In the permaculture design course I did last year, we learned to mark out contours using an A-frame. I’ve wanted to dig a few swales for harvesting rainwater on the sloping sections of our property and they have to be dug on contour, so that the water stays in them and doesn’t run off, but slowly percolates into the subsoil. So I’ve had ‘make A-frame’ on my to-do list for some time. Here’s a post from another blog on the construction of swales.
Early this week we got a deluge—27 mm of rain in an hour—and I was out in it, getting drowned, to see just where the water was going (or flowing, as it were).
I’d dug a small swale earlier, behind a group of plants that weren’t doing too well in the dryness, by the hit-&-miss method, i.e. dig out a ditch, fill it with water and adjust levels where necessary. But an A-frame makes it all much easier and so I collected some old garden stakes, the drill and a few screws. Instead of fiddling around with a line and plumb bob, I taped a small spirit level to the horizontal part of the ‘A’ (an idea I got from the book Rainwater Harvesting for Drylands and Beyond by Brad Lancaster—well worth reading).
Here’s what it looked like:
It’s only a small one—the legs of the A are only about 50 cm apart—but I’m only going to be doing short swales here and there; the property is too well endowed with plants now, to do any major stuff (that should have been done at the outset, but then I wasn’t into permaculture then, was I?).
To use the A-frame, the legs are placed on the ground and moved back & forth till the spirit level shows…er…level. This means those two points are on the same level and are marked with pegs. The frame is then pivoted about one leg (in whichever direction you want to move), levelled and the position of the moved leg marked with another peg. By moving, levelling & marking, you eventually end up with a line of pegs which are all at the same level. The line of pegs can be replaced by a flexible garden hose and viola, that’s the contour you need to dig on.
Here’s the swale I dug without the benefit of the A-frame. It’s only a bit over a metre long, but looks like being able to hold about 60 litres of water. I can always deepen it to hold more. This is looking from the front of the swale, so it’s behind the plants, on the upslope:
Here’s the view from behind the swale:
The logs behind the swale are to stop soil from upslope washing into the swale. Eventually a gravel path will run along the back of it. I may also try filling it with a coarse mulch.
I had this swale in place before the aforementioned deluge and was enthralled to see it quickly fill with water, so I can see the immediate future is going to be one of measuring & digging (by hand of course!) before the rainy season sets in.
Needless to say, the plants quickly greened up, enjoying their new-found water supply.