mulching – of course in some cases filling the swale full of wood mulch creates a big sponge that slowly releases water for your plantings.

    Reply
  15. Thom Foote

    Spokane area-17″ rainfall/year. My 10 acres in pine forest with 6-8″ forest duff. What are your thoughts on building swales to charge small ponds in a forest setting where the water does not “flow” donwhill but is absorbed by forest duff. Thansks

    Reply
  16. D. Cates

    what if u have an obvious downward slope in a small garden plot? is it really necessary to build an A-frame & do all the intense measuring that I’ve noticed on YouTube? Isn’t that for much larger pieces of acreage? My husband doesn’t want to learn anything about permaculture.

    Reply
  17. Shannon

    Does anyone know about using swales to help desalinate your bore water? Are these swales built on contour too? Does this create more of a problem then with the salt sitting in your topsoil or can salt loving plants soak it up?

    Reply

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