Rainwater Harvesting and Stormwater Reuse for Arid Environments - Design with the Desert: Conservation and Sustainable Development - page 375

with man-made perforated crate-like boxes that quickly remove standing surface water by
creating larger subsurface water storage through the presence of subsurface voids, which
will eventually empty as the infiltration process continues. An alternative to this system
would be the use of an underground natural rock or sand bed.
A second location for rain gardens can be relatively small scale areas located in land-
scape strips such as parking lot islands or along drives which can be used to naturally
infiltrate stormwater. In any rain garden without supplemental irrigation, plants must be
drought tolerant to sustain dry periods between harvesting events.
21.5.2.5 Porous/Pervious Pavements
Traditional asphalt and concrete surfaces are designed to be virtually impermeable,
with stormwater runoff often mitigated through the use of storm sewers and detention/
retention systems. Porous paving has proven to be durable enough for parking areas,
pedestrian uses, and some road surfaces. These materials are designed specifically to
reduce, or in some cases eliminate this stormwater runoff and direct the replenishing
benefits of rainwater naturally into the ground below.
Porous paving surfaces such as porous asphalt, porous concrete, or porous pavers will
permit water to infiltrate rapidly. Use of porous asphalt and concrete should be restricted
to parking lots and local roads since they support lighter loads than standard asphalt and
concrete. Porous concrete can typically support 1800-2400 psi and interlocking pavers are
designed to meet a minimum of 8000 psi. 2 Underlying soil strength also contributes to
the pavement strength and its porosity. This underlying soil layer and geotextile should
generally be effective in detaining pollutants from the infiltrated water. If pollution is of
special concern a collection pipe could be used to transport the filtered water to a specified
area for further treatment. This collection pipe is also effective for low permeability soils.
Porous concrete and pavers are cement-based and will not release harmful chemicals
into the environment whereas an oil-based asphalt might. With any porous surface, the
greater the slope the less time water has to infiltrate making the porous surface ineffective,
therefore flatter areas are more appropriate for porous materials.
Segmental concrete unit pavers offer unique advantages such as
• Resistance to severe loads
• Flexibility of repair
• Low maintenance
• Exceptional durability
• Consistently high quality
Concrete pavers have openings in the pavement surface that facilitate rainwater infiltration,
thereby reducing or eliminating stormwater runoff and maximizing groundwater recharge
and/or storage. These pavers also provide the following benefits:
• Lessen or eliminate downstream looding, streambed, and bank erosion
• Decrease project costs by reducing, or eliminating drainage, and retention systems
required by impervious pavements and reduce cost of compliance with many
stormwater regulatory requirements
• Provide a highly durable yet permeable pavement surface capable of supporting
vehicular loads