Which set of practices are best management practices for reducing urban stormwater runoff?

• A. Using chemical coagulants in rivers.
• B. Widening stormwater pipes without treatment.
• C. Increasing pavement coverage and road salt.
• D. Green infrastructure such as rain gardens, bioswales, and pervious pavements.

Answer: (D)

Managing urban stormwater runoff effectively comes from approaches that slow, store, and treat rainfall close to where it falls. Green infrastructure uses vegetation, soil, and permeable surfaces to capture rainfall, promote infiltration, and enhance evapotranspiration. Rain gardens soak up runoff, bioswales channel water through vegetated space to trap sediment and pollutants, and pervious pavements let water seep through instead of flowing off rooftops and streets. By keeping water in the landscape, these practices reduce the total runoff volume, lower peak discharge during storms, and give pollutants a chance to be removed by soil and microbes. They also bring co-benefits like cooling of urban areas, habitat for wildlife, and improved neighborhood aesthetics.

Widening pipes without treatment simply moves more water downstream without removing pollution and can worsen flood risk and pollutant transport. Expanding pavement increases impervious cover, which raises runoff and pollutant loads. Road salt affects water quality and aquatic life, and chemical coagulants in rivers don’t address the source of urban runoff; they solve different water-quality issues elsewhere and don’t reduce runoff at the source. Green infrastructure thus best reduces urban stormwater runoff.