Transcript Sanitary Sewers - Mohawk College

Sanitary Sewers
Design Criteria
Criteria
minimum pipe size
 minimum & maximum flow velocities
 minimum slope
 minimum cover depth
 location relative to other services
 manhole spacing

Minimum Pipe Size
sanitary sewers are normally smaller
than stormwater sewers
 minimum sizes set for maintenance & to
prevent clogging
 service line from house (lateral) min.
100 mm (4”)
 sanitary sewer min. 200 mm (8”)

Minimum Flow Velocity
need to keep sanitary sewers “flushed”
 min. flow velocity 0.6 m/s
 there are trade-offs between depth of
excavation and slope of sewers
 must keep sewage flowing to prevent
anaerobic action and crown corrosion

Maximum Flow Velocity
due to high “grit” load maximum
velocity is lower than storm sewers
 maximum flow velocity 3 m/s
 don’t want to scour and erode inside of
pipes prematurely

Minimum Slope
slope directly affects velocity
 must maintain sufficient slope to keep
minimum velocity
 must limit slopes from causing flow
velocities too high for pipes
 sometimes “lift stations” are needed to
avoid deep excavations

Minimum Cover Depth
pipes need to be lower than house
basements to accept sewage from all
drains
 keep pipes below frost line
 where houses are below sanitary
sewers, a pump is needed

Other In-ground Services
major concern involves leaks and
contamination
 place below water supply
 place below storm sewers
 normally on centerline of roads

Manhole Locations
Similar criteria as storm sewers...
manholes are need when:
 sewer changes direction
 sewer changes pipe size
 sewer changes slope
 sewers converge
 maintenance & cleaning requirements
Now let’s do some problems!