Keyhole Swale Experiment

In the UK it feels there’s been little effort in recent times to design agricultural systems that conserve water. Nonetheless we do need more effective means to harvest rainwater in-situ rather than rely on extraction and pumping. Using swales in rainwater harvesting is common across the world – usually involving a ditch and mound along the contour line of a bank. But creating pockets for water-saving is also effective. Some of the most arid regions use semi-circular bunds or “demi-lunes” for olive groves, figs and pistachios, catching water to hold where it is needed. This small scale approach seems to chime with our own permaculture plans so we decided to experiment with an adapted keyhole-swale-and-basin. The plan is to trial it during 2014 and if it works well then we can extend the idea when we plant the orchard in autumn.

keyhole swale

Keyhole Swale & Basin – Construction

We scooped out a smallish basin with a shallow slope going in (and out) and earth mounding around the keyhole. The idea is that water pools during heavy rains forming a sump that tree roots can access more readily. The shallow slope on the entry gives an emergency outlet if the central reserve fills too deeply, keeping the main body of the roots safe from permanent inundation. We planted half a dozen apple trees purchased locally from fellow grower Emma who supplies wonderful flowers and trees to St Dogmaels Local Producer’s market. Luckily we just made the bare root season (November to March) but the mild weather was already taking affect and buds were ready to break!

bud break

To test the experiment, (and to grow the trees on for flower production) we’ve planted close together and topped the mound with garden peas (bush type so no support) and onions on the edges. This means that demand on water throughout the summer will be really tested. We decided to cover the exposed soil within the keyhole with shavings which should reduce weed growth but still conserve moisture.

pea plants

The first rains after construction and water has begun to collect – looking good so far (in spite of trampling by cows)

keyhole swale for water conservation

And the fruit trees are now in leaf and blossom so shaping up well … we’ll follow up throughout the summer and see how the experiment works.

apple blossom