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Constructing Swales

constructing-swales
An excerpt from Edible landscaping with a permaculture twist: how to have your yard and eat it too. (Michael Judd, Ecologia 2013)

When it comes to growing anything, it’s all about water. You want to catch every drop of it. Moisture in the soil builds organic matter and fertility, which equals naturally healthy plants. Regardless of what you intend to grow, shaping your landscape to harvest the water is step one.

Contrary to modern landscape design, that does its best to get rid of water as quickly as possible, we want to look at our homescape as a mini-watershed where not one drop of water is going to leave. This goes for the overflow from the neighbours too; that problem is about to become a solution.

So what does this have to do with creating a planting bed? Everything: you want your beds to water themselves and pump fertility, naturally. Most raised beds you see are boxed up, and while that is a step in the right direction, you are still missing the flow.

Capture it! How it works

constructing-swales
Illustration by Matthew Von Herbulis
  1. find level ground
  2. dig out a basin
  3. mound the sod and soil downslope
  4. shape the bed
  5. fill the basin with chips
  6. let the rain fall!

Raised beds on-contour not only look beautiful and curvy on your landscape, but also hold and sink the rain. A bed on-contour is perpendicular to the slope, and each point along it is the same level. Unlike conventional swales, which are set off-contour to push water away, swales on-contour do the opposite by slowing and infiltrating the water right where it is needed most: your garden. To avoid confusion and help you visualise how to create these curvy beauties, I will use the terms basin and berm.

constructing-swales
Illustration by Matthew Von Herbulis

Water zooming down and off your landscape falls into the dug out portion of the swale – the basin – which is cut on a level contour so that the water stops and sinks in. This slow infiltration recharges the water table for a broad area stretching downslope of the swale. Like an underground plume, the absorbed rainwater hydrates and recharges the water table under your beds and beyond making your, or your neighbour’s, yard verdant. Adding a good layer of mulch to the raised bed – the berm – to hold in the harvested water, dramatically reduces, if not eliminates, the need to water, even in the heat of summer. With the texture of the basin and berm you are also creating microclimates that favour humidity and temperature control: what plants love.

constructing-swales
Illustration by Matthew Von Herbulis

Rain barrels (small tanks) fill and overflow within minutes of a good downpour. Imagine how much water falls on, and flows off, your yard. This often-forgotten rainwater is a huge source of passive irrigation that can catch and sink water into the landscape, much like a sponge, harvesting up to ten times more runoff than a rain barrel. By shaping your landscape to catch and sink the rain, it becomes not only a lush oasis, but also part of the community flood control system, and you can irrigate a swale or rain garden.

Getting started

Materials needed

  • three thin pieces of wood the same length, ideally scrap
  • electrical tape and wood screws
  • string level (small mason level, 50–75 mm)
  • landscape flags
  • shovel
  • metal rake
  • compost
  • cardboard
  • rocks, any shape, 150–200 mm or bigger
  • woodchips/mulch
  • mattock (optional).
constructing-swales
Find contour with the A frame. Photo by Michael Judd

Siting

Swales go just about anywhere they’re needed, as long as the slope does not exceed a 3:1 ratio, meaning not more than a one metre drop over a three metre run. Any steeper than this and you risk blowout from too much water buildup, overflow, and soil destabilisation. Terraces are recommended for steep slopes, and act in a similar way as the swales in harvesting the water on level ground.

constructing-swales

Where you begin and end your berm or raised bed, is up to you. Berms on-contour are sited, based on the restrictions of the surrounding landscape, for example property edge, driveway or fencing. They can be two metres long or extend all the way across your block. If possible, site your swales for gardens outside the kitchen window, close to the roof and maybe a patio or driveway, where rainwater is abundant. Meals can be inspired by seeing what is ready to harvest. But locate any swale at least three metres from the house.

If you have water sitting near your foundations, consider putting in a rubble drain to remove it to a point where you can sink it into a swale or rain garden. Alternatively, slope your swale slightly off-contour to move most of the water to a capture area.

Getting level

constructing-swales
Illustration by Matthew Von Herbulis

In map jargon, a contour is the squiggly line that holds the same elevation across a slope. Finding contour is easy. You don’t need fancy gadgets or training, just a simple ‘A frame’, and this can be any height you like. I usually make mine about 1200 mm tall.

Take two pieces of the wood, lay them flat on the ground and screw them together at one end. Spread the legs about one metre apart and make a mark one-third the distance from the bottom on one leg. At this mark, screw on one side of the third length, which becomes the crosspiece.

constructing-swales
Illustration by Matthew Von Herbulis

Now take thin strips of electrical tape and strap the string level to the center of the crosspiece. Find a completely level surface, such as a floor, and stand your (almost) A frame up. Slide the free end of the crosspiece slowly up and down the opposite leg looking for the bubble to sit level, and then mark the free leg where the crosspiece sits. Pinch it and screw it to the second leg. You now have a leveling tool! Cut off any excess length of the crosspiece that sticks out past the legs.

At the spot where you want the bed to begin, insert a small landscape flag and place one foot of the A frame next to it. Swivel the other leg in the direction you want to site the swale and slowly move it across the ground until the bubble on the crosspiece reads level; mark that leg with another flag. Swivel again and repeat, placing a flag at every leg. Simple and beautiful. Don’t be surprised if the level takes you in radically different directions from where you expected. Depending on your landscape, the line of flags will flow anywhere from almost straight (flat land) to undulating curves (sloped and varied land). Often you end up with a really beautiful serpentine shape. If the contour leads you into an area that doesn’t work for you, adjust your starting point and keep laying the flags until you like the placement. This is when you can play with where you set the beds and how they look on your landscape. If your A frame lands on a rock or hole, just move it a bit to get past it; otherwise, you won’t get an accurate reading.

constructing-swales
Stones set to manage overflow and double as pathway. Photo by Michael Judd

Diggin’ In –Shaping The Swale

Swales come in all sizes: from huge machinecarved ones, to backyard beauties created with a shovel which we’ll cover here.

The Basin

Start digging around 500 mm upslope of the flags. Dig out the sod up to the flags and flip the grass chunks upside down on the downslope side of the flags, no further than one metre away. These chunks become the first layer in the forming berm. As you keep digging out the basin, throw the earth on top of the inverted sod.

constructing-swales
Illustration by Matthew Von Herbulis

I keep my berms a maximum of one metre wide so that I can easily reach in without trampling the soil and plants; remember this as you lay the flipped sod. The bottom of the basin does not need to be perfectly level, but testing it with the A frame or long level is helpful to make sure you are close. The width and height of the berm is in direct relation to the basin size. A wider and deeper basin equals a wider and taller berm: a 500 mm wide by 150 mm deep basin gives you roughly a 900 mm wide by 230 mm high berm, once amended.

The basin is now your passive water harvester and pathway. I like to fill mine with large wood chips; mulch, pine needles or leaves also work well. This is mostly to create a nice walking surface and look, but the added organic matter also holds moisture which maintains a humid microclimate that the plants love. Depending on how weedy the site is, I often place cardboard in the bottom of the basin before putting in the chips. Over time, the path composts down, adding more fertility and water retention to the surrounding gardens. And to really stack your functions here, if the berm is planted with shade casting bushes or trees, the chips can be inoculated with mushrooms.

If you lay down cardboard over the outer edge of the berm, around 600–1200 mm from the flags downslope, before beginning to dig the basin, this will be your grass barrier once the berm is completed and is ready to be mulched. After the basin is dug, edge back 100 mm of the grass along the flag line so that it doesn’t resprout or stick out of your final mulch.

constructing-swales
A well mulched garden will capture the moisture.

This was printed with permission from the author. To purchase this book go to Amazon or Book Depository, http://www.bookdepository.com/Edible-
Landscaping-with-Permaculture-Twist-Michael-Judd/9780615873794.

constructing-swales
Mixing compost into berm
constructing-swales
Levelled berms and wood chip filled basins
constructing-swales
Full newspaper sections laid to cascade down the sides

Michael Judd works with agroecological and whole system designs throughout the Americas, focusing on applying permaculture and ecological design to increase local food security and community health in both tropical and temperate growing regions. The founder of both Ecologia, LLC, Edible & Ecological Landscape Design and Project Bona Fide, an international non-profit supporting agro-ecology research. Photos by Michael Judd

The Berm

The pile of sod and soil you have roughly piled up now needs some amending. I dump on our local municipal compost, which is basically composted leaves and grass, by the wheelbarrow full so that I have a ratio of two-thirds soil to one-third compost. I mix the compost with the loose soil to avoid bringing up the chunks of sod; this feeds the soil and creates a nice planting bed. Once mixed in, it’s time to shape it up.

constructing-swales

The goal is to shape the berm in a flowing pattern, much like a rolling hill with no high drop-off edges. As a general guide, make the width of the berm four times its height. Using a short-tined metal rake, make the top of the berm smooth, so that rainwater settles evenly. Don’t fret about some soil cascading down; over a season, the soil will ‘glue’ together, and the overall height will reduce with time. Always plan for an overflow. If your swale is hit with a crazy storm surge or will be receiving a high volume of water, plan how to direct and catch the overflow. I place overflows where I will want a pathway across the top of the berm, about every six metres along the berm. Choose your best path-crossing spot on the berm and remove one-third the height of the mixed soil/compost; make the path about 500–600 mm wide. Place rocks of any shape along the bottom and sides of the newly excavated path/overflow. Alternatively, wait and see where your new berm will naturally want to overflow after a big rain event and then build in the path.

I often design multiple swales, one right after the other, to ensure capturing every drop of water, and they look beautiful waving across the yard together. When I do this, I just copy the shape of the first swale on-contour, as it is catching the bulk of water, and ideally offset the overflows on each consecutive berm. On a larger landscape you’ll want to space out your swales to take advantage of the rainwater capture area between them. This distance varies depending on the slope of the land. The steeper the landscape, the closer the swales. A useful way to site the distance is to walk downslope until your eye level is at the swale above – place your next swale here.

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