Mesures de contrôle des eaux pluviales : enseignements
tirés de la mise en œuvre et de l’opération des systèmes
de suivi
R. Kertesz, D. Murray, W. Shuster
To cite this version:
R. Kertesz, D. Murray, W. Shuster. Mesures de contrôle des eaux pluviales : enseignements tirés de la
mise en œuvre et de l’opération des systèmes de suivi. Novatech 2013 - 8ème Conférence internationale
sur les techniques et stratégies durables pour la gestion des eaux urbaines par temps de pluie / 8th
International Conference on planning and technologies for sustainable management of Water in the
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NOVATECH 2013
Considerations for the implementation and operation
of stormwater control measure (SCM) performance
monitoring systems
Mesures de contrôle des eaux pluviales : enseignements
tirés de la mise en œuvre et de l'opération des systèmes
de suivi
Kertesz, R.*, Murray, D.1, Shuster, W.2
*USEPA/ORISE, kertesz.ruben@epa.gov;
1
USEPA, murray.dan@epa.gov;
2
USEPA, shuster.william@epa.gov
RÉSUMÉ
Des études des infrastructures vertes sont nécessaires pour permettre des décisions informées sur le
choix de telles technologies à la place des méthodes traditionnelles de contrôle de l’assainissement
urbain et pour contribuer à une planification d’entretien efficace. Deux mesures de gestion des eaux
pluviales par infiltration dans un revêtement drainant à Cincinnati, dans l’Ohio, aux Etats-Unis, ont été
effectuées avec des techniques de télédétection pour contrôler les flux d’eau et comprendre ainsi les
performances des mesures de contrôle des eaux pluviales. Parmi les conclusions, l’assainissement
privilégié, la coopération multidisciplinaire depuis la conception jusqu’à la mise en œuvre, l’analyse
topographique, les détails de l’installation de la technique de télédétection et les complications de
fonctionnement du capteur. Les leçons apprises sont résumées et les problèmes examinés en utilisant
des exemples spécifiques observés sur les sites. Une description des solutions et des moyens de
contournement est fournie pour chacun de ces défis, ainsi qu’une analyse de la meilleure façon de les
éviter lors de futures installations. Des recherches sont en cours pour mieux intégrer les technologies
de surveillance dans le processus de construction et la mise en œuvre des mesures de contrôle des
eaux de pluie.
ABSTRACT
Green infrastructure (GI) studies are needed to make informed decisions about whether or not to
select GI technologies over traditional urban drainage control methods and to assist in the timing of
effective maintenance. Two permeable pavement infiltration stormwater control measures (SCM) in
Cincinnati, OH, USA, were instrumented with sensing technologies to monitor water fluxes and
thereby better understand stormwater control measure performance. Findings cover preferential
drainage, multidisciplinary cooperation from design through to operation, topographic analysis, details
on installation of sensor technology, and complications with sensor operation. Our lessons-learned are
summarized and issues are examined using specific examples observed at the SCM sites. A
description of the solutions and workarounds are provided for each challenge as well as an analysis of
how to best avoid them in future installations. Research is ongoing to better integrate monitoring
technology with the construction process and actual SCM operations.
KEYWORDS
Best management practice, Green infrastructure, Infiltration, Low impact, Low impact development,
Permeable pavement, Sensor, Stormwater, Stormwater control measure, Urban drainage
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B1 - REVÊTEMENTS POREUX / POROUS SURFACING
1
INTRODUCTION
Urban drainage control has been an important social practice for many years. The ancient Greeks and
Romans had designed drainage canals that are still in use today (Angelakis et al. 2005; Mays 2010).
These canals often served as combined sewers. In fact, combined sewers are still in use globally
(Montalto et al. 2007). This is a particular concern in the earlier settled regions of the United States
such as Cincinnati, OH, the location of the study sites discussed in this article. It has been well
documented that, during significant rain events, combined sewers overburden wastewater treatment
plants and overwhelm conveyance infrastructure, leading to degraded water quality in receiving
waters, sewer backups, and sometimes dangerous conditions in streets during and directly following
rain events (Shear et al. 1996; Hall et al. 1998; Eganhouse and Sherblom 2001). Many engineered
hydraulic solutions have been implemented, typically denoted as “grey infrastructure” (Struck et al.
2009; Jaffe 2011). These solutions are generally very costly capital investment projects that provide
few ancillary benefits that green infrastructure (GI) stormwater control measures (SCM) often do, such
as restoring the hydrologic cycle, mitigating the urban heat island, etc. (Kessler 2011; Spatari et al.
2011).
A major issue limiting adoption of green infrastructure treatment processes (vs grey) is the lack of GI
performance information. Data are readily available regarding the hydraulic properties, storage
volumes, and particle settling mechanisms of grey infrastructure solutions. Green infrastructure is
relatively nascent and treatment mechanisms are somewhat more complex and are not as richly
documented, leading to a disadvantage in terms of adoption.
The authors of this article have installed sensors during and following the construction of a permeable
paver SCM and a porous concrete-bioretention treatment train in the Cincinnati area in an effort to
produce the necessary hydrologic data for comparison to grey solutions. Numerous obstacles,
setbacks, and learning opportunities were encountered while executing the study. The lessons learned
in designing, installing, and monitoring performance of the aforementioned SCMs provide useful
findings for future research and measurement. The methods, results, and discussion herein will
address the issues encountered and provide recommendations for practice changes to improve the
measurement process for future installations.
2
METHODS
Two pavement based SCMs in Cincinnati, OH were instrumented to monitor rainfall, water fluxes, and
water quality. The first was a 0.49 acre asphalt parking lot draining to a 0.15 acre porous concrete
area and 0.07 acre bioretention area (BA). It is located at Cincinnati Public School’s Clark Montessori
High School and is shown in Figure 1. Overflow weirs served to drain the BA if ponding occurs.
Subsurface moisture and temperature were measured using water content reflectometers [Campbell
Scientific CS-650]. Bioretention area water level was measured using two pressure sensors [Campbell
Scientific CS-450]. Rainfall was measured using a 0.1mm tipping bucket raingage [RM-Young 52203].
The second investigation site was a parking lot at Cincinnati State Technical and Community College
(Cincinnati State). The lot consisted of three cells of permeable paver SCMs that drain asphalt
roadways as shown in Figure 2: cells 3A, 82, and 90. The area for cell 82 was 0.061 acres, cell 3A
was 0.105 acres, and cell 90 was 0.038 acres. Contributing drainage areas were 0.153 acres, 0.210
acres, and 0.008-0.032 acres (depending on wind), for the respective cells. Cells were instrumented
with temperature sensors [Campbell Scientific CS-107], moisture sensors [Campbell Scientific CS616], and a meteorology station. Measurements were recorded at 1 minute intervals. The paver
system was drained by an exfiltration pipe installed at the invert of the storage layer. Flows out of cell
82 and cell 90 underdrains were measured using a flow-calibrated 1 inch Parshall flume instrumented
with an ultrasonic sensor.
2
NOVATECH 2013
Figure 1: Clark Montessori Public School stormwater treatment train.
Asphalt drainage (white) flows through porous pavement (grey) and then to bioretention area (green), or directly to bioretention area. North is to the top of the
figure. Note placement of lamp posts in bioretention area.
3
B1 - REVÊTEMENTS POREUX / POROUS SURFACING
Figure 2: Cincinnati State Technical Community College permeable paver parking lot.
Drainage areas are colored as follows: Grey (Cell 82); Green (Cell 90); Light Blue (Cell 3A). Grey lines
denote underdrain piping. Black arrows denote drainage culverts. Red circles denote sensor locations.
3
RESULTS AND DISCUSSION
During the experiment, notes were made to improve research outcomes, resulting in five main topics
which will be discussed, each in its own section: minimizing alternative flowpaths; sharing information
during the design-build process; measuring lot-level topography; creating mutual objectives between
research and construction; and taking care to minimize measurement error.
3.1
Minimizing preferential or alternative flowpaths
Careful attention to detail during construction is directly related to the success rate of any construction
project (Hendrickson and Au 1989). Infiltration based SCMs are particularly susceptible to construction
practices, as they are designed to convey water into the ground and are not generally lined with a
4
NOVATECH 2013
waterproof membrane. In the case of Clark, water was projected to infiltrate after soil core analyses
indicated the presence of well draining soils in and around the site of the SCM (a rarity in Cincinnati).
Conversely, at Cincinnati State, the soils were not found to drain well. Rather than amend the soils,
underdrains were installed and relied upon to provide drainage of the storage area beneath the
permeable pavement. At both sites, preferential flowpaths appear to have affected the measured
results. The significance of impact is still being assessed.
The cause for concern at Cincinnati State was a much diminished flow as measured through the
underdrain at cell 3A. The surface area of cell 3A is greater than cell 90, and the total contributing area
to cell 3A is larger than that of cell 82, suggesting that the measured flow would be proportional to that
of 82 and likely higher than cell 90. This was not the case. Flow, when measured using an area
velocity flow meter as well as a weir-bubbler apparatus, was found to be lower than from either of the
other two sites, except during peak flow conditions. Two example storms are shown in Figure 3.
Additionally, visual observation confirmed a lack of flow to the underdrain at cell 3A. It is theorized that
the installation of a stormwater conveyance pipe through cell 3A (Figure 2) may have entrained flow
through the bedding material (crushed stone) used to install the pipe. The invert of the pipe is below
that of the SCM itself and the pipe is sloped towards a steep gradient on the south side of the parking
lot, where it connects with an existing drainage system at the toe of a vegetated slope. While it has not
yet been confirmed that this indeed was the cause of diminished flow at the underdrain, it is a
plausible suggestion that preferential flow was occurring. The lesson learned was to carefully select
pipe bed material for conduits crossing through a SCM and to make use of measures to prevent the
entry of water into the pipe bed such as flow retardant material.
5.0
4.0
3.0
2.0
1.0
8
Site 82
Site 90
3A underdrain flow
Site 82
Site 90
3A underdrain
7
Flow (L/s)
6
0.3
0.2
5
4
3
1-Jun 12:00
Date/Time
1-Jun 08:00
1-Jun 04:00
08-M ay 14:00
08-M ay 10:00
08-M ay 06:00
0
08-M ay 02:00
0.0
07-M ay 22:00
1
1-Jun 00:00
2
0.1
07-M ay 18:00
Flow (L/s)
A preferential flowpath was also observed at the Clark site. The porous concrete – bioretention
treatment train is equipped with an underdrain but the underdrain has been temporarily sealed to
determine the infiltration capacity of the soil. Horizontal migration of water was not a focus of the
design plan. Emphasis was placed on vertical migration instead. However, after blocking the
underdrain, flow was seen draining into the drainage pipe on the west side of the SCM by seeping in
(or rather pouring) through the concrete bulkhead surrounding the drainage pipe that innervates with
the vault. It appears that hydraulic pressure following rain events was high enough to cause lateral
flow through the concrete wall at its weakest point. Attempts were made to quantify this flow (as a
function of head) in the bioretention area using area-flow velocity flow meters but water depths in the
drainage pipe were too low to provide confident measures of flow due to this drawdown. Future work
should incorporate a monitoring scheme that considers the possible lateral migration of flow through
the SCM. In the case of a site like Clark, this could be identified particularly well using moisture
detection devices placed beneath the relatively non-porous asphalt pavement surrounding the SCM.
At both sites, preferential flowpaths have confounded the research goals to quantify the hydrologic
response (and in the case of Clark, the infiltration capabilities) of the SCM.
Figure 3: Underdrain flow from three cells at the Cincinnati State parking lot during two events.
Note that 3A only responds during high flow events.
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B1 - REVÊTEMENTS POREUX / POROUS SURFACING
3.2
Sharing information during the design-build process
The second lesson learned during the establishment of these research projects was the need to
collaborate and coordinate from the inception of the project through construction and installation. GI is
multidisciplinary in nature. Those involved in the SCM at Clark included members from the school
district, the metropolitan sewer district, an engineering firm and a landscape architect, a landscaping
company, a construction management company and construction subcontractors, as well as the
research investigators and an environmental contracting firm with whom the researchers collaborated.
Cincinnati State did not involve a landscape architect or landscaper on the permeable paver project.
The school’s facilities department was, however, very heavily involved at Cincinnati State.
There were some success stories and some failures related to the entry of the research components
into the Clark and Cincinnati State GI sites. At Cincinnati State, the EPA was brought in approximately
1 month before installation, approached to provide information regarding the permeable paver
infiltration performance. Even within that short period of time plan changes were made and
underground vaults were installed (Figure 2) to provide a secure and accessible measurement area for
underdrain flow, sensors were purchased and installed to measure moisture and temperature in the
subsurface storage gallery, and some prototype sensors were installed for comparison with the
commercially available moisture sensors. A completely automated hydrologic data collection and
transmission system was installed. The only complication at Cincinnati state, in regards to
collaboration, was that the sensors themselves could not be purchased in enough number to densely
instrument the site. There was not enough time to trial the prototype sensors in a lab environment
before field deployment. The orientation of prototype sensors could likely have been changed to
improve sensor response characteristics. This simple fix cannot be done after the pavers are lain and
is a classic example of the need to be involved early enough to perform tests prior to deployment. The
EPA researchers were involved in the Clark Montessori project approximately 6 months before
construction was to begin, and while care was taken to integrate research components into the design
process, one engineering design aspect was changed after construction. The landscapers
recommended changing the engineered soil material in the bioretention area to one of higher organic
material after a sandy material was installed. This change could have been incorporated before the
engineered soil was first installed if the landscapers were better informed, saving both time and
money.
In general, it is of particular importance to collaborate when integrating data collection with GI because
the relative cost of installing monitoring equipment is lower when integrating it into the design of the
SCM and performance objectives can be realistically formed based upon the collective knowledge of
the purpose of the SCM and knowledge about various environmental factors (soil information,
topography, contributing area, land-use).
3.3
The importance of lot-level (micro) topography
High resolution topographic data of a drainage area can greatly improve the design process of an
SCM. Neither the Clark nor the Cincinnati State sites were built using optimal flowpath routing,
reducing the efficiency of the treatment system. At Cincinnati State, cell 90 received almost zero runon because it was placed in a higher topographic elevation relative to the area around it (but this
difference was found to be a couple of inches or less). Cell 82 achieved almost a 3:1 ratio of
contributing area to permeable paver area but channelization of flow along the roadway has caused
water to pool in certain areas of the SCM, while other areas were underutilized (Figure 4a). If careful
attention was placed on topography during design, this could have been corrected by regrading. At
Clark, some of the overland flow from the north portion of the parking lot shortcut the porous pavement
and entered directly into the bioretention area, underutilizing the peak flow reduction and filtration
properties of the porous pavement itself (Figure 4b). This is expected to lead to loading of particles
directly into the bioretention area and a shortened performance lifetime for the SCM. Uneven loading
of the porous pavement itself (particularly from the North) has resulted in localized areas of clogging
due to deposition while other parts of the BMP were not affected, effectively increasing the needed
maintenance frequency and reducing the overall performance of the SCM. This may be solved by
installing channel guides to direct flow towards the porous pavement more evenly.
In the future, smart regrading practices can use high resolution topography to identify preferential
surface flow paths, increasing capture area while extending SCM lifetime by masking lateral flowpaths,
thereby improving the SCM cost/benefit ratio.
6
NOVATECH 2013
(A)
(B)
Figure 4: Microtopography at Cincinnati State (A) and Clark Montessori (B).
Note concentration of flowlines towards blue circle: Southeast in figure A and Southwest in figure B.
3.4
Creating mutual objectives between research and construction
It is just as important to be in constant communication during the construction of an infiltration SCM as
during its design. The installation of sensor technology is disruptive to the build process and care must
be taken to ensure that the research and construction objectives are mutually fulfilled. The
consequence of not coordinating can be severe. At Clark, there were numerous entities involved in
construction, including the design firm, construction firm, a subcontractor who installed the crushed
stone, a subcontractor who excavated the bioretention area, a subcontractor who installed the
engineered soil, and the landscaping company which performed the planting in the bioretention area.
The sensor cables for the moisture and level logging hardware were pulled by a contractor while they
were operating and the wiring had to be re-aligned. Luckily, the cable conduits for the moisture
sensors could be repositioned by removing and reshaping the stone bed to accommodate the cable
conduits. It was not discovered until later that the level sensors were also affected, causing them to
measure at a different depth than installed, leading to erroneous values. This was rectified later. Both
of these issues could have been avoided if the construction personnel better understood the
purposeful placement of the instrumentation.
3.5
Taking care to minimize measurement error
The electronic circuits that are integral to most of today’s sensors are generally designed to be well
shielded against outside influence, however, when instrumenting an SCM, the immediate environment
should be assessed for sources of electromagnetic (EM) interference, and proper grounding should be
7
B1 - REVÊTEMENTS POREUX / POROUS SURFACING
provided for all sensors. If there is a strong possibility of potential interference, trials should be run in
the field before full scale deployment if at all possible. The authors observed significant electrical noise
at Clark but this was exclusive to one of the two brands of soil moisture sensors installed. What
occurred is that the signal for period (not temperature or other unrelated measurements however)
became noisy when the parking lot floodlights were activated during the night-time; an example of this
is shown in Figure 5. This suggests that certain technologies are more sensitive to electrical or EM
interference than others may be. More importantly, when given the opportunity to select from many
sites to study, interference sources should be considered as a part of the decision making process.
Also, dry soils and gravel layers may have contributed to ineffective ground. It should be noted,
however, that after re-grounding the sensors, the noise did not subside. Off-site grounding in native,
structured soils may be necessary in such conditions. The data are still suitable for analysis, as the
variation is about a smooth mean value.
Figure 5: Night-time noise in signal (volumetric water content) over a week period.
V5 is a measurement made in the parking space that is 5 spaces from the east side of the porous
pavement. Units are (v/v).Note the different scales for VWC. A rain event occurs on the 26th of
October.Upstream and Downstream sensors are buried beneath the porous concrete. Native sensors
are buried in the native soil. The Native soil is above 50% water content for the duration of the
graph.The sensors buried in the soil exhibit a higher magnitude of noise than the others.
4
CONCLUSION
Detailed monitoring studies of green infrastructure (GI) techniques were conducted so as to help make
informed decisions about the suitability of certain GI technologies over traditional urban drainage
control methods and to assess the need for effective maintenance. Permeable pavement infiltration
stormwater control measures (SCM) in parking lot settings near Cincinnati, OH, USA, were
instrumented with sensors to monitor water fluxes and thereby better understand stormwater control
measure performance over a continuum of storms. One installation is a part of a parking lot treatmenttrain and it contains porous concrete that then drains into a bioretention area. The second SCM is a
permeable paver lot fitted with underdrains to facilitate more rapid return to fuller capacity. The
process from design, through instrumentation, to data analysis has presented many lessons which
may help others in future research scenarios.
Results show that pavement system performance can be quantified using sensor technologies after
accounting and planning for the following: 1) Water will follow unidentified drainage paths if the site is
not precisely controlled, leading to incorrect performance results; 2) GI is multidisciplinary in nature;
when design information is shared during the design-build process, the final product has a higher
likelihood of successfully meeting multiple performance objectives; 3) It is critical to have knowledge of
lot-level topography before designing and siting a surface infiltration control measure; 4) The
8
NOVATECH 2013
installation of sensor technology is disruptive to the build process and care must be taken to ensure
that the research and construction cultures align to meet the objectives of both; 5) One should account
for complications due to the presence of other utilities in the deployment environment (particularly
electrical) when installing sensors. Our findings highlight the need for continual engagement in the
operation and maintenance of these measures, and opens the door for some creativity and intent in
the actual approach to monitoring and conducting collaborative research with wastewater authorities.
Current research includes evaluating the implementation of long term wireless sensors to minimize
disruption to construction, with a focus on designing and implementing wireless sensors that will serve
to provide information critical to the proper operation and maintenance of SCMs.
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