Pervious PERVIOUS PAVEMENT pavement (porous pavement, porous /asphalt) allows ervious pavement is made of either pervious asphalt or pervious concrete. precipitation Both materials resemble conventional asphalt and concrete, but have more to Pair spaces that allow to pass through the pavement into a reservoir percolate base of crushed aggregate, then infiltrate into the ground. Pervious pavement is through designed to accept precipitation only and is typically thicker than traditional con- to the crete to support the same loads. ground Pervious asphalt consists of coarse stone aggregate and asphalt binder, with very little fine aggregate. Water percolates through the small voids left in the fin- ished asphalt. A thick layer of gravel underneath allows water to drain through quickly. Pervious asphalt looks similar to conventional asphalt, although with a rougher surface, which accounts for its common name “popcorn mix.”

Pervious concrete consists of specially formulated mixtures of Portland , open-graded coarse aggregate, and water. It has enough void space to allow rapid percolation of water and resembles exposed aggregate concrete.

Benefits twice a year maintains porosity. Properly Pervious pavement reduces installed pervious paving systems last more runoff flow rate and volume, recharges than 20 years. groundwater and maintains base flows. The subgrade also filters pollutants. Cost Pervious pavement is less prone to cracking Pervious concrete pavements range in cost or buckling from freezing and thawing. depending on the size of the installation. In Studies indicate it requires less frequent the Bureau of Environmental Services North repair and patching than conventional Gay Avenue Project (Summer 2005), a pervi- paving. In some cases, pervious pavement ous concrete cost about $100 per may reduce or eliminate the need for an square yard installed, including base rock. underground system or a curb Safety and Siting Requirements and gutter system. Pervious pavement is an • Follow manufacturer’s installation effective method of managing stormwater instructions. runoff without limiting use of the space. • Weather conditions during installation can Maintenance affect the performance and longevity of It is important to control site erosion and pervious pavement. Check with manufac- sedimentation of the pavement surface to turers for guidelines. prevent clogging and maintain permeability. • Slope must be less than 10% over the Cleaning or vacuuming the surface once or paved area. • Use pervious pavement over that drain well, like gravelly or loamy sand. Permits • Pervious pavement systems used to • Do not use pervious pavements in areas replace public parking or walkway areas with high sediment loads. require a building permit from the City’s • Pervious pavement is not allowed in areas Bureau of Development Services. where hazardous material is stored or • Stormwater systems on non-residential transported. sites need commercial building permits. • Most systems include an under layer of at Examples least 12 inches of clean gravel over a layer The Rebuilding Center of our United Villages, of geotextile fabric. The under layer serves , 3625 N. Mississippi Ave. as an underground detention basin and should include an overflow outlet to pre- N. Gay Avenue vent water from rising through the pave- between N. Wygant and N. Sumner ment. (pervious concrete and asphalt) • Refer to Portland’s Stormwater Management Manual for details on sizing, Pervious Concrete at Broadway Pump Station, placement, and design. NE 91st and Broadway

Ecotrust Building Parking Lot (Drive aisles), 721 NW 9th Ave.

Pervious concrete

base rock

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