Permaculture and Water Management — How Do Swales Fit In?

Building Swales

Swales are shallow ditches or depressions dug across a slope to collect and slow down rainwater runoff. By placing a swale on a slope, you can capture and store rainwater, reducing erosion and allowing it to seep into the soil, recharging groundwater. A typical swale design is 3-5 feet wide, 12-18 inches deep, and is located 10-20 feet below the contour line. This design allows water to flow into the swale from the slope above and then slowly seep into the soil.

Using Contour Lines and Berms

Berms, or small dams, can be used in conjunction with swales to create a more effective water harvesting system. By placing a berm across a contour line, you can divert water from a swale into a pond or reservoir, allowing you to store larger amounts of rainwater. A berm can be as simple as a small mound of earth or as complex as a engineered dam, depending on the needs of your system. To create a berm, start by digging a shallow trench and then placing a series of logs or branches across it. Fill the trench with earth and compact it to create a solid barrier.

Rain Garden Swales

Rain garden swales are a variation of traditional swales that take into account the unique needs of urban or suburban areas. These swales are designed to capture and filter urban runoff, reducing stormwater pollution and helping to recharge local groundwater. To create a rain garden swale, choose a spot that receives at least 4 inches of rainfall per year and has a gentle slope. Dig a shallow depression, 2-3 feet deep, and fill it with a mix of soil, compost, and native plants. As rainwater flows into the swale, it will be filtered by the plants and soil, reducing pollutants and recharging groundwater.