What are swales?
Simply put, swales are ditches dug on contour. Being level, they are not designed to transport water from one place to another. Rather, their intention is to allow water to soak into the ground.
The term “swale” is a little confusing, as it is used in landscape architecture to describe a grassy ditch designed to gently drain water from an area. In permaculture, however, the term means a level water-harvesting ditch.
Why are swales used?
Swales stop runoff, allowing water to sink into the ground. The effect generally raises the water table. This makes them useful in supporting trees, and as part of a broader water-catchment strategy for a site. It should be noted, though, that many fruit trees do poorly in areas with a high water table. You will have to consider where you are installing swales, and to what end.
Where are swales used?
Swales can be used on sites with slopes from 0º up to 20º. Even seemingly flat sites can have circular swales used to capture water. On slopes greater than 20º, it is not only unsafe for most machinery used to dig swales, the volume of earth moved versus the volume of the swale makes swale construc