A swale is a very simple concept; a contour on the land that collects, conveys and filters water running through a site, removing pollutants by infiltration into the soil. Flat yards increase run-off, but the mounds on either side of a swale, known as berms, keep water on site, giving the water time to slowly infiltrate into the ground. If you have a sloping yard, you can create a berm to act as a barrier to keep your landscape irrigation water from escaping into the streetscape.
Swales, bio-retention ponds and rain gardens help reduce pollution reach our ocean environment and help recharge our ground water aquifers. The more rainwater you can keep in your landscape, the less water you need to add to your garden!