|Monday, May 31|
Assessing the function of stormwater management facilities in a changing climate
Nick Mocan, Canada
Kevin Stevens, Canada
Nick Mocan, Canada
Patrick Strzalkowski, Canada
* Amanda Pinto, x, Canada
Stormwater management (SWM) facilities are a common approach to stormwater management throughout southern Ontario. Historically, SWM design has assumed that nutrient and contaminant removal predominantly occurs during warmer months. Consequently, little attention has been paid to the hydrology and function of SWM facilities during colder seasons. Understanding this is particularly important as anticipated climate change scenarios forecast warmer, wetter winters. In a year long assessment of the hydrological processes within SWM facilities in southern Ontario, we observed they were receiving and discharging surface water throughout the winter. We also observed that contaminant removal varied seasonally and between consecutive periods of precipitation and snowmelt. Removal rates of total suspended solids, total phosphorus, and reactive phosphorus were highest in the fall. While vegetation within SWM facilities undergoes a dormant period during the winter, we identified several species that remained active. Cold chamber experiments are ongoing to assess the capacity of these cold tolerant species to contribute to contaminant removal during the winter. Our long-term goals are to improve our understanding of SWM facilities’ year-round function to enhance their operations in the face of a changing climate.
GIS-Based Mapping for Contaminant-based Hazards from Stormwater Releases
* Mohamed Gaafar, University of Alberta, Canada
Evan G. R. Davies, Canada
"Deterioration in surface water quality near urban centres has been attributed to polluted stormwater flows. Factors associated with urban sprawl such as land-use changes, soil erosion, intense runoff, and releases of chemical contaminants increase the polluting effects of stormwater effluents that reach receiving waters. A chemical commonly used in drinking water treatment, chloramine, can pose serious environmental risks as its long-lasting residuals and harmful disinfection by-products in treated water reach surface waters through different outdoor tap water uses. The present study draws on work incorporating stormwater monitoring, stormwater simulations, water quality modeling and GIS analyses to build efficient hazard assessment maps for chloramine pollution in stormwater flows. For a case study of a stormwater basin in Edmonton, Alberta, flow monitoring and field sampling programs were designed to collect stormwater flow and water quality characteristics. Flow data was used to calibrate and validate a MIKE URBAN stormwater model, while water quality data was used to determine the variable decay constants of chloramine in the sewer system. With these decay coefficients, a newly developed water quality model, VDCS, was able to anticipate temporal and spatial changes in chloramine concentration in the sewer system and down to its outfall. 2-, 5- and 10-year design storms were adopted to represent wet weather conditions along with dry weather flows, and were simulated in the stormwater model of MIKE URBAN. The VDCS water quality model was then used to predict consequent chloramine concentrations at the system outfall. Finally, a GIS-based mapping model was built to generate hazard maps under different weather conditions using the Inverse Distance Weighted model. Chloramine contamination hazard maps were developed using two approaches, 1) Event Mean Concentrations (EMC) considering the total pollutant mass, concentration and flow volume and 2) fuzzy logic to include more chloramine-affecting factors such as EMC, land-use types, chloramine decay coefficients, annual rainfall, ground slopes, and proximity to the drainage network. For 2- and 5- year design storms, 60% and 80% of the study area was found to generate concentrations less than the allowable chloramine discharge concentration of 0.02 mg/L, while the 10-year storm posed no significant concerns. Hence, system operators should be more concerned with chloramine releases under dry weather conditions and smaller rainfalls. For the GIS-based hazard maps, the EMC-based hazards approximated 25% of the basin to be at moderate to high risk of chloramine pollution. The fuzzy-based approach showed 54% of the basin at moderate to high risk of chloramine pollution. To improve the hazard maps, extensive pollutant monitoring programs can be utilized and more sophisticated hazard analysis techniques can reveal interactions among driving factors. This study shows that easy-to-use hazard maps can be developed even for complex pollutants like chloramine, and hence potentially adapted to other stormwater pollutants. Applying the hazard assessment mapping methodology presented here, stormwater pollution and unregulated release incidents can be effectively controlled, focusing resources on areas with higher hazard susceptibility without the need for long model simulations on a case-by-case basis"
* Billy Shecanapish, Department Of Public Works, Canada
"I work in the Water and Wastewater sector for my community of Kawawachikamach, Naskapi Nation. This summer our treatment plant will be undergoing a major upgrade funded by Indigenous Services Canada. It has been in the works since more than few years now with the help our Nations engineering consultant firm Bruser. Our water treatment plant will double in size namely more reservoir, better generating system which will be located outside the plant. We have another treatment system, we have been using a Nanofiltration Technology system compromising of membranes(44 of them), UV system, cartridge stage, sand filtration, discs. We do use our nearby Lake Peter as our source water. We have a raw water pump that pumps water from the lake into the plant for our treatment process consisting of five stages before it is distributed in our network for our users/community of 900 people. We have had this system since July, 2006 but another upgrade had to be done because of the increased population and more buildings/houses being built in our community. Thank you!"
Bioretention amendments for reducing phosphorus leaching: field investigation
* Yihui Zhang, University of Calgary, Canada
Anton Skorobogatov, Canada
Jianxun He, Canada
Angus Ch, Canada
Bert van Duin, Canada
"In the face of urbanization and climate change, stormwater management using conventional and centralized management strategies has been considered insufficient. Since the late 1990s, stormwater control measures, which are decentralized and of small footprint, have begun to be implemented to attenuate the impacts of urbanization as well as climate change. As one of the most beneficial source control practices for treating road runoff, bioretention systems have been showcased to reduce stormwater runoff volume and improve stormwater runoff quality. However, in practice media have often been mixed with compost, and potentially are the source of leaching (especially nutrients). Nutrient leaching from 24 bioretention mesocosms, situated in the Town of Okotoks, Alberta, was observed from their initial operation in 2017 to present. Amendments have been employed to reduce phosphorus (P) leaching and, further, to possibly affect P removal of bioretention systems. Therefore, the primary objective of this work was to observe the performance of a range of candidate amendments for a standard bioretention mix designated by the City of Calgary through field investigation. Two control cells and six cells, which are amended with eggshell, drywall, water treatment residuals (WTR), activated aluminum, SorptiveMEDIA, and Phosfilter, respectively, at 5% or 10% in volume, were constructed and monitored in 20 simulated events from June to October of 2020. Each cell has a surface area of 1 m x 1m, with a depth of 100 cm (60 cm media, 20 cm gravel, and 20 cm ponding on top). Over the study period, the overall removal rates of reactive phosphorus (RP) of the amended cells are in the range of -77% to 63%, while the average removal rate of two control cells is -400%. When comparing to the control cells, these six amended cells are effective in reducing P leaching, but to different degrees. In particular, the cells amended with WTR, SorptiveMEDIA and activated aluminum are shown to have positive P remove rates, and WTR is superior to all other amendments in terms of removal rate, at 63%. In addition, the event mean concentration (EMC) of P in the outflow from the amendment cells declined with the events (time); whereas, a slight increase in P EMC was observed from the control cells. All amendment cells leached nitrogen (N) to a similar degree (in terms of EMC) as the control cells, except the eggshell cell, which leached additional N from the eggshell itself. The hydrological performance (the water retention rate) of the cells was not largely affected by the addition of the amendments. The findings along with the cost, longevity, and vegetation performance impacts would provide insights to help practitioners select amendments for reducing P leaching from bioretention systems. "
Optimal Bioretention cell design under current and future climate conditions
* Rahmah Khalid, York University, Canada
Everett Snieder, Canada
Usman Khan , Canada
Increased extreme rainfall events, a direct consequence of climate change, contribute to the heightened risk pluvial flooding in urban cities. This risk is further amplified by urbanisation and the conversion of pervious to impervious areas. Stormwater runoff is generated in greater quantities, transporting with it an array of contaminants originating from the surfaces of impervious areas. Aquatic habitats in receiving waterbodies may be adversely affected as they are exposed to increased pollution. Bioretention Cells (BRCs), a subset of Low Impact Development (LID) measures, can be used to alleviate the risk of flooding and to enhance water quality of stormwater runoff by retrofitting them in urban areas. Existing design guidelines are based on current and historic climate trends, which may be inadequate under future climate conditions. BRC design is a highly iterative and time-consuming process due to the range of design values expressed in the guidelines. Using an optimisation algorithm such as the Non-dominated Sorting Genetic Algorithm (NSGA-II) can simplify this process, allowing designers to compare a host of design parameters, yielding site specific and optimum designs. Typically, BRCs designs are modelled using hydrological software such as the Stormwater Management Model (SWMM), which is computationally expensive due to the nature of process-based models. A Surrogate Model (SM) is proposed as an alternative tool for evaluating BRC designs, favoured for their computational efficiency and accuracy. Following a case study for BRC design in the City of Toronto, an ensemble of Artificial Neural Networks (ANNs) was developed as a SM to SWMM. To investigate whether current design guidelines based on historic trends are adequate for future climate change scenarios, the SM was trained on 30 years of historic climate data obtained from the IDF_CC tool developed by the University of Western. NSGA-II was used to optimise BRC design under 18 different rainfall events ranging in intensity and duration. Performance of the BRC in terms of runoff volume reduction and Total Suspended Solids (TSS) removal was studied under future climate conditions. To compare, an optimal design under future climate conditions (increased runoff and TSS concentration) was generated, for the periods of 2030 – 2059 and 2060 – 2089. Initial results indicate that minor increases to existing design guidelines will ensure BRCs meet performance targets under future climate conditions. The proposed framework allows decision makers to arrive at highly efficient BRCs with minimal cost in a fraction of the time previous methods used. Moreover, the optimal designs under future climate conditions can be used to aid policy makers in development of future design guidelines.