@article{shaneyfelt_johnson_hunt_2021, title={Hydrologic Modeling of Distributed Stormwater Control Measure Retrofit and Examination of Impact of Subcatchment Discretization in PCSWMM}, volume={7}, ISSN={["2379-6111"]}, DOI={10.1061/JSWBAY.0000938}, abstractNote={Modifications made to the landscape during urbanization can lead to increased stormwater runoff volumes and peak flows. Low-impact development (LID) techniques and green stormwater infrastructure are implemented to minimize the effects of urbanization on downstream environments. The United States Environmental Protection Agency's Storm Water Management Model (SWMM) can be used to simulate rainfall and runoff and evaluate the performance of existing or proposed urban water infrastructure. This study examined the performance of SWMM models developed using the Personal Computer Stormwater Management Model (PCSWMM) for a residential catchment before and after being retrofit with LID practices. Three preretrofit models at varying resolutions (low, middle, and high) and one postretrofit model were created and calibrated with observed stormwater outflow and rainfall data from a previous study in Wilmington, North Carolina. The LID retrofit included a bioretention cell bump-out and two permeable-pavement parking stalls. The uncalibrated low-resolution model was unsatisfactory for both runoff volume [Nash-Sutcliffe Efficiency (NSE) =0.49] and peak flow (NSE=−0.29) and overpredicted both with a percent bias of 65% and 70%, respectively. After calibration, the three preretrofit models all had very good agreement between observed and predicted results for runoff volume (NSE>0.95) and good agreement for peak flow (NSE>0.85). Runoff volume was still overpredicted by 23% in the middle-resolution model, but the difference in peak flows was minimal at −4%. The level of subcatchment discretization for the preretrofit models had little impact on overall model performance. Following the inclusion of LID retrofits, the postretrofit model was acceptable for event volumes (NSE=0.66) and peak flows (NSE=0.78), but overpredicted volumes by 56% and underpredicted peak flows by 10%. Using observed postretrofit data, the postretrofit model was recalibrated and greatly improved agreement between the observed and predicted data for runoff volume (NSE=0.88) while remaining acceptable for peak flow (NSE>0.78). More specifically, the calibrated postretrofit model reduced the overprediction of event volumes to 21%. These results highlight the need for observed rainfall and runoff data for both preretrofit and postretrofit calibration when modeling in SWMM.}, number={3}, journal={JOURNAL OF SUSTAINABLE WATER IN THE BUILT ENVIRONMENT}, author={Shaneyfelt, Kathryn M. and Johnson, Jeffrey P. and Hunt, William F.}, year={2021}, month={Aug} }
 @article{johnson_hunt_2020, title={Field Assessment of the Hydrologic Mitigation Performance of Three Aging Bioretention Cells}, volume={6}, ISSN={["2379-6111"]}, DOI={10.1061/jswbay.0000925}, abstractNote={AbstractIncreasing imperviousness has driven regulation and design philosophies to offset consequent increases in runoff volumes and peak flows. Previous research has shown bioretention to reduce r...}, number={4}, journal={JOURNAL OF SUSTAINABLE WATER IN THE BUILT ENVIRONMENT}, publisher={American Society of Civil Engineers (ASCE)}, author={Johnson, Jeffrey P. and Hunt, William F.}, year={2020}, month={Nov} }
 @article{doll_kurki-fox_page_nelson_johnson_2020, title={Flood Flow Frequency Analysis to Estimate Potential Floodplain Nitrogen Treatment during Overbank Flow Events in Urban Stream Restoration Projects}, volume={12}, url={http://dx.doi.org/10.3390/w12061568}, DOI={10.3390/w12061568}, abstractNote={Stream restoration for mitigation purposes has grown rapidly since the 1980s. As the science advances, some organizations (Chesapeake Bay Program, North Carolina Department of Environmental Quality) have approved or are considering providing nutrient credits for stream restoration projects. Nutrient treatment on floodplains during overbank events is one of the least understood processes that have been considered as part of the Chesapeake Bay Program’s Stream Restoration Nutrient Crediting program. This study analyzed ten years of streamflow and water quality data from five stations in the Piedmont of North Carolina to evaluate proposed procedures for estimating nitrogen removal on the floodplain during overbank flow events. The volume of floodplain flow, the volume of floodplain flow potentially treated, and the nitrogen load retained on the floodplain were calculated for each overbank event, and a sensitivity analysis was completed. On average, 9% to 15% of the total annual streamflow volume accessed the floodplain. The percentage of the average annual volume of streamflow potentially treated ranged from 1.0% to 5.1%. Annually, this equates to 0.2% to 1.0% of the total N load retained/removed on the floodplain following restoration. The relatively low nitrogen retention/removal rates were due to a majority of floodplain flow occurring during a few large events each year that exceeded the treatment capacity of the floodplain. On an annual basis, 90% of total floodplain flow occurred during half of all overbank events and 50% of total floodplain flow occurred during two to three events each year. Findings suggest that evaluating only overbank events may lead to undervaluing stream restoration because treatment is limited by hydrologic controls that restrict floodplain retention time. Treatment is further governed by floodplain and channel size.}, number={6}, journal={Water}, publisher={MDPI AG}, author={Doll, Barbara A. and Kurki-Fox, J. Jack and Page, Jonathan L. and Nelson, Natalie G. and Johnson, Jeffrey P.}, year={2020}, month={May}, pages={1568} }
 @article{winston_arend_dorsey_johnson_hunt_2020, title={Hydrologic Performance of a Permeable Pavement and Stormwater Harvesting Treatment Train Stormwater Control Measure}, volume={6}, DOI={10.1061/jswbay.0000889}, abstractNote={AbstractStormwater runoff from urban development causes undesired impacts to surface waters, including discharge of pollutants, stream erosion, and loss of in-stream habitat. Stormwater control mea...}, number={1}, journal={Journal of Sustainable Water in the Built Environment}, publisher={American Society of Civil Engineers (ASCE)}, author={Winston, Ryan J. and Arend, Kristi and Dorsey, Jay D. and Johnson, Jeffrey P. and Hunt, William F.}, year={2020}, month={Feb}, pages={04019011} }
 @article{johnson_hunt_2019, title={A Retrospective Comparison of Water Quality Treatment in a Bioretention Cell 16 Years Following Initial Analysis}, volume={11}, url={https://www.mdpi.com/2071-1050/11/7/1945}, DOI={10.3390/su11071945}, abstractNote={One of the most popular stormwater practices in (sub-)urban North Carolina is bioretention. While bioretention has been researched intensively to determine the most efficient designs, few long-term studies have attempted to assess the performance of older bioretention. However, previous research and design guidance for bioretention has predicted long-term water quality treatment. This study compared discharged concentrations and loads of nitrogen and phosphorus from a bioretention cell (1) post-construction and (2) following 17 years of treatment. A conventionally-drained bioretention cell with lateral underdrains in Chapel Hill, North Carolina, USA, was first monitored post-construction for 10-months from 2002–2003 and, again following continuous use, for 14 months from 2017–2018. Estimated mass load reductions during the initial monitoring period were 40% for total nitrogen (TN) and 65% for total phosphorus (TP). Mass load reductions were increased 17 years after construction, with reductions of 72% and 79% for TN and TP, respectively. Plant growth, death, and decay over the 17-year life of the bioretention cell are hypothesized to have contributed additional nitrogen assimilation and carbon to the fill media, serving as a catalyst for nitrogen treatment. Phosphorus removal remained relatively unchanged between the two monitoring periods. Filter media samples indicated the top 20 cm of filter media were nearing phosphorus saturation, but with 1.2 m of filter media, lower depths would most likely continue to provide treatment. If designed, built, and maintained correctly, bioretention appears to provide sustained treatment of stormwater runoff for nitrogen and phosphorus for nearly two decades, and likely longer.}, number={7}, journal={Sustainability}, publisher={MDPI AG}, author={Johnson, Jeffrey and Hunt, William}, year={2019}, month={Apr}, pages={1945} }
 @article{cizek_johnson_birgand_hunt_mclaughlin_2019, title={Insights from using in-situ ultraviolet–visible spectroscopy to assess nitrogen treatment and subsurface dynamics in a regenerative stormwater conveyance (RSC) system}, volume={252}, ISSN={0301-4797}, url={http://dx.doi.org/10.1016/j.jenvman.2019.109656}, DOI={10.1016/j.jenvman.2019.109656}, abstractNote={Regenerative stormwater conveyance (RSC) is a recently developed stormwater control measure that marries the concepts of bioretention and stream restoration. RSC mitigates stormwater runoff by converting surface flow to subsurface seepage using a series of pools and riffles built over a sand media bed. Subsurface seepage flows through media and exits the RSC beneath the outlet weir. Previous studies on RSC pollutant mitigation have focused on surface flow discharges from the RSC. To date, no known research has been conducted on the potential pollutant contributions of RSC seepage, despite the fact that this water also enters receiving waters. This research used Multi-Point Sampling coupled with in-situ ultraviolet–visual spectroscopy to measure nitrogen in seepage during simulated storm events (n = 9) at a field-scale RSC in Raleigh, North Carolina. Calibrations between light absorbance and concentrations were acceptable (Nash-Sutcliffe coefficient > 0.65) for nitrate and total ammoniacal nitrogen (TAN) and very good (Nash-Sutcliffe coefficient > 0.90) for total Kjehdahl nitrogen (TKN). Early storm simulations revealed some initial nutrient flushing from the substrate, which subsided by the third simulation. Overall, subsurface seepage nitrate, TAN, and TKN concentrations were lower by 29%, 57%, and 4% relative to storm inflow concentrations, respectively. Computed subsurface nitrogen concentrations demonstrated temporal variability, highlighting dynamic transport and biogeochemical transformations in saturated and unsaturated conditions. Nitrogen concentrations were lower in seepage than in surface flow; however, due to the high volume of runoff converted to seepage, nitrogen loads discharged in seepage can be larger than those of surface flow. Further research is needed to examine subsurface pollutant reductions under varying hydrologic and seasonal conditions.}, journal={Journal of Environmental Management}, publisher={Elsevier BV}, author={Cizek, Adrienne R. and Johnson, Jeffrey P. and Birgand, François and Hunt, William F. and McLaughlin, Richard A.}, year={2019}, month={Dec}, pages={109656} }
 @article{johnson_hunt_2016, title={Evaluating the spatial distribution of pollutants and associated maintenance requirements in an 11 year-old bioretention cell in urban Charlotte, NC}, volume={184}, ISSN={["1095-8630"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84994339362&partnerID=MN8TOARS}, DOI={10.1016/j.jenvman.2016.10.009}, abstractNote={Bioretention cells (BRCs) are an increasingly popular Stormwater Control Measure used to mitigate the hydrologic and water quality impacts of urbanization. Previous BRC research has demonstrated a strong capacity for pollutant removal; however, long-term sequestration of pollutants within soil media can elevate concentrations to levels fostering environmental and human health risks. Soil media samples were collected from an 11 year-old BRC in Charlotte, NC, and analyzed for the accumulation and spatial distribution of zinc, copper, and phosphorus. Pollutant distribution varied significantly with respect to depth and ordinate distance from the BRC inlet. Zinc concentrations (0.9–228.6 mg kg−1 soil) exceeded environmental thresholds and phosphorus concentrations (5.1–173.3 mg kg−1 soil) increased from initial levels by a factor of seven; however, notable accumulation was restricted to the BRC forebay. Maximum zinc and copper concentrations in soil media did not exceed 1% of mandatory cleanup levels and with regular maintenance of the forebay, the effective life of BRC media should exceed the life of the developments they treat.}, journal={JOURNAL OF ENVIRONMENTAL MANAGEMENT}, publisher={Elsevier BV}, author={Johnson, Jeffrey P. and Hunt, William F.}, year={2016}, month={Dec}, pages={363–370} }