Sewer Appurtenances

Sewer appurtenances are those structures of sewerage system which are constructed at suitable intervals and other locations along a sewer line to assist in efficient operation and maintenance of the system.

• Street inlets• Catch basins• Clean outs• Manholes• Drop manholes• Lamp holes• Flushing tanks• Grease and oil traps• Inverted siphons• Strom regulators

Street Inlets• Street inlets are openings provided along the street to admit storm water

or surface wash and convey it into a storm sewer or a combined sewer.• Three different types

• Curb or vertical inlets• Gutter or horizontal inlets• Combination inlets

• Maximum spacing of inlets on straight roads is 30 m. • Inlets are provided at street intersections.• The inlets are connected with nearby manhole by pipes.• These are concrete boxes with grating cover.

Gutter inlet

Combination inletCurb inlet

Catch Basin or Catchpits• Catch basin is also an inlet

with a basin for the purpose of collecting silts.• The outlet is usually trapped to

prevent escape of odour from sewer and to retain floating substances.• The settled matter is taken out

periodically.

Clean outs• A clean out is an inclined pipe with its one end

connected to the underground sewer line and other end brought upto ground level, with a proper cover at the top.• These are generally provided at upper ends of

laterals in place of manholes.• It helps in cleaning laterals through forcing

water jet.• For removing large obstructions, flexible rod

may be inserted.

Manhole• Masonary or RCC chamber

constructed on the alignment of a sewer for providing access to sewer for the purpose of • Inspection • Testing• Cleaning • Removal of obstructions from sewer line.

• It also helps in joining sewer lines or in changing the direction or alignment or both.

Location of manholes• Manholes are provided at every

bend, junction, change of gradient or change of diameter. • On straight reaches, manholes

are provided at convenient spacing depending on size of sewer. • Spacing also depends on nature

of sewer cleaning devices in use.

Size of sewer Recommended spacing (m)

Dia upto 0.3 m 45

Dia upto 0.6 m 75

Dia upto 0.9 m 90

Dia upto 1.2 m 120

Dia upto 1.5 m 250

Dia > 1.5 m 300

Dimension of manholesSl. No. Depth Min size specified

1 0.8 m or less 0.75 m x 0.75 m

2 0.8 – 2.1 m 1.2 m x 0.9 m

3 >2.1 m Circular chamber with min dia of 1.4 m or rectangular chamber with min dimension of 1.2 m x 0.9 m

Components of manhole

• Top cover• Access shaft• Working chamber• Bottom or invert• Side walls• Steps or ladder

Drop manhole• A drop manhole is a special

type of manhole on a sewer line which is constructed to provide a connection between a high level branch sewer to a low level main sewer.• The construction of drop

manhole avoids unnecessary steep gradient of branch sewer thus reducing the amount of earth work.

Lampholes• Lampholes are special

openings constructed to join a hole in the sewer and ground, for the purpose of lowering a lamp inside the sewer.• It serves the following

purposes• Inspection• Flushing in case of emergency• Ventilation

Flushing tank• Flushing tank is a device or

arrangement which holds water and then throws it into the sewer for the purpose of flushing it.• Sewer laid on flat terrain may

not produce self-cleaning velocity and may get blocked frequently; thus needs cleaning.• It can be operated either

manually or automatically.

Oil and grease traps• Oil and grease traps are

specially built chambers on to exclude grease and oil from sewage before they enter the sewer.• Such traps are located near

those sources, such as automobile repairing workshops, garages, kitchens of hotels, oil and grease industries etc.

Inverted siphons

• When a sewer line dips below the hydraulic grade line, it is called an inverted siphon.• Purpose is to carry the

sewer under the obstruction such as roadway, railway, stream, river etc.

Storm regulators• These are constructed for combined sewerage system so

as to permit the diversion of storm water when the discharge exceeds a certain value. • The excess water is diverted to a natural stream or river. • Different types of storm regulator• Over flow weirs• Leaping weirs• Siphon spillways

Overflow weir / side flow weir• The object is to keep the

discharge to the storm water down to a predetermined maximum and allow the surplus to overflow to water courses. • The overflow weirs may

be single acting or double acting.

Leaping weir• A leaping weir or jumping weir is a

special device by way of which excess wastewater during storm is allowed to escape to a watercourse while designed flow is permitted to flow to the intercepting sewer.• The arrangement consists of an opening

in the invert of the combined sewer and through this opening the normal flow is diverted to the intercepting drain while the excess flow leaps over the storm drain leading it to a nearby stream.

Siphon spillways• The overflow weirs require

considerable length, resulting in high cost of construction. • Siphon spillways, on the other

hand, are very effective since they have high discharge capacity. • The spillway is very sensitive.

Automatic in operation and diverts more flow in lesser time.