APPENDIX A: DETENTION CALCULATIONS

January 9, 2024Pages 237–2405 sections

Engineering calculations for runoff coefficients, IDF curves, and detention volume requirements for the development site.

3 MINUTES OF PREVIOUS MEETINGS, ADOPTION OF

Contributing Area: 0.16120 haPre-development Runoff (2 Year): 0.0024 m³/sRequired detention volume: 4.7 cu.m. for 2-year events and 7.9 cu.m. for 10-year events

APPENDIX A

Page 237–240

DETENTION CALCULATIONS

Project Name: Camden and Helcken Project File #: 2241-21077 Date: 9/27/2023

Page 237–240

RUNOFF COEFFICIENTS & IDF CURVE

Area: View Royal IDF Curve: Victoria Gonzales # 1018611 w climate change

Calculate Post Development C Typical C Coefficients*

Description of Area	Runoff Coefficients Range	Runoff Coeff. Selected	Pre-Development Contributing Area (m²)	C x A	Post Development Contributing Area (m²)	C x A	Notes / Comments
Business
Downtown Areas	0.70 - 0.95			0		0
Neighborhood Areas	0.50 - 0.70			0		0
Residential
single family areas	0.30 - 0.50	0.40	1612	645		0
multiunits, detached	0.40 - 0.60			0		0
multiunits, attached	0.60 - 0.75			0		0
Residential (suburban)	0.25 - 0.40			0		0
Apartment dwelling areas	0.50 - 0.70			0		0
industrial
light areas	0.50 - 0.80			0		0
heavy areas	0.60 - 0.90			0		0
Parks, cemeteries	0.10 - 0.25			0		0
Playgrounds	0.20 - 0.35			0		0
Railroad yard areas	0.20 - 0.40			0		0
Unimproved areas	0.10 - 0.30			0		0
Streets
Asphaltic	0.70 - 0.95	0.95		0		0
Concrete	0.80 - 0.95			0		0
Brick	0.70 - 0.85			0		0
Gravel (from LEED)	0.75			0		0
Drives and walks	0.75 - 0.85			0		0
Roofs	0.75 - 0.95	0.95	0	0	1092	1037	Hardscape
Lawns, sandy soil
Flat, < 2%	0.05 - 0.10			0		0
Aveage, 2-7%	0.10 - 0.15			0		0
steep, > 7%	0.15 - 0.20	0.15		0		0	ex. Steep lawns 10%
Lawns, heavy soil
Flat, < 2%	0.13 - 0.17			0		0
Aveage, 2-7%	0.18 - 0.22	0.20	0	0	520	104
steep, > 7%	0.25 - 0.32	0.50	0	0		0	landscape above parkade, limit infil.
*MoTI Section 1020
Mnt >30% (imp, for, rur, Urb)	1.00-0.90-x-x			0		0
Steep 20-30% (imp, for, rur, Urb)	0.95-0.80-x-x			0		0
Mod 10-20% (imp, for, rur, Urb)	0.90-0.65-0.75-0.85			0		0
Roll 5-10% (imp, for, rur, Urb)	0.85-0.50-0.65-0.80	0.45	0	0		0	ex. Forested varies up to 15%
flat <5% (imp, for, rur, Urb)	0.80-0.40-0.55-0.75			0		0
				0		0
				0		0
Contributing Area (ha) =			0.16120		0.16120		pre vs post areas match
Pre-Dev C=			0.400	Post-Dev C=	0.708

*Table from "Water Supply and Pollution Control, Seventh Edition, Viessman & Hammer" **See also MoT Section 1020, Supplement to TAC Geometric Guide, Table 1020.A ***IDF_CC Web-based Tool for Updating Intensity-Duration-Frequency Curves to Changing Climate – ver 6.5, Western University Facility for Intelligent Decision Support and Institute for Catastrophic Loss Reduction, open access https://www.idf-cc-uwo.ca.

Rainfall Intensity Interpolation @ Weather Station Victoria Gonzales # 1018611 w climate change

I = aT^b where I in mm/hr, T in hr

	2 year	5 year	10 year	25 year	50 year	100 year
Coefficient (A)	8.4	11.2	13.3	16.1	18.3	20.7
Exponent (B)	-0.416	-0.416	-0.418	-0.424	-0.429	-0.435

24hr rate (mm/day)	54	72	85	100	112	125

Project Name: Camden and Helcken Project File #: 2241-21077 Date: 9/27/2023

Page 237–240

RUNOFF DETENTION REQUIREMENTS

Area: View Royal IDF Curve: Victoria Gonzales # 1018611 w climate change Contributing Area (ha) = 0.16 Post Development C = 0.71 Return Period: 2 Year Rational Method: Q=CiA/360

Pre-development Conditions 2 Year


Time of Concentration Tc =	15.00	min.
Coefficient of Runoff C =	0.40
(Historic) Intensity i =	13.17	mm
Contributing Area A =	0.16	ha
Pre-Development Runoff =	0.0024	m³/s

(A) RAINFALL DURATION (min.)	(B) RAINFALL INTENSITY (mm/hr)	(C) POST-DEVELOPMENT PEAK RUNOFF RATE (m³/s)	(D) POST-DEVELOPMENT STORM RUNOFF VOLUME (m³)	(E) POST-DEVELOPMENT ACCUM. RUNOFF VOLUME (m³)	(F) RELEASE CONTROLLED RELEASE VOLUME (m³)	(G) RELEASE ACCUM. RELEASE VOLUME (m³)	(H) PEAK DETENTION VOLUME (m³)
15	14.95	0.005	4.27	4.27	2.12	2.12	2.14
20	13.27	0.004	1.26	5.53	0.71	2.83	2.70
25	12.09	0.004	1.15	6.68	0.71	3.54	3.14
30	11.21	0.004	1.07	7.74	0.71	4.25	3.50
35	10.51	0.003	1.00	8.74	0.71	4.95	3.79
40	9.94	0.003	0.95	9.69	0.71	5.66	4.03
45	9.47	0.003	0.90	10.59	0.71	6.37	4.22
50	9.06	0.003	0.86	11.45	0.71	7.08	4.37
55	8.71	0.003	0.83	12.28	0.71	7.79	4.50
60	8.40	0.003	0.80	13.08	0.71	8.49	4.59
65	8.12	0.003	0.77	13.85	0.71	9.20	4.65
70	7.88	0.002	0.75	14.60	0.71	9.91	4.69
75	7.66	0.002	0.73	15.33	0.71	10.62	4.71
80	7.45	0.002	0.71	16.04	0.71	11.33	4.71 <=
85	7.27	0.002	0.69	16.73	0.71	12.03	4.70
90	7.10	0.002	0.67	17.41	0.71	12.74	4.66
95	6.94	0.002	0.66	18.07	0.71	13.45	4.62
100	6.79	0.002	0.65	18.71	0.71	14.16	4.55
105	6.66	0.002	0.63	19.34	0.71	14.86	4.48
110	6.53	0.002	0.62	19.97	0.71	15.57	4.39
115	6.41	0.002	0.61	20.58	0.71	16.28	4.29
120	6.30	0.002	0.60	21.17	0.71	16.99	4.19
130	6.09	0.002	1.16	22.33	1.42	18.40	3.93
140	5.90	0.002	1.12	23.46	1.42	19.82	3.64
150	5.74	0.002	1.09	24.55	1.42	21.24	3.31
160	5.59	0.002	1.06	25.61	1.42	22.65	2.96
170	5.45	0.002	1.04	26.65	1.42	24.07	2.58
180	5.32	0.002	1.01	27.66	1.42	25.48	2.18
240	4.72	0.001	5.39	33.04	8.49	33.98
300	4.30	0.001	4.91	37.95	8.49	42.47
360	3.99	0.001	4.55	42.50	8.49	50.96
480	3.54	0.001	8.07	50.58	16.99	67.95
600	3.22	0.001	7.36	57.93	16.99	84.94

Peak Storage Volume (H) = G - E Controled Release Volune (F) = Pre-development Runoff (R) x Rainfall Duration (A) x 60 Storm Runoff Volume (D) = Peak Runoff Rate (C) x Rainfall Duration (A) x 60

X:\2241\Civil\Projects\21-077-00 Camden and Helmcken\4.0 ENGINEERING & DESIGN\4.3 Technical Reports & Memos\2023-09-08 SWMP[2241-21077 Camden and Helmcken Storm water r

Project Name: Camden and Helcken Project File #: 2241-21077 Date: 9/27/2023

Page 237–240

RUNOFF STORAGE REQUIREMENTS

Area: View Royal IDF Curve: Victoria Gonzales # 1018611 w climate change Contributing Area (ha) = 0.16 Post Development C = 0.71 Return Period: 10 Year Rational Method: Q=CiA/360

Pre-development Conditions 10 Year


Time of Concentration Tc =	15.00	min.
Coefficient of Runoff C =	0.40
(Historic) Intensity i =	20.38	mm
Contributing Area A =	0.16	ha
Pre-Development Runoff =	0.0036	m³/s

(A) RAINFALL DURATION (min.)	(B) RAINFALL INTENSITY (mm/hr)	(C) POST-DEVELOPMENT PEAK RUNOFF RATE (m³/s)	(D) POST-DEVELOPMENT STORM RUNOFF VOLUME (m³)	(E) POST-DEVELOPMENT ACCUM. RUNOFF VOLUME (m³)	(F) RELEASE CONTROLLED RELEASE VOLUME (m³)	(G) RELEASE ACCUM. RELEASE VOLUME (m³)	(H) PEAK DETENTION VOLUME (m³)
15	23.74	0.008	6.77	6.77	3.28	3.28	3.49
20	21.05	0.007	2.00	8.78	1.09	4.38	4.40
25	19.18	0.006	1.82	10.60	1.09	5.47	5.13
30	17.77	0.006	1.69	12.29	1.09	6.57	5.72
35	16.66	0.005	1.58	13.88	1.09	7.66	6.21
40	15.76	0.005	1.50	15.37	1.09	8.76	6.61
45	15.00	0.005	1.43	16.80	1.09	9.85	6.95
50	14.35	0.005	1.37	18.17	1.09	10.95	7.22
55	13.79	0.004	1.31	19.48	1.09	12.04	7.43
60	13.30	0.004	1.27	20.74	1.09	13.14	7.60
65	12.86	0.004	1.22	21.97	1.09	14.23	7.73
70	12.47	0.004	1.19	23.15	1.09	15.33	7.82
75	12.12	0.004	1.15	24.31	1.09	16.42	7.88
80	11.79	0.004	1.12	25.43	1.09	17.52	7.91 <=
85	11.50	0.004	1.09	26.52	1.09	18.61	7.91
90	11.23	0.004	1.07	27.59	1.09	19.71	7.88
95	10.98	0.003	1.04	28.63	1.09	20.80	7.83
100	10.74	0.003	1.02	29.65	1.09	21.90	7.75
105	10.53	0.003	1.00	30.66	1.09	22.99	7.66
110	10.32	0.003	0.98	31.64	1.09	24.09	7.55
115	10.13	0.003	0.96	32.60	1.09	25.18	7.42
120	9.95	0.003	0.95	33.55	1.09	26.28	7.27
130	9.63	0.003	1.83	35.38	2.19	28.47	6.91
140	9.33	0.003	1.78	37.16	2.19	30.66	6.50
150	9.07	0.003	1.73	38.88	2.19	32.85	6.03
160	8.83	0.003	1.68	40.56	2.19	35.04	5.52
170	8.61	0.003	1.64	42.20	2.19	37.23	4.97
180	8.40	0.003	1.60	43.79	2.19	39.42	4.38
240	7.45	0.002	8.50	52.30	13.14	52.56
300	6.79	0.002	7.75	60.05	13.14	65.70
360	6.29	0.002	7.18	67.22	13.14	78.84
480	5.58	0.002	12.73	79.95	26.28	105.12
600	5.08	0.002	11.60	91.55	26.28	131.40

Peak Storage Volume (H) = G - E Controled Release Volune (F) = Pre-development Runoff (R) x Rainfall Duration (A) x 60 Storm Runoff Volume (D) = Peak Runoff Rate (C) x Rainfall Duration (A) x 60

X:\2241\Civil\Projects\21-077-00 Camden and Helmcken\4.0 ENGINEERING & DESIGN\4.3 Technical Reports & Memos\2023-09-08 SWMP[2241-21077 Camden and Helmcken Storm water

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