Use of Small Swales – a Case Study

You might have seen Geoff Lawton’s wonderful ‘Greening the Desert’, and his ‘Establishing a Food Forest’ DVD where he wades through a swale metres wide. It’s not commonly discussed, but swales can be quite small too. It depends on the space you have available, the magnitude and intermittency of the rain events, how fast it will soak in and the capacity of your soil to hold it. As always, observing and interacting will yield good results, and you’ll learn as you make mistakes.


The partially completed swale is about to be extended.
The drain is near my right foot.

My latest project is a 25 square metre vegetable patch in subtropical Narangba, South East Queensland, Australia. I could choose the site, and although it wasn’t exactly ‘zone 1’, I settled on an area adjacent to the neighbour’s fence. The soil and solar access are good, and the adjacent fence reduced the amount of additional fencing needed to keep out the dogs, the most expensive purchase for the garden. Being out of the way was an advantage because the owners were not completely sold on having a vegetable patch. I was also hoping that the activity would encourage the neighbour to resurrect their neglected vegetable garden, and they did come out to enquire while the garden was being installed. There is hope.

These are all great qualities, but the main attraction was a downpipe from the house that drained onto the lawn. I could catch the water and distribute it along the length of the garden. Even a light shower would contribute. I have observed that apparently heavy showers can fail to penetrate more than a couple of inches of mulch, so I believe getting the water into the soil is important. I marked out the contour, used that as the upper boundary, and dug the swale trough about 20-25cm wide. I also put a few pavers in front of the drain to prevent erosion of the mound if the water came out in a gush. On the first day I did not get around to installing an overflow, and as it happened there was a storm the day after. The swale filled as predicted, but the water overflowed and flooded part of the garden, partly washing out the path.


The drain is at the bottom left, obscured by grass and pigeon pea.
The pavers for erosion prevention and flow restriction are visible.

The next task was to extend the swale away from the garden with a level sill spillway, as done in Geoff’s Harvesting Water DVD, so that the garden wouldn’t be flooded and it would release water gently onto the lawn. It took some time for me to observe this happening. In the meanwhile I heard that the extension was a little lower than the garden section – it was getting small downpours instead of the garden. Even if I leveled it properly the water could be wasted on the lawn. I placed another paver as a dam to the extension. On Christmas day I got to see it in action. The water didn’t gush, but the drain has since been cleaned so it could happen yet. The original garden section of the swale filled up and the paver slowed the water enough to direct it to the garden first. The mulch and absorption in the swale slowed the advance of the water as it moved through, so even with the paver the extension was getting some early water. While the swale was filling up, the water level on the garden side was higher. The spillway worked as designed when full, letting the water cascade down hill.


The swale is full and overflowing via the level sill spillway.

Further observation revealed that during heavy downpours, there was perhaps too much water in the garden. I had not noticed that the driveway and the neighbour’s driveway could feed the swale too. This explains the good soil, as the area is like a fertile valley, collecting water and sediment which is slowed by the grass and absorbed. After extended rains, the water was springing out of the garden and onto the path! A hole made for planting would fill up with water! To make use of this excess water, I’m considering installing another swale further up the hill, wide and shallow to prevent impeding vehicle access to the back yard. This should charge the soil above the first swale, providing a reserve for when the weather dries out.


The garden was a popular attraction on Christmas day. On the left you can see

the bean trellis, prayer flags and escaping pumpkin.

The garden, while it has some gaps in the planting, has so far been a success with only a few disappointments. There has been a constant supply of lettuce, zucchinis, cucumbers, and now some corn. The garden has pests but the predators seem to be keeping them in check after only 2 months. A 1kg zucchini was just harvested, there is a sunflower I can’t reach the top of, and the owners are talking about expansion!


Much more beautiful than lawn!

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8 thoughts on “Use of Small Swales – a Case Study

  1. Great stuff Tim. I have only recently seen Geoff Lawton’s videos and am completely inspired to put these concepts into practice on my 5-acre block just north of Perth, Western Australia.

    Do you see your swale garden requiring any watering in the drier and warmer months?

    Cheers,

    Dean

  2. Thanks, Dean! The garden was watered by hand for the couple of dry months leading up to Christmas. I am sure this will be required in the future, but I expect that as the humus content of the soil increases with decaying plants and the application of manure, compost and mulch, the water holding capacity will follow, reducing the irrigation requirement. The soil should act like a battery, lasting longer and longer between rain events.

    Good luck and be sure to document your efforts for everyone else to learn and be inspired!

  3. What a fabulous write up !! I had wondered how to apply all this knowledge to something small scale. I felt making a small garden might be insignificant !! But evidently not :-)

  4. Hi Chris,

    It’s definitely not insignificant and has inspired others. We estimate that the garden cost $300 to install (with some new and some salvaged materials), perhaps 16 hours to install including 3 citrus trees not pictured. It might take 3 or 4 hours to maintain each week which should decline with improved soil, predatory life and experience.

    Even with some crop failures (very few beans, not much corn and some other non-productive experiments), we estimate getting about $100 worth of fresh, organic produce in 2 months. We should break even soon.

    It’s also provided hours of priceless relaxation and entertainment :)

  5. I’m looking forward to giving this a go on my block. Given that I don’t have a regular water supply at this time, it will be a matter of waiting until the end of Summer so that I can set up an irrigation system that I can feed manually.

    Tim, can you give me an idea of how much water you feel you are using at this time (daily? weekly?) to maintain your swale garden?

  6. It varies according to the weather, but the garden might get about 30L of water daily by watering can at the base of the plants. It won’t get irrigation for a couple of days after rain, less if the weather is hot. I’m not there most of the time so I can’t monitor it directly, but I get regular reports.

  7. Thanks Tim, I might approach my neighbours who have a water tank about 30 metres from the back of my block to see if they can help me out with some water until I get my own tank in place. If it means sending a few dollars their way for the water I use it should be a good learning experience.

  8. Awesome work Tim! There is no reason why every backyard in Australia can’t have a productive edible landscape, hydrated by the proper harvesting of rainfall. Very nice use of Swales.

    PS. It looks as though you scored a few brownie points at xmas!

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