What is one primary purpose of a vegetated swale?

The primary purpose of a vegetated swale is to encourage infiltration and filter water. Vegetated swales are designed as landscape elements that have a gently sloped channel filled with vegetation. This structure allows rainwater runoff to collect and flow through the swale, promoting the infiltration of water into the ground rather than allowing it to run off quickly into drainage systems. As the water passes through the vegetation and the soil, pollutants are naturally filtered out, improving the quality of the water that eventually reaches local waterways. This function supports both stormwater management and environmental health by reducing the burden on urban drainage systems and enhancing groundwater recharge.

While other options mention aspects of water management or aesthetics, they do not reflect the fundamental role of a swale in promoting water quality and ecosystem function. For instance, increasing runoff velocity is counterproductive to what swales aim to achieve, while decorative landscaping and providing habitat, while beneficial, are secondary to the primary function of managing water efficiently.