How to Build Swales. What is a swale?

Swales are long, level excavations used to loosen soil and absorb water. They can be many forms and widths, including small ridges in the garden, rock piles on slopes, or hollows in flat lands. The main function is to interrupt the sheet flow of water, let it infiltrate the soil, and ultimately recharge the groundwater. Swales are a tree growing system, and trees are vital to their success. Generally, trees are planted on the excavated mound on the lower side of the swale (or possibly inside the swale in deserts), and leguminous trees are planted on the back slope to help with shade and stability. Trees take the water collected in the swale and transpire some of it back into the atmosphere, helping the water cycle. The crowns of trees can meet over the swale, preventing salting and evaporation. Animals can then be fenced off and grazed inside the swales, feeding on the grass and overhanging tree branches. Their manure adds nutrients to the water that soaks in, and that feeds the trees. Swales can be used across climates, and within seven years they can fully rehydrate a landscape and begin recharging groundwater. Water sits passively within a swale until it soaks into the landscape, so whichever season the rain occurs will become less significant because the soil will be hydrated. The size of swales will vary according to conditions like slope and soil type, but eventually they will not only hydrate the landscape but also support trees, which will create hummus from leaf drop. All of this serves to create a very high quality system.