Urban Runoff Mitigation by Impermeable Soils, FASSMAN & BLACKBOURN , 2010

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CE Database subject headings: Runoff; Urban areas; Porous media; Pavements; Permeability; Stormwater management; Nonpoint
pollution; Maintenance; Best management practice; Sustainable development.
Author keywords: Porous pavements; Permeable pavement; Permeability; Storm-water management; Low impact development; Non-
point pollution; Maintenance; Best management practice.
Introduction
Permeable pavement is one of many tools available to achieve a
low impact development �LID� scheme on a lot-level scale. The
term LID was coined by Prince George’s County, Maryland De-
partment of Environmental Resources to describe a new paradigm
for design of storm-water management systems �Dept. of Envi-
ronmental Resources Programs and Planning Div. 1999b�. To
mitigate or prevent receiving water degradation, all aspects of the
urban water cycle, including timing, rates, and volumes of storm-
water runoff must be incorporated into the basis of design for
storm-water management. Main drivers for this goal originated
from observation that peak flow-only type controls do not ad-
equately prevent stream erosion or physical habitat degradation. It
is proposed that if the overall hydrologic regime of the catchment
is kept to predevelopment levels, then the receiving stream should
be able to maintain its physical structure with an urbanized con-
dition, contributing to preservation of its ecological integrity.
From a technical standpoint, this hypothesis forms the basis of
design for LID hydrology.
Permeable pavement replaces conventional paving surfaces
with an at-source control to prevent or significantly delay runoff
generation. In most applications, permeable pavement “treats” or
manages only the surface over which it covers. Precipitation fall-
ing over the surface of the permeable pavement infiltrates into an
aggregate-filled storage reservoir �the basecourse� below the per-
meable surface �Fig. 1�. Designed as a retention system where site
conditions permit, water flows through the basecourse porous
media to exfiltrate into the surrounding subsoil. Otherwise, per-
meable pavement designed as a detention system �e.g., installed
over poorly draining subgrade or with an impervious liner� dis-
charges via an underdrain to reticulation or to the receiving water.
In some cases, permeable pavement may also manage runon
�flow� from adjacent impervious surfaces. “Outflow” from a per-
meable pavement area usually refers to discharge of treated, man-
aged flow from the underdrain. In very intense storm events, on
steep slopes, or during periods of frequent rainfall, surface runoff
may also occur from the permeable paving surface. The hydraulic
characteristics of a permeable pavement system contribute to four
areas of hydrologic control: peak flow, volume, hydrograph tim-
ing, and duration.
Studies of permeable or porous pavement retention systems
generally show a significant potential to reduce runoff volume
1Senior Lecturer, Dept. of Civil and Environmental Engineering,
Univ. of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland
1142, New Zealand. E-mail: e.fassman@auckland.ac.nz
2Environmental Engineer, AECOM, 6th Fl, 1901 Rosser Ave.,
Burnaby, BC, Canada V5C 6S3.
Note. This manuscript was submitted on October 12, 2009; approved
on February 18, 2010; published online on March 12, 2010. Discussion
period open until November 1, 2010; separate discussions must be sub-
mitted for individual papers. This paper is part of the Journal of Hydro-
logic Engineering, Vol. 15, No. 6, June 1, 2010. ©ASCE, ISSN 1084-
0699/2010/6-475–485/$25.00.
JOURNAL OF HYDROLOGIC ENGINEERING © ASCE / JUNE 2010 / 475
Urban Runoff Mitigation by a
over Imper
Elizabeth A. Fassman, Ph.D., A
Abstract: The respective runoff from a 200-m2 permeable pa
catchment in Auckland, New Zealand, was monitored concurrent
meable subgrade soils, and on an atypically high slope �6.0–7
permeable pavement was exceptional. Measured discharge from th
comparable to or below modeled predevelopment conditions for
24-h annual recurrence interval event. For large events �5% exceed
conditions, but it was substantially less than asphalt runoff for all
flow and volume were statistically different between the asphalt ca
level of significance�. Runoff coefficients ranged from 0.29–0.
0.41–0.74 when permeable pavement comprises about one-half
drograph duration were reminiscent of a vegetated area. Spearman
on runoff parameters from both catchments, while antecedent moi
infiltration measurement at four permeable pavement sites reveal
clogging than does traffic load. Permeable pavements should be gi
and can also mitigate conventional large design storm flows, but
DOI: 10.1061/�ASCE�HE.1943-5584.0000238
 J. Hydrol. Eng., 2010, 
ermeable Pavement System
able Soils
SCE1; and Samuel Blackbourn2
nt test site and an adjacent 850-m2 conventional asphalt road
ween 2006 and 2008. Despite installation over relatively imper-
nd active roadway, the overall hydrologic performance of the
meable pavement underdrain demonstrated peak flow �81 storms�
storms, regardless of antecedent conditions, including a 10-year,
underdrain discharge volume was comparable to predevelopment
s up to approximately 70% exceedance. The distributions of peak
nt runoff and the permeable pavement underdrain discharge �0.05
underdrain discharge �10th–90th percentile events�, and from
otherwise impervious catchment. Underdrain lag time and hy-
ation indicated influences of rainfall depth, intensity, and duration
ondition was correlated to underdrain discharge lag time. Surface
t surrounding land uses likely have more influence on pavement
rong consideration as an low impact development source control,
ust be taken during installation to ensure proper function.
15(6): 475-485 
francis
Realce
francis
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to do with clogging potential than direct vehicular loadings �Bean
et al. 2007�. Pezzaniti et al. �2009� measured a 59–75% decline in
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compared to that from asphalt surfaces �Gilbert and Clausen
2006; James and Thompson 1997; Pratt et al. 1995; Rushton
2001� or rainfall volume �Gilbert and Clausen 2006; James and
Thompson 1997; Pratt et al. 1995�. Gilbert and Clausen �2006�
compiled data from three studies which reported permeable pave-
ment system discharge to range from 37 to 61% of rainfall vol-
ume, whereas asphalt runoff volume was approximately equal to
rainfall volume. As most of these studies were performed on sys-
tems designed for exfiltration, peak flow effects were not readily
reported, except in a few instances of major storm events.
Several studies of permeable pavements installed over clayey
subgrade soils show meaningful stormwater retention. Dreelin et
al. �2006� found that for storms less than 20 mm, 93% of total
rainfall exfiltrated through grassed plastic grid pavement over
clay soils. Collins et al. �2008� compared runoff from an asphalt
parking space with underdrain discharge from four parking spaces
of different permeable pavements installedover sandy loam to
sandy clay loam soils. The study determined median underdrain
discharge volume was 36–67% less than rainfall volume for
storms less than 50 mm across the different types of permeable
pavements. Median peak flow differences of approximately 63–
83% were reported between asphalt runoff and permeable pave-
ment underdrain discharge. Tyner et al. �2009� measured
exfiltration from pervious concrete through a clay subgrade at 8
mm/d, which could be enhanced by preparing subgrade with ei-
ther boreholes �46 mm/d�, ripping �100 mm/d�, or trenching �258
mm/d�.
Regardless of outflow design, permeable pavement systems
can serve to increase times of concentration, thereby decreasing
hydraulic efficiency of the catchment and peak flow. Wetting,
pore space storage in the aggregate basecourse, and the tortuous
flow path through the basecourse all contribute to reports of 45–
145 min lag times, depending on storm size �Brattebo and Booth
2003; Gilbert and Clausen 2006; Schluter et al. 2002�. Antecedent
moisture conditions were also found to affect lag time and exfil-
tration rates to the subgrade �Brattebo and Booth 2003; Schluter
et al. 2002�. Collins et al. �2008� identified negative statistical
correlation of time to peak with rainfall intensity, rather than an-
tecedent moisture.
Surface clogging is the primary failure mechanism of perme-
able pavement in terms of stormwater management. The per-
ceived propensity for clogging and the associated maintenance
burden can deter application. Bean et al. �2007� reported the re-
sults of several studies as well as their own field investigation of
40 permeable pavement sites along the mid-Atlantic U.S. coast.
The writers observed that unstable catchments and catchments
with fine-graded soils exacerbate the potential for clogging. It
appears that catchment characteristics as a whole may have more
Fig. 1. Typical permeable pavement longitudinal section
476 / JOURNAL OF HYDROLOGIC ENGINEERING © ASCE / JUNE 2010
 J. Hydrol. Eng., 2010, 
hydraulic conductivity in laboratory studies simulating 35 years
of sediment delivery on three different types of permeable pave-
ments. Field tests showed rapid decline in hydraulic conductivity
at three sites that received runon from adjacent bitumen asphalt
catchments. Clogging was attributed to coarse sediments trapped
in joints, as opposed to the fine sediments which were retained by
the geotextile layer �Pezzaniti et al. 2009�. The different conclu-
sions by Pezzaniti et al. �2009� and Bean et al. �2007� regarding
the clogging potential and sediment size may be due to the types
of permeable pavements tested. The former tested primarily inter-
locking block pavers and grass pavers, where the latter also tested
pervious concrete.
Many LID manuals emphasize the importance of creating op-
portunities for infiltration within the developed landscape �Dept.
of Environmental Resources Programs and Planning Div. 1999a;
Hinman 2005�. This objective is challenging in the Auckland Re-
gion of New Zealand, where soils are largely characterized by
weathered mudstone and sandstone �Waitemata and Onerahi se-
ries clays� �Beca Carter Hollings & Ferner Ltd. 1999�, with hy-
drologic soil group C �poor infiltration capacity�, and very
frequent rainfall. Mean annual rainfall for the Auckland region is
1,240 mm with 137 wet days ��1.0-mm rainfall� spread rela-
tively evenly through the year �NIWA Science 2000�.
The viability of permeable pavement over impermeable soils
to substantially mitigate hydrologic effects of urban runoff ac-
cording to LID design objectives subject to the Auckland climate
is questionable. To consider it, this study investigates the hydro-
logic performance of a 200-m2 permeable pavement system in-
stalled over clay subsoils with an estimated permeability of 0.01
mm/d. The test site was located on an active roadway �Birkdale
Rd., Auckland, New Zealand� as it was hypothesized that in-
creased loading from frequent traffic would accelerate failure, and
hence yield a better understanding of long-term performance.
Current local �Auckland� regulations may require peak flow
reduction for the 2-year, 10-year, and 100-year, 24-h annual re-
currence interval �ARI� �based on rainfall depth� design storm
events to predevelopment conditions, and extended detention re-
lease of the first 34.5 mm of rainfall over a 24-h period, depend-
ing on site specific conditions. The aim of LID is to maintain
runoff at the predevelopment condition for frequently occurring
“every day” events �i.e., less than a 2-year return period� with
respect to all hydrograph characteristics �i.e., flow rate, volume,
and timing�.
Data from the permeable pavement and an adjacent conven-
tional asphalt roadway section were collected concurrently be-
tween 2006 and 2008. In addition, surface infiltration rates were
measured at the Birkdale Rd. site and three other permeable pave-
ment installations in Auckland to assess maintenance require-
ments as indicated by clogging. Site data are used herein to
evaluate the permeable pavement’s ability to achieve both regu-
latory goals and LID goals, despite installation over relatively
impermeable subgrade soils.
Site Description
Constructed in February 2006, the trial site �Fig. 2� comprises a
standard asphalt section and a permeable pavement section that
was purposely built for concurrent monitoring. Surface coverage
per catchment is described in Table 1. The entire 850 m2 asphalt
catchment includes pavement, sidewalk, and grass and drains to a
15(6): 475-485 
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single catchpit. The asphalt surface has a 8.9–10% longitudinal
slope and 3.6–5.9% cross fall. The catchpit discharges to a storm
sewer along Birkdale Rd. via a 225-mm-diameter concrete pipe.
The total permeable pavement catchment is 395 m2, including
200 m2 of permeable pavement and 195 m2 of sidewalk, drive-
way, and grass. The permeable pavement includes a live traffic
lane and a parking lane with a bus stop. Longitudinal surface
slope was measured at 6.0–7.4% over the permeable pavement,
with 3.0–3.7% cross fall toward a catchpit which also collects
overland flow from the sidewalk, driveway, and grass.
The �35-m-long, �6-m-wide permeable pavement test sec-
tion was constructed from impermeable paver blocks, with en-
larged joint spaces �Fig. 3� filled with 2–5 mm aggregate chip to
allow flow into a two-layer aggregate basecourse. Joint spacing
was calculated to allow infiltration of the peak flow generated by
a 2-year, 24-h ARI storm from an equivalent entirely impervious
area, and allow for deterioration over a 10-year pavement life,
resulting in a design surface infiltration rate of 1,200 mm/h and a
ratio of joint space to impervious paver area of 0.19. The same
Fig. 2. Birkdale Rd. test site. Asphalt catchment �white border�
=850 m2 including asphalt, sidewalk, and grass. Permeable pave-
ment catchment �black border�=395 m2 including 200 m2 perme-
able pavement, plus sidewalk, driveway, and grass.
Table 1. Catchment Characteristics
Catchment
�total area�
Fraction of area as surface
Asphalt
Other
imperviousa Grass verge
Permeable
pavement
Asphalt �850 m2� 0.58 0.19 0.23 0
Permeable pavement
�395 m2�
0.09 0.23 0.11 0.50
aConcrete sidewalk, curb, and driveway.
Fig. 3. Birkdale Rd. permeable pavement surface detail
JOU
 J. Hydrol. Eng., 2010, 
2–5 mm chip was used as bedding material for the pavers. A
geotextile was placed between the bedding layer andthe base-
course.
An overall two-layer 480-mm basecourse thickness was re-
quired to provide structural stability to support the daily 458
equivalent standard axle load along Birkdale Rd. �including 5%
heavy traffic�. Structurally, the top 150-mm-deep layer of a 12-
mm-diameter aggregate would only be adequate for lighter loads
�e.g., cars in parking lots�; the bottom 230-mm-deep layer of a
40-mm-diameter aggregate was required because of the truck traf-
fic and loading frequency in the live roadway. A secondary moti-
vation for the two layers is that the 40-mm aggregate costs less
than the 12-mm aggregate, resulting in a greater specified depth
of the former, but the latter is still necessary to prevent migration
of the 2–5 mm joint/bedding chip. A 2007 investigation into un-
derdrain construction revealed that the actual basecourse depth
varied from 590–660 mm in some areas near the down-hill end of
the test section. The extent of the thicker basecourse over the
entire test area is not known; investigation of approximately 10-m
upslope of the down-hill end revealed installation that conformed
to the 480-mm basecourse design depth.
In situ testing performed by the installation team �of which the
writers were not part� characterized the subgrade soils as silty
clay and clayey silt. The writers were informed that soil perme-
ability testing equipment broke during field measurements but
that permeability was later estimated at 0.01 mm/d via “perc”
testing. Information provided does not detail the specific testing
method, other than to assert a falling head methodology. The re-
sulting permeability falls into the range of fissured clay �Scott
1980�, but is also deemed “impermeable” �Bear 1972�. Experi-
ence of the writers in attempting to install a rain gauge on-site
anecdotally confirms dense clay soils �a gas-powered auger was
lodged into the soil, requiring significant creativity to extract it�.
As exfiltration was not expected to be significant compared to
storm volume, a single underdrain at the down-hill end of the test
section was installed. The underdrain discharges by a 150-mm-
diameter PVC pipe to a storm sewer along Birkdale Rd.
A subsurface perforated drain runs along the length of
Birkdale Rd. underneath the sidewalk for conventional pavement
basecourse drainage. To promote and isolate all permeable pave-
ment discharge through the underdrain �for measurement�, a poly-
thene lining was placed between the basecourse edge and the
existing road basecourse drain along the length of the test section,
which extended for approximately 1.5 m under the basecourse
�measured perpendicularly to the sidewalk�.
Supplemental to the Birkdale Rd. permeable pavement site,
three additional sites in the Auckland Region were tested for sur-
face infiltration capacity every 3 months in 2006. The Kahika Rd.
carpark is constructed from hexagonal shaped interlocking block
pavers with enlarged joint spacing �Fig. 4�. The site serves a
Fig. 4. Additional infiltration testing sites: Kahika Rd. car park �left�,
Upland Rd. driveway �middle�, and North Shore Events Centre car
park �right�
RNAL OF HYDROLOGIC ENGINEERING © ASCE / JUNE 2010 / 477
15(6): 475-485 
curve number of 74 �Beca Carter Hollings & Ferner Ltd. 1999�
for each measured rainfall depth. According to local procedures,
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wastewater pumping station, which is used infrequently to park
trucks during station maintenance. Trees surrounding the site de-
posit leaf litter onto the pavement. The Upland Rd. residential
driveway site is the same type of interlocking concrete pavers
with enlarged joint spacing �Fig. 4� as the Birkdale Rd. site. The
North Shore Events Centre carpark is constructed from permeable
blocks �Fig. 4�. It is occupied by buses at night and cars during
the day. The heavy loading from the buses was not anticipated
during the design of the pavement. There is a builder’s yard ad-
jacent to the carpark which deposits fines onto the pavement from
traffic and wind.
Methodology
Runoff Data Collection
For each monitoring station, equipment was installed in the 150
mm and 225 mm pipes from the underdrain and catchpit, respec-
tively, upstream of the discharge point to the storm sewer. Water
depth in the pipes was recorded at 5-min intervals by a Sigma
900MAX �Hach Company, Loveland, Colo.� automatic sampler
with pressure transducer rated for up to 1.75-m depth with �2
mm accuracy. The pressure transducers were installed upstream
of a 120° v-notch weir installed in each pipe. A Sigma 2149
�Hach Company, Loveland, Colo.� tipping bucket rain gauge lo-
cated near the end of the permeable pavement section recorded
total rainfall depth in 5-min intervals based on 0.25-mm bucket
tips.
Runoff Data Processing
Laboratory replicas were used to develop rating curves for each
monitoring station, including all equipment that might cause flow
turbulence. Each rating curve �Fig. 5� was determined from at
least 10 flow depths and a weighing bucket apparatus. Linear
interpolation between measured depth-flow data points was ap-
plied to calculate flow from field measurements. Field results
were normalized by the size of the contributing drainage area to
allow direct comparison.
Predevelopment hydrology was modeled using the TR-55/
NRCS curve number method as per local regulatory requirements,
assuming a grass paddock with Hydrologic Soil Group C and a
Fig. 5. Asphalt catchment and permeable pavement underdrain dis-
charge rating curves
478 / JOURNAL OF HYDROLOGIC ENGINEERING © ASCE / JUNE 2010
 J. Hydrol. Eng., 2010, 
an initial abstraction of 5 mm is applied to all pervious areas
�Beca Carter Hollings & Ferner Ltd. 1999�. While Pitt �1999�
demonstrated significant errors with applying the TR-55 method
in urban areas to individual events, it nonetheless remains the
method of choice for many regulatory authorities.
In lieu of direct measurement, asphalt catchment runoff can be
used to estimate the surface runoff from the 195 m2 of sidewalk,
driveway, and grass verge parts of the permeable pavement catch-
ment. Based on sustained high infiltration rates through the per-
meable pavement surface �refer to the discussion under “Surface
Infiltration”�, it was assumed that surface runoff rarely occurred
from the permeable pavement, which is also supported by Collins
et al. �2008�. Conversely, the grass verge �over clay soils� in
either catchment likely provides minimal infiltration especially
when wet �Pitt 1999�. Total permeable pavement catchment dis-
charge volume �surface runoff+underdrain discharge� was deter-
mined by Eq. �1�
Vppc =
195
395
Vasph +
200
395
Vperm �1�
where Vppc, asph, perm=discharge volume �millimeters �mm� per
unit area� from the permeable pavement catchment, asphalt catch-
ment, and permeable pavement underdrain, respectively. The ra-
tios represent the weighted contributions of each surface to the
total catchment discharge.
SPSS �PASW Statistics 18� was used to compare asphalt
catchment runoff, permeable pavement underdrain discharge, per-
meable pavement catchment discharge �underdrain+surface run-
off�, and modeled predevelopment conditions. The Mann-
Whitney U test for independent samples was used to test equality
of peak flow or volume distributions between the various sce-
narios. Correlation between measured climate parameters with as-
phalt catchment and permeable pavement underdrain discharge
characteristics were assessed by Spearman correlation. Nonpara-
metric tests were required as appropriatetransformations were not
easily identified.
Surface Infiltration Testing
Surface infiltration was measured using a modified double ring
infiltrometer apparatus �ASTM 2003�. A two-stage ring was de-
vised such that the water contact area with the pavement between
the rings was consistent with standard design, but the reservoir
volume was increased to slow the fall of water in the rings, al-
lowing for more accurate timing at high infiltration rates �Fig. 6�.
In addition, flush contact between the bottom of the infiltrometer
and the permeable pavement for the outer ring was incorporated
into apparatus design, as per Bean et al. �2007�.
During testing, the inner and outer infiltrometer rings were
sealed to the pavement using plumber’s putty; care was taken to
push the putty into the cracks between the pavers �Fig. 6�. The
seal was then tested by pouring water into the rings, which also
saturated the pavement basecourse.
The water in the rings was initially filled to a height of 10–25
cm above the pavement surface. The water depth in the inner ring
was recorded at regular intervals. As tests proceeded, the outer
ring water level was topped up so that it matched that of the inner
ring, to ensure that vertical flow through the inner ring.
Infiltration tests were conducted at various locations at each
test site. Along Birkdale Rd., quarterly road closures allowed for
15(6): 475-485 
ity of storms were less than 20 mm in depth, comprising 51% of
an 2-m
n of
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periodic testing within the live roadway in 2006/2007. All other
testing was in the parking lane. Wilcoxon rank-sum testing was
performed to determine if surface infiltration in the live roadway
was statistically different than in the parking lane, and if the rate
changed because of underdrain maintenance activity and joint
chip topup in April 2007.
Two locations were consistently tested at the Kahika Rd.
pumping station, one of which was underneath a tree canopy. The
original testing location at the North Shore Events Centre was
moved after the first round of testing to the end of the lot farthest
away from the builder’s yard �further explained in “Results and
Discussion”�. One location was consistently tested at the Upland
Rd. driveway.
Results and Discussion
Runoff Control
Field data collection occurred primarily over two periods, span-
ning from winter to early summer in both cases. A total of 566.3
mm of rainfall was monitored in September 2006–January 2007,
while 561.8 mm occurred during the July 2008–December 2008
monitoring period. Individual events considered for analysis had a
minimum of 2 mm of rainfall. The distribution and characteristics
of the storm events analyzed are presented in Table 2. The major-
Fig. 6. Modified double ring infiltrometer
Table 2. Hydrologic Characteristics from Complete Storms of Greater th
Number
of storms
Storm depth
�mm�
Fractio
total rai
dept
36 �2–7 0.13
10 �7–10 0.07
24 �10–20 0.31
5 �20–30 0.10
3 �30–50 0.10
3 �50 0.28
Overall mean 14
Overall median 8
Maximum 152
Minimum 2
Standard deviation 21
Note: “Complete” indicates flow measured at all monitoring stations.
aMaximum 5-min rainfall over storm duration.
JOU
 J. Hydrol. Eng., 2010, 
the total rainfall, and 86% of the number of events.
Distinct hydrographs were often difficult to isolate during
back-to-back events, when catchment discharge from the first
storm might still be occurring despite several hours’ gap in rain-
fall. Rainfall and runoff volume could be resolved across both
events, but hydrograph tails were somewhat arbitrarily cut off
between events with the result that apparent measured runoff
slightly exceeded rainfall for some individual events, and vice
versa. Total volume determinations were also challenged in the
asphalt catchment, where debris often washed through the catch-
pit or bypass flow from upstream a catchpit seemingly increased
measured catchment runoff volume. Conversely, extended dry pe-
riods that caused significant evaporation from the catchpit caused
questionably low discharge volumes. Where data from these
events could not be resolved, the volumes were excluded from
calculation of runoff coefficients.
Full discharge hydrographs from the permeable pavement un-
derdrain discharge for storms producing less than 7 mm of rainfall
could not be measured accurately, as they resulted in only a
trickle of water which was less than 2-mm depth over the weir.
Any fluctuation in water level was below the monitoring instru-
ments’ sensitivity. Hence these very small storms, which contrib-
ute 13% of the overall volume of rainfall, but 44% of the number
of storms monitored, can only be considered for limited analysis.
Peak flows were estimated based on 2-mm depth over the weir
and the rating curves for each monitoring station �Fig. 5�. For the
underdrain discharge, a best estimate for 26 of the 36 storms that
were less than 7 mm is that peak flow was less than 0.13–0.21
mm/h. The problem of low flow measurement applied to only 13
of the 36 storms in the asphalt runoff catchment; peak flows were
estimated at 0.01 mm/h �0.004 L/s�. Total volume, lag time, and
duration could not be satisfactorily estimated for these events.
Event-Based Performance
Representative hydrographs for small storms �25 mm�, and ap-
proximately 2-year �63 mm�, 5-year �98 mm�, and 10-year �152.3
mm�, 24-h ARI storms successfully captured are shown in Figs.
7–10. In all cases, asphalt runoff usually mirrored spikes in rain-
fall intensity, whereas discharge from the permeable pavement
underdrain was relatively stable once the peak rate was reached.
The hydrographs also demonstrate significantly reduced perme-
m Rainfall Depth
Rainfall intensity
�mm/h� Median
duration
�h�Mean Peaka
2.5 11.6 3.1
1.7 17.9 6.8
2.1 15.9 8.4
1.9 31.7 14.7
3.6 35.2 13.8
3.8 44.8 27.1
2.3 17.0 7.9
1.4 14.4 6.1
27.6 79.2 40.8
0.3 3.6 0.1
3.3 12.9 6.7
RNAL OF HYDROLOGIC ENGINEERING © ASCE / JUNE 2010 / 479
15(6): 475-485 
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able pavement underdrain discharge volume compared to the as-
phalt catchment runoff. Table 3 compares the hydrographs in
Figs. 8–10 plus one additional measured 5-year, 24-h ARI storm
against conventional stormwater management goals, for which
the system was not expressly designed. Assuming no surface flow
was assumed to occur from the permeable pavement �refer to
Fig. 7. Small storm hydrograph �25 mm�
Fig. 8. Approximate 2-year storm hydrograph �63 mm�
Fig. 9. Approximate 5-year storm hydrograph �98 mm�
480 / JOURNAL OF HYDROLOGIC ENGINEERING © ASCE / JUNE 2010
 J. Hydrol. Eng., 2010, 
Surface Infiltration section�, Table 3 demonstrates that the perme-
able pavement is able to reduce peak discharge below predevel-
opment conditions for conventionally regulated storm events.
Table 4 summarizes median hydrologic characteristics of the
monitored systems according to storm size, while Table 5 presents
Spearman correlations with measured climate parameters. The as-
phalt catchment peak flow unsurprisingly showed a steady in-
crease in depth with increasing storm size; parameters were
positivelycorrelated at the 0.05 level of significance, while rain-
fall intensity was also positively correlated at the 0.01 level of
significance. For the majority of events �storms up to 20 mm,
Table 2�, median asphalt peak flow is approximately an order of
magnitude greater than median modeled predevelopment peak
flow, and is approximately four times greater for the remainder of
events.
While permeable pavement underdrain peak flow was also
positively correlated to storm size and intensity �both at 0.01 level
of significance�, the median peak flow for each storm size range
�Table 4� were substantially less than the median asphalt catch-
ment peak flow. The Mann Whitney U test for independent
samples suggested statistically significant different peak flow dis-
tributions �0.05 level of significance�. For events exceeding
20-mm rainfall, median permeable pavement underdrain peak
flow was less than modeled predevelopment conditions, corrobo-
rating results from Table 3 over a wider range of events. The
difference in peak flow distributions was not statistically different
�0.05 level of significance� between underdrain discharge and
modeled predevelopment peak flow, when storms with greater
than 2 mm over the weir were considered. Interestingly, positive
correlation �0.01 level of significance� between peak rainfall in-
tensity and peak underdrain discharge suggests that intense storms
push flow through the basecourse, reducing flow control.
Effective capacity for stormwater retention despite clayey sub-
soils is demonstrated by substantially less median permeable
pavement underdrain discharge volume compared to the median
asphalt catchment discharge volume for each rainfall category
�Table 4�. As might be expected, discharge volumes were posi-
tively correlated to rainfall depth and average intensity for both
systems �0.01 level of significance�. Underdrain discharge volume
was also positively correlated to peak intensity �0.01 level of
significance�, suggesting that rainfall bursts push water through
Fig. 10. Approximate 10-year storm hydrograph �152.3 mm�
15(6): 475-485 
Table 3. Peak Flow Control for Conventional Design Storms
m Size
Pre
0.
0.
1.
3.
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the system. The Mann Whitney U test for independent samples
rejected the null hypothesis of equal volume distributions be-
tween the systems �0.05 level of significance�.
Greater than expected rainfall retention measured in 2006/
2007 prompted inspection of the permeable pavement underdrain.
In April 2007, the underdrain was reinstalled and all pipe joint
seals were checked to ensure positive drainage without leaks.
Consequently, approximately 3 m of the permeable pavement sur-
face and basecourse was replaced in the vicinity of the underd-
rain. Joint chip along the entire length of the test section was also
topped up. Subsequent data revealed that initial underdrain instal-
lation was not problematic �i.e., there was no measureable differ-
ence in retention�, and instead lead to the topic of the current
paper. Losses in the permeable pavement can be attributed to a
combination of:
 Significant storage in the subbase, followed by evaporation
�wetting and drying of the pavement basecourse�; or
 Leakage under the sidewalk to the perforated road drain; or
 Exfiltration into subgrade soils.
A presumed lack of capillary action viable in the generally
large size basecourse aggregates suggests evaporation should not
be significant. However, a few laboratory and field studies of
permeable pavements indicate that evaporation does occur
�Andersen et al. 1999; Gomez-Ullate et al. 2008; Karasawa et al.
2006�, and in one study, that it even contributes to surface cooling
�Karasawa et al. 2006�. Collins et al. �2008� also suggested
evaporation as a water loss mechanism between events, although
it was not specifically measured. With respect to exfiltration, the
Storm
date
Rainfall
depth
�mm�
Storm
duration
�h�
App
ARI
July 26, 2008 63.6 19.3
August 5, 2006 82.1 27.8
July 29, 2008 98.0 40.8
October 1, 2006 152.3 27.1
Note: n /a=not applicable.
aSource: Beca Carter Hollings & Ferner Ltd. �1999�.
Table 4. Median Discharge Hydrologic Characteristics according to Stor
Storm depth
�mm�
Duration �h�
Pred Aspha Perma
�2–7 n/a 2.7 7.5
�7–10 0.1 11.4 14.1
�10–20 7.7 9.7 12.0
�20–30 13.3 14.8 14.2
�30–50 10.0 16.7 26.7
�50 24.2 24.3 28.5
Overall mean 11.5 10.4 15.8
Overall median 8.3 9.3 13.1
Overall maximum 44.7 29.6 43.3
Overall standard deviation 10.7 7.7 8.7
Note: Asph=Asphalt Catchment Runoff, Perm=Permeable Pavement U
applicable.
aFull hydrograph analysis is not available for the permeable pavement sys
For 26 storms for the permeable pavement underdrain and 13 storms fo
0.13–0.21 mm/h and 0.01 mm/h, respectively. These events were exclude
JOU
 J. Hydrol. Eng., 2010, 
subgrade may not be homogeneous. Cracks, fissures, or other het-
erogeneity could promote exfiltration, as per Tyner et al. �2009�.
Leakage to the perforated drain is less likely; in addition to the
polythene liner, longitudinal slope toward the underdrain �6.0–
7.4%� is substantially greater than cross fall toward the road drain
�3.0–3.7%�.
Table 6 summarizes the overall fraction of rainfall that be-
comes runoff, a.k.a., the runoff coefficient, C, which is a fre-
quently endorsed approach by regulatory communities for storm-
water management design. The coefficients show that even when
permeable pavement is only about half of the total catchment area
�Table 1�, the total catchment discharge �underdrain+surface run-
off� is likely to be substantially less than from an asphalt catch-
ment with similar nonasphalt fractions, particularly for larger
events, presuming C increases with storm size �Pitt 1999�. For
storms greater than 7.0 mm of rainfall, the distribution of asphalt
catchment volume was statistically different from either the per-
meable pavement underdrain volume or the permeable pavement
catchment �underdrain+surface�. Storms less than 7.0 mm of
rainfall could not be compared, as asphalt catchment volume and
permeable pavement underdrain volume were not concurrently
available in most cases.
Flow Frequency Analysis
Impacts of urban runoff arise not only from the magnitude of
flows, but the frequency with which elevated flows occur. As
described in the “Introduction,” flow control under a conventional
te
�
Peak flow �mm/h�
Predevelopment
Asphalt
surface
Permeable
pavement
underdrain
7.7 16 2.9
7.4 n/a 5.5
12.4 46.0 6.5
24.5 48.6 14.9
Peak flow �mm/h� Volume �mm�
d Aspha Perma Pred Aspha Perma
0 3.0 0.2 0.0 3.2 3.3
1 9.5 0.8 0.1 7.7 4.4
0 9.5 1.2 0.9 14.1 7.1
3 13.3 1.3 2.5 11.4 10.6
6 28.6 3.4 7.4 28.9 21.4
4 46.0 6.5 47.9 105.3 56.9
4 11.5 1.2 2.9 13.2 9.5
2 7.7 0.6 0.1 8.7 6.0
5 48.6 14.9 92.5 109.8 82.4
6 12.2 2.1 11.8 19.1 13.1
rain Discharge, and Pred=Modelled Predevelopment Runoff. n /a=not
all storms of 2–7 mm rainfall due to low flow and instrument sensitivity.
sphalt catchment in this storm depth range, peak flow was estimated at
total volume and duration calculations.
6.
12.
1.
0.
24.
3.
nderd
tem for
r the a
d from
roxima
a �year
2
2
5
10
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Table 5. Spearman Rho Correlation between Climate and Runoff Char-
acteristics
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management scenario tends to match peak flow for isolated de-
sign storm events, whereas the LID approach calls for matching
flows and volumes over a range of conditions.
Statistically significant Spearman correlations �Table 5� dem-
onstrated that runoff control by permeable pavement is affected
by antecedent moisture conditions and storm characteristics. A
useful format to assess the reliability of a stormwater manage-
ment system for flow mitigation under varying conditions without
consideration of the sequence of events is with a flow duration
curve �Smakhtin 2001�. Under the context of assessing storm-
water management devices on an event basis, a flow frequency
curve �FFC� is suggested as a more apropos name, and is adopted
herein.
The number of observations affects the shape of the FFC. Data
included in the peak flow FFC �Fig. 11� include an equal number
of records �81� for peak flows across the three scenarios of asphalt
catchment runoff, permeable pavement underdrain discharge, and
modeled predevelopment conditions. Fig. 11 demonstrates that
regardless of conditions, measured underdrain discharge is ap-
proximately equal to modeled predevelopment peak flow for ap-
proximately 80% of occurrences. Excluding estimated permeable
pavement underdrain peak flows when flow over the weir was
approximately 2 mm, the modeled predevelopment peak flow dis-
tribution is not statistically different from the distribution of un-
Climate
Asphalt
runoff
Permeable
pavement
underdrain
Rainfall depth Volume �0.01� Volume �0.01�
Peak flow �0.05� Peak flow �0.01�
Duration �0.01� Duration �0.05�
Rainfall duration Duration �0.01� Duration �0.05�
Average rainfall intensity Volume �0.05� Volume �0.01�
Peak flow �0.01� Peak flow �0.01�
Peak rainfall intensitya Peak flow �0.01� Volume �0.01�
Peak flow �0.01�
Duration �0.01�
Antecedent dry period Lag time �0.05�
Note: Correlation tests exclude storms with estimated peak flow; all cor-
relations between lag time and runoff duration performed only for storms
with at least 7-mm rainfall; two-tailed level of statistical significance
indicated in “��”.
aMaximum 5-min rainfall over storm duration.
Table 6. Estimated Runoff Coefficients Based on Storms �7-mm Rain-
fall
Percentile
Asphalt
catchment
Permeable
pavement
underdrain
Permeable
pavement
catchment
0.10 0.48 0.29 0.41
0.25 0.60 0.43 0.53
0.50 0.85 0.49 0.64
0.75 0.94 0.57 0.71
0.90 0.98 0.63 0.74
Standard deviation 0.20 0.15 0.13
Note: Runoff coefficient C=runoff volume/rainfall volume.
482 / JOURNAL OF HYDROLOGIC ENGINEERING © ASCE / JUNE 2010
 J. Hydrol. Eng., 2010, 
derdrain peak flow �0.05 level of significance�. Approximately
15% of all storms did not produce measureable peak flow from
the observed or modeled scenarios.
The volume FFC �Fig. 12� is compiled from 68, 55, and 61
records among the asphalt catchment runoff, permeable pavement
underdrain discharge, and modeled predevelopment conditions,
respectively. To promote comparability between modeled data
and field observations, the number of modeled events was re-
stricted to the average number of observed events between the
two catchments for storm volume. Specific events excluded were
those that did not produce modeled runoff, as low flows were the
reason for exclusion of measured data. Permeable pavement total
catchment data were not included as only 45 data points were
available and did not contain any small storm ��7.0 mm� events.
For large infrequent events �5% exceedance�, permeable pave-
ment underdrain discharge again is shown to match predevelop-
ment conditions. While predevelopment volume is not matched
by the permeable pavement for frequently occurring events �at
least 50% exceedance�, likely due to the clay subsoils, it is still
substantially mitigated compared to the expected asphalt catch-
ment volume regardless of antecedent conditions. Volume distri-
butions were statistically different �0.05 level of significance�
between asphalt catchment and permeable pavement underdrain
discharge for storms greater than 7 mm of rainfall.
Fig. 11. Peak FFCs
Fig. 12. Volume frequency curves
15(6): 475-485 
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Together, results suggest that the permeable pavement can be
used to meet LID objectives for matching peak flows for “fre-
quently occurring” events, even when part of a larger impervious
catchment. Volume control is slightly less satisfactory according
to these objectives, but certainly the ability to self-mitigate even
with poor subgrade soils, steep slope, and frequent rainfall should
be acknowledged.
Lag Time and Runoff Duration
Antecedent dry period duration was positively correlated to lag
time for the underdrain discharge �Table 5, 0.05 level of signifi-
cance�, further supporting the concept of wetting and drying, and
possible exfiltration. However, individual event data indicate that
even when the permeable pavement is wet at the onset of rainfall
�i.e., a short interevent time�, there is still a delay in the onset of
runoff due to the tortuous flow path through the permeable pave-
ment basecourse. Over 54 events, a median value of 1 h �2.2-h
standard deviation� elapsed before discharge from the permeable
pavement was measured, whereas only a median 12 min �48-min
standard deviation� elapsed for the asphalt runoff over 61 events.
The large standard deviation of asphalt lag time is due to a few
storms where it is likely that the catchpit had to fill up before
discharge through the monitoring point could occur. Data are not
presented in Table 4, as lag time was not correlated to storm
depth.
Storage and flow through the aggregate basecourse can serve
to extend the underdrain’s hydrograph duration. Asphalt catch-
ment runoff and permeable pavement underdrain discharge dura-
tions were positively correlated to rainfall depth �Table 5�. For
storms with more than 2-mm depth over the weir, discharge from
the permeable pavement underdrain typically lasted 3–6 h longer
than from the asphalt catchment �Table 4�, reminiscent of a slow
release from a vegetated site. Altogether, the permeable pavement
can have an important effect on overall hydrograph timing, re-
gardless of antecedent moisture conditions.
Surface Infiltration
Substantial variation was observed in the Birkdale Rd. surface
infiltration rate �Fig. 13�. Removal of some paver blocks in April
2007 revealed that parts of the bedding layer had formed into
Fig. 13. Surface infiltration rates at f
JOU
 J. Hydrol. Eng., 2010, 
agglomerated chunks and a crust above the geotextile �Fig. 14�.
However, since 70% of results are greater than the 1,200-mm/h
design permeability and all results are greater than the 120-mm/h
required permeability, the chunking and crusting does not appear
to be a cause of concern for overall performance. Testing com-
menced 2 months after initial construction, and continued for ap-
proximately 1.5 years. The 2008 data �Fig. 13� is indicative of
approximately 1.25–1.5 years of operation without maintenance,
as joint chip was topped up in April 2007.
When all data at Birkdale Rd. are considered, the Wilcoxon
rank-sum testing is unable to detect statistically significant differ-
ences in surface infiltration rate between pre- and postmainte-
nance activity. Nordoes the surface infiltration rate in the live
road appear to be statistically different from the surface infiltra-
tion rate in the parking lane, but it is noted that roadway testing
did not occur in 2008. When data from only premaintenance ac-
tivity is tested, the surface infiltration on the roadway is statisti-
cally greater than in the parking lane at the 0.025 level of
significance.
Birkdale Rd. results may be due to high site slope �6.0–7.4%�;
over time, a large portion of the joint chip scoured out of cracks
�causing the need for the topup in 2007, and recurrence was con-
firmed in 2008�, effectively clearing any organic or other matter
which might otherwise clog pore space. The loss of joint chip
allowed paver blocks to shift under vehicle loads, deforming the
road surface and joints, thus explaining the statistically significant
rmeable pavement sites in Auckland
Fig. 14. Agglomerated bedding sand �left� and crusting above geo-
textile �right�, April 2007
RNAL OF HYDROLOGIC ENGINEERING © ASCE / JUNE 2010 / 483
15(6): 475-485 
difference in surface infiltration rate between the live road and
parking lane for the premaintenance period. In 2008, weeds and
not statistically different. Conversely, asphalt catchment peak
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leaf litter were also observed in joint space.
Loss of joint chip might also suggest that surface flow did in
fact occur from the permeable pavement. Flow measurement was
attempted in the permeable pavement catchment catchpit, but re-
sults were unreliable, despite checks on equipment calibration,
and would have been confounded with overland flow from the
driveway, sidewalk, and grass verge anyway. Sustained high sur-
face infiltration rates �Fig. 13� suggest that overall, surface flow
from the permeable pavement would have been a rare occurrence,
would likely be minimal compared to the other catchment area
contributions, and thus the underdrain discharge evaluation satis-
factorily represents typical system performance.
Trees overhanging one testing location at the Kahika Rd. site
dropped leaf litter into pavement joints, resulting in low compara-
tive permeability. Joints were pressure washed between the first
and second rounds of testing. While leaf litter continued to accu-
mulate throughout 2006, surface infiltration rate was well above
1,200 mm/h. Ultimately, pressure washing is not recommended as
a maintenance method, unless the wash water is captured.
Trapped pollutants are reentrained into a runoff system �the wash
water� or simply disbursed around the site, where they may once
again flow into the permeable pavement and cause clogging.
The North Shore Events Centre surface infiltration rates were
expected to be higher than the other sites due to its construction
from permeable blocks and hence a larger surface area available
for infiltration. However, the sediments tracked or wind blown
from the builder’s yard resulted in a permeability of 523 mm/h
when the end of the lot closer to the yard was tested. While it was
considered important to demonstrate the detrimental effects of
sediment deposition, alternative locations were chosen for future
testing. Permeability measured at the opposite end of the lot was
well above the design criteria despite the potential heavy loads
from bus parking every night. The testing clearly demonstrates
the importance of considering all land uses within a catchment
when assessing the suitability of a permeable pavement installa-
tion, as observed by Bean et al. �2007�. The Upland Rd. driveway
demonstrated consistently high permeability measurements
throughout the monitoring period, which is attributed to very low
site traffic.
Conclusions
A 200-m2 interlocking block permeable pavement site was tested
along an active roadway and parking lane with bus stop over
impermeable soils. Data from the permeable pavement underdrain
discharge and adjacent conventional asphalt section runoff were
collected concurrently between 2006 and 2008, and over a total of
1,128.1 mm of rainfall.
The permeable pavement compared favorably with modeled
predevelopment conditions against several criteria for LID objec-
tives: maintaining predevelopment conditions for runoff lag time,
peak flow, and duration of flow. Peak flow from the permeable
pavement underdrain was less flashy and tended to show less
variation overall, compared to the asphalt runoff which usually
mirrored spikes in rainfall intensity. Eighty-one complete storms
contributing to a peak flow frequency assessment indicate rela-
tively comparable peak flows between the permeable pavement
underdrain discharge and modeled predevelopment flows, regard-
less of antecedent conditions, and including large conventional
design storms �up to 10-year, 24-h ARI�. Flow distributions were
484 / JOURNAL OF HYDROLOGIC ENGINEERING © ASCE / JUNE 2010
 J. Hydrol. Eng., 2010, 
flow was substantially greater in all cases, and the flow distribu-
tion was statistically different from the underdrain discharge flow
distribution.
The tortuous flow path through the permeable pavement
basecourse delayed the onset of runoff compared to rainfall, with
a median 1-h lag time, compared to median 12 min for the asphalt
catchment. The permeable pavement underdrain extended the
total runoff duration by 3–6 h over that for asphalt catchment
during storms of 7–50 mm. Underdrain hydrograph timing was
reminiscent of modeled predevelopment conditions in most cases.
Relatively substantial volume control was measured, despite
presumed impermeable subgrade soils, steep slope, and frequent
rainfall occurrences, although predevelopment conditions were
not matched. Losses in the permeable pavement are most likely
attributed to significant storage in the subbase, followed by
evaporation �wetting and drying of the pavement basecourse�
and/or exfiltration into subgrade soils. Runoff coefficients for the
permeable pavement underdrain discharge were measured at
0.29–0.67 �10th–90th percentile values� which increases to 0.41–
0.74 when permeable pavement comprises about one-half of the
catchment area and the remainder is predominantly impervious
area. For both scenarios, a statistically significant difference be-
tween distributions was measured compared to the asphalt catch-
ment.
Assessment of maintenance requirements from the four tested
permeable pavement sites is inconclusive. At Birkdale Rd., sur-
face infiltration rate did not substantially deteriorate after 1 year
of operation. Subsurface investigation in the midst of the project
revealed crusting of the bedding layer below the pavers. One and
a half years after joint chip replacement, at the end of the moni-
toring period, surface infiltration rate was not significantly com-
promised. High site slope �6.0–7.4%� likely helped maintain high
surface infiltration rates, as joint chip was partially washed out in
about 1 year �which also caused paver blocks to shift position�. At
other testing sites, organic material and sediment significantly re-
duced permeability, yet even reduced rates well exceeded design
requirements of 120 mm/h to infiltrate the 2-year, 24-h ARI
storm. Where pressure washing occurred at one site to clear the
joints, surface permeability was restored by more than an order of
magnitude. Pressure washing is not recommended as a mainte-
nance procedure, however, as dislodged sediments may be
washed into the reticulation system and ultimately to the receiv-
ing water.
Interpretation of results with respect to system design is com-
plicated.Generally, greater system depth would positively con-
tribute toward all of the hydrologic performance metrics
considered herein. At Birkdale Rd., the basecourse depth was de-
termined for structural requirements rather than a detention stor-
age volume for a particular extent of flow control. Structural
design will vary from site to site, but it likely will always exceed
water quality design where vehicle loadings will be present �and
assuming the source area is only the permeable pavement itself�.
It is also likely that in practice, actual construction will always
deviate in some way from design on paper, as it did at Birkdale
Rd. �observed by the deeper subbase areas near the underdrain�.
In this case, perhaps construction deviations contributed posi-
tively toward performance, but it is also feasible that a different
deviation�s� could detract from performance. Overall, the
Birkdale Rd. system design could be considered typical; hence,
the hydrologic characteristics observed herein would be expected
elsewhere if the same design basis was adopted.
Altogether, permeable pavement appears to be an effective
15(6): 475-485 
tool for hydrologic mitigation of storms from “every day events”
up to the 10-year, 24-h ARI, even on steep slopes located over
impermeable soils and subject to frequent rainfall.
Acknowledgments
This study was funded by the North Shore City Council, the
Auckland Regional Council through the Storm Water Action Plan,
Maunsell, Ltd. �now AECOM�, and TechNZ. Viewpoints ex-
pressed in this paper are those of the writers and do not reflect
policy or otherwise of the funding agencies. Special thanks are
extended to David Kettle and Steve Crossland for technical sup-
port, and Miriam Ortheil and Matthias Sindern for conducting the
2008 site survey. Emily Voyde contributed substantially to the
formatting of the final paper.
References
Dreelin, E. A., Fowler, L., and Ronald Carroll, C. �2006�. “A test of
porous pavement effectiveness on clay soils during natural storm
events.” Water Res., 40�4�, 799–805.
Gilbert, J. K., and Clausen, J. C. �2006�. “Stormwater runoff quality and
quantity from asphalt, paver, and crushed stone driveways in Con-
necticut.” Water Res., 40�4�, 826–832.
Gomez-Ullate, E., Bayon, J. R., Castro, D., and Coupe, S. J. �2008�.
“Influence of geotextile on water retention in pervious pavements.”
Proc., 11th Int. Conf. on Urban Drainage.
Hinman, C. �2005�. Low impact development technical guidance manual
for Puget sound, Puget Sound Action Team and Washington State
University Pierce County Extension, ed., 256.
James, W., and Thompson, M. K. �1997�. “Contaminants from four new
pervious and impervious pavements in a parking lot.” Advances in
modeling and management of stormwater impacts, W. James, ed.,
CHI, Guelph, Canada, 207–222.
Karasawa, A., Toriiminami, K., Ezumi, N., and Kamaya, K. �2006�.
“Evaluation of performance of water-retentive concrete block pave-
ments.” Proc., 8th Int. Conf. on Concrete Block Paving, Sustainable
Paving for Our Future, ICPI, San Francisco.
D
ow
nl
oa
de
d 
fro
m
 a
sc
el
ib
ra
ry
.o
rg
 b
y 
U
TF
PR
 - 
U
ni
ve
rs
id
ad
e 
Te
cn
ol
og
ic
a 
Fe
de
ra
l d
o 
Pa
ra
na
 o
n 
10
/3
1/
17
. C
op
yr
ig
ht
 A
SC
E.
 F
or
 p
er
so
na
l u
se
 o
nl
y;
 a
ll 
rig
ht
s r
es
er
ve
d.
Andersen, C. T., Foster, I. D. L., and Pratt, C. J. �1999�. “Role of urban
surfaces �permeable pavements� in regulating drainage and evapora-
tion: Development of a laboratory simulation experiment.” Hydrolog.
Process., 13�4�, 597–609.
ASTM. �2003�. “Standard test method for infiltration rate of soils in field
using double-ring infiltrometer.” ASTM D3385-09, ASTM, West Con-
shohocken, Pa.
Bean, E. Z., Hunt, W. F., and Bidelspach, D. A. �2007�. “Field survey of
permeable pavement surface infitration rates.” J. Irrig. Drain. Eng.,
133�3�, 249–255.
Bear, J. �1972�. Dynamics of fluids in porous media, Dover, New York.
Beca Carter Hollings & Ferner Ltd.. �1999�. “Guidelines for stormwater
runoff modelling in the Auckland region.” Technical Publication 108
prepared for Auckland Regional Council, New Zealand.
Brattebo, B. O., and Booth, D. B. �2003�. “Long-term stormwater quan-
tity and quality performance of permeable pavement systems.” Water
Res., 37�18�, 4369–4376.
Collins, K., Hunt, W. F., and Hathaway, J. M. �2008�. “Hydrologic com-
parison of four types of permeable pavement and standard asphalt in
eastern North Carolina.” J. Hydrol. Eng., 13�12�, 1146–1157.
Dept of Environmental Resources Programs and Planning Div. �1999a�.
“Low impact development design strategies.” Technical Report Pre-
pared for Dept. of Environmental Resources, Prince George’s County,
Md.
Dept of Environmental Resources Programs and Planning Div. �1999b�.
“Low impact development hydrologic analysis.” Technical Report
Prepared for Prince George’s County, Md.
JOU
 J. Hydrol. Eng., 2010, 
NIWA Science. �2000�. Summary climate information for selected New
Zealand locations, National Institute of Water and Atmospheric Re-
search, New Zealand.
Pezzaniti, D., Beecham, S., and Kandasamy, J. �2009�. “Influence of
clogging on the effective life of permeable pavements.” Water Man-
agement, 162�WM3�, 211–220.
Pitt, R. �1999�. “Small storm hydrology and why it is important for the
design of stormwater control practices.” Advances in modeling the
management of stormwater impacts, Vol. 7, W. James, ed., CRC, Boca
Raton, Fla.
Pratt, C. J., Mantle, J. D. G., and Schofield, P. A. �1995�. “UK research
into the performance of permeable pavement, reservoir structures in
controlling stormwater discharge quantity and quality.” Water Sci.
Technol., 32�1�, 63–69.
Rushton, B. T. �2001�. “Low-impact parking lot design reduces runoff
and pollutant loads.” J. Water Resour. Plann. Manage., 127�3�, 172–
179.
Schluter, W., Spitzer, A., and Jefferies, C. �2002�. Performance of three
sustainable urban drainage systems in East Scotland, ASCE, Reston,
Va., 1–17.
Scott, C. R. �1980�. An introduction to soil mechanics and foundations, E
& FN Spon, London.
Smakhtin, V. U. �2001�. “Low flow hydrology: A review.” J. Hydrol.,
240�3–4�, 147–186.
Tyner, J. S., Wright, W. C., and Dobbs, P. A. �2009�. “Increasing exfil-
tration from pervious concrete and temperature monitoring.” J. Envi-
ron. Manage., 90�8�, 2636–2641.
RNAL OF HYDROLOGIC ENGINEERING © ASCE / JUNE 2010 / 485
15(6): 475-485