Quantifying clogging patterns of infiltration systems to improve urban stormwater pollution reduction estimates

Modeling the impact of future rainfall changes on the effectiveness of urban stormwater control measures

The convergence of urban expansion, deteriorating infrastructure, and a changing climate will escalate the risks of stormwater pollution and urban flooding in the coming decades. Using outputs from an ensemble of global climate models to drive a high spatial resolution stormwater model, we analyzed climate change impacts on urban stormwater runoff and control measures for 23 cities across the United States. Runoff model outputs for two future emissions scenarios ending in 2055 were compared against a historical scenario to assess changes. All cities showed increases in average annual stormwater runoff, with changes up to 30% over the next 30 years due to a greater frequency of high intensity storm events. Runoff model outputs showed substantial variation across cities with untreated stormwater runoff increasing by as much as 48%. Patterns of future runoff impacts within cities will affect the performance of distributed treatment strategies such as Green Stormwater Infrastructure (GSI) to meet municipal water quality improvement and runoff reduction goals. Results indicate that adoption of adaptable design standards and decision support tools that readily accommodate projected precipitation changes are critical for supporting more resilient designs of stormwater control measures.

Curbing sediment: The effects of added surface roughness in the curb and gutter as a novel pretreatment for green infrastructure stormwater control measures

Stormwater control measures (SCMs) are employed to reduce the multitude of deleterious impacts of urban runoff on receiving waters. Sediment accumulation in infiltration-based SCMs can clog these systems, resulting in lack of hydraulic function and reduced stormwater treatment efficacy. As such, pretreatment devices, such as forebays, filter strips, or catch basin sumps, are typically employed upstream of SCMs to remove sediment and prolong maintenance intervals. However, the tendency of SCMs to be retrofitted into space-constrained, ultra-urban areas makes including pretreatment technologies difficult. An alternative pretreatment device for green infrastructure SCMs was developed and tested in the laboratory; alterations were made to the standard curb and gutter, which is ubiquitous within urban environments, to increase the roughness of these surfaces. Roughness was added to the curb and/or gutter of mock road sections constructed of expanded polystyrene (EPS) foam using a computer numerical control (CNC) router. Twenty-one patterns with varying degrees of depth, shape, and spacing were implemented to trap sediment from simulated runoff; samples were collected upstream and downstream of the added roughness and analyzed for sediment removal and particle capture. Patterns which included added roughness in both the curb and gutter reduced total suspended solids (TSS) concentrations by up to 95% (median 85%) and reduced median d50 and d90 in runoff from 46.9 to 39.4 μm and 322 to 100 μm, respectively. Continued TSS removal was observed during repeated testing designed to simulate up to seven runoff events, indicating the potential for sustained sediment accumulation before the need for maintenance via regular street sweeping. With routine maintenance performed at appropriate intervals, these findings indicate that added roughness to curb and gutters could be utilized as a viable pretreatment technology for green infrastructure SCMs.

Application of filter media surface hydrophobic modification to reduce bioclogging in the infiltration system

Bioclogging is a commonly encountered operational issue that lowers hydraulic conductivity and the overall performance of the infiltration systems. In this paper, a novel processing for alleviating bioclogging by filter media surface hydrophobic modification was presented. Two-dimensional porous media cells were used to observe the influence of hydrophobic modification on biofilm growth in the pore structure. Moreover, two continuous-flow columns packed with gravel, one of which half gravel was hydrophobically modified, were operated with artificial wastewater to verify the effect of hydrophobic modification on bioclogging alleviation. The results showed that the biofilm growth in the cell with hydrophobic modification was slow, and the biomass was less and liable to wipe off after hydrophobic treatment. Meanwhile, the hydraulic efficiency of the flow seepage field was also improved after hydrophobic treatment. The column tests results showed that the hydraulic conductivity of the filter bed with hydrophobic modification (Column B) decreased more slowly than that of another without hydrophobic modification (Column A). Column B had the hydraulic conductivity (k) of 0.66 cm/s in the final stage of the experiment, while the k of Column A was 0.14 cm/s. It verified that hydrophobic modification of partial filter media can alleviate the bioclogging problem of the infiltration systems to some extent. The results provide a new idea and potential technical support for solving bioclogging problem.

Design-oriented evaluation of the hydrodynamics in a full-scale combined filter-lamella separator for urban stormwater treatment

The development of compact treatment devices with high removal efficiencies and low space requirements is a key objective of urban stormwater treatment. Thus, many devices utilize a combination of sedimentation and upward flow filtration in a single system. This study, for the first time, evaluates the flow field inside a combined filter-lamella separator via computational fluid dynamics. Herein, three objectives are investigated: (i) the flow field for different structural configurations, (ii) the distribution of particulate matter along the filter bed and (iii) the dynamic clogging in discrete filter zones, which is addressed by a clogging model derived from literature data. The results indicate that a direct combination of a filtration stage with a lamella separator promotes a uniform flow distribution. The distribution of particulate matter along the filter bed varies with configuration and particle size. Clogging, induced by particles in the spectrum <63 μm, creates gradients of hydraulic conductivity along the filter bed. After treating about half of Germany's annual runoff-efficient precipitation at a rainfall intensity of 5 L/(s·ha), the filtration rates increase in the front of the filter bed by +10%. Thus, long-term operating behavior is sensitive to efficient filter utilization in compact treatment devices.

Copper and Zinc Removal Efficiency of Two Reactive Filter Media Treating Motorway Runoff—Model for Service Life Estimation

The predominant techniques used for road runoff treatment are sedimentation and filtration. In filtration systems, the ability of the media to adsorb the contaminants is a finite process. Consequently, construction, operation and maintenance managers of such systems should know in advance the service life, i.e., when the used medium should be replaced, and associated costs of operation and maintenance. A batch experiment followed by a packed bed reactor (PBR) experiment addressed the kinetics of the studied media argon oxygen decarburization slag (AOD) and Polonite, followed by the development of a 1D-model to describe the change of concentration of Cu and Zn within time. The batch test results showed that Cu and Zn adsorption followed the Freundlich isotherms for AOD and Polonite. Those results coupled with the linear driving force model and the developed model resulted in good agreement between the PBR results and the simulation. The model was capable to predict (i), the service life at the hydraulic load of 0.18 m/h for AOD (Cu: 395 d; Zn: 479 d) and Polonite (Cu: 445 d; Zn: 910 d), to show (ii) the profile concentration in the PBR within time and the gradient of the concentration along the height of the reactor.

Successful mitigation of stormwater-driven nutrient, fecal bacteria and suspended solids loading in a recreational beach community

Marine and estuarine waterways adjacent to urban areas are often the final recipient of polluted stormwater runoff. Microbial degradation of coastal water quality is a direct threat to human health through fecal contamination of bathing waters and shellfish, as well as distressing local economies through the loss of waterways to commercial (shellfishing) and recreational use. In coastal waters reduction of nitrogen loading is a key strategy for prevention of noxious and toxic algal blooms. Best management practices (BMPs) can be successful tools for mitigating such pollutants in runoff, but BMPs must be tailored to individual situations for maximum effectiveness. This study examines the efficacy of a set of BMPs installed in the coastal resort Town of Wrightsville Beach, North Carolina, USA. The BMPs targeted the highly-impervious (90%+) drainage area of two stormwater outfall pipes emptying into recreationally used Banks Channel. Mitigation measures included replacement of impervious pavement with pervious concrete and construction of an infiltration chamber in the parking lot of a local recreational seaside club. Significant reductions were achieved in total stormwater discharge (62%), as well as loading of the fecal indicator bacteria Enterococcus (76%) and total nitrogen (TN - 87% decrease). Additionally, there were reductions in loading of total phosphorous (TP) and total suspended solids (TSS) to estuarine waters following BMP installment. The set of BMPs applied here have wide management applicability to coastal ecosystems, as well as freshwater riparian areas characterized by sandy, porous soils.

Assessing the Feasibility of a Cloud-Based, Spatially Distributed Modeling Approach for Tracking Green Stormwater Infrastructure Runoff Reductions

Use of green stormwater infrastructure (GSI) to mitigate urban runoff impacts has grown substantially in recent decades, but municipalities often lack an integrated approach to prioritize areas for implementation, demonstrate compelling evidence of catchment-scale improvements, and communicate stormwater program effectiveness. We present a method for quantifying runoff reduction benefits associated with distributed GSI that is designed to align with the spatial scale of information required by urban stormwater implementation. The model was driven by a probabilistic representation of rainfall events to estimate annual runoff and reductions associated with distributed GSI for various design storm levels. Raster-based calculations provide estimates on a 30-m grid, preserving unique combinations of drainage factors that drive runoff production, hydrologic storage, and infiltration benefits of GSI. The model showed strong correspondence with aggregated continuous runoff data from a set of urbanized catchments in Salinas, California, USA, over a three-year monitoring period and output sensitivity to the storm drain network inputs. Because the model runs through a web browser and the parameterization is based on readily available spatial data, it is suitable for nonmodeling experts to rapidly update GSI features, compare alternative implementation scenarios, track progress toward urban runoff reduction goals, and demonstrate regulatory compliance.