Which landscape feature uses vegetation to capture and treat stormwater runoff?

• A. A rain garden that uses soil and plants to filter runoff.
• B. A concrete curb that directs water away to the street.
• C. A rooftop solar array to generate electricity.
• D. A vegetated drainage swale that captures and treats stormwater runoff.

Answer: (D)

Using vegetation to treat stormwater relies on plants and soil to slow, filter, and infiltrate runoff as it moves through a landscape. A vegetated drainage swale fits this goal well because it is a shallow, planted channel designed to collect runoff from roofs, pavement, or other surfaces, route it along a planted path, and use the plant roots and soil to filter pollutants and promote infiltration. This setup slows the water, captures sediments, and helps cleanse what flows through before it leaves the site. While rain gardens also use soil and plants to filter runoff, their primary role is intercepting water in a small depressional area near the source; the swale explicitly combines capture, conveyance, and treatment along a drainage path, making it the best match for this function.