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 City, Jun 2013, Lyon, France. �hal-03303485� HAL Id: hal-03303485 https://hal.science/hal-03303485 Submitted on 28 Jul 2021 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. 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 1 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. 5 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. LIST OF REFERENCES Angelakis, A. N., Koutsoyiannis, D. and Tchobanoglous, G. (2005). Urban wastewater and stormwater technologies in ancient Greece, Water Research, 39(1), 210–220. Eganhouse, R.P. and Sherblom, P.M. (2001). Anthropogenic organic contaminants in the effluent of a combined sewer overflow: impact on Boston Harbor. Marine Environmental Research, 51(1), 51-74. Hall, K.J., McCallum, D.W., Lee, K. and Macdonald, R. (1998). 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Evaluation of the factors relating combined sewer overflows with sediment contamination of the lower Passaic River. Marine Pollution Bulletin, 32(3), 288-304. Spatari, S., Yu, Z. and Montalto,F.A. (2011). Life cycle implications of urban green infrastructure. Environmental Pollution, 159(8-9), 2174-2179. Struck, S.D., Field, R., Pitt, R., O’Bannon, D., Schmitz, E., Ports, M.A. and Jacobs, T. (2009). Green infrastructure for CSO control in Kansas City, Missouri. Proc. Of the Water Environment Federation, 2009(13), 3631-3640. 9