Green infrastructure is an approach to stormwater management that protects, restores, or mimics the natural water cycle. Green infrastructure is effective, economical, and enhances community safety and quality of life. It uses design features such as bio-treatment systems and permeable paving to infiltrate and filter stormwater prior to discharge to the storm drain system. As a result, less rainwater ends up as runoff, carrying pollutants, and more absorbs slowly into the ground, where it is filtered by soil, feeds plants and replenishes ground water.
Since 2005, most new private development projects in Alameda County are required to include Green Infrastructure elements. In addition, each member agency is creating a Green Infrastructure Plan, identifying publicly funded retrofit projects. The Clean Water Program provides technical guidance as well as public outreach to facilitate this work throughout Alameda County.
Some typical Green Infrastructure features include:
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.