Urbanization, in general, increases impervious cover in a watershed. When impervious cover is increased, precipitation does not infiltrate as it would naturally. Instead, rainfall is quickly piped and channeled directly to the watercourse. The impacts of increases to impervious cover are evident when comparing stream hydrographs. Rural areas show a gradual response to rainfall, as well as typically having a lower peak flow and extended receding limb. Changes in hydrology as a result of urban development can impact the amount, timing and quality of water reaching a natural feature, as well as the location of different flow paths. Increase in surface runoff from the urbanized areas can result in flooding and erosive damage to our streams and structures on public and private property. In addition, human activity produces pollution, which in combination with increased runoff can degrade the quality of our water resources. The practice of managing urban runoff is continuing to evolve as the science of watershed management and understanding of our watersheds grow. Effective management of urban runoff is critical to the continued health of our streams, rivers, lakes, fisheries and terrestrial habitats. Toronto & Region Conservation Authority (TRCA), as a watershed management agency, develops stormwater management criteria, provides guidance in the planning and design of stormwater management infrastructure for developers, consultants, municipalities, and landowners, and outlines the processes and infrastructure needed to address flooding, water quality, erosion, water balance, and natural heritage. This presentation will discuss TRCA’s stormwater and floodplain management applied within its nine watersheds.

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