With a booming population and growing immigration, Toronto has become one of the world’s most vertical cities. It now seems almost humorous to recall that the development of The Pantages on downtown Yonge Street in 2003 was seen as somewhat ‘controversial’ because of its 45-storey, 139.9 metre height. Today, 70, 80 and 90-storey proposals are commonplace as Toronto is entering the world of the "supertalls."

But this reach-for-the-sky approach has a resulting impact underground. Imagine the number of kitchen and bathroom sinks, bathtubs and toilets in a tower with 1,000 units. Imagine the flow rates at common mealtimes or in the evenings. The stress on the city’s sewer system is real, and developers need to take it into account when designing their projects.

For that expertise, many turn to Crozier Consulting Engineers. A sewer capacity assessment is an integral part of a zoning bylaw amendment or site plan application.  It looks at the capacity of the sewer shed for a particular piece of land. Often such an assessment impacts the size of the development being planned.

Crozier is a leading consulting engineering firm in the land development and building industry. They provide services in civil, water resources, transportation, structural, mechanical, and electrical engineering, complemented by hydrogeology, landscape architecture, and building science. In Toronto specifically, Crozier is known for being trusted advisors with expertise in mixed-use residential, industrial and commercial development projects with such clients as Altree Developments, Atria Development, SmartCentres, and Oxford Properties Group.

Brimley + Progress Towers designed by A & Architects Inc. for Atria Development

The sewer capacity assessment is a component of Crozier’s site services engineering in the Land Development division of its business. Although not directly listed on the City’s Planning Application Checklist, any development application that proposes a change in land use or a net increase in discharge to the municipal sewers compared to existing conditions, is expected to include a sewer capacity assessment.

“We encourage our clients to commission this assessment during their due diligence on a development parcel,” said Ashish Shukla, a Professional Engineer and Associate who heads Crozier’s Toronto office, one of four it has in Ontario. “An assessment is only ‘complete’ when acceptable by the city, meaning all its criteria have been met. However, an initial assessment determining current capacity in the sewer shed can be prepared even before a proposed development concept is finalized, as this assessment can play a key role in scaling the planned development.”

Shukla continues to say such an assessment plays an important role in the entire development application process. “The assessment could be required to accompany a servicing report during a zoning bylaw amendment if the proposed discharge is greater than existing discharge, which is generally always the case when adding density to a site. Submitting an application without this analysis may lead to a returned application deemed incomplete by Engineering and Construction Services (ECS),” he said.

Crozier’s first step in the assessment includes confirming the status of the sewer shed, and whether a base model of the site exists in the City’s InfoWorks hydraulic model.  If so, its assessment is carried out using the same model. If a base model does not exist, the City accepts a static pipe-by-pipe analysis.

Six Points Plaza designed by IBI Group for Liberty Development

“When completing the assessment using InfoWorks, the base model is updated to include a scenario with all other active developments within the sewer shed to confirm the impact of the proposed development. This scenario includes the population and groundwater contribution from the proposed development,” said Shukla. “The model is then run for dry and wet weather flow conditions to determine the capacity within the system. This scenario will ultimately determine whether the City’s criteria for capacity can be simply met, municipal infrastructure upgrades are required, or the proposed development needs to be scaled back to meet the capacity in the system.”

Getting approval on the sewer capacity assessment as part of the site plan application or zoning bylaw amendment ultimately relies on collaborating with approval authorities and developers to find a solution that satisfies all stakeholders’ needs.  One thing is certain, even if the term sewer capacity assessment is not part of the common lexicon – it impacts everything.

“Every single development application in the City of Toronto is impacted one way or another by this assessment,” said Shukla. “We’ve seen several proposed development concepts altered in both directions, either scaled up or down, based upon the results of this assessment.”

While Shukla believes Toronto has found ways to keep up with infrastructure challenges in the past, in the face of burgeoning population growth forecasts, it will take a collaborative effort going forward.

“I don’t believe the City can do this all by themselves,” he said. “It is going to take active collaboration and cooperation between City staff and developers to aid infrastructure improvements as a result of development.”

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