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Ville de Montréal modernizes the bylaw on hydraulic calculations

Since June 1, 2015, Ville de Montréal has made certain changes to bylaw C-1.1, more specifically, to the presentation of hydraulic calculations for storm water retention structures. In fact, after a trial period, the city chose to replace the rational method with the SWMM (Storm Water Management Model) method.

More accurate analyses

This is a significant shift in technology. By choosing the SWMM method, the city is opting for a determinist model that allows for continuous simulation, rather than an empirical approach. As such, it is possible to determine the condition of a network as a function of time, which allows for a more detailed analysis. The city used the Storm and Sanitary Analysis (SSA) tool, among others, to conduct the necessary calculations.

A reliable calculation tool

The SSA tool, which is included in the AutoCAD Civil 3D software, performs the hydrologic and hydraulic calculations needed to design retention structures using the SWMM method. Moreover, users can extract data from Civil 3D and process them in SSA, thus easing the transition between designs and engineering calculations, and vice versa. The connection between the two software speeds up the data transfer process, prevents certain errors, and ensures productivity gains.     

A brief history

The rational method was first used in North America in 1889. Since then, it has been used to estimate runoff flow based on three parameters (drainage basin area, runoff coefficient, and rainfall intensity). Despite the fact that certain studies place reservations on its use in large drainage basins, to this day the method is still considered valid for simple networks. Its ease of use has made it the preferred method for obtaining interesting results in a short period of time. However, the software used to conduct complex calculations (such as those involved in the SWMM method) are now more user friendly and have become the tools of choice.

For more information about Autodesk Storm and Sanitary Analysis, please contact:

Jean-Philippe Loisel

Consultant in civil engineering

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