@article{brown_birgand_hunt_2013, title={Analysis of Consecutive Events for Nutrient and Sediment Treatment in Field-Monitored Bioretention Cells}, volume={224}, ISSN={0049-6979 1573-2932}, url={http://dx.doi.org/10.1007/s11270-013-1581-6}, DOI={10.1007/s11270-013-1581-6}, number={6}, journal={Water, Air, & Soil Pollution}, publisher={Springer Science and Business Media LLC}, author={Brown, Robert A. and Birgand, Francois and Hunt, William F.}, year={2013}, month={May} }
 @article{brown_skaggs_hunt_2013, title={Calibration and validation of DRAINMOD to model bioretention hydrology}, volume={486}, ISSN={0022-1694}, url={http://dx.doi.org/10.1016/J.JHYDROL.2013.02.017}, DOI={10.1016/j.jhydrol.2013.02.017}, abstractNote={Previous field studies have shown that the hydrologic performance of bioretention cells varies greatly because of factors such as underlying soil type, physiographic region, drainage configuration, surface storage volume, drainage area to bioretention surface area ratio, and media depth. To more accurately describe bioretention hydrologic response, a long-term hydrologic model that generates a water balance is needed. Some current bioretention models lack the ability to perform long-term simulations and others have never been calibrated from field monitored bioretention cells with underdrains. All peer-reviewed models lack the ability to simultaneously perform both of the following functions: (1) model an internal water storage (IWS) zone drainage configuration and (2) account for soil–water content using the soil–water characteristic curve. DRAINMOD, a widely-accepted agricultural drainage model, was used to simulate the hydrologic response of runoff entering a bioretention cell. The concepts of water movement in bioretention cells are very similar to those of agricultural fields with drainage pipes, so many bioretention design specifications corresponded directly to DRAINMOD inputs. Detailed hydrologic measurements were collected from two bioretention field sites in Nashville and Rocky Mount, North Carolina, to calibrate and test the model. Each field site had two sets of bioretention cells with varying media depths, media types, drainage configurations, underlying soil types, and surface storage volumes. After 12 months, one of these characteristics was altered – surface storage volume at Nashville and IWS zone depth at Rocky Mount. At Nashville, during the second year (post-repair period), the Nash–Sutcliffe coefficients for drainage and exfiltration/evapotranspiration (ET) both exceeded 0.8 during the calibration and validation periods. During the first year (pre-repair period), the Nash–Sutcliffe coefficients for drainage, overflow, and exfiltration/ET ranged from 0.6 to 0.9 during both the calibration and validation periods. The bioretention cells at Rocky Mount included an IWS zone. For both the calibration and validation periods, the modeled volume of exfiltration/ET was within 1% and 5% of the estimated volume for the cells with sand (Sand cell) and sandy clay loam (SCL cell) underlying soils, respectively. Nash–Sutcliffe coefficients for the SCL cell during both the calibration and validation periods were 0.92.}, journal={Journal of Hydrology}, publisher={Elsevier BV}, author={Brown, R.A. and Skaggs, R.W. and Hunt, W.F., III}, year={2013}, month={Apr}, pages={430–442} }
 @article{effectiveness of lid for commercial development in north carolina_2012, volume={138}, number={6}, journal={Journal of Environmental Engineering (New York, N.Y.)}, year={2012}, pages={680–688} }
 @article{brown_hunt_2012, title={Improving bioretention/biofiltration performance with restorative maintenance}, volume={65}, ISSN={["1996-9732"]}, DOI={10.2166/wst.2012.860}, abstractNote={One of the most popular Stormwater Control Measures is bioretention, or biofiltration. Anecdotal evidence suggests that well-designed bioretention cells are often not adequately installed and that maintenance is lacking, leading to less-than-adequate water storage volume and/or surface infiltration rates post-construction. In March 2009, two sets of bioretention cells were repaired by excavating the top 75 mm of fill media, increasing the bioretention surface storage volume by nearly 90% and the infiltration rate by up to a factor of 10. Overflow volume decreased from 35 and 37% in the pre-repair state for two different sets of cells, respectively, to 11 and 12%. Nearly all effluent pollutant loads exiting the post-repair cells were lower than their pre-repair conditions. The bioretention systems employed two different media depths (0.6 and 0.9 m). The deeper media cells discharged less outflow volume than the shallower cells, with 10–11% more runoff volume leaving as exfiltration from the 0.9-m than from the 0.6-m media depth cells. This study showed that maintenance is both critical and beneficial to restore otherwise poorly performing bioretention. Moreover, while deeper media cells did outperform the shallower systems, the improvement in this case was somewhat modest vis-à-vis additional construction costs.}, number={2}, journal={WATER SCIENCE AND TECHNOLOGY}, author={Brown, Robert A. and Hunt, William F.}, year={2012}, pages={361–367} }
 @article{brown_line_hunt_2012, title={LID Treatment Train: Pervious Concrete with Subsurface Storage in Series with Bioretention and Care with Seasonal High Water Tables}, volume={138}, ISSN={["1943-7870"]}, DOI={10.1061/(asce)ee.1943-7870.0000506}, abstractNote={Two infiltrating low-impact development (LID) practices configured in-series, pervious concrete and bioretention (PC-B), were monitored for 17 months to examine the hydrologic and water quality response of this LID treatment train design. For the first LID practice, 0.53 ha of pervious concrete was installed to treat direct rainfall and run-on from 0.36 ha of asphalt parking lot. The pervious concrete was installed over a gravel subsurface storage basin, which was designed to store 25 mm (1 in.) of runoff from the parking lot before draining into the second LID practice, which was a 0.05 ha bioretention cell. The bioretention cell was conventionally drained, had a media depth of 0.5 m (1.6 ft), and was constructed at a location with a high water table. Outflow was only generated in 33 out of 80 monitored events, and over the course of the entire monitoring period, the total outflow volume reduction was 69%. The large outflow reduction subsequently led to high pollutant load reductions for total nitrogen (49%), total phosphorus (51%), and total suspended solids (89%). However, when the contribution of base flow was included in the calculation, the total nitrogen load discharged from the bioretention cell was 64% higher than that of the runoff load because of nitrite and nitrate, NO2- and NO3-(NO2,3-N), which were present in the base flow. The total nitrogen (TN) loads of runoff, storm flow (total outflow minus base flow), base flow, and outflow (total) were 7.70, 3.94, 8.69, and 12.64 kg/ha·year, respectively. Of the 8.69 kg/ha·year TN in the base flow, 92% was in the form of NO2,3-N. This study demonstrated the hydrologic benefits (peak flow and outflow reduction) gained by having two infiltration LID practices in-series. When compared with a single treatment practice (bioretention) that was monitored at the same site, the two LID practices in-series treated an additional 10% of annual runoff volume, discharged approximately one-half as much outflow volume, and discharged significantly lower peak outflow rates. However, the water quality results were not as promising because of the influx of groundwater in the bioretention cell and the lack of denitrifying conditions in either the bioretention cell or pervious concrete system. This study also quantified increased TN and NO2,3-N export to surface waters from a bioretention cell that was situated in an area with a high water table.}, number={6}, journal={JOURNAL OF ENVIRONMENTAL ENGINEERING}, author={Brown, R. A. and Line, D. E. and Hunt, W. F.}, year={2012}, month={Jun}, pages={689–697} }
 @article{brown_hunt_2011, title={Impacts of Media Depth on Effluent Water Quality and Hydrologic Performance of Undersized Bioretention Cells}, volume={137}, ISSN={["1943-4774"]}, DOI={10.1061/(asce)ir.1943-4774.0000167}, abstractNote={Fill media and excavation volume are the main costs in constructing bioretention cells, but the importance and impact of media depth in these systems is relatively unknown. Two sets of loamy-sand-filled bioretention cells of two media depths (0.6 m and 0.9 m), located in Nashville, North Carolina, were monitored from March 2008 to March 2009 to examine the impact of media depth on their performance with respect to hydrology and water quality. Construction and design errors resulted in the surface storage volume being undersized for the design event (2.5 cm). The actual surface storage volume was only 28% and 35% of the design volume for the 0.6-m and 0.9-m media depth cells, respectively. Overflow (bypass) occurred at least three times more frequently than intended. The exfiltration volume was much higher in the deeper media cells, presumably because of greater storage volume in the media and more exposure to side walls. Evapotranspiration (ET) plus exfiltration accounted for 42% of the inflow runoff in the 0.9-m media cells, while ET and exfiltration accounted for only 31% of the inflow runoff in the 0.6-m media cells. With the increase in exfiltration, the deeper media depth met a previously defined low-impact development (LID) hydrology goal of volume reduction more frequently than the shallower media system (44% of events compared to 21%). Larger outflow reduction consequently increased the reduction in pollutant loads. Estimated annual pollutant load reduction for total nitrogen, total phosphorus, and total suspended solids were 21, 10, and 71% for the 0.6-m media cells and 19, 44, and 82% for the 0.9-m media cells, respectively. Overall, nitrogen reduction was poor owing to suspected export of nitrate from the fertilizer use, and phosphorus removal was hampered because of irreducible concentrations in the inflow. Pollutant reduction was limited because the cells were undersized as a result of construction and design errors.}, number={3}, journal={JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING}, author={Brown, Robert A. and Hunt, William F., III}, year={2011}, month={Mar}, pages={132–143} }
 @article{brown_hunt_2011, title={Underdrain Configuration to Enhance Bioretention Exfiltration to Reduce Pollutant Loads}, volume={137}, ISSN={["1943-7870"]}, DOI={10.1061/(asce)ee.1943-7870.0000437}, abstractNote={The bioretention drainage configuration of raising the outlet to create an internal water storage (IWS) layer in the media was originally intended to promote denitrifying conditions. The goal was to reduce nitrate and total nitrogen concentrations in nutrient-sensitive watersheds. Two field studies in the Piedmont region of North Carolina, where the in situ soils typically have high clay content, showed this design feature had potential to enhance exfiltration and reduce drainage from bioretention. Two bioretention cells in Rocky Mount, North Carolina, were monitored for two year-long periods to measure the impact of varying IWS zone depths over sandier underlying soils. Nearly 99% of runoff entering the bioretention cell with sand underlying soil (sand cell) was never directly discharged to the storm water network. However, the hydraulic retention time (contact time) of runoff in the media was less than 3 h, and except for total suspended solids (TSS), minimal pollutant removal was achieved. The other bi...}, number={11}, journal={JOURNAL OF ENVIRONMENTAL ENGINEERING}, author={Brown, R. A. and Hunt, W. F.}, year={2011}, month={Nov}, pages={1082–1091} }
 @article{brown_hunt_2010, title={Impacts of Construction Activity on Bioretention Performance}, volume={15}, ISSN={["1943-5584"]}, DOI={10.1061/(asce)he.1943-5584.0000165}, abstractNote={Bioretention cells are incorporated as part of low impact development (LID) because of their ability to release influent runoff as exfiltration to the soil or evapotranspiration to the atmosphere. However, little care is taken as to the techniques used to excavate bioretention cells, and there is little concern as to the soil-moisture condition during excavation. Certain excavation techniques and soil-moisture conditions create higher levels of compaction which consequently reduce infiltration capacity. Two excavation techniques, the conventional “scoop” method which purposefully smears the underlying soil surface and the “rake” method which uses the teeth of an excavator’s bucket to scarify the underlying soil surface, were tested. Field tests were conducted on three soil types (sand, loamy sand, and clay) under a variety of antecedent soil-moisture conditions. Multiple hydraulic conductivity, surface infiltration, and soil compaction measurements were taken for each excavated condition. In all cases, the rake method of excavation tended to yield more permeable, less compacted soils than the scoop method. The difference of infiltration and hydraulic conductivity between the two excavation techniques was statistically significant (p<0.05) when tests were conducted in wet soil conditions. Also, the infiltration rate at the clay site was significantly lower (p<0.05), and the hydraulic conductivity at the sandy site was significantly lower (p<0.05) when the scoop methodology was used. Based on results of the experiment and because essentially no extra cost is associated with the rake method of excavation, it is recommended over the conventional scoop method. Another recommendation is to excavate under relatively dry soil conditions. The use of the rake method under dry soil conditions is expected to increase long-term exfiltration from bioretention cells.}, number={6}, journal={JOURNAL OF HYDROLOGIC ENGINEERING}, author={Brown, Robert A. and Hunt, William F., III}, year={2010}, month={Jun}, pages={386–394} }
 @article{passeport_hunt_line_smith_brown_2009, title={Field Study of the Ability of Two Grassed Bioretention Cells to Reduce Storm-Water Runoff Pollution}, volume={135}, ISSN={["1943-4774"]}, DOI={10.1061/(ASCE)IR.1943-4774.0000006}, abstractNote={Two grassed bioretention cells including internal storage zones (ISZs) were monitored for 16 months in central North Carolina. Each cell had a surface area of 106 m2 and fill media depths were 0.75 and 1.05 m for the north (North) and the south (South) cells, respectively. Asphalt parking lot inflow and outflows were analyzed for nitrogen and phosphorus forms and fecal coliform (FC). Outflow volumes and peak flows for individual storms were generally less than those of inflow. Overall, except for N O2,3 –N , effluent nitrogen species event mean concentrations (EMCs) and loads were significantly (α=0.05) lower than those of the inflow, and nitrogen species load reductions ranged from 47 to 88%. Apart from fall and winter, during which a longer hydraulic contact time seemed to be needed, the ISZs appeared to improve denitrification. Total phosphorus (TP) and OP O4 -P EMCs were significantly lower than those of the inlet. Reductions were 58% (South) and 63% (North) for TP and 78% (North) and 74% (South) for ...}, number={4}, journal={JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING}, author={Passeport, Elodie and Hunt, William F. and Line, Daniel E. and Smith, Ryan A. and Brown, Robert A.}, year={2009}, pages={505–510} }