World Environmental and Water Resources Congress 2009, 2009
A thorough understanding of the hydrology of a constructed stormwater wetland (CSW) is essential ... more A thorough understanding of the hydrology of a constructed stormwater wetland (CSW) is essential to develop a water budget; that is a comprehensive view of all inputs and outputs in the system. Two of the principal functions of a CSW are to 1) reduce peak flows and 2) improve water quality. The latter is achieved through biological, chemical, and physical processes that are ultimately governed by the hydraulics and hydrology of the system. As these built systems populate the watershed management landscape, it is necessary to account for all flows that pass through the CSW to ensure that it is providing a benefit and does not have any deleterious effects on the watershed. One of the most significant and least understood aspects of a CSW is the groundwater-surface water exchange. This exchange is difficult to quantify, but is deserving of consideration because of the potential impact this exchange has on groundwater and surface water quantity and quality in a CSW system. Therefore, the goals of this study are to 1) use hydraulic and hydrologic computer models to create a water budget of the CSW, with a focus on quantifying groundwater-surface water fluxes, and 2) discuss the implications of how hydraulic and hydrologic processes affect the water quality within a CSW.
Journal of Sustainable Water in the Built Environment
Advances in green stormwater infrastructure (GSI) and extensive implementation of GSI in urban ar... more Advances in green stormwater infrastructure (GSI) and extensive implementation of GSI in urban areas warrant further research by municipalities on different aspects of GSI systems (e.g., planning, modeling, design, construction, monitoring, and maintenance) to enhance operational efficiencies, reduce the overall cost of construction and maintenance, and increase the resilience of these systems. However, because of a limited budget and resources for GSI research at the municipal level, a multicriteria decision analysis (MCDA) method is needed to aid the prioritization of research needs using an array of technical, economic, social, and environmental considerations (criteria). To address this need, a hybrid, multicriteria, group decision making approach was used to inform the prioritization of GSI research needs. In this approach, the relative weights of decision criteria are determined using the Delphi method on the basis of input from multiple decision makers (DMs). Additionally, ranking the research topics is performed using a hierarchical simple additive weighting (SAW) method. The application of the hybrid MCDA method was shown in prioritizing GSI research needs to support a division within the Philadelphia Water Department’s GSI program for which a long- and short-list of GSI research topics, containing 67 and 13 items, respectively, and a hierarchy of multidisciplinary decision criteria, containing 39 items, were developed. Sensitivity analyses were conducted to partially address the uncertainties in the decision-making process. The presented method is simple (applicable to real case studies) yet systematic (adjustable in different geographic locations) and supports group decision making, making it suitable for adoption by urban GSI entities as a decisionsupport tool for prioritizing existing needs and developing future roadmaps for GSI research.
Effective green stormwater infrastructure (GSI) design requires comprehensive quantification of t... more Effective green stormwater infrastructure (GSI) design requires comprehensive quantification of the volume of water that can be treated or removed over a given time period. It is recognized that evapotranspiration (ET) can be a substantial pathway for stormwater volume reduction in bioretention systems. However, measuring ET is often difficult and expensive, such as with lysimeters or a mass balance approach. This research focused on a new technique for quantifying ET in bioretention systems by exploring an approach using thermal imaging to calculate ET by measuring the flux of energy at the canopy surface. This thermal imaging approach was compared to ET measurements given by a traditional mass balance approach. The experimental setup had three benchtop scale vegetated lysimeters planted with Switchgrass. Time lapse thermal images of the Switchgrass plants were taken at 10 second intervals and paired with meteorological data. The data were used in an energy balance to estimate the ...
Rain gardens are increasing in use as the shift from gray to green infrastructure continues. Wate... more Rain gardens are increasing in use as the shift from gray to green infrastructure continues. Water that enters a rain garden is removed by three mechanisms: overflow to an outlet, percolation to the underlying soil, and evapotranspiration (ET) to the atmosphere. Despite the importance of ET in aiding a rain garden to recover void space during the time between storm events, it is not often measured or calculated because it is so difficult to do so. This paper explores the use of soil moisture sensors to estimate ET, since they are relatively inexpensive to purchase and install. Three rain garden weighing lysimeters in Villanova, PA, were used for this study. Over a 3‐yr study period daily ET was calculated each dry day and summed during the time in between storm events >25 mm. The cumulative changes of soil moisture readings during the interevent time at three depths were compared with the concurrent cumulative changes in the lysimeter weight readings. Cumulative soil moisture cha...
Green infrastructure (GI) systems are often overdesigned. This may be a byproduct of static sizin... more Green infrastructure (GI) systems are often overdesigned. This may be a byproduct of static sizing (e.g., accounting for a design storm’s runoff volume but not exfiltration rates) or may be deliberate (e.g., buffering against performance loss through time). In tree trenches and other GI systems that require stormwater to accumulate in an infiltration bed before it contacts the planting medium, overdesign could reduce plant water availability significantly. This study investigated the hydrological dynamics and water relations of an overdesigned tree trench system and identified factors contributing to, compounding, and mitigating the risk of plant stress. Water in the infiltration bed reached soil pits only once in three years, with that event occurring during a hydrant release. Moreover, minimal water was retained in soil pits during the event due to the hydraulic properties of the soil media. Through a growing season, one of the two tree types frequently experienced water stress, w...
Infiltration is the primary mechanism in green stormwater infrastructure (GSI) systems to reduce ... more Infiltration is the primary mechanism in green stormwater infrastructure (GSI) systems to reduce the runoff volume from urbanized areas. Soil hydraulic conductivity is most important in influencing GSI infiltration rates. Saturated hydraulic conductivity (Ksat) is a critical parameter for GSI design and post‐construction performance. However, Ksat measurement in the field is problematic due to temporal and spatial variability and measurement errors. This review paper focuses on a comparison of methods for in‐situ Ksat measurement and the causes of temporal and spatial variations of Ksat within GSI systems. Automated infiltration testing methods, such as the Modified Philip–Dunne (MPD) and SATURO infiltrometers, show promise for efficient Ksat measurements. Soil Ksat values can change over time and substantially vary throughout a GSI, which can be attributed to multiple factors, including but not limited to temperature changes, soil composition and properties, soil compaction level, ...
Overdesign is a common strategy used by green infrastructure (GI) designers to account for unexpe... more Overdesign is a common strategy used by green infrastructure (GI) designers to account for unexpected performance loss, but such a strategy can create undesirable plant responses if it decreases water availability. The seasonal and event-based stomatal conductance data of two woody plant species in a green infrastructure (GI) was analyzed. The GI is a tree trench composed of five tree pits (each one was planted with a tree) in an infiltration bed. Runoff collected from the street was supplied to the bottom of the infiltration bed, although the system never filled completely indicating there was capacity for more runoff than what was observed over 3 years and the infiltration bed was overdesigned. Between the two tree species, evidence suggested that the root system of London plane spread beyond the boundary of the GI system and reached a subsurface water source, while that of hybrid maple did not. London plane showed a slower response to water added in the tree pit soil, which can i...
Many communities throughout the world are utilizing green infrastructure practices to mitigate th... more Many communities throughout the world are utilizing green infrastructure practices to mitigate the projected impacts of climate change. While some areas of the world are anticipating droughts, other areas are preparing for an increased flood risk, due to changes in precipitation volume and intensity. Cities rely on practices such as bioinfiltration to sustainably capture stormwater runoff and provide resilience against climate change. As cities aim to increase resilience and decrease climate-change-associated risks, a greater understanding of these risks is needed. A risk-based approach was used to evaluate bioinfiltration design and performance. Climate projections from the Couple Model Intercomparison Project Phase 5 were used to create near-term (2020–2049) and long-term (2050–2079) climate datasets for Philadelphia, Pennsylvania, using two representative concentration pathways (RCPs 2.6 and 8.5). Both near-term and long-term climate models demonstrated increased precipitation an...
World Environmental and Water Resources Congress 2009, 2009
A thorough understanding of the hydrology of a constructed stormwater wetland (CSW) is essential ... more A thorough understanding of the hydrology of a constructed stormwater wetland (CSW) is essential to develop a water budget; that is a comprehensive view of all inputs and outputs in the system. Two of the principal functions of a CSW are to 1) reduce peak flows and 2) improve water quality. The latter is achieved through biological, chemical, and physical processes that are ultimately governed by the hydraulics and hydrology of the system. As these built systems populate the watershed management landscape, it is necessary to account for all flows that pass through the CSW to ensure that it is providing a benefit and does not have any deleterious effects on the watershed. One of the most significant and least understood aspects of a CSW is the groundwater-surface water exchange. This exchange is difficult to quantify, but is deserving of consideration because of the potential impact this exchange has on groundwater and surface water quantity and quality in a CSW system. Therefore, the goals of this study are to 1) use hydraulic and hydrologic computer models to create a water budget of the CSW, with a focus on quantifying groundwater-surface water fluxes, and 2) discuss the implications of how hydraulic and hydrologic processes affect the water quality within a CSW.
Journal of Sustainable Water in the Built Environment
Advances in green stormwater infrastructure (GSI) and extensive implementation of GSI in urban ar... more Advances in green stormwater infrastructure (GSI) and extensive implementation of GSI in urban areas warrant further research by municipalities on different aspects of GSI systems (e.g., planning, modeling, design, construction, monitoring, and maintenance) to enhance operational efficiencies, reduce the overall cost of construction and maintenance, and increase the resilience of these systems. However, because of a limited budget and resources for GSI research at the municipal level, a multicriteria decision analysis (MCDA) method is needed to aid the prioritization of research needs using an array of technical, economic, social, and environmental considerations (criteria). To address this need, a hybrid, multicriteria, group decision making approach was used to inform the prioritization of GSI research needs. In this approach, the relative weights of decision criteria are determined using the Delphi method on the basis of input from multiple decision makers (DMs). Additionally, ranking the research topics is performed using a hierarchical simple additive weighting (SAW) method. The application of the hybrid MCDA method was shown in prioritizing GSI research needs to support a division within the Philadelphia Water Department’s GSI program for which a long- and short-list of GSI research topics, containing 67 and 13 items, respectively, and a hierarchy of multidisciplinary decision criteria, containing 39 items, were developed. Sensitivity analyses were conducted to partially address the uncertainties in the decision-making process. The presented method is simple (applicable to real case studies) yet systematic (adjustable in different geographic locations) and supports group decision making, making it suitable for adoption by urban GSI entities as a decisionsupport tool for prioritizing existing needs and developing future roadmaps for GSI research.
Effective green stormwater infrastructure (GSI) design requires comprehensive quantification of t... more Effective green stormwater infrastructure (GSI) design requires comprehensive quantification of the volume of water that can be treated or removed over a given time period. It is recognized that evapotranspiration (ET) can be a substantial pathway for stormwater volume reduction in bioretention systems. However, measuring ET is often difficult and expensive, such as with lysimeters or a mass balance approach. This research focused on a new technique for quantifying ET in bioretention systems by exploring an approach using thermal imaging to calculate ET by measuring the flux of energy at the canopy surface. This thermal imaging approach was compared to ET measurements given by a traditional mass balance approach. The experimental setup had three benchtop scale vegetated lysimeters planted with Switchgrass. Time lapse thermal images of the Switchgrass plants were taken at 10 second intervals and paired with meteorological data. The data were used in an energy balance to estimate the ...
Rain gardens are increasing in use as the shift from gray to green infrastructure continues. Wate... more Rain gardens are increasing in use as the shift from gray to green infrastructure continues. Water that enters a rain garden is removed by three mechanisms: overflow to an outlet, percolation to the underlying soil, and evapotranspiration (ET) to the atmosphere. Despite the importance of ET in aiding a rain garden to recover void space during the time between storm events, it is not often measured or calculated because it is so difficult to do so. This paper explores the use of soil moisture sensors to estimate ET, since they are relatively inexpensive to purchase and install. Three rain garden weighing lysimeters in Villanova, PA, were used for this study. Over a 3‐yr study period daily ET was calculated each dry day and summed during the time in between storm events >25 mm. The cumulative changes of soil moisture readings during the interevent time at three depths were compared with the concurrent cumulative changes in the lysimeter weight readings. Cumulative soil moisture cha...
Green infrastructure (GI) systems are often overdesigned. This may be a byproduct of static sizin... more Green infrastructure (GI) systems are often overdesigned. This may be a byproduct of static sizing (e.g., accounting for a design storm’s runoff volume but not exfiltration rates) or may be deliberate (e.g., buffering against performance loss through time). In tree trenches and other GI systems that require stormwater to accumulate in an infiltration bed before it contacts the planting medium, overdesign could reduce plant water availability significantly. This study investigated the hydrological dynamics and water relations of an overdesigned tree trench system and identified factors contributing to, compounding, and mitigating the risk of plant stress. Water in the infiltration bed reached soil pits only once in three years, with that event occurring during a hydrant release. Moreover, minimal water was retained in soil pits during the event due to the hydraulic properties of the soil media. Through a growing season, one of the two tree types frequently experienced water stress, w...
Infiltration is the primary mechanism in green stormwater infrastructure (GSI) systems to reduce ... more Infiltration is the primary mechanism in green stormwater infrastructure (GSI) systems to reduce the runoff volume from urbanized areas. Soil hydraulic conductivity is most important in influencing GSI infiltration rates. Saturated hydraulic conductivity (Ksat) is a critical parameter for GSI design and post‐construction performance. However, Ksat measurement in the field is problematic due to temporal and spatial variability and measurement errors. This review paper focuses on a comparison of methods for in‐situ Ksat measurement and the causes of temporal and spatial variations of Ksat within GSI systems. Automated infiltration testing methods, such as the Modified Philip–Dunne (MPD) and SATURO infiltrometers, show promise for efficient Ksat measurements. Soil Ksat values can change over time and substantially vary throughout a GSI, which can be attributed to multiple factors, including but not limited to temperature changes, soil composition and properties, soil compaction level, ...
Overdesign is a common strategy used by green infrastructure (GI) designers to account for unexpe... more Overdesign is a common strategy used by green infrastructure (GI) designers to account for unexpected performance loss, but such a strategy can create undesirable plant responses if it decreases water availability. The seasonal and event-based stomatal conductance data of two woody plant species in a green infrastructure (GI) was analyzed. The GI is a tree trench composed of five tree pits (each one was planted with a tree) in an infiltration bed. Runoff collected from the street was supplied to the bottom of the infiltration bed, although the system never filled completely indicating there was capacity for more runoff than what was observed over 3 years and the infiltration bed was overdesigned. Between the two tree species, evidence suggested that the root system of London plane spread beyond the boundary of the GI system and reached a subsurface water source, while that of hybrid maple did not. London plane showed a slower response to water added in the tree pit soil, which can i...
Many communities throughout the world are utilizing green infrastructure practices to mitigate th... more Many communities throughout the world are utilizing green infrastructure practices to mitigate the projected impacts of climate change. While some areas of the world are anticipating droughts, other areas are preparing for an increased flood risk, due to changes in precipitation volume and intensity. Cities rely on practices such as bioinfiltration to sustainably capture stormwater runoff and provide resilience against climate change. As cities aim to increase resilience and decrease climate-change-associated risks, a greater understanding of these risks is needed. A risk-based approach was used to evaluate bioinfiltration design and performance. Climate projections from the Couple Model Intercomparison Project Phase 5 were used to create near-term (2020–2049) and long-term (2050–2079) climate datasets for Philadelphia, Pennsylvania, using two representative concentration pathways (RCPs 2.6 and 8.5). Both near-term and long-term climate models demonstrated increased precipitation an...
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