Allison Plante
The city of Miami stands as a prime example of modern urban stormwater control systems and infrastructure. With an annual wet season from April through November, significant rainfall (about 59.73 inches annually) and storm surges infiltrate the city’s streets, causing flooding and sanitary sewage system overflows. To mitigate the impacts of stormwater in this urbanized and impervious area, man-made canals provide a control method of connecting any inland stormwater flow to the Biscayne Bay. The Miami-Dade County canal system includes primary and secondary canals, which are designed to handle significant water flow and prevent flooding. These canals are the backbone of urban stormwater management.
To maintain the overall physical and chemical quality of the collected stormwater before discharging into Biscayne Bay, there are multiple devices and infrastructure set in place. Physical water quality is influenced by solid waste such as oil, large debris, trash, plastic debris, and sediment particles which can enter a canal system through erosion, run-off, and construction activities. The most effective engineering device to mitigate the impacts of physical pollutants on the water quality is filtration systems. In general, surface filters achieve a pollutant removal efficiency rate of 85% to 95% for floating contaminants like oil, grease, and other hydrocarbons (Branford et al., 2024). Filtration system devices that are currently used in Miami-Dade County canals include Line Skimmers, Filter Cages, and StormBasins®. These devices’ pollutant removal efficiency rates are currently being studied as they are recent additions into the canal system by Miami-Dade Environmental Resource Management (DERM). The most effective device will be invested in and used in future water quality control projects.
In terms of chemical pollutants, heavy metals such as lead and mercury, pesticides and herbicides, nutrients from fertilizers like nitrogen and phosphorus, and industrial chemicals such as polychlorinated biphenyls (PCBs) all negatively affect water quality. Specifically in Miami, there are devices in place to control the amount of chemical pollutants within the stormwater drainage and ultimately in the canals. For nutrient and bacteria control, media devices such as Bold and Gold® Media are used to remove nitrogen, phosphorus, and bacteria from stormwater runoff. The device uses a combination of metal, clay, sand, and recycled rubber to effectively trap pollutants. Bold and GoldⓇ Media has removal rate efficiencies of 95% phosphate removal, 80% nitrogen removal, and 90% fecal indicator bacteria removal (Brandford et al., 2024). Another important device used within the Miami-Dade canal system is a water quality control infrastructure system called an EcoVault Chamber. This is an example of a baffle box design which incorporates screening, separating, and filtration in order to remove sediments, heavy metals, oils, and nutrients from stormwater run-off.
All the water quality control devices mentioned above are collectively a part of Miami-Dade Environmental Resource Management’s (DERM) recent pilot projects, which strive to improve the physical and chemical quality of the canal system for the betterment of human health and the environment. Thanks to the research and development teams at DERM, tracking the efficiency rates and limitations of each device helps environmental engineers and water resource engineers across the nation to better understand the best practices for water quality control and maintenance, especially in urbanized areas.
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