What role do vegetated swales play in stormwater management?

Vegetated swales are an essential component of stormwater management systems, primarily designed to filter and treat stormwater while facilitating the natural process of infiltration. When rainwater travels over surfaces, it picks up pollutants such as sediment, nutrients, and organic material. Vegetated swales, which are often shallow, vegetated channels, allow this runoff to flow through them, where the vegetation and soil work together to filter out these pollutants.

The plants in the swale absorb nutrients and provide a substrate that promotes microbial activity, which further breaks down contaminants. Additionally, as water percolates through the soil in the swale, it recharges groundwater supplies, reducing the volume of runoff that would otherwise enter municipal drainage systems or streams, thus minimizing flood risks and improving water quality.

The other options misrepresent the functions of vegetated swales. While they do help manage stormwater, they're not designed to collect all runoff or to speed up water flow, which can lead to increased erosion or flood risks. Instead, their primary function is to slow down and treat stormwater, making option B the accurate description of their role in stormwater management.