Automatic Calibration of the U.S. EPA SWMM Model for a Large Urban Catchment

The Storm Water Management Model was adapted and calibrated to the Ballona Creek Watershed, a large urban catchment in Southern California. A geographic information system (GIS) was used to process the input data and generate the spatial distribution of precipitation. An optimization procedure using the complex method was incorporated to estimate runoff parameters, and ten storms were used for calibration and validation. The calibrated model predicted the observed outputs with reasonable accuracy. A sensitivity analysis showed the impact of the model parameters, and results were most sensitive to imperviousness and impervious depression storage and least sensitive to Manning roughness for surface flow. Optimized imperviousness was greater than imperviousness predicted from land-use information. The results demonstrate that this methodology of integrating GIS and stormwater model with a constrained optimization technique can be applied to large watersheds.     

Compaction’s Impacts on Urban Storm-Water Infiltration

Soil infiltration is a critical component of most urban runoff models. However, it has been well documented that, during urbanization, soils are greatly modified, especially in relation to soil density. Increased soil compaction results in soils that do not behave in a manner predicted by traditional infiltration models. Laboratory and field tests were conducted to investigate detailed infiltration behavior of disturbed urban soils for a variety of soil textures and levels of compaction. The results from traditional permeability tests on several soil groups showed that, as expected, the degree of compaction greatly affected the steady-state infiltration rate. The field tests highlighted the importance of compaction on the infiltration rate of sandy soils, with minimal effect seen from antecedent moisture conditions. For the clayey soils, however, both the compaction level and antecedent moisture conditions were important in determining the steady-state infiltration rate.     

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.     

On Parameter Estimation of Urban Storm-Water Runoff Model

An existing accumulation and wash-off model was applied and calibrated on a standard asphalt parking lot located in the northeastern United States. The field measured data consisted of rainfall, flow, and runoff samples taken from over 26 storm events monitored from 2004 to 2006. The contaminants under consideration include: total suspended solids, total petroleum hydrocarbons-diesel range hydrocarbons (TPH-D), dissolved inorganic nitrogen (DIN) (comprised of nitrate, nitrite, and ammonia), and zinc (Zn). The objective of the study was to provide probability distributions of model parameters for contaminants that have not been documented much (TPH-D, DIN, and Zn). The best fitting parameter values were found on a storm by storm basis. Subsequently, the range and variability of these parameters are provided for modeling purposes and other urban storm-water quality applications. A normal distribution was fitted to the optimized model parameter values to describe their distributions. A simulated annealing algorithm was used as the parameter optimization technique. Several examples are given to illustrate the methodology and the performance of the model. Finally, a Monte Carlo simulation was performed to assess the capability of the model to predict contaminant concentrations at the watershed’s outlet.     

Comparison of Two Model Concepts for Simulation of Nitrogen Removal at a Full-Scale Biological Nutrient Removal Pilot Plant

The experimental studies conducted at the Hanover-Gümmerwald pilot wastewater treatment plant (WWTP) focused on minimizing nitrogen loads discharged during stormwater events. The data collected during the plant operation were used for a long-term process simulation. The aim of this study was to compare predictive capabilities of two different mechanistic models (ASM2d and ASM3P) in terms of nitrogen removal. The influent wastewater composition was generated using on-line measurements of only three parameters (COD, N–NH4+, P–PO43?) and the model predictions were primarily compared with on-line data (concentrations of N–NH4+, N–NO3?) originating from the aerobic zone of the bioreactor. The simulation results confirmed the experimental data concerning the capabilities of the system for handling increased flows during stormwater events. The predicted peaks of N–NH4+ at the line with the quadruple dry weather flow rate were normally exceeding 8?g?N?m?3 (similar to the observations), whereas no (or minor) peaks of N–NH4+ were predicted for the line with the double dry weather flow rate. The relationships between ASM2d and ASM3P predictions for N–NH4+ and N–NO3? were highly correlated (r2 = 0.83–0.99) with the slopes remaining close to 1.0. Both models appear to be equally suitable for practical applications in common municipal WWTPs.     

Calibrated Models of Deicing Agent Solids, Pavement Texture, and Specific Conductivity of Highway Runoff

Field data and existing theory suggest that pavement texture governs the seasonal persistence of deicing agent solids and the storm scale variability of the specific conductivity of highway runoff. We measured precipitation, runoff, and specific conductivity for 50 storms over four deicing seasons at a highway drainage system in southeastern Massachusetts. An average pavement texture of 2.44?mm was measured and 5.17×105?kg of calcium magnesium acetate, salt, and premix applications was reported as well. Catchments and a depression storage layer model the highway drainage system, which routes hyetographs and slowly dissolving deicing agent solids to storm scale hydrographs and specific conductivity pollutographs. We equate the average pavement texture to the depression storage layer depth, which receives applied deicing agent solids, controls their dissolution during a storm, and governs their seasonal scale persistence. The observed average pavement texture, precipitation, and deicing agent applications yield first flush (storm scale) specific conductivity values in the depression storage layer that range from a winter maximum of 15?mS/cm to summer values two orders of magnitude lower. The winter maximum, or seasonal scale first flush of specific conductivity, would be lower for rougher pavement due to slower dissolution. The rougher pavement would also induce stronger persistence of deicing agent solids throughout the year, so that appreciable storm scale first flushes would occur in the summer.     

Evaluation and Optimization of Bioretention Media for Treatment of Urban Storm Water Runoff

Bioretention is a relatively new urban storm water best management practice. The objective of this study is to provide insight on media characteristics that control bioretention water management behavior. Eighteen bioretention columns and six existing bioretention facilities were evaluated employing synthetic runoff. In columns, the runoff infiltration rate through different media mixtures ranged from 0.28 to 8.15?cm/min at a fixed 15 cm head. For pollutant removals, the results showed excellent removal for oil/grease (>96%). Total lead removal (from 66 to >98%) decreased when the total suspended solids level in the effluent increased (removed from 29 to >96%). The removal efficiency of total phosphorus ranged widely (4–99%), apparently due to preferential flow patterns, and both nitrate and ammonium were moderate to poorly removed, with removals ranging from 1 to 43% and from 2 to 49%, respectively. Two more on-site experiments were conducted during a rainfall event to compare with laboratory investigation. For bioretention design, two media design profiles are proposed; >96%?TSS, >96%?O/G, >98%?lead, >70%?TP, >9%?nitrate, and >20%?ammonium removals are expected with these designs     

Distributed Sensitivity Analysis of Flood Inundation Model Calibration

Uncertainties in hydrodynamic model calibration and boundary conditions can have a significant influence on flood inundation predictions. Uncertainty analysis involves quantification of these uncertainties and their propagation through to inundation predictions. In this paper the inverse problem of sensitivity analysis is tackled, in order to diagnose the influence that model input variables, together and in combination, have on the uncertainty in the inundation model prediction. Variance-based global sensitivity analysis is applied to simulation of a flood on a reach of the River Thames (United Kingdom) for which a synthetic aperture radar image of the extent of flooding was available for model validation. The sensitivity analysis using the method of Sobol’ quantifies the significant influence of variance in the Manning channel roughness coefficient in raster-based flood inundation model predictions of flood outline and flood depth. The spatial influence of the Manning channel roughness coefficient is analyzed by dividing the channel into subreaches and calculating variance-based sensitivity indices for each subreach. Replicated Latin hypercube sampling is used for sensitivity analysis with correlated input variables. The methodology identifies subreaches of channel that have the most influence on variance in the model predictions, demonstrating how far boundary effects propagate into the model and indicating where further data acquisition and nested higher-resolution model studies should be targeted.     

Steady Groundwater Transport of Highway Deicing Agent Constituents from an Infiltration Basin

The highway deicing agent groundwater plume from an infiltration basin in the Plymouth-Carver Aquifer near State Route 25 in southeastern Massachusetts is modeled and measured in order to assess the impact of the basin on groundwater transport processes. The advective transport model superimposes the existing steady models of axisymmetric basin hydraulics of Zlotnik and Ledder in 1992 and the two-dimensional ambient flow of Gelhar and Wilson in 1974. The basin component incorporates a surface source of finite-radius into a Hankel transform model for unconfined aquifers, whereas the ambient component varies linearly in the horizontal and vertical directions. Contaminant streamlines describe the resulting groundwater plume, and highway deicing agent constituents provide useful tracers. A simple vertical dispersion model quantifies the spread of contaminants across the bottom of the plume. Deicing agent constituent data calibrate a 17?m basin radius, a 45?m plume width, a bottom streamline 6–10?m below the water table, and a vertical dispersivity of 34?cm. The latter value is comparable to the amplitude of vertical excursions caused by storm scale fluctuations of hydraulic head, as measured by Ostendorf et al. in 2007. Infiltration basins alter ambient advection by displacing streamlines downward and augment vertical mixing by imposing aperiodic vertical fluctuations on the ambient flow field.     

Performance of Nitrogen-Removing Bioretention Systems for Control of Agricultural Runoff

This research evaluated nitrogen-removing bioretention systems for control of nutrients, organics, and solids in agricultural runoff. Pilot-scale experiments were conducted with bioretention systems incorporating aerobic nitrification and anoxic denitrification zones with sulfur or wood chips as denitrification substrates. Varying hydraulic loading rates (HLRs), influent concentrations, and wetting and drying periods were applied to the units during laboratory and two seasons of field tests with dairy farm runoff. Total N removal efficiencies greater than 88% were observed in both units with synthetic storm water. In first-season field tests, moderate removal efficiencies were observed for chemical oxygen demand (46%), suspended solids (69%), total phosphorous (TP) (66%), and total N (65%). During the second season, operational changes in the farm resulted in lower organic, solids, and nutrient loadings resulting in improved effluent quality, especially for suspended solids (81% removal) and total N (82% removal). The systems were not hydraulically overloaded even at 20 times the normal HLR.     

Diffusion Wave Model for Simulating Storm-Water Runoff on Highway Pavement Surfaces at Superelevation Transition

On a curved section of highway, the cross slope of the road is often designed to be superelevated to balance the centrifugal force and gravity applied on vehicles. The accumulation of storm-water runoff (sheet flow) near superelevation transitions may significantly increase due to the extended flow path and converging flow lines. A two-dimensional finite-volume-based diffusion wave model is developed to simulate the sheet flow on these geometrically complex surfaces. Both Dirichlet- and Neumann-type boundary conditions are developed for open boundaries based on kinematic wave theory. Results show that the distribution of sheet flow is closely related to the cross slope, longitudinal slope, rainfall intensity, and the width of the road. The analysis of sheet flow characteristics on superelevation transition areas suggests that the optimal longitudinal slope in the range of 0.3–0.4% minimizes the depth of storm-water runoff on the road surface.     

New Paradigm for Sizing Riparian Buffers to Reduce Risks of Polluted Storm Water: Practical Synthesis

Riparian buffers are commonly promoted to protect stream water quality. A common conceptual assumption is that buffers “intercept” and treat upland runoff. As a shift in paradigm, it is proposed instead that riparian buffers should be recognized as the parts of the landscape that most frequently generate storm runoff. Thus, water quality can be protected from contaminated storm runoff by disassociating riparian buffers from potentially polluting activities. This paper reviews and synthesizes some simple engineering approaches that can be used to delineate riparian buffers for rural watersheds based on risk of generating runoff. Although reference is made to specific future research that may improve the proposed methods for delineating riparian buffers, the approaches described here provide planners and engineers with a set of currently available scientifically defensible tools. It is recommended that planners and engineers use available rainfall and stream discharge data to parameterize the buffer-sizing equations and use variable-width buffers, based on a topographic index, to achieve a realistic representation of runoff generating areas.     

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.     

Integrated Storm-Water Management for Watershed Sustainability

One aspect of integrated watershed management evaluates the impact of development on the local hydrologic cycle and, in particular, drinking water, wastewater, and storm-water infrastructure. Sustainable storm-water management focuses on selecting storm-water controls based on an understanding of the problems in local receiving waters that result from runoff discharges. For example, long-term problems associated with accumulations of pollutants in water bodies include sedimentation in conveyance systems and receiving waters, nuisance algal growths, inedible fish, undrinkable water, and shifts to less sensitive aquatic organisms. Short-term problems associated with high pollutant concentrations or frequent high flows (event-related) include swimming beach closures, water quality violations, property damage from increased flooding, and habitat destruction. A wide variety of individual storm-water controls usually must be combined to form a comprehensive wet weather management strategy. Unfortunately, combinations of controls are difficult to analyze. This will require new modeling techniques that can effectively evaluate a wide variety of control practices and land uses, while at the same time ensure that the flood-control objectives also are met. The results of these new models and novel techniques used for storm-water control then can be incorporated into an evaluation of the urban water cycle for a specific service area to determine whether storm-water controls can provide additional benefits such as reduction of potable water use and reduction of sanitary sewer overflow events.     

Process Modeling of Storm-Water Flow in a Bioretention Cell

A two-dimensional variable saturated flow model was developed to simulate subsurface flow in bioretention facilities employing the Richards’ equation. Variable hydrologic performances of bioretention are evaluated using the underdrain outflow hydrographs, outflow volumes for 10 storms with various duration and depth, and flow duration curves for 25 different storms. The effects of some important design parameters and elements are tested, including media type, surrounding soils, initial water content, ratio of drainage area to bioretention surface area, and ratio of cell length to width. Model results indicate that the outflow volume via underdrain is less than the inflow; the flow peak is significantly reduced and delayed. Underdrain outflow volume from loamy sand media (with larger Ks) is larger than that from sandy clay loam media. The saturated hydraulic conductivity, storage capacity, and exfiltration into surrounding soils contribute to the hydrologic performance of a bioretention cell. Initial media storage capacity is affected by the hydraulic properties of media soils, initial water content, and bioretention surface area. The exfiltration volume is determined by the surrounding soil type and exfiltration area, dominated by flow through the bottom of the media.     

Groundwater Mounding at a Storm-Water Infiltration BMP

This research presents an initial study of the impacts of storm-water infiltration on a shallow unconfined aquifer at a bioinfiltration best management practice (BMP) on the campus of Villanova University. The study site is a vegetated infiltration basin with a 0.52?ha drainage area consisting of parking areas and recreational fields and features approximately 35% directly connected impervious area. The research utilized continuous monitoring of precipitation, groundwater elevation, and groundwater temperature in conjunction with surface water hydrologic modeling to assess the duration, magnitude, and extent of groundwater mounding at a storm-water infiltration BMP. Results indicate that precipitation greater than 1.80?cm causes increased mounding at wells adjacent to the site. In addition, it was found that precipitation less than approximately 1.80?cm leads to larger increases in groundwater elevation at an upgradient control well located near the edge of a large grass field. The extent of groundwater mounding is observed to be localized to the BMP and does not extend a significant distance downgradient. In addition, the magnitude and duration of groundwater mounding is related to both infiltration rate and groundwater temperature, such that cooler temperatures correlate to increased mounding. This study demonstrates the utility of groundwater monitoring for the purpose of BMP hydraulic performance assessment, and recommends that additional research be conducted in the future and that groundwater monitoring be considered for site monitoring plans.     

Oil and Grease Measurement in Highway Runoff—Sampling Time and Event Mean Concentrations

An event mean concentration (EMC), usually collected with an automatic, flow-weighted composite sampler, is often used to characterize stormwater pollutants. Automatic samplers are not recommended for collecting oil and grease (O&G) samples due to possible biases associated with interactions with tubing and pumps. To measure the EMC without sampler interferences, a series of grab samples (often over ten samples) must be collected along with the flow measurement to compute the EMC. This paper examines 22 O&G pollutographs from small, impervious highway sites, to determine when a single O&G grab sample most closely approximates a flow-weighted composite sample. Samples collected within the first hour of a storm event overestimated the O&G EMC by 20?mg/L or more, while samples collected toward the end of the event underestimated the EMC. The best time to collect a single grab sample ranged from 1 to 6 h after the beginning of runoff, and was related to site or storm-specific factors. Results obtained from this study also showed that strong correlations (R2 = 0.9) exist between O&G and other organic constituents, such as chemical oxygen demand (COD) and dissolved organic carbon (DOC). Correlations also exist between O&G EMC, antecedent dry days, and total rainfall. Depending upon site and regulatory specific factors, using COD or DOC EMCs in lieu O&G samples may be a better strategy.     

Retrofit Storm Water Retention Volume for Low Impact Development

The concept of low impact development (LID) applies decentralized on-site runoff source control to storm water management. LID is an integration of bioretention and vegetated landscapes to maintain a catchment’s hydrologic and ecological functions. In current practice, the LID implementation is quantified for the specified watershed development. During the dynamic development process, the existing LID facilities have to be improved according to the incremental changes in the watershed. This technical note presents an on-site hydrologic approach to relate the required incremental storm water retention volume to the alteration of surface imperviousness in the tributary area. This approach allows the storm water retention volume to be tailored according to the stage of the watershed development. Cumulatively, the total storage volume can be achieved though multiple stages of the watershed development. The incremental retention volume is found to be related to the local average event rainfall depth. Design charts were produced and normalized by the local average rainfall event depth for generalized applicability.     

Simulation Model for Level Furrows. I: Analysis of Field Experiments

The level-furrow irrigation system consists of furrowing a level basin. In level furrows, irrigation proceeds just like in level basins: the field is flooded from one point and water spreads to irrigate each furrow. Several writers have reported that this irrigation system has the potential to conserve water as compared to level-basin irrigation. However, no comparative studies on the performance of both irrigation systems are available, and the simulation of level furrows has not been attempted. In this work, two field experiments are reported. Both of them were performed in the same soil and in the same conditions. In the first experiment, infiltration was estimated for a series of furrow irrigation discharges and for a level basin. In the second experiment, a level furrow irrigation event was evaluated. A simulated level basin irrigation event in the level furrow experimental field required six times more time and water to complete advance. Infiltration equations including the irrigation discharge or the wetted perimeter as independent variables were proposed for the experimental furrow conditions. Application of a furrow simulation model to the level–furrow experiment resulted in an underestimation of the time of advance. To overcome this problem, a simulation model for level furrows was developed and is presented in a companion paper. The reported field experiments were used to validate the model, which was applied (in a companion paper) to explore adequate conditions for level furrow irrigation performance.     

Comparison of Sorptive Filter Media for Treatment of Metals in Runoff

Rainfall runoff and snowmelt impacted by anthropogenic activities can transport significant loads of metals. Ecological concerns and recent regulatory guidance have spurred development of unit operations such as ex situ sorptive filters and engineered media infiltration systems with the intent of including sorption mechanisms for metals as compared to conventional filter media. Applications of sorptive media for rainfall or snow unit operations include infiltration systems, sorptive clarifiers, separation systems, and deformable, cartridge, or tubular filters. Column breakthrough experiments were conducted for selected sorptive filter media and compared to conventional filter media. Comparing plain sand, granular activated carbon, and cementitious media to oxide coated/admixture media, manganese oxide coated media (MOCM) had the best overall operational behavior with 10% breakthrough bed volumes (Vb), breakthrough capacity (X/Mb), and exhaustion capacity (X/Mexh) two times higher than those of iron oxide coated sand (IOCS). As the empty bed contact time (EBCT) for MOCM increased from 0.5?to?1.1?min; the values of Vb, X/Mb, and X/M increased by a factor of 2. Compared to metal breakthrough for uncoated sand or polymeric media, manganese oxide polymeric media (MOPM) as well as bench scale partial exfiltration reactor media (combining uncoated cementitious media and oxide coated media) provided significant capacities for Pb, Cu, Cd, and Zn. Removal mechanisms for MOCM include adsorption, surface complexation, ion exchange, and filtration, accounting for MOCM’s high capacity. Although uncoated cementitious media also had a significant capacity for metals through precipitation and filtration, breakthrough instability of metal precipitates and high effluent pH can limit application in monomedium applications.