FINAL REPORT NO. 36 - Taurangaecontent.tauranga.govt.nz/data/projects/files/pipeline/rc13559... ·...

F I N A L R E P O R T N O . 3 6

Preliminary Hydraulic Design Report

Prepared for

91 Willow Street Tauranga

30 August 2007

42066678

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ry Hydraulic Design Report

P R E L I M I N A R Y H Y D R A U L I C D E S I G N R E P O R T

Contents

Contents

Glossary .....................................................................................................................v

Executive Summary .............................................................................................. 1-1

1 Introduction ................................................................................................... 1-1

2 Selected Pipeline Route ............................................................................... 2-2

.......................................................................................................... 2-2 2.1 Western Route E

............................................................ 2-2 2.1.1 Memorial to Strand Walkway Project

............................................................................. 2-2 2.1.2 Harbour Crossing Options

..................................................... 2-3 2.1.3 Sub-catchment Sewer Connection Points

3 Design Flows................................................................................................. 3-1

4 Pump Station and Pipeline Design Requirements ..................................... 4-1

................................................................................................... 4-1 4.1 Pump Station Design

.......................................................................................................... 4-1 4.1.1 General

.......................................................................................... 4-1 4.1.2 Number of Pumps

............................................................................................. 4-1 4.1.3 Pump Selection

................................................................................. 4-2 4.1.4 Low Flow Management

...................................................... 4-2 4.1.5 Flushing and Emergency Storage Tanks

.................................................................... 4-2 4.1.6 Impact on End-of-Line Facilities

....................................................................................................... 4-2 4.1.7 Wet Wells

........................................................................................................ 4-2 4.1.8 Materials

................................................................................ 4-3 4.1.9 Pump Station Structures

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4.1.10 ....................................................................................... 4-3 Odour Management

4.1.11 ................................................................................... 4-3 Control and Telemetry

............................................................................................................ 4-3 4.2 Pipeline Design

.................................................................................................. 4-3 4.2.1 Rising Mains

................................................................................................. 4-3 4.2.2 Gravity Mains

............................................................................................ 4-4 4.2.3 Inverted Siphons

.................................................................................................. 4-4 4.2.4 Pipe Material

................................................................. 4-4 4.2.5 Design Velocities and Roughness

......................................................................................................... 4-5 4.2.6 Flushing

............................................................. 4-5 4.2.7 Air Management and Odour Control

........................................................................................... 4-6 4.2.8 Transient Control

....................................................................... 4-6 4.2.9 Pipe Depth and Cover to Pipe


Contents

4.2.10 Manholes, Receiving Chambers, Energy Dissipaters and Access Points............................................................................................................. 4-7

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4.2.11 .................................................................. 4-7 Local Pump Station Connections

4.2.12 .................................................................. 4-8 Thrust Blocks and Pipe Restraint

5 Maleme to Memorial Section........................................................................ 5-1

........................................................................... 5-1 5.1 Maleme Street Trunk Pump Station

........................................................................................... 5-1 5.1.1 System Overview

................................................................................................. 5-2 5.1.2 Inlet Channel

...................................................................................................... 5-2 5.1.3 Low Flows

..................................................................................................... 5-2 5.1.4 High Flows

......................................................................................................... 5-2 5.1.5 Flushing

....................................................................................... 5-3 5.1.6 Emergency Storage

.......................................... 5-3 5.1.7 Rising Main Surge Control and Air Management

.................................................................. 5-3 5.2 Maleme Street to Memorial Park Pipeline

............................................................. 5-3 5.2.1 Maleme Street to Chadwick Section

.................................................................. 5-3 5.2.2 Chadwick to 18th Avenue Section

.......................................................... 5-4 5.2.3 18th Avenue to Memorial Park Section

6 Memorial to Te Maunga Section .................................................................. 6-1

...................................................................................... 6-1 6.1 Memorial Park Pump Station

........................................................................................... 6-1 6.1.1 System Overview

................................................................................................. 6-1 6.1.2 Inlet Channel

...................................................................................................... 6-2 6.1.3 Low Flows

..................................................................................................... 6-2 6.1.4 High Flows

......................................................................................................... 6-2 6.1.5 Flushing

....................................................................................... 6-3 6.1.6 Emergency Storage

.......................................... 6-3 6.1.7 Rising Main Surge Control and Air Management

....................................................................... 6-3 6.2 Memorial Park to Te Maunga Pipeline

................................................................ 6-3 6.2.1 Memorial Park to Matapihi Section

............................................................................................ 6-4 6.2.2 Matapihi Section

........................................................ 6-4 6.2.3 Matapihi to Te Maunga WWTP Section

7 Poike / Ila Pump Station System.................................................................. 7-1

.............................................................................. 7-1 7.1 Hairini, Ila and Poike Catchments

.................................................................................. 7-1 7.1.1 Ila Place Pump Station


Contents

....................................................................................... 7-1 7.1.2 Poike Pump Station

8 Limitations..................................................................................................... 8-1

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Tables, Figures, Appendices

Tables, Figures, Appendices

Tables ............................................................................................................... 1-1 Table 1-1: Hydraulic Constraints

.................................................................................. 2-3 Table 2-1: Contributory Sub-catchments Locations

............................................................. 3-1 Table 3-1 Design Populations and Incoming Contributory Flows

............................................... 4-5 Table 4-1 Recommended Design Criteria (Normal Peak Flow Operation)

.......................................................... 5-1 Table 5-1 Summary of Maleme Street Pump Station Components

.......................................................... 6-1 Table 6-1 Summary of Memorial Park Pump Station Components

Figures ................... 2-4 Figure 2-1: Sub-Catchment Location and Connection Plan for proposed Southern Pipeline

Error! No table of figures entries found.

Appendices

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A. Pipeline Long Section Drawings B. Updated Design Flows - Correspondence C. Pump Station Failure Scenarios and Storage Volumes


Glossary

Glossary

ADWF Average Dry Weather Flow: Flow experienced during dry weather, averaged over 24 hours.

AEP Annual Exceedence Probability (i.e. 1% is equivalent to 1 in 100 years)

Ch Chainage, the distance in metres from the starting point (Maleme Street Pump Station) along the proposed route

Gravity Sewer A pipe where the wastewater flows under the action of gravity only

Inverted Siphon The sewer route is deviated downwards and back up again to pass under an obstruction or across a low point

L/s Litres per second

m/s Metres per second, velocity

m3/s Cubic metres per second, flow rate

ONTRACK New Zealand Rail Corporation

PLC Programmable Logic Controller

PWWF Peak Wet Weather Flow: Instantaneous peak flow rate measured following a heavy rainfall event

Quadruple Bottom Line Assessment (QBLA) A qualitative evaluation and scoring procedure used to compare options – the areas scored are Social; Environmental; Cultural; and Economic

Rising Main A pipe where the wastewater is pumped under pressure from the pump station

Risk Evaluation A procedure used to identify and quantify the risks involved in a project, assuming practicable steps have been taken to mitigate the risk in all cases.

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Glossary

SP Southern Pipeline Project

Surge Tank An air vessel at the pump station. An air vessel is a pressure vessel (usually made of steel) which is partly full of compressed air and wastewater. The vessel provides energy storage to absorb pressure surges

TCC Tauranga City Council

Trunk Main Sewer A sewer pipe collecting wastewater from local reticulation. Typically greater than 300 mm diameter.

URS URS New Zealand Ltd

VSD Variable Speed Drive, an attachment to the pump motor used to ramp the speed of the pump up or down to vary the flow output.

WWTP Wastewater Treatment Plant

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Executive Summary

Executive Summary

URS New Zealand Ltd (URS) has been engaged by Tauranga City Council (TCC) to design, obtain consents for and oversee construction of a new trunk sewer pipeline, the Southern Pipeline, to transport wastewater from the southern Tauranga catchments of Welcome Bay, Maungatapu, Hairini, Greerton, Pyes Pa, Pukemapu/Neewood, and Pyes Pa West to the Te Maunga Wastewater Treatment Plant (WWTP).

As well as providing flow capacity for the expected population growth in the southern catchments up to 2051, the new Southern Pipeline also has the benefit of freeing up capacity in the already restricted pipes in western Tauranga up to Chapel St WWTP.

The Southern Pipeline can be divided into two separate hydraulic sections, the first from Maleme Street Pump Station to the inlet at Memorial Park. The second section is from Memorial Park Pump Station to the inlet at the Te Maunga Wastewater Treatment Plant. In summary, these two sections have been designed as described below.

Maleme Street Pump Station to Memorial Park

The first trunk pump station is located at Maleme Street, and will take flows from the southern catchments of Tauranga, including the new development at Tauriko / Pyes Pa West. The key characteristics of the pump station are:

a. ADWF (2011) 39 L/s, PWWF (2051) 454 L/s.

b. Two smaller jockey pumps will handle low flows during dry periods and in the early years of pipeline operation. During flushing or wet weather flows the two or three larger main pumps will operate.

c. The downstream pipeline is 5.7 km long, and divided into three sections:

Rising main 1.2 km - from Maleme Street Pump Station to Chadwick Road th Gravity inverted siphon 2.7 km – from Chadwick Road to 18 Avenue

th Gravity main 1.8 km – from 18 Avenue to Memorial Park

d. Transient pressures will be controlled with an air vessel located at the pump station.

e. Air valves will be used to control the air within the main pipeline.

Memorial Park Pump Station to Te Maunga Wastewater Treatment Plant

The second trunk pump station is located at Memorial Park (it will be constructed adjacent to the existing pump station which will remain in operation at least for the duration of the construction), and will take flows from the south-western and central-eastern catchments of Tauranga, including the upgraded siphon from Anchorage. The key characteristics of the pump station are:

f. ADWF (2011) 88 L/s, PWWF (2051) 820 L/s.

g. Two smaller jockey pumps will handle low flows during dry periods and in the early years of pipeline operation. During flushing or wet weather flows the two or three larger main pumps will operate.

h. The downstream pipeline is 8.8 km long, and divided into three sections:

Rising main 6.3 km - from Memorial Park Pump Station to Matapihi paper road

Gravity main (short section) – from Matapihi paper road

Gravity inverted siphon 2.5 km – from Matapihi paper road to Te Maunga inlet

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1


Executive Summary

i. Transient pressures may not be of concern, but if necessary will be controlled with an air vessel located at the pump station.

j. Air valves will be used to control the air within the main pipeline.

The hydraulic details given in this report are subject to confirmation during the detailed design phase.

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Section 1 Introduction

1 Introduction

URS New Zealand Ltd (URS) has been engaged by Tauranga City Council (TCC) to design, obtain consents for and oversee construction of a new trunk sewer pipeline, the Southern Pipeline, to transport wastewater from the southern Tauranga catchments of Welcome Bay, Maungatapu, Hairini, Greerton, Pyes Pa, Pukemapu/Neewood, and Pyes Pa West to the Te Maunga Wastewater Treatment Plant (WWTP).

As well as providing flow capacity for the expected population growth in the southern catchments up to 2051, the new Southern Pipeline also has the benefit of freeing up capacity in the already restricted pipes in western Tauranga up to Chapel St WWTP.

This report supersedes Report No. 8A, and sets out the proposed operational philosophy and hydraulic design parameters that have been used on the Southern Pipeline (the ‘Pipeline’) as well as the preliminary design sizing for the key components of the Southern Pipeline system. The report covers:

a. Background to the final pipe route selection, and the design flows.

b. General design requirements for the pump stations and the pipeline sections including:

- An explanation of the pipe operation and hydraulics

- An explanation of selection of pipe friction values

- An explanation on air and flow management

- An explanation of transient management (surge control)

c. A description of the proposed operational philosophy of the two main trunk pump stations.

d. A description of the hydraulic design of the pipeline sections.

e. A description of the proposed operational philosophy of the upstream Poike / Ila pump station system.

A preliminary transient analysis for the pipeline has been included in this conceptual design stage but will be reviewed and updated in more detail as part of the design process. A summary of the main physical components of the Southern Pipeline are in Table 1-1.

Table 1-1: Hydraulic Constraints

Structure Quantity

Main Pump Stations (No.) 2

Length in Urban Roads * (Tauranga city side) 6.3 km, Walkway option (or 7.2 km if along Devonport Road)

Total Length in Coastal Margin Area * (Walkway, excluding harbour crossing)

0.9 km

Harbour Crossing Length (Bridge or Submarine Pipeline, and Embankment)

1.1 km

Length in Rural Roads (Matapihi side) 3.6 km

Number of Inverted Siphons 2

Approximate Lengths of Inverted Siphons 2.8 km (Fraser Street) 2.5 km (Matapihi)

* Depends on the alternative Walkway route between Fifth Avenue East and the rail bridge (refer Section 2.1.1). Otherwise this section of pipe will be within the roadway (Devonport Road).

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Section 2 Selected Pipeline Route

2 Selected Pipeline Route

During 2006, TCC and URS undertook a process to identify the key route corridors available for the Southern Pipeline, and used a combination of Risk Evaluation and Quadruple Bottom Line Assessment to provide a comparison between the key routes. In December 2006 TCC confirmed that Western Route E was the preferred route. This report looks at the hydraulics of the proposed Southern Pipeline design along this Route E in more detail following this decision by Council.

2.1 Western Route E The Western Route (Route E) is located largely through the urban area of Tauranga city, and the majority of the alignment is located within TCC road reserve, thus avoiding private land and the State Highway corridors where security of tenure is less reliable. Partway along, the preferred pipeline route passes along the foreshore from Fifth Avenue East to The Strand, and then crosses the harbour from The Strand to Matapihi. These sections of the route all fall within the Coastal Margin Area (CMA) and are therefore subject to different design and consenting conditions compared to the main part of the pipeline.

In detail, the route heads east from the Maleme Street Pump Station along Maleme Street, and then north on Oropi Road to Fraser Street. The route follows the length of Fraser Street within road reserve, along 18th Avenue to follow Devonport Road and will connect into the pump station at Memorial Park. It is then proposed the pipe will follow Devonport Road to Fifth Avenue East. The pipeline will be placed along the foreshore up to the rail bridge at The Strand, and will then continue across the harbour to be laid within a widened rail embankment up to the Matapihi peninsula. The landing point at Matapihi is located at the western-most end of Matapihi Road. The route then follows Matapihi Road to the intersection of the paper road (NZ Map Series 260 U14:930 856). At the southern end of the paper road the pipeline passes under both the East Coast Main Trunk (ECMT) Railway and State Highway 2/29, continuing along the shore edge of the Te Maunga wetlands to the Te Maunga WWTP.

The route includes a new Maleme Street Pump Station, a new pump station at Memorial Park (while also retaining the existing Memorial Park Pump Station) and includes two major inverted siphons with an estimated total length of 5.2 km. The overall pipe route is about 14.5 km including the 1.1 km harbour crossing.

The plan and longitudinal profile of Route E is shown in Figures 12300-C-200-101 and 102 (Appendix A) together with the preliminary sizing of the pipeline and locations of associated structures and pump stations.

2.1.1 Memorial to Strand Walkway Project A separate project is currently underway for TCC, with the intention of laying the pipeline underneath the proposed public walkway from Memorial Park to The Strand along the foreshore edge. This project is known as the Memorial to Strand Walkway project and is TCC’s current preferred route option for the Southern Pipeline. The hydraulics of the preferred route options are evaluated in this report.

The alternative option is for the pipe to remain within Devonport Road from Fifth Avenue East to Elizabeth Street. Where there are key design differences between these two route options then the Devonport Road alternative has been addressed within a footnote. However this alternative route option has not been covered in detail in this report.

2.1.2 Harbour Crossing Options TCC in conjunction with ONTRACK are considering strengthening the existing rail bridge crossing of Tauranga Harbour by constructing new approximately 50 to 60 m deep piles for the bridge superstructure. This will bring the structure up to current design standards for seismic restraint, and provide a means for the Southern Pipeline to cross the harbour on the upgraded piers (refer URS Report No. 10 Harbour Crossing Options, and ONTRACK Report No. 56 Bridge 71 East Coast Main Trunk (Tauranga Harbour Railway Bridge) ONTRACK Underpinning Scheme. It is assumed within this hydraulic design report that the Pipeline will cross the harbour by connecting onto the upgraded rail bridge.





However, if agreement cannot be obtained with ONTRACK to upgrade the rail bridge in the immediate future, alternative harbour crossing options for the Southern Pipeline include construction of a new bridge for the pipeline, or placement of a submarine pipeline under the sea bed. A change to the crossing option will have only a minor effect on the hydraulic design that will be incorporated into the detailed design stage, and therefore has not been covered in any further detail in this report.

2.1.3 Sub-catchment Sewer Connection Points The locations for each sub-catchment sewer connection into the Southern Pipeline system are summarised in Table 2-1, with a description of the contributory sub-catchment pump station where relevant. A diagrammatic layout of the Southern Pipeline system and sub-catchments is in Figure 2-1.

Table 2-1: Contributory Sub-catchments Locations

Sub-Catchments Connection Point into the Southern Pipeline

Pump Station Name(s)

Pyes Pa West Tauriko Industrial

Pumped to Maleme Street Pump Station from Pyes Pa West Pump Station

Pyes Pa West

Pyes Pa Maleme Industrial Neewood/Pukemapu (not in 2011, future growth allowance only)

Drain directly to Maleme Street Pump Station

Maleme Street

Greerton (20% of catchment) Proposed injection into Southern Pipeline

Proposed Greerton

Hairini * Pumped to Maleme Street Pump Station from an upgraded Ila Pump Station

Ila

Poike Avenues Greerton (80% of catchment)

Drain directly to Memorial Park Pump Station via gravity trunk main

Memorial Park

Welcome Bay / Maungatapu Drain via Anchorage siphon and gravity trunk main to Memorial Park Pump Station

Otumanga and Wikitoria

Anchorage Pumped across estuary and drain via gravity trunk main to Memorial Park Pump Station

Anchorage

Matapihi Waikari Future connection allowed in design

None existing

* Note that flows from the small Poike catchment will continue to drain to Poike Pump Station and will most likely be pumped into the gravity trunk sewer near Yatton Park and will not be re-routed with Ila Pump Station to join the Maleme Street Pump Station. Refer Section 7. However, the option to pump to Maleme Street Pump Station is still possible.



2-4

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Figure 2-1: Sub-Catchment Location and Connection Plan for proposed Southern Pipeline

Hairini (Ila)

Te Maunga Wastewater Treatment

Plant

Maleme Street Pump

Station

Memorial Park

Pump Station

Tauriko Industrial

Pyes Pa West

Maleme Industrial

Pyes Pa

Pukemapu / Neewood

Greerton (20%) proposed

Welcome Bay

Maungatapu

Anchorage

Poike

Greerton (80%)

Avenues

Matapihi (future allowance)

injection point injection point

Pyes Pa West rising main


Section 3 Design Flows

3 Design Flows

The design flows for the Southern Pipeline Project are based on population projections and flow data provided by Tauranga City Council (TCC) and were first described in URS’s report, Basis of Design Flows and MOUSE Model Review dated 2 August 2005 and accepted by TCC on the 23 August 2005.

The flows and populations were updated following completion of the DHI MOUSE model of the city sewerage network which involved adjustment of the connections for some of the sub-catchments (Maungatapu, Welcome Bay), and addition of wastewater from more of the central city (Greerton and Avenues catchments) than under the original design. The revised populations and flows were sent in a letter to TCC on 28 February 2007 and accepted by TCC on 5 March 2007. A copy of these letters is included in Appendix B.

A summary of the population and design flows per sub-catchment are shown in Table 3-1:

Table 3-1 Design Populations and Incoming Contributory Flows


Sub-catchment 2011 Population

2011 ADWF

m3/day *

2051 2051 2051 Population ADWF PWWF

m3/day * L/s Total Pyes Pa West Pump Station

2,329 1,206 10,425 4,506 209

Total Maleme Pump Station

2,839 1,299 13,550 3,266 151

Total Ila Pump Station 4,652 854 11,084 2,035 94 Total Greerton (20%) Injection

1,793 329 3,094 568 26

Total Poike Pump Station

1,548 284 2,621 481 22

Total Memorial Park Pump Station

9,817 1,802 17,991 3,303 153

Total Anchorage Siphon and Pump Station catchment flow

9,999 1,836 19,253 3,535 164

Total Matapihi Injection

0 0 2,500 459 21

3 3Total Southern Pipeline

32,977 people 7,610 m /day 80,518 people 18,153 m /day 840 L/s

*Includes 2% additional commercial flow allowance.


Section 3 Design Flows

1Notes on TCC Wastewater Flow Characteristics

i) Average Dry Weather Flow (ADWF) shall be 180 litres/person/day for combined residential and employment populations.

ii) Industrial and commercial flow allowances have been incorporated into the total volumes and flow rates shown. Tauriko Maleme Industrial areas have been calculated individually on a per hectare basis (i.e. # ha x 0.0004 Litres/second/hectare for PWWF). The area of industry was provided by TCC from the city planning zone data. The remaining catchments have a 2% allowance for commercial/large point flows from the mainly residential sub-catchments.

iii) Peaking factor to obtain PWWF shall be 4.0 times the ADWF in Litres/second, as verified by historical flow rates at the Chapel Street WWTP.


1 Details of these flow characteristics are described in URS report Future Mouse Model Report No. 25, February 2007.

3-2


Section 4 Pump Station and Pipeline Design Requirements

4 Pump Station and Pipeline Design Requirements

4.1 Pump Station Design

4.1.1 General

The location of both Maleme Street and Memorial Park Pump Stations were considered carefully. Both will be re-built adjacent to the existing pump stations (so that the existing drainage network can remain under operation while the full Pipeline is built over several years). These locations were dictated predominantly by the system hydraulics. However the actual locations also took into account the following:

i) Key locations at the start of the two main hydraulic sections of the Pipeline.

ii) Proximity of existing power supply.

iii) Can be constructed above the 1:100 AEP flood zone (both sites are at risk of flooding).

iv) Both sites have a large enough site to allow for emergency generators, biofilter odour treatment system, underground storage and transient controls as well as the main pump station structures.

v) Both pump stations will be on TCC owned land, with simple vehicle access.

vi) Memorial Park Pump Station has a buffer distance of at least 50 metres to the nearest residential dwelling to mitigate noise and potential odour. Maleme Street Pump Station is located within a heavy industrial area and so odour and noise are of less of a concern.

vii) Both sites are already linked to the TCC telemetry communications system.

All sewage pump stations have been assumed to use purpose designed submersible sewage pumps with a minimum throughput of 75 mm object size.

The hydraulic designs of the Trunk Sewer Pumping Stations (Maleme Street and Memorial Park) are based on a number of parameters, which are outlined below.

4.1.2 Number of Pumps Following typical procedure, TCC require N+1 pumps at each pump station. The number N pumps will have capacity to pump the PWWF from 2051, with the additional +1 pump in place on standby in case of failure of one of the duty pumps.

4.1.3 Pump Selection A combination of small jockey pumps and larger main pumps has been selected for each pump station. The jockey pumps will be used to pump during low flow periods – particularly during the early years of the pipeline operation and during night time low flows. The larger pumps will be used for daily flushing, and for pumping of wet weather flows.

It is expected that each pump will be controlled using a VSD, although the details of this will be determined at detailed design stage when the current draw from each VSD will be checked for efficiency against alternative methods of pump controls (soft start and stop for example).

It has been assumed that the pumps selected will be submersible pumps. This allows the wastewater to collect within a single wet well chamber, which typically has significant cost savings in comparison with dry-mounted pumps that require a separate dry chamber for installation of the pumps and equipment.




4.1.4 Low Flow Management In the early years of Pipeline operation, both the ADF and peak instantaneous flow expected during the day will be lower than that required to reach the design minimum velocity of 0.75 m/s. The preliminary sizing indicates that the normal velocities will vary up to a maximum of about 0.6 m/s during normal dry days, sufficient to keep most solids within the wastewater suspended, but not compliant with the design requirements shown in Table 4-1. Daily flushing however is expected to prevent the accumulation of solids to the point that the pipeline performance is compromised.

It is also expected that TCC will monitor the performance of the Pipeline over these early years, looking at the rate of grit accumulation in each pump station and at the Pipeline drainage points to confirm whether additional flushing (or even the addition of further flow from stream or piped water) may be needed to increase the flow velocities within the Pipeline.

4.1.5 Flushing and Emergency Storage Tanks

Storage has been allowed for both pumping stations for emergencies and to provide storage for flushing flows. A number of emergency scenarios were identified for each pump station, each requiring differing amounts of emergency storage. Analysis of practice elsewhere in New Zealand indicates that providing four hours ADWF storage for the local gravity catchment into the pump station is reasonable. This volume presently excludes any allowance for storage in the upstream reticulation. TCC are presently reviewing the total emergency storage requirements for large sewer systems.

An allowance for the upstream pumped systems draining into the wet well, depending on the failure scenario was also included. The highest volume was then selected for sizing of the storage tanks. Flushing storage for 20 mins of flow at 1.2 m/s has also been included to the storage volume provided. Details of the failure scenarios and resulting storage volumes are given in Appendix C.

Checks will also be made as part of the detailed design to ensure that the emergency storage provided at each pump station will be sufficient to cater for the draining of the rising main during maintenance.

The storage allowances may change as further detailed assessment of the storage provided within the upstream gravity network is carried out and TCC confirm that the level of storage is compliant with their emergency response requirements for the trunk pump stations.

4.1.6 Impact on End-of-Line Facilities

Flows in the pipeline need to ‘match’ the treatment plant throughput capabilities. URS is working with TCC and other Consultants as part of the design process to ensure the timing and size of peak flows arriving at Te Maunga WWTP can be handled effectively.

4.1.7 Wet Wells The wet well(s) have been configured to minimise accumulation of debris and fat deposits, and to provide good entry conditions to pump intakes, to prevent build up within the Pipeline or at critical areas such as within the inverted siphons.

The confirmation of pump station layout may also need computational fluid dynamics (CFD) to check for dead spots and ensure no pre-swirl would occur at the pump volutes. This will be done at the detailed design stage.

4.1.8 Materials It is likely that the internal components of the pumps, valves and associated mechanical items within the pump station will be made of the appropriate grade stainless steel to prevent corrosion in the likely acidic environment of the enclosed chambers. The valve and pump bodies will be of cast iron, ductile iron or steel with appropriate corrosion protection coatings on inside and outside surfaces.




As far as practicable, the equipment will be selected to match TCC’s existing plant and equipment so that operators are familiar with the equipment.

4.1.9 Pump Station Structures The main pump station structures will be built mostly below ground level. These will include the wet well, and flushing and emergency storage tanks. These will be reinforced concrete tanks, lined with a corrosion resistant coating on the roof and walls. The floors are generally left uncoated for safety reasons as they become slippery if coated.

The method of construction will be determined as part of the detailed design, but is likely to involve installation of caissons, sheet piles or similar to the depth of the structure before the soil is excavated ready for placement of the concrete chambers.

The control building, surge tanks (air vessels), emergency generator building and any odour treatment structures will be above ground. Electrical and control equipment will be placed in buildings with 500 mm freeboard above the TCC specified design flood levels for the site.

4.1.10 Odour Management Air will be extracted at each pump station wet well to ventilate both the incoming sewer (assuming a wet well inlet) and the wet well. Air treatment will also be needed for any flow balancing or emergency storage structures, to prevent accumulation of sewer gas, and to minimise corrosion and odour nuisance. Foul air extracted at each pump station will be deodorised, probably through a biofilter, before discharge to the atmosphere.

4.1.11 Control and Telemetry Both pump stations will have a PLC, with flow and level meters to monitor and control pumping operations at each site. A telemetry link will connect each new pump station with the TCC central control in the city.

4.2 Pipeline Design

4.2.1 Rising Mains The design guideline recommendations for flow resistance of wastewater pressure mains by HR Wallingford (Report SR641 March 2004) apply to the rising mains. Based on the review, assessments and the design guidelines, the other design criteria adopted for the Maleme Street rising main for the Southern Pipeline are summarised below:

i) The hydraulic capacity of the rising main will be based on Colebrook-White equation with a roughness Ks factor of between 0.3 mm and 0.7 mm irrespective of pipe size or material.

ii) The minimum target slope downgrade will be 1:300 to assist in managing air.

iii) The minimum target slope rising grade will be 1:500 to assist in managing air.

Daily flushing will prevent the accumulation of sediment within the rising main. However, inlet tees have been included on both trunk pump stations to be used to insert a pig if cleaning by pigging is determined as necessary.

4.2.2 Gravity Mains The design criteria adopted for gravity pipes for the Southern Pipeline is summarised below:




i) The hydraulic capacity of the pipeline will be based on Mannings formula, with the range of Mannings n values between 0.009 to 0.015 irrespective of pipe size or material.

ii) The number of pipes will be one as gravity pipes can be flushed via access from manhole chambers.

iii) The minimum grade of the pipe will be 1:1000, although this will be steeper where possible.

iv) Minimum velocity at peak flow shall be 1.0 m/s in any single pipe.

Gravity pipes can be cleared by high pressure hosing if necessary.

4.2.3 Inverted Siphons In addition to the review design guidelines the recommendations for flow resistance of wastewater pressure mains by HR Wallingford (Report SR641 March 2004) is also applicable to inverted siphons. Based on the review, assessments and the design guidelines, the design criteria adopted for inverted siphons for the Southern Pipeline at Matapihi is summarised below:

v) The hydraulic capacity of the inverted siphon will be based on the HR Wallingford Inverted Siphon Manual, with a roughness Ks factor of between 0.3 mm and 0.7 mm irrespective of pipe size or material.

vi) The minimum target number of pipes in the siphon will be two. The main section of pipe will be on a gently rising gradient.

vii) The maximum grade of falling pipe inlet section (down leg) will be 1:3.

viii) The maximum grade of the rising outlet pipe section (up leg) will be 1:3 to 1:6.

ix) Minimum flushing velocity shall be 1.2 m/s in any single pipe.

Inverted siphons have a tendency to accumulate a settled layer of solids even if self-cleansing velocities are reached regularly. Arrangements will be incorporated into the design of inverted siphon to enable individual barrels of the siphon to be closed for cleaning by flushing with clean water, or by pigging. It may also be possible to use a portable pump to remove the wastewater and/or settled grit through the draw off valve and discharge it via the corresponding “draw-off” valve in one of the other parallel barrels that is still operational.

4.2.4 Pipe Material The choice of pipe material is addressed separately in URS Report No. 7, Materials Options Report, November 2005. The proposed material is generally expected to be Polyethylene PE100 for the pressure sections of the Southern Pipeline. The gravity sections may also be constructed of PVC, concrete or GRP polymer concrete. The Walkway and harbour crossing sections may use either Polyethylene PE100, concrete-coated steel or glass-reinforced plastic (GRP) material as necessary depending on the final selected route.

4.2.5 Design Velocities and Roughness The design capacity of the trunk rising main and inverted siphons pipelines has been based on the Colebrook-White formula for pipeline friction.




A review of the roughness factor, and minimum and maximum velocities was conducted for gravity and pressure sewers adopted by various water authorities in Australia and New Zealand, which was discussed in URS Report No. 8A, Conceptual Hydraulic Design Report, November 2005. The outcomes are summarised in Table 4-1 and provide recommended design flow and velocity criteria for normal operating conditions of the rising mains.

The selected longer term design range of pipe roughness values (currently 0.3 mm to 0.7 mm) is dependent on the pipe cleaning regime expected for the Southern Pipeline. A pipe that is regularly flushed and clean will be represented by the selected friction values. However, if the pipe is subject to significant growth of slime and grit collection on the inside of the pipe then a larger friction value (1.5 mm) may be more representative. Therefore, the final design friction should be selected in consideration of the proposed operation and cleaning procedures for the pipeline.

Table 4-1 Recommended Design Criteria (Normal Peak Flow Operation)

Gravity Pressure Inverted Mains Mains Siphons

Minimum velocity for operating (for sediment movement)

0.75 m/s to 0.85 m/s

0.75 to 0.85 m/s 1.0 m/s @ PDWF 2.0 m/s @ PWWF

Target flushing velocity 1.0 m/s 1.2 to 1.5 m/s 1.2 to 1.5 m/s Maximum allowable velocity 2.5 m/s 2.5 m/s 2.5 m/s Minimum roughness K value (used for surge analysis)

0.1 mm 0.1 mm 0.1 mm

Typical operating roughness 1.5 mm 0.3 mm to 0.7 mm 0.3 mm to 0.7 mm

4.2.6 Flushing URS’s experience of rising main sewers and inverted siphons is that periodic flushing by temporarily increasing the flow is required. The purpose of this is to flush out settled solids from the invert of the pipe2. In rising mains the typical minimum normal operating velocity is higher than in gravity sewers, and is set to prevent sediment accumulation (especially in the steeper upward sloping sections of the pipeline). This velocity is typically 1.0 m/s or slightly greater. For the Southern Pipeline a minimum flushing velocity of 1.2 m/s has been adopted.

4.2.7 Air Management and Odour Control Air entrained or carried along with the wastewater flow can cause problems during operation of the pressure sections of pipeline by collecting into large bubbles at high points, blocking the passage of the wastewater along the pipe. Specific air management design allows the air within the pressure wastewater pipeline to be controlled, and directed to specified high points of the pipeline. Installation of air release valves at these points then allows the air to be discharged from the Southern Pipeline before the performance is compromised by air pockets forming in the pipeline.

2 If solids remain settled for long periods they coalesce and can form a hard surface layer, increasing the internal friction of the pipeline and reducing the cross section area available for the wastewater to travel through. These two changes can have a significant negative impact, critically reducing the performance of the pipeline.




Air release valves will be installed at specified high points along the rising mains, as well as at regular (typically 500 m) intervals along the pressurised portions of the Southern Pipeline. The type and size of the air valves will be determined at the detailed design stage. 3

In sections of gravity pipe, large volumes of air will be drawn in, and discharged from the pipeline at the upstream ends of the gravity pipe sections as the flow in the pipe decreases or increases. Air will be allowed into the pipeline in the gravity sections through manhole and chamber lids, but specialist vents may be required at the start of gravity sections and the start of siphons to facilitate the process.

The presence of an inverted siphon will interrupt the flow of air in a gravity pipe which will therefore seek to escape from the system, either at the inlet chamber or, if that chamber has air-tight covers, at manholes farther upstream. Similarly, the flow of water in the downstream pipes will create a new air demand and tend to suck in air from the atmosphere at the outlet chamber.

It is likely that odour control will therefore be required to “scrub” the air expected from some of the air release valves, receiving chambers, vents and manholes located on the gravity and siphon sections of pipeline. This odour treatment will be in the form of a bark biofilter as long as there is sufficient space in the road reserves, otherwise an activated carbon or similar cartridge filter will be used.

4.2.8 Transient Control The Southern Pipeline rising mains were analysed to a preliminary level for transient pressures arising from pump stopping, starting, and power failure. Pump speed controls, air pressure vessels, anti-vacuum and air release valves were then located at the pumping stations and along the pipeline routes, as determined by the transient analysis.

For pump operation, the main risk is created by a sudden unplanned pump shut down caused by power failure at the pump stations which results in a low pressure wave propagating along the pipeline. The return positive pressure wave also has to be managed. At this preliminary stage allowance in terms of providing sufficient space for protection devices has been included.

At Maleme Street, an air pressure vessel has been included as protection against surge pressures in the pipeline. An air pressure vessel has been provided at Memorial Park at this stage although control of transient pressures by using air valves may be possible after detailed design.

Along the pipeline routes, waterhammer protection will also be provided by using air valves to control pipeline vacuum. Air valves can be a “cheaper” solution for vacuum control than the more expensive air vessels or potable water feed tanks. Air valves require more maintenance, and so careful design modelling, appropriate valve selection and a robust maintenance schedule will be prepared as part of the detailed design to ensure the rising mains operate reliably and effectively.

4.2.9 Pipe Depth and Cover to Pipe The depth of Southern Pipeline will be dependent on the levels of the existing services, requirement for air management and other hydraulic constraints, ground conditions and the method(s) of installation. Generally traditional open trench construction will be used for shallower sections of the pipeline (estimated at 90% of the total Southern Pipeline length). Directional drilling, microtunnelling or conventional tunnelling may be used for deeper construction in localised areas (such as the State Highway and Railway corridor underpasses), or where it is necessary to avoid surface disturbance (for example at the entrance to Fraser Cover shopping centre or at busy road intersections).

The minimum cover to the top of the Southern Pipeline is expected to be 1.0 metres for both gravity and pressure sections. The pipe may need to be constructed at a greater depth as a means to avoid clashing with existing services within the road corridor. This is a particular concern through the central city area


3 If the Devonport Road option proceeds (as an alternative to the Walkway project) then further air valves will also be required along Devonport Road for air management.

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about Devonport Road where the pipe cover may be as great as 3 metres to reduce the chances of services clashing with the new pipeline.

Where minimum cover cannot be achieved at localised areas, other protective measures such as concrete capping may be required.

4.2.10 Manholes, Receiving Chambers, Energy Dissipaters and Access Points

Gravity Pipeline

Manholes are normally required for gravity sewers for the purpose of cleaning and maintenance. Sewer manholes and access points shall be provided on gravity sections of the Pipeline at the following locations:

i) At each change of direction.

ii) At each change of gradient.

iii) At a maximum spacing of

• 120 metres for 225 mm to 300 mm diameter pipes,

• 180 metres for 325 mm to 875 mm diameter pipes, and

• 240 metres for 900 mm and larger diameter pipes.

Larger spacings could be considered if TCC have access to appropriate maintenance cleaning equipment.

iv) Where any gravity connection into the Southern Pipeline is required.

In some of the steeper sections along the Southern Pipeline, energy dissipating structures may be installed to minimise downstream abrasion and reduce the energy of the flow.

Pressure Pipeline

Access points will include 600 mm diameter pipeline tees at anti-vacuum and air release valves to allow equipment access. Drain valve connections and/or grit collection will be provided at low points which will also allow for some limited access.

thAt 18 Avenue the rising main/inverted siphon will discharge into a Receiving Chamber. This will also occur at the end of the Memorial Park rising main on Matapihi. Typically the chamber will be a large manhole, and the structures may need to be sized to suit pressure surges from pump start-up. An air inlet vent with non-return flap will be provided to allow ventilation of the gravity sewer downstream of the chamber.

4.2.11 Local Pump Station Connections The design of any smaller local pump stations (flow less than 200 L/s) will be based on the TCC document ‘Wastewater Pump Stations and Rising Mains, Appendix E’ ,from the 2006 TCC Code of Practice for Development. This is based on the WSA 02 2002 — Sewerage Code of Australia, and NZS 4404:2004 Land Development and Subdivision Engineering.

One such pump station (if constructed in the future) is the proposed Greerton Pump Station that would inject (under pressure) into the Southern Pipeline rising main at or near the Oropi Road / Chadwick Road intersection.




4.2.12 Thrust Blocks and Pipe Restraint Thrust blocks and/or pipe restraint may be required (depending on the pipe material) where the pipeline is either turning a sharp angle (anything over about 10 degrees), is located in soft soil or above ground, at the end of steep grades, and they will be required at each air valve and drainage point. Other locations include the connection of the pipeline at each end of the rail bridge, at sharp changes in route direction (i.e. corner of 18th Avenue on to Devonport Road) and the end of steep grades such as Matapihi Road and Oropi Road. Each thrust block will be specified during detailed design.



Section 5 Maleme to Memorial Section

5 Maleme to Memorial Section

The Southern Pipeline can be divided into two main hydraulic sections, the first being that from Maleme Street Pump Station to the inlet at Memorial Park. This section of the pipeline is discussed below. The second section from Memorial Park Pump Station through to Te Maunga WWTP is described in detail in Section 6. The pipeline long sections are given in Appendix A.

5.1 Maleme Street Trunk Pump Station Maleme Street Pump Station has been designed to pump a range of flows, from a design average dry weather flow of 39 L/s in 2011 up to a design PWWF of 454 L/s in 2051. The static head for the rising main is approximately 29 m (at the receiving chamber at 18th Avenue) with an intermediate high point of 33 m RL (Chadwick Road). The pump station discharge is located at approximately -2 m RL (assuming the wet well operating water level will be approximately 5 m below ground level).

Downstream at Oropi Road, flow from the proposed Greerton Pump Station (if installed in the future) will inject into the Southern Pipeline, increasing the 2011 ADWF by 4 L/s and the 2051 PWWF by 26 L/s. This has no significant effect on the pipe diameter at this point.

5.1.1 System Overview A summary of the key components of the Maleme Street Pump Station are in Table 5-1. Note that the pump flows and storage volumes are indicative and subject to adjustment as the specific pumps and details of the pump station are selected and refined during the detailed design process.

Table 5-1 Summary of Maleme Street Pump Station Components

2011 design Average Dry Weather Flow 39 L/s 2011 design Peak Wet Weather Flow 155 L/s


Daily Flushing Flow 380 L/s


Pump Station in 2011 • 470 m3 wet well and flushing storage volume

• two jockey pumps (single flow 100 L/s, combined flow 155 L/s) in duty + assist

• two main pumps (combined flow at least 380 L/s) for flushing and peak flows, plus third main pump on standby

Pump Station by 2051 • 470 m3 wet well and flushing storage volume


• three main pumps (combined flow 454 L/s) for flushing and peak flows, plus fourth main pump on standby

3Emergency Storage 700 m3Total storage (emergency, lag & flushing volumes) 1,200 m

The following sections provide an outline description of normal operation of the pump station.



5.1.2 Inlet Channel An inlet channel will be constructed at the upstream end of the pump station to allow for future retrofit of a macerator if ever required. Inlet flow meters will also be installed at this location if required by TCC.

5.1.3 Low Flows A single ‘jockey’ pump will operate in start/stop mode between the defined start and stop levels in the pump station wet well, pumping up to the estimated daily dry weather peak flow rate of 100 L/s 4. This will be the typical operation during low flow times – especially during the morning hours for the first years of the Southern Pipeline operation. The duty pump will operate on a Variable Speed Drive (VSD) to ensure smooth starting and stopping of flows within the pipeline, with the assist pump on soft start/stop or VSD.

5.1.4 High Flows For this pump station, the second ‘jockey’ pump will provide combined pumping capacity up to about 155 L/s in a duty / assist arrangement with the first jockey. In this manner the two smaller pumps will handle both the normal dry weather flows, and higher flows during wet weather in the early years of operation. The pump station will operate at or near a set level in the wet well using VSDs, with the pumps starting and stopping as required to maintain the wastewater level inside the wet well.

Under even higher flow conditions (which in the initial years is expected to only be the daily flushing regime) the first two main pumps (combined up to 380 L/s) will start under VSD.

A third main pump will be installed in the wet well on standby.

In future years a fourth main pump will be installed within the pump station wet well providing total peak flows of 454 L/s (with three main pumps operating in parallel, and the fourth on standby), able to discharge the calculated PWWF for 2051. It is expected that the final main pump will not be installed immediately, but later as the peak flows to Maleme Street Pump Station regularly reach above 380 L/s.

Note that it is expected that when the two or more main pumps operate in parallel any potential flow contribution from the smaller jockey pumps would be very small – however this needs to be confirmed as part of the detailed design process and is subject to the specific pumps selected and how the operating curves between the smaller and larger pumps interact.

5.1.5 Flushing 3It has been calculated that a total volume of 470 m is required for satisfactory flushing of the rising main

and inverted siphon. This volume will be stored within the pump station wet well chamber and an adjacent storage tank, although allowances for incoming flow during the flushing operation may allow this storage volume to be reduced as part of detailed design. The flushing operation will involve filling of the partially emptied pipeline (at Chadwick Road, this takes about 10 minutes) followed by pumping at a minimum velocity of 1.2 m/s through the pipeline for a minimum 10 minute period. This is sufficient time for wastewater and accumulated sediment at the base of Oropi Road to be moved over the crest of the hill at Chadwick Road. This portion is the critical length of the pipeline for flushing.

Flushing will require the two main pumps to ramp up and discharge at the estimated flushing flow rate of 380 L/s for this short period (approximately 20 minutes).

It is likely that flushing will be timed to coincide with the peak incoming flows each morning, namely about 9 am. Flushing will take place once every 24 hours. It is intended that this control will be automated.


4 For the given ADWF of 39 L/s, the TCC design standard assumes the peak instantaneous flow to be 2.5 times this flow rate, giving a peak dry weather flow rate of 100 L/s.

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5.1.6 Emergency Storage TCC require the trunk pump station emergency storage to hold a minimum four hours of ADWF from the local gravity catchment (assumed at this stage of design), plus an allowance for pumped flow lag and pipe emptying from the upstream rising mains. This is a total of 700 m3 for Maleme Street in 2051 over and above the flushing volume.

The emergency storage tank will be constructed off-line, with wastewater draining into the tanks by gravity as required. Small pumps located in the storage tank will pump the stored wastewater back into the inlet pipeline upstream of the wet well chamber once the incoming flows drop within the pump capacity.

5.1.7 Rising Main Surge Control and Air Management Preliminary surge analysis has shown that there is a requirement for an air vessel at Maleme Street. This tank will be approximately 10 m3 in volume. A second standby vessel will also be installed.

In addition, an air release valve will be installed immediately downstream of the pumps to allow retained air to discharge from the pressure system before passing along the pipeline. General air management and transient control within the pipeline are discussed in Section 4.2.

5.2 Maleme Street to Memorial Park Pipeline The Maleme Street to Memorial Park pipeline is a trunk sewer, transferring wastewater over a long distance (5.7 km) without intercepting the local sewer reticulation network. The trunk sewer is designed to operate in three distinct hydraulic sections. These are discussed individually below.

The general long section and hydraulic gradient for the rising main is shown on Drawing 12300-C-200-101- Rev E in Appendix A.

5.2.1 Maleme Street to Chadwick Section The first section of this pipeline (from Maleme Pump Station to the Chadwick Road intersection) has been designed to permanently operate under pressure as a pumped pressure main (rising main) of a length approximately 1.2 km. The preliminary design internal diameter is 635 mm, which is large enough to handle the PWWF for 2051 (454 L/s). However, during some periods the flow will be very low or zero (especially during the early morning hours). Any build up of solids within the pipe due to these lower velocity periods will be prevented by the scouring effect of the daily flushing flows. Thus a single pipeline can be constructed that will operate satisfactorily for the full 50 year design life of the Southern Pipeline.

A check valve on each pump riser will ensure flow within the pipeline will not back drain to the pump station during periods of no pumping. As part of detailed design the effect of a leaking check valve will be evaluated as part of the contingency planning process.

The Maleme Street rising main has an outlet structure, called a “Receiving Chamber”, located at the downstream end in 18th Avenue.

A pigging access tee will be included at the end of the pump manifold to allow for future pigging of the rising main. No other allowance for pigging will be included in the pipe design.

Provision has been made at this stage to drain the rising main sections for pipeline maintenance or repair, either to the pump emergency storage tank, the adjacent sewer network pump station or via drain valves and pump-out structures into road tankers if there is no local sewer/pump station available for use.

5.2.2 Chadwick to 18th Avenue Section thThe second portion of the trunk sewer is from Chadwick Road to the Receiving Chamber at 18 Avenue.

This 2.7 km long section of pipeline operates during normal flow conditions as an inverted siphon, fed by




the flows from the Maleme Street Pump Station. The design internal diameter is 635 mm, following the possible injection of additional flows from the proposed Greerton pump station at or near Chadwick Road. During normal operations the inverted siphon pipe will be partially full at the high points between Chadwick Road and Merivale Shops, providing a hydraulic break between the pumped flows from Maleme Street pump station and the downstream gravity section of pipe (which starts at the receiving chamber in 18th Avenue). This means that the air will be present within the pipeline during all normal operations and the second section of the pipeline up to 18th Avenue will act as a gravity inverted siphon.

During periods of high flows (such as daily flushing, and PWWF in future) the full length of pipe from Maleme Street Pump Station to the receiving chamber in 18th Avenue can operate as a single, 3.9 km long pressurised rising main. The air movement in the pipeline will be managed by strategic placement of air valves along this high section of pipeline to allow the pipe to fill entirely with liquid to operate as a full rising main.

Therefore careful design of this section of pipe will be required, to ensure that the single pipe will operate satisfactorily as both an inverted siphon during normal flows and as a pressure main during the usually short periods of high flows. In particular, re-start of the full rising main from operation as an inverted siphon will be specifically designed at the next stage of the project, looking in detail at both the hydraulic design as well as air management.

Adjustments to the Original Design

The design concept above is a modification to the original hydraulic design where there was an inverted siphon inlet structure located at Chadwick Road. This inlet structure provided a permanent break between the Maleme Street rising main and the inverted siphon (Ch 1200 m to Ch 3900 m). However, further design work and investigations indicated that the original design needed some refinement. The benefits of the revised design are:

1. Normal flows between Chadwick Road and 18th Avenue result in the second section of pipe operating as a gravity inverted siphon during low and normal flows. At these times, as the driving head available between the inlet and outlet is limited, flows through the pipe are expected to be below the minimum normally advised for operation of an inverted siphon.

2. However, daily flushing of the siphon by pumping from the Maleme Street Pump Station ensures the concern over low velocities and siphon blockages is mitigated. The preliminary design has determined that the daily flushing flows from the Maleme Street Pump Station may be used for this purpose by suitable design and operation of the pumps.

3. A consequence of the daily flushing being provided by pressurised flows is that significant cost savings can be made by installation of a single pipe between Chadwick Road and the 18th Avenue receiving chamber. A traditional inverted siphon would require two parallel pipes to be installed at much greater cost.

5.2.3 18th Avenue to Memorial Park Section This third and final section of the Maleme Trunk Sewer carries wastewater from the high point at 18th Avenue as a gravity pipe to the wet well at the Memorial Park Pump Station. The length of the trunk sewer is approximately 1.8 km.

In gravity sewers the minimum Dry Weather Flow (DWF) velocity at some period of the daily cycle has to be high enough to prevent sediment accumulation. This is approximated at 0.75 m/s which is in line with typical design practice in the wastewater industry (refer Table 4-1). The pipe has been selected with an internal diameter of 723 mm which means in early years this minimum velocity will not be met without the daily flushing flows from Maleme Pump Station. Calculations confirm that a minimum flow of 0.9 m/s will be reached daily during flushing which is expected to satisfactorily maintain a clean pipe.

The diameter and velocity through this gravity section will be refined as part of the detailed gravity design process.




This gravity pipe is also large enough to transfer PWWF for 2051 of 454 L/s along this section without surcharging or flooding.



Section 6 Memorial to Te Maunga Section

6 Memorial to Te Maunga Section

6.1 Memorial Park Pump Station Memorial Park Pump Station has been designed to pump a range of flows, from a design average dry weather flow of 88 L/s in 2011 up to a design PWWF of 820 L/s in 2051. The static head for the rising main is approximately 20 m. The pump station discharge is located at approximately -2 m RL assuming a wet well operating water level depth of 5 m below ground level.

The injection from Matapihi (if installed in the future) for a population of 2,500 would contribute a further 21 L/s from Matapihi onwards, bringing the 2051 PWWF to 840 L/s.

6.1.1 System Overview A summary of the key components of the Memorial Park Pump Station are in Table 6-1.

Table 6-1 Summary of Memorial Park Pump Station Components



Daily Flushing Flow 480 L/s


Pump Station in 2011 • 350 m3 wet well and flushing storage volume


• two main pumps (combined at least 480 L/s) for flushing and peak flows, plus third main pump on standby

Pump Station by 2051 • 350 m3 wet well and flushing storage volume


• three main pumps (combined 840 L/s) for flushing and peak flows, plus fourth main pump on standby

3Emergency Storage 1,400 m3Total storage (emergency, lag & flushing volumes) 2,000 m

The section below provides an outline description of normal operation of the pump station.

6.1.2 Inlet Channel An inlet channel will be constructed at the upstream end of the pump station to allow for future retrofit of a screen if ever required. Inlet flow meters will also be installed at this location if required by TCC.



6.1.3 Low Flows A single ‘jockey’ pump will operate in start/stop mode between the defined start and stop levels in the pump station wet well, pumping up to the estimated daily dry weather peak flow rate of 220 L/s 5. This will be the typical operation during low flow times – especially during the morning hours for the first years of the Southern Pipeline operation. The duty pump will operate on a Variable Speed Drive (VSD) to ensure smooth starting and stopping of flows within the pipeline, with the assist pump on soft start/stop or VSD.

6.1.4 High Flows For this pump station, the second ‘jockey’ pump will provide combined pumping capacity up to about 352 L/s in a duty / assist arrangement with the first jockey. In this manner the two smaller pumps will handle both the normal dry weather flows, and higher flows during wet weather in the early years of operation. The pump station will operate at or near a set level in the wet well, with the pumps starting and stopping as required to maintain the wastewater level inside the wet well.

Under even higher flow conditions (which in the initial years is expected to only be the daily flushing regime) the first two main pumps (combined flow 480 L/s) will start under VSD.

A third main pump will be installed in the wet well on standby.

In future years a fourth pump will be installed within the pump station wet well providing total peak flows of 840 L/s (with three main pumps operating in parallel), able to discharge the calculated PWWF for 2051. It is expected that the final main pump will not be installed immediately, but later as the peak flows to Memorial Park Pump Station regularly reach above 480 L/s.

In general it is expected that when two or more main pumps operate in parallel that any potential flow contribution from the smaller jockey pumps would be very small – however this needs to be confirmed as part of the detailed design process and is subject to the specific pumps selected and how the operating curves between the smaller and larger pumps interact.

6.1.5 Flushing For the Southern Pipeline a minimum flushing velocity of 1.2 m/s has been adopted for the Memorial Park rising main.

3It has been calculated that a total volume of 350 m is required for satisfactory flushing of the rising main. This volume will be stored within the pump station wet well chamber and an adjacent storage tank. The flushing operation will involve pumping at a minimum velocity of 1.2 m/s through the pipeline for a minimum 10 minute period (it may take an additional 10 minutes or so of pumping for the wastewater to attain the desired velocity, this has also been allowed for in the stored flushing volume).

In the early years of operation, flushing will require the two main pumps to ramp up and discharge at the estimated minimum flushing flow rate of 480 L/s for the short period.

Flushing will be timed to suit TCC’s flow requirements at Te Maunga WWTP as well as to coincide with the peak incoming flows each morning namely at about 11 am (morning peaks take longer to arrive downstream, and it will take some time for peak flows to arrive from the Maleme Street section of pipeline if these are to be used in flushing). Flushing will take place once every 24 hours. It is intended that this control will be automated.


5 For the given ADWF of 88 L/s, the TCC design standard assumes the peak instantaneous flow to be 2.5 times this flow rate, giving a peak dry weather flow rate of 220 L/s.

6-2



6.1.6 Emergency Storage TCC require trunk pump station emergency storage to hold a minimum four hours of Average Dry Weather Flow from the local gravity catchment (assumed at this stage of design), plus an allowance for pumped flow lag and pipe emptying from the upstream rising mains. This is a total of 1,400 m3 for Memorial Park in 2051, additional to the flushing storage volume. It is assumed all upstream pump stations (including Maleme Street) have sufficient storage for individual catchments.

The emergency storage tank will be constructed to be an off-line tank, with wastewater draining into and out of the tank by gravity as required. A valve will allow the emergency storage tank to be isolated from the pump station wet well if necessary.

6.1.7 Rising Main Surge Control and Air Management A preliminary surge analysis has been undertaken and an air vessel / surge protection may be required at Memorial Park to manage transient pressure waves in the downstream pipeline. Alternatively it may be possible to control transient pressures using air valves. The exact method of surge control will be selected in the detailed stage.

An air release valve will be installed immediately downstream of the pumps to allow retained air to discharge from the pressure system before passing along the pipeline. Air management and transient controls within the pipeline are discussed in Section 4.2.

6.2 Memorial Park to Te Maunga Pipeline The Memorial Park to Te Maunga pipeline is a trunk sewer, transferring wastewater over a long distance (8.7 km) without intercepting the local sewer reticulation network. The trunk sewer is designed to operate in three distinct hydraulic sections. These are discussed individually below. The general long section and hydraulic gradient for the rising main is shown in Figure 12300-C-200-102 (Appendix A).

6.2.1 Memorial Park to Matapihi Section The first section of this pipeline (from Memorial Park Pump Station to the high point at Matapihi Road) has been designed to permanently operate under pressure as a pumped pressure main (rising main) of 6.3 km approximate length. This includes the 0.9 km walkway and the 1.1 km long harbour crossing and embankment. The preliminary design internal diameter is 715 mm, which is large enough to handle the PWWF in 2051 (840 L/s). However, during some periods the flow will be very low or zero (especially during the early morning hours). Any build up of solids within the pipe due to these lower velocity periods will be prevented by the scouring effect of the daily flushing flows. Thus a single pipeline can be constructed that will operate satisfactorily for the full 50 year design life of the Southern Pipeline.

There will be some short periods (i.e. at night time during the early years of operation) when no flow will be pumped through the rising main.

Harbour Crossing

For the pipeline to be laid over the strengthened rail bridge, the pipe must be constructed with an acute bend to reach the bridge platform from the Concourse (CBD side of the harbour). This ‘bend’ will be subject to specific detailed design, and will require the bend to be tied back to the bridge embankment as a means of restraining the bend and providing thrust resistance at the sharp corner.

It is currently proposed that the diameter of the pipe leading up to and within the bend will be reduced (to approximate 640 mm diameter, which will locally increase the velocity of the flow through the bend. For a small increase in pumping head, this will provide a means to prevent accumulation of sediments at the base of the lower bend.

On the eastern side of the harbour crossing the return to trenching installation towards the end of Matapihi Road will require a gentler angle and so has no special design criteria.




Design Criteria

The Memorial Park rising main terminates in a Receiving Chamber located at the downstream end in the paper road at Matapihi.

The rising main downstream of Memorial Park Pump Station will be positioned so that there are no intermediate high points. This means that the pipe will remain full of wastewater whilst the pumps are not operating and no specific siphon flow or air management (other than small air release valves) is necessary.

A check valve on each pump riser will ensure flow within the pipe will not back drain to the pump station during periods of no pumping. As part of detailed design the effect of a leaking check valve will be evaluated as part of the contingency planning.

Provision has been made at this stage to drain the rising main sections for pipeline maintenance or repair, to the emergency storage tank and either to an adjacent sewer network pump station, or via drain valves and pump-out structures and into road tankers if there is no local sewer/pump station available for use.

A pigging access tee will be included at the end of the pump manifold to allow for future pigging of the rising main. To other allowance for pigging will be included in the pipe design.

6.2.2 Matapihi Section The second section of the Memorial Park trunk sewer is from the high point on the Matapihi paper road to the inlet structure of the Te Maunga gravity inverted siphon. This section of pipeline is expected to be just metres long, and therefore is likely to be incorporated as a short connection between the Receiving Chamber and Siphon Inlet Chamber structures as part of the detailed design. The key is that the hydraulic break will occur at this location.

The length and gradient of this section will only be determined at detailed design, however the size of pipe will be selected to ensure a minimum velocity of 0.75 m/s to prevent sediment accumulation, inline with typical design practice in the wastewater industry (refer Table 4-1).

The flow through the gravity section will be controlled by the flows discharged from the Memorial Park Pump Station and rising main, and will therefore also benefit from the daily flushing provided ensuring that scour of settled solids is reached at least daily.

6.2.3 Matapihi to Te Maunga WWTP Section This third and final section of the Memorial Park Trunk Sewer carries wastewater from the inlet structure on the Matapihi paper road as a gravity inverted siphon to the inlet chamber at the Te Maunga WWTP. The length of the inverted siphon is approximately 2.5 km. An outlet structure will not be required, as the siphon discharge has been incorporated by TCC into the inlet works at the Te Maunga WWTP.

Due to the wide range in expected flows (88 L/s immediate ADWF to 840 L/s PWWF in the future) a twin-barrelled 650 mm internal diameter siphon is recommended for this section, with only a single barrel used during the initial years of the Southern Pipeline operation. This will ensure the high velocity flushing necessary to maintain and operate an inverted siphon is achievable from the first day of operation when total flows through the Southern Pipeline will be lowest. In future (by 2051) both siphon barrels will be used during PWWF. The second barrel also allows one barrel to continue operating while the other is repaired in case of siphon malfunction 6.


6 The HR Wallingford Self-cleansing flow condition for inverted siphons, June 2000, indicates that such malfunctions are not uncommon when operating inverted siphons, although careful design should overcome most of the issues that contribute to typical problems.

6-4


Section 7 Poike / Ila Pump Station System

7 Poike / Ila Pump Station System

7.1 Hairini, Ila and Poike Catchments The Hairini and Poike catchments currently drain into Ila Place Pump Station which pumps to the Poike Pump Station. This then discharges into the existing low-level sewer running around the western shoreline of the estuary, towards Memorial Park. Poike is currently one of the major waste water transfer pump stations for TCC although its own wet well and catchment are relatively small.

The options for connection of the south-eastern catchments draining into the Poike and Ila pump stations were investigated at the request of TCC to confirm the best location to add these catchments into the Southern Pipeline.

The recommended configuration is to pump from Ila Pump Station directly to the Maleme Street Pump Station along a new 355 mm diameter rising main. The recommended route is 3.6 km long and follows the existing rising main route to the top of Windermere Drive, then along Windermere Drive to Poike Road, across the Waimapu Stream (Waimapu) on a new pipe bridge, up Oropi Road and down Maleme Street.

The pipeline needs to be operational by 2015. The key driver for this is because the works will take a significant load off the low-level gravity trunk sewer from Yatton Park to Memorial Park that is currently operating near capacity.

7.1.1 Ila Place Pump Station The existing Ila Place Pump Station, rising main and gravity sewer to the Poike Pump Station are hydraulically limited by the existing pumps to about the 2010 PWWF. If the pumps are upgraded in the future, the capacity limits are delayed (depending on the pump upgrade) to around the 2016 PWWF when the capacity of the 375 mm diameter gravity line downstream is exceeded.

The emergency storage of nine hours of the ADWF will need to be provided at Ila Place by construction of further storage tanks.

7.1.2 Poike Pump Station The existing gravity sewer from Yatton Park to Memorial Park will be at capacity at around the 2016 PWWF. Once the Southern Pipeline is in operation and the Maleme Street Pump Station flows are diverted away, the gravity sewer downstream of the Poike rising main will be hydraulically adequate for the Ila and Poike pump station flows to around the 2021 PWWF.

3The Poike storage in the local reticulation is already approximately 130 m and this is sufficient for the 9 hour ADWF storage requirement until 2051, because of the small flows expected from the local Poike gravity catchment.

For further detail of the upstream Poike and Ila pump system refer to URS Report No. 45, ‘Options for the Poike and Ila Pump Stations System Configuration’, August 2007.



Section 8 Limitations

8 Limitations

URS New Zealand Ltd (URS) has prepared this report in accordance with the usual care and thoroughness of the consulting profession for the use of Tauranga City Council and only those third parties who have been authorised in writing by URS to rely on the report. It is based on generally accepted practices and standards at the time it was prepared. No other warranty, expressed or implied, is made as to the professional advice included in this report. It is prepared in accordance with the scope of work and for the purpose outlined in the contract documents signed July 2005 and subsequent Variations to the contract scope.

The methodology adopted and sources of information used by URS are outlined in this report. URS has made no independent verification of this information beyond the agreed scope of works and URS assumes no responsibility for any inaccuracies or omissions. No indications were found during our investigations that information contained in this report as provided to URS was false.

This report was prepared between July and August 2007 and is based on the conditions encountered and information reviewed at the time of preparation. URS disclaims responsibility for any changes that may have occurred after this time.

This report should be read in full. No responsibility is accepted for use of any part of this report in any other context or for any other purpose or by third parties. This report does not purport to give legal advice. Legal advice can only be given by qualified legal practitioners.



Appendix A Pipeline Long Section Drawings

A. Pipeline Long Section Drawings



Appendix B Updated Design Flows - Correspondence

B. Updated Design Flows - Correspondence



Appendix C Pump Station Failure Scenarios and Storage

Volumes


C. Pump Station Failur e Scenarios and Stor age Vol umes

Pump Station Failure Scenarios and Storage Volumes

Southern Pipeline

Memorial Park Storage Volumes 2051: 4 hours ADWF Storage

Scenario

used to size

the tank

Description Immediate Action Comment

4 hrs ADWF for

the local gravity

catchment of

this pump

station

5 mins lag to

turn off the

upstream pump

station

10 mins flow

while the

upstream pump

station(s) ramp

down

Upstream

pumped mains

drain down into

the pump

station

Local

reticulation

backed up to

highest known

safe level

4 hrs ADWF for

the local gravity

catchment of

this pump

station

5 mins lag to

turn off the

upstream pump

station

10 mins flow

while the

upstream pump

station(s) ramp

down

Upstream

pumped mains

drain down into

the pump

station

Local

reticulation

backed up to

highest known

safe level

Total Emergency

Storage Volume at PS

Flushing

Volume

Total Volume of

Storage Tank

1 Local power blackoutGenerator restarts pumps

after 10 mins

Takes place during

PWWF10 mins only no no 10 mins at PWWF yes 47 0 0 194 0 242 578 820

2

Pipe breakage

downstream of pump

station

Shut down all PS until

repairs complete

Divert some flow

through Chapelyes yes

emergency off -

not applicableyes yes 1140 38 0 296 0 1473 578 2051

3Significant seismic

event


repairs complete

Note that both the water

and waste water

systems could be

damaged

yes not applicable not applicable not applicable not applicable 1140 0 0 0 0 1140 578 1718

4

Electrical or controls fire

or other failure at

subject pump station

Emergency call out, turn off

U/S pump stationsN/A yes yes yes yes yes 1140 38 38 296 0 1511 578 2,089

5

Blockage of pump

station or downstream

pipeline from objects or

debris


U/S pump stations

Retrieve and clean

pump. Divert some

flows through Poike /

Chapel

yes yes not applicable yes yes 1140 38 0 296 0 1473 578 2,051

Maleme Street Storage Volumes 2051: 4 hours ADWF Storage

Scenario

used to size

the tank


4 hrs ADWF for

the local gravity

catchment of

this pump

station

5 mins lag to

turn off the

upstream pump

station

10 mins flow

while the

upstream pump

station(s) ramp

down

Upstream

pumped mains

drain down into

the pump

station

Local

reticulation

backed up to

highest known

safe level

4 hrs ADWF for

the local gravity

catchment of

this pump

station

5 mins lag to

turn off the

upstream pump

station

10 mins flow

while the

upstream pump

station(s) ramp

down

Upstream

pumped mains

drain down into

the pump

station

Local

reticulation

backed up to

highest known

safe level

Total Emergency

Storage Volume at PS

Flushing

Volume

Total Volume of

Storage Tank


after 10 mins

takes place during


2Pipe breakage

downstream of PS

Shut down upstream PS

until repairs complete

Divert some flow

through Poikeyes yes

emergency off -



event


repairs complete


and waste water

systems could be

damaged


4


or other failure at

subject PS


U/S pump stationsN/A yes yes yes yes yes 544 24 24 291 215 669 466 1135

5

Blockage of PS or

downstream pipeline

from waterlogged wood

or debris etc


U/S pump stations

Retrieve and clean

pump. Divert some


Chapel

yes yes not applicable yes yes 544 24 0 291 215 644 466 1110

Volume (m3)

Volume (m3)

Storage Volumes Required

Are these storage volumes required?

J:\Jobs\42066678\5000 Cals\Hydraulic\Preliminary Design 2007\X087 Emergency Storage Volumes.xls

Printed 5/09/2007

Pump Station Failure Scenarios and Storage Volumes

Southern Pipeline

Memorial Park Storage Volumes 2051: 9 hours ADWF Storage

Scenario

used to size

the tank


9 hrs ADWF for

the local gravity

catchment of

this pump

station

5 mins lag to

turn off the

upstream pump

station

10 mins flow

while the

upstream pump

station(s) ramp

down

Upstream

pumped mains

drain down into

the pump

station

Local

reticulation

backed up to

highest known

safe level

9 hrs ADWF for

the local gravity

catchment of

this pump

station

5 mins lag to

turn off the

upstream pump

station

10 mins flow

while the

upstream pump

station(s) ramp

down

Upstream

pumped mains

drain down into

the pump

station

Local

reticulation

backed up to

highest known

safe level

Total Emergency

Storage Volume at

pump station

Flushing

Volume

Total Volume of

Storage Tank


after 10 mins

takes place during


2Pipe breakage

downstream of PS


repairs complete

Divert some flow

through Poike/Chapelyes yes

emergency off -

not applicableyes yes 2564 38 0 296 0 2898 578 3,476


event


repairs complete


and waste water

systems could be

damaged

yes not applicable not applicable not applicable not applicable 2564 0 0 0 0 2564 578 3,142

4


or other failure at

subject PS



5

Blockage of PS or

downstream pipeline


or debris etc


U/S pump stations

Retrieve and clean

pump. Divert some


Chapel


Maleme Street Storage Volumes 2051: 9 hours ADWF Storage

Scenario

used to size

the tank


9 hrs ADWF for

the local gravity

catchment of

this pump

station

5 mins lag to

turn off the

upstream pump

station

10 mins flow

while the

upstream pump

station(s) ramp

down

Upstream

pumped mains

drain down into

the pump

station

Local

reticulation

backed up to

highest known

safe level

9 hrs ADWF for

the local gravity

catchment of

this pump

station

5 mins lag to

turn off the

upstream pump

station

10 mins flow

while the

upstream pump

station(s) ramp

down

Upstream

pumped mains

drain down into

the pump

station

Local

reticulation

backed up to

highest known

safe level

Total Emergency

Storage Volume at

pump station

Flushing

Volume

Total Volume of

Storage Tank


after 10 mins

takes place during


2Pipe breakage

downstream of PS

Shut down upstream PS

until repairs complete

Divert some flow

through Poike/Chapelyes yes

emergency off -



event


repairs complete


and waste water

systems could be

damaged


4


or other failure at

subject PS



5

Blockage of PS or

downstream pipeline


or debris etc


U/S pump stations

Retrieve and clean

pump. Divert some


Chapel


Volume (m3)

Volume (m3)

Storage Volumes Required

Are these storage volumes required?

J:\Jobs\42066678\5000 Cals\Hydraulic\Preliminary Design 2007\X087 Emergency Storage Volumes.xls

Printed 5/09/2007

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