NE Siskiyou Green Street transformed the way a 80-year-old street manages stormwater. The street retrofit project exemplifies how stormwater can be managed sustainably, instead of being allowed to overflow into already inundated local water and sewage systems.
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The green street uses curb extensions to capture street runoff. Conventional curb extensions are often used for traffic calming and pedestrian safety. The curb extensions at NE Siskiyou Street share many of the same benefits of conventional curb extensions. However, they are different in that they are also designed to elegantly capture, slow, cleanse, and infiltrate street runoff.
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Stormwater runoff from 10,000 square feet of NE Siskiyou Street and neighboring driveways flows downhill along the existing curb until it reaches the seven-foot wide, 50-foot long curb extensions. An 18-inch wide curb cut allows this water to enter each curb extension.
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Once water is within the landscape area, the water is retained to a depth of seven inches by a series of checkdams. Depending on the intensity of a rain event, water will cascade from one "cell" to another until plants and soil absorb the runoff or until the curb extensions reach their storage capacity.
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Street runoff flowing into the curb extensions is slowed, cleansed, and filtered by a variety of plant species. One plant species, Juncus Patens, has an upright growth structure that slows down water flow and captures pollutants. Juncus Paten’s deep penetrating roots are good water absorbers.
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Nearly all of NE Siskiyou’s annual street runoff, estimated at 225,000 gallons, is now managed by its landscape system. Multiple simulated flow tests have shown that the curb extensions at NE Siskiyou Street have the ability to reduce the runoff intensity of a typical 25-year storm event by 85 percent.
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Portland has a waiting list of residents who want similar sustainable stormwater facilities for their own streets. Using stormwater checkdams made out of packed earth covered with river rock is one example of a simple, attractive, and environmentally sustainable design element that costs very little to install. Cost-effective solutions such as these allowed the project to be built for under $20,000.
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