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

Section 24 Disposition versions

2020-12-31

24. The following rules apply to the factors of equations 3-1 and 3-2:

(1)  the runoff coefficients Crj used may not be less than the values indicated in Table 3.4;

Table 3.4 Runoff coefficients Crj according to the various types of surface return periods

Surface		Return period
		2 to 10 years	11 to 25 years	26 to 50 years	51 to 100 years
Gravel
	Compacted (unpaved road, shoulder, etc.)	0.75	0.83	0.95	0.95
	Non compacted	0.60	0.66	0.79	0.95
Paving
	Asphalt, concrete	0.90	0.95	0.95	0.95
	Bricks	0.80	0.88	0.95	0.95
Conventional roof		0.95	0.95	0.95	0.95
Green roof
	Thickness < 100 mm	0.50	0.55	0.66	0.83
	Thickness from 100 to 200 mm	0.30	0.33	0.40	0.50
	Thickness from 201 to 500 mm	0.20	0.22	0.26	0.33
	Thickness > 500 mm	0.10	0.11	0.13	0.17
Grass (sandy soil)
	Flat (slope < 2%)	0.08	0.09	0.11	0.13
	Average (slope of 2 to 7%)	0.13	0.14	0.17	0.21
	Steep (slop > 7%)	0.18	0.20	0.24	0.30
Grass (dense soil)
	Flat (slope < 2%)	0.15	0.17	0.20	0.25
	Average (slope of 2 to 7%)	0.20	0.22	0.26	0.33
	Steep (slope > 7%)	0.30	0.33	0.40	0.50
Wooded area (sandy soil)
	Flat (slope < 2%)	0.05	0.06	0.07	0.13
	Average (slope of 2 to 7%)	0.08	0.09	0.11	0.18
	Steep (slope > 7%)	0.11	0.12	0.15	0.23
Wooded area (loamy or silty soil)
	Flat (slope < 2%)	0.08	0.09	0.11	0.13
	Average (slope of 2 to 7%)	0.11	0.12	0.15	0.18
	Steep (slope > 7%)	0.14	0.15	0.18	0.23
Wooded area (sandy clay soil)
	Flat (slope < 2%)	0.10	0.11	0.13	0.17
	Average (slope of 2 to 7%)	0.13	0.14	0.17	0.21
	Steep (slope > 7%)	0.16	0.18	0.21	0.26
Wooded area (clay soil)
	Flat (slope < 2%)	0.12	0.13	0.16	0.20
	Average (slope of 2 to 7%)	0.16	0.18	0.21	0.26
	Steep (slope > 7%)	0.20	0.22	0.26	0.33

(2)  the rain intensity, i, to be used is the intensity associated with a rainfall duration equal to the concentration time, tc, of the territory drained to the storm water management system established using equation 3-3 and associated with the return period considered, without considering a concentration time of less than 10 minutes.

Equation 3-3: tc = max (te + tf)

where:

	tc	=	Concentration time (min); if the concentration time is equal to or less than 10 minutes, the duration of the concentration time is 10 minutes
	te	=	Entry time established using equation 3-4 (min);
	tf	=	Water flow time in the storm water management system (min);
	max	=	Function of maximization indicating that the concentration time corresponds to the time associated with the combination of an entry time te, and a water flow time, tf, in the storm water management system that produces the highest peak flow.

Equation 3-4:

where:

	te	=	Entry time (min);
	L	=	Maximum distance covered by the water at the surface before reaching the intake of the storm water management system (m); maximum vale: 365 m;
	N	=	Roughness coefficient of the sheet flow according to the flow surfaces indicated in the Table 3.5 (s/m1/3);
	S	=	Average slope of the path travelled by the water before reaching the intake of the storm water management system (m/m).

Table 3.5 Roughness coefficients

Flow surface		Roughness coefficient
Asphalt/concrete		0.01 to 0.015
Smooth impervious surface		0.02
Bare soil, compacted, without debris, without rocks		0.10
Short and sparse vegetation		0.05
Cultivated soil
	Surface of residues ≤ 20%	0.06
	Surface of residues > 20%	0.17
Grass
	Short grass	0.15
	Dense grass	0.24
	Very dense grass	0.41
Natural grassland		0.13
Pastureland		0.40
Forest
	Sparse undergrowth	0.40
	Dense undergrowth	0.80

O.C. 871-2020, s. 24.

Not in force

In force: 2020-12-31

24. The following rules apply to the factors of equations 3-1 and 3-2:

(1)  the runoff coefficients Crj used may not be less than the values indicated in Table 3.4;

Table 3.4 Runoff coefficients Crj according to the various types of surface return periods

Surface		Return period
		2 to 10 years	11 to 25 years	26 to 50 years	51 to 100 years
Gravel
	Compacted (unpaved road, shoulder, etc.)	0.75	0.83	0.95	0.95
	Non compacted	0.60	0.66	0.79	0.95
Paving
	Asphalt, concrete	0.90	0.95	0.95	0.95
	Bricks	0.80	0.88	0.95	0.95
Conventional roof		0.95	0.95	0.95	0.95
Green roof
	Thickness < 100 mm	0.50	0.55	0.66	0.83
	Thickness from 100 to 200 mm	0.30	0.33	0.40	0.50
	Thickness from 201 to 500 mm	0.20	0.22	0.26	0.33
	Thickness > 500 mm	0.10	0.11	0.13	0.17
Grass (sandy soil)
	Flat (slope < 2%)	0.08	0.09	0.11	0.13
	Average (slope of 2 to 7%)	0.13	0.14	0.17	0.21
	Steep (slop > 7%)	0.18	0.20	0.24	0.30
Grass (dense soil)
	Flat (slope < 2%)	0.15	0.17	0.20	0.25
	Average (slope of 2 to 7%)	0.20	0.22	0.26	0.33
	Steep (slope > 7%)	0.30	0.33	0.40	0.50
Wooded area (sandy soil)
	Flat (slope < 2%)	0.05	0.06	0.07	0.13
	Average (slope of 2 to 7%)	0.08	0.09	0.11	0.18
	Steep (slope > 7%)	0.11	0.12	0.15	0.23
Wooded area (loamy or silty soil)
	Flat (slope < 2%)	0.08	0.09	0.11	0.13
	Average (slope of 2 to 7%)	0.11	0.12	0.15	0.18
	Steep (slope > 7%)	0.14	0.15	0.18	0.23
Wooded area (sandy clay soil)
	Flat (slope < 2%)	0.10	0.11	0.13	0.17
	Average (slope of 2 to 7%)	0.13	0.14	0.17	0.21
	Steep (slope > 7%)	0.16	0.18	0.21	0.26
Wooded area (clay soil)
	Flat (slope < 2%)	0.12	0.13	0.16	0.20
	Average (slope of 2 to 7%)	0.16	0.18	0.21	0.26
	Steep (slope > 7%)	0.20	0.22	0.26	0.33

(2)  the rain intensity, i, to be used is the intensity associated with a rainfall duration equal to the concentration time, tc, of the territory drained to the storm water management system established using equation 3-3 and associated with the return period considered, without considering a concentration time of less than 10 minutes.

Equation 3-3: tc = max (te + tf)

where:

	tc	=	Concentration time (min); if the concentration time is equal to or less than 10 minutes, the duration of the concentration time is 10 minutes
	te	=	Entry time established using equation 3-4 (min);
	tf	=	Water flow time in the storm water management system (min);
	max	=	Function of maximization indicating that the concentration time corresponds to the time associated with the combination of an entry time te, and a water flow time, tf, in the storm water management system that produces the highest peak flow.

Equation 3-4:

where:

	te	=	Entry time (min);
	L	=	Maximum distance covered by the water at the surface before reaching the intake of the storm water management system (m); maximum vale: 365 m;
	N	=	Roughness coefficient of the sheet flow according to the flow surfaces indicated in the Table 3.5 (s/m1/3);
	S	=	Average slope of the path travelled by the water before reaching the intake of the storm water management system (m/m).

Table 3.5 Roughness coefficients

Flow surface		Roughness coefficient
Asphalt/concrete		0.01 to 0.015
Smooth impervious surface		0.02
Bare soil, compacted, without debris, without rocks		0.10
Short and sparse vegetation		0.05
Cultivated soil
	Surface of residues ≤ 20%	0.06
	Surface of residues > 20%	0.17
Grass
	Short grass	0.15
	Dense grass	0.24
	Very dense grass	0.41
Natural grassland		0.13
Pastureland		0.40
Forest
	Sparse undergrowth	0.40
	Dense undergrowth	0.80

O.C. 871-2020, s. 24.