Stormwater Quality Design Manual (May 2007) - City of Sacramento ...

Runoff Reduction Control Measure Fact SheetPorous PavementCobblestone Block PavementCobblestone block pavement (Figure PP-4) consistsof concrete block units with at least 8% void spacewhere the beveled corners meet. The units areinstalled on a gravel subgrade, and the void space isfilled with sand. This is one of the most attractiveporous pavement options and allows for the greatestflexibility in pattern and color. Cobblestone blockpavement can be used wherever modular blockpavement is appropriate, and similarly, does notrequire utility cuts; instead the blocks can be takenout and replaced after utility installation. Refer toTable PP-1 for design criteria for this type of porouspavement.Photo: Puget Sound Action TeamFigure PP-4. Cobblestone BlockPavement, Typical Section*(source: adapted from Denver)*Installation specifications may vary by site;check with local permitting agencyWoven geotextile fabric meeting:ASTM D4751-AOS of 50-70ASTM D4633 min. trapezoidal tear strength 100 x 60 lbs.Minimum COE specified open area of 4%.When certified tests show percolation rates of less than60 minutes per inch of drawdown under the PP bottomand infiltration is allowed, eliminate the bottom sandlayer and underdrains.When Type C soils are present and when infiltration isallowed, unless permeability shows otherwise, eliminatethe bottom sand layer, use underdrains and geotextileliner instead of an impermeable one under the gravel.When the underlying soils are Type D or expansive, useunderdrains and 16 mil minimum thickness impermeableliner under and on sides of the pavement sand andgravel media.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007PP-9