Concurrent Session 6

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9:30 am – 10:45 am
Salon A Salon B Windsor Ballroom
Session Title Watershed Approaches Water Quality Stormwater – Bioretention
Moderator David Sample Tom Franti Stacy Hutchinson
9:30 am – 9:45 am (71) Joshua Robinson – Field-based Assessment of an Urbanized Mountane Headwater Catchment: The Impact of Watershed-wide Green Stormwater Infrastructure Retrofits on Sediment Washload (76) McNamara Rome – The Case for Cyanobacteria-Based Water Quality Grades (81) Andrea Ludwig – Thinking Twice About Rock Surface Cover in Nashville-Area Bioretention Applications
9:45 am – 10:00 am (72) Roderick Lammers – Uniting Stormwater Management and Stream Restoration Strategies for Greater Water Quality Benefits (77) Jeffrey Kast – Simulating the Role of Manure and Inorganic Fertilizer Applications on Water Quality in the Maumee River Watershed (82) Thorsten Knappenberger – Bayesian Approach to Assess Stormwater Pollutant Reduction in Bioretention Cells
10:00 am – 10:15 am (73) Hannah Kuhl – Stormwater and Tidal Hydraulics in an Urban Watershed: Land Use Change Impacts (78) Fernando Rojano – Use of pH, Conductivity, and Temperature as Tracers to Assess Water Quality Changes in the Kanawha River, West Virginia (83) Michael  Ament – Assessment of Drinking Water Treatment Residuals to Enhance Phosphorus Retention within Green Stormwater Infrastructure
10:15 am – 10:30 am (74) Cameron Jernigan – Forested Stormwater Wetland Demostration in Greenville, NC (79) Yin-Phan Tsang – Characterizing Natural Barriers to Non-native Stream Fauna in Hawai‘i (84) Aaron Akin – The Influence of Active Control on Urban Bioretention Systems
10:00 am – 10:45 am (75) Peter May – The Performance of Two Simultaneously Operated Experimental Algal Floways Supporting Water Treatment on Anacostia River in Prince George’s County, Maryland and Washington, D.C. (85) Whitney Lisenbee – Enhanced Bioretention Cell Modeling: Moving From Water Balances To Hydrograph Production

(71) Field-based Assessment of an Urbanized Mountane Headwater Catchment: The Impact of Watershed-wide Green Stormwater Infrastructure Retrofits on Sediment Washload

Presenter: Joshua Robinson, Robinson Design Engineers,

Abstract: Most stormwater research in the southeastern US has occurred near the major academic research institutions located within the Piedmont. As a result, performance standards and design guidelines for green stormwater infrastructure (GSI) and other types of stormwater control measures (SCMs) do not readily transfer to the steep mountain environment, which is characterized by shallow soils, steep gradients, and intense rainfall. To provide insight into regionally-specific performance standards and design guidelines for GSI and SCMs, the author helped to establish an experimental watershed in Asheville, NC.

Storm event measurements of creek stage, discharge, and sediment concentration were collected within a first-order mountain stream draining approximately 100 acres of developed headwaters. These measurements were collected before and after the construction of six green stormwater infrastructure (GSI) retrofits upstream throughout the watershed. The experimental watershed is fully contained within the campus of Givens Estates, a retirement community of the United Methodist Church. The project is funded by the NC Clean Water Management Trust Fund, and the project is sponsored by RiverLink, an Asheville-based non-profit dedicated to promoting the environmental and economic vitality of the French Broad River and its watershed.

In this presentation the author will provide an overview of the experimental watershed and project history, outline the goals of the grant-funded project, and present data from storm event measurements before and after implantation of GSI retrofits. The author will also describe the applicability of the research, and how the lessons learned through this project can benefit the design of GSI projects in the difficult montane landscapes of the Southern Appalachians.

Biography: Joshua Robinson is the principal of Robinson Design Engineers, a group of water resources specialists working from offices in Charleston, SC and Asheville, NC. Joshua holds an MS degree in civil engineer environmental hydraulics from Georgia Tech, and a BS degree in civil engineering from The Citadel.

(72) Uniting Stormwater Management and Stream Restoration Strategies for Greater Water Quality Benefits

Presenter: Roderick Lammers, University of Georgia,

Co-Authors: Tyler Dell, Colorado State University,; Brian P. Bledsoe, University of Georgia,

Abstract: Urbanization alters the delivery of water, sediment, and pollutants to receiving streams. In response, channels erode which increases loading of sediment and nutrients, degrades habitat, and damages or destroys sensitive biota. Stormwater control measures (SCMs) are constructed in an attempt to mitigate some of these effects. In addition, stream restoration practices such as bank stabilization are increasingly promoted as a means of improving water quality by reducing downstream sediment and pollutant loading. Each unique combination of SCMs and stream restoration practices results in a novel hydrologic regime and set of geomorphic characteristics that interact to determine stream condition, but in practice implementation is rarely coordinated. In this study, we examine linkages between basin scale implementation of SCMs and stream restoration in Big Dry Creek, a suburban watershed in the Front Range of northern Colorado. We combine continuous hydrologic model simulations of watershed scale response to SCM design scenarios with channel evolution modeling to examine interactions between stormwater management and stream restoration strategies for reducing loading of sediment and adsorbed phosphorus. Model results indicate that integrated design of SCMs and stream restoration interventions can result in synergistic reductions in sediment and adsorbed pollutant loading. Not only do piecemeal and disunited approaches to stormwater management and stream restoration lose out on these synergistic benefits, they make restoration projects more prone to failure, wasting valuable resources that could be better applied for pollutant mitigation.

Biography: Roderick Lammers is a post-doctoral researcher and instructor at the University of Georgia. His research interests include stream erosion modeling, river restoration, and urban water management.

(73) Stormwater and Tidal Hydraulics in an Urban Watershed: Land Use Change Impacts

Presenter: Hannah Kuhl, College of Charleston,

Co-Authors: Timothy J Callahan, College of Charleston,; Joshua Robinson, Robinson Design Engineers,

Abstract: The purpose of this study is to develop a water balance method for a suburban tidal creek watershed located in Charleston, South Carolina. The major objectives are to separate the relative functions and dynamics of tidal flows and stormwater runoff in the watershed at two spatial scales, and to characterize the vegetation cover types of selected sub-watersheds in this altered suburban landscape. Discharge (volumetric flow rate) and channel geometry of James Island Creek will be measured under a variety of tidal conditions to characterize the creek’s stage-discharge and hydraulic geometry relationships and to compare those with four previously studied tidal creeks in the region. Stormwater runoff modeling will be conducted to provide estimates of runoff volumes that may enter the creek system during storm events. Variability in stormwater responses will be compared among sub-watersheds in relation to levels of development, and variation in extent of major vegetation cover types in these sub-watersheds will be evaluated in relation to the variation in stormwater responses. The broader impact of this study is that identifying locations or events of high stormwater delivery (“hot spots” and “hot moments”) will enable scientists and managers to identify potential problem areas in urbanized tidal creek systems.

Biography: My name is Hannah Kuhl, I’m a graduate student at the College of Charleston. Originally from Austin, TX with a B.S. from Trinity University (in San Antonio, TX), I moved to Charleston, SC to pursue my Masters in Environmental Studies. During my time at Trinity I completed a number of things, including: a double major in Biology and Environmental Studies, a minor in Spanish, a study abroad program in Madrid, an internship with the Greater Edwards Aquifer Alliance, and a research assistantship studying grasses in the Texas Hill Country. Since I’ve lived in Charleston, I’ve primarily worked as a research assistant and teaching assistant (for introductory Biology labs) with the College of Charleston. I have many interests in the broad fields of biology and ecology, and have just recently become fascinated with the interactions between hydrology and ecology. This graduate program and thesis project have given me the opportunity to learn about both the hydraulic dynamics and the ecology of the unique ecosystems in the Charleston area, including tidal creeks and salt marshes. I presented at AEES last year without results, and hope to give an update this year with completed results!

(74) Forested Stormwater Wetland Demonstration in Greenville, NC

Presenter: Cameron Jernigan, North Carolina State University,

Abstract: NC Sea Grant and NC State University’s Biological and Agricultural Engineering Department worked with Sounds Rivers, Inc. to conduct stormwater assessment, design and construction oversight for the retrofit of an existing abandoned and non-functioning farm pond into a forested stormwater treatment wetland. The project site is located on public land at Jaycee Park in Greenville, North Carolina and is protected by the Tar-Pamlico buffer rules. The existing condition of the pond provided a unique retrofitting opportunity due to the presence of mature tree species in the project boundaries combined with a desire to minimize riparian buffer impact. The design was based on current stormwater wetland practices but it limited the removal of trees and planted vegetation more specific to a natural forested wetland system. Construction of the forested wetland was completed in February 2019. Water quality monitoring is being conducted by East Carolina University to evaluate the treatment capability of the forested stormwater wetland.

Typically, constructed stormwater wetlands (CSWs) are designed to mimic the functions of natural wetlands to treat stormwater. The storage, complex microtopography, and vegetative community in CSWs combine to form an ideal matrix for the removal of many pollutants (NC DEQ). In North Carolina, the design and implementation of all Stormwater Control Measures (SCM) including wetlands must adhere to NC DEQ’s Stormwater Design Manual. The Minimum Design Criteria (MDC) for CSWs prohibits trees on wetland dams and berms, and restricts tree planting within and around a CSW. So, an herbaceous vegetative community is the target for all CSWs. These rules stem from historic conditions of the first stormwater ponds and wetlands that were installed before maintenance was required and guidelines and training were developed for maintenance and inspection. These early SCMs became overgrown with trees, neglected, and failed to function. However, inland watersheds in the southeastern and south central United States were historically dominated by forested wetland systems (bottomland hardwood forests) that serve critical roles in water storage and treatment. With proper management, design, and ideal site conditions, a CSW that mimics forested wetland function may be a more appropriate BMP in certain situations. Trees could help to improve aesthetics, stabilization, and reduce temperature but also generate a well-functioning stormwater wetland and diverse ecosystem.

Biography: Cameron Jernigan, an eastern North Carolina native, serves as an Extension Assistant and member of the Stream Restoration Program at the BAE Department at North Carolina State University. His work involves assessment, design, implementation, and applied field research of stream restoration, ecological engineering, and a variety of Stormwater Control Measures. Cameron received his B.S. in Biological and Agricultural Engineering from NCSU in 2017.

(75) The Performance of Two Simultaneously Operated Experimental Algal Floways Supporting Water Treatment on Anacostia River in Prince George’s County, Maryland and Washington, D.C.

Presenter: Peter May, University of Maryland Environmental Science and Technology,

Co-Authors: Patrick Kangas, University of Maryland Environmental Science and Technology,

Abstract: Two experimental algal floways were set-up and operated for water quality improvement on the Anacostia River, which drains a largely urban watershed and passes through Washington DC.  One floway was 1.0 square meter in area and the other was 3.6 square meters in area.  Algae was harvested approximately once per week from late July to November 2018.  Biomass productivity was 61.2 grams/m2/day for the larger floway and 45.5 grams/m2/day for the smaller one over the study period.  The differences between the two systems may have been due to the greater edge effect in the small compared to the larger floway.  Nutrient contents of the algae were relatively low at 0.9% for nitrogen and 0.1% for phosphorus.  Multiplying the biomass productivity by the nutrient content shows that the algal floway could potentially remove 1200 kg of nitrogen/ha/year and 143 kg of phosphorus/ha/year.  These performance data from the Anacostia River are compared with data from similar systems that have been operated around the Chesapeake Bay for perspective.

Biography: Peter has 30 years of experience in the environmental sector working in municipal, state, and federal government, NGO’s and the private and academic sectors. He has a comprehensive background in urban ecology, the ecology of tidal marsh, urban stream and urban estuarine river system restoration.  He has applied his skills to numerous projects throughout Maryland and the District of Columbia, New York City, Philadelphia and the San Francisco Bay area.  He has applied ecological engineering principles in developing and deploying models for floating wetland islands, vertical wetland green bulkheads, boat wastewater and marina washwater “living machine” ecosystem treatment systems as well as the Algal Turf Scrubber® (ATS™) water treatment system which he was exposed to while working for its inventor, Dr. Walter Adey, at the Smithsonian Marine Systems Lab. He has applied the ATS™ ecotechnology to wastewater systems in NYC converting algal biomass to ethanol and biobutanol as well as the Port of Baltimore converting algae to a methane biogas and electricity using a microbial fuel cell.

(76) The Case for Cyanobacteria-Based Water Quality Grades

Presenter: McNamara Rome, Northeastern University,

Co-Author: Ralph Edward Beighley, Northeastern University

Abstract: The lower basin of the Charles River, where it runs between Cambridge and Boston, is typical of an ecologically degraded urban river recovering from decades of pollution. Since the closure of combined sewer outfalls into the Charles River began in 1988, water quality in the lower basin has gradually improved. Consistent decreases can be seen with respect to nutrient levels as well as E. coli concentrations. However, elevated phosphorous levels and summer blooms of cyanobacteria remain a persistent hazard and obstacle to achieving the EPA’s stated goal of a safe and swimmable Charles. We combine and analyze publicly available data sets from the Charles River Watershed Association, Massachusetts Water Resource Authority and the Environmental Protection Agency to understand trends in algal bloom duration, timing, and severity. Two years of daily summer water quality monitoring are used to elucidate the relationship between common in-vivo measurements (e.g. chlorophyll a, turbidity, and phycocyanin) and actual cell counts of toxin producing species.  Our analysis shows that (a) current water quality fails to meet chlorophyll a standards set by the 2007 TMDL and (b) Chlorophyll a fails to capture the dynamics of algal blooms. We recommend a turbidity based framework for long-term cyanobacteria monitoring and trend assessment and suggest a revision to the EPA annual water quality report card to include consideration of cyanobacteria related health advisories.

Biography: Max Rome is a Ph.D. candidate at Northeastern University studying the role that biotic factors play in regulating harmful algal blooms in mildly eutrophic waterbodies.  Previous to Northeastern Max worked on the design and construction of ecological wastewater treatment systems as a project manager at John Todd Ecological Design.

(77) Simulating the Role of Manure and Inorganic Fertilizer Applications on Water Quality in the Maumee River Watershed

Presenter: Jeffrey Kast, The Ohio State University,

Co-Authors: Jay Martin, The Ohio State University,; Margaret Kalcic, The Ohio State University,; Anna Apostel, The Ohio State University,; Grey Evenson, The Ohio State University,; Rebecca Muenich, Arizona State University,; Awoke Dagnew, Graham Sustainability Institute, University of Michigan; Colleen Long, Graham Sustainability Institute, University of Michigan

Abstract: In the Western Lake Erie Basin, as in other watersheds supporting livestock, greater focus has been directed to the water quality impact of manure applications. Specifically, for Lake Erie, the focus is on phosphorus runoff, which drives the harmful algal blooms that occur annually in the lake. These concerns have led to recent regulations of manure application practices within the basin including a restriction of the potential window for manure applications. These concerns and actions are in response to nutrient reduction targets developed to improve Lake Erie’s water quality. This study uses a field-scale SWAT model of the Maumee River watershed to simulate the impact manure and inorganic fertilizer applications have on phosphorus loadings from the basin. Results indicate that when phosphorus is removed from basin-wide manure applications total phosphorus (TP) spring-loads are reduced by 8% while dissolved reactive phosphorus (DRP) spring-loads are reduced by 12%. When inorganic phosphorus fertilizer is removed from the basin-wide fertilizer applications TP spring-loads decreased by 44% and DRP spring-loads decreased by 60%. Although removing inorganic phosphorus from basin-wide fertilizer applications resulted in greater spring-load reductions in both TP and DRP than basin-wide manure applications, both fertilizer types had similar phosphorus delivery factors. Manure applications resulted in a delivery factor of 15% and 6% respectively for TP and DRP while inorganic fertilizer applications resulted in a delivery factor of 13% and 4% for TP and DRP, respectively.

Biography: Jeffrey is a PhD student in the Environmental Science Graduate Program at Ohio State. The focus of his current work is on integrating farmer decision making into watershed modelling efforts in the Western Lake Erie basin. His work focuses on simulating the water quality impacts of changing land use and land management decisions made by agricultural producers within the Western Lake Erie basin during demographic, economic, political, and historical changes.

(78) Use of pH, Conductivity, and Temperature as Tracers to Assess Water Quality Changes in the Kanawha River, West Virginia

Presenter: Fernando Rojano, West Virginia State University,

Co-Authors: Fernando Rojano, West Virginia State University,; Ifeoma R. Ugwuanyi, Rutgers University,; Vadesse Lhilhi Noundou, West Virginia State University,; Andrielle L. Kemajou Tchamba, West Virginia State University,; Jesus E. Chavarria-Palma, West Virginia State University,; David H. Huber, West Virginia State University,

Abstract: The present study depicts an effort that combines experiments and modeling of a catchment area along the Kanawha river, West Virginia. Several stressors in the area regarding to mine activities, industry, agriculture and urban areas contribute to the deterioration of water quality of the Kanawha river. This study identified the effect of those stressors by means of tracers already embedded in the water. Tracers were used as they were measured on the field to minimize disturbance, and the changes were observed to determine effects of the drainage area between sondes. The experimental stage entailed four sondes, which were installed along the river to continuously measure pH, conductivity and temperature in an hourly time step during the period January-March, 2018. Such period was sufficient to capture dynamics of the tracers when subjected to storm-events. On the other hand, data about flow gages, meteorological data and land use were retrieved in BASINS and a hydrologic HSPF model was developed for the same area of study. Based on data availability, the calibration was conducted using a period of four years, and the HSPF model validation was conducted for January-March, 2018. In this way, it was possible to join water flow predictions with tracer measurements to identify the contribution of drainage areas between sondes. Consequently, this study deduces from a three-month-period of observation, mainly driven by storm-events, an adequate description of the area of study and assess water quality of the mainstream focusing on various point and non-point sources and correlating them with land use as well as discussing the capabilities and drawbacks of implementing this approach.

Biography: Fernando Rojano obtained the PhD degree on Biosystems Engineering by the University of Arizona in 2013. After that, Dr. Rojano went for a postdoctoral stay in Agrocampus Ouest-Angers in France to conduct research about environmental engineering. In specific, about fluid dynamics in conjunction with heat and mass transfer applied to agricultural buildings. Dr. Rojano went back to his home country and started working as a scientist in the Instituto de Ecologia in Mexico being focused on modeling bioprocesses. After September 2018, Dr. Rojano is assistant research professor at the West Virginia State University, being involved in water systems modeling and environmental engineering.

(79) Characterizing Natural Barriers to Non-native Stream Fauna in Hawai‘i

Presenter: Yin-Phan Tsang, University of Hawaiʻi at Mānoa,

Co-Authors: Brendan Martina, Ralph W. Tingley III, Hannah Clilverd, Dana M. Infante

Abstract:Waterfalls, caused by the abrupt changes of elevation in streams, are natural barriers that influence the distribution and dispersion of aquatic species. While resulting habitat fragmentation has contributed to species specialization, the steep elevation changes are also considered barriers that inhibit passage of non-native species upstream. In Hawaiʻi, it is assumed that non-native species are unable to surpass waterfall barriers, yet they are present above some waterfalls, possibly facilitated by human introduction. In this study, we used a landscape approach to identify likely human introductions and examine the ability of non-native stream fauna to bypass waterfalls. We found that when a given catchment has a population density higher than 4.24 people/km2 or when road length density is greater than 0.01 km/km2 in a stream catchment, the presence of non-native species in the stream was likely due to human introduction. After filtering human-facilitated introduction, we found that 12 out of the examined 14 taxa were absent upstream of waterfalls, indicative of their inability to traverse waterfalls. Without human interference, waterfalls can be considered effective barriers to non-native species and can be instrumental in supporting exotic species eradication and control strategies.

(81) Thinking Twice About Rock Surface Cover in Nashville-Area Bioretention Applications

Presenter: Andrea Ludwig, University of Tennessee,

Co-Authors: Blue Curry, University of Tennessee,; Joshua Hayes, Metro Water Services Nashville-Davidson County,; Rebecca Dohn, Metro Water Services Nashville-Davidson County,

Abstract: Bioretention practice failures have led to costly renovations and repairs in Tennessee cities, creating uncertainty in the future of these practices as part of effective green infrastructure systems for stormwater runoff management. Modifications, such as using river rock surface cover in place of a plant-based mulch cover and minimizing species diversity of plantings, have been implemented by designers and practice owners in an attempt to minimize maintenance and failure susceptibility. A field survey of 52 bioretention practices was conducted across Davidson County, Tennessee, to determine functional status and identify common failures in order to support maintenance recommendations for property owners and municipal governments. Specific research questions included: 1) Does surface cover affect media bulk density? 2) What is the organic matter content in bioretention media and does it change with practice age? 3) Is plant canopy establishment related to media bulk density? 4) What plants are successful? and 5) What conclusions can be drawn regarding media characteristics related to practice maturation and what maintenance recommendations can be made to address common failures. Results showed that media bulk density under rock surface cover was significantly higher than that under plant-based mulch cover (p<0.01); that media bulk density levels known to affect plant establishment in sandy loams (> 1.6) were reached in rock covered applications in a shorter practice age as compared to plant-based mulch applications; and that relationships exist between practice age, plant canopy, organic matter, and bulk density and that these findings could be used to inform function-driven maintenance activities.

Biography: Andrea Ludwig is an Associate Professor of Ecological Engineering in the Biosystems Engineering & Soil Science Department at the University of Tennessee and serves as the State Stormwater Management Specialist for UT Extension. In this role, she works with municipal governments across the state to educate stakeholders and create demonstrations of effective green infrastructure systems for sustainable urban landscapes. She is a lifetime member of AEES, holds a BS and MS from the University of Arkansas and PhD from Virginia Tech, and eagerly awaits the student design competition presentations at this amazing conference.

(82) Bayesian Approach to Assess Stormwater Pollutant Reduction in Bioretention Cells

Presenter: Thorsten Knappenberger, Auburn University,

Co-Authors: Anand Jayakaran, Washington State University,; John D. Stark, Washington State University,

Abstract: Nutrients like nitrogen and phosphate as well as heavy metals are ubiquitous in stormwater runoff and stormwater is often introduced into surface waters without treatment. Thus, receiving waters are impacted, with serious consequences for aquatic organisms and the food web. Bioretention systems are suitable elements to reduce the nutrient load of stormwater and manage the amount of stormwater introduced to receiving waters. But most effective compositions of bioretention systems need yet to be determined.

We built 16 mesocosms with different porous media to study the contaminant retention capacities. We used four media (mix 1: 80% sand, 20% compost; mix 2: 60% sand, 40% compost; mix 3: 60% sand, 15% compost, 15% shredded cedar bark, 10% water treatment residuals; mix 4: 60% sand, 30% compost, 10% water treatment residuals) that had been replicated four times. We continuously acquired outflow data since 2011 and measured the contaminant transport for several storms.

We monitored 13 storms between 2012 and 2015 at our research facility on the Washington State University Research and Extension Center campus in Puyallup, Washington. Inflow and outflow concentrations were assessed with a Bayesian statistics. Inflow concentrations where then modelled based on Western Washington State phase 1 permittee stormwater data resulting in an outflow data set of realistic effluent concentrations per pollutant and tested bioretention mix.

None of the four tested bioretention mixes outperformed the other mixes. Effects of age of the bioretention system were found for nutrients but not for heavy metals. Nutrient removal increased with age of the bioretention mix while chemical oxygen demand increased with age. Removal of copper, zinc, and lead varied between 60 and 99%.

Biography: Thorsten Knappenberger has received his MS and PhD in agricultural engineering from Hohenheim University in Stuttgart, Germany. He joined Washington State University as a post doc in 2011 studying the colloid facilitated pollutant transport and stormwater mitigation. In 2014, he jointed Auburn University in Alabama as an assistant professor for soil physics.

(83) Assessment of Drinking Water Treatment Residuals to Enhance Phosphorus Retention within Green Stormwater Infrastructure

Presenter: Michael Ament, University of Vermont,

Co-Authors: Eric Roy,University of Vermont,; Stephanie Hurley, University of Vermont,; Eric Perkins, EPA,; Yongping Yuan, EPA,; Mark Voorhees, EPA,

Abstract: Bioretention systems are a form of green stormwater infrastructure that are becoming increasingly common for managing runoff from impervious surfaces. While bioretention systems function well for hydraulic control and sediment removal, their phosphorus (P) removal performance is highly variable. Amending bioretention soil media with P sorbing materials, such as drinking water treatment residuals (DWTRs), has potential to greatly enhance P removal from stormwater and improve downstream water quality. Here, we aim to assess this potential by 1) quantifying the P sorption capacity of different DWTRs, 2) determining the contact time required for effective P removal and 3) measuring P removal by bioretention soil media amended with DWTRs. To do this, we conducted P sorption isotherm experiments, continuous-flow small column experiments and contact time experiments on three different sources of DWTRs. We then conducted large column experiments using bioretention media blends with and without DWTRs. Finally, we measured a suite of physicochemical parameters in order to understand the drivers of P sorption by DWTRs at fine scales.

The DWTRs used in this study demonstrated high but variable capacities for P sorption (8-40 g P kg-1). Specific surface area correlated strongly with P sorption, but the total abundance of metal oxides in DWTRs did not. Contact time experiments revealed that P sorption is very rapid and that over 95% of P can be sorbed after one minute of contact. Preliminary large column results showed that P removal by DWTRs in bioretention media is effective but variable across DWTRs (70%-100% removal). These results suggest that amending bioretention media with DWTRs can greatly increase P removal from stormwater, but the longevity of this mechanism depends on physicochemical properties of the DWTR.

Biography: Mike is a first-year PhD student in the Department of Plant and Soil Science at the University of Vermont. His past research focused on ecosystem responses to variables of global change within natural and managed systems. As a PhD student, he’s combining ecological knowledge with engineering principles to design systems that reduce the flow of nutrients into the environment.  In particular, he’s investigating the potential for drinking water treatment residuals to remove phosphorus from stormwater.

(84) The Influence of Active Control on Urban Bioretention Systems

Presenter: Aaron Akin, University of Tennessee,

Co-Authors: Padmini Persaud, University of Tennessee,; Jon Hathaway, University of Tennessee,

Abstract: Extreme weather has coupled with the proliferation of impervious areas in urban areas to increase the frequency of flood events and deepen water quality concerns. Bioretention is a type of green infrastructure practice developed to mitigate peak flows, reduce runoff volume, and reduce nutrient loads in stormwater through physical and microbial processes. However, studies have shown inconsistency in the ability of bioretention to manage nutrients, specifically nitrogen. At the same time, innovative sensor and control technologies are being tested to actively manage urban stormwater, primarily in open water control systems to date. Through these controls, it may be possible to optimizing storage time and/or soil moisture dynamics within bioretention cells to influence microbial nutrient processing facilities within a system. A column study testing the influence of active control on bioretention system performance was conducted over a nine-week period. Active control columns were given 1 of 2 treatments: volume control where the system was held at a specific water level to the extent possible, or soil moisture control where the system was held near field capacity. These treatments were compared to two current operational standards in terms of water quality: free draining and internal water storage. The results suggest that active controls can improve upon standard bioretention designs, but further optimization is required to balance the water quality benefits of retention time, and storage needs within these systems for impending storms.

Biography: Aaron Akin is a graduate research student at the University of Tennessee pursuing a doctoral degree in Water Resources Engineering. His research focuses on integrating instrumentation and control systems with stormwater networks to create smart and adaptive stormwater systems.

(85) Enhanced Bioretention Cell Modeling: Moving From Water Balances To Hydrograph Production

Presenter: Whitney Lisenbee, University of Tennessee,

Co-Authors: Dr. Jon Hathaway, University of Tennessee,; Dr. Ryan Winston, Ohio State University,; Dr.Mohamed Youssef, North Carolina State University;; Dr. Lamyaa Negm; North Carolina State University;

Abstract: Over the last few decades, bioretention systems have become a leading stormwater control measure that improve urban runoff volumes and peak flows through increased infiltration. Although these systems have performed well in many site-scale field studies, less is known about how to model these systems. Modeling of bioretention provides an avenue for evaluating the effectiveness of an individual bioretention cell prior to devoting time and resources into a project. However, many hydrologic models capable of simulating bioretention largely consist of lumped parameters and simplifications that do not fully account for fundamental hydrologic processes such as soil-water interactions. DRAINMOD is an agricultural drainage model that has shown promise when applied to bioretention systems by using the soil-water characteristic curve to obtain detailed daily water balances over a continuous time-period (advances over most other models for bioretention). For this study, DRAINMOD was recoded to develop DRAINMOD-Urban which allows high temporal resolution inputs and outputs, more closely matching the travel times of urban systems. DRAINMOD-Urban simulations were conducted for two bioretention cells and compared to original DRAINMOD simulations. Resulting modeling revealed: (1) if DRAINMOD-Urban can effectively produce hydrographs, (2) how parameters calibrated for the original DRAINMOD model translate to DRAINMOD-Urban, and (3) how the performance of this enhanced model, DRAINMOD-Urban, compares to the previous DRAINMOD model as applied to bioretention.

Biography: Whitney Lisenbee received her B.S. and M.S. degrees in Biosystems and Agricultural Engineering from Oklahoma State University. Whitney is currently a Graduate Research Assistant, and recipient of the Chancellor’s Fellowship, working on her Ph.D. is in Civil and Environmental Engineering from University of Tennessee-Knoxville. Her dissertation research is primarily focused on improving modeling of bioretention cells for stormwater management and watershed restoration. Her research concentration is in water resources and hydrology with interests including soil erosion, streambank stabilization, land use changes, urban hydrology, water quantity/quality, stormwater mitigation, and low impact development. She is also interested in conflicts between urban and agricultural water quantity and quality. Whitney is a member of the American Society of Agricultural and Biological Engineers (ASABE) where she received 3rd place in the Boyd-Scott graduate research award competition and 1st place in the K.K. Barnes undergraduate research competition. She is also a member of the American Society of Civil Engineers-Environmental & Water Resources Institute (ASCE-EWRI), American Ecological Engineering Society (AEES), and the American Society of Engineering Education (ASEE).