Appendix A: Stormwater Calculation - Runoff Coefficients and IDF Curve

June 13, 2023Pages 129–1313 sections

Technical calculations for stormwater runoff, including pre- and post-development coefficients and rainfall intensity data.

2. APPROVAL OF AGENDA (motion to approve)

January 19, 2023Victoria Gonzales # 1018611Pre-Development C = 0.520Post-Development C = 0.760

APPENDIX A: STORMWATER CALCULATION - RUNOFF COEFFICIENTS AND IDF CURVE

Underground Utilities Brief | Prepared for Boardwalk REIT 339 / 341 / 345 Island Highway, View Royal, BC

Page 129–131

RUNOFF COEFFICIENTS & IDF CURVE

Project Name: 3339 Island Hwy Project File #: 2241-22149 Date: 1/19/2023 Area: View Royal IDF Curve: Victoria Gonzales # 1018611

Calculate Post Development C

Description of Area	Runoff Coefficients Range	Runoff Coeff Selected	Pre-Development Contributing Area (m²)	Pre-Development C x A	Post Development Contributing Area (m²)	Post Development 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		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	2385	2266	2820	2679	as/conc/dw/sw
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	1205	1145	4250	4038
Lawns, sandy soil
Flat, < 2%	0.05 - 0.10			0		0
Average, 2-7%	0.10 - 0.15			0		0
steep, > 7%	0.15 - 0.20	0.15	3150	473		0	ex. Steep lawns 10%
Lawns, heavy soil
Flat, < 2%	0.13 - 0.17			0		0
Average, 2-7%	0.18 - 0.22			0		0
steep, > 7%	0.25 - 0.32	0.50		0	5150	2575	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	5480	2466		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) = 1.22200 (Pre-Development), 1.22200 (Post Development) Pre-Dev C = 0.520 Post-Dev C = 0.760 pre vs post areas match

*Table from "Water Supply and Pollution Control, Seventh Edition, Viessman & Hammer" **See also MoT Section 1020, Supplement to TAC Geometric Guide, Table 1020.A