Resources
NCSU Stormwater Publications +
NCSU-BAE Assisted Design Chapters of NCDEQ Stormwater Design Manual
Dr. Hunt and his colleagues assist North Carolina Department of Environmental Quality (NCDEQ) personnel with the crafting of the state’s Stormwater Design Manual. For the entire manual, please click here.
Here are the specific links to chapters that have been heavily influenced by NCSU-BAE personnel:
Extension Fact Sheets, Guidebooks & Design Bulletins +
Urban Waterways Series (Stormwater Control Measure Design & Maintenance Bulletins)
- Mosquito Control for Rainwater Harvesting Systems (2021)
- Rainwater Harvesting: Guidance for Homeowners (2008/ rev. 2021)
- Mosquito Control for Stormwater Facilities (2005/ rev. 2020)
- Swale Terminology for Urban Stormwater Treatment (2020)
- Plant Selection for Infiltrating Wet Ponds (2020)
- Designing Dry Swales (2016)
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Select Legacy Factsheets/ Bulletins
- Dune Infiltration Systems for Reducing Stormwater Discharge to Coastal Recreational Beaches (2013)
- Stormwater Wetlands for Golf Courses (2012)
- Permeable Pavement Maintenance (2011)
- Ecosystem Services of Stormwater Wetlands (2011)
- Stormwater Wetland Construction Guidance (2010)
- Level Spreader – VFS Research (2010)
- Internal Water Storage (IWS) for Bioretention (2009)
- Water Harvesting Rooftop Runoff Water Quality (2009)
- Permeable Pavement: Research Update & Design Implications (2008)
- Selecting a Pump for Rainwater Harvesting Systems (2008)
- Stormwater Wetland Design Update (2007)
- Stormwater Wetland and Wet Pond Maintenance (2006)
- Bioretention Performance, Design, and Construction and Maintenance (2006)
- Stormwater Management for Coastal Homeowners (2003)
Other Guidebooks and Factsheets
Referred Journal Articles +
Bacteria and Stormwater
Bioretention
Climate Change, Carbon Sequestration & Ecosystem Services
Green Roofs
Level Spreaders, Vegetated Filter Strips & Swales
Low Impact Development & SCMs/BMPs in Series
Maintenance and Installation of SCMs/BMPs
Metrics and Nomenclature for SCM/BMP Evaluation
Permeable Pavement & Pervious Friction Course Overlays
Rainwater Harvesting
Roadway Runoff Characterization and Treatment
Runoff and Watershed/Catchment Characterization
SCMs/BMPs and Modeling
Stormwater Wetlands & Wet Ponds
Thermal Pollution & Mitigation
Bioretention
Climate Change, Carbon Sequestration & Ecosystem Services
Green Roofs
Level Spreaders, Vegetated Filter Strips & Swales
Low Impact Development & SCMs/BMPs in Series
Maintenance and Installation of SCMs/BMPs
Metrics and Nomenclature for SCM/BMP Evaluation
Permeable Pavement & Pervious Friction Course Overlays
Rainwater Harvesting
Roadway Runoff Characterization and Treatment
Runoff and Watershed/Catchment Characterization
SCMs/BMPs and Modeling
Stormwater Wetlands & Wet Ponds
Thermal Pollution & Mitigation
Bacteria and Stormwater
- The intra-event characteristics of total suspended solids (TSS) and three types of fecal indicator bacteria (FIB), fecal coliform, E. coli, and enterococci, were analysed for a watershed in this study to detect the presence of pathogens. FIB showed higher variability than TSS among intra-event characteristics, such as normalized peak concentration, rate of change, and normalized concentration, in the first 3 mm of rainfall, but similar variability in concentrations throughout each storm. FIB intra-event statistics were mostly affected by climate variables, whereas TSS intra-event statistics were mostly affected by hydrologic variables.
- Autosamplers are used to monitor water quality and create large sets of data with minimal efforts. The extent to which autosamplers can be utilized for microbial monitoring is largely unknown due to concerns over contamination. Strict sterilization regimes for components contacting the water being sampled are difficult, and sometimes logistically implausible, when utilizing autosamplers.
- Data from Raleigh and Durham, North Carolina, suggest the ratio of E. coli to fecal coliform (EC/FC) varies significantly by season throughout the year (p<0.05). These seasonal differences are not accounted for in most translator equations, which assume a single linear relationship between E. coli and fecal coliform regardless of season.
- Two experimental Dune Infiltration Systems were installed beneath sand dunes to divert stormwater from two existing beach outfalls into subsurface chambers for temporary storage and infiltration into the existing sand dunes. A 3-year study examined the long-term performance of the two systems including enterococci treatment.
- A study of five urbanized catchments monitored for pathogen indicator bacteria. Variations in TSS concentration between rain events were related to hydrologic parameters (mostly rainfall intensities), while E. coli was observed to be influenced by mainly climatic factors, and less so by rainfall intensity.
- Two stormwater wet ponds, two bioretention cells, and two stormwater wetlands in a sandy, coastal watershed were monitored for bacteria E. coli and enterococci concentration reduction. Results demonstrated 70 and 98% reductions for the two wet ponds and a bioretention cell with a 60-cm-deep fill media, while the other practices demonstrated poor or negative reductions.
- Two adjacent bioretention areas were studied, one with 60 cm of fill soil and one with 25 cm of fill soil. The 60 cm fill cell showed reductions of 70% and 89% for E. coli and enterococci, respectively, while the 25 cm fill cell showed reductions of -119% and -102% for E. coli and enterococci, respectively.
- Two dune infiltration systems systems were designed to divert storm water runoff from 1.9 ha and 3.2 ha watersheds into the beach dunes. The systems captured 95% of the total runoff volume over 25 monitored storms and groundwater fecal coliform and enterococci concentrations were statistically similar to preconstruction levels (p<0.05).
- Indicator bacteria concentrations in both the water and sediment of a CSW were evaluated at multiple locations. Results suggested that fecal coliform concentrations in stormwater runoff decrease through the system, with relatively consistent concentrations noted throughout the second half of the wetland.
- Data were evaluated to determine if a first flush effect was present for indicator bacteria and TSS in stormwater runoff. Analyses suggested there was a significant first flush effect for fecal coliform and TSS, although the first flush effect for fecal coliform was relatively weak. For E. coli and enterococci, no significant first flush effect was noted.
- Samples were compared based on seasonality and were found to be statistically different (p<0.05), with pairwise comparisons indicating significantly lower concentrations of E. coli and fecal coliform during the winter (p<0.05). Enterococci concentrations were substantially lower in the winter and fall, but no significant differences were found between seasons during pairwise comparisons (p<0.05).
- Sand columns were loaded over a 60-day period with either bacteria-free storm water or storm water spiked with Escherichia coli. The seepage rate for the bacteria-spiked storm-water treatment was significantly lower (p<0.05) than the seepage rate of the bacteria-free treatment, particularly toward the end of the study. Bacteria application likely compounds the impact of sediment clogging at the sand/storm-water interface.
- A study monitored nine storm-water BMPs (one wet pond, two storm-water wetlands, two dry detention basins, one bioretention area, and three proprietary devices) for fecal coliform and Escherichia coli (E. coli). A wet pond, two wetlands, a bioretention area, and a proprietary device all removed fecal coliform with an efficiency higher than 50%; however, only the wetlands and bioretention area had significantly different influent and effluent concentrations (p<0.05). For E. coli, only one of the wetlands and the bioretention area provided a concentration reduction greater than 50%, both of which had a significant difference in influent and effluent concentrations (p<0.05).
Bioretention
- 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 exceeded environmental thresholds and phosphorus concentrations 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.
- Three bioretention cells constructed in low permeability soils in northeast Ohio were monitored for non-winter quantification of inflow, drainage, ET, and exfiltration. The inclusion of an internal water storage (IWS) zone allowed the three cells to reduce runoff by 59%, 42%, and 36% over the monitoring period, in spite of the tight underlying soils.
- In a joint project between two agencies in Singapore, the National Parks Board and the National University of Singapore—Singapore Delft Water Alliance, more than 30 plants species were screened and tested to select those that are suitable for application as vegetation in bioretention systems. The research project investigated the remediation capacity of the plants and their associated rhizosphere microbial communities.
- World-wide implementation of stormwater treatment practices is increasing. These are integral to Water Sensitive Urban Design (WSUD).
- Runoff was routed through the root-soil matrix of two Silva Cell™ systems for detention and treatment. At one retrofit, 80% of runoff was treated by the system and all nutrient, sediment and heavy metals concentrations decreased significantly at both retrofit sites.
- A paired study examining the impacts of SCM retrofits on the hydrology of a small urban drainage area. These included a bioretention cell, four permeable pavement parking stalls, and a tree filter device within a public right-of-way.
- Data from downscaled climate projections for 2055 through 2058 were utilized in these models to evaluate changes in system hydrologic function under two climate change scenarios (RCP 4.5 and 8.5). Results suggest substantial additional storage is required to ameliorate the effect of climate change.
- Twelve rain gardens were constructed to analyze the effectiveness of three different filter bed substrates to support plant growth and remove nutrients from urban stormwater runoff. Overall, all three substrates functioned in reducing the quantity of pollutants in urban stormwater runoff; yet, the impact of substrate on remediation appeared to lessen by Season 2 because there were few differences between substrate in the effluent nutrient concentration.
- This study examines the influence that previous events have on outflow concentrations by analyzing flow-weighted composite samples from four to six consecutive events during three different seasons for two sets of field-monitored bioretention cells. As a means to analyze performance from consecutive events, the evolution of cumulative pollutant loads was presented by plotting cumulative load versus cumulative volume.
- DRAINMOD, a widely-accepted agricultural drainage model, was used to simulate the hydrologic response of runoff entering a bioretention cell. Detailed hydrologic measurements were collected from two bioretention field sites to calibrate and test the model.
- Two infiltrating low-impact development (LID) practices configured in-series, pervious concrete and bioretention (PC-B), were monitored for 17 months. The large outflow reduction 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.
- 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.
- This study compiles work from three research sites in three states to provide some fundamental underpinnings to bioretention design. Although all sites demonstrate different levels of performance, water volumetric performance trends, related to available media porosity and storage in the surface bowl, are common to all.
- The purpose of this manuscript is to synthesize research to recommend a suite of design standards focused on the purpose of bioretention SCM. Both hydrologic (peak flow mitigation, infiltration, annual hydrology, and stream stability) and water quality [total suspended solids (TSS) and particulates, pathogen-indicator species, metals, hydrocarbons, phosphorus, nitrogen, and temperature] regulatory and stream ecology needs are addressed.
- Forty-three bioretention cells (BRCs) throughout North Carolina were assessed for maintenance needs, soil media composition, and as-built surface storage volume to determine whether BRCs are typically constructed per their intended design specifications. Evaluations were done using a combination of visual inspections, particle-size distribution and soil media permeability measurements, topographic surveys, and field drawdown tests.
- Two adjacent bioretention areas were studied, one with 60 cm of fill soil and one with 25 cm of fill soil. The 60 cm fill cell showed reductions of 70% and 89% for E. coli and enterococci, respectively, while the 25 cm fill cell showed reductions of -119% and -102% for E. coli and enterococci, respectively.
- Two bioretentionc cells with different underlying soils were compared. Nearly 99% of runoff entering the bioretention cell with sand underlying soil (sand cell) was never directly discharged to the stormwater 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 bioretention cell had a sandy clay loam underlying soil (SCL cell); the percentage of runoff leaving via exfiltration and evapotranspiration from this cell was 87% during the monitoring period with a 1.03 m IWS zone depth and 75% when the depth was 0.73 m. For events monitored with drainage from the SCL cell, efficiency ratios of all the nitrogen species and TSS exceeded 0.5.
- This study analyzes influent and effluent total nitrogen (TN) and total phosphorous (TP) concentrations from 11 bioretention cells in the mid-Atlantic United States. Pooled data showed only a slight association between influent and effluent TN. Essentially no relationship exists between influent and effluent TP concentration.
- Two grassed bioretention cells, one full-size and one undersized, were constructed in the easement of a bridge deck. During 13 months of data collection, the large cell’s median effluent concentrations and loads were less than those from the small cell. The small cell’s TN and TSS load reductions were 84 and 50%, respectively, of those achieved by the large cell, with both cells significantly reducing TN and TSS. TP loads were not significantly reduced by either cell, likely due to low TP concentrations in the highway runoff which may have approached irreducible levels.
- Two sets of loamy-sand-filled bioretention cells of two media depths (0.6 m and 0.9 m) 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 and 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.
- Streamflow from three small, nonurban watersheds was compared with bioretention outflow from four cells. After normalizing the flow rates and volumes by watershed size, results indicate that there is no statistical difference between flow rates in streams draining undeveloped watersheds and bioretention outflow rates for the first 24 h following the commencement of flow and no difference between cumulative volumes released by the two systems during the 48 h following the start of flow.
- 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. In all cases, the rake method of excavation tended to yield more permeable, less compacted soils than the scoop method.
- Four bioretention areas were monitored during the summers of 2006 and 2007. It was found that smaller bioretention areas, with respect to the size of their contributing watershed, were able to significantly reduce both maximum and median water temperatures between the inlet and outlet. The proportionately larger bioretention areas were only able to significantly reduce maximum water temperatures between the inlet and outlet; however, these systems showed evidence of substantial reductions in outflow quantity, effectively reducing the thermal impact.
- Two grassed bioretention cells including internal storage zones (ISZs) were monitored for 16 months. 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). When considering effluent concentrations in addition to removal rates, the grassed cells showed promising results for FC and nutrient pollution abatement when compared to previously studied conventionally vegetated bioretention (trees, shrubs, and mulch).
- This study investigated hydrologic performance at six bioretention cells. A large cell media volume: drainage area ratio, and adjustments to the drainage configuration appear to improve the performance. Media layer depth may be the primary design parameter controlling hydrologic performance.
- The assessment consisted of monitoring inflow, outflow, and on-site rainfall for at least 13 storm events. All samples were analyzed for solids, turbidity, and nitrogen and phosphorus forms and selected samples were analyzed for metals. The level spreader-grass filter strip had the best overall efficiency with load reduction efficiencies in all pollutants ranging from 24 to 83% and the highest reduction for total suspended solids (TSS).
- Limited research suggests that bioretention can effectively manage other pollutants, such as pathogenic bacteria and thermal pollution, as well. Reductions in pollutant load result from the combination of concentration reduction and runoff volume attenuation, linking water quality and hydrologic performance. Nonetheless, many design questions persist for this practice, such as maximum pooling bowl depth, minimum fill media depth, fill media composition and configuration, underdrain configuration, pretreatment options, and vegetation selection.
- A bioretention cell in an urban setting was examined. Flow-weighted, composite water quality samples were collected for 23 events and analyzed for TKN, NH4-NNH4-N, NO2-3-NNO2-3-N, TP, TSS, BOD-5, Cu, Zn, Fe, and Pb. Grab samples were collected from 19 storms for fecal coliform and 14 events for Escherichia coli (E. coli). Results indicated that in an urban environment, bioretention systems can reduce concentrations of most target pollutants, including pathogenic bacteria indicator species. Additionally, bioretention can effectively reduce peak runoff from small to midsize storm events.
- The field studies confirmed high annual total nitrogen mass removal rates at two conventionally drained bioretention cells (40% reduction each). Nitrate-nitrogen mass removal rates varied between 75 and 13%, and calculated annual mass removal of zinc, copper, and lead from one Greensboro cell were 98, 99, and 81%, respectively. All high mass removal rates were due to a substantial decrease in outflow volume.
- A Filterra biofiltration unit was installed and monitored in Fayetteville, North Carolina for its effect on water quality. A Filterra unit is a box filter combining high-flow engineered media with potential for biological treatment from a planted tree. The device proved to significantly reduce event mean concentrations and total loadings of sediment, nutrients, and zinc.
- Two stormwater management practices, impervious cover limits and pollutant-load regulations, were compared in a nutrient-sensitive watershed. Hydrology and water quality were monitored pre and post development to quantify changes to stormwater volumes, pollutant concentrations, and annual export loading rates.
Climate Change, Carbon Sequestration & Ecosystem Services
- Data from downscaled climate projections for 2055 through 2058 were utilized in these models to evaluate changes in system hydrologic function under two climate change scenarios (RCP 4.5 and 8.5). Results suggest substantial additional storage is required to ameliorate the effect of climate change.
- Carbon density of North Carolina highway stormwater control measures were studied. Piedmont VFS/VSs sequestered C at a rate of 0.09 kg C/m2/yr (segmented model) and wetland swales were found to have higher carbon density than dry swales.
- A framework for predicting carbon emissions attributable to SCMs and conveyances were applied to present a comparison of the carbon footprint of eight common SCMs and three stormwater conveyance types. The carbon embodied in construction materials represented a prominent part of the carbon footprint for green roofs, permeable pavement, sand filters, rainwater harvesting systems, and reinforced concrete pipes while material transport and construction dominated that of bioretention systems, ponds, wetlands, level spreader-grassed filter strips and concrete-lined swales.
- A comparison of the abilities of 20 wet ponds and 20 constructed stormwater wetlands to provide ecosystem services including carbon sequestration, biodiversity, and cultural services.
Green Roofs
- Despite substantial performance evidence in the literature, the lack of a curve number (CN) or volumetric runoff coefficient (Cv) to apply to prescribed methodologies for planning and regulatory submissions may be perceived as a barrier for implementation. Paired rainfall–runoff data were analyzed for up to 21 living roofs with varying configurations and in different climates from studies identified in the literature and previously-unpublished data.
- The hydrologic and water quality performance of two extensive green roofs were investigated: a flat 70 m2 area with an average media depth of 75 mm, and a 3% pitch 27 m2 surface area roof with an average media depth of 100 mm. Each green roof retained a significant (p < 0.05) proportion of the rainfall observed, 64% of the total rainfall measured at each site, however it was determined that the media, composed of 15% compost, was leaching TN and TP into the green roof outflow.
- This study evaluates the long term performance of bioretention cells. Nitrogen and phosphorous discharge concentrations were recorded post-construction and after 17 years of treatment. Mass load reductions of both nitrogen and phosphorous were found to have increased after 17 years of treatment. The top portion of soil in the media within the bio retention cell was near its phosphorous saturation quantity, however, the remaining filter media at lower depths is still capable of providing treatment. Bioretention cells proved to provide lasting treatment of stormwater runoff.
Level Spreaders, Vegetated Filter Strips & Swales
- Four paired residential downspout disconnection sites were studied to quantify volume and peak flow reduction. For each site, the performance of disconnected downspouts discharging water over existing lawn was compared for three varying factors: slope of lawn, length of run over lawn, and proportion of contributing roof area to receiving lawn area.
- Carbon density of North Carolina highway stormwater control measures were studied. Piedmont VFS/VSs sequestered C at a rate of 0.09 kg C/m2/yr (segmented model) and wetland swales were found to have higher carbon density than dry swales.
- The purpose of this study was to determine the runoff volume and pollutant reductions of two vegetated filter strips (VFSs) of 8 m long by 6 m wide, two VFSs of 20 m by 6 m, and a trapezoidal swale with 3:1 side slopes (0.15 m bottom width and 10.4 m long). One VFS of each size was amended with a mixture of sand and ViroPhos, a proprietary phosphorus (P) sorptive aggregate.
- This study examined the quantity and quality of highway runoff at four sites over a 48-km stretch. The highway had a 4-cm overlay of permeable asphalt, known as permeable friction course (PFC), which influenced the export of sediment-bound pollutants. Two vegetative filter strips (VFSs), two traditional dry swales, and two wetland swales were also tested for pollutant removal efficacy at the four highway research sites.
- Two LS-VFS systems draining an urban catchment were monitored, one 7.6 m wide and entirely grassed, the other 15.2 m wide with the first-half grassed and the second-half wooded. Median and maximum storm temperatures were significantly reduced across both the 7.6-m and 15.2-m LS-VFSs. However, median and maximum effluent temperatures for both filter strip lengths were significantly greater than the 21°C trout threshold.
- An assessment of the performance of four level spreader–vegetative filter strip (LS-VFS) systems designed to treat urban storm-water runoff was undertaken at two sites. At each site, a 7.6-m grassed filter strip and a 15.2-m half-grassed, half-forested filter strip were examined. Monitored parameters included rainfall, inflow to, and outflow from each LS-VFS system.
- A 19.4 m long reinforced concrete level spreader upslope of a 900 m2 mixed grass/weed vegetated filter strip was monitored for runoff reduction for 23 precipitation events, only 3 of which produced outflow. The practice treated runoff from a 0.87 ha residential watershed. All events which produced outflow exceeded 40 mm of precipitation and cumulative volume reduction associated with the events was 85%.
- The assessment consisted of monitoring inflow, outflow, and on-site rainfall for at least 13 storm events. All samples were analyzed for solids, turbidity, and nitrogen and phosphorus forms and selected samples were analyzed for metals. The level spreader-grass filter strip had the best overall efficiency with load reduction efficiencies in all pollutants ranging from 24 to 83% and the highest reduction for total suspended solids (TSS).
- 24 level spreaders were evaluated and detailed observations were made at 20 of these locations. The results of the study indicate that level spreaders may not be the versatile structure they are perceived to be. No level spreader-riparian buffer system was able to provide diffuse flow through the riparian buffer from the level spreader to the stream.
Low Impact Development & SCMs/BMPs in Series
- Four paired residential downspout disconnection sites were studied to quantify volume and peak flow reduction. For each site, the performance of disconnected downspouts discharging water over existing lawn was compared for three varying factors: slope of lawn, length of run over lawn, and proportion of contributing roof area to receiving lawn area.
- In this study, a conventional development (centralized stormwater management) and an adjoining infiltration-based LID commercial site were compared with respect to hydrology and water quality. The LID site consisted of an aboveground cistern used for indoor toilet flushing, two underground cisterns used for landscape irrigation, and an underground detention system, which overflowed into a series of infiltration galleries beneath the parking lot of the shopping center.
- This paired watershed study evaluated the impacts of multiple SCM retrofits on water quality at a catchment scale in a 0.53 ha urban residential drainage area with sand underlying soils. An in-street bioretention cell (BRC) retrofit, four permeable pavement parking stalls, and a tree filter device were installed, after which concentrations of total Kjeldahl nitrogen (TKN), total phosphorous (TP), total suspended solids (TSS), copper (Cu), lead (Pb), and zinc (Zn) significantly decreased by 62%, 38%, 82%, 62%, 89%, and 76%, respectively.
- This discussion suggests a more refined means of evaluating cognate conditions for SCMs in terms of hydrology and effluent water quality by discretizing SCM discharge into three pathways: runoff, shallow interflow, and groundwater surge. Preliminary evidence using deuterium isotopes from bioretention outflow supports this concept, and future research routes are suggested.
- This study used previously established unit critical discharges, annual allowable erosional hours, and annual allowable volume of eroded bed-load standards to evaluate two types of stormwater control measures (SCMs): low-impact development (LID) practices and a large detention SCM (wet pond). Nine initial scenarios modeled in PCSWMM incorporated different combinations to determine the best scenario for reducing stream erosion potential within a highly urbanized watershed.
- Two infiltrating low-impact development (LID) practices configured in-series, pervious concrete and bioretention (PC-B), were monitored for 17 months. The large outflow reduction 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.
- The purpose of this project was to characterize runoff and pollutant export from three commercial sites: one with no storm water control measures, one with a wet detention basin, and one with low impact development (LID) measures. Rainfall, runoff, and pollutant concentrations were monitored at each site for more than one year by using automated rain gauges and samplers.
- This study examined the quantity and quality of highway runoff at four sites over a 48-km stretch. The highway had a 4-cm overlay of permeable asphalt, known as permeable friction course (PFC), which influenced the export of sediment-bound pollutants. Two vegetative filter strips (VFSs), two traditional dry swales, and two wetland swales were also tested for pollutant removal efficacy at the four highway research sites.
- A system of three wetlands “in-series” was built to treat runoff from a highly impervious 30 acre watershed. The configuration of the wetlands allowed monitoring of water quality parameters at the outlet of each of the three stormwater wetlands. The results of this study indicate that water quality improvement for a number of pollutants experiences diminishing returns as it passes through the three wetland cells.
- Green streets are used to help mitigate stormwater runoff, however, they can also be used to help mitigate air pollution. By strategically placing green streets and by choosing plants that specifically disperse pollutants, green streets can reduce particulate matter concentrations and improve air quality.
- Regenerative stormwater conveyance (RSC) is a form of low-impact development (LID) stormwater control measures (SCMs). This study analyzes the hydrologic and water quality efficiencies of such a system. The RSC under investigation proved to be useful in stormwater runoff mitigation by drastically decreasing surface flow and allowing for filtered water to seep out at slower rates than conventional conveyance channels.
- A regenerative stormwater conveyance system was installed in an eroded channel and monitored for 14 months. There were small reductions in event mean concentrations of total suspended sediment, total phosphorous, and total nitrogen as well as an overall increase in the mass loading of nitrogen.
- An experimental regenerative stormwater conveyance (RSC) system was installed and subjected to simulated hydrographs. Dissolved nitrogen and phosphorous were mixed with inflow from a managed retention pond. Results proved that RSCs can significantly reduce surface flow, but have little impact on dissolved pollutant concentrations. Subsurface concentrations, however, experienced a large reduction in TKN and orthophosphate.
Maintenance and Installation of SCMs/BMPs
- ASTM standard methods may be used to measure permeable pavement IR; however, these tests can take hours to complete and require infiltrometers not readily available to maintenance contractors. A simple infiltration test (SIT) has been devised which (1) is conducted using easily acquired materials, (2) has a larger surface area (i.e., more representative of average pavement conditions), and (3) requires, on average, 72% less time to conduct than the ASTM test.
- Key maintenance needs for wet ponds, constructed stormwater wetlands, bioretention, infiltration practices, permeable pavement, swales, and rainwater harvesting systems are reviewed with many tasks, such as the cleaning of pre-treatment areas and the preservation of infiltration surfaces, being common maintenance themes among SCMs. Consequences of lacking maintenance are illustrated (mainly insufficient function or failure).
- This paper presents implementation and maintenance considerations developed based on the monitoring of three full-scale ponds retrofitted with FTWs. Results suggest that the size and relative surface cover of the FTW, the relative root depth, and the capability of the plants to tolerate periodic anaerobic conditions are crucial factors to promote good removal across a spectrum of pollutants.
- In a joint project between two agencies in Singapore, the National Parks Board and the National University of Singapore—Singapore Delft Water Alliance, more than 30 plants species were screened and tested to select those that are suitable for application as vegetation in bioretention systems. The research project investigated the remediation capacity of the plants and their associated rhizosphere microbial communities.
- World-wide implementation of stormwater treatment practices is increasing. These are integral to Water Sensitive Urban Design (WSUD).
- Previous studies have not shown whether rainfall patterns in North Carolina and other east coast United States states justify a 2-day drawdown rate of the water quality event to limit the annual average overflow volume to 10% for detention-based stormwater control measures. To investigate this, rainfall patterns in Raleigh, North Carolina, were evaluated from Years 2001 to 2010 to determine the fraction of untreated overflow that would result from various design configurations and their associated drawdown periods.
- Effective maintenance techniques are needed to ensure the hydraulic functionality and water quality benefits of permeable pavements. Eight different small-scale and full-scale maintenance techniques aimed at recovering pavement permeability were evaluated at ten different permeable pavement sites.
- The specific objective of this research was to investigate the effects that wetland maturation and lack of maintenance have on the ability of a 5-year-old CSW to mitigate hydrology and improve water quality. A CSW was monitored from 2012–2013 that had not been maintained since construction in the spring of 2007.
- The fraction of the volume associated with vegetation mass was unknown and designers have been unsure as to (1) how they should account for volume occupied by vegetation and (2) whether this was a significant design issue. Twelve storm water wetlands and one hybrid wet pond were sampled to assess their percent vegetative occupancy by volume.
- 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.
- This technical note presents a stormwater management perspective of the strategy of plant harvesting at the water surface to remove nutrients that would otherwise be deposited back into the wetland during senescence. Vegetation was harvested from two stormwater wetlands to evaluate the ability of five wetland plant species to sequester nitrogen.
- Forty-three bioretention cells (BRCs) throughout North Carolina were assessed for maintenance needs, soil media composition, and as-built surface storage volume to determine whether BRCs are typically constructed per their intended design specifications. Evaluations were done using a combination of visual inspections, particle-size distribution and soil media permeability measurements, topographic surveys, and field drawdown tests.
- Wetlands can become the very mosquito breeding grounds if they are allowed to become monocultures of specific mosquito-protective plants, such as Typha spp. (commonly referred to as cattails in the United States). Wetlands also fail frequently if the water level becomes too deep due to construction error or clogging of the outlet structure.
- To test for the potential toxicity of forebay spoils, 30 stormwater wetland and wetpond forebays of varying age, size, and upstream landuse were sampled across North Carolina and analyzed for seven metals: cadmium, chromium, copper, iron, lead, nickel, and zinc. Ten of 30 sites were also sampled near the outlet structures for spatial comparison of settled sediment and pollutant presence. All samples indicated that land application of forebay sediment is unlikely to pose an environmental threat.
- 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. In all cases, the rake method of excavation tended to yield more permeable, less compacted soils than the scoop method.
- The surface infiltration rates of 40 permeable pavement sites were tested in North Carolina, Maryland, Virginia, and Delaware. Two surface infiltration tests (pre- and postmaintenance) were performed on 15 concrete grid paver lots filled with sand. Maintenance was simulated by removing the top layer of residual material (13–19 mm).
Metrics & Nomenclature for BMP/SCM Evaluation
- ASTM standard methods may be used to measure permeable pavement IR; however, these tests can take hours to complete and require infiltrometers not readily available to maintenance contractors. A simple infiltration test (SIT) has been devised which (1) is conducted using easily acquired materials, (2) has a larger surface area (i.e., more representative of average pavement conditions), and (3) requires, on average, 72% less time to conduct than the ASTM test.
- A research article documenting the history, scope, application and underlying principles of terms used in urban drainage and providing recommendations for clear communication of these principles.
- Metrics for thermal performance of stormwater control measures were reviewed. Event mean temperature, LID, and groundwater temperature metrics appear useful. Thermal load and stream mixing analysis are more data intensive but more defensible. Uniform continuous above threshold metric affords species-specific biotic integrity.
- This study examines the influence that previous events have on outflow concentrations by analyzing flow-weighted composite samples from four to six consecutive events during three different seasons for two sets of field-monitored bioretention cells. As a means to analyze performance from consecutive events, the evolution of cumulative pollutant loads was presented by plotting cumulative load versus cumulative volume.
- This discussion suggests a more refined means of evaluating cognate conditions for SCMs in terms of hydrology and effluent water quality by discretizing SCM discharge into three pathways: runoff, shallow interflow, and groundwater surge. Preliminary evidence using deuterium isotopes from bioretention outflow supports this concept, and future research routes are suggested.
- This study used previously established unit critical discharges, annual allowable erosional hours, and annual allowable volume of eroded bed-load standards to evaluate two types of stormwater control measures (SCMs): low-impact development (LID) practices and a large detention SCM (wet pond). Nine initial scenarios modeled in PCSWMM incorporated different combinations to determine the best scenario for reducing stream erosion potential within a highly urbanized watershed.
- A comparison of the abilities of 20 wet ponds and 20 constructed stormwater wetlands to provide ecosystem services including carbon sequestration, biodiversity, and cultural services.
- To investigate the potential temporal mismatch between nutrient-sensitive periods in receiving water bodies and average annual reporting periods adopted for SCM performance metrics, a case study is presented for four SCM types (constructed stormwater wetlands, bioretention, vegetated filter strips, and swales). Outbreaks of harmful algal blooms (HABs) have been related to different nutrient forms at different times of the year, resulting in a “window” of importance for a given nutrient.
- The d65 substrate size, pattern, profile, and dimension of 33 reference stream cross-sections in Piedmont North Carolina were modeled using the continuous simulations program, SWMM, to develop (1) a unit critical discharge metric, (2) allowable annual erosional hour standard, and (3) allowable volume of eroded bedload standard for watersheds containing SCMs discharging into surface waters. These standards represented benchmarks of stable, naturally eroding reference streams.
- In this study, a storm-water wetland constructed and monitored in the coastal plain of North Carolina is evaluated for water quality and hydrologic performance using four different metrics: concentration reduction, load reduction, comparison to nearby ambient water quality monitoring stations, and comparison to other wetlands studied in North Carolina. Results discouraged sole reliance on a concentration reduction metric.
- 193 ambient water quality monitoring stations were paired with benthic macroinvertebrate health ratings collected in very close proximity. Water quality for the sites ranged from excellent to poor and was divided into three distinct ecoregions: Mountain, Piedmont, and Coastal. Statistically significant relationships were found in one or more ecoregions for dissolved oxygen, fecal coliform, NH3NH3 , NO2−3−NNO2−3−N , total Kjeldahl nitrogen, total nitrogen (TN), and total phosphorus (TP).
Permeable Pavement & Pervious Friction Course Overlays
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- ASTM standard methods may be used to measure permeable pavement IR; however, these tests can take hours to complete and require infiltrometers not readily available to maintenance contractors. A simple infiltration test (SIT) has been devised which (1) is conducted using easily acquired materials, (2) has a larger surface area (i.e., more representative of average pavement conditions), and (3) requires, on average, 72% less time to conduct than the ASTM test.
- This study examined the non-winter water quality performance of two side-by-side permeable pavements in the Ohio snowbelt. Nutrient reduction was similar to past studies—organic nitrogen and particulate phosphorus were removed through filtration and settling, while dissolved constituents received little treatment.
- A paired study examining the impacts of SCM retrofits on the hydrology of a small urban drainage area. These included a bioretention cell, four permeable pavement parking stalls, and a tree filter device within a public right-of-way.
- Effective maintenance techniques are needed to ensure the hydraulic functionality and water quality benefits of permeable pavements. Eight different small-scale and full-scale maintenance techniques aimed at recovering pavement permeability were evaluated at ten different permeable pavement sites.
- A newly constructed permeable interlocking concrete paver (PICP) parking lot was monitored for 1 year in the mountain region of North Carolina to quantify runoff reduction, temperature buffering, and thermal load export. The effects on hydrology caused by internal water storage (IWS) in the pavement profile were also investigated by dividing the lot into three cells with varying aggregate depths and drainage configurations.
- Two infiltrating low-impact development (LID) practices configured in-series, pervious concrete and bioretention (PC-B), were monitored for 17 months. The large outflow reduction 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.
- This paper presents water quality measurements for PFC and conventional pavement collected over six years near Austin, TX and two years in eastern North Carolina. The data show that concentrations of total suspended solids from PFC are more than 90% lower than from conventional pavement.
- This study examined the quantity and quality of highway runoff at four sites over a 48-km stretch. The highway had a 4-cm overlay of permeable asphalt, known as permeable friction course (PFC), which influenced the export of sediment-bound pollutants. Two vegetative filter strips (VFSs), two traditional dry swales, and two wetland swales were also tested for pollutant removal efficacy at the four highway research sites.
- A 1 year-old parking lot was monitored for water quality differences among four permeable pavement sections: pervious concrete (PC), two different types of permeable interlocking concrete pavement (PICP) with small-sized aggregate in the joints and having 12.9% (PICP1) and 8.5% (PICP2) open surface area, and concrete grid pavers (CGP) filled with sand. The site was located in poorly drained soils, and all permeable sections were underlain by a crushed stone base with a perforated pipe underdrain.
- Four types of permeable pavement and standard asphalt were monitored for hydrologic differences in pavement surface runoff volumes, total outflow volumes, peak flow rates, and time to peak. The four permeable sections were pervious concrete (PC), two types of permeable interlocking concrete pavement (PICP) with small-sized aggregate in the joints and having 12.9% (PICP1) and 8.5% (PICP2) open surface area, and concrete grid pavers (CGP) filled with sand. The site was located in poorly drained soils, and all permeable sections were underlain by a crushed stone base layer with a perforated underdrain.
- Four permeable pavement applications were constructed and monitored to determine their effectiveness of reducing runoff quantity and improving water quality. Sites were either constructed of permeable interlocking concrete pavers (2), porous concrete (1), or concrete grid pavers (1). One site of each pavement type was monitored for runoff reduction for periods ranging from 10 to 26 months.
- The surface infiltration rates of 40 permeable pavement sites were tested in North Carolina, Maryland, Virginia, and Delaware. Two surface infiltration tests (pre- and postmaintenance) were performed on 15 concrete grid paver lots filled with sand. Maintenance was simulated by removing the top layer of residual material (13–19 mm).
- A permeable pavement over a low conductivity, low permeability, clay soil was monitored for one year. The site used an elevated underdrain to increase exfiltration and evaporation and, therefore, reduce the total influent runoff volume. The permeable pavement proved to produce significantly less event mean concentrations (EMCs) of allpollutantsexceptnitrate,which was significantly higher. Nitrogen species may have increased due to the possibility of denitrification occurring in the internal water storage zone (IWS). The use of permeable pavements over less permeable soils can significantly improve long term hydrology and water quality.
- Four permeable pavements over low permeability soils were monitored for their hydrologic performance. All four utilized internal water storage. Peak flow was substantially reduced in the majority of storm events as was volume. Permeable pavements proved to be successful in bettering water quality even over low permeability soils.
Rainwater Harvesting
- Two novel approaches were implemented to improve the ability of RWH systems to serve as both water-conservation practices and stormwater-management practices. The passive release mechanism divided the storage tank into a detention storage volume that was slowly drained between storm events, and a retention storage volume, which was retained for harvesting. The active release mechanism automatically released harvested water based on real-time forecasted precipitation and current RWH system conditions.
- Collecting and storing runoff via RWH systems can potentially provide water quality benefits due to physical and chemical processes that occur within the storage tank. This study quantified the water quality improvement provided by storing rooftop runoff via RWH systems at four sites.
- A 57,900-liter RWH tank used for landscape irrigation was monitored to determine influent and effluent water quality. Samples were analyzed for total nitrogen, total phosphorus, total Kjeldahl nitrogen (TKN), total ammoniacal nitrogen (TAN), nitrite-nitrate (NOX), orthophosphate (Ortho-P) and total suspended solids (TSS).
- The objectives of this study were twofold: (1) present usage characteristics and performance results for four RWH systems installed in humid North Carolina (NC) as compared with systems located in arid/semiarid regions and (2) identify system benefits and modifications that could help improve the performance of RWH systems installed in humid regions of the world.
- A monitoring study was conducted at three rainwater cistern, a computer model was developed to simulate system performance, and simulations were conducted for 208 l rain barrels and larger cisterns. Results of the monitoring study showed that the rainwater harvesting systems were underutilized, which was suspected to result from poor estimation of water usage and public perception of the harvested rainwater.
Roadway Runoff Characterization and Treatment
- Roadside soils were found to have low plant-available zinc and copper concentrations. Metals do not appear to adversely affect plants in roadside environments, and traffic volume and site age may be better predictors of metal pollution than traffic volume alone.
- Runoff was routed through the root-soil matrix of two Silva Cell™ systems for detention and treatment. At one retrofit, 80% of runoff was treated by the system and all nutrient, sediment and heavy metals concentrations decreased significantly at both retrofit sites.
- A paired study examining the impacts of SCM retrofits on the hydrology of a small urban drainage area. These included a bioretention cell, four permeable pavement parking stalls, and a tree filter device within a public right-of-way.
- This paired watershed study evaluated the impacts of multiple SCM retrofits on water quality at a catchment scale in a 0.53 ha urban residential drainage area with sand underlying soils. An in-street bioretention cell (BRC) retrofit, four permeable pavement parking stalls, and a tree filter device were installed, after which concentrations of total Kjeldahl nitrogen (TKN), total phosphorous (TP), total suspended solids (TSS), copper (Cu), lead (Pb), and zinc (Zn) significantly decreased by 62%, 38%, 82%, 62%, 89%, and 76%, respectively.
- This study compared bridge runoff concentrations of nutrients, sediment, and heavy metals to effluent concentrations from six commonly used SCMs. Runoff quality samples from 15 bridges were collected and compared to those from 41 different SCMs.
- Carbon density of North Carolina highway stormwater control measures were studied. Piedmont VFS/VSs sequestered C at a rate of 0.09 kg C/m2/yr (segmented model) and wetland swales were found to have higher carbon density than dry swales.
- This paper presents water quality measurements for PFC and conventional pavement collected over six years near Austin, TX and two years in eastern North Carolina. The data show that concentrations of total suspended solids from PFC are more than 90% lower than from conventional pavement.
- This study examined the quantity and quality of highway runoff at four sites over a 48-km stretch. The highway had a 4-cm overlay of permeable asphalt, known as permeable friction course (PFC), which influenced the export of sediment-bound pollutants. Two vegetative filter strips (VFSs), two traditional dry swales, and two wetland swales were also tested for pollutant removal efficacy at the four highway research sites.
- Two grassed bioretention cells, one full-size and one undersized, were constructed in the easement of a bridge deck. During 13 months of data collection, the large cell’s median effluent concentrations and loads were less than those from the small cell. The small cell’s TN and TSS load reductions were 84 and 50%, respectively, of those achieved by the large cell, with both cells significantly reducing TN and TSS. TP loads were not significantly reduced by either cell, likely due to low TP concentrations in the highway runoff which may have approached irreducible levels.
- The assessment consisted of monitoring inflow, outflow, and on-site rainfall for at least 13 storm events. All samples were analyzed for solids, turbidity, and nitrogen and phosphorus forms and selected samples were analyzed for metals. The level spreader-grass filter strip had the best overall efficiency with load reduction efficiencies in all pollutants ranging from 24 to 83% and the highest reduction for total suspended solids (TSS).
Runoff & Watershed/Catchment Characterization
- In this study, six diverse catchments in two continents are evaluated for thermal dynamics. This study is the first to identify a runoff temperature first flush, and highlights the need to carefully consider the appropriate methodology for such analyses.
- Previous studies have not shown whether rainfall patterns in North Carolina and other east coast United States states justify a 2-day drawdown rate of the water quality event to limit the annual average overflow volume to 10% for detention-based stormwater control measures. To investigate this, rainfall patterns in Raleigh, North Carolina, were evaluated from Years 2001 to 2010 to determine the fraction of untreated overflow that would result from various design configurations and their associated drawdown periods.
- This discussion suggests a more refined means of evaluating cognate conditions for SCMs in terms of hydrology and effluent water quality by discretizing SCM discharge into three pathways: runoff, shallow interflow, and groundwater surge. Preliminary evidence using deuterium isotopes from bioretention outflow supports this concept, and future research routes are suggested.
- The objectives of this study were twofold: (1) present usage characteristics and performance results for four RWH systems installed in humid North Carolina (NC) as compared with systems located in arid/semiarid regions and (2) identify system benefits and modifications that could help improve the performance of RWH systems installed in humid regions of the world.
- A year-long study of 36 storm events at two catchments (one primarily impermeable and the other substantially wooded) to evaluate the first flush effect (the assumption that the initial portion of a rainfall-runoff event is more polluted than the later portions) for total suspended solids and various nutrient species. On average, most pollutants exhibited a slight first flush effect, but substantial pollutant loading still occurred in the latter portion of the storm’s total runoff volume.
- To investigate the potential temporal mismatch between nutrient-sensitive periods in receiving water bodies and average annual reporting periods adopted for SCM performance metrics, a case study is presented for four SCM types (constructed stormwater wetlands, bioretention, vegetated filter strips, and swales). Outbreaks of harmful algal blooms (HABs) have been related to different nutrient forms at different times of the year, resulting in a “window” of importance for a given nutrient.
- Research on stormwater control measures (SCMs) has shown that meeting the 21°C trout threshold is not consistently feasible with current SCM technologies. Thus, it is important to consider other factors in storm water temperature management, such as catchment characteristics.
- Data were evaluated to determine if a first flush effect was present for indicator bacteria and TSS in stormwater runoff. Analyses suggested there was a significant first flush effect for fecal coliform and TSS, although the first flush effect for fecal coliform was relatively weak. For E. coli and enterococci, no significant first flush effect was noted.
- The objectives of this study were to characterize asphalt parking lot runoff quality and determine factors influencing nutrient concentrations and loads. Event mean concentrations (EMCs) and loads were measured from eight asphalt parking lots using automated flow meters and rain gauges.
SCMs/BMPs and Modeling
- Data from downscaled climate projections for 2055 through 2058 were utilized in these models to evaluate changes in system hydrologic function under two climate change scenarios (RCP 4.5 and 8.5). Results suggest substantial additional storage is required to ameliorate the effect of climate change.
- DRAINMOD, a widely-accepted agricultural drainage model, was used to simulate the hydrologic response of runoff entering a bioretention cell. Detailed hydrologic measurements were collected from two bioretention field sites to calibrate and test the model.
- A framework for predicting carbon emissions attributable to SCMs and conveyances were applied to present a comparison of the carbon footprint of eight common SCMs and three stormwater conveyance types. The carbon embodied in construction materials represented a prominent part of the carbon footprint for green roofs, permeable pavement, sand filters, rainwater harvesting systems, and reinforced concrete pipes while material transport and construction dominated that of bioretention systems, ponds, wetlands, level spreader-grassed filter strips and concrete-lined swales.
- The possible use and form of these monitored data for modeling and how the BMPs could be represented in a watershed model is discussed. For this analysis, the Soil and Water Assessment Tool (SWAT) model is considered because of its wide use and successful track record of modeling rural watersheds throughout the world.
- A coupled hydraulics and particle-settling model was created to provide more flexibility in design of swales and filter strips. The model uses catchment area, longitudinal slope, side slope, cross section type, and length to predict the reduction in total suspended solids.
Stormwater Wetlands & Wet Ponds
- This paper presents implementation and maintenance considerations developed based on the monitoring of three full-scale ponds retrofitted with FTWs. Results suggest that the size and relative surface cover of the FTW, the relative root depth, and the capability of the plants to tolerate periodic anaerobic conditions are crucial factors to promote good removal across a spectrum of pollutants.
- The specific objective of this research was to investigate the effects that wetland maturation and lack of maintenance have on the ability of a 5-year-old CSW to mitigate hydrology and improve water quality. A CSW was monitored from 2012–2013 that had not been maintained since construction in the spring of 2007.
- The fraction of the volume associated with vegetation mass was unknown and designers have been unsure as to (1) how they should account for volume occupied by vegetation and (2) whether this was a significant design issue. Twelve storm water wetlands and one hybrid wet pond were sampled to assess their percent vegetative occupancy by volume.
- A study of two wet ponds prior to and following the installation of floating treatment wetlands. Results suggested a minimum percent coverage of 18% for improvement in TP and TSS, but there was no significant improvement observed in TN concentration.
- This technical note presents a stormwater management perspective of the strategy of plant harvesting at the water surface to remove nutrients that would otherwise be deposited back into the wetland during senescence. Vegetation was harvested from two stormwater wetlands to evaluate the ability of five wetland plant species to sequester nitrogen.
- A comparison of the abilities of 20 wet ponds and 20 constructed stormwater wetlands to provide ecosystem services including carbon sequestration, biodiversity, and cultural services.
- This study used previously established unit critical discharges, annual allowable erosional hours, and annual allowable volume of eroded bed-load standards to evaluate two types of stormwater control measures (SCMs): low-impact development (LID) practices and a large detention SCM (wet pond). Nine initial scenarios modeled in PCSWMM incorporated different combinations to determine the best scenario for reducing stream erosion potential within a highly urbanized watershed.
- Wetlands can become the very mosquito breeding grounds if they are allowed to become monocultures of specific mosquito-protective plants, such as Typha spp. (commonly referred to as cattails in the United States). Wetlands also fail frequently if the water level becomes too deep due to construction error or clogging of the outlet structure.
- Indicator bacteria concentrations in both the water and sediment of a CSW were evaluated at multiple locations. Results suggested that fecal coliform concentrations in stormwater runoff decrease through the system, with relatively consistent concentrations noted throughout the second half of the wetland.
- To test for the potential toxicity of forebay spoils, 30 stormwater wetland and wetpond forebays of varying age, size, and upstream landuse were sampled across North Carolina and analyzed for seven metals: cadmium, chromium, copper, iron, lead, nickel, and zinc. Ten of 30 sites were also sampled near the outlet structures for spatial comparison of settled sediment and pollutant presence. All samples indicated that land application of forebay sediment is unlikely to pose an environmental threat.
- Effluent organic nitrogen concentrations from seven constructed stormwater wetlands were examined to compare background organic nitrogen (ON) concentrations and the fraction of organic nitrogen relative to total nitrogen discharged. Though stormwater wetlands will not completely remove total nitrogen loads from runoff, these results suggest constructed wetlands can play a role in restoring the balance between organic and inorganic nitrogen forms closer to that of an undisturbed landscape.
- In this study, a storm-water wetland constructed and monitored in the coastal plain of North Carolina is evaluated for water quality and hydrologic performance using four different metrics: concentration reduction, load reduction, comparison to nearby ambient water quality monitoring stations, and comparison to other wetlands studied in North Carolina. Results discouraged sole reliance on a concentration reduction metric.
- A study was conducted in western North Carolina, along the southeastern extent of U.S. trout populations, to determine the effect of storm-water wetlands and wet ponds on the temperature of urban storm-water runoff. Despite similar inflow temperatures, effluent temperatures from the wet pond were significantly warmer than those from the storm-water wetland for the period from June to September.
- A system of three wetlands “in-series” was built to treat runoff from a highly impervious 30 acre watershed. The configuration of the wetlands allowed monitoring of water quality parameters at the outlet of each of the three stormwater wetlands. The results of this study indicate that water quality improvement for a number of pollutants experiences diminishing returns as it passes through the three wetland cells.
- 52 stormwater retention facilities were sampled to characterize the seasonal occurrence and relative abundance of mosquito species in relation to the structural complexity and biological diversity of the facilities. The three different types of facilities included standard wet ponds (n=20), innovative ponds (n=14), and wetland ponds (n=18). Over all samplings, mosquitoes were collected from 34% of the retention structures.
- Stormwater retention ponds were developed to reduce peak flow by detaining stormwater runoff. Wet ponds struggle to remove dissolved pollutants, but treatment could be improved with the installation of a retrofitted upflow filter. The filter did not improve nitrogen retention, however, the variability of TSS effluent concentrations was substantially reduced as were the mean effluent concentrations of orthophosphate.
Thermal Pollution & Mitigation
- In this study, six diverse catchments in two continents are evaluated for thermal dynamics. This study is the first to identify a runoff temperature first flush, and highlights the need to carefully consider the appropriate methodology for such analyses.
- Metrics for thermal performance of stormwater control measures were reviewed. Event mean temperature, LID, and groundwater temperature metrics appear useful. Thermal load and stream mixing analysis are more data intensive but more defensible. Uniform continuous above threshold metric affords species-specific biotic integrity.
- A newly constructed permeable interlocking concrete paver (PICP) parking lot was monitored for 1 year in the mountain region of North Carolina to quantify runoff reduction, temperature buffering, and thermal load export. The effects on hydrology caused by internal water storage (IWS) in the pavement profile were also investigated by dividing the lot into three cells with varying aggregate depths and drainage configurations.
- Research on stormwater control measures (SCMs) has shown that meeting the 21°C trout threshold is not consistently feasible with current SCM technologies. Thus, it is important to consider other factors in storm water temperature management, such as catchment characteristics.
- Two LS-VFS systems draining an urban catchment were monitored, one 7.6 m wide and entirely grassed, the other 15.2 m wide with the first-half grassed and the second-half wooded. Median and maximum storm temperatures were significantly reduced across both the 7.6-m and 15.2-m LS-VFSs. However, median and maximum effluent temperatures for both filter strip lengths were significantly greater than the 21°C trout threshold.
- A study was conducted in western North Carolina, along the southeastern extent of U.S. trout populations, to determine the effect of storm-water wetlands and wet ponds on the temperature of urban storm-water runoff. Despite similar inflow temperatures, effluent temperatures from the wet pond were significantly warmer than those from the storm-water wetland for the period from June to September.
- Four bioretention areas were monitored during the summers of 2006 and 2007. It was found that smaller bioretention areas, with respect to the size of their contributing watershed, were able to significantly reduce both maximum and median water temperatures between the inlet and outlet. The proportionately larger bioretention areas were only able to significantly reduce maximum water temperatures between the inlet and outlet; however, these systems showed evidence of substantial reductions in outflow quantity, effectively reducing the thermal impact.
- Stormwater wet retention ponds were monitored for their carbon sequestration services in four different climate zones. Different climate zones were chosen in order to analyze the affect of climate on carbon accumulation and, in return, sequestration. High rainfall and long growing seasons had a greater affect on decomposition rates than high temperatures.
Stormwater Design Models for Download+
Documents, Models & Spreadsheets
Please note: When files or graphics are used, please be sure to credit NCSU-BAE.
- Rainwater Harvester 5.0 for Windows (6/2024) .zip
- Rainwater Harvester 5.0 for Mac (6/2024) .zip
- Rainwater Harvester 5.0 Users Guide (6/2024)
- SNAP 4.2 (2023) – NC DEQ’s Stormwater Nutrient Accounting Tool
- SwaleMod_0.9.4 (12/2014) 824 kb .xlsm
- Permeable Pavement Hydrologic Performance Model (PermPave HyPerMod) (revised 4/29/2016) 1.1 MB .xlsm
- NC Bioretention HyPerTool VBA (WIN) 1203 kb .xlsm
Powerpoint files / Photos
Please note: When files or graphics are used, please be sure to credit NCSU-BAE.
- Images to Copyright: Structural Stormwater BMPs 13.5 MB .ppt
NCSU Stormwater Web Links
NC State University Links
- Department of Biological and Agricultural Engineering
- Water Quality Group at NCSU
- Stream Restoration Program
- NCSU BAE Extension
State of North Carolina Links
Regional and National Links
Green Stormwater Infrastructure Researchers at other Universities
- University of Maryland(Dr. Allen Davis)
- Villanova University(Dr. Robert Traver)
- University of Minnesota(Dr. John Gulliver)
- University of New Hampshire(Dr. Jaime Houle & Dr. Tom Ballestero)