There’s also a possibility that porous pavement can reduce
the heat island effect. The theory holds that because the
pavement can breathe and moisture isn’t trapped, it will hold
in less heat. It’s like the difference between wearing a loose
cotton and a heavy polyester shirt.
According to the “Cool Pavements” chapter of the EPA re-
port Reducing Urban Heat Islands: Compendium of Strategies,
“wet, [permeable] pavements can lower temperatures through
evaporative cooling. The water passes through the voids and
into the soil or supporting materials below. Moisture within
the pavement structure evaporates as the surface heats, thus
drawing heat out of the pavement, similar to evaporative
cooling from vegetated land cover. Some permeable pave-
ment systems contain grass or low-lying vegetation, which
can stay particularly cool because the surface temperature of
well-hydrated vegetation is typically lower than the ambient
air temperature.”
More research is needed, however, to understand the effects
of these pavements when dry, the guide notes. It’s possible
they can limit heat transfer by increasing convection over the
surface or releasing heat in the evening. Without adequate
documentation, facility managers should address the heat
island effect through conventional strategies such as reducing
overall pavement areas or installing reflective roofing and use
permeable materials for stormwater management.
GREENERFACILITIES
Concrete and asphalt may be necessary for parking lots, courtyards, and sidewalks at your property, but large xpanses won’t help your efforts to manage stormwater.
These traditional materials are impervious, meaning they resist
moisture, so rainwater has nowhere to go but into the sewers.
As stormwater fees continue to climb, facility managers are
turning to permeable options that allow water to infiltrate into
the ground. Learn how these eco-friendly pavement choices
can put rainwater to better use.
From Drizzles to Downpours
Often lumped together, porous pavement and permeable
pavers are two methods that help rainwater reach the ground.
Pervious materials have voids in them that allow moisture to
run through, like pouring liquid through a fine mesh sieve. Permeable options use spacing between tiles or pavers to direct
water around the surface. The purpose of either choice is to
ensure stormwater can penetrate the ground rather than flow
to a municipal drain, retention pond, or public waterway.
Ground infiltration is a passive way to remove contaminants
from runoff. Think of the pollutants that dirty your pavement –
fluids from cars, spilled food, bird droppings, plant debris, salt,
sand, trash, and soil erosion. These particulates pose a burden
on city treatment plants or can make their way directly into
nearby lakes and rivers. Sandy and clay soils can capture these
elements, but only if water has a way to percolate through
to them.
Permeable Pavement Battles Stormwater Runoff
Direct rainwater into the ground rather than sewer drains
continued
PERVIOUS PAVEMENT IS COMMONLY USED AT THE EDGES OF PARKING LOTS or as pathways (left). The porous material has a
slightly stippled texture but is not noticeably different than traditional concrete or asphalt. Permeable pavers can either be
nearly invisible to the eye (middle) or clearly spaced as an architectural grid (right).
