Sasha W. Eisenman, Ph.D.,Assistant professor, Temple University
June 9th, 10:30 AM, CEER 312
Water relations of trees growing in Green Infrastructure (GI) storm water trenches
Storm water management is a major concern for cities with outdated combined sewer systems. Uncontrolled storm water pollutes urban watersheds, and impairs ecological functions in streams and rivers. Evapotranspiration by trees is expected to be a significant GI component that diverts water from sewer systems, and storm water interception by green infrastructure (GI) installations with urban trees will likely be a major contributor to improving overall runoff control. It is important to assess the performance of these trees to better understand their contributions to storm water management.
The first research project has focused on water relations of trees in a GI tree trench system in the Mt. Airy section of Philadelphia. Acer rubrum ‘Armstrong’ and Platanus × acerifolia ‘Bloodgood’ were evaluated from May through November for stomatal conductance, leaf water potential (Ψlf) and leaf area index (LAI). Water relation trends were evident, and a one-way ANOVA with post-hoc Tukey HSD test showed a significant difference between stomatal conductance rates of the two species, but not within species. Analysis of Ψlf data was performed using a Kruskal-Wallis test rank sum test followed by Dunn’s test of multiple comparisons. These analyses also showed significant differences between the ranked data of the two species. In general, through the entire growing season, P. × acerifolia had greater stomatal conductance and lower susceptibility to water stress than A. rubrum ‘Armstrong’.
A second research project has evaluated the stomatal conductance of 25 trees of 13 different species/cultivars located at the same site. The trees were monitored from June-October 2015. In the preliminary analyses, tree species exhibited significantly different levels of stomatal conductance throughout the season, implying that some species are better suited as urban stormwater trench trees than others. Furthermore, pairwise t-tests reveal that Koelreuteria paniculata and Prunus sargentii trees consume significantly more water within stormwater trenches compared to traditional, isolated tree pits, whereas Quercus macrocarpa trees showed the opposite tendency.
This research not only confirms that stormwater tree trenches can be effective at managing stormwater but it also holds implications for further application of stormwater tree trenches since the selection of tree species can determine the effectiveness of the system.
Tobias Müller, May 19th, 12:30 PM, CEER 312
Forensic analysis and retrofit of an aged infiltration trench
Infiltration trenches are stormwater control measures (SCM) that are designed in urban, residential or commercial areas to temporarily store and treat stormwater runoff by infiltration. These SCMs can provide significant runoff volume reduction, groundwater recharge and can also help with nutrient removal through soil sorption and filtration. Especially in highly urban areas where space is limited, underground infiltration trenches are well suited to help fulfill current stormwater regulations and prevent flooding. However, not much data is available on long-term performances, longevity and effectiveness with respect to suspended solids and nutrient removal.
In 2004, an infiltration trench was constructed on campus at Villanova University to capture runoff from a 100% impervious drainage area (parking deck). The trench was significantly under-designed with an SCM surface area to drainage area ratio of 160:1 (5:1 recommended by most BMP manuals). The highly increased loading of suspended solids and debris, quickly decreased the system's performance and recession rates dropped just one year after being set online. The old trench was then excavated in October 2015 and a forensic analysis of sediments inside the trench and the surrounding soils was performed to assess the eventual failure of the system.
A new infiltration trench with a pretreatment system was constructed at the same location with the exact same footprint but a smaller SCM surface area to drainage area surface (40:1). Water quantity and quality instrumentation of the new trench are currently being installed. The new system is planned to be set online and monitored in fall 2016.
Taylor DelVecchio, April 25th, 12:15 PM, CEER 312
Evaluating Different Soil Mixes for Rain Gardens
Rain gardens have proven to be an effective means to control stormwater; thus, in Pennsylvania’s Stormwater Best Management Practice’s Manual, rain gardens are the preferred stormwater control measure (SCM). Currently, volume capture in Pennsylvania is calculated using a static bowl equation that does not include the dynamics of infiltration and evapotranspiration (ET). In addition, many states’ design guidelines for rain garden soil mixes are often restrictive and vague. The goal of the work described in this presentation is to develop guidelines for soil mixes that consider the balance of infiltration and ET using bench-scale experiments at Villanova University. A total of twelve discrete weighing lysimeters were filled with soils that span the lower portion the USDA classification triangle. The lysimeters were divided evenly into two flow path configurations: vertical 46 cm deep columns and horizontal 20 cm deep boxes at a 2.5% slope. Both lysimeter configurations utilized loamy sand, sandy loam (typical rain garden mix in PA), loam, silt loam, and clay loam soils. Switchgrass was planted in all but two lysimeters to provide a non-vegetated control with sandy loam soil. Runoff was added into the lysimeters during rainfall events to simulate actual rain garden performance and the lysimeters were weighed daily for two weeks after the event. Preliminary results of five storm simulations provide an average ET rate of 3.3 mm/d for the vertical lysimeters and 2.6 mm/d for the horizontal lysimeters. In the vertical configuration the silt loam soil produces the most volume removal through ET at 44% of the total volume removal with an average ET rate of 4.2 mm/d. In contrast, the loamy sand soil produces the least volume removal through ET at 25% of the total volume removal.
Stephanie Rindosh, April 4th, 12:15 PM, CEER 312
It’s raining, it’s pore-ing, are your sensors snoring? An analysis of hydraulic monitoring equipment for inflow and outflow structures in urban SCMs
Accurately monitoring stormwater control measurements (SCMs) in the urban environment is extremely difficult because conditions are variable, space is limited, there is the potential for vandalism, and the normal flow of urban life cannot be interrupted. Outside of seasonal variability, monitoring equipment is subjected to harsh conditions with trash, sedimentation, debris, and vandalism that may disrupt the performance of monitoring equipment and the SCM. An investigation is conducted to analyze the differences in accuracy between ideal laboratory settings and urban field conditions. The purpose of this research is to select the most appropriate monitoring equipment for urban SCMs and analyze the accuracy of sensors. The focus is on the inflow and outflow structures of two different urban SCMs (i.e. rain garden and tree trench) a part of Philadelphia Water Department’s Green City, Clean Waters. The accuracy and reliability of monitoring equipment is determined with laboratory experiments. Ultimately, the goal is to implement the best suited equipment in the field that will record the most accurate data. This presentation involves the analysis of existing equipment supplied by manufacturers, and also requires thinking outside the box for typical flow measurement devices, including the development of new approaches to accurately monitor flow.
Pablo Garza and Zachary Zukowski, March 7th, 12:15 PM, CEER 312
Comparison of Field and Laboratory Methods for measuring Hydraulic Conductivity in the Unsaturated Zone in Engineered and Native Soils
Stormwater control measures (SCMs) are used in urban and suburban areas to control runoff volume and peak flow rates, as well as improve the quality of runoff water. Rain gardens are one type of vegetated SCM which can contain engineered or native media. A major component used in design and performance of SCMs and rain gardens is hydraulic conductivity, which can be measured in the field using various infiltration testing techniques. Infiltration testing can be performed during initial site investigations to determine the appropriate SCM design and performed post-construction to ensure the SCM is performing well. The most common infiltration testing technique used in industry is the double-ring infiltrometer (ASTM D3385). However, this technique can be cumbersome because the infiltrometers are large and require a great deal of energy to install and a large quantity of water to perform.
In this study, the authors employed various infiltration techniques to determine the in-situ hydraulic conductivity at various sites. These sites included rain gardens of varying ages with engineered media, as well as a site with native soils where test pits were dug during an investigation to determine future SCM design. The authors built a Modified Philip-Dunne Infiltrometer and compared it to other field methods such as the double-ring and single-ring infiltrometer. Additionally, a falling-head PVC pipe test was designed by the authors and is also used in the comparison study. The in-situ measurements obtained with the Modified Philip-Dunne test was also compared to laboratory values obtained with the UMS KSAT Benchtop Saturated Hydraulic Conductivity Instrument, which complies with DIN 19683-9 and DIN 18130-1. Preliminary results indicate that the Modified Philip-Dunne provides results similar to the other tests methods, producing hydraulic conductivities in the same order of magnitude or within one order of magnitude as the other methods.
Sarah Rife, Feb 22nd, 12:15 PM, CEER 312
Chloride Movement and Retention of a Rain Garden at Villanova University, Pennsylvania
Every year thousands of tons of rock salt are used as a deicing agent in the winter and spring months to control snow and ice in the state of Pennsylvania. Although chloride ions are naturally occurring in the natural environment, this additional chloride becomes part of the water system once the snow and ice melt. Rain gardens, which are increasingly being used to control stormwater, divert runoff, and allow infiltration and evapotranspiration to restore the hydrologic cycle that was disrupted by development. In the winter months, however, rain gardens concentrate chlorides and there is concern about the effect these chlorides may have on the rain garden soils and groundwater beneath these infiltration features. To determine if the chloride concentrations in the rain garden soils and the groundwater beneath a rain garden at Villanova University were elevated, conductivity was measured. Surface water samples were taken of inflow and ponding water, conductivity probes at various depths were installed in the soil, and groundwater probes were installed to monitor the vertical movement of chlorides. Preliminary results indicate that chloride ions are elevated during winter and spring months, as evidenced by spikes in conductivity in both soil and groundwater. The elevated levels remain days to months after the deicing season, and the chloride concentrations in the soil do not completely return to baseline conditions, even in the summer. Groundwater conductivity values will be evaluated seasonally to determine if the rain garden is causing a chloride plume during the winter.
Kellen Pastore, Feb 1st, 12:15 PM, CEER 312
Development of Low Cost Data Logging for use in Green Infrastructure Monitoring
Abstract: Philadelphia has been installing green infrastructure across the city to help manage the increasing demand on existing stormwater infrastructure, as a part of the Green City Clean Waters plan. In order to verify that the green infrastructure that is being installed is effective in decreasing the load on the combined sewer system the sites need to be monitored. To help accomplish this, low cost data loggers were developed for use in unpowered and disconnected sites. While the initial data loggers have been successful in collecting data, there are many improvements that can still be made. This presentation will cover topics like the need for monitoring Green Infrastructure sites, the technology used to do so, successes and failures in the initial field deployment, and future directions.
Catherine Barr, December 2nd, 11:30 AM, CEER 312
Water quality performance of a green roof in comparison to other land uses
Recent studies on green roof water quality have indicated that extensive green roofs are a source of phosphates, and occasionally nitrates, as compared to conventional roofing systems. However, due to the presence of soil media and vegetation, green roofs should be compared to other vegetated sites, as opposed to conventional roofs, for a fairer comparison. In this study, the impact of green roofs on surface water quality is placed in the context of other vegetated land uses, including two types of stormwater control measures (SCMs) as well as non-SCM sites. Site runoff and SCM effluent were evaluated for nitrogen and phosphorus species, chlorides, total suspended solids, and total dissolved solids. Comparisons of concentrations against EPA recommended criteria suggested that the green roof generally retained nitrogen and released phosphorus. Its performance was similar to that of a wooded area, a grassy area, and a mixed-use area, while it was outperformed by a rain garden and a constructed stormwater wetland.
To better gage the effect of the green roof’s volume retention performance on its water quality impact, a nutrient mass balance was conducted for the green roof, and mass loads for the comparison sites were calculated. Mass balance estimation suggests that the green roof’s water quality impacts could be mitigated by its volume retention capabilities. The green roof exports less nutrients than are input to the system from fertilization and atmospheric wet deposition, although overall it exports more than wooded areas, based on drainage area-scaled values. Findings may be used to guide land use planning including implementation of green infrastructure and management of urban green spaces. It is suggested that if nutrient export is a concern and space is available, green roof overflow could be diverted to other SCMs which are designed to remove excess nutrients from stormwater runoff.
Maggie Chase, November 11, 11:30am
The Design and Implementation of a Green Roof Shelter Research Site (People Hub)
Abstract: Green roofs are becoming increasingly popular as urban stormwater control measures (SCMs). Further understanding of the relation between design characteristics, like media depth and vegetation type, and stormwater performance is crucial to effective green roof design. The VUSP’s newest on-campus research site is a green roof shelter, designed to optimize stormwater volume reduction with a small footprint. The semi-intensive modular green roof is a living laboratory for stormwater research and community education. The research focuses on green roof performance for different configurations of growing media, plants, drainage designs and more. The monitoring system includes a custom orifice restricted device (ORD) designed to measure the relatively small magnitude of overflow. The presentation will give an overview of the shelter design and construction process, monitoring system implementation, data logging system, target research questions and STEM outreach.
Gerald Zaremba, October 1, 1:00 PM
“What’s with that huge tank on the third floor of CEER?” A Look into Smarter Stormwater Control Measures (SSCMs) on Villanova’s Campus
As stormwater infrastructure becomes an ever increasing priority in site development, property owners and designers are becoming increasingly tasked with mitigating stormwater in creative ways. While many other sectors of infrastructure and development have embraced new technologies and worked with other branches of engineering, stormwater management has been stuck with the age old practice of infiltration. Unfortunately designers have been held back by outdated design regulations that have been slow to adopt the latest research in their guidelines.
A recent grant through the NSF will allow Villanova University to retrofit 3 of its on campus SCMs with some of the latest technology for stormwater management. In partnership with OptiRTC and The University of Pennsylvania, Villanova will be retrofitting The Green Roof Research Site, The Constructed Stormwater Wetland, and The Treatment Train in order to increase their performance as well as to study maintenance programs for stormwater infrastructure. The benefits of this technology can help downsize traditional SCMs, help ensure an SCMs longevity and continued performance, as well as drive down costs of installation and long term maintenance. This presentation will explore the three sites above and discuss present and future modifications underway as well as goals and expected outcomes of the project.
Andrea Welker, Ph.D., PE
My observations of the status of stormwater management practices in Ireland
Low Impact Development (LID) or Green Infrastructure (GI) stormwater practices are gradually gaining acceptance in the United States. These practices are also being used to control stormwater in Ireland, where they are dubbed Sustainable Drainage Systems (SuDS). This talk will describe the observations made by the author about the status of SuDS in Ireland.
Erica Forgione, August 19th, 12:00 pm
"Fate and Transport of Road De-Icing Salt in a Constructed Stormwater Wetland"
Road de-icing salt is one contaminant of concern in stormwater runoff with an estimated 15 million tons of salt being applied to U.S. roads every year. Road salt (usually NaCl) is soluble, and chloride (Cl) is a conservative tracer, meaning that it will not degrade over time. While many assumed that road de-icing salt would wash through watersheds with spring rains, as much as 77% of chloride has been shown to be retained within a watershed (Liptak and Mitsch 1996-98) and chloride levels may remain elevated late into summer months (Gardner and Royer 2010). Chloride has been shown to affect the survival and health of many amphibians at heightened levels (Karraker and Gibbs 2011) and increased chloride concentrations has resulted in increased metals concentrations (Endreny et al 2012). Because chloride poses a possible threat to downstream waters, a study was performed to study the fate and transport of chloride on Villanova’s campus.
The study aims to do a mass balance of chloride over two years in Villanova University’s constructed stormwater wetland (CSW) from the campus’ impervious surfaces, through the wetland, and into Mill Creek (the natural downstream waters) to see if there is any net retention or export of chloride. In addition, concentrations of chloride taken at intervals over a four year period for both storms and base flow events are compared to EPA chloride freshwater recommended standards to determine if Villanova’s CSW outflow meets that criteria. Correlations for TDS, conductivity, and chloride concentration are created in the course of this study and equations were formed to compare values of TDS, conductivity, and chloride. A unique k value for the CSW was determined for the equation Conductivity = k * TDS. The study aims to educate about the fate of road de-icing salts to inform sustainable action moving forward.
Ryan Lee, July 7th, 10:00 am
Evaluation of Soil Proxies for Rain Garden Design
The three main components that determine the performance of a rain garden are the inflow volume, the size of the rain garden, and the soil hydraulic properties. Because soil hydraulic properties are often difficult to determine, proxies such as soil textural class or hydrologic soil group are often used instead of actual properties. The use of class-average soil properties for these proxies is a persistent practice in water resources engineering, but the effect of this practice has not been assessed or validated for use in rain garden design. This research uses a large dataset of soil hydraulic properties along with computer simulations of a rain garden to determine the effectiveness of these soil proxies for rain garden designs, specifically showing whether such proxies can determine the need for an underdrain, the effectiveness of fill media, and the overall expected performance of rain gardens during a design storm.
Jhoanna Montaño Valdez, July 6th, 12:00 pm
Fate and Transport of Algae in a Constructed Stormwater Wetland
Abstract: Constructed Stormwater Wetlands (CSWs) are one type of Stormwater Control Measure (SCM) to treat stormwater runoff. The main objective of this research is to analyze the fate and transport of phytoplankton (i.e. free floating algae) in the Villanova University Constructed Stormwater Wetland (VU CSW). The VU CSW receives runoff from the Main and West campus and this runoff contains nutrients such as nitrogen and phosphorus which contribute to the algae growth, and hence, leads to eutrophication of the VU CSW. It also produces a measurable amount of algae during baseflow conditions that are washed away during storm events.
The concentrations of chlorophyll a (an indicator of algal content), dissolved oxygen, organic matter, temperature and nutrients in the VU CSW will be presented in an attempt to correlate algae growth with nutrient depletion. In addition, the mass of algae washed from the wetland during storm events will be quantified to determine if this export of algae may have a negative effect on downstream water quality.
Kyle Johnson, June 4th, 12:00 pm
SCMs are Forever: Towards Sustainable Design and Maintenance Practices for Multiple Generations of SCMs
Abstract: Over the past several decades research for green stormwater infrastructure (GSI) has been successful in demonstrating proof-of-concept and has resulted in large cities investing in large-scale GSI implementation projects that will span decades. While proper design, installation, and regular maintenance practices have evolved, there are still a lot of questions and assumptions made regarding the longevity and end-of-life of GSI systems. Using a multiple life cycle perspective, the potential cost and environmental impact savings of GSI “renewal” – as opposed to full decommissioning/replacement – are outlined for several stormwater control measures by incorporating elements of eco-efficiency, the Circular Economy, and industrial ecology. A “multi-generational approach” that aims to support the development of best practices for SCM design, maintenance, disassembly, and material reuse is broadly discussed. Recommendations are made for future studies that focus on extending the useful life of SCM materials.
Amanda Hess, May 6th, 12 pm
Evapotranspiration and Infiltration in Rain Garden Systems
Abstract: Quantification of evapotranspiration (ET) and infiltration from vegetated stormwater control measures (SCMs), such as rain gardens, is necessary to properly assess their volume reduction potential. Weighing lysimeters at Villanova University mimic three bioretention rain garden designs and measure water budget parameters to determine how design elements impact ET and infiltration (percolation). The designs compare two soil medias: a loamy sand (72% sand, 12% silt, 1% clay) and sand (96% sand, 4% silt, 0% clay), and different drainage systems: a controlled valve and internal water storage (IWS) outflow. The controlled valve outflow allows a user defined flow rate. The IWS outflow maintains a storage volume within the media.
A custom distribution system was built to simulate excess rain delivered to a rain garden during natural storm events. In Pennsylvania, SCMs are often sized to control a multiple (typically 5:1 for rain gardens) of a selected rain event. Trials were performed in April and August 2014 for half open controlled valve configurations. Both loamy sand and sand soils with a controlled valve configuration showed an average ET of 3.1 mm per day for 7 days after simulated 5:1 events. Sand soil with an IWS showed an average of 6.0 mm per day for 7 days after simulated 5:1 events. Simulated storm events produced larger ET rates, on average, than that of a 1:1 ratio. Comparisons of predictive equations show the ASCE Penman-Monteith under-predicting and Hargreaves over-predicting observed ET, but follows the trend of each lysimeter.
Raquel Burlotos, April 29th, 11:30am
A study on porous asphalt at the Morris Arboretum
Abstract: The Morris Arboretum has one of the oldest porous asphalt sites in the country dating back to 1982. Today the asphalt is being replaced because it no longer infiltrates, and is wearing down. Because of this, the Villanova Urban Stormwater Partnership decided that it would be advantageous to perform a forensic study on the asphalt examining its current condition before replacement. The study focused on observing why the asphalt no longer infiltrates, quantifying the amount contaminants trapped in the asphalt, determining the asphalt's porosity and determining the asphalt's current infiltration rates. Results revealed high metal concentrations from the asphalt, low infiltration rates, and failure due to age and clogging.
Ashley Neptune, April 29th, 11am
Water Quality Evaluation of Storm Sampling Techniques for a Constructed Stormwater Wetland
Abstract:Stormwater control measures are built in order to address the issues of stormwater runoff. These issues are primarily focused around volume control and water quality treatment. Villanova University's Constructed Stormwater Wetland (CSW) was recently reconstructed in 2010 to improve treatment efficiency by adding meanders to hold runoff in the treatment system longer. From 2011 to present the CSW is sampled once to twice a month for storm and baseflow events. Until April 2014, sample collection for storms involved gathering samples 12 to 24 hours after rainfall ended. Though the flow rates during this time are still above average baseflows, the concentrations are not representative of first flush conditions. The use of automated samplers at the inlet and outlet permit for real time stormwater quality monitoring at the CSW. A comparison study between the grab sampling storms and autosampler events was performed, in addition to mass analysis for the automated samples.
Catherine Barr, March 25th, 12pm
Nutrient Export for a Green Roof in Comparison to Other Land Uses
Recent studies on green roof water quality have indicated that extensive green roof systems are a source for phosphorus, and occasionally a source for nitrogen as compared to conventional roofing systems. Due to the presence of soil media and vegetation on green roofs, a comparison to traditional roofs reveals little about relative nutrient quantities released. The Villanova green roof was compared to other suburban vegetated areas for nutrient export. The water quality parameters evaluated included nitrogen and phosphorus species, chlorides, total suspended solids, and total dissolved solids. Where applicable, US EPA recommended nutrient criteria for rivers and streams, and for lakes and reservoirs, were used as a reference point to nutrient parameters. Results indicated that the green roof generally retained nitrogen and released phosphorus; its performance was similar to or better than that of a grassy area and a wooded area in terms of nutrient retention, and performed similarly to an area that was at least 50% impervious. In addition, a comparison of quality data from overflow samples revealed that a nearby wetland and rain garden outperformed the green roof in terms of nutrient retention. It is suggested that if nutrient export is a concern and space is available, green roof overflow could be diverted to other stormwater control measures which are designed to remove excess nutrients from stormwater runoff.
Zachary Zukowski,March 25th, 12:30 pm
Selection of Sites, Instrumentation, and Equipment for a Rain Garden Comparison Study
Rain gardens are vegetated stormwater control measures (SCMs) that reduce runoff volume and high peak flows. Rain gardens promote infiltration and evapotranspiration (ET), thus mitigating the effects of high stormwater runoff that have become common in developed areas. In addition to runoff quantity, rain gardens also help improve water quality by allowing water to infiltrate into an engineered or native soil media. Engineered soils typically contain a high sand content with lower amounts of silts, clays, and organics. Native soils can be used if the hydraulic properties indicate that an adequate infiltration rate is attainable. Additionally, to save construction costs, engineered soils can be mixed with native soils. Rain gardens may also contain a liner and an underdrain. Systems without a liner allow for evapotranspiration and infiltration into the native soil layer, which promotes recharge to the underlying aquifer. Systems with a liner and underdrain typically favor evapotranspiration.
A study was proposed to determine the best rain garden design and configuration for optimum hydrologic performance. This included the use of a liner, the use of an underdrain, soil media, and age of the rain garden. Many rain gardens on Villanova University’s campus were considered, and three rain gardens were selected: the Bioinfiltration Traffic Island, Fedigan Rain Gardens, and Pavilion Traffic Island. The three sites have notably different configurations, soil mixtures, and other defining characteristics. After site investigations, instrumentation was selected for each site, which included pressure transducers, soil moisture sensors, and rain gages. This talk will describe the challenges and soil properties encountered during the site investigations, as well as the process of instrumentation and equipment selection for each site.
Margaret Chase, February 25th, 12pm
The Measurement of Runoff from Vegetated Roof Shelter
Funded by the EPA Urban Waters Small Grant program, the project's purpose is to design, construct and monitor two shelters (e.g. bus shelter or picnic table covering) with vegetated roofs in the Darby Creek watershed in southeastern Pennsylvania. The shelters will be living laboratories used for community education and stormwater research. The research component will focus on green roof performance for different configurations of growing media, plants, drainage designs and more. The education component includes collaboration with the Eastern Delaware County Stormwater Collaborative and Upper Darby High School to introduce community members to green roof technologies and introduce students via the science curriculum to the hydrologic processes of green roofs.
A key component of these living laboratories is to precisely and accurately measure the inputs and outputs of the green roof to quantify performance. The magnitude of outflow (drainage) measurements is relatively small for these small-scale green roofs, thus requiring a custom solution to measure outflow. The presentation will give an overview of the project goals and also focus on the method developed for runoff measurement from the green roofs.
Conor Lewellyn, January 14th 2015, 12pm
An Extremely Undersized Infiltration Trench 10 Years Later
Infiltration trenches are a stormwater control measure (SCM) used in urban and ultra-urban areas to provide stormwater runoff volume reduction. Legacy infiltration trenches are difficult if not impossible to maintain and were often built without pretreatment. As runoff with high suspended solid loads enters an infiltration trench there is continual buildup of solids that clog the infiltrating surface, decreasing the hydraulic conductivity at the soil interface and the performance and longevity of these systems.
The present study builds on previous work at Villanova University on an extremely undersized infiltration trench (directly connected impervious drainage area to SCM area of 160:1) to artificially accelerate annual loading to evaluate long-term performance. Ten years and 1270 cm of rain later, infiltration through the bottom of the trench has ceased and the sides have slowed as well. Recession rates have reached an equilibrium point where they no longer improve or decrease. Although recession rates have slowed considerably since 2004, reduced infiltration still occurs in the bottom layer of the IT.
Gerald Zaremba, January 14th 2015, 12:30 pm
Optimizing Green Roof Design for Evapotranspiration
Green roofs are an effective, yet costly stormwater control measure that reduces runoff volume through ET, and can provide other services, such as improved building insulation and reduced urban heat island effect. For green roof systems to be competitive as a low impact development strategy, they must be designed to maximize ET. Understanding each component’s process in a green roof design is the key to designing a green roof to perform optimally.
Evapotranspiration (ET) is a primary mechanism for removal of water in a green roof. When adequate water is available, the ET rate is limited by the energy-available. However, when the system is water-limited then less ET will occur than is climatologically possible, thus causing the green roof to perform sub-optimally. One way to retain more water within the green roof is to minimize drainage (outflow) by altering or restricting the drainage layer within a green roof. In the present work, a green roof with a drainage layer is compared to a lysimeter without a drainage layer to determine if hydrologic performance is enhanced or compromised in either system.
Preliminary results from the Villanova University green roof systems show that the under drained system has approximately 65% of rainfall go to ET, while the undrained system showed 77% ET from April through November 2013. However, the system without drainage has seen as high as 88% annually go to ET in drought years. Additionally, the plants appeared healthier during the drought in the undrained system than in the drained system.
For all other recent talks, click here to go to the catalog.