Section 7
Wastewater
Tauranga City Council
Code Of Practice For Development Tauranga City Council SECTION SEVEN Wastewater
Print Date May 2007 VERSION ONE TCC Ref 790837
2
Section 7: WASTEWATER 7.1 Scope
7.2 General
7.2.1 Objectives
7.2.2 Referred documents and relevant guidelines
7.2.3 Connection to Existing Sewer Networks/Approved Contractors
7.2.4 Private drainage
7.2.5 Rural and Rural Residential areas
7.3 Reticulation System
7.3.1 Design responsibilities
7.3.1.2 District Plan
7.3.1.3 Catchment Design
7.3.1.4 Topographical Considerations
7.3.1.5 Geotechnical Investigations,Foundation Design And Groundwater
Control
7.3.1.6 Easements
7.3.2 Design of the wastewater reticulation system
7.3.2.1 Prime Considerations
7.3.2.2 Scheme Layout
7.3.2.3 Pipeline Definitions
7.3.2.4 Proposed & Existing Pipes in Private Property
7.3.2.5 Horizontal Curves
7.3.2.6 Vertical Curves
7.3.2.7 Maintenance Structure Location
7.3.2.8 Underground Services
7.3.2.3 Pipe Materials
7.3.3.1 Acceptable Pipe Materials
7.3.3.2 Pipe Fittings
7.3.3.3 Joints
7.3.4 Clearances
7.3.4.1 Clearance From Underground Services
7.3.4.2 Clearance From Structures
7.3.5 Pipeline design
7.3.5.1 Design Flow
7.3.5.2 Hydraulic Design of Pipes
7.3.5.3 Minimum Pipe Sizes
7.3.5.4 Limitation on Pipe Size Reduction
7.3.5.5 Minimum Grades For Self Cleaning
7.3.5.6 Maximum Velocity
7.3.5.7 Minimum Cover
7.3.5.8 Steep Grades
7.3.5.9 Near Horizontal Bores
Code Of Practice For Development Tauranga City Council SECTION SEVEN Wastewater
Print Date May 2007 VERSION ONE TCC Ref 790837
3
7.3.5.10 Venting
7.3.6 Maintenance structures
7.3.6.1 General
7.3.6.2. Location of Manholes
7.3.6.3 Manhole Spacing
7.3.6.4 Manhole Materials
7.3.6.5 Size of Manholes
7.3.6.6 Base Layout
7.3.6.7 Allowable Deflection Through MHs
7.3.6.8 Internal Falls Through MHs
7.3.6.9 Effect of Steep Grades on MHs
7.3.6.10 Floatation
7.3.6.11 Access
7.3.6.12 Covers
7.3.6.13 Areas Subject to Flooding
7.3.6.14 Rodding Eyes (RE)
7.3.7 Laterals/Connections
7.3.7.1 Subdivision of 4 Lots or More
7.3.7.2 Infill Subdivision – Three Lots or Less
7.3.7.3 Multi Unit Properties (Such as Apartment buildings & Body
Corporation Developments)
7.3.8 Property connections
7.3.8.1 General Considerations
7.3.8.2. Requirements of Design
7.3.8.3 Number of Connections
7.3.8.4 Location of Connection
7.3.8.5 Connection Depth
7.3.8.6 Installation of Connections
7.3.9 Building Close Proximity Rules/Alteration of Ground Levels
7.3.9.1 Rising Mains and Trunk Sewers
7.3.9.2 Reticulation Sewers & Laterals/Connections
7.3.9.3 Ancillary Buildings May Be Exempt
(For Reticulation Sewers and Lateral/Connections)
7.3.9.4 Carports/Decks/Sunrooms
(For Reticulation Sewers)
7.3.9.5 Filling over Pipes
7.3.9.6 Cutting Down Over Pipes
7.3.9.7 Retaining Structures
7.3.9.8 Carriageway Trench Reinstatement
7.4 Construction Specifications (See Appendix C)
7.5 Wastewater pump stations and rising mains (See Appendix E)
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7.1 SCOPE
This Code is based on WSA 02 2002 — Sewerage Code
of Australia, and NZS 4404:2004 Land Development
and Subdivision Engineering. This section of the Code
sets out requirements for the design of wastewater
systems up to and including DN 300 (nominal diameter
300mm) or DN 355mm for PE (polyethylene). The
Code covers wastewater services for both new
developments and re-development areas. For pipes
larger than DN 300 refer to WSA 02 and Council for
specific requirements.
7.2 GENERAL
7.2.1 Objectives
The objectives of the design are to ensure that the
wastewater system is functional and complies with the
requirements of the Council’s wastewater systems. In
principle the wastewater system shall provide:
• A single gravity connection for each property;
• A level of service to the Council’s customers in
accordance with Council’s policies;
• Minimal adverse environmental and community
impact;
• Compliance with environmental requirements;
• Compliance with statutory OSH requirements;
• Adequate hydraulic capacity to service the entire
upper full catchment;
• Long service life with minimal maintenance and
least life cycle cost;
• Zero level of pipeline infiltration on
commissioning of pipes;
• Low level of pipeline infiltration/ex-
filtration/inflow over the life of the system;
• Resistance to entry of tree roots;
• Resistance to internal and external corrosion and
chemical degradation;
• Structural strength to resist applied loads;
• “Whole of life” costs that are acceptable to
Council..
7.2.2 Referenced documents and relevant guidelines
Wastewater designs shall incorporate all the special
requirements of Council and shall be in accordance
with the most appropriate Standards, Codes and
Guidelines including those set out below:
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AS/NZS 1260:1999 PVC pipes and fittings for drain,
waste and vent applications
NZS 7643:1979 Code of Practice for the installation
of unplasticised PVC pipe systems NZS 7649:1988 Unplasticised PVC sewer and drain
pipe and fittings
AS/NZS 1462-6:1998 Methods of test for plastic pipes and fittings
AS/NZS 4130:2001 Polyethylene pipes for pressure
applications
AS/2033:1980 Installation of polyethylene pipe
systems
AS 2200:1998 Design charts for water supply and
sewerage
AS/NZS 3500:1996 National plumbing and drainage part
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7.2.3 Connection to Existing Sewer
Networks/Approved Contractors
Connection of new sewer mains to the existing sewer
network shall be undertaken in accordance with the
requirements of S2.8 of this Code.
Connection of private drains, infill subdivisions or
developments not the subject of a development plan
approval to an existing sewer network shall be
undertaken by a Registered Drainlayer. The connection
shall be inspected by Council staff prior to backfilling of
the connection occurs.
7.2.4 Private Drainage
All wastewater pipes installed between a building and
the connection point to Council’s sewers mains are
private assets. The Building Act requires that a consent
be obtained for their installation or alteration and that
this work must only be carried out by a registered
drainlayer. A second consent must be obtained before
they may be connected to the sewer main and this
connection may only be carried out by a contractor who
has been awarded a Category F licence by Council.
Consent must also be obtained from Council before
these drains may be connected to the sewer main.
This connection may only be carried out by a contractor
who has been awarded a Category E or F licence by
Council.
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7.2.5 Rural and Rural Residential areas
Connection to Council’s wastewater system will not be
provided to Rural or Rural Residential allotments.
Council has no provision for Rural and Rural Residential
areas to be incorporated into Council’s wastewater
system.
7.3 RETICULATION SYSTEM
All wastewater reticulation systems shall be designed for
an asset life of at least 100 years. Some components
such as valves may require earlier renovation or
replacement. Refer to WSA 02 for the classification of
life expectancy for various components.
7.3.1 Design Responsibilities
7.3.1.2 District Plan
Council maintains a District Plan which sets out
information to be used in the design of new
subdivisions. See Clause 15.1.1 Wastewater Disposal
and Table 15.1 Engineering Performance Criteria.
Where the development area is not included in the
District Plan, the designer shall determine this
information by investigation using this Code of Practice
and recognized engineering principles.
7.3.1.3 Catchment Design
Pipes within any project area shall be designed to be
consistent with the optimum design for the entire upper
catchment area and any future extension of the system
shall be accommodated. This may affect the pipe
location, diameter, depth and maintenance structure
location and layout. Designers shall particularly assess
the depth of the proposed works, adopting the best
design practice to ensure a system with lowest life cycle
cost.
Pipes shall be designed with sufficient depth and
capacity to cater for all existing and potential
development of the catchment. Where future extension
of the pipe is possible, it may be necessary to carry out
preliminary designs for large areas of subdivided and
un-subdivided land. This design shall use safety factors
agreed with Council and include future subdivisions to
determine the necessary depth and diameter for an
extension.
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Where pipes are to be extended in the future, the ends of
pipes if possible shall extend past the far boundary of
the development by a distance equivalent to the depth to
invert and to terminate in a manhole or rodding eye.
This ensures that a future extension of the pipe does not
require unnecessary excavation within lots or
streetscapes already developed.
7.3.1.4 Topographical considerations
In steep terrain the location of pipes is governed by
topography. Gravity pipelines operating against natural
fall create a need for deep installations which can be
very expensive. The pipe layout shall conform to natural
fall as far as possible
7.3.1.5 Geotechnical Investigations, Foundation Design
and Groundwater Control
The designer shall take into account any geotechnical
requirements determined under Section 2 of this Code of
Practice.
The designer shall consider whether special precautions
are necessary against difficult geological and foundation
conditions.
If the predicted foundation conditions and/or the
predicted groundwater conditions (present or likely to
occur) do not call for special design details or
construction practices, then the designer shall state this
on the design drawings. However, if foundation
treatments are necessary, and/or groundwater conditions
affect either the design or construction of the wastewater
system, then the designer shall indicate the following on
the design drawings:
• The extent and all design details of any special foundation treatments required for the pipes and
other structures;
• The extent and all design details of any special methods necessary to control groundwater flow
along the pipe embedment and/or trench backfill
material e.g. bulkheads;
• All sections of the wastewater system where the constructor will need to pay particular attention
to controlling groundwater prior to excavation to
prevent heave or loss of density in the trench
floor material (e.g. “boiling” sand);
• Areas subject to subsidence;
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• Other geotechnical considerations, e.g. “Zone of
Influence” near structures. (See Drawing
WW15)
7.3.1.6 Easements
Easements are required:
• In favour of Council for all rising mains and trunk sewers installed in private property. The
easement shall be a minimum width of 3m,
located centrally about the pipe. The depth and
size of the pipeline may determine the need for
easements of greater width. These easements
shall be agreed at the time of development plan
approval.
• In favour of a property owner whose private drain passes through another property. These
easements shall have a minimum width of 1.5m
centrally located over the pipe.
• Where a main through a property is not parallel or close to a boundary, the easement shall be a
minimum of 3m wide, centrally located over the
pipe.
Easements for reticulation mains under 225mm dia. ID
through private property are generally not required.
7.3.2 Design of the Wastewater Reticulation System
7.3.2.1 Prime Considerations
Pipes shall be designed to:
• Have adequate capacity, grades and diameters;
• Have adequate grade for self-cleaning;
• Be deep enough to provide gravity service to all
lots;
• Comply with minimum depth requirements to
ensure mechanical protection and safety from
excavation;
• Avoid all underground services, whilst
maintaining all the necessary clearances;
• Allow for various drops and losses through
manholes.
• Be laid at sufficient depth to avoid interference
with land drains and gardening activities within
private property.
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7.3.2.2 Scheme Layout
Pipes should be positioned as follows:
• Within the street according to the locally
applicable utilities allocation code. A location
clear of carriageways is preferred;
• Within public land with the permission of
Council;
• Within drainage reserves outside the 1 in 100
year flood area;
• Within private property:- parallel to and located
between 1m and 1.5m from the front, rear and/or
side boundaries.
7.3.2.3 Pipeline Definitions
• Trunk mains - A gravity pipeline with an internal
diameter of 225mm or larger.
• Reticulation main – A gravity pipeline with an
internal diameter of 150mm which terminates
upstream at a manhole.
• Lateral/Connection – A 150mm or 100mm dia
pipeline branch which has no terminal manhole
structure. It may however terminate in a rodding
eye. Lateral/Connection pipes connect a
property’s private drainage to a public main, and
are Council assets.
• Connection Point – The location in a sewer
system where a property’s private drainage
system connects to the public system.
Generally if the pipe connecting the
property to the main is a single straight
length of pipe, it is defined as a connection pipe. If this pipe serves more than one
property then it is known as a lateral and
the upstream pipes serving each allotment
are the connections.
Apart from the junction into the sewer
main a lateral must not include any change
of horizontal direction.
7.3.2.4 Proposed and Existing Pipes in Private
Property
Where pipes are designed to traverse any vacant or
occupied private property, the design shall as far as
practicable allow for possible future building
development.
The design shall allow access for all equipment required
for construction and future maintenance.
Where pipes are designed to traverse properties
containing existing structures e.g. retaining walls,
buildings and swimming pools, the current and future
stability of the structure shall be considered. Pipes
adjacent to existing buildings and structures shall be
located clear of the “Zone of Influence”
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(See Drawing WW15). If this is not possible,
protection of the pipe and associated structures shall
be specified for evaluation and approval by Council.
7.3.2.5 Horizontal Curves
Horizontal curved pipes shall only be used where
approved by Council. Design standards for curved pipes
can be found in WSA 02.
7.3.2.6 Vertical Curves
Vertical curves may be specified where circumstances
provide a significant saving or where maintenance
structures would be unsuitable or inconvenient. The
curvature limitations for vertical curves can be found in
WSA 02.
7.3.2.7 Maintenance Structure Location
Maintenance structures include:
• Manholes (MH).
• Rodding eyes (RE).
7.3.2.8 Underground Services
The location of underground services affecting the
proposed pipe alignment shall be determined. Where
pipes will cross other services, the depth of those
services shall be investigated, and exposed where
necessary. Services upstream of the project area may
affect the design. A future extension of the pipe that will
cross existing and proposed upstream services may
determine the level for the current project infrastructure.
7.3.3 Pipe Materials
7.3.3.1 Acceptable Pipe Materials
Sanitary gravity reticulation systems constructed of the
following materials will be accepted:
• PVC to be manufactured in accordance with AS/NZS
1260 as grade SN16 for up to 5m depth.
Specific design for depths greater than 5m.
• Pipe type to be plain wall construction conforming to
AS/NZS 2566.
• Ductile Iron pipe to AS 2280 (concrete lined with loose
sleeve protection)
• Concrete pipe and other materials (e.g. Hobas GRP to AS
3571) may be approved by Group Manager: City
Services.
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• In general only uPVC shall be used for gravity reticulation
and service connections.
• DN 175mm is not be used in Council’s wasterwater reticulation network.
• PE 100 SDR17 may be used for steeper gradients where specifically approved by Council.
7.3.3.2 Pipe Fittings
• All fittings and service connections shall be factory fabricated of compatible materials to the proposed system
chosen and comply with the relevant Standards. PVC fittings
and service connections DN 100mm and DN 150mm
injection moulded fittings to conform to AS/NZS 1260.
DN225mm and larger factory fabricated PVC fittings to be
made of same grade materials as specified for the pipeline.
• Where the reticulation system is of uPVC the main line connection to each manhole structure is to be with a standard
uPVC proprietary connector (See Drawing WW02). The
requirements for drop connectors are detailed in Drawings
WW03 and WW04.
• In potentially unstable ground or where special protection is required, the sewer pipelines should be specifically
designed, using structural design as specified in either
AS/NZS 2566 “Buried Flexible Pipelines – Structural
Design”.
7.3.3.3 Joints
• All joints on pipes and fittings shall be factory made
flexible type.
• Under no circumstances will mortar joints be permitted.
• Gibault joints shall be “denso” wrapped and sealed with
approved outer wrapping.
• Pipe to manhole joints shall be of proprietary type and
shall incorporate a “pipe short” for each joint (see Drawing
WW02).
7.3.4 Clearances
7.3.4.1 Clearance FromUnderground Services
For normal trenching and trenchless technology
installation, clearance from other service utility assets
shall not be less than the minimum vertical and
horizontal clearances shown in Table 7.1. Written
.
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agreement on reduced clearances and clearances for
shared trenching shall be obtained from Council.
Table 7.1
Clearances between wastewater pipes and other
underground services
Utility (Existing
service)
Minimum
horizontal
clearance (mm)
Minimum
vertical
clearance (1)
(mm)
Gas mains 300(²) 150
Telecommunication
conduits & cables
300(²) 150
Electricity conduits
and cables 500(²) 225
Stormwater/Waste
water 300(²) 150
Water mains 1000/600 (³) 500
NOTE:
(¹) Vertical clearances apply when wastewater pipes
cross one another, except in the case of water mains
when a vertical separation shall always be
maintained, even when the wastewater pipe and
water main are parallel. The wastewater pipe should
always be located below the water main to minimize
the possibility of backflow contamination in the
event of a main break.
(²) Clearances can be further reduced to 150mm for
distances up to 2m when passing installations such
as poles, pits and small structures, providing the
structure is not destabilized in the process.
(³) When the wastewater pipe is at the minimum
vertical clearance below the water main (500mm)
maintain a minimum horizontal clearance of
1000mm. This minimum horizontal clearance can be
progressively reduced to 600mm as the vertical
clearance increases to 750mm.
7.3.4.2 Clearance From Structures
Pipes adjacent to existing buildings and structures shall
be located clear of the “Zone of Influence” (Drawing
WW15) of the building foundations. If this is not
possible, a specific design shall be undertaken to cover
the following:
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• Protection of the pipeline;
• Long term maintenance access for the pipeline;
and
• Protection of the existing structure or building
shall be specified by the designer for evaluation
and acceptance by Council.
7.3.5 Pipeline Design
7.3.5.1 Design Flow
The design flow comprises domestic wastewater,
industrial wastewater, infiltration and direct ingress of
stormwater.
Pipe size shall be based on the need to transport the
design flow without surcharging.
The design flow shall be calculated by the method
nominated by Council. In the absence of this
information from Council the following design
parameters are recommended:
(a) Residential Flows
i. Average dry weather flow of 210 litres per day per person
ii. Dry weather diurnal peak flow of 2.5
iii. Dilution/infiltration factor of 2 for wet weather
iv. Number of people per dwelling: 2.7
In practical terms, in a catchment not exceeding 250 dwelling units, and where no pumping
station is involved, DN 150 pipes laid within the
limits of table 7.5 will be adequate without
specific hydraulic design
For small contributing catchments, peak flows can be
significantly higher but, due to the requirement for a
minimum pipe size of DN150, such flows will not
govern the design.
(b) Industrial / Commercial Flows
i. Where flows from a particular industry or commercial development are known they
should be used as the basis of design. Where
there is no specific flow information available
and Council has no design guide, Table 7.2 is
recommended as a design basis. These flows
include both sanitary wastewater and trade
wastes and include peaking factors.
ii. Notwithstanding the above, provision for trade waste must be agreed by Council and shall be
subject to the provisions of the Council Trade
Waste Bylaw.
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iii. Pre-treatment of trade waste may be a condition of any Trade Waste Agreement.
Table 7.2 Industrial/commercial flows (Peak Wet Weather
flows)
Industry type Design flow
(Water usage) (Litre/second/hectare)
Light 0.4
Medium 0.7
Heavy 1.3
7.3.5.2 Hydraulic Design of Pipelines
The hydraulic design of wastewater pipes should be
based on either the Colebrook-White formula or the
Manning formula.
The coefficients to be applied to the various materials
are shown in Table 7.3.
Table 7.3 Coefficients for gravity lines
Material Colebrook-White
coefficient
Manning roughness coefficient
K(mm) (n)
UPVC 0.6 0.011
PE 0.6 0.011
GRP 0.6 0.011
Cement lining 1.5 0.012
PE or epoxy lining 0.6 0.011
7.3.5.3 Minimum Pipe Sizes
Irrespective of other requirements, the minimum sizes of
property connection and reticulation pipes shall be not
less than those shown in Table 7.4.
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Table 7.4 Minimum pipe sizes for wastewater
reticulation and connections to property
Pipe Minimum size DN
Lateral servicing 1 or 2 dwelling units 100
Lateral servicing more than 2 dwelling units
150
Lateral servicing commercial and industrial lots
150
Reticulation servicing residential lots 150
NOTE: For infill subdivisions, particularly where
upgrading of existing DN 100 connections in sound
condition and at reasonable grades would be impractical,
up to four dwelling units may be connected subject to
the Council approval.
7.3.5.4 Limitation on Pipe Size Reduction
In no circumstances shall the pipe size be reduced on
any downstream section.
7.3.5.5 Minimum Grades for Self-Cleaning
Self-cleaning of grit and debris shall be achieved by
providing minimum grades, as specified in Tables 7.5
and 7.6.
In practical terms, in a catchment not
exceeding 250 dwelling units, and where no pumping station is involved, DN 150
pipes laid within the limits of table 7.5
will be adequate without specific
hydraulic design.
Table 7.5 Minimum grades for wastewater mains
Pipe size
DN
Minimum grade
(%)
150
225
300
0.55
0.33
0.25
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Table 7.6 Minimum grades for lateral connections
and permanent upstream ends
Situation Minimum grade
(%)
DN 100 lateral pipes
DN 150 lateral pipes
1.65
1.20
1 .00
7.3.5.6 Maximum Velocity
The preferred maximum velocity for peak wet weather
flow is 3.0 m/s. Where a steep grade that will cause a
velocity greater than 3.0 m/s is unavoidable see WSA 02
for precautions and design procedures.
7.3.5.7 Minimum Cover
• In Private Property: The minimum cover for
unreinforced pipes shall be 600mm. Where due
to topography this cover cannot be provided,
approved protection shall be provided to the
pipeline or a ductile iron pipe used. Where the
reticulation lines are located in the front yard of
lots, the invert level shall be deep enough so as
not to interfere with any future driveway
construction.
• Under Carriageways or in the Road Reserve:
Pipes shall be specifically designed to support an
8.2 tonne axle design loading. Manufacturers’
certification shall be required for all pipes
installed under carriageways with less than
750mm cover.
7.3.5.8 Steep Grades
Bulkheads and trench stop configuration shall be
detailed on the design drawings and shall be in
accordance with the drawing WW18. Spacing of
bulkheads shall be in accordance with Table 7.7.
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Table 7.7 Bulkhead Spacing
Grade
%
Requirement Spacing (S)
(m)
15 – 35 Concrete bulkhead S = 100/Grade (%)
>35 Special design Refer to Council
NOTE: On flat grades where scour is a problem, sand bags
are often used to stabilize the trench backfill.
Where the natural transfer of water from the trench into
the surrounding ground will not provide sufficient
drainage, trench drainage shall be provided to divert the
water.
7.3.5.9 Near Horizontal Bores
Near horizontal boreholes may be used to facilitate the
economic installation of pipes, usually in difficult areas
such as under railway lines, highways, to avoid
environmentally sensitive areas, and where excavation
may pose a high risk to adjacent building or structures.
For design guidelines and tolerances refer to Appendix C
Stormwater and Wastewater Construction Specifications..
7.3.5.10 Venting
In urban developments, pipes will normally be
adequately ventilated within the private property
drainage via the terminal vent stacks. However there are
some situations where additional vent stacks will be
needed such as:
• At pumping stations
• At manholes where pumping station rising mains
discharge to a gravity pipe.
In such situations vent stacks shall be installed as per the
requirements of WSA 02 and WSA 04.
7.3.6 Maintenance Structures
7.3.6.1 General
This section describes the requirements for structures
which permit access to the wastewater system for
maintenance. Theses are categorized as:
• Manholes (MH);
• Rodding eyes (RE);
The selection of a suitable location for maintenance
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structures may influence the pipe alignment. Generally,
a minimum clearance of 1000mm should be provided
around maintenance structures clear of the opening to
facilitate maintenance and rescue. Council may
determine other specific requirements subject to the
individual site characteristics.
Maintenance structures shall be located: -
• Where long term, safe access is available; (if
possible / practicable)
• Clear of floodways, stormwater detention areas,
stormwater secondary flow paths and inter-tidal
regions
7.3.6.2 Location of Manholes
The design shall include manholes at the following
locations:
• Intersection of pipes except for junctions
between mains and laterals;
• Changes of pipe size;
• Changes of pipe direction, except where
horizontal curves are used;
• Changes of pipe grade, except where vertical
curves are used;
• Combined changes of pipe direction and grade,
except where compound curves are used.
• Changes of pipe invert level;
• Changes of pipe material, except for
repair/maintenance locations;
• Permanent or temporary ends of a pipe
• Discharge of a pressure main into a gravity pipe
7.3.6.3 Manhole Spacing
For reticulation pipes, the maximum distance between any
two consecutive manholes shall be 120m.
7.3.6.4 Manhole Materials
Standard MHs shall be manufactured in pre-cast
reinforced concrete. However, if aggressive groundwater
or other special conditions exist, alternative materials
may be more appropriate as MHs.
For alternative materials check with the manufacturer on
their suitability for the purpose intended. Approval by
the Council would be required.
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Trunk mains require specific manhole design.
7.3.6.5 Size of manholes
The standard internal diameter of circular MHs is
1050mm and preferred nominal internal diameters are
1050mm, 1200mm and 1500mm. When considering the
appropriate MH diameter, consideration shall be given
by the designer to the base layout to ensure hydraulic
efficiency and adequate working space in the chamber.
Where the effective working space is reduced by internal
drop pipes, a larger diameter may be required. Where
there are several inlets, the designer may require
guidance as to the best layout of the chamber
7.3.6.6 Base Layout
• An area shall be provided in the base of each MH
that provides a safe place to stand for
maintenance purposes.
• The area will be close to flat with a cross fall
(2H:1V) into the MH pipe system for drainage
purposes.
• Channels shall have a minimum inside radius of
300mm.
7.3.6.7 Allowable Deflection Through MHs
A maximum allowable deflection through a MH
shall comply with Table 7.8.
Table 7.8 Maximum allowable deflections through MHs
Pipe size
DN
Maximum deflection
Degrees (º)
150 to 300
150 to 300
Up to 120º for internal fall
along MH channel
Up to 150º when using an
internal or external drop
structure
7.3.6.8 Internal Falls Through MHs
a) Reticulation pipes
• The minimum internal fall through a reticulation channel in a MH shall comply with Table 7.9.
• The maximum benched fall through a MH is to be 600mm.
• Where the outlet diameter at a MH is greater than the inlet diameter, the minimum fall through the
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MH shall be not less than the difference in
diameter of two pipes, in which case the pipes
shall be aligned soffit to soffit.
• On pipes where the maximum internal fall of 600mm across the base of the MH is not
achievable due to a large difference between the
levels of incoming and outgoing pipes then
internal or external drops shall be provided. (see
Drawings WW03-04)
Table 7.9 Minimum internal fall through MH joining
sewer main pipes of same diameter
Deflection angle at MH
Degrees (°)
Minimum internal fall
(mm)
0 to 30
>30 to 60
>60 to120
30
50
80
b) Lateral/Connections to Manhole
• The invert of a lateral/connection must connect to
the MH at a level no lower than the average of
the soffit levels of the main inlet and outlet pipes.
• Maximum angle of deflection of
lateral/connection into the manhole main channel
shall be 90 degrees.
7.3.6.9 Effect of Steep Grades on MHs
Where a pipe of grade >7 % drains to a MH, the
following precautions shall be taken:
• No change of grade is permitted at inlet to a MH;
• Steep grades are to be continuous through the
MH at the same grade;
• Depth of MH is to exceed 1.5m to invert for DN
150 and DN 225 pipes;
• Depth of MH is to exceed 2.0m deep for DN 300
pipes;
• Change of direction at the MH is not to exceed
45 degrees;
• No drop junctions or verticals are to be
incorporated in the MH;
• Inside radius of channel inside the MH is to be
greater than 6 times the pipe diameter; and
• Benching is to be taken 150mm above the top of
the inlet pipe.
21 TCC Ref: 790837
• To avoid excessively deep channels within MHs,
steep grades (>7 %) shall be “graded-out” at the
design phase where practicable. The design of
pipelines on gradients over 7% must be agreed
with Council.
• Benching of channels must ensure that the final
platform is parallel with the main channel so that
maintenance workers are able to stand
comfortably on a flat surface. The benching shall
be sloped towards the channel.
7.3.6.10 Flotation
In areas of high water table, all MHs shall be designed
to provide a factor of safety against flotation of 1.25.
7.3.6.11 Access
MH steps shall comply with Drawing WW05
7.3.6.12 Covers
MH covers with a minimum clear opening of 500 mm in
diameter, shall be used.
• “Non-rock” covers must be used on all State
Highway and Level 2 roads. (roads with greater
than 10,000 vehicles per day).
• “Heavy Duty” covers must be used in the road
reserve, carriageway, commercial and industrial
properties and all public areas.
• “Standard” covers may only be used on
residential properties.
• All covers must be painted with white road
marking paint.
7.3.6.13 Areas Subject to Flooding
Watertight type bolt-down metal access covers:
• In systems where the possibility of surcharge
exists; and
• Along creeks subject to flooding above the level
of the cover, in tidal areas, or in any location
where surface waters could inundate the top of a
MH.
The top of MHs in areas subject to flooding shall be a
minimum of 300 mm above the 1% AEP flood level.
7.3.6.14 Rodding Eyes (RE)
• An RE is required to be constructed at the ends of
some lateral pipes that are installed between a
22 TCC Ref: 790837
property connection point and the Council sewer
main network. (See Clause 7.3.7.1)
• uPVC bends up to 45 degrees are acceptable.
• A manhole frame and cover shall be installed
over the entry point where the RE is to be located
in areas other than permanent hardstand areas.
• The cover type shall be as required by Clause
7.3.6.12.
• A fire hydrant base and RE cover may only be
installed in permanent hardstand areas.
• Typical details of RE structures are shown on
Drawings WW08 and WW09
7.3.7 Laterals/Connections
The general levels and locations of all wastewater pipes
shall conform with Council’s overall plan for
reticulation. Provision must be made for connection into
the existing reticulation system. Refer to Section 7.3.5
for pipeline design.
• Where practicable and where connection is to be
within 5m of a manhole the connection shall be
to the manhole.
• Where the main line is within public property
and within 5m of the property boundary a
separate connection shall be provided to each
allotment.
• Connections to trunk mains will generally not be
approved by Council.
7.3.7.1 Subdivision of 4 Lots or More
Minimum pipe sizes are 150mm diameter nominal size
for reticulation sewers and 100mm diameter nominal
size for laterals. For the purposes of this clause a
reticulation sewer is any pipeline terminating with a
manhole at its upstream end and a lateral is any public
pipeline connecting from the reticulation sewer to an
individual allotment
23 TCC Ref: 790837
• Lateral with single connection (out of manhole)
Fig.1:
For 100mm dia lateral up to 25m no RE required.
For 100mm dia lateral between 25m and 50m in
length terminate in a RE or where lateral passes
through adjacent property.
Above 50m normal sewerage reticulation standards
apply.
150mm diameter lateral pipe must be used under all
carriageways.
• Lateral with two connections (out of manhole) Fig.
2:
For 100mm dia laterals up to 25m in length
terminate in a RE.
For laterals over 25m and up to 50m use 150mm dia
pipe and terminate with RE.
Above 50m normal sewerage reticulation standards
apply.
150mm diameter lateral pipes must be used under all
carriageways.
• Lateral with greater than 2 connections and a max of
6 connections (out of manhole) Fig. 3:
Use a 150 mm dia pipe up to 50m in length and
terminate in RE.
Above 50m normal sewer reticulation standards
apply.
150mm diameter pipes must be used under all
carriageways.
24 TCC Ref: 790837
• Lateral Out of Main Servicing One Allotment: Fig 4
For 100mm dia pipe up to 25m no RE required.
For 100mm dia pipe between 25m and 50m in length
or where the line passes through an adjoining lot
terminate in RE.
150mm diameter pipes must be used under all
carriageways.
• Lateral Out of Main Servicing 2 Allotments, Fig. 5 and Fig. 5A:
For 100mm diameter up to 25m terminate in RE.
For 25m to 50m in length use 150mm dia pipe and
terminate in RE.
150mm diameter pipes must be used under all
carriageways.
25 TCC Ref: 790837
7.3.7.2 Infill Subdivision - Three Lots or Less
(Excludes Existing Lot)
It is recognized that infill subdivisions require flexibility
in their reticulation layout. However, normal trade
practices and standards are needed to ensure that the
desired service life is achieved.
Reticulation of infill subdivisions shall comply with the
following criteria.
• Infill subdivisions are to be reticulated on a site
by site basis to the approval of Group Manager:
City Services
• Where practicable, drainage reticulation should
be constructed or upgraded in accordance with
this Code. (See 7.3.7.1 above) These drains can
therefore be declared public and provide each
allotment with the same standard of individual
connection as new ‘greenfields’ allotments. (Fig
6.) Where this is considered impractical or
unnecessary, the Consent Holder may make
application to Council to accept the drain as
private within an appropriate easement.
However common private drains are not
encouraged so as to alleviate the friction that
sometimes occurs between neighbours when
shared services are involved. (Fig 7)
• Drainage lines are to be separated at the point of
connection to Council’s reticulation system and
remain separate for each lot unless specific
approval is granted by Council (Fig 6 and 7).
Where the main is within a neighbours property,
the new junction may be installed immediately
within the property being subdivided.
7.3.7.3 Multi-Unit Properties (Such as Apartment
Buildings and Body Corporate
Developments)
• For multiple occupancies (unit title, cross lease
or company lease), service of the whole property
shall be achieved by providing a single point of
connection to the wastewater system. Connection
of the individual units is by joint service pipes
owned and maintained by the body corporate,
tenants in common or the company as the case
may require.
26 TCC Ref: 790837
In this instance the whole of the multiple
occupancy shall be regarded as a single lot. All
drainage within the development boundary would
be private.
• Alternatively, if authorized by Council,
developers may have the option of providing
wastewater facilities to the individual titles or
tenements in new developments by extending the
public line into the lot and providing a separate
lateral/connection to each unit. If so all internal
drainage must be to the normal Code of Practice
standards
• Where the above developments are proposed a
single DN 150 lateral/connection will be required.
Multi-unit developments will generally be required
to upgrade existing laterals if less than DN 150.
• The connection shall include a surface accessible
inspection chamber or manhole immediately inside
the boundary.
7.3.8 Property Connections
A connection is the point of union between a property’s
private drain and the public wastewater network. Private
drainage generally extends through to the property
boundary, at which point Council accepts responsibility
for the downstream pipelines.
7.3.8.1 General Considerations
• The property connection should be designed to
suit the existing situation and any future
development.
Where practicable, pipes shall be designed to
provide a service for the whole of the property
they serve. Where, for physical reasons, it is not
practical to fully service a property, a partial
service may be acceptable to Council provided the
unserviceable area is identified by a building line
restriction or minimum floor level consent notice.
7.3.8.2 Requirements of Design
The design shall specify the requirements for the
property connections including:
• Plan location and lot contours;
• Invert level at property boundary or junction with
the main as applicable.
27 TCC Ref: 790837
7.3.8.3 Number of Connections
It is normal practice to provide one connection per lot.
Provision of additional connections shall be subject to
justification by the developer and approval by Council.
7.3.8.4 Location of Connection
• The connection shall be located to service the lowest practical building platform on the property
and where possible:
• Be clear of obstructions, e.g. tree, tree roots, paved areas;
• Be easily accessible for future maintenance;
• Be clear of any known future developments, e.g. swimming pools or driveways;
• Be no deeper than 1.5m where practicable
7.3.8.5 Connection Depth
Connection depths shall be set to drain the whole
serviced area recognizing the following factors:
• Surface level at plumbing fixtures of buildings
(existing or proposed);
• Depth to invert of pipe at plumbing fixture or
intermediate points;
• Minimum depth of cover over connection to be
600mm unless protected by hard surface.
• Invert of public main at junction point;
• Allowance for crossing other services (for
clearances see 7.3.4);
• Allowance for minimum gradients of laterals and
private drainage;
• Lateral junctions installed at minimum of 45
degrees (vertical) to main(refer to drawing
WW13);
• Connections deeper than 3.0m must be approved
by Council.
The designed invert level at the connection shall be not
higher than the lowest calculated level consistent with
these factors.
Deep connections shall be brought up to within 1.5m of
finished surface (Drainlayer can then cut connection
down to required level if necessary)
28 TCC Ref: 790837
7.3.8.6 Installation of Connections
• Connection of a private wastewater drain to the
public system can only be carried out by a
Contractor holding a Category E licence and
after drainage consent has been approved by
Council.
• The end of each connection pipe shall be sealed
with a solvent welded cap, painted red, in
greenfield developments or if connection does
not to occur immediately.
• All connection points shall include an
underground inspection fitting the same size as
the lateral connection to the property. Where the
inspection is to a property servicing multiple
residential units then refer to 7.3.7.3 for a surface
accessible inspection chamber.
• Each connection point shall be marked with a 50
x 50mm timber stake which shall extend from
the invert to a minimum of 300mm above
finished ground level. A PVC marker tape
labelled “sewer” shall be attached to the
connection pipe, brought up and tied to the top of
the stake.
7.3.9 Building Close Proximity Rules and Alteration
Of Ground Levels (see drawings WW15 and 16)
7.3.9.1 Rising Mains and Trunk Sewers
• Buildings or structures to be constructed close to a
rising or trunk main shall comply with the
requirements of Drawing WW15. Piles and ground
beams shall be designed by a Chartered Professional
Engineer.
• Minimum horizontal clearance between pipe exterior
and piles/building shall be 1500mm.
• All buildings shall be at least 500mm clear of the
external wall of a manhole.
• No building or concrete slab may be constructed
over a connection point to a sewer main.
7.3.9.2 Reticulation Sewers and
Laterals/Connections
• Buildings or structures to be constructed close to a
public reticulation main or lateral/connection must
comply with the requirements of Drawing WW15.
Piles and ground beams must be designed by a
Chartered Professional Engineer.
29 TCC Ref: 790837
• Minimum horizontal clearance between pipe
centreline and piles/building shall be 1000mm.
• All buildings shall be at least 500mm clear of the
external wall of a manhole.
• No building /concrete slab to be constructed over a
connection point to a sewer main.
7.3.9.3 Ancillary Buildings may be Exempt (for
Reticulation Sewers and
Lateral/Connections)
• No enclosed building or structure shall be sited over
a manhole or closer than 500 mm from the outside
wall of the manhole structure.
• Corner foundations shall be a minimum of 600mm off the pipe centre line.
• Where dispensation has been granted for a building or structure to be built over a reticulation sewer or
lateral/connection, foundations shall be designed by
a Chartered Professional Engineer. Piles and /or
foundations must conform with specifications shown
in Drawing WW15.
• No buildings will be allowed over the sewer main if
there is a connection closer than 1000mm to the
buildings, unless the connection is relocated to the
satisfaction of Council.
7.3.9.4 Carports / Decks / Sunrooms (for
reticulation sewers)
These structures may be sited over reticulation sewer
pipelines provided:
• There is no connection point closer than 1000mm to
the structure.
• No enclosed building or structure shall be sited over
a manhole or closer than 500 mm off the outside
wall of the manhole structure.
• The structure is designed such that it can be
dismantled easily in sections (bolting is the preferred
method of construction);
7.3.9.5 Filling over Pipes
Any ground level raising carried out on a property must not
result in a depth of fill material greater than 3.0 metres over
a sewer pipe invert, within the 45 degree “Zone of
Influence” of the pipe.
30 TCC Ref: 790837
7.3.9.6 Cutting Down Over Pipes
The cover over the top of a public sewer in private property
shall not be reduced to less than 600mm.
7.3.9.7 Retaining Structures
Minimum design constraints for retaining structures/piles
shall be as in WW16
7.3.9.8 Carriageway Trench Re-instatement.
Where pipe servicing in the carriageway is required, the
trench re-instatement works shall follow the minimum
requirements shown in drawing D16 and R32.
Pipe trenches within a carriageway shall be backfilled using
an approved hardfill placed immediately above the pipe
surround and compacted in layers not exceeding 200mm in
depth.
In existing sealed streets, the top section of the trench shall
be backfilled as specified by TNZ M/4. The depth of base
course and type of finishing coat seal shall conform at least
to the standard of the existing road construction, but may
require being greater.
7.4 CONSTRUCTION SPECIFICATION
Construction Specification for both wastewater and
stormwater are provided in Appendix C.
7.5 WASTEWATER PUMPSTATIONS
AND RISING MAINS. Construction Specifications for wastewater pumpstations
and rising mains are contained in Appendix E.
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