What environmental problems are associated with urban runoff and what green infrastructure options mitigate them?

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Urban runoff happens when rain hits city surfaces and can’t soak in, so it flows into streams and rivers carrying pollutants and excess water. This creates two main problems: more frequent and larger floods, and water quality degradation from sediments, nutrients, metals, oils, and other contaminants carried by the runoff. The best option pairs these problems with practical solutions that mimic natural drainage: green roofs, permeable pavements, bioswales, and rain gardens. Green roofs store and slowly release rainfall, reducing quick runoff; permeable pavements allow water to infiltrate rather than run off; bioswales channel and treat runoff through vegetation and soil, trapping pollutants; rain gardens collect runoff and promote filtration while also slowing flow. Together, these approaches lessen peak flows and improve water quality by filtering pollutants, recharging some groundwater, and reducing the pollutant load reaching waterways. In contrast, solutions focusing on asphalt surfaces imply less infiltration and more runoff, which would worsen floods and degrade water quality. Saying there’s no impact or that only groundwater issues exist ignores the clear effects on surface water and flood risk, so those choices don’t fit.