Curve Number for Porous Asphalt
Curve Number for Porous Asphalt
(OP)
Does anyone know the curve number for porous asphalt? Thanks for your help!
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Curve Number for Porous Asphalt
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Curve Number for Porous AsphaltCurve Number for Porous Asphalt(OP)
Does anyone know the curve number for porous asphalt? Thanks for your help!
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RE: Curve Number for Porous Asphalt
Under ideal conditions, porous pavement will accept (infiltrate) many inches of water. So there may be zero "runoff" in the traditional sense. In this case, you actually need to evaluate the "runoff" that is penetrating through the pavement, and route it through the base layers, and perhaps an underdrain. This can be modeled by using a high CN value (98), together with a long Tc value, to simulate the travel time through the base and underdrain, or perhaps a "pond" to simulate the storage in the stone voids.
In the worst case, the pavement could be fully blocked with ice or debris, in which case you would be modeling normal surface runoff with a standard CN of 98 and a relatively short Tc.
A third option is to calculate an equivalent CN value, based on the potential maximum retention of the base.
Unfortunately, standards for modeling porous pavement are still developing. So your approach will depend on the exact design, and what you and the reviewing agency can agree on. Some states are starting to encourage porous pavement, and are developing standard designs and modeling procedures. As an example, see the work by the UNH Stormwater Center at www.unh.edu/erg/cstev/
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Curve Number for Porous Asphalt
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Curve Number for Porous Asphalt
"Zero" runoff is highly unlikely for any type of surface during a design rainfall event even with perfect design and maintenance. It is not reasonable to assume that during your design storm the pavement is in "ideal" condition. In fact, unless your parking lot is dished out with no slope to promote runoff, I don't believe you could ever see "zero runoff". This certainly flies in the face of the research and even the manufacturers claims. You should evaluate "porous" pavement similar to normal pavement with a "small" reduction in runoff. The size of that reduction is still very much open for debate.
RE: Curve Number for Porous Asphalt
That said, we are starting to see more instances of porous pavement being modeled with no surface runoff - as well as agencies that accept this approach. There is still an eventual discharge through exfiltration and/or underdrains, but it is considerably attenuated by the storage and travel-time through the base material.
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Curve Number for Porous Asphalt
A few more references that may better illustrate the properties of porous pavement.
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RE: Curve Number for Porous Asphalt
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See the following posts...
Rational C Value for Brick Pavers in a Sand Bed
(thread162-200106: Rational C Value for Brick Pavers in a Sand Bed)
Pervious Concrete
(thread162-214283: Pervious Concrete)
.
tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation
http://hhwq.blogspot.com
RE: Curve Number for Porous Asphalt
RE: Curve Number for Porous Asphalt
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Curve Number for Porous Asphalt
RE: Curve Number for Porous Asphalt
RE: Curve Number for Porous Asphalt
RE: Curve Number for Porous Asphalt
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Curve Number for Porous Asphalt
RE: Curve Number for Porous Asphalt
RE: Curve Number for Porous Asphalt
Different layers of base material will also slow the longitudinal flow so it doesn't form an immediate level pool, and underdrains can be placed at low points to prevent overflow.
Sure, there are plenty of engineering challenges, but there are also lots of benefits.
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Curve Number for Porous Asphalt
RE: Curve Number for Porous Asphalt
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Try this site for some simplified comparisons of structural stormwater management measures, including Pervious Pavers / Permeable Pavements (PP/PP)...
http://greenvalues.cnt.org/calculator
.
tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation
http://hhwq.blogspot.com