Attachment 9 - Stormwater Management Calculations and Information

298 Old Island Highway Preliminary Site Servicing Plan

Sheet Notes:

1. CRD crews to cap and abandon existing water service at developers expense.
2. CRD crews to install water service complete with water meter at developers expense.
3. Town of View Royal crews to cap and abandon existing sewer and drain services at developers expense.
4. Town of View Royal crews to install new sewer and drain service at developers expense.
5. Contractor to construct 6.0m driveways complete with 2.0m flares as per Town of View Royal standards.
6. Contractor to remove existing tree. See arborist report.
7. Contractor to relocate existing 150Ø sewer main to centerline of existing sewer right of way complete with new sewer services, inspection chambers, and manholes.
8. Contractor to install stormwater detention system to meet the required storage volume of 64.5 m³. Storm tank design to be finalized at building permit stage.

Stormwater Management Calculations and Information:

As per Town of View Royal specifications, post development flows must be equal to pre development flows.

• REQUIRED STORMWATER STORAGE TO BE CALCULATED BY SCS METHOD IN HYDROCAD MODELING SOFTWARE.
• PRE-DEVELOPMENT AND POST-DEVELOPMENT FLOW RATES CONFIRMED BY RATIONAL METHOD, USING C VALUES OF 0.35 FOR PRE-DEVELOPMENT AND 0.9 FOR POST-DEVELOPMENT.

Pre-Development Flow:

• CN = 65 (FORESTED AREA)
• RUNOFF DEPTH = 17 mm (10-YEAR STORM)
• AREA = 0.1854 ha
• Q = 5.0 L/s

Pre-Development Flow:

• CN (WEIGHTED) = 75 (NON IMPERVIOUS AREA)
• RUNOFF DEPTH = 70 mm (10-YEAR STORM)
• AREA = 0.1854 ha
• Q = 12.5 L/s

Orifice Sizing to Control Outlet Flow:

• RELEASE RATE = 4.6 L/s
• ORIFICE SIZING:
  • USE ORIFICE EQUATION Q = 0.6A√(2GH)
  • WHERE Q IS RELEASE RATE = 0.0046 m³/s
  • A IS ORIFICE AREA = πD²/4
  • H IS HEAD ON ORIFICE = 0.76 + 0.15m = 0.91m
  • G IS GRAVITATIONAL CONSTANT = 9.81 m/s²
  • SOLVING, d = 38 mm

Required Storage Based on HydroCAD Software:

• REQUIRED STORAGE = 64.5 m³
• STORMWATER STORAGE PROVIDED VIA ABOVE GROUND RAINWATER PLANTERS LOCATED AT THE DOWNSPOUTS, DETAILS TO BE DETERMINED AT BUILDING PERMIT STAGE.

Key Plan

Legal Description: LOT 1, SECTION 8, ESQUIMALT DISTRICT, PLAN 35505 Benchmark: TRAVERSE HUB #526 ELEV. 23.63m

Issued for Development Permit 2021-10-04

Project Identification

• Project Name: 298 OLD ISLAND HIGHWAY PRELIMINARY SITE SERVICING PLAN
• Eng. Project No.: 32668
• Scale horiz.: 1:200
• Scale vert.: N/A
• Sheet: 1 of 1
• Firm: J E ANDERSON & ASSOCIATES, SURVEYORS - ENGINEERS
• Address: VICTORIA - NANAIMO - PARKSVILLE - CAMPBELL RIVER
• Phone: 250-727-2214
• Email: info@jeanderson.com