Slowing down fast-running water in desert conditions can be important to prevent erosion and help vegetation take hold.
Swales are designed to slow down water and spread it horizontally across an area. They are used in arid areas and deserts to slow the effects of precipitation runoff and spread the water more evenly, lessening erosion and serving as water collection points.
A swale can be small, and built with a shovel or hoe, or it can be large and require a bulldozer.
It consists of digging a ditch on contour along a hillside, piling the dirt on the downstream side to create a berm. Precipitation runs into the uphill ditch and is absorbed by the earthen berm on the downstream side. For additional absorption capabilities, hay, mulch, rolled newspaper or any other absorbent material is buried in the berm.
Vegetation can also be planted on the uphill side of the berm. The vegetation benefits from the absorbed water, helps prevent erosion, and adds organic matter (from leaves and other detritus) into the soil.
