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Wastewater flow estimation and servicing guidelines

1. Wastewater flow estimation

  • Proponents must provide the City with the expected peak wastewater flows for the proposed development.
  • For property developments with no on-site land drainage system, peak dry weather flows are required.
  • For property developments with an on-site land drainage system, peak wet weather flows are required.
  • All assumptions must be explicitly stated and properly documented.
  • Wastewater flow generations must be stamped and signed by a Professional Engineer licensed to practice in the Province of Manitoba.
  • All units must be in metric; wastewater flows must be in L/s.
  • For residential, commercial, and industrial properties, wastewater flows must be estimated by mathematically calculating the flows generated from the property.
Average Dry Weather Flow: ADWF = Daily average wastewater flows
Peak Dry Weather Flow: PDWF = ADWF x peaking factor
Peak Wet Weather Flow: PWWF = PDWF + extraneous flows
Residential wastewater generation
ADWF: Number of Dwelling Units x Number of People Per Unit
x 270 L/capita/day
Daily wastewater generation = 270 L/capita/day
Single Family Dwelling
  Population/dwelling: 3.05
  Dwelling/ha: 12.29 *
Multi-Family Dwelling
  Population/dwelling: 2.30
  Dwelling/ha: 74.13 *
PDWF: ADWF x Harmon's Peaking Factor
  Harmon's Peaking Factor = 1 + (14 / (4 + (P / 1000)0.5))  
  P = Number of Dwelling Units x Number of People Per Unit  

* where actual dwelling units are unknown, these values should be used

Non-residential wastewater generation**
Commercial ADWF: 16,800 L/ha/day PDWF: 28,100 L/ha/day
Light Industrial ADWF: 22,500 L/ha/day PDWF: 37,600 L/ha/day
Wet Industrial ADWF: 33,600 L/ha/day PDWF: 44,900 L/ha/day

** where actual discharge rates are known, these values should be used. For design purposes, where specific land uses are known, wastewater generation rates can be derived from literature values; references must be included with design assumptions. A fixture unit can be used if no other option is available.

Extraneous flow contributions

Ground water infiltration: (2,200 L/ha/day)

Groundwater infiltration into wastewater sewers shall be determined using 2,200 L/ha/day and the catchment area. Park areas shall be included in groundwater infiltration calculations when wastewater sewers are nearby.

Manhole infiltration: (12 L/min/manhole)

Manhole density may be determined by count for developed areas. For design purposes:

  • residential manhole density of 1.6 manholes/ha
  • commercial/industrial manhole density can not be below 1.0 manhole/ha

Weeping tile flow: (4.55 L/min/service connection)

Residential areas built prior to 1990 must include weeping tile flow

2. Wastewater design guidelines: public right-of-way

  • Wastewater sewers must be designed:
    • to prevent surcharging under peak flow conditions,
    • with a minimum full flowing velocity of 0.6 m/s,
    • using a roughness co-efficient (n) of 0.013,
    • with minimum pipe slopes corresponding to the following table:
    Pipe Diameter (mm) Minimum Slope
    250 0.245%
    300 0.192%
    375 0.143%
    450 0.112%
    525 0.091%
    600 0.076%
    750 0.057%
    900 0.044%
    1050 0.036%
    1200 0.030%
    1350 0.026%
    1500 0.022%
    1650 0.020%
    1800 0.018%
    1950 0.016%
    2100 0.014%
    2250 0.013%
  • The minimum wastewater sewer size is 250 mm.
  • Wastewater manhole spacing on common sewers can not exceed 150 m.
  • Wastewater manholes should be a minimum of 1 m off property lines.
  • All newly constructed sewers must be separate sewers, even in existing combined sewer districts.
  • All wastewater sewers, appurtenances, and service connections must be constructed in accordance with the latest revision of the City of Winnipeg Standard Construction Specifications. For further information regarding City of Winnipeg Construction Specifications see:

3. Wastewater servicing guidelines: private services

  • For combined sewer districts, post-development site runoff must not exceed pre-development runoff.
  • Private wastewater and land drainage services must have separate connections to the common sewer main.
  • The minimum wastewater service size is 150 mm.
  • Wastewater service connections are not permitted to connect directly into manholes.
  • Land drainage service connections may not connect into the wastewater collection system.
  • Sump pump discharge lines must be directed onto private property and not into the wastewater sewer system unless otherwise approved by Water & Waste. For further information regarding sump pump discharge placement see: Sump pump discharge.
  • Roof drain downspout discharges must be directed onto private property and not into the wastewater sewer system unless otherwise approved by Water & Waste. For further information regarding downspout placement see Downspouts.
  • Oil/Grit interceptors installed indoors(e.g. repair facilities) shall be directed to the building's internal wastewater sewer system.
  • Hydraulic elevator sumps must have an oil containment unit or oil interceptor to ensure no contaminants enter into the wastewater sewer system. The elevator sump pump must be directed to the wastewater sewer.

Contact us for more information or if you have questions.

Last updated: February 12, 2020