The City of Richmond Hill selected CIMA+ as prime consultant for the Mill Street-Altamira Road Drainage Improvements project, to resolve a persistent flooding problem in this highly sought after, tranquil community. The work involved the replacement of an undersized open-channel and aging storm sewer infrastructure with a controlled inline storage system, contained completely within the City’s road right-of-way, designed to reduce flooding impacts and improve stormwater management.
Despite complex constraints, such as limited working space, construction within and adjacent to private properties, utility conflicts and outdated infrastructure operating below required capacity, the team successfully advanced the project’s design and implementation with the aid of detailed subsurface utility engineering, geotechnical investigations and staged construction planning.
The project won an Ontario Public Works Association (OPWA) Environment Award in 2026.
No room to spare: Making every millimetre count
The team strictly adhered to a quality assurance and quality control process, which helped resolve technical issues related to stormwater modelling, road regrading, driveway slopes, utility conflicts and sanitary service impacts. Design adjustments to storm pipe slopes, catch basin locations, driveway treatments and sidewalk geometry were made collaboratively with residents to improve performance while minimizing downstream construction impacts.
One of the project’s greatest challenges was mitigating crossing conflicts associated with the installation of the large 1,800 mm pipe, which effectively created an underground “wall”. Very large maintenance holes ranging in size between 3,000 mm and 3,600 mm, as well as a box maintenance hole measuring 2,400 x 3,000 mm, were also challenging to integrate. The project team had to verify that it was physically possible to fit all of these elements within the constrained road right-of-way.
Careful consideration had to be given to eliminate crossing conflicts with sanitary sewers and their service laterals, as well as the existing watermain and their water services. This entailed revisiting the slopes and depths of the storm pipe, as well as introducing an elliptical pipe.
Designed with nature in mind
Environmental protection was a defining element of the project and was embedded into every aspect through compliance with Consolidated Linear Infrastructure Environmental Compliance Approval (CLI ECA) requirements, erosion and sediment control planning, tree inventory and protection measures, and excess soil management in accordance with O. Reg. 406/19 and O. Reg. 388/22. The project required coordination with regulatory agencies and incorporation of environmental protection measures into both design and construction phases.
Working with, and for, the community
The project was initiated because of an identified flood risk that posed a direct health and safety concern to residents, including potential property damage, loss of access and the need for emergency response during significant storm events. Therefore, safety and community protection were central considerations throughout the design and construction process.
Comprehensive measures were implemented to protect residents, road users and workers: detailed staging, traffic management plans and clear regulatory signage provided real‑time information to motorists.
As a result, the project not only delivered critical infrastructure improvements but also strengthened relationships between the City and the community through responsiveness and transparency.