Land development changes how water naturally travels and can impact the water quality in our rivers, lakes, streams, and wetlands.
When rain falls on land with natural ground cover about 50% of stormwater infiltrates into the ground, 40% evaporates or is transpired through plants (these together are called evapotranspiration), and only about 10% washes along the surface as stormwater runoff.
But when development occurs, impervious surfaces (roads, rooftops, parking lots, sidewalks, and driveways) result in increased stormwater runoff and decreased stormwater infiltration. When an area is changed to 35%-50% impervious surfaces, about 35% of stormwater infiltrates into the ground, 35% evaporates, and about 30% goes through storm drains directly to lakes, rivers, and wetlands. The volume of water runoff increases and the amount of cool, clean groundwater flow to rivers and streams decreases.
Stormwater runoff from impervious surfaces washes off common pollutants like pesticides, fertilizers, oils, metals, pathogens, salt, sediment, litter, and other debris. These pollutants enter the storm sewer system through the open grates in streets and parking lots, called storm drains, then travel through storm sewer systems into rivers, lakes, streams, and wetlands.