Field Evaluation of 

Permeable Pavements for 

Stormwater Management

Olympia, Washington

Key Concepts:

ÿ Structural Controls

ÿ Volume Reduction

ÿ Space Savings

Project Benefits:

ÿ Elimination of Stormwater 

Ponds

ÿ Demonstration of Water 

Quality Benefits

ÿ Lower Maintenance

LOW-IMPACT 

DEVELOPMENT 

CENTER

United States Office of Water (4203) EPA-841-B-00-005B

Environmental Protection Agency Washington, DC 20460 October 2000

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. 

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. 
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 352700

Roberts Annex 100

(206) 543-7923

dbooth@u.washington.edu

DRIVEWAY

DRAIN

SAMPLE 

CONTAINER

TIPPING BUCKET WOOD BOX

FLOW MEASUREMENT

EQUIPMENT

FILTER 

PLUG

1/2 ROUND

FULL ROUND

AC BERM

TREATED 2x8 LUMBER BETWEEN

TRIAL PAVING SYSTEMS

ASPHALT 

CONTROL

90% IMPERVIOUS BLOCK 

W/GRAVEL

60% IMPERVIOUS CONCRETE 

BLOCK W/GRASS

REINFORCED GRASS PAVEMENT REINFORCED GRAVEL AND 

GRASS PAVEMENT

Figure 2. Schematic of the test facility showing treatments and runoff collection devices. 

0.00

0.20

0.40

0.60

0.80

1.00

0.00 200.00 400.00 600.00

Time (minutes) 

Runoff (mm precipitation) 

 Asphalt

 60% impervious concrete

 block w/grass

Figure 3. Runoff volumes from asphalt and permeable 

pavements.