DESIGN OF LID SYSTEMS - Low Impact Development and Sustainable Stormwater Management - page 133

Figure 7-3 Porous concrete sidewalk, State College, Pennsylvania.
Description and Function
A pervious pavement system consists of a pervious surface course underlain by a
storage reservoir placed on uncompacted subgrade to facilitate stormwater infil-
tration (Figure 7-4). The storage reservoir may consist of a stone bed of uniformly
graded and clean-washed course aggregate, 1.5 to 2.5 in. in size, with a void space
of at least 40% or other premanufactured structural storage units. The pervious
pavement may consist of pervious bituminous asphalt, pervious concrete, pervious
pavers, or other types of pervious structural materials. Stormwater drains through
the surface course, is held temporarily in the voids of the stone bed (Figure 7-5),
and then slowly ex-filtrates into the underlying, uncompacted soil mantle.
The stone bed can be designed with an overflow control structure so that dur-
ing large storm events peak rates are controlled, and at no time does the water
level rise to the pavement level (Figure 7-6). A layer of nonwoven geotextile filter
fabric separates the aggregate from the underlying soil, preventing the migration
of fines into the bed. The bed bottoms should be level and uncompacted to allow
for even and distributed stormwater infiltration. If new fill is required, it should
consist of additional stone and not compacted soil. It is recommended that a fail-
safe factor be built into the system in the event that the pervious surface should
be affected adversely and suffer reduced performance. Many designs incorpo-
rate a riverstone/rock edge treatment or inlets tied directly to the bed so that
the stormwater system will continue to function despite the performance of the
pervious pavement surface.
Pervious pavement is well suited for parking lots (Figures 7-7), walking paths
(Figure 7-8), sidewalks, playgrounds (Figure 7-9), plazas, tennis courts, and sim-
ilar uses. Pervious pavement can be used in driveways if the homeowner is
aware of the stormwater functions of the pavement and willing to maintain it.
Pervious pavement roadways have seen wider application in Europe and Japan