United States
Environmental Protection Agency
Office of Water (4203)
Washington, DC 20460
EPA-841-B-00-005B
October 2000
Field Evaluation of
Permeable Pavements for
Stormwater Management
Olympia, Washington
Introduction
This study demonstrates the potential of
permeable pavement systems to restore soil
infiltration functions in the urban landscape. It is
based on the results of a project that included
installing and monitoring several porous
pavement systems in a parking area. The project's
objectives were to
- Review existing information on permeable
pavements
- Construct full-scale test sites
- Evaluate the long-term performance of
these systems
The report outlines the difficulties encountered,
costs of installing and maintaining the systems,
performance based on existing soil systems,
special benefits of filling the open cells with grass
as opposed to gravel, and other water quality
benefits.
Project Area
The demonstration site was in an office
parking lot in Olympia, Washington. Two
adjacent parking stalls were constructed
using four types of permeable pavement
systems that consisted of a combination of
grass and gravel, as shown in Figure 1. The
designs were
1. A flexible system consisting of a
plastic network of cells with grass
infill and virtually no impervious
area coverage.
2. A flexible system consisting of a
plastic network of cells similar to
design 1 but filled with gravel.
Key Concepts:
> Structural Controls
> Volume Reduction
> Space Savings
LOW-IMPACT
DEVELOPMENT
CENTER
Project Benefits:
> Elimination of Stormwater
Ponds
> Demonstration of Water
Quality Benefits
> Lower Maintenance
3. A system consisting of impervious blocks
with the space between the blocks filled
with grass. (Total surface area is 60
percent impervious).
4. A system consisting of impervious blocks
with the space between the blocks filled
with gravel. (Total surface area is 90
percent impervious).
A control stall was constructed out of traditional
asphalt. A system of pipes, gutters, and automatic
sampling gauges was installed to collect and
measure the quantity and chemistry of surface
runoff and subsurface infiltrate. Figure 2 shows a
schematic of the test facility.
Figure 1. Different types of permeable pavement. From top
left: reinforced gravel and grass pavement, reinforced grass
pavement, 60% impervious concrete blocks with grass, 90%
impervious blocks with gravel.
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ASPHALT
CONTROL
90% IMPERVIOUS BLOCK
W/GRAVEL
60% IMPERVIOUS CONCRETE
BLOCK W/GRASS
REINFORCED GRASS PAVEMENT
REINFORCED GRAVEL AND
GRASS PAVEMENT
TREATED 2x8 LUMBER BETWEEN
•TRIAL PAVING SYSTEMS
I 1/2 ROUND
\Jf
TIPPING BUCKET
FLOW MEASUREMENT
EQUIPMENT
Figure 2. Schematic of the test facility showing treatments and runoff collection devices.
Project Summary and Benefits
The results of this study showed the following
relationships:
- The use of permeable pavement systems
dramatically reduced surface runoff
volume and attenuated the peak discharge,
as shown in Figure 3.
- Although there were significant structural
differences between the systems, the
hydrologic benefits were consistent.
- Storm characteristics and weather
conditions influenced the hydrologic
responses of the systems.
- Permeable pavement system types vary
widely in cost and are more expensive
than typical asphalt pavements. Cost
comparisons between permeable pavement
installations and conventional ponds or
underground vaults are limited. However,
the elimination of conventional systems
and reduced life cycle and maintenance
costs can result in significant cost savings
over the long term.
- A significant contribution of permeable
pavements is the ability to reduce effective
impervious area, which has a direct
connection with downstream drainage
systems. This strategy of hydrologic and
hydraulic disconnectivity can be used to
control runoff timing, reduce runoff
volume, and provide water quality
benefits.
Contact Information
Derek Booth, Director
Center for Urban Water Resources Management
Box 3 52700
Roberts Annex 100
(206)543-7923
dbooth@u.washington.edu
--- Asphalt
— 60% impervious concrete
block w/grass
Time (minutes)
Figure 3. Runoff volumes from asphalt and permeable
pavements.
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