Sewer, Water and Storm Drain Servicing Review - Design Brief Memo
Civil engineering memo reviewing the multi-family development's impact on sanitary, storm, and water distribution systems.
LEGAL SURVEYS MUNICIPAL ENGINEERING LAND DEVELOPMENT AND MANAGEMENT
November 24, 2023
JEA File No. 33862
View Royal File No. REZ 2023-04
Royale Ventures Corp
Re: Pebbles - Proposed Development at 294 & 296 Eltham Rd & 242 Helmcken Rd Sewer, Water and Storm Drain Servicing Review
REVIEWED By lleung at 4:07 pm, Dec 07, 2023 File: ENG2022-06 Conditions:
- Reviewed for rezoning only
- Detail Design SWMP required prior to building permit. Stormwater storage volumes and detail design to be confirmed as part of servicing agreement
- S219 Covenant on title required for maintenance of stormwater management structures, to be completed as a condition of building permit
- Water servicing requirements deferred to CRD for comment
1.0 Introduction
JE Anderson and Associates has been retained as the civil consultant for the proposed multi-family development which consists of 20 town houses. The following design brief will review the post-development impact to The Town of View Royal’s sanitary and storm drainage systems as well as the CRD water distribution system.
2.0 Design Criteria Applied/Assumptions Made
The following assumptions and design guidelines have been used in this review.
Sewer loads:
- 2.8 capita per unit
- Average daily sewage flows = 240 L/cap/day
- Harmon formula for Peaking Factor
- Inflow and Infiltration rate of 0.12 L/ha/s
Water demands:
- 2.8 capita per unit for each townhouse dwelling
- Average daily demand of 545 L/cap/day (as per CRD design guidelines)
- Fire flow demand as per Fire Underwriter Survey and CRD minimums
Drainage calculations:
- Rational Method for pre and post development flow
- SCS Method through HydroCAD for post-development flow
- 2022 Victoria Gonzales IDF Curve
- Pre-development Tc = 10 min and combined runoff coefficient based on c = 0.35 for pervious and c = 0.9 for impervious areas
- Post-development Tc = 10 min due to routing through SWM systems
- SWM system will release at the pre-development 10-year flowrates.
- 10% climate change factor added to 10-year post development flows
3.0 Calculations
3.1 Sewer
The calculations enclosed in Appendix A indicate that the post-development peak wet-weather flow (PWWF) is 0.70 L/s.
3.2 Water
The calculations enclosed in Appendix B indicate that the post-development average daily demand (ADD) is 30 520 L/day (0.35 L/s).
Preliminary Fire Underwriters Survey calculations indicate the required fire flow for the development is 4,000 L/min. CRD requires a minimum fire flow of 4,800 L/min.
3.3 Storm Drainage
The calculations enclosed in Appendix C indicate that the pre-development 10-yr storm flow is 6 L/s and post-development flow is 15 L/s.
The proposed on-site stormwater management (SWM) system will reduce the post-development flow to the permitted release rate of the pre-development 10-yr storm event.
3.4 Stormwater Management
The proposed stormwater management systems are designed to release the post-development flow at the 10-yr pre-development flow rates. The stormwater management calculations include a 10% climate change factor for the 10-yr post-development. Each catch basin within the proposed roadway will enter a Type 1 oil and grit separator to treat the runoff before entering the storm main and stormwater management systems.
The required storage volume is 24.7 cubic meters. The stormwater will be stored via storage chamber, and will be fully designed at the building permit stage of this development.
A stormwater operations and maintenance covenant will be required to be registered on title.
6.0 Downstream Impacts
Sewer – The proposed flow is 0.53 L/s. The downstream sanitary system is a 150mm PVC sewer main @ 1.6% which has a capacity of approximately 19.3 L/s. The proposed development meets the allowable FSR from the Sewer Master Plan and will use 2.75% of the downstream 150mm PVC during a full-flow event.
A review of the Town of View Royal Sewer Master Plan – Draft (2017) indicates that the proposed development is consistent with the report’s assumptions for FSR and there are no identified capacity issues downstream.
Water – From the given hydrant curve for VRF061 at Helmcken & Eltham, we determined the Hydraulic Grade Line for the site is approximately 116 m under max day demand. The resultant head for the existing hydrant is sufficient in meeting the FUS flow of 4,000 L/min with a remaining head of 133.6 m.
Drain – The proposed post-development flow is 6 L/s for the 10-yr. The downstream storm system is a 300mm PVC storm main @ 2.5% slope, which has a capacity of approximately 51.8 L/s. The proposed development will use 29% of the downstream 300mm PVC during a full-flow event.
Summary
We trust this meets your requirements for the design brief memo. If you have any questions regarding this memo, please contact the undersigned at your convenience.
Yours truly,
J.E. Anderson and Associates
Colton Killip, EIT
Reviewed by: Ross Tuck, P. Eng Principal