“Green streets” are landscape designs that mimic drainage patterns of natural landscapes by using permeable pavement and depressions in the ground that help divert water away from roads and other impervious surfaces.
As a result, less rainwater ends up as runoff and more absorbs slowly into the ground, where it is filtered by soil, feeds plants and replenishes ground water.
“Green streets” features help prevent flooding and reduce the amount of rain water that runs off into storm drains, carrying pollutants such as motor oil and brake dust that were washed off our roadways. Because stormwater is not treated, these contaminants degrade the water quality in creeks, wetlands and the Bay.
Some typical “green streets” features are described below. To see examples of “green streets” in Alameda County, click here.
Rain gardens are shallow, vegetated basins that collect and absorb runoff from rooftops, sidewalks, and streets. Plants most suitable for rain gardens have deep fibrous roots, can withstand the extremes of moisture and drought, and tolerate pollutants typically found in stormwater runoff.
Stormwater curb extensions are landscaped areas placed right next to the curb and designed to capture runoff from the street. Typically, the planted area is slightly lower than the street, with an opening in the curb to allow water to flow in. In addition to helping absorb and filter stormwater, curb extensions often make pedestrian crossings shorter and therefore safer.
Vegetated trenches (“bioswales”) are planted ditches typically running alongside a street. Similar to rain gardens, these sloped and planted areas slow the flow of runoff from streets, absorb the water and help it infiltrate into the ground. Often replacing paved curbs, vegetated bioswales create wildlife habitat and add beauty.
Permeable pavement replaces impervious surfaces used for parking lots, roads and other paved areas. Made from porous asphalt, pervious concrete, pavers or plastic grids filled in with gravel or turf, permeable pavement allows rainwater to percolate into the ground below.
Green roofs are roofs covered with soil or soil-like substrate and plants growing in it. Green roofs can look and function like ground-level gardens—offering living and recreation space—or consist of only shallow substrate and hardy, drought-tolerant vegetation. Both types of green roofs collect and retain rainwater and reduce runoff, while providing wildlife habitat and improving aesthetics.
To see examples of “green streets” in Alameda County, click here.