Q-2, r. 9.01 - Design code of a storm water management system eligible for a declaration of compliance

Section 22 Disposition versions

2020-12-31

22. When, in the application of the rational method or a computer model, intensity-duration-frequency values of the rainfalls are used, the values must result from the statistical analysis of the rainfall data from a weather station whose rain conditions and altitude are representative of those prevailing in the territory drained to the storm water management system and have been produced by Environment and Climate Change Canada, Agrométéo Québec or a municipality.

The intensity-duration-frequency values of rainfalls associated with a return period must be based on a number of years of recording rainfall data complying with the number of years of recording indicated in Table 3.2:

Table 3.2 Number of years of recording associated with a return period

Return period	Number of years of recording
< 2 years	5
2 years	5
10 years	10
25 years	15
50 years	20
100 years	25

For every hydrological calculation carried out with projected conditions, the intensity-duration-frequency values of the rainfalls must be increased by the minimum value indicated in Table 3.3 on the basis of the return period, unless the intensity-duration-frequency curves used in the calculation already take into account the effects of climate change by at least the values indicated in Table 3.3:

Table 3.3 Increase

Return period	Increase
< 2 years	No increase
≥ 2 years	+ 18%

O.C. 871-2020, s. 22.

Not in force

In force: 2020-12-31

22. When, in the application of the rational method or a computer model, intensity-duration-frequency values of the rainfalls are used, the values must result from the statistical analysis of the rainfall data from a weather station whose rain conditions and altitude are representative of those prevailing in the territory drained to the storm water management system and have been produced by Environment and Climate Change Canada, Agrométéo Québec or a municipality.

The intensity-duration-frequency values of rainfalls associated with a return period must be based on a number of years of recording rainfall data complying with the number of years of recording indicated in Table 3.2:

Table 3.2 Number of years of recording associated with a return period

Return period	Number of years of recording
< 2 years	5
2 years	5
10 years	10
25 years	15
50 years	20
100 years	25

For every hydrological calculation carried out with projected conditions, the intensity-duration-frequency values of the rainfalls must be increased by the minimum value indicated in Table 3.3 on the basis of the return period, unless the intensity-duration-frequency curves used in the calculation already take into account the effects of climate change by at least the values indicated in Table 3.3:

Table 3.3 Increase

Return period	Increase
< 2 years	No increase
≥ 2 years	+ 18%

O.C. 871-2020, s. 22.