Hydrologic response to watershed metrics describing urban development and mitigation with stormwater control measures

Watershed Hydrology lab collaborator and Ph.D. candidate Colin Bell will be giving a talk in T106. From Green Roofs and Gutters to Urban Streams: Advancing Urban Watershed Hydrology through Innovative Field and Modeling Approaches on Monday, 2 November 2015 at 2:25 pm in Room 342 (Baltimore Convention Center).

HYDROLOGIC RESPONSE TO WATERSHED METRICS DESCRIBING URBAN DEVELOPMENT AND MITIGATION WITH STORMWATER CONTROL MEASURES

BELL, Colin D., Agricultural and Biological Engineering, Purdue University, West Lafayette, IN 47907, MCMILLAN, Sara K., Agricultural and Biological Engineering, Purdue University, West Lafayette, IN 47907-2093, JEFFERSON, Anne J., Department of Geology, Kent State University, Kent, OH 44242 and CLINTON, Sandra, Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, NC 28223, bell137@purdue.edu

Stormwater control measures (SCMs) are designed to mitigate changes in hydrologic response to hydrometeorological forcing caused by urban development. Total imperviousness (TI) is a metric that effectively quantifies this urban development, but does not contain information about the extent of SCM mitigation within the watershed. The hydrologic records of 16 urban watersheds in Charlotte, NC spanning a range of TI (4.1 to 54%) and mitigation with SCMs (1.3% to 89%) were analyzed to identify which of a suite of easily-determined watershed metrics best predict hydrologic behavior. We tested the watershed metrics TI, percent forested coverage, impervious area unmitigated by SCMs, effective impervious area, percent SCM-mitigated area, and a newly-developed metric called the mitigation factor. Linear models proved TI to be the best predictor of the 10th, 30th, 50th, 70th, and 90th percentiles of the distributions of peak unit discharge and rainfall-runoff ratios. In addition, TI was the best predictor of a watershed’s ability to buffer small rain events and the rate at which a stream responds once that buffering capacity is exceeded. Additional variables describing hydrograph record flashiness and water yield were best correlated to unmitigated imperviousness and forest coverage, respectively. For the range of watersheds considered, simple metrics that quantify SCM mitigation of both total watershed area and impervious area were neither the strongest primary control nor a consistent, secondary control on storm event behavior across sites. The dominance of TI as a control on hydrology over metrics of stormwater mitigation could either be attributed to the range of sites considered (14 out of 16 sites had less than 20% SCM mitigated area) or because the watershed metrics were not able to consider the spatial arrangement of impervious surfaces and SCMs. Our results have implications for policy makers designing standards that seek to minimize stream ecosystem degradation due to hydrologic disturbances from urbanization.

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.

Retrofitting stormwater retention on headwater streets: hydrologic effects of catchment-scale green infrastructure

At the Geological Society of America meeting, Anne will be giving an invited talk in (T106) From Green Roofs and Gutters to Urban Streams: Advancing Urban Watershed Hydrology through Innovative Field and Modeling Approaches. On Monday, November 2nd, at 1:35 pm in BCC room 342, Anne will be talking about:

Retrofitting stormwater retention on headwater streets: hydrologic effects of catchment-scale green infrastructure
Anne J. Jefferson1*, Kimberly M. Jarden1, and Jennifer M. Grieser2
1. Department of Geology, Kent State University, 221 McGilvrey Hall, Kent, OH 44242 kimberly.jarden@gmail.com; ajeffer9@kent.edu
2. Cleveland Metroparks, 2277 W Ridgewood Dr, Parma, OH 44134 jmg2@clevelandmetroparks.com
*corresponding author
Abstract
The detrimental effects of urban stormwater can be lessened by disconnecting impervious surfaces and redirecting runoff to stormwater control measures, but retrofitting stormwater ponds into fully-developed urban landscapes is challenging. Decentralized green infrastructure, such as rain barrels, rain gardens, and street-connected bioretention cells, may be a more feasible and attractive approach, but the catchment-scale effectiveness of such retrofits is poorly understood. In a residential neighborhood in suburban Cleveland, Ohio, a before-after-control-impact design, in which streets served as subcatchments, was used to quantify hydrologic effectiveness of street-scale investments in green infrastructure. On a residential treatment street, voluntary participation resulted in 13.5% of parcels having green infrastructure installed over a two year period. Storm sewer discharge was measured pre– and post- green infrastructure implementation and peak discharge, total runoff volume, and hydrograph lags were analyzed. Green infrastructure installation succeeded in reducing peak discharge by up to 33% and total storm runoff by up to 40%. Lag times increased following the first year’s installation of green infrastructure, in which street side bioretention cells were built with underdrains. In the second year, bioretention cells were built without underdrains and lag times did not change further. We conclude that voluntary green infrastructure retrofits that include treatment of street runoff can be effective for substantially reducing stormwater, but that small differences in design and construction can be important for determining the level of the benefit.

Woodchips and young plants in foreground, rain garden in middle distance, and houses in the background.

Example of a bioretention cell and rain garden studied in this project.

AGU Abstract: Dynamic Hydraulic Conductivity, Streambed Sediment, and Biogeochemistry Following Stream Restoration

The Watershed Hydrology Lab will be represented at the AGU Fall Meeting in December in the session on “Groundwater-Surface Water Interactions: Identifying and Integrating Physical, Biological, and Chemical Processes.”

Dynamic Hydraulic Conductivity, Streambed Sediment, and Biogeochemistry Following Stream Restoration

Anne Jefferson, Stuart Baker, and Lauren Kinsman-Costello, Kent State University, Kent, OH, United States

Stream restoration projects strive to improve water quality and degraded habitat, yet restoration projects often fall short of achieving their goals. Hyporheic exchange facilitates biogeochemical interaction which can contribute to positive water quality and habitat, but there are limited data on how restoration affects hyporheic processes. Hyporheic flowpaths can be altered by the processes and products of stream restoration, as well as the transport of fine sediment through the stream bed post-restoration. In two northeastern Ohio headwater streams, variations in hydraulic conductivity and pore water chemistry were monitored following restoration, as measures of hyporheic functioning. A second-order stream restored in August 2013, had a slight decrease in average hydraulic conductivity but an increase in heterogeneity from pre-restoration to four months post-restoration. Data collected 10 and 15 months post-restoration show continued declines in hydraulic conductivity throughout large constructed riffles. These piezometers also indicate dominance of downwelling throughout the riffles with only isolated upwelling locations. Grain size analysis of freeze cores collected in streambed sediments show differences suggesting fluvial transport and sorting have occurred since construction was completed. Pore water sampled from piezometers within the riffles had Mn2+ concentrations ten times higher than surface water, suggesting redox transformations are occurring along hyporheic flowpaths. A first-order stream reach, immediately downstream of a dam, restored in April 2014 had no significant change in average hydraulic conductivity between 1 and 2 months post-restoration, but many individual piezometers had increases of over 100% in high gradient positions or decreases of over 50% in low gradient positions. Changes in hydraulic conductivities in both restored streams are thought to be an adjustments from disturbance to a new dynamic equilibrium influenced by the morphology and sediment regime established by restoration, suggesting these are important processes to consider in the design of such projects.

One of the study streams, 3 months post-restoration.

One of the study streams, 3 months post-restoration.

Anne’s academic year-end update

Anne on a roof, covered with brown vegetation, dramatic sky

On the (dormant) green roof at Cleveland Metroparks’ Watershed Stewardship Center, April 2015

As I finish my third year at Kent State and prepare to go up for tenure, my work is taking me to exciting new heights. My newest project involves monitoring the hydrologic and water quality performance of different types of green infrastructure for Cleveland Metroparks. I never thought I’d be measuring soil moisture on a rooftop, but here I am. My work on green infrastructure brings with it enthusiastic students and stimulating collaborations with faculty in Biological Sciences, Geography, and Architecture. Kimberly Jarden defended her M.S. in April, and I have two graduate students beginning in the fall. Three more graduate students are close to defending, and I’ve had the pleasure to work with undergraduates Allison Reynolds, Sean Robertson, and Mitch Ladig as well. All of my students joined me at the Geological Society of America meeting in Vancouver in October, where we had a total of 7 presentations and a lot of fun. In the fall, I also taught an honors class of Environmental Earth Science, which was a good reminder of the big issues facing our planet and the urgent need for earth scientists to engage with these problems and their potential solutions. In the spring, I was mostly on leave following the birth of my baby boy, but I did manage to get a number of papers and proposals submitted, so it was a productive year in every sense.

[This blurb brought to you by needing to write something for the departmental newsletter.]

Abstract: Assessing the Possibilities of the West Creek Watershed Stewardship Center Vegetated Roof

Results of our work on green infrastructure at Cleveland Metroparks Watershed Stewardship Center will make its debut at the CitiesAlive 13th Annual Green Roofs & Walls Conference, in New York, NY from October 5th to October 8th, 2015.

Assessing the Possibilities of the West Creek Watershed Stewardship Center Vegetated Roof

Jessie Hawkins, Reid Coffman, Anne Jefferson, Lauren Kinsman-Costello

The vegetated roof at the Cleveland Metroparks’ Watershed Stewardship Center is an element in a suite of green infrastructure approaches, intended to be educational components, showcasing various methods of stormwater management. This study reviews estimation and design decision making tools to understand expected performance. Field data will be used to assess the current conditions of the roof in order to make recommendations for improvement of the existing vegetated roof system.

The planting design for the roof was intended to intercept rainfall with prostrate vegetation, pre-grown in 4 inch thick trays planted with varieties of Sedum spp. and Allium senescens. Plant species composition and biomass will be assessed in regard to stormwater performance and biodiversity, allowing for an invertebrate habitat. Soil samples taken from the roof have been analyzed for infiltration and nutrient content. Nutrient concentrations will be assessed in rainwater and compared to water flowing off the roof, determining if the roof is a source of nutrients to the downstream ecosystems. Sound reduction and thermal properties will be assessed with the results used for recommendation, serving as a resource guideline for local implementation.

Ground level view of the green roof, April 2015. Photo by A. Jefferson.

Ground level view of the green roof, April 2015. Photo by A. Jefferson.

The person behind the science: A podcast interview with Anne

There’s a fantastic podcast called “People Behind the Science” that “explore the lives and experiences of the people behind the research and scientific discoveries of today.” It was my honor to be interviewed on the podcast and talk about my own journey into research and my life outside of science. You can listen to the podcast episode on-line or download it on iTunes. The whole thing runs 43 minutes, and I’ve found it a useful tool for putting my baby to sleep. Hopefully, if you give it a listen, you’ll find it a bit more stimulating!

People Behind the Science logo (from its Facebook page)

Post-doc Opportunity in Watershed Modeling at Kent State University

This position has been filled. Thanks for your interest.

Post-doctoral Associate in Watershed Modeling

A post-doctoral position focusing on hydrologic modeling of urban watersheds is available in the Department of Geology, Kent State University, in the lab of Anne Jefferson (http://all-geo.org/jefferson/research/). The successful candidate will have experience using RHESSys or another distributed watershed model and interest in applying their skills to questions about the effects of green infrastructure and climate change in urban areas. The post-doc will be expected to contribute to research design and undertaking, publication, and pursuit of external funding. There will also be the potential to develop additional projects building on the strengths, interests, and expertise of the successful candidate. The post-doc will have access to a wealth of data sets, field sites and instrumentation; an interdisciplinary, collaborative group of researchers and external partners focused on urban ecosystems; and a campus mentoring program for postdocs.

Kent State University (www.kent.edu), the second largest university in Ohio, is a state-supported, doctoral degree granting institution ranked as ‘high research’ by the Carnegie Foundation. The Department of Geology (www.kent.edu/geology/) has a strong graduate program (both MS and Ph.D. degrees) in both applied and basic areas of geologic research. The city of Kent combines the eclectic atmosphere of a small midwest college town with easy access to major metropolitan centers, including Cleveland, Akron, Columbus, and Pittsburgh.

Salary will be commensurate with experience and includes a competitive benefits package. Funding is initially available to support 1.5 years of work and opportunities will be sought to extend the support. If you are interested in learning more about the position, e mail Anne Jefferson (ajeffer9 at kent edu) with your CV, a description of your interests and experiences, and contact information for three people willing to serve as references. Review of applications will begin March 1st and continue until the position is filled. Kent State University is an Affirmative Action/Equal Opportunity Employer and encourages interest from candidates who would enhance the diversity of the University’s faculty.