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.
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.
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.
|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.|
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.
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.
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The spot where I stood to take this photo is already about 8 inches (20cm) higher than the strawberry bed.
XXXX ««««« ((()) )) arboring two strawbale swales.
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
XXXXooTooooXXXX Each strawbale is a component of the berm.
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.