Swales
A swale is a ditch dug on contour — following a line of constant elevation across a slope. Water running downhill hits the swale and stops. It spreads along the length of the ditch instead of concentrating into erosive channels. Then it sinks into the soil rather than running off.
The technique is ancient but was systematized by P.A. Yeomans in 1950s Australia and adopted by permaculture designers. In arid climates, swales can be the difference between parched hillsides and productive land.
The key is the level construction. Even a slight gradient along the swale concentrates water at one end, defeating the purpose. Yeomans used an A-frame level — two sticks hinged at the top with a plumb line — to mark contour lines with 6-inch accuracy.
Swales are typically paired with berms — the soil dug from the ditch is piled on the downhill side. Trees planted on the berm access the moisture stored below. The swale becomes the irrigation system for a tree line.
Geoff Lawton’s “Greening the Desert” project in Jordan demonstrated the technique dramatically. Ten acres of salty, barren land transformed into productive food forest within three years, using swales as the primary water harvesting strategy. Annual rainfall of 4 inches became sufficient.
Swales work best on gentle to moderate slopes (2-15%). Steeper terrain risks overflow and erosion. Flatter terrain doesn’t concentrate water enough to make swales worthwhile.
The intervention is permanent and passive. Once dug, the swale works every time it rains, for decades, with no maintenance. The landscape itself becomes the irrigation infrastructure.
Related: [[keyline-design]], [[stacking-functions]], [[zone-5]]