Stormwater management encompasses the planning, design, and implementation of systems to control the quantity and quality of rainfall runoff from developed land. It addresses flooding, erosion, and pollution from urban surfaces.
Stormwater management refers to the comprehensive set of practices, infrastructure, and regulations used to control the quantity, quality, timing, and velocity of rainfall runoff from urban and developed landscapes. When natural land is converted to impervious surfaces such as roads, parking lots, and rooftops, the volume and rate of stormwater runoff increase dramatically while infiltration decreases, leading to flooding, stream channel erosion, habitat degradation, and transport of pollutants to receiving waters. Traditional stormwater infrastructure (gray infrastructure) includes storm sewers, detention basins, culverts, and channels designed to convey runoff quickly away from developed areas. Modern approaches emphasize green infrastructure and low-impact development (LID) practices that mimic natural hydrology, including bioretention cells (rain gardens), permeable pavements, green roofs, vegetated swales, constructed wetlands, and rainwater harvesting. The EPA's Municipal Separate Storm Sewer System (MS4) permit program under the Clean Water Act requires municipalities to implement stormwater management programs addressing six minimum control measures. Many communities are adopting stormwater utilities that charge property owners based on impervious area, creating financial incentives for on-site stormwater management. Integrated stormwater management considers both quantity and quality, recognizing that stormwater carries pollutants including sediment, nutrients, bacteria, heavy metals, oil and grease, pesticides, and trash into waterways.