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stormwater

Quantifying the influences of stormwater control measures on urban headwater streamflow

The Watershed Hydrology Lab will be at the Geological Society of America meeting in November in Baltimore. Anne will be giving an invited talk in the Urban Geochemistry session (T32) on Sunday, November 1st at 9 am in BCC room 308. Here’s what she’ll be talking about:

Quantifying the influences of stormwater control measures on urban headwater streamflow

Anne Jefferson1, Colin Bell2, Sara McMillan2, and Sandra Clinton3
1. Department of Geology, Kent State University, 221 McGilvrey Hall, Kent, OH 44242 USA. Phone: 1-330-672-2746 Email: ajeffer9@kent.edu
2. Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, Indiana, USA.
3. Department of Geography and Earth Sciences, University of North Carolina at Charlotte, 9201 University City Boulevard, Charlotte, NC 28223, USA.

Stormwater control measures are designed to mitigate the hydrological consequences of urbanization, but their as-built effectiveness in altering patterns of urban streamflow remains poorly quantified. Stream gaging and water stable isotopes were used to understand the effects of stormwater ponds and wetlands on hydrograph characteristics and water sourcing in four urban headwater streams in Charlotte, North Carolina. At the small watershed scale (0.15-1.5 km2), runoff ratio and peak discharge are more strongly related to impervious area than area treated by stormwater controls. For one stream during 10 events, we used stable isotopes to quantify contributions of retention pond discharge to streamflow, taking advantage of the unique isotope signature of pond outflow. The pond, which drains 25% of the watershed’s impervious area, contributed an average of 10% (0-21%) of the streamflow on the rising limb and 12% (0-19%) of discharge at peak flow. During recession, this pond contributed an average of 32% (11-54%) of the stream’s discharge, reflecting the pond’s design goals of temporarily storing and delaying runoff. The isotopic signature of the pond’s discharge also reveals varying water residence times (hours to weeks) within the structure, which may have implications for nutrient and metal fluxes into the stream. Our results suggest that even when individual stormwater control measures are working as designed, they are insufficient to fully mitigate the effects of urbanization on stream hydrology. They also demonstrate the combination of traditional hydrometric and tracer-based techniques can reveal a nuanced view of stormwater influences on urban streams. Such hydrological nuance will be necessary to develop strong mechanistic understanding of biogeochemical processes in urban streams and watersheds.

Stormwater control measures modify event-based stream temperature dynamics in urbanized headwaters

Next week, the Watershed Hydrology Lab will be well represented at the CUAHSI 2014 Biennial Colloquium. We’ll be presenting four posters, so here come the abstracts…

Stormwater control measures modify event-based stream temperature dynamics in urbanized headwaters

Grace Garner1, Anne Jefferson2*, Sara McMillan3, Colin Bell4 and David M. Hannah1
1School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
2Department of Geology, Kent State University, Kent, OH, 44240, USA
3Department of Civil and Environmental Engineering, University of North Carolina at Charlotte, Charlotte, NC, 28223, USA
4Department of Infrastructure and Environmental System, University of North Carolina at Charlotte, Charlotte, NC, 28223, USA

Urbanization is a widespread and growing cause of hydrological changes and ecological impairment in headwater streams. Stream temperature is an important control on physical, chemical and ecological processes, and is an often neglected water quality variable, such that the effects of urban land use and stormwater management on stream temperature are poorly constrained. Our work aims to identify the influence of stormwater control measures (SCMs) of differing design and location within the watershed on the event-based temperature response of urban streams to precipitation in the North Carolina Piedmont, in order to improve prediction and management of urban impacts. Stream temperature was measured within SCMs, and upstream and downstream of them in two streams between June and September 2012 and 2013. Approximately 60 precipitation events occurred during that period. To unambiguously identify temperature increases resulting from precipitation, surges were identified as a rise in water temperature of ?0.2°C between the hours of 15:30 and 5:30, when the diurnal temperature cycle is either decreasing or static on days without precipitation. Surges up to 5°C were identified in response to precipitation events, with surges occurring both upstream and downstream of the SCM under some conditions. Surges were also recorded within the SCMs, confirming that temperature surges are the result of heated urban runoff. Classification tree modeling was used to evaluate the influence of hydrometeorological drivers on the generation and magnitude of temperature surges. In both streams, event precipitation, antecedent precipitation, and air temperature range were identified as the drivers of whether or not a surge was observed and how large the surge was, though the order and thresholds of these variables differed between the two sites. In a stream with an off-line, pond SCM, the presence of the pond in the lower 10% of the watershed did not affect the magnitude of temperature surges within the stream, but the pond itself had a wider range of surge magnitudes than did the stream. In a watershed with a large in-line pond, and a downstream contributing wetland SCM receiving flow from 40% of the watershed, the wetland increased both the frequency and magnitude of temperature surges observed in the stream. Our results suggest dynamic hydrometeorological conditions, SCM design, and position within a watershed all influence whether stormwater management reduces or enhances temperature surges observed within urban headwater streams, and that these factors should be considered in the recommendations for urban stormwater management systems.

Assessing impacts of green infrastructure at the watershed scale for suburban streets in Parma, Ohio

Next week, the Watershed Hydrology Lab will be well represented at the CUAHSI 2014 Biennial Colloquium. We’ll be presenting four posters, so here come the abstracts…

Assessing impacts of green infrastructure at the watershed scale for suburban streets in Parma, Ohio

Kimberly Jarden, Anne Jefferson, Jennifer Grieser, and Derek Schaefer

High levels of impervious surfaces in urban environments can lead to greater levels of runoff from storm events and overwhelm storm sewer systems. Disconnecting impervious surfaces from storm water systems and redirecting the flow to decentralized green infrastructure treatments can help lessen the detrimental effects on watersheds. The West Creek Watershed is a 36 km2 subwatershed of the Cuyahoga River that contains ~35% impervious surface. We seek to evaluate the hydrologic impacts and pollution reduction of street scale investments using green infrastructure best management practices (BMPs), such as rain gardens, bioretention, and rain barrels. Before-after-control-impact design will pair two streets with 0.001-0.002 ha. lots and two streets with 0.005-0.0075 ha. lots. Flow meters have been installed to measure total discharge, velocity, and stage pre– and post-construction. Runoff data has been preliminarily analyzed to determine if peak discharge for large (> 10 mm) and small (<10 mm) storm events has been reduced after installation of BMPs on the street with 0.001-0.002 ha. lots. Initial results show that the peak flows have not been reduced for most storm events on the street with the green infrastructure. However, several larger events show that peak flows have been reduced on the treatment street and need to be further investigated to ensure no outside hydrological impacts are having an effect on the flow. Initial analysis of total flow volume for each event, pre- and post-construction, show that total volume has increased on the street with green infrastructure treatments. Possible explanation for the increase on flow volume could be attributed to under drains from bioretention creating a more connected flow path to the storm drain or an upstream leak in the control street storm drain. Each scenario will be investigated further to confirm results. Further research will include analysis of the total effect of street-scale BMPs on storm hydrograph characteristics including, hydrograph regression behavior and lag time. Analysis on the accumulation of metals in the bioswales and the reduction of metals in street runoff will also be conducted to determine if the BMP treatments are capturing pollutants associated with storm water. After studying the effect of each individual treatment, we will define the level of disconnected impervious surfaces needed in order to achieve a natural hydrologic regime in this watershed.

Abstract: Using Computer Modeling To Asses Hydraulic Parameter Transferability From An Undeveloped To An Urban Watershed With Stormwater Infrastructure

Rounding out the abstracts from our group for the 2012 Geological Society of America meeting, Colin Bell will be presenting preliminary model results.

USING COMPUTER MODELING TO ASSES HYDRAULIC PARAMETER TRANSFERABILITY FROM AN UNDEVELOPED TO AN URBAN WATERSHED WITH STORMWATER INFRASTRUCTURE

BELL, Colin D., Dept. Infrastructure and Environmental Systems, UNC Charlotte, Charlotte, NC 28262, cdbell01@yahoo.com, MCMILLAN, Sara, Department of Engineering Technology, University of North Carolina at Charlotte, Charlotte, NC 28223, JEFFERSON, Anne J., Department of Geology, Kent State University, 221 McGilvrey Hall, Kent, OH 44240, TAGUE, Christina, Bren School of Environmental Science and Management, University of California-Santa Barbara, Santa Barbara, CA 93106, and CLINTON, Sandra, Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, NC 28223

Urban infrastructure expansion causes the alteration of hydrologic and nutrient regimes during storms, elevating peak discharges and nitrogen (N) concentrations in receiving streams. The inclusion of stormwater Best Management Practices (BMPs) in urban watersheds has been found to help ameliorate these problems by attenuating hydrographs and reducing N concentrations through denitrification and uptake. The Regional Hydro-Ecological Simulation System (RHESSys) is a distributed, process-based model that simulates hydrologic activity as well as natural and anthropogenic N processing and export. RHESSys is being used to develop hydro-ecological models to assess the impact of different BMP implementation strategies on instream N in a developing residential watershed in Charlotte, NC where water quality and land use data accompany 10 years of hydrologic data. Hydraulic parameter sets have been calibrated to simulate subsurface water propagation in a nearby, undeveloped watershed with no existing stormwater infrastructure. The suitability of these parameter sets has been assed using the GLUE uncertainty prediction procedure, a calibration and uncertainty estimation method that addresses the equifinality of parameter sets given errors in model structure and observed data. The viability for transferring the model parameters to the urban watershed has been analyzed by comparing an observed discharge record with one predicted using calibrated parameters. Future RHESSys simulations will test multiple, spatially-explicit scenarios to identify the BMP treatment scenarios that minimize aquatic ecosystem degradation.

Abstract: Using Watershed Modeling to Optimize Management of Urban Stormwater to Control Stream Nitrogen

Ph.D. student Colin Bell will be presenting the following poster at the American Ecological Engineering Society meeting this week in Syracuse, New York.

Using Watershed Modeling to Optimize Management of Urban Stormwater to Control Stream Nitrogen

Colin Bell
Dr. Sara McMillan
Dr. Christina Tague
Dr. Anne Jefferson
Dr. Sandra Clinton

Urban infrastructure expansion causes the alteration of hydrologic and nutrient regimes, elevating nitrogen (N) concentrations in the streams that receive stormwater runoff. The inclusion of stormwater Best Management Practices (BMPs) in urban watersheds has been found to help ameliorate these problems by retaining water and reducing N concentrations through denitrification and uptake. The Regional Hydro-Ecological Simulation System (RHESSys) is currently being used to test the impact of different BMP implementation strategies and fertilizer application regimes to simulate their effects on instream N in an urbanizing, residential watershed in Charlotte, NC. RHESSys is a distributed, process-based model that simulates natural and anthropogenic N and carbon (C) sources, processing and export. Watershed characterization of two watersheds with contrasting land uses (suburban and forested), along with field monitoring of instream and BMP water chemistry is currently being completed. This will allow us to parameterize the influences of existing BMPs on instream N concentrations, and allow RHESSys to scale up their observed functionality. RHESSys will test multiple, spatially-explicit scenarios to identify the combination of N loading and BMP treatment that minimizes aquatic ecosystem degradation so that land developers can urbanize responsibly.

AGU 2011 abstract from our NSF stormwater project

I’m not claiming credit for this project, as it was as undergraduate summer research project advised by my collaborator Sara McMillan, but it is one tangible bit of results that have come out of our NSF-funded stormwater project. More good things are coming soon.

The following poster was presented at the AGU 2011 fall meeting.

The influence of stormwater management practices on denitrification rates of receiving streams in an urban watershed

AU: *Cronenberger, M S
AF: Environmental Sciences, Winthrop University, Rock Hill, SC, USA
AU: McMillan, S K
AF: Engineering Technology, University of North Carolina at Charlotte, Charlotte, NC, USA

Increasing urbanization and the subsequent disruption of floodplains has led to the need for implementing stormwater management strategies to mitigate the effects of urbanization, including soil and streambank erosion, increased export of nutrients and contaminants and decreased biotic richness. Excessive stormwater runoff due to the abundance of impervious surfaces associated with an urban landscape has led to the ubiquitous use of best management practices (BMPs) to attenuate runoff events and prevent the destructive delivery of large volumes of water to stream channels. As a result, effluent from BMPs (i.e. wetlands and wet ponds) has the potential to alter the character of the receiving stream channel and thus, key ecosystem processes such as denitrification. The purpose of this study was to determine the extent to which BMPs, in the form of constructed wetlands and wet ponds, influence in-stream denitrification rates in the urban landscape of Charlotte, NC. Four sites, two of each BMP type, were evaluated. Sediment samples were collected upstream and downstream of the BMP outflow from May-July 2011 to determine the effect of wetland discharge on in-stream nitrogen removal via denitrification. Denitrification rates were determined using the acetylene block method; water column nutrient and carbon concentrations and sediment organic matter content were also measured. Generally, wetland sites exhibited higher denitrification rates, nitrate concentrations and sediment organic matter content. Our work and others has demonstrated a significant positive correlation between nitrate concentration and denitrification rates, which is the likely driver of the higher observed rates at the wetland sites. Geomorphology was also found to be a key factor in elevated denitrification rates at sites with riffles and boulder jams. Sediment organic matter was found to be higher downstream of BMP outflows at all four sites, but demonstrated no significant relationship with denitrification rates. We are continuing to investigate these spatial (e.g. BMPs, streams) and temporal (e.g. storm pulse, delayed wetland release) patterns, particularly in the context of factors that influence the specific drivers of denitrification. Understanding these patterns is critical to managing stormwater in urban landscapes as we aim to improve water quality while enhancing ecosystem functions.

REU Opportunity on Stormwater Management and Ecosystem Function

A National Science Foundation Research Experience for Undergraduates (REU) summer fellowship is open at the University of North Carolina Charlotte. We invite applications from qualified, highly motivated undergraduate students from U.S. colleges/universities to participate in a 12-week lab and field based summer research experience. The program runs from May 23 – August 12 but start and end dates are flexible. The student will participate in an NSF-funded project studying the effects of stormwater management on ecosystem function (e.g. nutrient dynamics, biological integrity, temperature attenuation and hydrology) in urban streams. The student will learn field and laboratory techniques, experimental design and data analysis to develop his/her own research project within this topic. The student will be required to write a report in the format of a scientific paper and give a presentation on their project at the end of the summer. The student will also be encouraged to submit an abstract of their work for presentation at a scientific meeting (e.g. American Geophysical Union). The REU provides a $450/week stipend for living expenses and travel costs to the scientific meeting will be covered.

Applicants must be enrolled in an accredited undergraduate institution and a citizen or permanent resident of the United States. Students from underrepresented groups and institutions with limited research opportunities are especially encouraged to apply. Interested applicants should send: (1) a statement of interest, (2) resume, (3) unofficial transcript, (4) one letter of recommendation and (5) contact information for one additional reference. The statement of interest should include the following information: (i) professional goals, (ii) interest in position and (iii) relevant experience and be sent to Dr. Sara McMillan (smcmillan (at) uncc.edu). The letter of recommendation should be sent directly from the recommender (please include the applicant’s name in the subject line for emails). Incomplete applications will not be considered. Applications will be accepted through April 22, 2011.

Graduate Assistantships: Biogeochemistry, Stream Ecology, and Hydrology at UNC Charlotte, NC

Come work with me!

Research assistantships are available at the MS or Ph.D. level at the University of North Carolina at Charlotte to participate in a recently funded NSF project investigating the effects of stormwater management on ecosystem function in urban watersheds.  The overall goal is to better understand and predict the impacts of stormwater BMPs on receiving streams over a range of spatial and temporal scales through a combination of field based research and watershed scale ecological modeling.  This interdisciplinary project will link (1) mass-balance based monitoring of individual BMPs, (2) ecosystem processes (nutrient uptake, metabolism, temperature and biological indices) in the receiving stream and (3) monitored and modeled watershed outputs of flow, nitrogen, and carbon.

Applicants interested in aquatic biogeochemistry, hydrology, stream ecology and/or watershed modeling are encouraged to apply.  Students will have flexibility to develop independent research questions within the context of this project that broadly address the interactions among hydrology, biogeochemistry and ecology in aquatic ecosystems.

Qualifications:  degree in biology, ecology, environmental engineering, hydrology or related field is required.  Successful applicants should have a strong interest in working in an interdisciplinary research environment, be creative, motivated and capable of working well both independently and cooperatively and possess strong communication and quantitative skills. Competitive stipends and tuition waivers are available for highly motivated students.  For more information on admission requirements and deadlines, visit http://graduateschool.uncc.edu.  Additional information about the McMillan Lab can be found at http://www.coe.uncc.edu/~smcmil10.  Opportunities exist for collaboration with the labs of Sandra Clinton and Anne Jefferson at UNC Charlotte who are collaborators on the project.

Interested students with strong motivation to succeed in research should contact Sara McMillan via email (smcmillan@uncc.edu).  Please submit a statement of career goals and research interests, full CV, unofficial transcripts and GRE scores, and contact information for three potential references.  Review of applications will begin immediately and continue until suitable candidates are found. The anticipated start date is flexible, but should be sometime between January and August 2011.