The swale technique :
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Water is one of the great forces of nature.
It is a source of life and energy that we can
slow down, accumulate and redirect as it flows
down towards the lowest point of a property.
We can take advantage of this precious resource
in many different ways.
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A principle that is essential in permaculture is to retain water on your property as long as possible, to take advantage of all its benefits, in as many manners as you find uses for it. Evidently, this applies when and where it is logical and profitable to retain and/or slow down rainwater.
Swales are earth works designed to slow down the water flow passively to benefit more fully from this resource. A swale is made of a ditch (an elongated depression in the ground) and a berm (a mound or bank of earth serving as a barrier). They are constructed perpendicularly to the slope, and they redirect the water flow to prevent sudden floods and erosion by managing water movements in a gentler way. This implies that they must be level. In other words, they follow the contour of the terrain. On a topographic map, the contour lines are represented by curved lines that allow us to visualise hilly and mountainous areas and to know their altitude. The swale has exactly the same altitude (the same height relative to sea level) along all its length.
Swales can be spaced along the descent of the slope, each one lower than the other, like uneven, but leveled, stairs. At one end of the swale, water can overflow gently into the other swale. When building swales, it is necessary to design and construct them carefully to prevent their destruction and even cause landslides, especially in areas with steep slopes or heavy rainfall.
(There is another earth work that I don't know well, the Keyline technique, which differs from the swale. The ground is less disturbed, the water is not redirected and it's possible to make parallel lines. This video will further explain its advantages. My understanding is that both systems - Keyline technique and Swales - each present advantages that differ a bit. Look at this video of Geoff Lawton explaining this.)
Swales apply basic principles similarly to rice fields, whether on mountainside or on flat terrain. But while rice is planted directly in the water (since it doesn't mind this treatment), usually, vegetables will be put on the berm, to avoid drowning. Each time the ditch accumulates streaming water, the berm will absorb and store it, allowing plants access to water well after the ditch will dry off. Also, with passing seasons and with a good vegetation cover, the soil's capacity to retain water will increase.
Usually the berm is the ideal plantation spot, protecting plants and trees from floods while giving them access to the water that has been retained in the ditch. But in areas liable to flooding, a wide enough berm may also be used as a dry pathway, readily accessible even after heavy downpours.
Various examples of working swales :
When applying the earthwork technique of swales, we can redirect the water in excess where it can serve other uses before allowing it to exit the area. In this first example from "PermaculturePA", we can see a spillway directing rainwater away from a building into a small pond, oxygenatinig it at the same time. Once the pond is full, it overflows passively into a swale, which is used to irrigate what seems to be a young orchard. By the way, swales have the effect of improving the growth rate of nearby trees.
In this other example, on a hill side, a series of swales gather a big volume of rain water for young plantations. The excess water flows down into an existing pasture. We can plant a diversified vegetation, including trees and bushes, for instance to shelter wild life, and to stabilise an nourrish the soil and grow diverse crops, from lumber trees to berries, herbs and traditional vegetables.
This way of slowing things down gives water enough time to penetrate deeply in the soil. At the lowest pond level, the volume of water becomes important enough to form a reserve in case of a drought. Once constructed, this system works passively, e.g. without human intervention or mecanisation.
But a water pump could be installed in the lowest pond, making it possible to bring back the precious resource uphill. And if its spillway feeds a small descending brook, a small turbine could also be installed, which could produce at least enough electricity to make the water pump function. A reservoir of a few thousand liters are one more insurance against an eventual drought. Anyway, this system already accumulates enough water in the soil to allow the plants to withstand long streches without rain.
The swale also works well on flat terrains. The one presented here is 3/4 of an acre and its owner take advantage of a building's roof to collect rain water. He directs it into his swale and can accumulate an impressive amount of water.
Portions of deserts has been rehabilitated with swales, just in a matter of months.
Micro-swales may be installed in a small thirsty urban garden and obtain good results in a few time and with little effort. In this example, the rain water collected by the house gutters was already accumulating in tanks. From now on, part of the surplus go in the little swales and, with the passing months, the ground, formerly arid, is now able to retain enough water to sustain planting.
Swales and my gardens :
Going back to my own property, I'm blessed with a swale that I never intended in our front yard. Look at the following photo.
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| In our frontyard garden, at home, the cement pathway (at the right on the photo) starts at the foot of our porch stairs and winds through the flowers up to the city sidewalk. And all along, it is lower than everything that is surrounding it. In fact, to step on this pathway from the sidewalk, you have to take a step down. Therefore, it creates a 5-8 cm (2-3 in.) recess, perfect to collect and retain rain water, which has no other escape route than the surrounding soil that absorbs it quickly. No flood. With the help of the natural layer of mulch produced annually by the plants themselves, I never need to water these flower beds, even when we have a dry spell. |
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| This snap shot had been taken a few month after we took possession of our woodland. On the opposite side of our entrance way, relative to my position as a photograph, construction material, bushes and trees block the view to another open space, which is located just behind, and which has become our vegetable garden one year later. Nevertheless, we can appreciate how flat is this field. |
On the farm, the vegetable garden is located on this small, level plateau that stands raising over the surroundings. It receives a lot of sun and is somewhat protected from strong winds by a few bushes. But its configuration does not retain rain water effectively. My husband worked during a whole summer digging long, deep trenches to bring running water to the garden and to the paddocks. Right now, our main source of irrigation is our surface well, located in a much lower spot on the property.
In each event of a power cut, we must do without our electric water pump. Therefore, during a drought, a prolongated blackout would be very hard on the garden. We would have to rely on our pond and transport the precious water up the hill, a tiresome task, obviously, or to buy or rent a generator. Naturally, I want to reduce that risk. We have a few reservoirs, including one 1000 litres. But right now, we don't have a mean to collect rainwater directly on site.
In July and August 2017, we erected a summer chicken coop next to the vegetable garden. This will enable us to collect rain water from its roof into a series of rain barrels. I would like this to be one of our 2018 summer projects. But in 2016, I also started to encircle the garden with a swale to retain rain water before it flows towards lower parts of the properties.
On the Northern side of the vegetable garden, the declivity is quite important (around 4 feet - 120 cm). The barrels on this photo are at the garden level. I was standing 4 feet lower when I took this snapshot, taken in 2014.
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The following photo shows a swale dug in the soil. It is the narrow ditch of earth right behind the cardboard-covered mound that we see on the foreground. This mound is made of the earth and sod that was dug to from the ditch. There is also cardboard behind the ditch. It's used to smother the grass, at least temporarily.The ditch and the mound are perfectly level from one end to the other.
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| The Eastern and Southern outer limits of the garden are not made of strawbales. So I built a swale directly in the ground, in a conventional manner. We can see quite easily that this earthwork follows the circular limits of the garden, horizontally from on end to the other : just look at the black stakes and the white string running towards the South-West end of the garden.The rain water is gathered by the swale and can only escape by being absorbed by the soil. I deviated from the general rules of using swales by planting my 36 rhubarb plants in the bottom of the ditches instead of on top of the mound. I'll explain my choice in one of the following paragraphs. |
At the end of this swale, on the right of the photo, you can note a small flood barrier made of packed earth (it's dark brown, as it was not yet covered with cardboard). This spillway is a bit lower than the mound. Our cat is heading right towards it. In the event of an overflow, the water can spillover through this end without eroding the mound itself. Up to now, it never happened. Furthermore, I have yet to see standing water in this ditch. It will happen, eventually, but for now, the soil is still too thirsty and it will probably take a long time to recharge in humidity.
You can notice the slumping strawbales behind the swale. Some of them were already 3 years old on this photo of 2017. They are a little higher than the swale. But towards the North (on the right) they go down a slope that gets steeper as it goes. I would need to make another swale on this side too. But I could have done it in the first place with my bales. Except that I did not know how at the time. Now I know and I'll explain myself a little bit later. Back to my earthen swale for the time being.
Normally, as the bottom of the ditch is supposed to fill up with water on a regular basis, it is not considered a logical planting spot. After all, most plants don't appreciate frequent floodings, even for short periods. The ditch may better serve as pathways once they dry out. But some plants do like these occasional events. Just think of all those species growing at the bottom of road ditches.
When planting on an arid site or in a spot that cannot accumulate water (as on the top a a small hillock opened to the elements), the most probable danger is to lose plants to droughts. And it is exactly the case for my garden. Therefore, I prefered to plant my rhubarbs in the ditch instead of on top of the mound, so they can readily make profit of every drop of rain. Up until now, it works well. As I said earlier, I've never seen enough rain to fill up the ditch and flood the rhubarb. On the mound itself, I intend to experiment with complementary crops, starting with oregano, which has the reputation to be invasive under certain conditions. I bet that my rhubarbs will hold them at bay ! Anyway, we will see what we will see. (Hélène's commentary : "Bof, it's not that bad ! Not as bad as mint or lemon balm, after all !" Thanks, Hélène, for this reassurance.)
There are different tools to find the contour lines on a land. This video presents the A-Frame Technique (it's the one I used to build my swale; you can see my A-frame level on the last photo in this article.) It's easy and cheap to build one and easy to use it. Laser levels are expressely made for that task, but they are expensive surveying tools. I heard that it's possible to rent them, though.
How to shape into curves an alignment of strawbales ?
Decomposing strawbales are naturally absorbent and they stand above ground. Therefore, they can form a berm. Between each row of bales, the pathways can act as ditches. Good ! I don't need to dig - or at least, not much. But unless some heavy equipment is used to level the ground perfectly, the creation of a swale entails to put the berm along a natural contour line, in other words, to form the berm into a topographic line, which will be more or less curved, as you can see in this video (in French) presenting another perfect example of a swale.
I decided to remodel the design of my garden to make sure that the beds would follow the terrain contour, at least in the parts where the slopes are the strongest. In the spring of 2016, I tackled my two lowest beds, with the idea of working a few more beds each following year. It will take time, but I'm in no rush.
The next photo shows my ditch situated in the lowest spot of the garden, blocked by its berm made of strawbales, which is very short and straight. At each end, the terrain starts to elevate. In other words, my strawbales are sitting in a small natural depression. All around it, the ground raises again in a very gentle slope.
3. 2. 1.
⇙ ⇙ ⇙
1. Here is the garden's lowest and shortest strawbale swale, planted with strawberries. It's about 12 feet (3,6m) long.
2. A pathway (covered in brown paper bags) is flanked by two strawbale beds (1 and 3). It's the lowest ditch of the garden.
3. We discern only the extremity of the second strawbale bed. Though it is not apparent on this photo, this bed is higher on the slope than the first one.
The spot where I stood to take this photo is already about 8 inches (20cm) higher than the strawberry bed.
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On this photo, the strawbale berm forms a straight, short line. It is filled with strawberry plants, along with a few orange marigolds (Tagetes). The ditch, covered in cardboard, runs behind the berm, forming a curved pathway and joining with the black surface of a wider pathway, on each extremity of the berm. By wrapping itself around its berm, it takes the form of an elongated letter "C". The black surface in the foreground is 3 to 4 inches (7 to 10 cm) higher than the ditch. You must take my word for it, since it's undetectable on this photo. Despite this weird configuration, the rule is followed : the ditch must be level along all its surface area, to prevent water from running into a mini stream to the lowest edge. The second berm, located behind the first, is 8 inches (20 cm) higher and just happens to follow quite the same curve as the ditch. We see this second berm almost in its entirety, only its extremity to the left is outside the photo frame. Young strawberry plants are nested in its right extremity.
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My problem, with the second swale's strawbales, was to build forming a curved line, my strawbales holding a rectangular form. It's not that complicated, when we think of it. All we have to do is to place tightly the strawbales besides each other, but to move them on their lenght, in order to put them out of alignment with each other, just like in figure number 2.
Figures 1 and 2 show a strawbale swale filled with water after a rainfall event
XXXX ««««««««««« Figure 1 : cross-section of a slope
XXXX ««««« ((()) )) arboring two strawbale swales.
((() )))
Both strawbale berms are represented by XXXX. Their function is to harbour the plants and to retain the water trapped inside the two ditches long enough that both the soil and the straw can absorb and store it.
In the second figure, you see an aerial vue of the two same swales, but only the lower ditch is represented.
The berm to the right is already full of growing plants (in green). Between both berms, the ditch is temporarily flooded (in blue). Normaly, it serves as a pathway. In a relatively flat garden that is not flooded, usually, the rainwater will be absorbed swiftly by the berms and the soil at the bottom of the ditch. Then, the pathway will be functional again.D
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Figure number 2
presents the aerial view of two
((())))lololol)))))( garden beds, separated by a pathway
XXXXo DoooXXXX (in blue). Each block XXXX represents a
XXXXoooIoooXXXX single strawbale.
XXXXooTooooXXXX Each strawbale is a component of the berm.
PLANTS--> XXXXoo CooooXXXX Each strawbale will harbour plants XXXX
PLANTS--> XXXX oHCooooXXXX eventually. Each strawbale is squeezed in
PLANTS--> XXXXoo oooXXXX in place against the neighboring bales,
XXXXoo DooooXXXX with no empty space in between.
XXXXoo OooooXXXX We can see that it is possible to position
STRAW --> XXXXoooU oooXXXX them out of alignment in order to form a
BALES --> XXXXo B ooooXBXX winding path.
--> XXXXo oL o oXEXX By grouping several strawbales alongside,
XXXXoo I o oXRXX we form a berm which follow the contour of
XXXXoooNo oXMXX the terrain.
XX Xoo GoooXXXX Between both berms, the ditch's width may
X X Xoo oo oXXXXX vary significally and quite often, but its
XX Xoo Aoo oXXXXX bottom remains level.
XX Xoo So ooXXXX In each of its extremities, we can create a
X Xo ooooXXXX spillway on the ground in order
XXXXo oAooXXXX to create a micro dam, 4 to 8 inches
XXXXo o ooXXXX (10-20 cm) high to retain water even more.
XXXXo oPooXXXX Whether from a rainfall or a watering
XXXXo oAooXXXX session, water ditch will be trapped
XXXXo ToooXXXX between both berms, giving it time to
XXXXo oHooXXXX humidify them, creating a reservoir
XXXXo oWooXXXX for the plants growing on the
XXXXo oAooXXXX strawbales forming the berms.
XXXXo oYooXXXX
XXXX ooXXXX
XXXXo WATERooXXXX
SPILLWAY --> ( (())))lololol)))))(
Higher than the ditch, but lower than
the strawbales. It allows any excess
of water to overflow there instead of
disturbing the bales.
Note that in the first weeks, the strawbales won't be able to absorb much water, because they are not decomposed enough yet. But given time, they will absorb more and more. Plus, the root system of the plants will go straight to the bottom where any moisture they need is much more available.
Conclusion :
The more uneven terrain you have to work with, the more your swale system will be winding and the more your ditches will vary in width. Therefore, don't expect your garden to look as square as a bunch of city blocks. After all, perfectly straight lines are rare in nature.
Sure enough, this curving garden will bring charm, but along with it will come a few inconviences. For instance, imagine yourself rolling a wheelbarrow up a pathway which would be uneven in width. But on the other end, it would also mean moving it on a level terrain. Much easier. Or a row cover, being rectangular, would be more difficult to adjust over such a bed.
And finally, I don't see how I could fit a chicken tractor over such a winding bed. It would be too much of a challenge, not even counting the difference of altitude between the rows on each side of your bed (one being much lower than the other if the slope is steep.
In this case, enclosing my chooks inside the perimeter of an electronet could be an alternative.
But smartly built on the right place, swales can prove themselves valuable design to make a garden working optimally, making its irrigation much more naturally with the help of the laws of gravity, while cutting on one's work load and the need of pricey equipment.
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Here, you can see where the slope starts on the eastern edge of the vegetable garden. Before constructing the swale around the eastern and southern sides of my garden, I erected the black poles of our portable electric fence to find the contour line of the garden's edge. First, I planted the poles without any instrument, and then, I used the wooden instrument in the foreground to place it more accuratly. This instrument is an A frame (built by my husband). It's a simple homemade level accurate enough to find the contour lines on a property with sufficient precision. And you know what ? My first estimation wasn't bad at all and I had only a few adjustments to make before starting the digging !
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