Shallow catch basins planted as flower beds, rain gardens allow water to pool during a downpour, then slowly percolate into the soil. Where a swale is mostly a travel route for water, a rain garden is a destination. A fast-draining soil mix encourages water to sink in and promotes lush plant growth. Runoff may flow into a rain garden from a swale or pipe, or may simply run in from a sloping yard.
Rain gardens are appropriate drainage spots for steeper slopes than swales can handle, but where the surface drops more than 3 feet over a 15-foot horizontal distance, you should get professional design help. Although a low spot in the yard might seem an ideal placement, if it stays soggy, it’s already saturated. Instead, pick an area that dries out quickly.