Hydrologic calculations and stormwater retention
Flows, retention volumes and sizing of structures: clear calculations to design the site drainage and meet the project’s requirements.
When are calculations needed?
As soon as a project changes a site’s surfaces, it changes the amount of water to manage. The municipality may then require the project to limit the flow discharged to the sewer and to retain water on site. The calculations show how much water to manage, where to hold it and how to release it.
Determine how much water must be managed, and how
We start from the site’s actual surfaces and the available outlet to determine flows and volumes, then size the structures that will meet them.
- Peak flows before and after the project
- Required retention volumes
- Sizing of basins, pipes and catch basins
- Flow regulators and roof target flows
The criteria that apply
Allowable flow, design storms, retention requirements: the criteria vary with the municipality and the project. We check them at the outset and document the assumptions used. In Montreal, see also civil plans and By-law 20-030.
Modelling, when needed
For complex sites (several drainage areas, structures that interact, an existing network under constraint), we model the drainage in PCSWMM or SWMM to check how it behaves over the full duration of a storm.
What you get
Results the whole team can use: the architect knows how much space to reserve, the contractor knows what to build and the municipality has the demonstration it asked for.
- Clear calculation notes
- Sized structures
- Calculations integrated into the civil plans
- Replies to municipal comments
Related services
- Drainage and stormwater management Drainage plans, stormwater retention and flow control, from the roof to the municipal connection.
- Civil engineering plans for municipal permits The civil plans your project needs, coordinated with the architecture and prepared for municipal applications.
- Site servicing: sewer, water and municipal connections Sanitary sewer, storm sewer, water service and connections to existing municipal networks.
- Drainage assessments, expert reports and water problems We identify the probable cause of a water problem and document it in an engineer’s technical report.
Flow or retention requirements to meet?
Send us the project and the requirements you received: we will set out the calculations needed and what they must demonstrate.