A swale is an old English word for a shady spot, often nearby a sunken or marshy place. In its natural role it facilitates overflow run-off, mitigating soil erosion and providing a habitat for water life. However, nowadays we are more likely to encounter swale channels with gently-sloping sides alongside motorways.
A Swale Is a Vegetated Channel
Road engineers usually plant seed grass in these channels to stabilise them, and soften the environmental impact. Some laypeople refer to them as roadside ditches, although we should not underestimate their importance. Natural ones sometimes appear alongside rivers after heavy rain, to the delight of small birds and kids in gumboots.
Some gardeners encourage swales if their piece of land is large enough. This idea is popular among proponents of permaculture, because they allow natural harvesting of rainwater. In this instance, the ditches follow the natural contours of the land, and almost blend into the background as they manage run-off and erosion.
A Natural Solution for Eavestrough Water
A generous building on a large piece of land may create challenges for rainwater disposal. Especially if the contour is flat, and the water stands. A swale may help control this, and preserve the moisture for irrigation. With imagination, it may even enhance the overall appearance of the garden!
How to Build Your Own Catchment Channel
There are no particular rules for building these ditches. Indeed, they may almost have their own mind, due to the lie of the land, tree roots and rocks. Aim for the shape and size that matches your water catchment needs. The length and depth are likewise need-driven. To summarise at this point:
- Artificial drainage swales should slope gently to a convenient drainage point.
- Their cross-section should be consistent, in terms of water flow at discharge.
- The channel should slope gently, unless conserving the water for irrigation.
- Line the swale with low-maintenance ground cover to prevent soil erosion.
- Always dig the swale deeper than necessary, to allow for exceptional rainfall.
Things to Remember Before You Leap In
Consider the neighbours first, before doing anything that affects natural water flow. Consult your local council, in case they have standards in this regard. Check your eavestroughs out before you start. With forethought, a swale can improve the lay of your garden.
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Artificial Swale Alongside Road (Michael Hogan BY CC 2.0)