Swales

Swales are a permaculture thing. A swale is a water-holding ditch dug on contour, usually on a slope but not always. The contour bit is very important. If you remember your high-school geography, a contour line on a map joins places at the same height above sea level. In a ditch dug on contour, water stays level in the ditch. Not on contour and it will run out the lowest end.

Huge rainfall events on a slope means water runs off faster than it can soak in. Swales trap the water and allow it to permeate slowly. Water permeates into the soil and facilitates plant growth where it would not be as successful otherwise. Remember the three S‘s of water harvesting: Slow; Store; Soak. Slow it down; store it; let it soak in.

When a swale is dug across a slope, the soil removed is mounded up on the low side of the slope and the mound is planted with suitable plants to hold the soil in place and provide a yield of some sort. In Australia, we call them swales and mounds; in the US they’re often referred to as berms (the mound) and basins (the ditch).

When we bought this property, I didn’t know anything about permaculture. The only spot that was cleared of natural bush was on a slope. The only spot in full sun. The only place to put a vegetable garden and fruit trees. Good drainage, I thought. Yes, but the soil had been introduced. The original sandy soil had been removed (and sold) by a previous owner and the site had been filled with clayey rubbish that water wouldn’t penetrate. If I’d only known—I would have had the whole site swaled and mounded before planting, and be in a far better position than I am now.

So I did a Permaculture Design Course, learned the hard way and had to retrofit. That meant digging individual swales behind each fruit tree, by hand.

The swale behind the orange. It holds about 80 litres of water:

I remember the first major rain after digging the swales, dashing down the back in the pouring rain and being overjoyed to find each small swale full of water.

The swales saved the fruit trees during this past hot, dry summer. Once a week, I filled each of them a couple of times over with the hose.

I used an A-frame to mark out the contours. It’s only small, but just right for the size of the swales I’m digging. I wrote about how I made it here.

There’s an article about water harvesting & storage at the Permaculture Research Institute here.