Wet Ponds Research Articles

Assessing the Importance of Temporary Storage Volume Occupied by Emergent Vegetation in Constructed Storm Water Wetlands

Vegetation in a constructed storm water wetland (CSW) is essential for nutrient removal and thermal pollution reduction. However, a portion of the storage volume designed to retain the water quality event is occupied by vegetation, which may result in the CSW being undersized from a hydrologic perspective. 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 in North Carolina were sampled to assess their percent vegetative occupancy by volume. Vegetation was harvested from randomly selected 0.1 m2 grids at the normal pool elevation, and displacement tests were used to calculate the volume added by vegetation at elevations of 30 and 45 cm. Combining these data with observed vegetative cover, a water quality volume factor of safety accounting for vegetative occupancy was calculated for use in CSW design. Of the thirteen practices sampled, the highest factor of safety calculated for temporary pool elevations of 30 and 45 cm are 1.019 and 1.018, respectively. Therefore, a conservative recommended factor of safety is 1.025. Species-specific factors of safety (FOS) were also calculated; at the 30-cm temporary pool elevation, the Iris (Iris spp.) FOS was highest at 1.020, and the mixed vegetation FOS was lowest at 1.005. When designing a wetland, a more specific FOS may be calculated using a weighted average of the FOS for each species in the planting plan. The outcomes of this research allow designers to account for the volume taken up by emergent wetland vegetation; however, the uncertainty in other factors such as discrepancies between designed and as-built bathymetry probably have a greater impact on the design volume loss when compared with vegetation occupancy (<2%).

Improved urban stormwater treatment and pollutant removal pathways in amended wet detention ponds

Dissolved and colloidal bound pollutants are generally poorly removed from stormwater in wet detention ponds. These fractions are, however, the most bio-available, and therefore three wet detention ponds were amended with planted sand filters, sorption filters and addition of precipitation chemicals to enhance the removal of dissolved pollutants and pollutants associated with fine particles and colloids. The three systems treated runoff from industrial, residential and combined (residential and highway) catchments and had permanent volumes of 1,990, 6,900 and 2,680 m3, respectively. The treatment performance of the ponds for elimination of total suspended solids (TSS), total nitrogen (Tot-N), total phosphorous (Tot-P), PO4-P, Pb, Zn, Cd, Ni, Cr, Cu, Hg were within the range typically reported for wet detention ponds, but the concentrations of most of the pollutants were efficiently reduced by the planted sand filters at the outlets. The sorption filters contributed to further decrease the concentration of PO4-P from 0.04 ± 0.05 to 0.01 ± 0.01 mg L−1 and were also efficient in removing heavy metals. Dosing of iron sulphate to enrich the bottom sediment with iron and dosing of aluminium salts to the inlet water resulted in less growth of phytoplankton, but treatment performance was not significantly affected. Heavy metals (Pb, Zn, Cd, Ni, Cr and Cu) accumulated in the sediment of the ponds. The concentrations of Zn, Ni, Cu and Pb in the roots of the wetland plants were generally correlated to the concentrations in the sediments. Among 13 plant species investigated, Rumex hydrolapathum accumulated the highest concentrations of heavy metals in the roots (Concentration Factor (CF) of 4.5 and 5.9 for Zn and Ni, respectively) and Iris pseudacorus the lowest (CF < 1). The translocation of heavy metals from roots to the aboveground tissues of plants was low. Therefore the potential transfer of heavy metals from the metal-enriched sediment to the surrounding ecosystem via plant uptake and translocation is negligible.

Regulatory and Resource Management Practices for Urban Watersheds: The Florida Experience

Urban water quality management is becoming an increasingly complex and widespread problem. The long-term viability of aquatic ecosystems draining urban watersheds can be addressed through both regulatory and nutrient and water management initiatives. This review focuses on U.S. regulatory (federal, state, and local) and management (runoff, atmospheric deposition, and wastewater) impacts on urban water quality, specifically emphasizing programs in Florida. Because of rapid population growth in recent decades, and projected increases in the future, appropriate resource management in Florida is essential. Florida enacted stormwater regulations in 1979, before the U.S. Environmental Protection Agency (USEPA) amended the Clean Water Act (CWA) to regulate stormwater discharges. However, in the United States, more research has been conducted on larger structural best management practices (BMPs) (e.g., wet ponds, detention basins, etc.) compared with smaller onsite alternatives (e.g., green roofs, permeable pavements, etc.). For atmospheric deposition, research is needed to investigate processes contributing to enhanced deposition rates. Wastewater (from septic systems, treatment plants, and landfills) management is especially important in urban watersheds. Failing septic systems, elevated nutrient concentrations in discharged effluent, and landfill leachate can all potentially degrade water quality. Proposed numeric nutrient criteria from the USEPA and innovative technologies such as bioreactor landfills are emergent regulatory and management strategies for improved urban water quality.

Integrated Surface–Groundwater Model for Storm-Water Harvesting Using Basic Mass Balance Principles

AbstractStorm-water harvesting from a pond for irrigation of adjacent lands is promoted as one way that may reduce pond discharge while supplementing valuable potable water used for irrigation. Reduction of pond discharge reduces the mass of pollutants in the discharge. In this study, a storm water harvesting and assessment for reduction of pollution (SHARP) model was developed to predict operation of a wet pond used for storm-water harvesting at Miramar Lakes, Miramar, FL. The model integrates the interaction of surface water and groundwater in a catchment area. The SHARP model was calibrated and validated for pond-water elevation. Model evaluation showed adequate prediction of pond-water elevation with root mean square error (RMSE) between 0.07 and 0.12 m, mean absolute error (MAE) between 0.018 and 0.07 m, and relative index of agreement (drel) between 0.74 and 0.98 for both calibration and validation periods. The SHARP model is capable of assessing harvest safe yield and discharge from a pond, includi...

Treatability aspects of urban stormwater stressors

Pollution from diffuse sources (pollution from contaminants picked up and carried into surface waters by stormwater runoff) has been identified as a significant source of water quality problems in the U.S. scientists and engineers continue to seek solutions that will allow them to optimize existing technologies and develop new ones that will provide the best possible protection to people, wildlife, and the environment. This paper addresses the various pollutants or stressors in urban stormwater, including flow (shear force), pathogens, suspended solids/sediment, toxicants (organic and metals), nutrients, oxygen demanding substances, and coarse solids. A broad overview of the pollutants removed and the removal mechanisms by and of conventional best management practices (BMPs) is also presented. The principal treatment mechanisms of conventional wet ponds, vegetative swales/buffer strips, and wetlands are sedimentation and filtration. These mechanisms have the capability to remove significant amounts of suspended solids or particulate matter and are a vital component of strategies to reduce pollutant loads to receiving waters. In addition, because most of the nation’s receiving water violations are caused by pathogen indicator bacteria, it is of utmost importance that research efforts address this problem. Further research is also needed on the treatment of emerging contaminants in BMPs and on the costs and affects of maintenance and maintenance schedules on the long-term performance of BMPs.

Monitoring prairie wet area with an integrated LANDSAT ETM+, RADARSAT-1 SAR and ancillary data from LIDAR

The provincial wetland (“status quo”) maps of the Prairie Pothole Region, Central Canada, do not adequately depict wetland resources and properties. Using satellite remote sensing data from both LANDSAT Enhanced Thematic Mapper Plus (ETM+) and RADARSAT-1 Synthetic Aperture Radar (SAR) results in a more complete picture, although using both sources together is better than when either source is used alone. This study integrates LANDSAT ETM+, RADARSAT-1 SAR, and LIght Detection And Ranging (LIDAR) data, taking advantage of the synergy in their integration. A simple density slicing of the ETM-5 band was used to map inundated areas from LANDSAT ETM+. A fuzzy thresholding technique was used to map wet areas using RADARSAT-1 SAR data after information from LIDAR-DEMs had been used to correct confusing radar backscatter overlaps between open water and dry, flat, smooth surfaces. Compared to the “status quo”, the integrated approach mapped 113% to 600% and 217% to 467% increases in the size of wet areas and pond densities, respectively. Maps based on the ETM-5 band alone detected 133% to 333% and 50% to 350% increases in the size of wet areas and pond densities, respectively over the “status quo” map, while maps based on the RADARSAT-1 SAR data detected 63% to 450% and 100% to 333% increases. The improved mapping capability is attributed to a combinatory power of the integrated approach in detecting small, transient and saturated wet areas. ► This study integrates LANDSAT ETM+, RADARSAT-1 SAR, and LIDAR data for prairie mapping. ► A fuzzy thresholding technique was used to map wet areas using RADARSAT−1 SAR data. ► LIDAR was used to correct radar backscatter overlaps between open water and dry, flat surfaces. ► The integrated approach increases in the size of wet areas and pond densities.

Optimization Model for BMP Placement in a Reservoir Watershed

The purpose of this study was to develop an optimization model for the optimal placement of structural best management practices (BMPs) at the watershed scale for a reservoir. In this research, the authors considered three types of structural BMPs (i.e., a wet detention pond, a grass swale, and an infiltration trench). The complete model consists of three interacting submodels: a watershed water quality simulation model [the Hydrologic Simulation Program-FORTRAN (HSPF) model], a reservoir water quality model (the CE-QUAL-W2 model); and an optimization model that uses a well-developed genetic algorithm (GA) software. This research used the Feitsui Reservoir and its watershed in northern Taiwan as the area of application. For the optimization model, the objective function was to minimize the total annual cost of BMPs, within the constraints of achieving minimum water quality standards for the concentrations of phosphorus, ammonium, nitrate-nitrite and for the total suspended solids in the reservoir. The study first simulated the discharge and pollutant loads for the watershed in 2002–2003 by using HSPF. The reservoir model CE-QUAL-W2 was then used to simulate variations in pollutant concentrations in the reservoir on the basis of the input discharge and pollutant loads from HSPF. The optimization model was finally used to search for the near-optimal selection and placement of BMPs in the watershed. The results obtained from the completed model effectively demonstrate its viability in improving water quality in the reservoir by adopting optimal BMPs placement strategies.

Stormwater control measure (SCM) design standards to limit stream erosion for Piedmont North Carolina

Summary This study evaluated the potential impacts of sub-bankfull flows produced by stormwater control measures (SCMs) on stream geomorphic stability. In part, design standards for SCMs include peak flow attenuation to maintain pre-development flow conditions to those of undeveloped watersheds or return urbanized, developed watersheds back to the pre-developed state. Most SCMs target lower frequency storms, usually the 2-and/or 10-year discharge events, but leave peak flows resulting from higher frequency storms uncontrolled. SCMs are possibly subjecting streams to longer and more frequent periods of erosion, increasing stream channel instability. The d 65 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 in L/s/ha, Q c = 0.0035( d 65 ) 1.5048 , (2) allowable annual erosional hour standard, Log(AAEH) = −1.26Log( d 65 ) + 1.21, and (3) allowable volume of eroded bedload standard, Log(AV) = −0.64( Q c ) − 1.52, for watersheds containing SCMs discharging into surface waters. The unit critical discharge represents a threshold that, once exceeded, incipient motion of the d 65 particle can occur. These standards represented benchmarks of stable, naturally eroding reference streams. Ninety-four percent of the unit critical discharges were less than the 2-year 24-h event, indicating the necessity of controlling higher frequency sub-bankfull flows. The standards were applied to an urbanized watershed (one sub-catchment containing a structural SCM and two sub-catchments without) in Raleigh, North Carolina. The unit critical discharge metric appeared to adequately represent urbanized stream geomorphic processes for the sub-catchment undergoing urbanization (4.5% difference) but not for the mature urbanized sub-catchments (47.5% and 68.8% difference). Depending on the long-term management goal of the unstable stream, this metric is not applicable for all urbanized watersheds due to the discrepancy between the field and calculated unit critical discharges. Standards developed from urbanized reference streams could possibly better represent SCMs in urbanized watersheds. All three sub-catchments failed to meet the erosional standards demonstrating the ability of the standards to predict unstable geomorphic processes in streams. The addition of a detention SCM (wet pond), in the urbanized sub-catchment extended the duration of erosive flows from 37 to 87 h/ha/yr, but reduced the estimated volume of eroded bedload from 1.81 to 0.99 m 3 /m/ha/yr when compared to uncontrolled urbanization (no wet pond). Alterations to the design of the wet pond, increased volume size and change in orifice diameter, were explored to see if erosional standards could be better met. This study demonstrated the effect of current SCM design standards on stream stability and why geomorphic processes of stream channels should be incorporated in SCM design standards.

STORMWATER MANAGEMENT DESIGN: MODEL FOR A SENIOR UNDERGRADUATE COURSE

Stormwater management design makes up half of a fourth year undergraduate course that also includes design of water distribution systems and wastewater and stormwater collection systems. Learning is supported by lectures with PowerPoint presentations that include many images. Early emphasis is placed on understanding the effects of urbanization, in terms of hydrology, geomorphology, water quality and stream ecology. This leads to the objectives of stormwater management and discussion of both traditional and emerging design criteria, as well as provincial guidelines and municipal standards. The students gain an appreciation of the need for a ‘treatment train’ approach – prevention followed by lot-level, conveyance, and if necessary, end-of-pipe measures – to achieve the multiple objectives of stormwater management. Students master screening-level design that addresses land use, physical feasibility, climate, watershed opportunities and constraints, community factors, and the capability for various stormwater management practices (SWMPs) to meet various water quantity and quality objectives. Details and design examples for a range of SWMPs such as infiltration trenches, biofiltration swales, and extended detention wet ponds are presented, and a field trip reinforces the in-class information. The students gain design experience by means of a term project in which four person teams design the water-related infrastructure of a new subdivision. A Terms of Reference is provided at the beginning of the term. The design teams are responsible for a proposal, which initiates early project management, an oral progress report, and a final design report and presentation. Design labs provide an opportunity to introduce students to the software (EPA SWMM 5.0) but are primarily devoted to working on the design project. The design project is evaluated in terms of product and process, and both group and individual marks are assigned. Designs are evaluated prior to the final presentations enabling the instructor to provide substantive feedback before the course concludes. For the most part, the quality of work done by the students over the last several years has been exceptional. During the course, common feedback from the students includes “lack of direction” and “heavy work load.” Following the course, students appreciate the understanding of the subject material and the design experience gained, which they find to be very relevant to employment opportunities.

Elimination and accumulation of polycyclic aromatic hydrocarbons in urban stormwater wet detention ponds

The concentrations of polycyclic aromatic hydrocarbons (PAHS) in water and sediments of seven wet detention ponds receiving urban stormwater were investigated. The ponds comprised traditional wet detention ponds with a permanent wet volume and a storage volume as well as ponds that were expanded with sand filters and other means to improve the removal of micropollutants. The concentrations of sigmaPAH in the sediments varied between 6 +/- 5 and 2,222 +/- 603 ng g(-1) dry weight (mean +/- standard deviation), and were highest in the ponds with lower pond volume per catchment area and did not clearly reflect different activities in the catchments. In general, the concentrations of PAHS in the sediments decreased from inlet to outlet, especially in the systems with good conditions for sedimentation such as systems with flow perpendicular sand dikes and extensive submerged vegetation. High molecular weight PAHs were predominant in the sediments indicating the pyrogenic origin of the PAHS. There was no correlation between PAH species concentrations in water or sediments and their hydrophobicity (log K(ow)). PAH concentrations in water fluctuated in response to intensity and frequency of rain events, whereas concentrations in the sediments integrated the pollutant load over time. Pond systems expanded with sand filters and other technologies to enhance removal of micropollutants consistently had concentrations of PAHS in the effluents below the detection level.

Constructed Storm-Water Wetland Installation and Maintenance: Are We Getting It Right?

Constructed storm-water wetlands (CSWs) have become one of the more popular storm-water control measures (SCMs). CSWs offer a hybrid between larger detention technologies like storm-water wet ponds and newer green infrastructure technologies. The systems are characterized as being predominately shallow retention practices, with water elevations sufficiently low to support diverse flora and fauna. Figs. 1(a–c) illustrate several successful examples of CSWs. Many researchers have found that CSWs remove sediment, nutrients, and metals from storm-water runoff (Greenway 2004; Hathaway and Hunt 2010; Line et al. 2008; Kohler et al. 2004; Wadzuk et al. 2010). One of the principal drivers for the use of storm-water wetlands is the amount of credit awarded to them by various governmental agencies with respect to nutrient removal and sequestration [North Carolina Department of Environment and Natural Resources (NCDENR) 2009]. The apparent improvement in nutrient capture from storm-water runoff over that of storm-water wet ponds is one of the main reasons designers choose CSWs over the more traditional wet pond. Extensive coverage of vegetation allows for several pollutant removal mechanisms: filtration of particles, stabilization of sediments, nutrient uptake, microbialrhizophere interaction to promote nitrification and denitrification, and the provision of increased surface area for biofilm/periphyton growth (Greenway 2004). In regions where thermal loads threaten cold water fisheries, CSWs have been shown to release cooler water to streams than do wet ponds because of the shading caused by the vegetation—but absent from wet ponds (Jones and Hunt 2010). Some concerns have also presented themselves with respect to CSWs, which have prevented the practice from outright replacing the wet pond. Foremost among them is the threat of mosquito infestation that wetlands invariably face in relation to the public (QDNR 2000). Research has shown that exorbitantly high mosquito populations need not accompany CSWs, provided they are diversely vegetated (Greenway et al. 2003; Hunt et al. 2006). However, if wetlands are allowed to become monocultures of specific mosquito-protective plants, such as Typha spp. (commonly referred to as cattails in the United States), they can become the very mosquito breeding grounds that the public fears (Greenway et al. 2003; Hunt et al. 2005). If storm-water wetlands are to be constructed, they must both (1) meet their intended water quality (and hydrologic) design goals and (2) not be a public nuisance. Anecdotal observation of CSWs constructed worldwide shows how many well-intended CSW designs fail. Two principal reasons were identified: One appears to be that not enough care was taken to ensure the storm-water wetlands’ normal pool elevation was appropriately shallow (that is, often the elevation of water in CSWs is too deep). The cause has been previously identified by Greenway et al. (2007). The second is clogging of the outlet structure that artificially raises the elevation above normal pool for extended periods of time. In both cases, simple preventative actions could be taken to ensure constructed storm-water wetlands maintain their designed integrity. The purpose of this forum is to document how poor design and inadequate management of two CSWs caused each to effectively become wet ponds, which results in (1) a reduced efficiency in the removal of some pollutants; (2) a degradation of biodiversity, which leads to an increased risk of having the wetlands become mosquito breeding grounds; and (3) degraded aesthetics.

Heavy metals, PAHs and toxicity in stormwater wet detention ponds

Concentrations of 6 different heavy metals and total polycyclic aromatic hydrocarbons (PAHs) were determined in stormwater runoff and in the pond water of two Danish wet detention ponds. The pond water samples were analyzed for toxic effects, using the algae Selenastrum capricornutum as a test organism. Stormwater and pond water from a catchment with light industry showed high levels of heavy metals, especially zinc and copper. The pond water showed high toxic effects and copper were found to be the main toxicant. Additionally, a large part of the copper was suspected to be complex bound, reducing the potential toxicity of the metal. Another catchment (residential) produced stormwater and pond water with moderate concentration of heavy metals. The pond water occasionally showed toxic effects but no correlation between heavy metals and toxicity was identified. PAHs concentrations were for both catchments low and no correlations between PAH concentrations in the pond and toxicity were found.

Development of Sub-Daily Erosion and Sediment Transport Algorithms for SWAT

New Soil and Water Assessment Tool (SWAT) algorithms for simulation of stormwater best management practices (BMPs) such as detention basins, wet ponds, sedimentation filtration ponds, and retention irrigation systems are under development for modeling small/urban watersheds. Modeling stormwater BMPs often requires time steps as small as minutes to realistically capture the instantaneous flow and sediment load coming from upland areas. SWAT2005 uses the Modified Universal Soil Loss Equation (MUSLE) for modeling upland erosion and sediment load. The MUSLE model is an empirical soil loss equation, which was formulated based on field observations rather than theoretically derived relationships to predict long-term average soil loss. This article presents modified physically based erosion models in SWAT for seamless modeling of erosion processes with the recently developed sub-hourly flow models. In the new algorithms, splash erosion is calculated based on the kinetic energy delivered by raindrops, adapted from the European Soil Erosion Model, and overland flow erosion is estimated using a physically based equation adapted from the Areal Nonpoint-Source Watershed Environment Response Simulation (ANSWERS) model. The Yang model and the Brownlie model were also modified for in-stream sediment routing. The SWAT model with the modified sub-daily sediment algorithms was calibrated and validated each for a one-year period at 15 min intervals with measured data from the USDA-ARS Riesel watersheds in Texas. Results show that SWAT with the sub-daily algorithms performed as well or better in terms of sediment yield prediction than SWAT with the current daily output structure. In addition, SWAT (sub-daily) was able to adequately represent the timing, peak, and duration of sediment transport events. Thus, this initial evaluation indicates that the new sub-daily flow and sediment structure in SWAT is a promising tool for water quality assessment studies in small watersheds or urban watersheds where sub-daily process are so important to quantify.

A Field‐Based Evaluation of Wet Retention Ponds: How Effective Are Ponds at Water Quantity Control?1

Hancock, Gregory S., Jonathan W. Holley, and Randolph M. Chambers, 2010. A Field‐Based Evaluation of Wet Retention Ponds: How Effective Are Ponds at Water Quantity Control? Journal of the American Water Resources Association (JAWRA) 46(6):1145–1158. DOI: 10.1111/j.1752‐1688.2010.00481.xAbstract: Wet retention ponds are widely used structural stormwater best management practices (BMPs) with the primary goals of reducing peak flows and extending flow duration. Despite widespread use, few field‐based studies have evaluated the success of wet retention ponds at meeting these goals. We determined pond elevation, flow rate, and pond volume over four years in five suburban watersheds in James City County, Virginia. We selected five ponds designed under regulations requiring a 24 hour inflow‐to‐outflow centroid lag time for a one year, 24 hour design storm. We used pressure transducers to measure pond water surface elevation at 5 min intervals, and calculated pond outflow and volume using rating curves obtained from site stormwater management plans (SWMPs). Peak inflows, peak outflows, and runoff ratios frequently exceeded SWMP calculations in measured events. Four ponds never achieved the required 24 hour inflow‐to‐outflow centroid lag for storms similar to the one year, 24 hour storm. These BMPs fail to achieve regulatory goals for channel protection because of regulatory loopholes, underprediction of rainfall intensity, unrealistic predictions of postdevelopment flows in SWMPs, and the inability of wet retention ponds to reduce overall runoff volume. While specific to one locality, the shortcomings highlighted suggest similar field‐based assessments of retention pond performance are needed in other locations.

3D modelling of transport, deposition and resuspension of highway deposited sediments in wet detention ponds

The paper presents results from an experimental and numerical study of flows and transport of primarily particle bound pollutants in highway wet detention ponds. The study presented here is part of a general investigation on road runoff and pollution in respect to wet detention ponds. The objective is to evaluate the quality of long term simulation based on historical rains series of the pollutant discharges from roads and highways. A three-dimensional hydrodynamic and mud transport model is used for the investigation. The transport model has been calibrated and validated on e.g. experiments in a 30 m long concrete channel with width of 0.8 m and a water depth of approximately 0.8 m and in circular flume experiments in order to reproduce near-bed specific processes such as resuspension and consolidation. With a fairly good agreement with measurements, modelling of hydrodynamics, transport of dissolved pollutants and particles in wet detention ponds is possible with application of a three dimensional RANS model and the advection/dispersion equation taken physical phenomena like wind, waves, deposition, erosion and consolidation of the bottom sediment into account.

Opportunities and challenges for managing nitrogen in urban stormwater: A review and synthesis

Although nitrogen (N) is prevalent in urban stormwater, regulation of this pollutant has occurred only more recently. This paper reviews the concerns over N in urban stormwater, mechanisms and design enhancements for N uptake and denitrification through various stormwater control measures (SCMs), and presents opportunities to integrate this current knowledge into the regulatory framework. A survey of personnel directly involved in various aspects of US state and territory NPDES programs revealed that the top three pollutants of concern were total suspended solids (TSS), pathogens and bacteria, and total phosphorus (TP). Surprisingly, nitrate (NO 3 −) was of little concern among the survey respondents, with 3.9% giving it the highest level of concern, 2.0% ranking it second, and 6.0% ranking it third. When asked which strategies were currently used in their geographic area for stormwater management, the most common results were wet ponds and dry ponds. At the same time, wet ponds and dry ponds were recognized as less effective practices to manage stormwater. A review of current literature reveals that several alternative SCMs, such as bioretention, filters, and wetlands, show greater promise in their ability to remove N from stormwater than more conventional practices such as dry ponds and wet ponds. Enhanced N removal via denitrification and plant uptake is often observed under the combination of aerobic followed by sustained anoxic conditions, the presence of a carbon source (organic material), and the presence of mature, dense vegetation. Given the lack of concern or awareness of local officials related to N loading from urban stormwater, and variation in the efficacy of various SCMs, it is not surprising that regulators remain focused on conventional dry pond and wet pond control measures. More needs to be done to quantify the impact of urban sources of N on water quality and aquatic ecosystems. In addition, greater focus needs to be placed on the development of design criteria for SCMs, such as bioretention, filters, and constructed wetlands, which show more promise for N removal.

Effect of Storm-Water Wetlands and Wet Ponds on Runoff Temperature in Trout Sensitive Waters

With increasing development in areas of trout sensitive waters, the effect of urban storm-water runoff temperature on the aquatic ecosystem has become a concern. 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. Measurements included temperature at the inlets, outlets, and at several depths within the best management practices (BMPs). Parking lot runoff temperatures were significantly higher than the 21°C temperature threshold for trout during peak summer months and water temperatures consistently increased from the inlet to the outlet in the storm-water wetland and wet pond, implicating these BMPs as sources of thermal pollution. 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. Substantial cooling was observed ...

Aeolian dune‐field development in a water table‐controlled system: Skeiđarársandur, Southern Iceland

AbstractAeolian dune fields characterized by partly vegetated bedforms undergoing active construction and with interdune depressions that lie at or close to the water table are widespread on Skeiđarársandur, Southern Iceland. The largest aeolian dune complex on the sandur covers an area of 80 km2 and is characterized by four distinct landform types: (i) spatially isolated aeolian dunes; (ii) extensive areas of damp and wet (flooded) interdune flat with small fluvial channels; (iii) small aeolian dune fields composed of assemblages of bedforms with simple morphologies and small, predominantly damp, interdune corridors; and (iv) larger aeolian dune fields composed of assemblages of complex bedforms floored by older aeolian dune deposits that are themselves raised above the level of the surrounding wet sandur plain. The morphology of each of these landform areas reflects a range of styles of interaction between aeolian dune, interdune and fluvial processes that operate coevally on the sandur surface. The geometry, scale, orientation and facies composition of sets of strata in the cores of the aeolian dunes, and their relationship to adjoining interdune strata, have been analysed to explain the temporal behaviour of the dunes in terms of their mode of initiation, construction, pattern of migration, style of accumulation and nature of preservation. Seasonal and longer‐term flooding‐induced changes in water table level have caused episodic expansion and contraction of the wet interdune ponds. Most of the dunes are currently undergoing active construction and migration and, although sediment availability is limited because of the high water table, substantial aeolian transport must occur, especially during winter months when the surface of the wet interdune ponds is frozen and sand can be blown across the sandur without being trapped by surface moisture. Bedforms within the larger dune fields have grown to a size whereby formerly damp interdune flats have been reduced to dry enclosed depressions and dry aeolian system accumulation via bedform climb is ongoing. Despite regional uplift of the proximal sandur surface in response to glacial retreat and unloading over the past century, sediment compaction‐induced subsidence of the distal sandur is progressively placing aeolian deposits below the water table and is enabling the accumulation of wet aeolian systems and increasing the likelihood of their long‐term preservation. Wet, dry and stabilizing aeolian system types all co‐exist on Skeiđarársandur and the dunes are variously undergoing coeval construction, accumulation, bypass, stabilization and destruction as a result of interactions between localized factors.

Nutrient Reduction in Stormwater Pond Discharge Using a Chamber Upflow Filter and Skimmer (CUFS)

Stormwater runoff is a known pollutant source capable of causing surface water degradation, especially in highly populated areas such as Central Florida. Wet detention ponds manage this stormwater, but most of the ponds do not remove enough nutrients, specifically nitrogen and phosphorus, to meet total maximum daily load regulations. This paper presents the use of a chamber upflow filter and skimmer (CUFS) filled with a specific green sorption medium as process modification of stormwater retention ponds, which can increase the removal of nitrogen and phosphorus in the stormwater runoff. Green sorption medium consists of recycled and natural materials that provide a favorable environment for pollutant removal. Water enters the system through the skimmer, which floats on the surface of the detention pond. It travels from the skimmer to the bottom of the chamber where heavier particles settle out before entering the upflow filter. The upflow filter contains 61 cm (24 in.) of green sorption medium providing physicochemical and microbiological processes to remove nitrogen and phosphorus under anoxic/anaerobic conditions. After this treatment, water flows up through the filter and out of the system and eventually travels to Lake Jesup, a eutrophic lake in Central Florida. A total of 28 storm events and seven baseflows were sampled from the site in Seminole County, and ten storm events were sampled from a pilot study of CUFS for statistical analysis and performance evaluation. Significant reductions by the CUFS were confirmed in terms of turbidity, orthophosphorus, total phosphorus, and total suspended solids when the mean values were compared at a 95% confidence level. Reductions also occurred for total nitrogen (TN), but could not be proved by the mean comparison in the field test, whereas the pilot-scale application of the CUFS proved effective for reducing TN at a 95% confidence level. Hydraulic retention time should be increased so as to improve the design for TN removal in future applications.

Impact of Microbial Partitioning on Wet Retention Pond Effectiveness

Wet detention basins are among the most common best management practices (BMPs) being implemented as means of complying with United States Phase II storm-water rules and impending Total Maximum Daily Load limits. The effectiveness of these basins for removal of microbial contaminants, one of the most frequent causes of water quality impairment, may be significantly affected by the degree to which microbes associate with particles in storm water. Little is known with regard to where microbial-particle associations are initiated within the storm-water transport chain as flow travels from upland sources (e.g., lawns, parking lots) through storm sewer systems and BMPs and finally on to receiving waters. A similar lack of information exists on the relative concentrations of microbes at each point in the transport chain. Both of these factors have important implications for the location of wet detention basins within a watershed, as well as their anticipated effectiveness. This study tracked the concentrations and partitioning behavior of three indicator organisms (fecal coliform, E. coli, and enterococci) at several locations in the transport chain and also explored the impacts of partitioning on wet pond removal efficiency. Results suggest that microbial-particle association is primarily initiated at upland sources and the degree of microbial partitioning does not vary greatly throughout the transport chain; therefore, treatment ponds will likely be most effective if located near upland contaminant sources. The overall reduction in microbial concentration brought about by the ponds was less than that assumed by most regulatory agencies, but the ponds did show some evidence of preferentially removing particle-associated fecal coliform and E. coli, suggesting that sedimentation is a key removal process. These findings should provide insights useful in the design and implementation of storm-water management strategies.