Traditional streets are designed to direct stormwater runoff into storm sewer systems (gutters, drains, pipes) that discharge directly into local waters with little to no treatment. A green street is designed to use biofiltration to slow and treat stormwater runoff before it is discharged into local waters. Green streets help protect local water quality by removing up to 90% of pollutants from stormwater runoff. In addition to protecting water quality, green streets also absorb carbon, improve air quality and neighborhood aesthetics, and provide green connections for pedestrians and cyclists in urban areas.
Video + info source: epa.gov
When rain falls on undeveloped land, it is naturally filtered through vegetation and soils before it enters into local waters. However as our region has developed, a larger percentage of the land is covered in impermeable surfaces that prevent natural filtration of stormwater from occurring.
According to the Washington State Department of Ecology (DoE), regional stormwater runoff is now the largest source of pollution in Puget Sound. As rain hits roofs, roads, parking lots, and other hard surfaces, it picks up contaminants from those surfaces and carries them into stormwater drains. These contaminants include petroleum, zinc, lead, PCBs, and copper, amongst other toxins. The stormwater then flows mostly untreated into Puget Sound. Per the DoE, the highest concentrations of toxic pollutants come from developed areas of residential, commercial/industrial, and agricultural land uses.
Image source: King Co.
Green streets are designed to capture and treat stormwater runoff before it enters local waters. Stormwater runoff is channeled into green street planters, also known as rain gardens or bioswales. Through a process called biofiltration, these landscaped areas between the street and sidewalk use plants, trees, and soils to slow, filter, and clean stormwater runoff before it is discharged into local waters.
Image source: Grey to Green
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