Temperature Effects on the Infiltration Rate through an Infiltration Basin BMP

Infiltration Best Management Practices (BMPs) are becoming more readily acceptable as a means of reducing postdevelopment runoff volumes and peak flow rates to pre-construction levels, while simultaneously increasing recharge. However, the design, construction, and operation of infiltration basins to this point have not been standardized due to a lack of understanding of the infiltration processes that occur in these structures. Sizing infiltration BMPs to hold and store a predetermined volume of runoff, typically called the Water Quality Volume, has become a widely accepted practice. This method of sizing BMPs does not account for the infiltration that is occurring in the BMP during the storm event; which could result in significantly oversized BMPs. The objective of this study was to develop a methodology to simulate varying infiltration rates observed from a large scale rock infiltration basin BMP. The results should aid in improved design of such structures. This methodology is required to predict the performance of these sites using single event and continuous flow models. The study site is a Pervious Concrete Infiltration Basin BMP built in 2002 in a common area at Villanova University. The system consists of three infiltration beds filled with coarse aggregate, lined with geotextile filter fabric, overlain with pervious concrete and underlain by undisturbed silty sand. The BMP is extensively instrumented to facilitate water quantity and quality research. The infiltration performance of the site is the focus of the study. Recorded data indicates a wide variation of linear infiltration rates for smaller storm events. A model was developed using the Green–Ampt formula to characterize the infiltration occurring in the basin for small storm events characterized by an accumulated depth of water in the infiltration bed of less than 10?cm. The effectiveness and accuracy of the model were measured by comparing the model outputs with observed bed water elevation data recorded from instrumentation on site. Results show that for bed depths of <10?cm, hydraulic conductivity is the most sensitive parameter, and that the storm event measured infiltration rate is substantially less then the measured saturated hydraulic conductivity of the soil. The governing factor affecting hydraulic conductivity, and subsequently, infiltration rate is temperature; with higher rates occurring during warmer periods, affecting the infiltration rate by as much as 56%.     

Fines Accumulation and Distribution in a Storm-Water Rain Garden Nine Years Postconstruction

Storm water control measures (SCMs), also known as best management practices (BMPs), such as rain gardens, are designed to infiltrate storm-water runoff and reduce pollutant transport to surface waters. The life span of these SCMs may be limited depending on the composition of sediments in runoff water. Settling of fine sediments may clog soil pore spaces, reducing the infiltration capacity of the soil and reducing the potential benefits of this SCM. A study was conducted on a Villanova campus rain garden that accepts runoff from an adjacent parking lot to determine if there was a relationship between the accumulation of fine sediments over time and the infiltration capacity. The soil textural profile within the rain garden was characterized prior to SCM installation (2001), after installation, after five years, and after seven years of receiving storm-water runoff. Infiltration data were collected by the single-ring infiltrometer method in 2006 and 2009. Differences in soil texture were found between locations within the infiltration basin, and accumulation of fines smaller than 0.1 mm was observed at both locations sampled in 2009. Infiltration rates were significantly different between the two locations measured within the rain garden, but infiltration rates did not change significantly over time within those regions. This SCM was designed at a 10:1 watershed to SCM area ratio, which is twice what is recommended by the PA DEP BMP Manual. The data collected over the seven years since installation indicate that while fines have accumulated in the SCM there has been no significant change in infiltration potential.     

Simulation of the Performance of a Storm-Water BMP

Vegetated storage-infiltration best management practices (BMPs) have become an increasingly popular means of attenuating and treating runoff from developed land. However, the hydrologic and pollutant removal performances of these facilities can be highly variable. A mathematical model of an idealized BMP was developed in order to quantify the impact of variable hydrologic and pollutant concentration input on BMP performance by simulating the treatment performance of the model system during 1,250 non-steady-state storm events generated based on historic Maryland rainfall data. The model BMP was effective in attenuating volume (42% total volume reduction) and peak flow (median peak output to peak input flow ratio was 0.058). The simulated mean effluent pollutant event mean concentration was much less than the influent (0.284 compared with 1.51 mg/L) and the overall mass load reduction was 92%. However, the performance parameters demonstrated significant variability. Consequently, the results suggest a need to incorporate into BMP performance guidelines the impact of the variable influent hydrologic and pollutant concentration characteristics. Emphasis should be placed on discharge water quality and statistical distributions rather than on single-percent removal values.     

Comparison of BMP Performance Using the International BMP Database

This paper explores the performance and relative pollutant removal of several common best management practices (BMPs) using data contained in the International Stormwater BMP Database. These BMPs include retention (wet) ponds, extended detention basins, vegetated swales, and sand filters. Although the database contains numerous studies with varying amounts of detail, this comparison is based on the performance of only those sites with reported basic design characteristics and water quality data (event mean concentrations) so that constituent concentrations can be accurately determined and related to the design of the individual BMP. The use of selected BMPs has a number of advantages. Some of the variability in performance observed for facilities of a specific type can be explained by differences in design and/or watershed characteristics; consequently, the expected performance for a given set of conditions can be predicted more accurately. In addition, the differences in performance among BMP types for a given set of conditions can also be established with a higher degree of certainty. The principle measure for comparing the performance between the selected BMPs is their discharge quality, which was found to be a function of the influent concentrations for many constituents. A comparison of the discharge quality as a function of the concentration in untreated runoff demonstrates substantial differences in performance among these BMPs for many constituents.     

Slope Interrupter Best Management Practice Experiments on a Tilting Soil Bed with Simulated Rainfall

This paper documents an experimental study conducted to evaluate the performance of two commonly used sediment treatment control products, albeit with contrasting treatment technologies: a fiber roll or wattle (i.e., three-dimensional filter) and a perforated pipe wrapped by a pervious geosynthetic material (i.e., boundary filter). Emphasis was placed on (1) simulating field conditions and (2) describing performance via runoff, sediment yield, and particle-size measurements. Scaling problems typically associated with erosion experiments were minimized by using standard-size products (not scaled models) and a large-scale erosion bed with overhead rainfall simulators, with which dominant forms of soil erosion and sediment transport were attained. The results indicate that the experimental procedures and measurements utilized are appropriate for quantifying the erosion control performance of the products tested. In particular, the measurements revealed the important role of installation quality on BMP performance. Results also indicate that the magnitudes of peak discharge and total runoff from compacted, bare soils on steep slopes can approach values typical of highly impervious surfaces.     

Evaluating Four Storm-Water Performance Metrics with a North Carolina Coastal Plain Storm-Water Wetland

Storm-water best management practices (BMPs) are typically assessed using the performance metric of pollutant concentration removal efficiencies. However, debate exists whether this is the most appropriate metric to use. 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. The River Bend storm-water wetland was constructed in spring 2007 and was monitored from June 2007 through May 2008. Twenty-four hydrologic and 11 water quality events were captured and evaluated. The wetland reduced peak flows and runoff volumes by 80 and 54%, respectively. Reductions were significant. Concentrations for the following pollutants increased: total kjeldahl nitrogen (TKN), NH4–N, total nitrogen (TN), and total suspended solids (TSS); inflow and outflow concentrations did not change for total phosphorus (TP), while only NO2–3–N and orthophosphorus (OP) concentrations were lower at the outlet. Using a load reduction metric, results were strikingly different, showing positive load reductions of 35, 41, 42, 36, 47, 61, and 49% for these respective pollutants: TKN, NO2–3–N, NH4–N, TN, TP, OP, and TSS. When comparing the effluent concentrations from the wetland to ambient water quality in the Trent River, all effluent nitrogen species concentration were either similar or lower. TP and TSS concentrations leaving the wetland were higher than ambient water quality data. Finally, by comparing pollutant concentrations among different North Carolina wetlands, it is apparent the River Bend wetland received relatively “clean” water and released water with pollutant concentrations comparable to all other studies examined. Major conclusions from this study include: (1) storm-water wetlands sited in sandier soils (such as those of the North Carolina coastal plain) should be considered a low impact development tool and (2) the selection of performance metric has a pronounced bearing on how a BMP’s performance is perceived. Sole reliance on a concentration reduction metric is discouraged.     

Multiyear and Seasonal Variation of Infiltration from Storm-Water Best Management Practices

Reduction of storm-water volumes through infiltration is becoming a commonly applied practice in the effort to mitigate the negative hydrologic impacts commonly associated with land development. The hydrologic impacts generally include increases in both the volume and peak flow rate of runoff along with an associated decrease in groundwater recharge. Infiltration best management practices (BMPs) are the foundation of many low impact development and Green infrastructure practices. As the movement to volume reduction is a relatively recent concept, there remains a lack of detailed long-term monitoring data to support the implementation of storm-water infiltration BMPs. Two storm-water infiltration BMPs on the campus of Villanova University located in Southeastern Pennsylvania have been continuously monitored to determine the long-term and seasonal variation related to the engineered infiltration of storm-water runoff. The analysis of continuous monitoring data indicates that both BMPs show considerable seasonal variation but exhibit no evidence of a systematic decrease in performance to date. The seasonal variation of the BMPs is explained primarily by the temperature dependency of the viscosity of water.     

Evaluation of Storm-Water Wetlands in Series in Piedmont North Carolina

Three storm-water wetlands in series were monitored in a heavily urbanized 12.5 ha watershed in Mooresville, North Carolina. Monitoring of this system allowed an examination of the diminishing returns provided by three successive best management practices (BMPs) of a similar type. At least 80% of the total concentration reduction for all pollutants occurred within the first wetland cell. Only the first wetland cell significantly (p<0.05) reduced all pollutants tested. No pollutant was significantly reduced from the outlet of Wetland Cell 2 to the outlet of Wetland Cell 3 (p<0.05). Median complete system (outlet of Wetland Cell 3) effluent concentrations for total suspended solids, total phosphorus, total nitrogen, and turbidity were 8, 0.09, 0.73 mg/L, and 10 NTU, respectively, which compared favorably to published results. Organic nitrogen generated from wetland vegetation seemed to result in a background source of nitrogen in the wetlands, supporting the idea of an irreducible concentration for nitrogen in these systems. The results indicate that the successive BMPs in a series do not perform as well as the first when each BMP uses similar removal mechanisms.     

Runoff Characteristics for Construction Site Erosion Control Practices

Controlling soil erosion during and after construction is a major concern due to the impacts of sediment on stream water quality, and many studies have focused on the effectiveness of erosion control best management practices (BMPs) to prevent erosion. However, their ability to reduce runoff volume and peak discharge is not commonly studied or integrated into storm water designs due to lack of data and design guidelines. This study investigated runoff characteristics (total runoff, peak flow rate, curve number, and rational method runoff coefficient) from bare compacted soil conditions with and without erosion control BMPs, with an emphasis on compost erosion control blankets (CECBs), at three different slope (2H:1V, 3H:1V, and 4H:1V). Experiments were performed in the San Diego State University, Soil Erosion Research Laboratory on a 3-m by 10-m indoor titling soil bed using simulated rainfall based on conditions specified in ASTM D-6459. Eleven erosion control BMPs were evaluated at a slope of 2H:1V, three at 3H:1V, and three at 4H:1V. The variations in slope were used to assess the effects of slope and CECB thickness on runoff. The results from this study provide new insight regarding the runoff characteristics from bare soil and erosion control BMPs that can be used to improve construction-site storm water design. The results show that 2.5- and 5.0-cm-thick CECBs on top of netting or an excelsior fiber blanket provided a significant reduction in runoff relative to the bare soil and the other BMPs (e.g., 1.3-cm CECBs, other blankets) due to water storage within the CECB, the mass of the CECB providing a strong bond between the soil surface and the bottom of the blanket reducing the potential for flowing water from coming in contact with the soil surface, and the netting/blanket under the CECB providing additional friction that helps keep the CECB from sliding down slope. The results show that slope impacts on runoff are minimal but that as CECB thickness increases runoff was reduced due to the added storage within the blanket. The results from this study can be used to aid in the selection of CECB thickness and to assess the effects of CECBs on runoff for more efficient cost effective storm water designs.     

Integration of Low-Impact Development into the International Stormwater BMP Database

Low impact development (LID) strategies are being encouraged in many communities as an approach to reduce potential adverse impacts of development on receiving streams. Many questions exist regarding how well various LID strategies perform in different settings, just as similar questions have been raised regarding performance of traditional stormwater best management practices (BMPs). Whereas historical focus on BMP performance has been water quality concentrations or loads, characterization of volume reduction benefits for both conventional and LID practices is increasingly an objective of researchers and stormwater managers. More than a decade ago, Urban Water Resources Research Council (UWRRC) members worked to develop a set of standardized monitoring and reporting protocols for traditional BMPs and to establish a master database for the purpose of evaluating BMP performance and the factors affecting performance. This effort culminated in the International Stormwater BMP Database (www.bmpdatabase.org), which contains data for more than 360 BMPs and continues to operate as a clearinghouse for stormwater BMP data and performance analyses. During 2008–2009, the International Stormwater BMP Database project expanded to better integrate LID into the database and develop a set of metrics that can be used to characterize BMP performance with regard to surface runoff volume reduction. This paper provides a condensed overview and progress report on the LID-focused effort, including the following topics: (1)?monitoring guidance for LID at the overall site development level, (2)?an overview of recent changes to the International Stormwater BMP Database to better accommodate LID studies, (3)?a summary of LID studies currently included in the database, and (4)?a proposed approach for evaluating performance of LID studies with regard to reducing surface runoff volumes.     

Storage Volume and Overflow Risk for Infiltration Basin Design

This study presents a risk-based approach for the design of infiltration basins. The design parameters include basin storage volume, drain time, and overflow risk. At a basin site, the storm-water detention storage volume is determined by design runoff capture volume, tributary watershed area, and runoff coefficient. The basin geometry is dictated by the water volume balance between the surface storage volume in the basin and the subsurface storage capacity in soil pores. The drain time at a basin site is found to be a function of initial soil water content, soil porosity, infiltration rate, and distance to the ground-water table. After knowing the basin geometry and size, the basin's performance can be evaluated by the overflow risk analysis using the local average event rainfall depth and interevent time. In practice, a sensitivity test on overflow risk can be conducted with a range of basin storage volumes. The risk-based approach presented in this study provides an algorithm to calculate the long-term runoff capture percentage for a basin size. The diminishing return on runoff capture percentage can serve as a basis to select the proper basin storage volume at the site.     

Incentive Index Developed to Evaluate Storm-Water Low-Impact Designs

In practice, the challenge of storm-water low-impact-development (LID) design is often related to how to quantify the effectiveness of a LID layout. In this study, the watershed imperviousness was chosen as a basis to evaluate the performances of various LID designs. Often, LID designs apply cascading planes to drain the runoff flow from the upstream impervious area to the downstream pervious area. In this study, the conventional area-weighting method is revised with a pavement-area-reduction factor (PARF) to produce the effective imperviousness. PARF is employed as an incentive index to quantify the on-site runoff volume reduction and cost savings from downsized sewers. Two sets of PARF are derived: conveyance-based and storage-based LID designs. The conveyance-based LID approach is to drain runoff flows on various porous surfaces while the storage-based LID approach is to temporarily store runoff flows in an on-site basin. For a specified LID layout, the PARF provides a consistent basis to translate the infiltration and storage effects into the reduction on the area-weighted imperviousness. The nondimensional governing equation derived in this paper indicates that the PARF depends on the ratio of the soil infiltration rate to rainfall intensity, the ratio of receiving pervious area to upstream impervious area, and the on-site storm-water storage capacity. The PARF serves as a basis for the engineers, planners, and/or developers to select a LID design and also for regulatory agencies to assess meritorious credits for cost savings.     

Laboratory Simulation of Urban Runoff and Estimation of Runoff Hydrographs with Experimental Curve Numbers Implemented in USEPA SWMM

The prognostic capabilities of a lumped hydrologic modeling approach may be complicated by routing and connectivity among infiltrative and impervious surfaces. We used artificial rainfall to generate runoff from impervious and bare soil boxes arranged in series to simulate different extents and connectivity of impervious surfaces under different moisture conditions for pervious areas. Curve numbers were calculated from observed rainfall and runoff data, compared with published values, and used in the curve number infiltration algorithm in the U.S. EPA Storm Water Management Model 5 (USEPA SWMM5) to generate runoff hydrographs. Experimental curve numbers were higher than tabular USDA values, ranging from 91 to 96. Simulations of infiltration and runoff response with experimental curve numbers showed overall good agreement with observed data, although SWMM5 was unable to re-create early term infiltration patterns, and simulated runoff lagged observed, which is attributed to implicit accounting for soil moisture and other assumptions of the SWMM5 curve number application. Our results highlight some prospects for the use of curve numbers in modeling infiltration and runoff.     

Water Quality Improvement through Reductions of Pollutant Loads Using Bioretention

As an increasingly adopted storm-water best management practice (BMP) to remedy hydrology and water quality impairment from urban development, bioretention facilities need rigorous investigation to quantify performance benefits and to allow design improvements. This study examines water quality improvements [total arsenic, total cadmium, chloride, total chromium, total and dissolved copper, E. coli, fecal coliform, lead, mercury, nitrogen species, oil and grease, phosphorus, total organic carbon (TOC), total suspended solids, and total zinc] via monitoring for a 15-month period at two bioretention cells in Maryland. Both bioretention cells effectively removed suspended solids, lead, and zinc from runoff through concentration reduction. Runoff volume reduction promotes pollutant mass removal and links BMP water quality benefits with hydrologic performance. From a load perspective (kg/ha?year), all but TOC at one cell showed pollutant reduction. Bioretention effluents exhibited good water quality for all significant pollutants except for nitrate, copper, and phosphorus in one cell, the latter two of which may be attributed to media organic matter dissolution. Copper dissolved/particulate analyses showed that significant changes in copper speciation behavior result from transport through the bioretention media.     

Particle Size Distribution in Highway Runoff

Particles in highway runoff contain various sorbed pollutants, and many best management practices (BMPs) are selected for particle removal efficiency, which makes particle size distribution a crucial BMP design parameter. Particles between 2 and 1,000?μm in diameter were quantified for three rainfall events during the 2002–2003 rainy season at three highway sites in west Los Angeles. Rainfall, runoff flow rate, and a large suite of water quality parameters were also measured. An experimental protocol was developed for bottle cleaning, sample storage, and mixing that provided repeatable results. Particle aggregation occurred which required samples to be analyzed in less than 6?h; the concentration of small particles decreased with a corresponding increase in the concentration of larger particles in stored samples. The particle concentration decreased as the storm progressed and the number of large particles decreased more rapidly than the total number of particles. Particles demonstrated a strong first flush. On average, 40% of the particles were discharged in the first 20% of the runoff volume.     

Evaluating the Effectiveness of Best Management Practices Using Dynamic Modeling

Structural best management practices (BMPs) have become a tool for stormwater managers to achieve water quality improvement and regulatory compliance. Existing empirical evaluation of BMP performance is valuable, but has limited applicability to predict BMP performance over extended durations under a variety of storm types. This study applies a dynamic model to simulate BMP performance over a 10-year period. The BMP model used hourly output from a calibrated and validated land-use model to evaluate two BMP types: a retention facility and a flow-through swale. The model evaluated each BMP alone and in series targeting volume, total suspend solids, and total copper. Effectiveness was based on load reduction, event mean concentrations, and frequency of exceedence of relevant water quality standards. The model predicted over 60% removal of solids and copper over most conditions; however, effectiveness was reduced during large storms and wet years. Although performance was similar based on load reduction and water quality standard exceedence, the latter was most sensitive to storm size. This study demonstrates that BMP modeling can help managers understand expected BMP performance over a range of storms, time periods, and design parameters, and, perhaps more significantly, evaluate BMPs in series.     

In Situ Partial Exfiltration of Rainfall Runoff. I: Quality and Quantity Attenuation

Rainfall runoff impacted by anthropogenic activities transports significant quantities of particulate, aqueous, and complexed constituents. These diffuse, unsteady, and stochastic event-based loadings are unique challenges for water quality (concentration, mass) and quantity control (volume, peak flow). While many infiltration/exfiltration structural best management practices (BMPs) or low impact development practices are implemented, few in situ data sets are examined for actual events and temporal-based BMP behavior, in part due to costs of such examinations. Fewer studies provided a statistical and mechanistic interpretation for event-based BMP performance. The design, water quality, and quantity functions of a partial exfiltration reactor (PER) utilizing Fe-coated sand is examined specifically across three water quality type rainfall-runoff events over a 10-month period. Reduction of total concentrations for metals (Zn, Pb, Cu, and Cd), ranged from 24 to 93%, while total mass reductions ranged from 57 to 98% due to exfiltration. Reduction in total suspended solids concentrations ranged from 23 to 86% while reduction in total mass ranged from 69 to 96%. Chemical oxygen demand concentrations reductions ranged from 37 to 70%. Storm water volume reductions ranged from 55 to 70% through variably saturated exfiltration to surrounding clayey glacial till soils (Ksat = 10?6?cm/s), while peak flow reductions ranged from 36 to 85%. Results of statistical analysis indicate that a passive downflow PER is capable of functioning as an in situ water quality and quantity control BMP for rainfall runoff. Results indicate that as structural and nonstructural controls are implemented, monitoring, examination, and understanding of event-based and life-cycle performance are critical to achieve both quantity and quality goals.     

Bioretention Impact on Runoff Temperature in Trout Sensitive Waters

A study was conducted in western North Carolina, along the southeastern extent of the U.S. trout populations, to examine the effect of bioretention areas on runoff temperature. 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. Despite temperature reductions, effluent temperatures still posed a potential threat to coldwater streams during the peak summer months. During the summer months, effluent temperatures were generally coolest at the greatest soil depths, supporting evidence of an optimum drain depth between 90 and 120 cm. The ability of bioretention areas to reduce storm-water temperature and flows supports their application to reduce the thermal impacts of urban storm-water runoff.     

Hydraulic Model for Sedimentation in Storm-Water Detention Basins

Treatment of storm-water runoff may be necessary before discharge to surface waters. In urban areas, space constraints limit selection of conventional treatment systems, and alternative systems are needed. This research program involves design and laboratory testing of a small footprint nonproprietary detention basin which consists of pipes and box culvert sections with a specialized inlet and outlet system. This system can be placed below grade near the roadway section as part of the conventional drainage system and does not require additional right-of-way. A mathematical model, based entirely on hydraulic principles, is developed to estimate particle removal efficiency of the rectangular detention basin for the treatment of storm-water runoff by extending ideal horizontal tank theory under the condition in which water level is varied. A physical model was built in 1/5 scale to measure particle removal performance and validates the conceptual model. Experiments were performed for steady inflow conditions with different inflow rates, durations, and suspended sediment concentrations. Measured time series outflow suspended sediment concentrations and particle removal efficiency compare well with calculated results from the conceptual model. The outflow particle-size distribution can also be estimated using the conceptual model.     

Sediment Discharge from a Storm-Water Retention Pond

A small storm-water retention pond is primarily designed to reduce the peak rate of surface runoff. From a water quality standpoint, that same pond may be irregular in shape and trap suspended sediment carried by the surface runoff generated upstream of the site. Considering different pond inlet locations, the writer’s numerical model is used to investigate the change in peak concentration of sediment discharge at the pond outlet. It has been found that the various hydraulic conditions can have a significant impact on sediment discharge. Three different cases are presented to show the flexibility of modeling changes in boundary conditions. The results may help designers evaluate sediment discharge to determine the most effective pond inlet locations.