Kent Wired, the electronic version of Kent State University’s student media, ran a story on Saturday about the work Kimm Jarden and I have been doing on the effectiveness of green infrastructure retrofits in a neighborhood in Parma, Ohio. Hopefully I’ll have more to say about this in the next few days. In the meantime, if you want a glimpse of what we’ve been up to, you can check out the news article here.
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Most members of the Watershed Hydrology lab chose to go to GSA this year, and we had a blast sharing our science and enjoying Vancouver and surrounding areas. But now we are sadly missing out on the American Geophysical Union (AGU) meeting going on this week. Fortunately, a small piece of our work will be represented by outstanding summer REU student Sidney Bush. She’s giving a poster on Thursday afternoon in the Moscone West poster hall at H43F-1017. Here’s her abstract:
Soil moisture dynamics and their effect on bioretention performance in Northeast Ohio
Sidney A. Bush1, Anne Jefferson2, Kimberly Jarden2, Lauren E Kinsman-Costello2 and Jennifer Grieser3, (1)University of Virginia Main Campus, Charlottesville, VA, United States, (2)Kent State University Kent Campus, Kent, OH, United States, (3)Cleveland Metroparks, Parma, OH, United States
Urban impervious surfaces lead to increases in stormwater runoff. Green infrastructure, like bioretention cells, is being used to mitigate negative impacts of runoff by disconnecting impervious surfaces from storm water systems and redirecting flow to decentralized treatment areas. While bioretention soil characteristics are carefully designed, little research is available on soil moisture dynamics within the cells and how these might relate to inter-storm variability in performance. Bioretentions have been installed along a residential street in Parma, Ohio to determine the impact of green infrastructure on the West Creek watershed, a 36 km2 subwatershed of the Cuyahoga River. Bioretentions were installed in two phases (Phase I in 2013 and Phase II in 2014); design and vegetation density vary slightly between the two phases. Our research focuses on characterizing soil moisture dynamics of multiple bioretentions and assessing their impact on stormwater runoff at the street scale. Soil moisture measurements were collected in transects for eight bioretentions over the course of one summer. Vegetation indices of canopy height, percent vegetative cover, species richness and NDVI were also measured. A flow meter in the storm drain at the end of the street measured storm sewer discharge. Precipitation was recorded from a meteorological station 2 km from the research site. Soil moisture increased in response to precipitation and decreased to relatively stable conditions within 3 days following a rain event. Phase II bioretentions exhibited greater soil moisture and less vegetation than Phase I bioretentions, though the relationship between soil moisture and vegetative cover is inconclusive for bioretentions constructed in the same phase. Data from five storms suggest that pre-event soil moisture does not control the runoff-to-rainfall ratio, which we use as a measure of bioretention performance. However, discharge data indicate that hydrograph characteristics, such as lag time and peak flow, are altered relative to a control street. This analysis suggests that street-scale implementation of bioretention can reduce the impact of impervious surface on stormflows, but more information is needed to fully understand how soil moisture of the bioretentions affects inter-storm variability in performance.
Sidney’s poster is part of a session on “Water, Energy, and Society in Urban Systems” that Anne nominally helped convened. Check out all of the stimulating morning talks and awesome afternoon posters on Thursday. The rest of us are sorry to be missing it, but if *you* are in San Francisco at AGU this week, don’t miss out on all the great science in the session.
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.
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.
I’ll be at the 2013 Upper Midwest Stream Restoration Symposium in LaCrosse, Wisconsin in February. Even though the conference focuses on the Upper Midwest (of which Ohio is a part), I’m going to be talking about work from the southeastern US. Of course, the conference will be a great chance for me to learn from and make connections with stream restoration practicioners and scientists in the Midwest. I’m really looking forward to it, and hopefully they won’t call me out as a carpetbagger. I actually grew up ~25 miles from the conference location. Here’s the abstract.
Evaluating the success of urban stream restoration in an ecosystem services and watershed context
Anne Jefferson1, Sandra Clinton2, Mackenzie Osypian3, Sara McMillan3, Alea Tuttle2
1. Department of Geology, Kent State University
2. Department of Geography and Earth Sciences, University of North Carolina at Charlotte
3. Department of Civil Engineering, University of North Carolina at Charlotte
In urban watersheds, the capacity of streams to provide essential ecosystem services is often limited as a result of channel straightening, incision and removal of geomorphic features. Stream restoration seeks to provide stream stability while reestablishing ecosystem services, but restoration alone may not mitigate the effects of watershed land-use change and urbanization. Stream restoration activities frequently impact transient storage and hyporheic exchange, the processes by which water movement is slowed down or temporarily detained at the surface or in the streambed. Transient storage and hyporheic exchange zones are important regulators of nutrient retention and stream temperature, and they harbor diverse biological communities. However, it is unknown how successful stream restoration activities are at creating ecologically effective storage and exchange zones that promote improved water quality and nutrient retention. In a series of studies in Charlotte, North Carolina, we have evaluated restored and unrestored streams to quantify and compare transient storage and nutrient retention. Our goal is to evaluate the relative success of restoration activities for ecosystem services in urban and forested watersheds. We measured increased transient storage and greater variability in upwelling and downwelling vertical hydraulic gradients in restored relative to unrestored reaches. However, restored reaches also had lower hydraulic conductivity of bed sediments, which was likely related to to restoration practices such as streambed compaction and installation of landscaping fabric and cement below structures that may reduce the magnitude of hyporheic exchanges. Restored streams also have higher water temperatures than unrestored streams. The removal of riparian vegetation and soil disturbance and compaction during the restoration process, along with continued input of nutrients from fertilizers in urban watersheds can result in a unique water quality signature in urban restored streams. Denitrification rates were variable between sites, but channel complexity and restoration of urban streams appear to increase denitrification, even though hyporheic exchange was generally low. In unrestored urban streams, allochthonous anthropogenic debris (e.g., shopping carts) may contribute to channel complexity and nutrient retention. While current practices of urban stream restoration may be successful in creating channel stability, coupling watershed-scale management of stormwater and nutrients with restoration techniques designed to enhance ecologically effective storage and exchange may be required for restoration success in a holistic sense.
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, email@example.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.
EVALUATING RESTORATION EFFECTS ON TRANSIENT STORAGE AND HYPORHEIC EXCHANGE IN URBAN AND FORESTED STREAMS
OSYPIAN, Mackenzie L., Civil Engineering, University of North Carolina at Charlotte, Charlotte, NC 28262, firstname.lastname@example.org, JEFFERSON, Anne J., Department of Geology, Kent State University, 221 McGilvrey Hall, Kent, OH 44240, and CLINTON, Sandra, Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, NC 28223
Millions of dollars are spent each year on restoration projects designed to improve stream habitat, but few studies have investigated effects of restoration on hyporheic exchange and transient storage. Stream water-groundwater interactions and transient storage in four second-order streams (urban/forest; restored/urestored) were studied by measuring geomorphology, streambed vertical head gradients and water fluxes, and by using conservative, impulse-loaded tracer studies along with the OTIS model. The magnitude of upwelling and down welling was observed to be greatest in the restored urban stream, which contains large step structures, while the smallest gradients were observed in the unrestored urban stream, which is incised to bedrock. OTIS results show that the 120 m unrestored urban reach with a debris dam has an average transient storage of 1.8×10^-2 m2/m and an ? of 9.5×10^-4 s^-1 while a 55m restored forested reach with log sills has an average transient storage of 8.3×10^-2 m2/m and an ? of 1.5×10^-4 s^-1. Based on these results, we conclude that restoration changes transient storage metrics, and ongoing work aims to understand how these changes affect ecosystem health.
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.
The “blue book” has been updated and you can read and download a pre-publication PDF on the National Academies’ website for free. I’ve just been listening to a CUAHSI webinar summarizing the report, and I was please to see that a lot of the questions I’m interested in were highlighted by the committee that updated the report. For instance, there was specific mention of urban hydrology (and how changes to flowpaths and quantity alter water quality), the co-evolution of hydrology, landscapes, and life, and the need to understand the controls on the low flow extent of streams. I’ll be reading sections of this report in coming months, and if you want to get a sense of the state of hydrologic science, you would probably do well to start here too.