RODNEY DISTRICT COUNCIL
Wastewater Master Plans in Rodney Area
Volume 5: Northeast Rodney Wastewater Master
Plan
March 2010
HG Project No. 1014-122862-99
HG Document No. R001Dv2-WSL-AK122862-99
HARRISON GRIERSON CONSULTANTS LIMITED
Document Control Record
Client
RODNEY DISTRICT COUNCIL
Project
Wastewater Master Plans in Rodney Area
HG Project No.
1014-122862-99
HG Document No.
R001Dv2-WSL-AK122862-99
Document
Volume 5: Northeast Rodney Wastewater Master
Plan
ISSUE AND REVISION RECORD
Date of Issue
March 2010
Status
Final
Originator
Ian Ho - Senior Process Engineer
Stephen Finnemore – Senior Principal
Reviewed
Stephen Finnemore - Senior Principal
Approved for Issue
Stephen Finnemore - Senior Principal
Office of Origin
Auckland
Telephone
09 917 5000
Facsimile
09 917 5001
Email
[email protected]
HARRISON GRIERSON CONSULTANTS LIMITED
Page i
RODNEY DISTRICT COUNCIL
Wastewater Master Plans in Rodney Area
Volume 5: Northeast Rodney Wastewater Master Plan
March 2010
HG Project No. 1014-122862-99
HG Document No. R001Dv2-WSL-AK122862-99
CONTENTS
Page
Volume 1: Summary Document
Volume 2: Wastewater Projects in Helensville
Volume 3: Wastewater Projects in Kumeu-Huapai
Volume 4: Wastewater Projects in Muriwai
Volume 5: Wastewater Projects in Northeast Rodney
1.0
INTRODUCTION
1
2.0
STUDY AREA - NORTHEAST RODNEY
1
3.0
LIMITATIONS
2
APPENDICES
Appendix
Appendix
Appendix
Appendix
Appendix
5.1
5.2
5.3
5.4
5.5
Mahurangi Wastewater Master Plan – Project Data Summary
Mahurangi Wastewater Strategy – Population Sensitivity Analysis
Treatment and Disposal Infrastructure Constraints Assessment
Northeast Rodney Wastewater Strategy
Northeast Rodney Wastewater Master Plan
Volume 6: Wastewater Projects in Omaha
Volume 7: Wastewater Projects in Waiwera
Volume 8: Wastewater Projects in Warkworth
Volume 9 Wastewater Projects – Wellsford
HARRISON GRIERSON CONSULTANTS LIMITED
Page ii
Wastewater Master Plans in Rodney Area
Volume 5: Northeast Rodney Wastewater Master Plan
1.0
March 2010
HG Project No. 1014-122862-99
INTRODUCTION
This volume is a compilation of the various studies under the Northeast Rodney
Wastewater Master Planning Project.
A list of all water and wastewater master planning reports and conceptual
designs is presented in Appendix 1.1 in Volume 1.
2.0
STUDY AREA - NORTHEAST RODNEY
The Northeast Rodney region covers approximately 45,000 hectares and
encompasses a number of townships and villages including Warkworth, SnellsAlgies, Omaha, Point Wells, Matakana, Leigh and others.
This master plan was undertaken in several stages: historical studies review,
population projection, capacity and constraints assessment, strategic options
assessment and master planning.
The master plans were issued to Rodney
District Council in mid-2009 and the project is on hold pending further inputs
from various stakeholders.
The purposes of this master planning study include:
•
Comprehensive review of historical studies and investigations
•
Assessment of capacity bottlenecks and other constraints
•
Evaluation of various wastewater servicing options (treatment and
disposal) for the Northeast Rodney area including the options providing
centralised treatment and effluent disposal
•
Developing the three short-listed options into the master plans for
stakeholder consultation.
In addition, there are other engineering studies in the area. Refer to “Volume 6
– Wastewater Projects in Omaha” and “Volume 8 – Wastewater Projects in
Warkworth” for details. Harrison Grierson also undertook several investigations
of wastewater pumping stations (e.g. Martins Bay) and outfall capacity
assessment and replacement programme.
Below is a summary of the reports under the Northeast Rodney Wastewater
Strategy project.
HARRISON GRIERSON CONSULTANTS LIMITED
HG Document No. R001Dv2-WSL-AK122862-99
Page 1
Wastewater Master Plans in Rodney Area
Volume 5: Northeast Rodney Wastewater Master Plan
March 2010
HG Project No. 1014-122862-99
Mahurangi Wastewater Master Plan – Project Data Summary (Sept
2008)
This report summarises the historical studies and investigations for wastewater
collection, conveyance, treatment and effluent disposal in the Mahurangi and
Northeast Rodney area.
Mahurangi Wastewater Strategy – Population Sensitivity Analysis (Sept
2008)
This report presents a population growth assessment based on the district-wide
growth model.
Mahurangi
Wastewater
Master
Plan
–
Treatment
and
Disposal
Infrastructure Constraints Assessment (April 2009)
This report is an assessment of wastewater infrastructure capacities and
constraints based on the projected wastewater flow data.
The report also
reviews and identifies any information gaps. It was concluded that the three
wastewater treatment plants (Warkworth, Snells-Algies and Omaha) in the area
will need to be upgraded for higher capacity and/or higher treated effluent
quality.
Northeast Rodney Wastewater Strategy (July 2009)
This strategy report examines a total of fourteen service options for the
Northeast Rodney area.
The details of the options have been developed to a
conceptual level. Based on the cost comparison and risks analysis, three service
options were short listed for further consideration in the master planning stage.
Northeast Rodney Wastewater Master Plan (Final Draft Aug 09)
This report presents a draft master plan for the three short listed service
options. Project timeline and capital programmes for each option are presented
to highlight the key milestones and main expenditure items.
3.0
LIMITATIONS
The reports described in this volume have been prepared for the particular
scope described to Harrison Grierson by Rodney District Council. The extent of
the assessments was limited to the scope of work agreed between Rodney
District Council and Harrison Grierson Consultants Limited. No responsibility is
accepted by Harrison Grierson Consultants Limited or its directors, servants,
agents, staff or employees for the accuracy of information provided by third
parties and/or the use of any part of this report in any other context or for any
other purposes.
HARRISON GRIERSON CONSULTANTS LIMITED
HG Document No. R001Dv2-WSL-AK122862-99
Page 2
APPENDIX 5.1
Mahurangi Wastewater Master Plan
– Project Data Summary
(Sept 2008)
RODNEY DISTRICT COUNCIL
Mahurangi Wastewater Master Plan
Work Package 1: Project Data Summary
September 2008
HG Ref 1014-125641-01
Doc Ref rep-rdc-CE005V2-ich-gja
HARRISON GRIERSON CONSULTANTS LIMITED
Document Control Record
Client
RODNEY DISTRICT COUNCIL
Project
Mahurangi Wastewater Master Plan
HG Ref.
1014-125641-01
Doc Ref.
rep-rdc-CE005V1-ich-gja
Document
Work Package 1: Project Data Summary
ISSUE AND REVISION RECORD
Status
Final
Date of Issue
September 2008
Originator
Ian Ho - Process Engineer
Grant Anderson – Environmental Scientist
Reviewed
Ash Deshpande - Associate
Approved for Issue
Stephen Finnemore - Senior Principal
Office of Origin
Auckland
Telephone
09 917 5000
Facsimile
09 917 5001
Email
[email protected]
HARRISON GRIERSON CONSULTANTS LIMITED
Page i
RODNEY DISTRICT COUNCIL
Mahurangi Wastewater Master Plan
Work Package 1: Project Data Summary
September 2008
HG Ref 1014-125641-01
Doc Ref rep-rdc-CE005V2-ich-gja
CONTENTS
Page
PROJECT SCOPE
1
1.0
INTRODUCTION
1
2.0
WARKWORTH
1
2.1
PREVIOUS INVESTIGATIONS
2
2.2
CATCHMENT STATUS
8
3.0
SNELLS BEACH / ALGIES BAY
3.1
PREVIOUS INVESTIGATIONS
10
3.2
CATCHMENT STATUS
13
4.0
MARTINS BAY / MAHURANGI EAST
14
4.1
PREVIOUS INVESTIGATIONS
14
4.2
CATCHMENT STATUS
15
5.0
SANDPIT
15
5.1
PREVIOUS INVESTIGATIONS
16
5.2
CATCHMENT STATUS
16
6.0
MATAKANA
16
6.1
PREVIOUS INVESTIGATIONS
16
6.2
CATCHMENT STATUS
17
7.0
POINT WELLS
18
7.1
PREVIOUS INVESTIGATIONS
18
7.2
CATCHMENT STATUS
19
8.0
OMAHA
20
8.1
PREVIOUS INVESTIGATIONS
20
8.2
CATCHMENT STATUS
21
9.0
LEIGH
23
9.1
PREVIOUS INVESTIGATIONS
23
9.2
CATCHMENT STATUS
23
10.0
LIMITATIONS
23
10.1
GENERAL
23
10
APPENDICES
Appendix 1
Executive Summary for Selected Reports
HARRISON GRIERSON CONSULTANTS LIMITED
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Rodney District Council
Mahurangi Wastewater Master Plan – Project Data Summary
September 2008
HG Ref 1014-125641-01
PROJECT SCOPE
The project scope for this study was defined and agreed between Rodney
District Council and Harrison Grierson Consultants Limited.
This report
presented a summary of previous wastewater investigations and monitoring
reports undertaken as well as a review of the current catchment status for
various settlements in the Northeast Rodney area (Mahurangi region).
1.0
INTRODUCTION
Harrison Grierson is commissioned by Rodney District Council to undertake the
Mahurangi Wastewater Master Plan.
The outcome of this strategic study will
devise solutions for reticulation, treatment and disposal in the Mahurangi region.
The region encompasses the following townships and communities: Warkworth,
Snells Beach, Algies Bay, Mahurangi East (Martins Bay), Sandpit, Matakana,
Omaha and Point Wells.
Leigh is also included as this community may be
connected to a reticulation system some time in the future.
Due to the nature and scale of this project, this master plan is undertaken in a
number of logical sequenced tasks. This will provide a sustainable and practical
solution in a cost effective manner without major delays or hold-ups.
Over the years, a number of small and large projects have been commissioned
by Council for the study area.
These ranged from growth feasibility studies,
strategic investigations to detailed engineering and construction projects.
The purpose of this report is:
•
to summarise previous studies and investigations associated with the
sewerage infrastructure in the Mahurangi region
•
to review current status of the catchment in terms of resource consents
and Rodney District Council’s long term plan (LTP).
It is envisaged that this document will provide essential reference points in the
future stages of the Master Plan Study.
2.0
WARKWORTH
Warkworth is a major township in the study area.
Sewage is collected via a
gravity network and pumped to the Warkworth Wastewater Treatment Plant.
Treated effluent is then discharged to the nearby Mahurangi River which flows
into the Mahurangi Harbour.
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Mahurangi Wastewater Master Plan – Project Data Summary
September 2008
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The treatment plant is currently being upgraded by the installation of peak flow
treatment system.
The aim is to improve the treatment performance during
high flow events as a result of storm conditions.
2.1
PREVIOUS INVESTIGATIONS
GHD
(May
2004),
Warkworth
Wastewater
System
–
Inflow
and
Infiltration Assessment Report.
Brief Description of Contents
This report examined the inflow and infiltration in various sub-catchments in
Warkworth.
The study included flow monitoring, dry weather flow analysis,
hydrologic model calibration and determination of inflow/filtration assessment
parameters.
Their findings showed that areas around the Palmer Pump Station, Lilburn Pump
Station and Alnwick Street suffers from significant groundwater infiltration.
Most sub-catchments suffered from high stormwater inflow which caused high
wet weather flow peaks when rains.
The report recommended several conceptual I/I reduction methods including
inspection, sewer sealing and other rehabilitation work.
H2Q (Dec 2005), Warkworth Wastewater System Performance Report.
Draft
Brief Description of Contents
This report was a review of the previous reticulation modelling work by Opus
and GHD.
The author examined the reticulation performance based on an
updated MOUSE model.
The modelling results showed that there was no dry
weather overflow, but there were spills along the reticulation network.
The
recommendations included model validation with revised information and survey
data.
Tri-Aqua Solutions (December 2006) Report for McKinney, Earlsway and
Woodcock
Road
Block
subdivisions
Warkworth.
Preliminary
Investigation for Low Pressure Sewer System.
Brief Description of Contents
This report examined a number of options for connecting these new subdivision
blocks via low pressure sewer system.
assessed.
A number of connection options were
The flow was estimated based on 225L/d per capita and an
occupancy ratio of 2.5.
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It was concluded that all three blocks can be serviced by low pressure sewer
system. Part of the subdivision blocks could only be serviced by low pressure
sewer system due to its topography.
GHD (July 2007) Report for Warkworth Wastewater Strategy. Draft
Brief Description of Contents
This report investigated and compared the future reticulation options to service
Warkworth.
Low pressure sewer system was recommended to connect to the
new subdivisions. Three options were discussed in this report. The first option
was to provide a separate pressure sewer network to service the new growth
area.
The second option was to upgrade the gravity sewer network as the
pressure sewer network discharges into the end of the gravity sewer network.
The third option was to undergo progressive abandonment of gravity sewer
network and replace with pressure sewer network.
The options were then taken to modelling and costing which was not completed
at the time.
GHD
(August
2007)
Report
for
Warkworth
Wastewater
Network
Modelling. Model Development. Draft
Brief Description of Contents
This report presented a modelling exercise and preliminary results for the
wastewater network at Warkworth. The modelling work was an extension of the
H2Q model with refined GIS data and survey information. This report is a
progress report of the model development.
It is understood that the project is currently in progress.
URS & Environmex NZ (June 2005), Warkworth WWTP Wastewater
Treatment Upgrade & Disposal Options
Brief Description of Contents
This report considered the infrastructure requirements at the WWTP between
2004 and 2044, where the design PE increases from 3550 to 8800.
The
infrastructure upgrade review covers short-term upgrades, long-term upgrades
and plant relocation (to Snells-Algies).
The infrastructure requirements
examined in the report included reticulation, treatment plant and a disposal (or
transfer) pipeline.
This report looked at various options of replacing the existing sewer network
with low pressure system. As part of this report, a number of short-term and
long-term upgrade options were investigated.
HARRISON GRIERSON CONSULTANTS LIMITED
The recommended short term
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Mahurangi Wastewater Master Plan – Project Data Summary
September 2008
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plant upgrade option was the installation of a peak flow treatment system for
alleviating hydraulic overloading that occurs during storm flows. The long term
upgrade options considered in this study were the FAST system and membrane
bioreactor (MBR) /sequencing batch reactor (SBR) upgrade in parallel with the
peak flow treatment system, however no recommendations were made.
A
disposal option of conveying sewage or treated effluent to Snells-Algies for
treatment / disposal was investigated.
Rodney District Council (November 2005) Amendments to Warkworth
Wastewater Treatment Plant Resource Consent Renewal Applications
Brief Description of Contents
This document summarised the findings of a number of environmental and
upgrade investigations. A upgrade and decision timetable was also presented.
The resource consent renewal was successful and the renewed resource consent
expires in 2011.
HGCL (December 2006), Warkworth WwTP Peak Flow Treatment
Upgrade – Concept Review
Brief Description of Contents
This concept review was a review of the short term upgrade options presented
in previous studies.
This study also evaluates the upgrade requirements in the short term for
installing the peak flow treatment process in parallel to the oxidation ditch. The
peak flow treatment process will improve the plant to handle high flows
associated from rainfall events as excess flow is diverted from the biological
process to avoid process upsets.
This would improve the discharge effluent
quality during and after rainfall events.
The proposed process layout from this study was different to the one presented
in the previous reports by URS / Enviromex. An upstream buffer storage and
peak flow treatment UV unit were added to the peak flow treatment process to
provide robustness to the process.
HGCL (September 2007), Warkworth WWTP Upgrade: Scoping Report
Part 1
Brief Description of Contents
This report presented a review of plant equipment for the peak flow treatment
upgrade following the concept review.
HARRISON GRIERSON CONSULTANTS LIMITED
The review was undertaken at a
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Mahurangi Wastewater Master Plan – Project Data Summary
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preliminary design level, from which information was subsequently incorporated
into detailed engineering.
The review was divided into two areas: process engineering and mechanical
engineering.
The
process
engineering
review
identified
the
upgrade
requirements to meet the process changes and modifications. The mechanical
engineering review evaluated the upgrade requirements in more details to
satisfy the mechanical engineering aspects.
The upgrade requirements identified were inlet pump station upgrade, selector
hydraulic control upgrade, new sludge wasting mechanism and new sludge
thickener for the existing biological process.
The new peak flow treatment
process consisted of Actiflo process, PFT buffer tank, Chemical storage and
dosing and associated civil and mechanical works.
The findings formed part of the detailed engineering design.
HGCL (March 2008), Warkworth WWTP Upgrade: Scoping Report Part 2
Brief Description of Contents
This report summarised the process review of the oxidation ditch process at
Warkworth WwTP. A biological process model was built to assess the potential
capacity of the oxidation ditch.
The modelling was based on the influent and
effluent sampling data collected in September and October 2007.
The capacity
estimation was required to determine the future upgrade requirements of the
oxidation ditch process.
The calibrated process model was tested with a number of scenarios.
It was
found that with some plant optimisation, the oxidation ditch process could treat
up to 1100m³/day which is similar to the average dry weather flow expected
from the Area of Benefit of Warkworth in 2017.
NIWA (Feb 2005), Modelling of Viral Dispersion and deactivation within
Mahurangi Estuary
Brief Description of Contents
The report discussed findings of a virus distribution modelling study which
examined the concentration of virus at the marine farms in the Mahurangi River
downstream to the treated effluent discharge from the Warkworth WWTP. The
modelling was based on the virus concentration prediction under a number of
scenarios.
It examined the effects of increased discharge due to population growth,
continuous discharge, freshwater inflow into the estuary and deactivation rate
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variations on the virus concentration at a number of downstream locations from
the effluent discharge point.
From the modelling, the predicted viral concentration at the oyster farms was
higher when the wastewater discharge was staged (intermittent), of higher
discharge quantity and higher river flows which result in lower deactivation time.
VKCEE(April 2005), Warkworth WWTP - Virus Risk Assessment
Brief Description of Contents
This virus risk assessment examined the public health risk in terms of
recreational water users and oyster farms downstream to the effluent discharge
point.
The associated risk was evaluated on the basis of consumption of
shellfish and contact from recreational activities.
The virus risk assessment was developed on the basis of NIWA's viral model.
The report presented a number of discharge flow and virus concentration
scenarios for the risk assessment.
The risk assessment was divided into risk
associated with shellfish consumption and contact and ingestion as a result of
recreation use.
The assessment identified that the staged discharge regime posed a higher
public health risk due to higher virus concentrations in shorter time periods,
particularly during high flows. The report recommended a 4 log virus removal
target to minimise the public health risk associated with shellfish consumption
and recreational use.
The findings of both NIWA and VKCEE reports were incorporated in the resource
consent application and the proposed 4 log removal target was incorporated into
the resource consent issued.
The resource consent specified a 4 log virus
removal in the viral monitoring requirement section.
Tonkin & Taylor (August 2005) Warkworth Wastewater Treatment Plant
Discharge Receiving Environment Review. Draft
Brief Description of Contents
This was a review of the receiving environment to determine the effect of the
effluent discharge from the Warkworth wastewater treatment plant.
The report concluded that the effluent discharge has little broad-scale effect on
water quality in the downstream estuary.
This was due to generally good
effluent quality (compared with the Mahurangi River water quality) and dilution
in the river.
The report indicated that at very low river flow, the river water
dilution may not be sufficient for reducing ammonia below toxic level.
HARRISON GRIERSON CONSULTANTS LIMITED
It also
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September 2008
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indicated that a continuous discharge regime would be beneficial for reducing
risk of the Cowan Bay oyster farm exposing to virus.
Diffuse Sources Ltd (Nov 07) Warkworth Wastewater Treatment Plant:
Receiving Environment Monitoring August 06 to July 07
Brief Description of Contents
The monitoring report examined the water quality at two sites to assess the
effect of the treated effluent discharge from Warkworth WwTP as well as
monitoring of the shellfish near the Cowan Bay oyster farm.
The monitoring
report concluded that the discharge did not contribute to any significant effect
on the water quality in the Mahurangi River estuary. The catchment runoff had
significant impacts on the microbiological water quality in the harbour
particularly during and after rainfall events and the shellfish quality at the oyster
farm was good except during and after rainfall events.
URS (May 2005) Warkworth Wastewater Strategy – Effluent Irrigation –
Draft Report
Brief Description of Contents
The irrigation report undertook a GIS data assessment of potential land
irrigation
sites
and
a
preliminary
assessment
of
land
requirements based on wastewater flow and loads data.
irrigation
area
Two final effluent
disposal options were assessed; one was disposing all of the final effluent all
year round and the other option was disposing final effluent during summer
months. The estimated nett land disposal area requirement for full-year round
operation would be in the order of 400ha or more because of the allowance of
wet weather flow while the area requirement was estimated to be 25 to 50 ha
for partial summer flow.
The application rate used was 6.6mm/day in dry
weather and 1mm/day for wet weather. The report adopted a cost rate of $2550,000/ha for pop-up irrigation system.
The estimated capital cost for the
400ha land irrigation system (excluding conveyance pipeline) was up to $20M
while the estimated cost for 50ha effluent disposal system was $2.5M.
It was reported that one of the advantages associated with the partial flow
disposal was potential beneficial reuse at golf course or sport turfs. The report
concluded that a comprehensive site selection process and field investigation
would be required after Council reached a decision of the land disposal
mechanism.
URS (Nov 2005) Warkworth Wastewater Strategy Stage 2
Brief Description of Contents
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The report was a stage 2 of the May 2005 irrigation report. The report further
examined a number of potential irrigation areas at a desktop study.
Three
effluent disposal options were examined, full flow all year round land disposal of
final effluent, partial flow summer months land disposal of final effluent on
unmodified soil and partial flow summer months land disposal of final effluent on
modified soil.
Three sites were identified for full flow all year round land disposal of final
effluent.
It was estimated that the long term acceptance rate could be 2 to
3mm/day for winter months and 5 to 7 mm/day for summer months.
The
estimated cost for a 8.5km rising main to convey final effluent from Warkworth
WwTP to the nearest site was $2.6M.
Three sites were identified for summer flow disposal of final effluent on unmodified soil option. The assessment of the un-modified soil option was based
on similar application rates for the full-year round land disposal of final effluent.
The estimated nett disposal area required was 24ha in total. The estimated cost
for a 2.5km rising main to convey final effluent from Warkworth WwTP to the
nearest site was $0.75M and the estimated land disposal system cost was
$1.8M.
Three sport turfs of total area 16.6ha were identified for the option of summer
flow land disposal of final effluent on modified soil. Because higher application
rate of 10mm/day was assumed, the estimated nett disposal area of 16.5ha
were identified. The estimated cost for a 3.5km rising main to convey final
effluent from Warkworth WwTP to the nearest site was $1.05M and the
estimated land disposal system cost was $2.2M.
2.2
CATCHMENT STATUS
Warkworth sewage catchment has undergone significant changes in recent
years. Low pressure reticulation will gradually be installed across the catchment
area for reducing inflow and infiltration. Reticulation network optimisation and
modelling are currently in progress for reducing inflow and infiltration and
network overflows from the existing network.
Moreover, the treatment plant is being upgraded to improve its ability to handle
high flow events associated with wet weather patterns. This upgrade provides a
parallel treatment to the excess flow while the biological treatment process (the
oxidation ditch and clarifiers) can remain in operation.
This is expected to
improve the discharge effluent quality during rainfall events.
Various receiving environment monitoring studies indicated that the wastewater
treatment plant does not have a detrimental effect to the receiving environment
(Mahurangi Harbour/Estuary) as the catchment run-off has a more significant
impact on the water quality of the receiving environment. However, the Tonkin
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Taylor study did indicated that the dilution of ammonia in the river may not be
sufficient during significant drought periods.
Resource Consent of Wastewater Discharge
The current resource consent expires on 31 December 2011.
To discharge into the Mahurangi River 1500m3/day on a continual dry weather
basis and up to 8000m3/day during peak wet weather events.
Note: The ARC previously considered this consent to be a temporary measure
and there was a preference to cease the discharge of treated wastewater to the
Mahurangi River as the preferred method on expiry of this consent.
This has
since changed since new technologies have been identified, and it proven that
treated wastewater can be of a suitable standard to be discharged to the river.
Capital Expenditure Programme in the Long Term Plan
RDC has made the following financial plans to upgrade the sewerage
infrastructure.
Table 1: Warkworth Wastewater Capital Expenditure Programme from LTP
Items
Est. Total between
2006 - 2016($)
Example Projects
(Timeframe)
Wastewater Treatment
Plant Upgrade
$3.5M
Peak Flow Treatment
Upgrade
(2006-2009)
New reticulation /pipeline
$3.1M
Overflow Control
(2007-2009)
McKinney
Vallye/Woodcocks Trunk
(2007-2010)
Renewal
$1.6M
Renewal
Key Sewerage Infrastructure Capacities
From the recent investigations, the estimated capacities of the key sewerage
infrastructure in the Warkworth area are summarised in Table 2. The capacity
figures of local reticulation network or individual plant items are not included.
Table 2: Key Sewerage Infrastructure Capacity Estimates of Warkworth
Area
Warkworth
HARRISON GRIERSON CONSULTANTS LIMITED
Infrastructure
Capacity
Lilburn Pump Station
~375m³/h1
Low Pressure Sewer
In Progress2
Wastewater Treatment
Plant
1100m³/day
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Table 2: Key Sewerage Infrastructure Capacity Estimates of Warkworth
Area
Infrastructure
Capacity
Note:
3.0
1.
The capacity estimate of the rising mains at the Lilburn pump station is based on the flow
data estimates and rising main theoretical calculations.
2.
The design of the low pressure sewer connection to the treatment plant is in progress.
3.
Capacities of local reticulation network and individual plant items are not included.
SNELLS BEACH / ALGIES BAY
Snells Beach and Algies Bay are located east of Warkworth. The wastewater is
currently collected via a conventional system before it is pumped to SnellsAlgies Wastewater Treatment Plant.
Cornel Circle PS and
There are two terminal pump stations,
Hamatana PS.
The final effluent from Snells-Algies
Wastewater Treatment Plant is then pumped to an ocean outfall.
Martins Bay (Mahurangi East) is also connected to the sewer network via the
Martins Bay pump station in a campground.
3.1
PREVIOUS INVESTIGATIONS
Opus (Oct 2002) Snells Beach and Algies Bay Wastewater Review
Brief Description of Contents
This report reviewed the studies been carried out for wastewater services in the
area and identified a number of further studies.
The issues in the reticulation network reported were inflow/infiltration problem
during wet weather events, sea water infiltration and the need for upgrade to
the Bridgitte pumping station upgrade.
The report also identified a number of new areas for connection. They included:
Martins Bay, Willjames, Goodall, Governor Grey and Muncaster.
The report also summarised a number of earlier investigations, one of which
stated that the disposal pumps can deliver up to 41L/s.
Opus (Sept 2003) Muncaster and Governor Grey Sewerage System
Detailed Scheme Report
Brief Description of Contents
The report discussed details of the upgrade scheme for Muncaster and Governor
Grey areas.
The scheme involved construction of a new pump station
(Sunhurst pump station) and a rising main for collecting sewage from the
Governor Grey area. The rising main would discharge into a gravity main which
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collects sewage from the Muncaster valley. The flow would then discharge into
one of the terminal pump stations (Hamatana PS).
The proposed design of the Sunhurst pump station consisted of two pumps in
duty/assist configuration. The duty pump would deliver 13L/s and two pumps
would deliver up to 16.5L/s. The Hamatana PS pumps were sized for 23L/s at
9m head for one pump running and 33L/s at 11m head for two pumps in
operation.
HGCL (July 2007) Alexander Road Sewage Pump Station: Stage 1
Catchment Study
Brief Description of Contents
The pump station at Alexander Road in Algies Bay was constructed in 1982.
This pump station receives wastewater from Algies Bay and Martins Bay
(Mahurangi East). The rising main had a number of failure reports, and hence
this study examined a number of upgrade and renewal options of the pump
station and rising main.
The design average flow and peak flow of the pump station were 10 and 50L/s
respectively.
The study concluded that the capacity upgrade of pumps and
rising main is not required and that a condition assessment of the rising main to
be conducted to determine the upgrade timetable.
Enviromex (Sept 2006) Snells-Algies WwTP Operation Manual. Draft
Brief Description of Contents
This is a plant operation manual.
capacity of various equipment.
It describes the plant operation and the
The treatment process consists of an influent
flow splitting chamber followed by two aerated lagoons in parallel and two
oxidation ponds in series prior to ocean outfall.
The capacity of each aerated lagoon was quoted 3200 capita equivalent.
The
oxidation ponds have a total volume of 20,200m³. The outfall discharge pump
is rated at 30L/s.
HGCL (Dec 2007) Snells WWTP Outfall Effluent Rising Main Replacement
Options: Assessment
Brief Description of Contents
This letter report examined the required size for upgrading this outfall rising
main. The 200NB asbestos concrete rising main had suffered from a number of
failures.
The assessment included a number of scenarios that included
continuous discharge, peak flow balancing and tidal discharge.
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The preliminary estimated peak wet weather flow from a high growth scenario is
expected to be in the order of 24,400m³/d (including both Warkworth and
Snells-Algies catchments). By excluding the flow from Warkworth catchment in
this outfall pipe, the estimated peak wet weather flow is approximately
8,900m³/d.
As the decision to include Warkworth catchment in this outfall
rising main was still pending in December 2007, the proposed solution was that
a 355mmOD rising main size to be considered for servicing only the Snells &
Algies catchment and this would increase to 400mmOD if the Warkworth
catchment is included.
HGCL (Mar 2008) Snells WWTP Outfall Effluent Rising Main Replacement
Options: Assessment
Brief Description of Contents
This was a continuation of December 2007 study. A total of 18 scenarios were
examined for determining the optimum size of the outfall rising main.
The
report recommended that a 400mmOD section to be used for replacing the
failed section at the Lifeways Ministries Trust property as this section allows
flexibility for the strategic decision regarding long term wastewater treatment of
the Warkworth and Snells-Algies catchments.
The options considered a peak
flow figure approximately 400m³/h.
Diffuse Sources Ltd (April 07) Snells-Algies Wastewater Treatment
Plant: Receiving Environment Monitoring September 05 to March 07
Brief Description of Contents
The monitoring report examined the effect of the treated effluent discharge from
Snells Algies WwTP on the near-shore microbiological water quality, shellfish
quality, off-shore water quality and microbiological water quality at Martins Bay.
It was concluded that the microbiological indicators in the water and shellfish
from the vicinity of the outfall did not show any signs of impacts from the
treated effluent discharge.
The water quality (faecal coliform levels) at both
near shore and off shore sites meet the Ministry for Environment (MfE)
guidelines for shellfish gathering.
The off-shore water quality was found to be of similar standards to three other
ARC’s coastal monitoring sites. The overall water quality was good.
The water quality in Martins Bay bathing beach was found to be variable and
this is probably due to rainfall and run-off.
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CATCHMENT STATUS
It is intended that two nearby communities, Mahurangi East and Sandpit will be
included in the catchment of the Snell-Algies Wastewater Treatment Plant. Part
of Mahurangi East is already included in the catchment while Sandpit will be
connected in the future. New connections in the Snells Beach area will be made
for more dwellings.
From the O&M manual, the estimated capacity of the aerated lagoons is 3200.
The plant will require a major upgrade to increase its capacity for the projected
incoming loads.
Wastewater Discharge Resource Consent
The discharge consent (#24748) expires on 31 December 2011.
The consent allows the use of the existing pipeline to discharge effluent to the
sea.
Capital Expenditure Programme in the Long Term Plan
RDC has made the following financial plans to upgrade the sewerage
infrastructure.
Table 3: Snells-Algies Wastewater Capital Expenditure Programme from LTP
Items
Wastewater Treatment
Plant Upgrade
New reticulation /pipeline
Renewal
Est. Total between
2006 - 2016($)
Example Projects
(Timeframe)
$3.5M
Plant Upgrade
(2008-2011)
-
-
$1.3M
Renewal
Key Sewerage Infrastructure Capacities
The estimated capacities of the key sewerage infrastructure in the Snells-Algies
area from the recent investigations are summarised in Table 4.
The capacity
figures of local reticulation network or individual plant items are not included.
Table 4: Key Sewerage Infrastructure Capacity Estimates of Snells-Algies
Area
Infrastructure
Capacity
Snells-Algies
Cornel Circle PS
Not Mentioned1
Hamatana PS
33L/s2
Wastewater Treatment
Plant
3200PE
Outfall Disposal
41L/s (2002)
397m³/h (2008)
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Table 4: Key Sewerage Infrastructure Capacity Estimates of Snells-Algies
Area
Infrastructure
Capacity
Note:
1.
4.0
The capacity estimate of the rising mains at Cornel Circle PS and Hamatana PS
2.
The design of the low pressure sewer connection to the treatment plant is in progress.
3.
Capacities of local reticulation network and individual plant items are not included.
MARTINS BAY / MAHURANGI EAST
Currently sewage is collected at the Martins Bay pump station before it is
pumped to the Algies Bay reticulation network (Willjames Ave PS and Alexander
Road PS). Wastewater is conveyed to the terminal pump station (Cornel Circle
PS) before it is discharged into the Snells-Algies Wastewater Treatment Plant.
4.1
PREVIOUS INVESTIGATIONS
HGCL (April 2007) Martins Bay Pump Station Emergency Storage Tank:
Preliminary Design Report
Brief Description of Contents
This report set out the design of an emergency storage tank for the pump
station at the campground in Martins Bay. A fibreglass tank was proposed with
odour venting set-up to minimise odour accumulation.
HGCL (August 2007) Scandrett Road, Martins Bay Gravity Sewer
Replacement – Options Assessment
Brief Description of Contents
This report examined the replacement options of a gravity sewer between
Scandrett Road and Willjames Pump Station.
found to be in a very poor condition.
The gravity sewer section was
This gravity sewer also receives sewage
from the Martins Bay Pump Station. The study examined a number of options to
replace this 1.4km sewer.
A number of options were examined which included directional drilling
replacement, open trenching replacement and bypass arrangement.
After
considering the costs and risk issues, this study recommended the gravity sewer
to be replaced with a new 150NB sewer with a combination of open trenching
and directional drilling.
HGCL (June 2008) Martins Bay Pump Station Upgrade
Brief Description of Contents
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Harrison Grierson was recently commissioned to undertake a preliminary design
of the pump station. A recent draw-down test indicated that the existing pump
station has capacity of 12.3L/s (single pump). The pump station is designed to
pump a maximum flow of 14.3L/s (PWWF).
It was stated that the selected
pump will deliver flow up to 18.5L/s.
4.2
CATCHMENT STATUS
The area is connected to the Snell-Algies wastewater treatment plant.
The
scheduled wastewater infrastructure upgrades will require an increase of the
conveyance capacity to the treatment plant.
Capital Expenditure Programme in the Long Term Plan
RDC has made the following financial plans to upgrade the sewerage
infrastructure.
Table 5: Mahurangi East Wastewater Capital Expenditure Programme from
LTP
Items
New reticulation /pipeline
Renewals
Est. Total between
2006 - 2016($)
Example Projects
(Timeframe)
$0.4M
Pipeline and Pump Station
(2006-8)
-
-
Key Sewerage Infrastructure Capacities
The estimated capacities of the key sewerage infrastructure in the Martins Bay
area from the recent investigations are summarised in Table 6.
The capacity
figures of local reticulation network or individual plant items are not included.
Table 6: Key Sewerage Infrastructure Capacity Estimates of Mahurangi East
Area
Infrastructure
Capacity
Mahurangi East / Martins
Bay
Martins Bay PS
14.3L/s
Treatment System
-
Note:
1.
5.0
Capacities of local reticulation network and individual plant items are not included.
SANDPIT
Sandpit is a small area northeast to Snells-Algies. It is currently not connected
to any community wastewater treatment plant.
It is understood that Council
intends to connect this area to the wastewater treatment facility in Snell-Algies
in future.
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5.1
September 2008
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PREVIOUS INVESTIGATIONS
No previous report received.
5.2
CATCHMENT STATUS
The wastewater infrastructure of this catchment is under planning at present.
Capital Expenditure Programme in the Long Term Plan
Under the current long term plan (2006-2016), there is no specific allowance for
connecting Sandpit to the Snells-Algies wastewater treatment plant.
6.0
MATAKANA
Matakana is a community located northeast of Warkworth.
The wastewater
treatment is currently collected in septic tank system followed by central
collection system to convey to a wetland system for further treatment.
Council has recently commissioned preliminary design of the low pressure sewer
network connection for Matakana. The sewage will be collected and pumped to
Omaha WwTP.
6.1
PREVIOUS INVESTIGATIONS
HGCL
(April
2007)
Matakana
Wastewater
Servicing
Strategy:
Conceptual Design Report
Brief Description of Contents
The Matakana wastewater treatment system is located on a leasehold site and is
understood that the lease will not be renewed when it expires. This report was
commissioned to undertake a conceptual design for a low pressure sewer
network to convey the sewage to the Omaha WwTP.
The projected peak flow of Matakana is 5.4L/s and the maximum flow
anticipated in the low pressure network is 8.7L/s to account for the maximum
number of grinder pumps in operation.
The
terminal
pump
station
evaluation
compares
a
configuration with an inline booster pump configuration.
pump
configuration
was
recommended
as
the
submersible
pump
The inline booster
terminal
pump
station
configuration. A number of rising main alignment options were investigated and
the option of “rising main alignment via Tongue Farm Road” was preferred.
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HGCL (April 2008) Matakana Main Pressure Sewer Pumping Station:
Conceptual Design Report
Brief Description of Contents
This design report described the new pump stations and rising main design for
the
connection
between
Matakana
and
Omaha
WwTP
at
a
conceptual/preliminary design level.
The study compared a number of pump station configuration options (drymounting, pumps in series and mono-pumps). It was found the dry-mounting
pump
option
was
most
favourable
in
terms
of
capital
and
operating
expenditures, thus this was the preferred pump station configuration option.
The pumps are sized to deliver up to 12.5L/s.
Diffuse Source Ltd (February 2006) Matakana Wastewater Discharge
Receiving Environment Monitoring Plan. Draft Version 2
Brief Description of Contents
This report is an environmental monitoring plan to track and assess the effects
of the discharge from the Matakana Wastewater Treatment Plant on the lower
Matakana River and Matakana Estuary.
The historical effluent data (2001-5)
were quoted and the report concluded that the effluent quality is poor in terms
of high ammonia and faecal coliform concentrations.
In contrast, Matakana
River is in relatively good state.
Due to the high concentration of pollutants, it was estimated that a dilution
factor of 2000 fold was need to meet with recreation contact guidelines and
20000 times to meet the shellfish gathering guidelines.
This
report
has
also
presented
a
monitoring
schedules
to
assess
the
environmental impact associated with the effluent discharge.
6.2
CATCHMENT STATUS
The
existing
Matakana
wastewater
treatment
system
does
not
deliver
satisfactory treatment performance particularly high ammonia and faecal
coliform concentrations. It is envisaged that the sewage from the Matakana
community will be pumped to Omaha WwTP as the existing system will be decommissioned.
Capital Expenditure Programme in the Long Term Plan
RDC has made the following financial plans to upgrade the sewerage
infrastructure.
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Table 7: Matakana Wastewater Capital Expenditure Programme from LTP
Items
Est. Total between
2006 - 2016($)
Example Projects
(Timeframe)
$3M
Pump to Omaha WwTP
(2008-10)
$0.5M
Renewals
Wastewater Treatment
Plant Upgrade
Renewals
Key Sewerage Infrastructure Capacities
The estimated capacities of the key sewerage infrastructure in the Matakana
area from the recent investigations are summarised in Table 8.
The capacity
figures of local reticulation network or individual plant items are not included.
Table 8: Key Sewerage Infrastructure Capacity Estimates of Matakana
Area
Matakana
Infrastructure
Capacity
Low Pressure Sewer
12.5L/s
Treatment System
-
Note:
1.
7.0
Capacities of local reticulation network and individual plant items are not included.
POINT WELLS
Currently there is no communal sewerage infrastructure at Point Wells.
The
sewage from the household is treated and disposed by onsite systems.
7.1
PREVIOUS INVESTIGATIONS
HGCL (April 2007) Point Wells Wastewater Servicing Strategy: Issues
and Options Report.
Brief Description of Contents
This report examined the long term wastewater service strategy for Point Wells.
The population of Point Wells was projected to increase from 350 to 1300 by
2051.
The long term wastewater strategy option was to provide wastewater
connection to the Omaha WwTP.
A number of reticulation network configuration options were assessed.
pressure sewer system was preferred.
A low
The projected peak flow from the low
pressure network in Point Wells is expected to reach 3.8L/s by 2051.
compares to 15.8L/s for the conventional gravity sewer network).
(This
The rising
main from Point Wells is connected to the Omaha Road Pump Station.
The report mentioned that the measured peak flow of the Omaha Road Pump
Station from the telemetry data was 35L/s and it was understood that the
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pumps have been run at reduced frequency.
The theoretical capacity of the
pump is between 53 and 55L/s (single pump running).
Ecogent (December 2007) Assessment of Sustainability of On Site
System at Point Wells.
Brief Description of Contents
This report was a review of the on site wastewater systems in Point Wells. The
study concluded that the environment around Point Wells was adversely affected
by on site wastewater disposal.
The problem was caused by small sections,
poor soakage and low-lying areas, the problem has been exacerbated during
wet weather events.
The high groundwater level caused ponding of disposed
effluent and the effluent ended up in the estuary. Furthermore, odour has been
noticed after rains.
The small section size and the poor soil draining properties made the
continuation of on site wastewater systems not a sustainable option.
As a
result, this study recommended a community wastewater collection and
treatment system to replace the existing on site systems.
7.2
CATCHMENT STATUS
It is envisaged that the sewage from Point Wells will be pumped to Omaha
WwTP.
Capital Expenditure Programme in the Long Term Plan
RDC has made the following financial plans to upgrade the sewerage
infrastructure.
Table 9: Point Wells Wastewater Capital Expenditure Programme from LTP
Items
Est. Total between
2006 - 2016($)
Example Projects
(Timeframe)
New reticulation /pipeline
-
-
Renewals
-
-
Key Sewerage Infrastructure Capacities
The estimated capacities of the key sewerage infrastructure in the Point Wells
area from the recent investigations are summarised in Table 8.
The capacity
figures of local reticulation network or individual plant items are not included.
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Mahurangi Wastewater Master Plan – Project Data Summary
September 2008
HG Ref 1014-125641-01
Table 8: Key Sewerage Infrastructure Capacity Estimates of Point Wells
Area
Point Wells
Infrastructure
Capacity
Low Pressure Sewer pump
station to Omaha WwTP
3.8L/s
Treatment System
-
Note:
1.
8.0
Capacities of local reticulation network and individual plant items are not included.
OMAHA
Omaha is a community northeast of Warkworth.
Sewage is collected by a
conventional system before is pumped to the Omaha WwTP. Omaha Road PS
collects all the wastewater in the catchment before it is pumped to the
treatment plant.
The treated effluent is disposed in the nearby forest block and golf course.
8.1
PREVIOUS INVESTIGATIONS
Enviromex (September 2005) Omaha, Pt Wells, Matakana, Leigh and
Whangateau Sewerage Servicing Strategy. Draft
Brief Description of Contents
This report presented a centralised servicing strategy option for a few
settlements around Omaha WwTP.
The process configuration of Omaha WwTP was two lagoons followed by
polishing filters and storage dam. The first aeration lagoon is 1800m³ and 3m
water depth and the second lagoon is 4200m³ and 1.2m water depth.
polishing filters were rated to 1100m³/day.
38000m³.
The
The storage dam volume is
The treated effluent is then disposed into the forest.
The study
reported that the polishing filters were restricted to deliver between 750 and
800m³/day due to the presence of algal solids.
This strategy report also recommended a number of upgrades for the Omaha
WwTP to cater for the additional flows from growth and expansion of sewerage
catchment.
Ecogent (Nov 06) Omaha – Jones Road Groundwater Monitoring Report
Brief Description of Contents
This is a groundwater monitoring report for the treated effluent disposal of
Omaha WwTP.
The treated effluent was disposed in the James Road forestry
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block and Omaha Beach Golf Course. The monitoring report concluded that the
treated effluent disposal from Omaha WwTP did not have a significant effect on
the groundwater chemistry at Jones Road.
Ecogent (May 06) Omaha Beach Groundwater Monitoring Report
Brief Description of Contents
This is a groundwater monitoring report for the treated effluent disposal of
Omaha WwTP on the Omaha Beach Golf Course.
The monitoring report concluded that the treated effluent disposal did not have
a significant effect on the groundwater level, quality and groundwater
chemistry.
PDP
(May
2007)
Omaha
Sewage
Treatment
Plant
–
Irrigation
Assessment
Brief Description of Contents
This report examined a water and nutrient balance through modelling of the
existing irrigation fields (Omaha Golf Course and Jones Road Irrigation Blocks).
The
modelling
results
indicated
that
the
nitrogen
loads
reaching
the
groundwater from the golf course irrigation and Jones Road irrigation block wer
600kg/year and 300kg/year respectively.
Despite the results, the actual
monitoring data did not reveal any noticeable effect on the groundwater quality
trends and the modelling results seemed to have over-predicted the nitrate
concentration results in the groundwater.
The estimated application rate at Omaha Golf Course is 2mm/day (annual
average figure).
The recommendations of this report included refining the mass balance model
by incorporating daily flow and individual block data, collection of percolating
water quality for nutrient analysis and surveying groundwater gradients of the
aquifer.
8.2
CATCHMENT STATUS
Two nearby community, Matakana and Point Wells will be connected to the
Omaha WwTP in the future.
A treatment plant upgrade will be required to
increase its capacity.
Wastewater Discharge Resource Consent
The resource consent (#34101) expires on 31 May 2015.
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Volumetric Discharge Condition: To discharge up to 860m3/day from 1 October
to 30 April and up to 570m3 from 1 May to 30 September to land on
Mangatawhiri Spit.
Total discharge not to exceed 180,000m3/year or up to 6000m3/week from 1
October to 30 April and up to 4000m3 from 1 May to 30 September.
The resource consent (#34100) expires on 31 May 2016.
Volumetric Discharge Condition: To discharge up to 1200m3/day of treated
wastewater from Omaha WW treatment plant to land at Jones Road.
Capital Expenditure Programme in the Long Term Plan
RDC has made the following financial plans to upgrade the sewerage
infrastructure.
Table 9: Omaha Wastewater Capital Expenditure Programme from LTP
Items
Wastewater Treatment
Plant Upgrade
Est. Total between
2006 - 2016($)
Example Projects
(Timeframe)
$5.3M
Plant Land Purchase
(2012-14)
Treatment Plant Upgrade
(2012-15)
New pipeline
Renewals
-
-
$0.7M
Renewals
Key Sewerage Infrastructure Capacities
The estimated capacities of the key sewerage infrastructure in the Omaha area
from the recent investigations are summarised in Table 8. The capacity figures
of local reticulation network or individual plant items are not included.
Table 8: Key Sewerage Infrastructure Capacity Estimates of Point Wells
Area
Infrastructure
Capacity
Point Wells
Omaha Road PS
53-55L/s
Treatment System
1100m³/day2
Disposal to Forest
Not known3
Disposal to Golf Course
Not known3
Note:
1.
Capacities of local reticulation network and individual plant items are not included.
2.
Wastewater treatment plant capacity is estimated based on the rated capacity of the tertiary
filters.
3.
The capacity of the disposal fields was not discussed in the reports.
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9.0
September 2008
HG Ref 1014-125641-01
LEIGH
Leigh is located north east to Matakana and Point Wells.
9.1
PREVIOUS INVESTIGATIONS
No previous investigation reports received.
9.2
CATCHMENT STATUS
The catchment area is currently un-reticulated. Council intends to connect the
community to the Omaha WwTP. This will include a pump station and a rising
main to the wastewater treatment plant.
Under the current long term plan (LTP), Council has not made any financial
planning to connect this community before 2016.
10.0
LIMITATIONS
10.1
GENERAL
This report is for the use by Rodney District Council only, and should not be
used or relied upon by any other person or entity or for any other project.
This report has been prepared for the particular project described to us and its
extent is limited to the scope of work agreed between the client and Harrison
Grierson Consultants Limited. No responsibility is accepted by Harrison Grierson
Consultants Limited or its directors, servants, agents, staff or employees for the
accuracy of information provided by third parties and/or the use of any part of
this report in any other context or for any other purposes.
HARRISON GRIERSON CONSULTANTS LIMITED
Page 23
APPENDIX 1
Executive Summary of Selected Reports
APPENDIX 5.2
Mahurangi Wastewater Strategy –
Population Sensitivity Analysis
(Sept 2008)
RODNEY DISTRICT COUNCIL
Mahurangi Wastewater Strategy
Population Sensitivity Analysis
March 2008
HG Ref 1014-125641-01
Doc Ref rep-rdc-CE001V3-gja-bmr
HARRISON GRIERSON CONSULTANTS LIMITED
Document Control Record
Client
RODNEY DISTRICT COUNCIL
Project
Mahurangi Wastewater
Sensitivity Analysis
HG Ref.
1014-125641-01
Doc Ref.
rep-rdc-CE001V3-gja-bmr
Document
Report
Strategy
-
Population
ISSUE AND REVISION RECORD
Status
Draft
Date of Issue
March 2008
Originator
Grant Anderson - Environmental Scientist
Reviewed
Stephen Finnemore – Senior Principal
Approved for Issue
Stephen Finnemore – Senior Principal
Office of Origin
Auckland
Telephone
09 917 5000
Facsimile
09 917 5001
Email
[email protected]
HARRISON GRIERSON CONSULTANTS LIMITED
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RODNEY DISTRICT COUNCIL
Mahurangi Wastewater Strategy
Population Sensitivity Analysis
March 2008
HG Ref 1014-125641-01
Doc Ref rep-rdc-CE001V3-gja-bmr
CONTENTS
Page
PROJECT SCOPE
1
1.0
INTRODUCTION
1
1.1
BACKGROUND
2
2.0
AUCKLAND
STRATEGY
REGIONAL
COUNCIL
-
REGIONAL
GROWTH
3
3.0
DESIGN FLOW RATES
4
4.0
POPULATION GROWTH
4
4.1
APPROACH
4
4.2
LOW, MODERATE AND HIGH GROWTH RATES
5
4.3
WARKWORTH
4.4
SNELLS BEACH AND ALGIES BAY
11
4.5
SANDSPIT
14
4.6
MATAKANA
17
4.7
POINT WELLS
20
4.8
OMAHA
23
4.9
LEIGH
26
4.10
MAHURANGI EAST
29
4.11
TOTAL POTENTIAL POPULATION 2051
32
4.12
2016 AND 2026 PROJECTED POPULATION
36
5.0
SNELLS-ALGIES WASTEWATER OUTFALL CONDITION REPORT
37
6.0
RODNEY DISTRICT COUNCIL LTCCP (2006-2016)
38
6.1
DEVELOPMENT CONTRIBUTIONS
42
7.0
TRANSIT NZ - RODNEY DISTRICT COUNCIL MEMORANDUM
OF UNDERSTANDING
43
8.0
CONCLUSION
44
9.0
LIMITATIONS
44
9.1
GENERAL
44
7
APPENDICES
Appendix 1
Planning Area Unit Map (Mahurangi East)
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Mahurangi Wastewater Strategy
March 2008
HG Ref 1014-125641-01
PROJECT SCOPE
The project scope for this study was defined and agreed between Rodney
District Council and Harrison Grierson Consultants Limited.
This study is a
population projection analysis for the Northeast Rodney area (Mahurangi
Region).
The scope of this investigation encompassed:
•
Summary of the district-wide population growth model developed by Rob
Bates, whom was separately commissioned by Rodney District Council
•
Presentation of the population growth projection data specific for the study
area
•
Identification of the population trend based on the population growth
model
The population growth projection data summarised in this report was used in the
master plan.
The report was still in draft as there were a number of ongoing studies
conducted in parallel.
1.0
INTRODUCTION
This report seeks to outline the needs of the Wastewater for the Mahurangi East
region (incorporating Snells Beach, Algies Bay, Warkworth, Omaha, Matakana
and Wells Point). The document:
•
identifies the requirements of the wastewater infrastructure based on
current future growth estimates of the region
•
identifies trends of older population to remain as permanent population
It is not intended to present issues and options or identify or develop the
preferred strategy, rather it is a broad population assessment.
It is important to emphasise that this document will identify the future demand
drivers in terms of population growth (when and where) that will ultimately lead
to new infrastructure capacity requirements, out to 2051.
It is therefore
necessary to ensure that where possible, any assumptions are justifiable and
quantified.
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BACKGROUND
The Mahurangi & Warkworth regions comprise of the Warkworth Township and
other smaller townships to the east of Warkworth. These include Snells Beach
and Algies Bay.
The greater Mahurangi region also encompasses Sandspit,
Omaha, and Point Wells.
There is also the possibility that Leigh could be
connected to a reticulated system some time in the future, therefore
consideration is given to the outlying towns as well.
The treatment plant at Warkworth was originally designed to cater for a
population equivalent of 3000.
There have been various upgrades since the
initial plant was constructed in 1980, and the plant is currently being upgraded
to treat the peak storm water flows by the installation of an Actiflo “Peak Flow
Treatment System” supplied by Veolia.
The Warkworth treatment plant
presently discharges into the Mahurangi River.
The river discharge was
historically considered a temporary measure by the Auckland Regional Council.
The discharge Resource Consent expires in 2011, by which time the fate of the
river discharge shall be known.
The treatment plant at Snells Algies was commissioned in 1982 and designed to
service the population of the Snells Beach and Algies Bay communities with a
permanent population of approximately 700 people, rising to around 3500
during the summer holidays. This system is a lagoon system with twin oxidation
ponds which discharge via a marine outfall located 2km south of Martins Bay.
In 2005 Rodney District Council stated the following:
In 2005 we find ourselves in a situation where both treatment
plants are running out of capacity to service growth and where
goal
posts have
moved
in
terms
of higher
environmental
expectations. The council is therefore in a position where it needs
to review the strategy for wastewater servicing and implement
systems that will serve the area for at least the next 20 years with
consideration to the 50 year planning horizon.
The council has received resource consents from the ARC for the
Snells-Algies marine discharge, air discharge and occupation of
the coastal marine area.
All these consents expire at the same
time in December 2011. If the expected population growth comes
to pass, the plant and outfall will have reached its capacity by this
time.
The council is pursuing short term consents for the Warkworth
Plant to also expire in 2011, at the same time as the Snell-Algies
consent, with the view to applying for a new resource consent
once the Warkworth and Mahurangi Wastewater Strategy has
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been completed. The new consent may not necessarily be for a
continued discharge into the Mahurangi River.
The Warkworth and Mahurangi Wastewater Strategy will identify
the future solutions for both towns; Council has already started
work on this strategy at a concept level.
The Jones Road treatment system (Omaha) receives and treats effluent from
Omaha, and in the future (2008/09) will receive effluent from Point Wells, and
later Matakana (2009/10). A comprehensive study was undertaken in 2005 and
new resource consents for discharge was obtained.
2015.
This consent expires in
In 2005, it was predicted that the Jones Road plant had sufficient
capacity to cater for growth until 2015.
The treatment plant at Jones Road
theoretically has capacity for the Omaha development, Point Wells and
Matakana communities only.
2.0
AUCKLAND REGIONAL COUNCIL - REGIONAL GROWTH STRATEGY
The Auckland Regional Growth Strategy ("ARGS") is a document which outlines
the future growth of the Auckland region up to 2050. The ARGS focuses on a
large area extending from Pukekohe in the south to Wellsford in the north. As a
high-level policy document, it does not provide specific growth rates for the
smaller centres, rather it makes general statements like "… the north including
the Hibiscus Coast could be home to 440,000 people by 2050, compared to
233,000 in 1996." (Regional Growth Strategy, November 1999, p. 32).
The
ARGS is not area-specific, defining the 'north' region to include everything from
the northern side of the Auckland Harbour Bridge to Wellsford. Proposed Plan
Change 6 (2006) seeks to lift the status of Warkworth from the Regional
Analysis of Centres Activity (2003) of Rural to Town Centre.
It is noted that Warkworth is considered only as a centre within the report titled
"Establishing a Classification for Auckland's Centres and Corridors" insofar that
there is no recognition of the newly extended SH1 as a corridor to provide a link
with Orewa.
This effectively means that the new motorway extension is not
given any particular regard, and that the Warkworth area is not considered as
an area which may be utilised as a satellite town to Auckland.
Notwithstanding the information provided by the Regional Growth Strategy, it is
recognised that townships within the Mahurangi East region are used as satellite
towns which provide workers to Auckland, and people commute on a day to day
basis.
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DESIGN FLOW RATES
Information is available on the existing flows from data provided by Rodney
Water within their monthly and quarterly reports. This data has been used by
URS in a report titled "Warkworth Wastewater Treatment Upgrade and Disposal
Options" provided a value of 140 L/person/day for the average dry weather flow
(ADWF) and 280 L/person/day for the peak wet weather flow (PWWF).
The
Rodney District Council Engineering Code utilises the Auckland Regional Council
publication TP58 which specifies 200L/person/day for a household with standard
fixtures and fittings and 220L/person/day for upmarket and luxury houses.
4.0
POPULATION GROWTH
4.1
APPROACH
A Growth Model has been developed by Rodney District Council (Rob Bates,
version 14 26/08/08) which models the growth between 2007 and 2051 for the
areas under RDC’s jurisdiction. The model presents anticipated growth based on
a straight-line population increase.
The Bates model looks specifically at the
occupied dwellings. This model grows only the occupied dwellings, and leaves
the unoccupied dwellings at a constant rate for the next 50 years. The model
illustrates that each increase in occupied dwellings represents a greater overall
level of occupancy rates.
In conjunction with Rob Bates, HG have altered this model.
Rather than the
unoccupied dwellings remaining constant, they are consumed at a rate
determined by the current age structure. In addition, rather than keeping the
population at the standard (from 2006 census data) 2.59 people/household, we
have tended the population to 2.2 at the ultimate demand.
From the available census data, we were able to map the current structure of
the population. This was done for each planning area unit (PAU). Results from
this confirmed thoughts that the Mahurangi east region was top heavy with
older, retired people.
Data was available from Statistics New Zealand (Stats NZ) which illustrated that
there is a large proportion of baby boomers. This transposes to a shift in the
average population age and a large number of retirees (those who are older
than 65 years of age).
Base data for the RDC (Rob Bates) Growth Model is derived from the 2006
census. For example, the census indicates that the permanent occupancy rate
for Warkworth is high, at 92.3%, which is typical for a stable residential
community, with minimal, if any, seasonal population. Conversely, Omaha has
a permanent occupancy rate of 50%, indicating that a high proportion of
dwellings are used as holiday baches.
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The total number of dwellings in each area has been split into normally occupied
and normally unoccupied dwellings, to account for the percentage of baches in
each area that change the population count over the peak period in summer,
particularly during Christmas and New Year.
The RDC (Rob Bates) Model
projects the number permanently occupied dwellings and the unoccupied
dwellings remain static. From this, the projected number of unoccupied
dwellings has been calculated by dividing the number of occupied dwellings by
the percentage of permanent occupancy (giving the total number of dwellings),
and multiplying the total dwellings by the percentage of unoccupied dwellings
(from the 2006 census data).
For the percentage of permanently occupied dwellings for each area, the
average household occupancy figures for the Northern Ward region have been
used, being 2.59 people per dwelling. This is the value used by Rob Bates in his
population predictions and thus it has been retained for consistency.
During the peak Christmas/New Year period, a factor of 2 is applied to normally
unoccupied dwellings to model the itinerant/summer population (i.e. the influx
of people into the area over busy summer periods with high occupancy rates in
baches which are normally unoccupied).
This means that the normally
unoccupied dwellings are assumed to have an occupancy rate of 5.2 (2.59 x 2).
This is used to calculate the summer peak population, by adding the expected
increase (assuming all unoccupied dwellings are now occupied with 5.2 people
per dwelling) to the usual population (2.59 people per dwelling for the
percentage of permanently occupied dwellings). As this has only been applied
to the percentage of dwellings which are not permanently occupied (and thus
assumed to be baches), there will be larger shifts in population for holiday
destinations than for more stable residential communities. Guidance from the
planning department at Rodney District Council have indicated the estimated
proportions of permanently occupied dwellings in the future. It should also be
noted that the peak summer population is likely to occur for only approximately
14 days of the year, over the busy Christmas / New Year period.
4.2
LOW, MODERATE AND HIGH GROWTH RATES
Whilst the recent RDC (Rob Bates) Growth Model is the most accurate and upto-date model available, it is also essential to consider the sensitivity of the
model. For example, growth bottlenecks may be removed if developers agree to
provide additional infrastructure such as roads or water/wastewater to facilitate
a specific development/private plan change (thus increasing the ultimate
number of lots).
Alternatively, growth may be slower if economic growth is lower than
anticipated, or growth occurs elsewhere in regions that are considered more
“attractive”.
This may be due to accelerated provision of infrastructure
(particularly roads enabling commuting) or job creation.
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To model the potential sensitivities of the current growth model, three growth
rates have been modelled: the normal (Moderate Growth) rate, 100% of that
predicted by the RDC (Rob Bates) Model; a High Growth rate, 200% of the
Moderate Growth rate with reference to the population as at the 2006 census;
and a Low Growth rate, 50% of the Moderate Growth rate, also measured from
the 2006 census population. Note these Low and High population predictions are
calculated from growth figures, rather than actual population projected.
The growth rate selected will determine:
1.
When
the
existing
infrastructure
will
reach
capacity
(and
require
upgrading).
2.
The ultimate infrastructure demand.
The basic growth curves are illustrated in Figure 1 below. Figure 1 models an
existing community with 100 lots and an additional available 100 lots, equating
to an ultimate development of 200 lots.
The low growth curve models 100
existing lots plus only 50 additional lots, equating to a development of 150 lots
by 2051. Conversely, the high growth curve models 100 existing lots plus 200
additional lots equating to a development of 300 lots by 2051.
Clearly, to accommodate additional lots over and above the capacity presented
in the “Structure Plan” there has to be either more intensive development or the
re-zoning of land not originally identified in current growth model. The impact
of the sensitivity analysis will be more dramatic for newer communities where
potential growth is equivalent or in excess of the current level of development.
Conversely, the impact will be less pronounced for mature communities with
minimal future growth. For instance if there is a current development of 2000
lots and the “normal growth” potential of only 100 allotments, the sensitivity
analysis development range will be between 2050 and 2200 lots.
Note that because the Low and High Growth figures have been based on the
Northern Region average occupancy rate of 2.59 people per dwelling, and added
to the 2006 census data with occupancy rates in individual areas varying from
2.00-3.09 people per dwelling, the 2051 total permanent population figures are
not equal to 2.59 people per dwelling.
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350
300
250
200
150
100
50
0
2006
2051
Normal Growth
Low Growth
High Growth
Figure 1: High and Low Growth Rates
4.3
WARKWORTH
The population of Warkworth in 2006 (from census data 2006) was 3,273. This
is considered to be consistent with the Warkworth Structure Plan (2004) with
stated a population of 2,800.
Future growth presented in the Structure Plan is
given in Table 2 below.
Table 2:
Warkworth Growth Strategy (Warkworth Structure Plan 2004)
Growth
Projected Population
(people)
Capacity to be provided
(with preferred bypass)
Existing (2004)
2,800
2004 - 2024
4,400
5,200
2024 - 2044
6,000
7,000
Up to 8,000
8,800
2044 +
4,400
(1997 Structure Plan)
A summary of the census data regarding the total number of dwellings in
Warkworth, also detailing the number of occupied and unoccupied dwellings, is
shown below in Table 3.
The percentage of permanent occupancy has been
calculated for each individual area in Warkworth, and the average percentage of
permanent occupancy for Warkworth has been calculated using the total number
of occupied and total unoccupied dwellings for the three sub-areas. It is thus
assumed that the percentage of permanent occupancy will be approximately
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equal throughout Warkworth in future, so this average percentage has been
used for subsequent calculations.
Table 3:
Summary of 2006 Census Data for Warkworth
Occupied
Dwellings
Unoccupied
Dwellings
Total
Percentage
Permanent
Occupancy (%)
Warkworth
Central
678
51
729
93.0
Warkworth
North
348
27
375
92.8
Warkworth
South
312
33
345
90.4
1338
111
1449
92.33
Area
Total
Table 4 below presents the latest RDC (Rob Bates) Growth Model for Warkworth,
which calculates only the number of occupied dwellings, however the number of
unoccupied dwellings (and thus the total number of dwellings) may be
calculated using the average percentage of permanent occupancy for the area.
The table shows that the total number of dwellings by 2051 will have reached
2661, 70.0% of the proposed Ultimate Development Capacity.
Table 4:
Warkworth 2051 Dwelling Statistics
Occupied
Dwellings1
Unoccupied
Dwellings2
Total Dwellings
(2051)
Ultimate
Development3
Warkworth
Central
1470
122
1592
2421
Warkworth
North
385
32
417
430
Warkworth
South
602
50
652
949
2457
204
2661
3800
Area
Total
1. The projected number of occupied dwellings is taken directly from the RDC (Rob
Bates) Growth Model. This is assumed to be equal to 92.3% (average permanent
occupancy rate for Warkworth) of the total number of dwellings in 2051.
2. The percentage of unoccupied dwellings is assumed to remain stable at an average of
7.7% for the area. Thus the number of unoccupied dwellings may be calculated by
dividing the number of occupied dwellings by 92.3%, and multiplying by 7.7%.
3. Ultimate Development figures provided by Rob Bates model and based on total land
available for development.
Table 5 below presents the 2051 projected normal (permanent) and peak
(summer) populations. For Warkworth, the expected peak population over the
peak Christmas and New Year period is 7,410.
It should be noted that the permanent population estimate of 6,355 by 2051 is
lower than the Structure Plan, which proposed a population of 8,000 at 2044.
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Table 5:
March 2008
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Warkworth Projected Permanent and Summer Populations (2051)
Total
Dwellings
Potential
Permanent
Population
Summer
Increase
Potential Total
Peak
Occupancy
Occupied plus
unoccupied
dwellings
2.59 people per
occupied dwelling
Scale factor of 2
applied to
unoccupied
dwellings
Permanent plus
summer
population
Warkworth
Central
1592
3802
631
4433
Warkworth
North
417
997
165
1162
Warkworth
South
652
1556
258
1814
2661
6355
1055
7410
Area
Total
Table 6 below presents the potential permanent and peak populations by 2051,
with ‘Low Growth’ based on 50% of the growth projected in the RDC (Rob
Bates) Growth Model, ‘Moderate Growth’ based on 100% of the growth
projected in the Growth Model, and ‘High Growth’ based on 200% of the growth
projected in the Growth Model, as described in Section 6.2.
The ‘Growth’
segment is shown because the final calculated figures for Low, Moderate and
High Growth are calculated from the ‘Growth’ segment figures, and added to the
2006 census data.
For Warkworth, the Low Growth projection shows a peak population of 5,644,
the Moderate Growth projection shows a peak population of 7,410, and the High
Growth projection shows a peak population of 11,034. This summer increase is
small compared to the permanent population, due to the low proportion of
normally unoccupied dwellings.
Table 6:
Warkworth Projected Permanent and Summer Populations with
Various Growth Scenarios
Growth Scenario
2006
Census
Low
(50%)
Total Dwellings 2006
1449
Permanent Population
3273
Summer Increase
3847
Total New Dwellings
645
1212
2580
Occupied Dwellings
596
1119
2383
Permanent Population
1541
3082
6164
Unoccupied Dwellings
49
93
198
256
480
1023
1797
3562
Summer Increase
Summer Peak Population
Total
High
(200%)
574
Summer Peak Population
Growth
Moderate
(100%)
Total Dwellings 2051
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2661
7187
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Table 6:
March 2008
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Warkworth Projected Permanent and Summer Populations with
Various Growth Scenarios
Low
(50%)
Moderate
(100%)
Occupied Dwellings
1934
2457
3721
Permanent Population
48142
6355
94372
Unoccupied Dwellings
160
204
309
Summer Increase
830
1055
1597
5644
7410
11034
Growth Scenario
(2051)
Summer Peak Population
High
(200%)
1. Remaining development capacity: 1139 lots (from RDC (Rob Bates) Growth Model).
2. Occupancy rate used for Growth Model is the Northern Region average of 2.59 people
per dwelling. Total permanent population in 2051 is not equal to 2.59 people per
dwelling due to lower occupancy per dwelling in Warkworth at 2006 census.
NB: Rates used for occupancy are 2.59 people per occupied dwelling. For unoccupied
dwellings, this is multiplied by a factor of 2 for expected summer occupancy. The
average permanent occupancy percentage of 92.33% is applied to all calculations.
Table 6 above illustrates that under the High Growth scenario, the potential
summer population may increase to 11,034, thus exceeding the numbers
presented in the Structure Plan. Conversely, if growth is lower than anticipated,
the population would be around 5,644 people during the peak summer period,
significantly lower than the Structure Plan.
In order to ensure that the future growth is aligned with the relevant nonstatutory documents, such as the LTCCP, it is prudent to present the projected
population growth for the next ten and twenty years. This ensures that forward
planning can be achieved from both a fiscal and engineering perspective. Table
7 below presents the projected permanent and summer peak populations for
Warkworth in 2016 and 2026 (2051 figures also listed for quick reference). As
with the calculations for the above table, the Low and High populations for each
timespan have been calculated from the growth predicted by the Moderate
projection (the RDC (Rob Bates) Model) and added to the 2006 census figures.
Table 7:
Year
Warkworth 2016 & 2026 Populations with Various Growth Scenarios
Growth
Scenario
Potential
Permanent
Population
(2.59 people per
dwelling, 92%
occupancy)
2016
2026
Low
3704
1
Summer Increase
(2 times average
occupancy of
unoccupied
dwellings)
Potential
Summer Peak
Population
614
4318
Moderate
4136
686
4822
High
4999
829
5828
Low
4033
669
4702
1
Moderate
4794
795
5589
High
6315
1047
7362
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Table 7:
Year
March 2008
HG Ref 1014-125641-01
Warkworth 2016 & 2026 Populations with Various Growth Scenarios
Growth
Scenario
Potential
Permanent
Population
Summer Increase
(2.59 people per
dwelling, 92%
occupancy)
2051
Low
(2 times average
occupancy of
unoccupied
dwellings)
4814
1
Potential
Summer Peak
Population
830
5644
Moderate
6355
1055
7410
High
9437
1597
11034
1. Prediction from RDC (Rob Bates) Growth Model.
4.4
SNELLS BEACH AND ALGIES BAY
The Snells-Algies Structure plan is outdated (following district plan decisions for
Snells future development area which effectively reduced the area available for
development), thus the data presented is entirely based on the RDC (Rob Bates)
Growth Model.
A summary of the census data regarding the total number of dwellings in SnellsAlgies, also detailing the number of occupied and unoccupied dwellings, is
shown below in Table 8.
The percentage of permanent occupancy has been
calculated for each individual area in Snells-Algies, and the average percentage
of permanent occupancy for Snells-Algies has been calculated using the total
number of occupied and total unoccupied dwellings for the three smaller areas.
It is thus assumed that the percentage of permanent occupancy will be
approximately equal throughout Snells-Algies in future, so this average
percentage has been used for subsequent calculations.
Table 8:
Summary of 2006 Census Data for Snells-Algies
Occupied
Dwellings
Unoccupied
Dwellings
Total
Dwellings
Percentage
Permanent
Occupancy (%)
Snells Beach
516
156
672
76.8
Snells Beach
South
609
153
762
79.9
Algies Bay
246
183
429
57.3
1371
492
1863
73.59
Area
Total
Table 9 below presents the latest RDC (Rob Bates) Growth Model for SnellsAlgies, which calculates only the number of occupied dwellings, however the
number of unoccupied dwellings (and thus the total number of dwellings) may
be calculated using the average percentage of permanent occupancy for the
area.
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The table shows that the total number of dwellings by 2051 will have reached
2356, 96.8% of the proposed Ultimate Development Capacity.
Table 9:
Snells-Algies 2051 Dwelling Statistics
Occupied
Dwellings1
Unoccupied
Dwellings2
Total Dwellings
(2051)
Ultimate
Development
Snells Beach
663
238
9013
840
Snells Beach
South
747
268
10153
913
Algies Bay
444
159
603
681
Average
1854
665
2519
2434
Area
1. The projected number of occupied dwellings is taken directly from the RDC (Rob
Bates) Growth Model. This is assumed to be equal to 73.6% (average permanent
occupancy rate for Snells-Algies) of the total number of dwellings in 2051.
2. The percentage of unoccupied dwellings is assumed to remain stable at an average of
26.4% for the area. Thus the number of unoccupied dwellings may be calculated by
dividing the number of occupied dwellings by 73.6%, and multiplying by 26.4%.
3. Exceeds Ultimate Development Capacity.
Table 10 below presents the 2051 projected normal (permanent) and peak
(summer) populations. For Snells-Algies, the expected peak population over the
peak Christmas and New Year period is 8,238.
Table 10:
Snells-Algies Projected Permanent and Summer Populations (2051)
Total
Dwellings
Potential
Permanent
Population
Summer
Increase
Potential Total
Peak
Occupancy
Occupied plus
unoccupied
dwellings
2.59 people per
occupied
dwelling
Scale factor of 2
applied to
unoccupied
dwellings
Permanent plus
summer
population
Snells Beach
901
1715
1231
2946
Snells Beach
South
1015
1933
1387
3320
603
1148
824
1972
2519
4796
3442
8238
Area
Algies Bay
TOTAL
Table 11 below presents the potential permanent and peak populations by 2051,
with ‘Low Growth’ based on 50% of the growth projected in the RDC (Rob
Bates) Growth Model, ‘Moderate Growth’ based on 100% of the growth
projected in the Growth Model, and ‘High Growth’ based on 200% of the growth
projected in the Growth Model, as described in Section 6.2.
The ‘Growth’
segment is shown because the final calculated figures for Low, Moderate and
High Growth are calculated from the ‘Growth’ segment figures, and added to the
2006 census data.
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For Snells-Algies, the Low Growth projection shows a peak population of 7,136,
the Moderate Growth projection shows a peak population of 8,238, and the High
Growth projection shows a peak population of 10,890. The summer increase is
significant due to a highly seasonal occupancy rate, as 26.4% of the dwellings
are not permanently occupied. (This compares with only 7.7% at Warkworth,
which is a more seasonally stable residential community.)
Table 11:
Snells-Algies Projected Permanent and Summer Populations with
Various Growth Scenarios
Growth Scenario
2006
Census
Growth
Moderate
(100%)
Total Dwellings 2006
1863
Permanent Population
3339
Summer Increase
2545
Summer Peak Population
5884
High
(200%)
Total New Dwellings
383
656
1531
Occupied Dwellings
282
483
1126
Permanent Population
729
1457
2914
Unoccupied Dwellings
101
173
404
Summer Increase
523
897
2091
1251
2354
Summer Peak Population
Total
(2051)
Low
(50%)
1
5005
Total Dwellings 2051
2246
2519
3394
Occupied Dwellings
1653
1854
2497
2
Permanent Population
4068
4796
62532
Unoccupied Dwellings
593
665
896
Summer Increase
3068
3442
4637
Summer Peak Population
7136
8238
10890
1. Value shown includes Snells Beach and Snells Beach South exceedances of Ultimate
Development Capacity. Remaining development capacity: 78 lots at Algies Bay only
(from RDC (Rob Bates) Growth Model).
2. Occupancy rate used for Growth Model is the Northern Region average of 2.59 people
per dwelling. Total permanent population in 2051 is not equal to 2.59 people per
dwelling due to lower occupancy per dwelling in Snells-Algies at 2006 census.
NB: Rates used for occupancy are 2.59 people per occupied dwelling. For unoccupied
dwellings, this is multiplied by a factor of 2 for expected summer occupancy. The
average permanent occupancy percentage of 73.6% is applied to all calculations.
In order to ensure that the future growth is aligned with the relevant nonstatutory documents, such as the LTCCP, it is prudent to present the projected
population growth for the next ten and twenty years. This ensures that forward
planning can be achieved from both a fiscal and engineering perspective. Table
12 below presents the projected permanent and summer peak populations for
Snells-Algies in 2016 and 2026 (2051 figures also listed for quick reference). As
with the calculations for the above table, the Low and High populations for each
HARRISON GRIERSON CONSULTANTS LIMITED
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timespan have been calculated from the growth predicted by the Moderate
projection (the RDC (Rob Bates) Model) and added to the 2006 census figures.
Table 12:
Year
2016
2026
2051
Snells-Algies
Scenarios
Growth
Scenario
2016
&
2026
Potential
Permanent
Population
Populations
with
Summer
Increase
Various
Growth
Potential
Summer Peak
Population
(2.59 people per
dwelling, 92%
occupancy)
(2 times average
occupancy of
unoccupied
dwellings)
3588
2575
6163
Low
1
Moderate
3837
2754
6591
High
4335
3111
7446
Low
3731
2677
6408
1
Moderate
4122
2958
7080
High
4905
3520
8425
Low
4068
3068
7136
1
Moderate
4796
3442
8238
High
6253
4637
10890
1. Prediction from RDC (Rob Bates) Growth Model.
4.5
SANDSPIT
There is no Structure Plan for Sandspit, so the Snells Algies methodology using
the RDC (Rob Bates) Model was used to assess population growth. Given the
proximity of Sandspit to Snells Algies, it may ultimately become a part of the
larger Mahurangi Wastewater Scheme servicing Warkworth and Snells Algies.
A summary of the census data regarding the total number of dwellings in
Sandspit, also detailing the number of occupied and unoccupied dwellings, is
shown below in Table 13. The average percentage of permanent occupancy for
Sandspit has been calculated using the total number of occupied and total
unoccupied dwellings.
It is assumed that the percentage of permanent
occupancy will be approximately equal throughout Sandspit in future, so this
average percentage has been used for subsequent calculations.
Table 13:
Area
Sandspit
Summary of 2006 Census Data for Sandspit
Occupied
Dwellings
Unoccupied
Dwellings
Total
Dwellings
Percentage
Permanent
Occupancy (%)
156
42
198
78.8
Table 14 below presents the latest RDC (Rob Bates) Growth Model for Sandspit,
which calculates only the number of occupied dwellings, however the number of
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HG Ref 1014-125641-01
unoccupied dwellings (and thus the total number of dwellings) may be
calculated using the average percentage of permanent occupancy for the area.
The table shows that the total number of dwellings by 2051 will have reached
377, 80.9% of the proposed Ultimate Development Capacity.
Table 14:
Sandspit 2051 Dwelling Statistics
Area
Sandspit
Occupied
Dwellings1
Unoccupied
Dwellings2
Total Dwellings
(2051)
Ultimate
Development
297
80
377
466
1. The projected number of occupied dwellings is taken directly from the RDC (Rob
Bates) Growth Model. This is assumed to be equal to 78.8% (average permanent
occupancy rate for Sandspit) of the total number of dwellings in 2051.
2. The percentage of unoccupied dwellings is assumed to remain stable at an average of
21.2% for the area. Thus the number of unoccupied dwellings may be calculated by
dividing the number of occupied dwellings by 78.8%, and multiplying by 21.2%.
Table 15 below presents the 2051 projected normal (permanent) and peak
(summer) populations. For Sandspit, the expected peak population over the
peak Christmas and New Year period is 1,182.
Table 15:
Area
Sandspit Projected Permanent and Summer Populations (2051)
Total
Dwellings
Potential
Permanent
Population
Summer
Increase
Potential Total
Peak
Occupancy
Occupied plus
unoccupied
dwellings
2.59 people per
occupied
dwelling
Scale factor of 2
applied to
unoccupied
dwellings
Permanent plus
summer
population
377
768
414
1182
Sandspit
Table 16 below presents the potential permanent and peak populations by 2051,
with ‘Low Growth’ based on 50% of the growth projected in the RDC (Rob
Bates) Growth Model, ‘Moderate Growth’ based on 100% of the growth
projected in the Growth Model, and ‘High Growth’ based on 200% of the growth
projected in the Growth Model, as described in Section 6.2.
The ‘Growth’
segment is shown because the final calculated figures for Low, Moderate and
High Growth are calculated from the ‘Growth’ segment figures, and added to the
2006 census data.
For Sandspit, the Low Growth projection shows a peak population of 892, the
Moderate Growth projection shows a peak population of 1,182, and the High
Growth projection shows a peak population of 1,826.
Table 16:
Sandspit Projected Permanent
Various Growth Scenarios
HARRISON GRIERSON CONSULTANTS LIMITED
and
Summer
Populations
with
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Mahurangi Wastewater Strategy
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HG Ref 1014-125641-01
Low
(50%)
Growth Scenario
2006
Census
Growth
Total Dwellings 2006
198
Permanent Population
363
Summer Increase
217
Summer Peak Population
580
High
(200%)
Total New Dwellings
99
179
397
Occupied Dwellings
78
141
313
Permanent Population
203
405
810
Unoccupied Dwellings
21
38
84
Summer Increase
109
196
436
Summer Peak Population
312
601
1246
1
Total Dwellings 2051
297
377
595
Occupied Dwellings
234
297
469
768
11732
2
Permanent Population
Total
(2051)
Moderate
(100%)
566
Unoccupied Dwellings
63
80
126
Summer Increase
326
414
653
Summer Peak Population
892
1182
1826
1. Remaining development capacity: 89 lots (from RDC (Rob Bates) Growth Model).
2. Occupancy rate used for Growth Model is the Northern Region average of 2.59 people
per dwelling. Total permanent population in 2051 is not equal to 2.59 people per
dwelling due to lower occupancy per dwelling in Sandspit at 2006 census.
NB: Rates used for occupancy are 2.59 people per occupied dwelling. For unoccupied
dwellings, this is multiplied by a factor of 2 for expected summer occupancy. The
average permanent occupancy percentage of 78.8% is applied to all calculations.
In order to ensure that the future growth is aligned with the relevant nonstatutory documents, such as the LTCCP, it is prudent to present the projected
population growth for the next ten and twenty years. This ensures that forward
planning can be achieved from both a fiscal and engineering perspective. Table
17 below presents the projected permanent and summer peak populations for
Sandspit in 2016 and 2026 (2051 figures also listed for quick reference).
As
with the calculations for the above table, the Low and High populations for each
timespan have been calculated from the growth predicted by the Moderate
projection (the RDC (Rob Bates) Model) and added to the 2006 census figures.
Table 17:
Year
2016
Sandspit 2016 & 2026 Populations with Various Growth Scenarios
Growth
Scenario
Potential
Permanent
Population
Summer
Increase
Potential
Summer Peak
Population
(2.59 people per
dwelling, 92%
occupancy)
(2 times average
occupancy of
unoccupied
dwellings)
425
228
653
262
750
Low
Moderate
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1
488
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Table 17:
Year
2026
2051
March 2008
HG Ref 1014-125641-01
Sandspit 2016 & 2026 Populations with Various Growth Scenarios
Growth
Scenario
Potential
Permanent
Population
Summer
Increase
Potential
Summer Peak
Population
(2.59 people per
dwelling, 92%
occupancy)
(2 times average
occupancy of
unoccupied
dwellings)
High
613
330
943
Low
467
251
718
1
Moderate
571
307
878
High
779
419
1198
Low
566
326
892
Moderate
1
768
414
1182
High
1173
653
1826
1. Prediction from RDC (Rob Bates) Growth Model.
4.6
MATAKANA
There is no Structure Plan for Matakana, so the Snells-Algies methodology using
the RDC (Rob Bates) Model was used to assess population growth.
The
population projections for are as follows.
A summary of the census data regarding the total number of dwellings in
Matakana, also detailing the number of occupied and unoccupied dwellings, is
shown below in Table 18.
The percentage of permanent occupancy has been
calculated for each individual area in Matakana, and the average percentage of
permanent occupancy for Matakana has been calculated using the total number
of occupied and total unoccupied dwellings for the three smaller areas.
thus
assumed
that
the
percentage
of
permanent
occupancy
It is
will
be
approximately equal throughout Matakana in future, so this average percentage
has been used for subsequent calculations.
Table 18:
Summary of 2006 Census Data for Matakana
Occupied
Dwellings
Unoccupied
Dwellings
Total
Dwellings
Percentage
Permanent
Occupancy (%)
Matakana
105
30
135
77.8
Matakana
Valley
348
87
435
80.0
Area
Rainbows End
Total
39
12
51
76.5
492
129
621
79.23
Table 19 below presents the latest RDC (Rob Bates) Growth Model for Matakana,
which calculates only the number of occupied dwellings, however the number of
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unoccupied dwellings (and thus the total number of dwellings) may be
calculated using the average percentage of permanent occupancy for the area.
The table shows that the total number of dwellings by 2051 will have reached
1171, 80.7% of the proposed Ultimate Development Capacity.
Table 19:
Matakana 2051 Dwelling Statistics
Occupied
Dwellings1
Unoccupied
Dwellings2
Total Dwellings
(2051)
Ultimate
Development
Matakana
375
98
473
700
Matakana
Valley
508
133
641
700
45
12
573
51
928
243
1171
1451
Area
Rainbows End
Average
1. The projected number of occupied dwellings is taken directly from the RDC (Rob
Bates) Growth Model. This is assumed to be equal to 79.2% (average permanent
occupancy rate for Matakana) of the total number of dwellings in 2051.
2. The percentage of unoccupied dwellings is assumed to remain stable at an average of
20.8% for the area. Thus the number of unoccupied dwellings may be calculated by
dividing the number of occupied dwellings by 79.2%, and multiplying by 20.8%.
3. Exceeds Ultimate Development Capacity.
Table 20 below presents the 2051 projected normal (permanent) and peak
(summer) populations. For Matakana, the expected peak population over the
peak Christmas and New Year period is 3,659.
Table 20:
Matakana Projected Permanent and Summer Populations (2051)
Total
Dwellings
Potential
Permanent
Population
Summer
Increase
Potential Total
Peak
Occupancy
Occupied plus
unoccupied
dwellings
2.59 people per
occupied
dwelling
Scale factor of 2
applied to
unoccupied
dwellings
Permanent plus
summer
population
Matakana
473
971
509
1480
Matakana
Valley
641
1314
689
2003
57
115
61
176
1171
2400
1259
3659
Area
Rainbows End
TOTAL
Table 21 below presents the potential permanent and peak populations by 2051,
with ‘Low Growth’ based on 50% of the growth projected in the RDC (Rob
Bates) Growth Model, ‘Moderate Growth’ based on 100% of the growth
projected in the Growth Model, and ‘High Growth’ based on 200% of the growth
projected in the Growth Model, as described in Section 6.2.
The ‘Growth’
segment is shown because the final calculated figures for Low, Moderate and
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High Growth are calculated from the ‘Growth’ segment figures, and added to the
2006 census data.
For Matakana, the Low Growth projection shows a peak population of 2,828, the
Moderate Growth projection shows a peak population of 3,659, and the High
Growth projection shows a peak population of 5,133.
Table 21:
Matakana Projected Permanent and Summer Populations with
Various Growth Scenarios
Growth Scenario
2006
Census
Low
(50%)
Total Dwellings 2006
621
Permanent Population
1392
Summer Increase
Total
(2051)
High
(200%)
667
Summer Peak Population
Growth
Moderate
(100%)
2059
Total New Dwellings
246
550
984
Occupied Dwellings
195
436
779
Permanent Population
504
1008
2016
Unoccupied Dwellings
51
114
204
Summer Increase
264
591
1057
Summer Peak Population
768
1599
3073
Total Dwellings 2051
867
11711
1605
Occupied Dwellings
687
928
1271
Permanent Population
1896
2400
34082
Unoccupied Dwellings
180
243
333
Summer Increase
932
1259
1725
2828
3659
5133
Summer Peak Population
2
1. Value shown includes Rainbows End at Ultimate Development Capacity. Remaining
development capacity: 280 lots at Matakana and Matakana Valley only (from RDC (Rob
Bates) Growth Model).
2. Occupancy rate used for Growth Model is the Northern Region average of 2.59 people
per dwelling. Total permanent population in 2051 is not equal to 2.59 people per
dwelling due to higher occupancy per dwelling in Matakana at 2006 census.
NB: Rates used for occupancy are 2.59 people per occupied dwelling. For unoccupied
dwellings, this is multiplied by a factor of 2 for expected summer occupancy. The
average permanent occupancy percentage of 79.2% is applied to all calculations.
In order to ensure that the future growth is aligned with the relevant nonstatutory documents, such as the LTCCP, it is prudent to present the projected
population growth for the next ten and twenty years. This ensures that forward
planning can be achieved from both a fiscal and engineering perspective. Table
22 below presents the projected permanent and summer peak populations for
Matakana in 2016 and 2026 (2051 figures also listed for quick reference). As
with the calculations for the above table, the Low and High populations for each
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March 2008
HG Ref 1014-125641-01
timespan have been calculated from the growth predicted by the Moderate
projection (the RDC (Rob Bates) Model) and added to the 2006 census figures.
Table 22:
Year
2016
2026
2051
Matakana 2016 & 2026 Populations with Various Growth Scenarios
Growth
Scenario
Potential
Permanent
Population
Summer
Increase
Potential
Summer Peak
Population
(2.59 people per
dwelling, 92%
occupancy)
(2 times average
occupancy of
unoccupied
dwellings)
1464
767
2231
Low
1
Moderate
1536
805
2341
High
1680
880
2560
Low
1528
801
2329
1
Moderate
1665
873
2538
High
1938
1016
2954
Low
1896
932
2828
1
Moderate
2400
1259
3659
High
3408
1725
5133
1. Prediction from RDC (Rob Bates) Growth Model.
4.7
POINT WELLS
There is no Structure Plan for Point Wells, so the Snells Algies methodology
using the RDC (Rob Bates) Model was used to assess population growth. The
population projections for are as follows.
A summary of the census data regarding the total number of dwellings in Point
Wells, also detailing the number of occupied and unoccupied dwellings, is shown
below in Table 23. The average percentage of permanent occupancy for Point
Wells has been calculated using the total number of occupied and total
unoccupied dwellings.
It is assumed that the percentage of permanent
occupancy will be approximately equal throughout Point Wells in future, so this
average percentage has been used for subsequent calculations.
Table 23:
Area
Point Wells
Summary of 2006 Census Data for Point Wells
Occupied
Dwellings
Unoccupied
Dwellings
Total
Dwellings
Percentage
Permanent
Occupancy (%)
132
69
201
65.67
Table 24 below presents the latest RDC (Rob Bates) Growth Model for Point
Wells, which calculates only the number of occupied dwellings, however the
number of unoccupied dwellings (and thus the total number of dwellings) may
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HG Ref 1014-125641-01
be calculated using the average percentage of permanent occupancy for the
area.
The table shows that the total number of dwellings by 2051 will have reached
322, 73.2% of the proposed Ultimate Development Capacity.
Table 24:
Point Wells 2051 Dwelling Statistics
Area
Point Wells
Occupied
Dwellings1
Unoccupied
Dwellings2
Total Dwellings
(2051)
Ultimate
Development
212
111
323
441
1. The projected number of occupied dwellings is taken directly from the RDC (Rob
Bates) Growth Model. This is assumed to be equal to 65.7% (average permanent
occupancy rate for Point Wells) of the total number of dwellings in 2051.
2. The percentage of unoccupied dwellings is assumed to remain stable at an average of
34.3% for the area. Thus the number of unoccupied dwellings may be calculated by
dividing the number of occupied dwellings by 65.7%, and multiplying by 34.3%.
Table 25 below presents the 2051 projected normal (permanent) and peak
(summer) populations. For Point Wells, the expected peak population over the
peak Christmas and New Year period is 1,120.
Table 25:
Area
Point Wells Projected Permanent and Summer Populations (2051)
Total
Dwellings
Potential
Permanent
Population
Summer
Increase
Potential Total
Peak
Occupancy
Occupied plus
unoccupied
dwellings
2.59 people per
occupied
dwelling
Scale factor of 2
applied to
unoccupied
dwellings
Permanent plus
summer
population
323
547
573
1120
Point Wells
Table 26 below presents the potential permanent and peak populations by 2051,
with ‘Low Growth’ based on 50% of the growth projected in the RDC (Rob
Bates) Growth Model, ‘Moderate Growth’ based on 100% of the growth
projected in the Growth Model, and ‘High Growth’ based on 200% of the growth
projected in the Growth Model, as described in Section 6.2.
The ‘Growth’
segment is shown because the final calculated figures for Low, Moderate and
High Growth are calculated from the ‘Growth’ segment figures, and added to the
2006 census data.
For Point Wells, the Low Growth projection shows a peak population of 910, the
Moderate Growth projection shows a peak population of 1,120, and the High
Growth projection shows a peak population of 1,658. The summer increase is
significant due to the high proportion of normally unoccupied dwellings (34.3%),
which are assumed to be occupied during summer.
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Table 26:
March 2008
HG Ref 1014-125641-01
Point Wells Projected Permanent and Summer Populations with
Various Growth Scenarios
Low
(50%)
Growth Scenario
2006
Census
Growth
Total
(2051)
Moderate
(100%)
Total Dwellings 2006
201
Permanent Population
303
Summer Increase
357
Summer Peak Population
660
High
(200%)
Total New Dwellings
72
122
287
Occupied Dwellings
47
80
189
Permanent Population
122
244
488
Unoccupied Dwellings
25
42
99
Summer Increase
128
216
510
Summer Peak Population
250
460
998
Total Dwellings 2051
273
3231
488
Occupied Dwellings
179
212
321
2
Permanent Population
425
547
7912
Unoccupied Dwellings
94
111
168
Summer Increase
485
573
867
Summer Peak Population
910
1120
1658
1. Remaining development capacity: 118 lots (from RDC (Rob Bates) Growth Model).
2. Occupancy rate used for Growth Model is the Northern Region average of 2.59 people
per dwelling. Total permanent population in 2051 is not equal to 2.59 people per
dwelling due to lower occupancy per dwelling in Point Wells at 2006 census.
NB: Rates used for occupancy are 2.59 people per occupied dwelling. For unoccupied
dwellings, this is multiplied by a factor of 2 for expected summer occupancy. The
average permanent occupancy percentage of 65.7% is applied to all calculations.
In order to ensure that the future growth is aligned with the relevant nonstatutory documents, such as the LTCCP, it is prudent to present the projected
population growth for the next ten and twenty years. This ensures that forward
planning can be achieved from both a fiscal and engineering perspective. Table
27 below presents the projected permanent and summer peak populations for
Point Wells in 2016 and 2026 (2051 figures also listed for quick reference). As
with the calculations for the above table, the Low and High populations for each
timespan have been calculated from the growth predicted by the Moderate
projection (the RDC (Rob Bates) Model) and added to the 2006 census figures.
Table 27:
Year
Point Wells 2016 & 2026 Populations with Various Growth Scenarios
Growth
Scenario
Potential
Permanent
Population
(2.59 people per
dwelling, 92%
occupancy)
HARRISON GRIERSON CONSULTANTS LIMITED
Summer
Increase
(2 times average
occupancy of
unoccupied
dwellings)
Potential
Summer Peak
Population
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Rodney District Council
Mahurangi Wastewater Strategy
Table 27:
Year
2016
2026
2051
March 2008
HG Ref 1014-125641-01
Point Wells 2016 & 2026 Populations with Various Growth Scenarios
Growth
Scenario
Potential
Permanent
Population
Summer
Increase
Potential
Summer Peak
Population
(2.59 people per
dwelling, 92%
occupancy)
(2 times average
occupancy of
unoccupied
dwellings)
343
358
701
Low
1
Moderate
384
401
785
High
465
486
951
Low
366
382
748
1
Moderate
429
448
877
High
555
580
1135
Low
425
485
910
1
Moderate
547
573
1120
High
791
867
1658
1. Prediction from RDC (Rob Bates) Growth Model.
4.8
OMAHA
There is no Structure Plan for Omaha, so the Snells Algies methodology using
the RDC (Rob Bates) Model was used to assess population growth.
The
population projections for are as follows.
A summary of the census data regarding the total number of dwellings in
Omaha, also detailing the number of occupied and unoccupied dwellings, is
shown below in Table 28. The average percentage of permanent occupancy for
Omaha has been calculated using the total number of occupied and total
unoccupied dwellings.
It is assumed that the percentage of permanent
occupancy will be approximately equal throughout Omaha in future, so this
average percentage has been used for subsequent calculations.
Table 28:
Area
Omaha
Summary of 2006 Census Data for Omaha
Occupied
Dwellings
Unoccupied
Dwellings
Total
Dwellings
Percentage
Permanent
Occupancy (%)
156
591
747
20.88
Table 29 below presents the latest RDC (Rob Bates) Growth Model for Omaha,
which calculates only the number of occupied dwellings, however the number of
unoccupied dwellings (and thus the total number of dwellings) may be
calculated using the average percentage of permanent occupancy for the area.
The table shows that the total number of dwellings by 2051 will have reached
997, more than 100% of the proposed Ultimate Development Capacity.
HARRISON GRIERSON CONSULTANTS LIMITED
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Rodney District Council
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Table 29:
March 2008
HG Ref 1014-125641-01
Omaha 2051 Dwelling Statistics
Area
Omaha
Occupied
Dwellings1
Unoccupied
Dwellings2
Total Dwellings
(2051)
Ultimate
Development
373
1413
17863
997
1. The projected number of occupied dwellings is taken directly from the RDC (Rob
Bates) Growth Model. This is assumed to be equal to 20.9% (average permanent
occupancy rate of Omaha) of the total number of dwellings in 2051.
2. Exceeds Ultimate Development Capacity.
Table 30 below presents the 2051 projected normal (permanent) and peak
(summer) populations. For Omaha, the expected peak population over the peak
Christmas and New Year period is 8,275.
Table 30:
Area
Omaha Projected Permanent and Summer Populations (2051)
Total
Dwellings
Potential
Permanent
Population
Summer
Increase
Potential Total
Peak
Occupancy
Occupied plus
unoccupied
dwellings
2.59 people per
occupied
dwelling
Scale factor of 2
applied to
unoccupied
dwellings
Permanent plus
summer
population
1786
964
7311
8275
Omaha
Table 31 below presents the potential permanent and peak populations by 2051,
with ‘Low Growth’ based on 50% of the growth projected in the RDC (Rob
Bates) Growth Model, ‘Moderate Growth’ based on 100% of the growth
projected in the Growth Model, and ‘High Growth’ based on 200% of the growth
projected in the Growth Model, as described in Section 6.2.
The ‘Growth’
segment is shown because the final calculated figures for Low, Moderate and
High Growth are calculated from the ‘Growth’ segment figures, and added to the
2006 census data.
For Omaha, the Low Growth projection shows a peak population of 6,028, the
Moderate Growth projection shows a peak population of 8,275, and the High
Growth projection shows a peak population of 13,876. The very high increase in
population over the peak summer period is a result of the low permanent
occupancy rate of 20.9%, which means that in peak time, the population could
swell to more than four times its usual size (based on Moderate Growth). This
also accounts for the high difference between the Low, Moderate and High
Growth figures. In reality however, such a huge increase is unlikely because the
permanent occupancy rate will most likely rise as the area develops, leaving
fewer dwellings contributing to the summer influx.
Table 31:
Omaha Projected Permanent and Summer Populations with Various
Growth Scenarios
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HG Ref 1014-125641-01
Low
(50%)
Growth Scenario
2006
Census
Growth
Total Dwellings 2006
747
Permanent Population
354
Summer Increase
3058
Summer Peak Population
3412
High
(200%)
Total New Dwellings
565
1039
2258
Occupied Dwellings
118
217
472
Permanent Population
305
610
1220
Unoccupied Dwellings
447
822
1787
Summer Increase
2311
4253
9244
Summer Peak Population
2616
4863
10464
Total Dwellings 2051
Occupied Dwellings
Total
(2051)
Moderate
(100%)
1
1312
1786
3005
274
373
628
15742
2
Permanent Population
659
964
Unoccupied Dwellings
1038
1413
2378
Summer Increase
5369
7311
12302
Summer Peak Population
6028
8275
13876
1. Value exceeds Ultimate Development Capacity; remaining development capacity: 0
lots (from RDC (Rob Bates) Growth Model).
2. Occupancy rate used for Growth Model is the Northern Region average of 2.59 people
per dwelling. Total permanent population in 2051 is not equal to 2.59 people per
dwelling due to lower occupancy per dwelling in Omaha at 2006 census.
NB: Rates used for occupancy are 2.59 people per occupied dwelling. For unoccupied
dwellings, this is multiplied by a factor of 2 for expected summer occupancy. The
average permanent occupancy percentage of 20.88% is applied to all calculations.
In order to ensure that the future growth is aligned with the relevant nonstatutory documents, such as the LTCCP, it is prudent to present the projected
population growth for the next ten and twenty years. This ensures that forward
planning can be achieved from both a fiscal and engineering perspective. Table
32 below presents the projected permanent and summer peak populations for
Omaha in 2016 and 2026 (2051 figures also listed for quick reference). As with
the calculations for the above table, the Low and High populations for each
timespan have been calculated from the growth predicted by the Moderate
projection (the RDC (Rob Bates) Model) and added to the 2006 census figures.
Table 32:
Year
2016
Omaha 2016 & 2026 Populations with Various Growth Scenarios
Growth
Scenario
Potential
Permanent
Population
Summer
Increase
(2.59 people per
dwelling, 92%
occupancy)
(2 times average
occupancy of
unoccupied
dwellings)
437
3311
Low
HARRISON GRIERSON CONSULTANTS LIMITED
Potential
Summer Peak
Population
3748
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Mahurangi Wastewater Strategy
Table 32:
Year
2026
2051
March 2008
HG Ref 1014-125641-01
Omaha 2016 & 2026 Populations with Various Growth Scenarios
Growth
Scenario
Potential
Permanent
Population
Summer
Increase
Potential
Summer Peak
Population
(2.59 people per
dwelling, 92%
occupancy)
(2 times average
occupancy of
unoccupied
dwellings)
Moderate
5201
3940
4460
High
686
5197
5883
Low
497
3765
4262
1
Moderate
641
4856
5497
High
928
7031
7959
Low
659
5369
6028
1
Moderate
964
7311
8275
High
1574
12302
13876
1. Prediction from RDC (Rob Bates) Growth Model.
4.9
LEIGH
There is no Structure Plan for Leigh, so the Snells Algies methodology using the
RDC (Rob Bates) Model was used to assess population growth. The population
projections for are as follows.
A summary of the census data regarding the total number of dwellings in Leigh,
also detailing the number of occupied and unoccupied dwellings, is shown below
in Table 33. The percentage of permanent occupancy has been calculated for
each individual area in Leigh, and the average percentage of permanent
occupancy for Leigh has been calculated using the total number of occupied and
total unoccupied dwellings for the three smaller areas. It is thus assumed that
the percentage of permanent occupancy will be approximately equal throughout
Leigh in future, so this average percentage has been used for subsequent
calculations.
Table 33:
Summary of 2006 Census Data for Leigh
Area
Occupied
Dwellings
Unoccupied
Dwellings
Total
Dwellings
Percentage
Permanent
Occupancy
(%)
Leigh/Whangateau
Rural
159
87
246
64.6
54
141
195
27.7
Leigh Town
165
111
276
59.8
Total
378
339
717
52.72
Matheson Bay
Town
HARRISON GRIERSON CONSULTANTS LIMITED
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HG Ref 1014-125641-01
Table 34 below presents the latest RDC (Rob Bates) Growth Model for Leigh,
which calculates only the number of occupied dwellings, however the number of
unoccupied dwellings (and thus the total number of dwellings) may be
calculated using the average percentage of permanent occupancy for the area.
The table shows that the total number of dwellings by 2051 will have reached
1210, 87.0% of the proposed Ultimate Development Capacity.
Table 34:
Leigh 2051 Dwelling Statistics
Area
Occupied
Dwellings1
Unoccupied
Dwellings2
Total Dwellings
(2051)
Ultimate
Development
Leigh/Whangat
eau Rural
298
267
565
700
Matheson Bay
Town
90
81
171
195
Leigh Town
250
224
474
496
Average
638
572
1210
1391
1. The projected number of occupied dwellings is taken directly from the RDC (Rob
Bates) Growth Model. This is assumed to be equal to 52.7% (average permanent
occupancy rate for Leigh) of the total number of dwellings in 2051.
2. The percentage of unoccupied dwellings is assumed to remain stable at an average of
47.3% for the area. Thus the number of unoccupied dwellings may be calculated by
dividing the number of occupied dwellings by 52.7%, and multiplying by 47.3%.
Table 35 below presents the 2051 projected normal (permanent) and peak
(summer) populations. For Leigh, the expected peak population over the peak
Christmas and New Year period is 4,614.
Table 35:
Leigh Projected Permanent and Summer Populations (2051)
Total
Dwellings
Potential
Permanent
Population
Summer
Increase
Potential
Total Peak
Occupancy
Occupied plus
unoccupied
dwellings
2.59 people
per occupied
dwelling
Scale factor of
2 applied to
unoccupied
dwellings
Permanent plus
summer
population
Leigh/Whangateau
Rural
565
772
1383
2155
Matheson Bay
Town
171
234
418
652
Leigh Town
474
648
1160
1808
1210
1654
2960
4614
Area
TOTAL
Table 36 below presents the potential permanent and peak populations by 2051,
with ‘Low Growth’ based on 50% of the growth projected in the RDC (Rob
Bates) Growth Model, ‘Moderate Growth’ based on 100% of the growth
projected in the Growth Model, and ‘High Growth’ based on 200% of the growth
HARRISON GRIERSON CONSULTANTS LIMITED
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March 2008
HG Ref 1014-125641-01
projected in the Growth Model, as described in Section 6.2.
The ‘Growth’
segment is shown because the final calculated figures for Low, Moderate and
High Growth are calculated from the ‘Growth’ segment figures, and added to the
2006 census data.
For Leigh, the Low Growth projection shows a peak population of 3,702, the
Moderate Growth projection shows a peak population of 4,614, and the High
Growth projection shows a peak population of 6,812.
Table 36:
Leigh Projected Permanent and Summer Populations with Various
Growth Scenarios
Growth Scenario
2006
Census
Growth
Moderate
(100%)
Total Dwellings 2006
717
Permanent Population
912
Summer Increase
1754
Summer Peak Population
2666
High
(200%)
Total New Dwellings
272
493
1088
Occupied Dwellings
143
260
574
Permanent Population
371
742
1484
Unoccupied Dwellings
129
233
514
Summer Increase
665
1206
2662
1036
1948
4146
Summer Peak Population
Total
(2051)
Low
(50%)
1
Total Dwellings 2051
989
1210
Occupied Dwellings
521
638
952
2
1805
Permanent Population
1283
1654
23962
Unoccupied Dwellings
468
572
853
Summer Increase
2419
2960
4416
Summer Peak Population
3702
4614
6812
1. Remaining development capacity: 181 lots (from RDC (Rob Bates) Growth Model).
2. Occupancy rate used for Growth Model is the Northern Region average of 2.59 people
per dwelling. Total permanent population in 2051 is not equal to 2.59 people per
dwelling due to lower occupancy per dwelling in Leigh at 2006 census.
NB: Rates used for occupancy are 2.59 people per occupied dwelling. For unoccupied
dwellings, this is multiplied by a factor of 2 for expected summer occupancy. The
average permanent occupancy percentage of 52.7% is applied to all calculations.
In order to ensure that the future growth is aligned with the relevant nonstatutory documents, such as the LTCCP, it is prudent to present the projected
population growth for the next ten and twenty years. This ensures that forward
planning can be achieved from both a fiscal and engineering perspective. Table
37 below presents the projected permanent and summer peak populations for
Leigh in 2016 and 2026 (2051 figures also listed for quick reference). As with
the calculations for the above table, the Low and High populations for each
HARRISON GRIERSON CONSULTANTS LIMITED
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Rodney District Council
Mahurangi Wastewater Strategy
March 2008
HG Ref 1014-125641-01
timespan have been calculated from the growth predicted by the Moderate
projection (the RDC (Rob Bates) Model) and added to the 2006 census figures.
Table 37:
Year
2016
2026
2051
Leigh 2016 & 2026 Populations with Various Growth Scenarios
Growth
Scenario
Potential
Permanent
Population
Summer
Increase
Potential
Summer Peak
Population
(2.59 people per
dwelling, 92%
occupancy)
(2 times average
occupancy of
unoccupied
dwellings)
1015
1820
2835
Low
1
Moderate
1118
2005
3123
High
1324
2374
3698
Low
1088
1951
3039
1
Moderate
1264
2267
3531
High
1616
2898
4514
Low
1283
2419
3702
1
Moderate
1654
2960
4614
High
2396
4416
6812
1. Prediction from RDC (Rob Bates) Growth Model.
4.10
MAHURANGI EAST
There is no Structure Plan for Mahurangi East, so the Snells Algies methodology
using the RDC (Rob Bates) Model was used to assess population growth. The
population projections for are as follows.
A summary of the census data regarding the total number of dwellings in
Mahurangi East, also detailing the number of occupied and unoccupied
dwellings, is shown below in Table 38. The average percentage of permanent
occupancy for Mahurangi East has been calculated using the total number of
occupied and total unoccupied dwellings. It is assumed that the percentage of
permanent occupancy will be approximately equal throughout Mahurangi East in
future, so this average percentage has been used for subsequent calculations.
Table 38:
Summary of 2006 Census Data for Mahurangi East
Area
Occupied
Dwellings
Unoccupied
Dwellings
Total
Dwellings
Percentage
Permanent
Occupancy (%)
Mahurangi East
144
144
288
50.00
Table 39 below presents the latest RDC (Rob Bates) Growth Model for Mahurangi
East, which calculates only the number of occupied dwellings, however the
number of unoccupied dwellings (and thus the total number of dwellings) may
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Mahurangi Wastewater Strategy
March 2008
HG Ref 1014-125641-01
be calculated using the average percentage of permanent occupancy for the
area.
The table shows that the total number of dwellings by 2051 will have reached
700, 100% of the proposed Ultimate Development Capacity.
Table 39:
Mahurangi East 2051 Dwelling Statistics
Area
Occupied
Dwellings1
Unoccupied
Dwellings2
Total Dwellings
(2051)
Ultimate
Development
Mahurangi East
397
397
7943
700
1. The projected number of occupied dwellings is taken directly from the RDC (Rob
Bates) Growth Model. This is assumed to be equal to 50.0% (average permanent
occupancy rate for Mahurangi East) of the total number of dwellings in 2051.
2. The percentage of unoccupied dwellings is assumed to remain stable at an average of
50.0% for the area. Thus the number of unoccupied dwellings may be calculated by
dividing the number of occupied dwellings by 50.0%, and multiplying by 50.0%.
3. Exceeds Ultimate Development Capacity.
Table 40 below presents the 2051 projected normal (permanent) and peak
(summer) populations. For Mahurangi East, the expected peak population over
the peak Christmas and New Year period is 3,080.
Table 40:
Mahurangi East Projected Permanent and Summer Populations
(2051)
Area
Total
Dwellings
Potential
Permanent
Population
Summer
Increase
Potential Total
Peak
Occupancy
Occupied plus
unoccupied
dwellings
2.59 people per
occupied
dwelling
Scale factor of 2
applied to
unoccupied
dwellings
Permanent plus
summer
population
794
1026
2054
3080
Mahurangi East
Table 41 below presents the potential permanent and peak populations by 2051,
with ‘Low Growth’ based on 50% of the growth projected in the RDC (Rob
Bates) Growth Model, ‘Moderate Growth’ based on 100% of the growth
projected in the Growth Model, and ‘High Growth’ based on 200% of the growth
projected in the Growth Model, as described in Section 6.2.
The ‘Growth’
segment is shown because the final calculated figures for Low, Moderate and
High Growth are calculated from the ‘Growth’ segment figures, and added to the
2006 census data.
For Mahurangi East, the Low Growth projection shows a peak population of
2,124, the Moderate Growth projection shows a peak population of 3,080, and
the High Growth projection shows a peak population of 5,296.
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Mahurangi Wastewater Strategy
Table 41:
Mahurangi East Projected Permanent and Summer Populations with
Various Growth Scenarios
Growth Scenario
2006
Census
March 2008
HG Ref 1014-125641-01
Low
(50%)
Total Dwellings 2006
288
Permanent Population
321
Summer Increase
745
Summer Peak Population
Growth
Total
(2051)
Moderate
(100%)
High
(200%)
1066
Total New Dwellings
273
506
1090
Occupied Dwellings
136
253
545
Permanent Population
353
705
1410
Unoccupied Dwellings
136
253
545
Summer Increase
705
1309
2820
Summer Peak Population
1058
2014
4230
Total Dwellings 2051
561
7941
1378
Occupied Dwellings
280
397
689
2
Permanent Population
674
1026
17312
Unoccupied Dwellings
280
397
689
Summer Increase
1450
2054
3565
Summer Peak Population
2124
3080
5296
1. Exceeds Ultimate Development Capacity; remaining development capacity: 0 lots
(from RDC (Rob Bates) Growth Model).
2. Occupancy rate used for Growth Model is the Northern Region average of 2.59 people
per dwelling. Total permanent population in 2051 is not equal to 2.59 people per
dwelling due to lower occupancy per dwelling in Mahurangi East at 2006 census.
NB: Rates used for occupancy are 2.59 people per occupied dwelling. For unoccupied
dwellings, this is multiplied by a factor of 2 for expected summer occupancy. The
average permanent occupancy percentage of 50.0% is applied to all calculations.
In order to ensure that the future growth is aligned with the relevant nonstatutory documents, such as the LTCCP, it is prudent to present the projected
population growth for the next ten and twenty years. This ensures that forward
planning can be achieved from both a fiscal and engineering perspective. Table
42 below presents the projected permanent and summer peak populations for
Mahurangi East in 2016 and 2026 (2051 figures also listed for quick reference).
As with the calculations for the above table, the Low and High populations for
each timespan have been calculated from the growth predicted by the Moderate
projection (the RDC (Rob Bates) Model) and added to the 2006 census figures.
Table 42:
Mahurangi East 2016 & 2026 Populations with Various Growth
Scenarios
HARRISON GRIERSON CONSULTANTS LIMITED
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Mahurangi Wastewater Strategy
Year
Growth
Scenario
2016
March 2008
HG Ref 1014-125641-01
Potential
Permanent
Population
2051
Potential
Summer Peak
Population
(2.59 people per
dwelling, 92%
occupancy)
(2 times average
occupancy of
unoccupied
dwellings)
423
846
1269
Low
2026
Summer
Increase
1
Moderate
525
1050
1575
High
729
1458
2187
Low
497
994
1491
Moderate
1
673
1346
2019
High
1025
2050
3075
Low
674
1450
2124
Moderate
10261
2054
3080
High
1731
3565
5296
1. Prediction from RDC (Rob Bates) Growth Model.
4.11
TOTAL POTENTIAL POPULATION 2051
Table 43 below provides a summary of occupied and unoccupied dwellings from
2006 census data for the entire Mahurangi East area, inclusive of Warkworth.
Table 43:
Summary of 2006 Census Data for Mahurangi East Area
Occupied
Dwellings
Unoccupied
Dwellings
Total
Dwellings
Percentage
Permanent
Occupancy
(%)
Warkworth Central
678
51
729
93.0
Warkworth North
348
27
375
92.8
Warkworth South
312
33
345
90.4
Snells Beach
516
156
672
76.8
Snells Beach South
609
153
762
79.9
Algies Bay
246
183
429
57.3
Sandspit
156
42
198
78.8
Matakana
105
30
135
77.8
Matakana Valley
348
87
435
80.0
39
12
51
76.5
Point Wells
132
69
201
65.7
Omaha
156
591
747
20.9
Leigh/Whangateau
Rural
159
87
246
64.6
54
141
195
27.7
Leigh Town
165
111
276
59.8
Mahurangi East
144
144
288
50.0
4167
1917
6084
68.49
Area
Rainbows End
Matheson Bay Town
Total
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HG Ref 1014-125641-01
From the above table it is clear that there is wide variation between
communities in terms of their permanent ocupancy rates. It is expected that in
bach communities such as Omaha and Matheson Bay Town, with a large
proportion of unoccupied dwellings, the percentage of permanent occupancy will
increase as the areas develop, and there may be less of a hike in population
over the peak summer period. However, this trend is difficult to quantify, and
so has not been modelled in this report.
Areas with a higher permanent
occupancy rate, such as Warkworth and Matakana Valley, are likely to remain
stable with similar occupancy rates as at present.
Table 44 below presents the latest RDC (Rob Bates) Growth Model for the total
Mahurangi East area, which calculates only the number of occupied dwellings,
however the number of unoccupied dwellings (and thus the total number of
dwellings) may be calculated using the average percentage of permanent
occupancy for the area.
The table shows that the total number of dwellings by 2051 will have reached
9,814, 84.0% of the proposed Ultimate Development Capacity.
Table 44:
Mahurangi East Area 2051 Dwelling Statistics
Area
Occupied
Dwellings1
Unoccupied
Dwellings2
Total Dwellings
(2051)
Ultimate
Development
Warkworth Central
1470
122
1592
2421
Warkworth North
385
32
417
430
Warkworth South
602
50
652
949
Snells Beach
663
238
840
840
Snells Beach
South
747
268
913
913
Algies Bay
444
159
622
681
Sandspit
297
80
377
466
Matakana
375
98
473
700
Matakana Valley
508
133
641
700
45
12
57
51
Point Wells
212
111
323
441
Omaha
373
1413
997
997
Leigh/Whangateau
Rural
298
267
565
700
90
81
171
195
250
224
474
496
Rainbows End
Matheson Bay
Town
Leigh Town
Mahurangi East
Total
397
397
700
700
7156
3686
9814
11680
1. The projected number of occupied dwellings is taken directly from the RDC (Rob
Bates) Growth Model. This is assumed to be equal to 68.5% (average permanent
occupancy rate) of the total number of dwellings in 2051.
2. The percentage of unoccupied dwellings is that of each individual town; refer to
appropriate section for details.
HARRISON GRIERSON CONSULTANTS LIMITED
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HG Ref 1014-125641-01
Table 45 below presents the 2051 projected normal (permanent) and peak
(summer) populations. For the Mahurangi East area, the potential permanent
population as per the RDC (Rob Bates) Growth Model is 18,510, and the
expected peak population over the Christmas and New Year period is 35,568.
Table 45:
Mahurangi East Area Projected Permanent and Summer Populations
(2051)
Total
Dwellings
Potential
Permanent
Population
Summer
Increase
Potential
Total Peak
Occupancy
Occupied plus
unoccupied
dwellings
2.59 people
per occupied
dwelling
Scale factor of
2 applied to
unoccupied
dwellings
Permanent plus
summer
population
1592
3802
630
4432
Warkworth North
417
997
165
1162
Warkworth South
652
1556
258
1814
Snells Beach
840
1715
1230
2945
Snells Beach
South
913
1933
1386
3319
Algies Bay
622
1148
824
1972
Sandspit
377
768
413
1181
Matakana
473
971
508
1479
Matakana Valley
641
1314
689
2003
57
115
61
176
Point Wells
323
547
573
1120
Omaha
997
964
7310
8274
Leigh/Whangateau
Rural
565
772
1382
2154
Matheson Bay
Town
171
234
417
651
Leigh Town
474
648
1159
1807
Mahurangi East
700
1026
2053
3079
9814
18510
19058
37568
Area
Warkworth
Central
Rainbows End
TOTAL
As shown is Table 45 above, there are large fluctuations between the potential
permanent and summer populations, due to low permanent occupancy rates in
many communities.
In addition, there are further fluctuations based on the
growth scenario (low, medium or high), as shown in Table 46 below.
Table 46:
Mahurangi East Area Projected Permanent and Summer Populations
with Various Growth Scenarios
Growth Scenario
HARRISON GRIERSON CONSULTANTS LIMITED
Low
(50%)
Moderate
(100%)
High
(200%)
Page 34
Rodney District Council
Mahurangi Wastewater Strategy
Table 46:
March 2008
HG Ref 1014-125641-01
Mahurangi East Area Projected Permanent and Summer Populations
with Various Growth Scenarios
Low
(50%)
Growth Scenario
2006
Census
Total Dwellings 2006
6084
Permanent Population
10257
Summer Increase
Total
(2051)
High
(200%)
9918
Summer Peak Population
Growth
Moderate
(100%)
20175
Total New Dwellings
2329
3730
9316
Occupied Dwellings
1595
2989
6381
Permanent Population
4127
8253
16506
Unoccupied Dwellings
734
2957
2935
Summer Increase
3797
15296
15187
Summer Peak Population
7923
23549
31693
Total Dwellings 2051
8413
98141
15400
Occupied Dwellings
5762
7156
10548
2
Permanent Population
14384
18510
267632
Unoccupied Dwellings
2651
3686
4852
Summer Increase
13715
19058
25105
Summer Peak Population
28098
37568
51868
1. Some areas exceed their Ultimate Development Capacity but are still counted towards
total dwellings. Remaining development capacity: 1866 lots (from RDC (Rob Bates)
Growth Model).
2. Occupancy rate used for Growth Model is the Northern Region average of 2.59 people
per dwelling. Total permanent population in 2051 is not equal to 2.59 people per
dwelling due to overall lower occupancy per dwelling throughout the Mahurangi East
area at 2006 census.
NB: Rates used for occupancy are 2.59 people per occupied dwelling. For unoccupied
dwellings, this is multiplied by a factor of 2 for expected summer occupancy. The
average permanent occupancy percentage for Mahurangi East (68.5%) is applied to Low
and High Growth calculations.
Given that the Moderate Growth scenario is based on the RDC (Rob Bates)
Growth Model, it would be prudent to assume that the potential permanent
population would be around 23,000, being approximately halfway between the
Moderate Growth scenario potential permanent population and the High Growth
scenario potential permanent population. The potential peak population (likely
to occur for only 14 days of the year, around Christmas and New Year) may be
estimated at between 30,000 and 40,000.
From the RDC (Rob Bates) growth model, there are still 1,866 allotments
available
for
development
beyond
2051,
based
on
land
available
for
development in the relevant Structure Plans, despite some areas having reached
their Ultimate Development Capacity.
Using the average occupancy of the
Northern (Rodney) Ward of 2.59 persons/household, this would potentially add a
further 4,851 people to the Moderate Growth scenario, equating to a potential
HARRISON GRIERSON CONSULTANTS LIMITED
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HG Ref 1014-125641-01
permanent population of 23,361.
Thus the High Growth scenario of 15,400
dwellings (with a potential permanent population of 26,763) exceeds the current
Structure Plans.
Finally, private plan changes resulting in developments outside the current
structure plan could provide the balance of growth to meet the High Growth
scenario.
4.12
2016 AND 2026 PROJECTED POPULATION
As the LTCCP is based around 10-year funding cycles, it is important to present
the projected population increases to 2016 and to 2026. From the RDC (Rob
Bates)
Growth
Model,
the
projected
Low,
Moderate,
and
High
Growth
development of the Mahurangi East area is presented in Table 47. To provide
the correct information for the input of the next LTCCP and for quick reference,
the projected population up to 2051 is also presented. As with the calculations
for Table 46 above, the Low and High populations for each timespan have been
calculated from the growth predicted by the Moderate Growth projection (from
the RDC (Rob Bates) Model) and added to the 2006 census figures.
Table 47:
Year
2016
2016 & 2026 Populations with Various Growth Scenarios for
Mahurangi East Area
Growth
Scenario
Potential
Permanent
Population
(2 times average
occupancy of
unoccupied
dwellings)
11400
10488
21888
11541
24085
Low
12544
1
High
14831
13645
28476
Low
12208
11232
23440
13027
27186
Moderate
2051
Potential
Summer Peak
Population
(2.59 people per
dwelling, 92%
occupancy)
Moderate
2026
Summer
Increase
14159
1
High
18061
16617
34678
Low
14384
56634
71018
19068
37578
161860
188623
Moderate
High
18510
1
26763
1. Prediction from RDC (Rob Bates) Growth Model.
HARRISON GRIERSON CONSULTANTS LIMITED
Page 36
Rodney District Council
Mahurangi Wastewater Strategy
5.0
March 2008
HG Ref 1014-125641-01
SNELLS-ALGIES WASTEWATER OUTFALL CONDITION REPORT
A report was prepared by Opus International Consultants Limited ("OIC") in
August 2007 which outlined the condition of the Outfall Pipeline to Martins Bay.
This report recognises that with the upgrade of the pipeline, any renewal will
require specific consideration to population growth and any long-term strategy
that may have an impact on the sewage disposal options for the whole of the
Rodney District. OIC made the following conclusions regarding the condition of
the pipeline:
•
The long-term design capacity for the effluent pipeline is the most
important issue and a replacement pipe size is essential before any
pipeline sections are renewed.
•
The AC (Asbestos Cement) pipe from Te Whau estuary to beyond Dawson
Road should be replaced without delay, especially through the Lifeway
property.
•
Condition of the CLMS (Concrete Lined Mild Steel) pipes across the Te
Whau Estuary and the gully crossings is needed to determine if these pipes
can be incorporated in the long-term solution.
•
The outfall section of the main is no longer a restriction and 35L/s can be
safely accommodated without risk of overflowing the terminal manhole.
•
The diffusers on the outfall end of the steel pipe need to be replaced.
•
Planning for renewal of the DN200 Class A AC pipe inside the cliff and
across the beach to the steel outfall pipe should start without delay, with
pipe replacement completed within two years.
•
At any areas where pipe joint pull-out failure has occurred in the past the
existing PVC (or AC) pipe should be replaced with continuously fusion
welded PE 100.
•
Any AC pipe sections installed from Ridge Road to the coast should be
replaced when they are at risk of failure, a proportion of this may be
delayed until 2020.
•
The DN 200 "Garnite" PVC pipes currently installed in areas where joint
pull-out has not occurred can remain in service until 2050 or until more
capacity is needed.
•
Increasing the pumping capacity from 27 to 35L/s should be possible when
the vulnerable sections of the rising main pipeline to Ridge Road have
been renewed.
HARRISON GRIERSON CONSULTANTS LIMITED
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Rodney District Council
Mahurangi Wastewater Strategy
March 2008
HG Ref 1014-125641-01
The OIC report states that continuous pumping of 35L/s is possible through
some of the existing infrastructure and with the upgrade of the existing
(deteriorating) infrastructure.
This equates to 3024m3/day (based on 24/7
discharge), or if the population is producing 200L/day, provides the capacity for
a population of 15,120 persons.
From the RDC (Rob Bates) Growth Model and utilising the existing data for the
average household size (varies according to different meshblocks), the total
potential population for Snells Algies and Sandspit is 5,564 people. This means
that if the pipeline is upgraded to the standard as outlined by OIC, then there is
easily the capacity to accommodate the growth of the Snells Algies area.
Given that future consent conditions may limit discharges to an outgoing tide
(similar to the Auckland-Mangere WWTP), there would be a reduction in pipeline
utilisation by approximately 55-60% (i.e. only 9-10 hours/day).
Thus future
Resource Consent conditions may significantly reduce the volumes which can be
discharged.
There would however, be the requirement to replace the concrete asbestos
pipeline for the majority of the way from Snells Algies to Martins Bay which is in
relatively poor condition. It has been recognised that the pipeline through the
'Lifeways property’ is in a state of disrepair, and requires replacement.
A
meeting held at Council with various stakeholders on the 14th December
resolved that a larger diameter pipe (which can handle the load from SnellsAlgies and Warkworth [High Growth scenario]) would be installed through this
property.
6.0
RODNEY DISTRICT COUNCIL LTCCP (2006-2016)
This document provides the general outline for presently allocated funding for
infrastructure upgrades which have been planned and accounted for (as at
2006) for the next 10 years.
The desired water services contribution is that "by ensuring adequate
wastewater collection and treatment systems are available to all residents and
that there is sufficient capacity within the wastewater systems for future
development" and "by providing adequate infrastructure as a key requirement
for business".
Within the water services planning within the LTCCP there are the following
assumptions:
•
That the average household size will be 2.5-2.6 people;
•
The average wastewater production will be 200 litres per person each day;
and
HARRISON GRIERSON CONSULTANTS LIMITED
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Rodney District Council
Mahurangi Wastewater Strategy
•
March 2008
HG Ref 1014-125641-01
That regulatory framework will require greater emphasis on water quality
treatment.
Table 48 below illustrates the wastewater infrastructure Operating Expenditure
for the whole Rodney District for the next ten years.
Table 48:
Operating Expenditure - Wastewater 2006-2016 ($000)
06/07
07/08
08/09
09/10
10/11
11/12
12/13
13/14
14/15
15/16
Total
14,741
16,162
17,461
18,598
19,802
20,988
21,825
22,292
22,590
22,852
197,311
For the purposes of this study, Table 49 below illustrates a better scenario for
the areas of interest.
HARRISON GRIERSON CONSULTANTS LIMITED
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Rodney District Council
Mahurangi Wastewater Strategy
March 2008
HG Ref 1014-125641-01
Table 49:
Situation
Rural
&
Townships
(Total)
–
Significant
growth is being
catered for in
Warkworth,
Snells/Algies
and
Matakana
with
major
upgrades to the
the
treatment
plants. Also, it’s
planned
to
expand services
to
un-serviced
areas at Point
Wells
and
Martins Bay
Warkworth
Service
new
developments
and
achieve
Resource
Consent
Proposed
Action
Cost
How it will be
funded
Sample projects
during the first 3
years
Boost
Capacity
and/or
increase
level of
service
$50.0m
Financial
Contributions,
connection
charges, rates,
subsidies and
loans
Renew
Existing
assets
$7.2m
Depreciation
Replace plant, pumps,
electrics and pipelines
as needed.
Boost
capacity
and/or
increase
level of
service
$6.6m
Financial
contributions,
connection
charges, rates,
subsidies and
loans
Warkworth wastewater
treatment plant system
upgrading including:
Wastewater treatment
plant upgrade
Flow balancing
Upgrading reticulation
to prevent overflows
McKinny/Woodcocks
low pressure trunk
main
Pulham Road gravity
main
Snells Beach /
Algies Bay
Upgrade to cope
with growth in
the area
Renew
Existing
Assets
$1.6m
Depreciation
Replace plant, pumps,
electrics and pipelines
as needed.
Boost
Capacity
and or
increase
level of
service
$4.0m
Financial
contributions,
connection
charges, rates,
subsidies and
loans
Snells/Algies - prepare
for wastewater
treatment plant
upgrade
Renew
Existing
Assets
$1.3m
Depreciation
Replace plant, pumps,
electrics and pipelines
as needed.
HARRISON GRIERSON CONSULTANTS LIMITED
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Rodney District Council
Mahurangi Wastewater Strategy
March 2008
HG Ref 1014-125641-01
Table 49:
Situation
Proposed
Action
Matakana
Current system
is
at
100%
capacity,
with
population
expected
to
double in next
10 years. The
council is aiming
to link Matakana
with
Omaha
WWTP
Install new
collection
system and
transfer
Matakana
wastewater
to Omaha
WWTP
Additional
land
purchase at
Omaha
WWTP to
cater for
Matakana
Renew
Existing
Assets
Omaha - The
plant
will
be
upgraded
with
the ability to
serve
Point
Wells
and
Matakana.
Install new
collection
system and
transfer to
Omaha
WWTP
WWTP
Algae
control in
Dam
Renew
Existing
Assets
Cost
$3.0m
Financial
contributions,
connection
charges, rates,
subsidies and
loans
$1.3m
Sample projects
during the first 3
years
New transfer main
from Matakana to
Omaha - 2008/09
Retro-fit existing
reticulation with low
pressure system 2008/09
$0.54m
Depreciation
Replace plant, pumps,
electrics and pipelines
as needed.
$3.6m
Primarily
contributions
New low pressure
collection system and
transfer from Pt Wells
to Omaha by June
2009
$0.4m
Rates and
development
contributions
$0.69m
TOTAL
EXPENDITURE
RURAL
$57.2m
TOTAL
EXPENDITURE
WARKWORTH/
SNELLS
ALGIES
$13.5m
TOTAL
EXPENDITURE
MATAKANA /
OMAHA
$9.53m
TOTAL
How it will be
funded
Depreciation
WWTP algae control in
dam.
Replace plant, pumps,
electrics and pipelines
as needed.
$80.23m
The above table is expenditure planned only for the next ten years. If growth
exceeds the anticipated 10-year growth, then there may be the requirement to
update the infrastructure prior to the stated timeframes, and conversely if the
development is slower, the development may not occur at the same rate.
HARRISON GRIERSON CONSULTANTS LIMITED
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Rodney District Council
Mahurangi Wastewater Strategy
6.1
March 2008
HG Ref 1014-125641-01
DEVELOPMENT CONTRIBUTIONS
The present development contributions for sewerage only are shown in Table 50
below.
Table 50:
Wastewater Development Contributions
Area
Household Unit Contribution
Matakana
$13768
Omaha
$3921
Snells Beach-Algies Bay
$5603
Warkworth
$6811
Based on the population projections and additional capacity for the following
areas, development contributions will provide approximately $35m for the next
50 years, as shown in Tables 51-53 below.
Table 51:
10 Year Development Contribution based on projected household
units
Area
Current HH Unit
Contribution
Matakana
Omaha
Snells Beach-Algies Bay
Number of
New HH
Units
(2016)
Total
$13,768
63
$867,384
$3,921
45
$176,445
$5,603
113
$633,139
Sandspit
$6,000 (est.)
33
$198,000
Leigh
$6,000 (est.)
18
$108,000
Point Wells
$6,000 (est.)
17
$102,000
Mahurangi East
$6,000 (est.)
59
$354,000
261
$1,777,671
609
$4,216,639
Warkworth
$6,811
TOTAL
Table 52:
20 Year Development Contribution based on projected household
units (2016-2026)
Area
Matakana
Current HH Unit
Contribution
Number of
New HH
Units (2016)
Total
$13,768
61
$839,848
Omaha
$3,921
47
$184,287
Snells Beach-Algies Bay
$5,603
110
$616,330
Sandspit
$6,000 (est.)
32
$192,000
Leigh
$6,000 (est.)
18
$108,000
Point Wells
$6,000 (est.)
17
$102,000
Mahurangi East
$6,000 (est.)
Warkworth
HARRISON GRIERSON CONSULTANTS LIMITED
$6,811
57
$342,000
255
$1,736,805
Page 42
Rodney District Council
Mahurangi Wastewater Strategy
Table 52:
March 2008
HG Ref 1014-125641-01
20 Year Development Contribution based on projected household
units (2016-2026)
Area
Current HH Unit
Contribution
Number of
New HH
Units (2016)
TOTAL
Table 53:
Total
$4,121,270
50 Year Development Contribution based on projected household
units
Area
Current HH Unit
Contribution
Matakana
Number of
New HH
Units
(20082051)
Total
$13,768
565
$7,778,920
Omaha
$3,921
250
$980,250
Snells Beach-Algies Bay
$5,603
597
$3,344,991
Sandspit
$6,000 (est.)
270
$1,620,000
Leigh
$6,000 (est.)
220
$1,320,000
Point Wells
$6,000 (est.)
303
$1,818,000
Mahurangi East
$6,000 (est.)
Warkworth
$6,811
TOTAL
412
2,472,000
2351
$16,012,661
4028
$35,346,822
The above calculations do not include inflation, which would be expected to be in
the vicinity of 2% per annum and has been calculated based on the maximum
number of dwellings at the moderate growth rate from the RDC (Rob Bates)
Growth Model.
As illustrated in the 2008-2016 and 2016-2026 tables,
development contributions do not provide a significant budget for wastewater
capital expenditure over the next ten years for all these communities.
7.0
TRANSIT NZ - RODNEY DISTRICT COUNCIL MEMORANDUM OF
UNDERSTANDING
The memorandum of understanding ("MOU") between Transit New Zealand and
the Rodney District Council demonstrates the future road growth required for
the adequate provision of roading in the Warkworth area.
The MOU has a
relatively finite life out to 2021, which is less than the present study of the area
to 2051. It is noted that within the MOU there is a statement which forecasts
traffic growth at 110% of the present traffic volumes. This effectively doubles
and it is assumed that the vast majority of this traffic is generated from
population increases.
As the MOU from Transit constrains the road at
Warkworth to other areas within the Mahurangi region, it is considered that this
growth for 20 years is consistent with that presented in the growth model
prepared by Rob Bates.
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8.0
March 2008
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CONCLUSION
The RDC (Rob Bates) growth model has been used as the basis for the future
demand drivers and is presented as a Moderate Growth case.
A sensitivity
analysis was carried out on the RDC (Rob Bates) Growth Model: a High Growth
model with an additional 100% growth, and a Low Growth model of only 50%
growth compared to the Moderate case.
Under the Moderate Growth Model, there are still 1,866 allotments available for
development beyond 2051, based on land available for development in the
relevant Structure Plans, despite some areas having reached their Ultimare
Development Capacity under Moderate Growth (namely Snells Beach, Snells
Beach South, Omaha and Mahurangi East). Thus the Moderate Growth scenario
can be catered for within the current Structure Plans, but not High Growth
(which requires an extra 5,586 lots above Moderate Growth).
The permanent population in the Mahurangi East region is projected to grow
significantly in the future, and at this stage it is recommended to provide
infrastructure for approximately 23,000 people in this region. If growth exceeds
that in the RDC (Rob Bates) Growth Model, it may be necessary to provide
infrastructure for 26,000 to 51,000 people in this region.
9.0
LIMITATIONS
9.1
GENERAL
This report is for the use by Rodney District Council only, and should not be
used or relied upon by any other person or entity or for any other project.
This report has been prepared for the particular project described to us and its
extent is limited to the scope of work agreed between the client and Harrison
Grierson Consultants Limited. No responsibility is accepted by Harrison Grierson
Consultants Limited or its directors, servants, agents, staff or employees for the
accuracy of information provided by third parties and/or the use of any part of
this report in any other context or for any other purposes.
HARRISON GRIERSON CONSULTANTS LIMITED
Page 44
APPENDIX 1
Planning Area Unit Map (Mahurangi East)
DRAWINGS
Appendix 5.3
Mahurangi Wastewater Master Plan –
Treatment and Disposal
Infrastructure Constraints Assessment
(April 2009)
RODNEY DISTRICT COUNCIL
Mahurangi Wastewater Master Plan
Treatment and Disposal Infrastructure
Constraints Assessment
April 2009
HG Ref 1014-125641-01
Doc Ref R004v2-AK125641-01-ich
HARRISON GRIERSON CONSULTANTS LIMITED
Document Control Record
Client
RODNEY DISTRICT COUNCIL
Project
Mahurangi Wastewater Master Plan
HG Ref.
1014-125641-01
Doc Ref.
R004v2-AK125641-01
Document
Treatment and Disposal Infrastructure Constraints
Assessment
ISSUE AND REVISION RECORD
Date of Issue
April 2009
Status
Final
Originator
Ian Ho - Process Engineer
Reviewed
Ash Deshpande - Associate/Lead Process Engineer
Approved for Issue
Stephen Finnemore - Senior Principal
Office of Origin
Auckland
Telephone
09 917 5000
Facsimile
09 917 5001
Email
[email protected]
HARRISON GRIERSON CONSULTANTS LIMITED
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RODNEY DISTRICT COUNCIL
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Treatment and Disposal Infrastructure Constraints
Assessment
April 2009
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Doc Ref R004v2-AK125641-01
CONTENTS
Page
EXECUTIVE SUMMARY
III
PROJECT SCOPE
1
1.0
INTRODUCTION
1
1.1
METHODOLOGY
2
1.2
STUDY AREA
3
2.0
CONNECTED POPULATION PROJECTION
4
3.0
WASTEWATER FLOW AND LOADS PROJECTION
9
3.1
COMPARING WITH CURRENT FLOW AND LOAD DATA
9
3.2
WASTEWATER FLOW AND LOADS PROJECTION TABLES
4.0
CURRENT AND
CONDITIONS
LIKELY
FUTURE
RESOURCE
10
CONSENT
19
4.1
CURRENT RESOURCE CONSENT CONDITIONS
19
4.2
LIKELY FUTURE RESOURCE CONSENT CONDITIONS
20
5.0
ASSESSMENT OF CAPACITY AND OTHER CONSTRAINTS
23
5.1
SUB-AREA 1: WARKWORTH
24
5.2
SUB-AREA 2: SNELLS-ALGIES
29
5.3
SUB-AREA 3: OMAHA
34
5.4
OTHER AREAS
39
6.0
GAP ANALYSIS AND DESIGN ASSUMPTIONS PROPOSED
39
6.1
INFORMATION GAPS IDENTIFIED
39
6.2
DESIGN ASSUMPTIONS FOR THE INFORMATION GAPS
40
7.0
NEXT STAGE
41
8.0
REFERENCES
42
9.0
LIMITATIONS
43
9.1
GENERAL
43
9.2
PEER REVIEW
43
APPENDICES
Appendix 1
Appendix 2
Study Area Map – Existing Wastewater Infrastructure
Omaha Irrigation Capacity Assessment
HARRISON GRIERSON CONSULTANTS LIMITED
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Treatment and Disposal Infrastructure Constraint Assessment
April 2009
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EXECUTIVE SUMMARY
This report presented an assessment of capacity and constraints of the wastewater
infrastructure (terminal pump station, wastewater treatment plant and final effluent
disposal) for the Mahurangi Region.
The study area encompasses townships and
communities including Warkworth, Snells-Algies, Mahurangi East, Sandspit, Matakana,
Rainbows End, Omaha, Point Wells, Leigh-Mathesons Bay, Baddeleys Beach and
Buckleton Beach.
This report is an update of October 2008 Final Draft issue to incorporate the additional
land disposal irrigation investigations by others previously.
This report summarised the population growth model provided by Rob Bates.
The
population growth model predicted that the population of Warkworth will reach 9,500 by
2051. The other high growth areas include Omaha and Snells-Algies.
A capacity assessment of various wastewater infrastructure was undertaken; it was
found that Warkworth WwTP, Omaha WwTP and Snells-Algies WwTP would need to be
upgraded in the next 5 to 10 years to provide for additional treatment capacity for future
growth and increase in treatment level.
From the recent environmental monitoring studies, the final effluent discharge of
Warkworth WwTP, Snells-Algies WwTP and Omaha WwTP have not resulted in noticeable
adverse environmental effects.
Smaller communities, such as Rainbows End, Baddeleys Beach, Buckleton Beach etc, are
currently not reticulated to public wastewater collection and treatment systems. These
communities are expected to be connected at some stage in the future, however the
details of these new wastewater schemes have not been confirmed. In the next phase of
this master plan study, the potential of implementing de-centralised wastewater
treatment schemes (at community level) for these communities will be examined in
more details.
The next phase of this master plan is the identification and evaluation of Long List
Options. This will include developing and evaluating of an exhaustive list of wastewater
options.
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Treatment and Disposal Infrastructure Constraint Assessment
April 2009
HG Ref 1014-125641-01
PROJECT SCOPE
The project scope for this study was defined and agreed between Rodney
District Council and Harrison Grierson Consultants Limited. The study assessed
the existing wastewater infrastructure, mostly treatment plants and effluent
disposal facilities.
The scope of the investigation included the following tasks:
•
Estimation of future wastewater flows based on the population growth
model prepared by Rob Bates (Version 14, 26.08.2008)
•
Assessment of capacity bottlenecks
•
Assessment of other constraints (e.g. environmental issues, topography,
location etc)
•
Identification of information gaps and ways to find out these missing
information
The outcomes of this report were then incorporated in the strategy study report.
1.0
INTRODUCTION
Harrison Grierson is commissioned by Rodney District Council to undertake the
Mahurangi Wastewater Master Plan.
The outcome of this strategic study will
recommend solutions for reticulation, treatment and disposal in the Mahurangi
region. The region encompasses the following townships and communities:
Warkworth, Snells Beach, Algies Bay, Mahurangi East (Martins Bay), Sandspit,
Matakana, Omaha and Point Wells. Leigh is also included in this study as this
community may be connected to a reticulation system some time in the future.
Due to the nature and scale of this project, this master plan is undertaken in a
number of logical sequenced tasks. This will provide a sustainable and practical
solution in a cost effective manner without major delays or hold-ups.
Following the first report titled “Work Package 1: Project Data Summary”, this
report presents the following:
•
Population projection data to project future wastewater flow and loads
•
Capacity
estimation
of
key
wastewater
treatment
and
disposal
infrastructure items
•
Identification of capacity constraints in key wastewater treatment and
disposal infrastructure items
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Treatment and Disposal Infrastructure Constraint Assessment
•
April 2009
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Identification of information gaps and presentation of assumptions or
further actions to fill these information gaps.
This report is an update of September 2008 issue to incorporate additional
investigations that were previously undertaken on the capacity constraints of
Omaha
Golf
Course
Irrigation,
Effect
of
Treated
Effluent
Irrigation
on
Whangateau Harbour and Snells-Algies Outfall Investigation.
1.1
METHODOLOGY
This section describes the methodology for projecting wastewater flow and
loads, estimating the capacity and identify capacity shortfalls of key wastewater
treatment and infrastructure items.
Wastewater Flow and Loads Projection
The following parameters are included as part of the projection:
•
•
Wastewater Flow:
-
Average Dry Weather Flow, ADWF (m³/d)
-
Peak Wet Weather Flow, PWWF (m³/d)
-
Annual Average Flow, AAF (m³/d) if applicable
Influent Pollutant Loads:
-
Carbonaceous BOD5 (kg/d)
-
Total Suspended Solids, TSS/NFR (kg/d)
-
Total Kjeldahl Nitrogen, TKN (kg/d)
-
Total Phosphorus, TP (kg/d)
The recent wastewater flow figures (2006/7) will be used for estimating the per
capita contribution rates for flow and loads. These values have been compared
with typical generation data.
Capacity Assessment of Key Wastewater Treatment and Disposal
Infrastructure Items
The capacity assessment includes terminal pump stations, inlet screens,
treatment process (biological capacity) and effluent disposal fields.
Previous investigations were referred to for capacity assessments of these
infrastructure items. The values were compared with typical design guidelines.
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HG Ref 1014-125641-01
Where capacity values were not available, the capacity of these items were
estimated from discussions with operational staff, best design guidelines or from
suppliers.
Assessment of Constraints
In addition to identifying capacity constraints, other constraints such as land
availability, environmental effects and cultural issues were also considered. The
information was collected from discussions with Council engineers.
Information Gap Analysis and Study Assumptions
From the capacity and constraints assessment, a number of areas where are
information gaps were identified.
As some of these information gaps may
require significant time to confirm through investigations or consultation,
assumptions that have been made in this report as a basis for later study stages
(strategic options evaluation and consultation).
1.2
STUDY AREA
The study area encompasses major townships including Warkworth, Snells
Beach, Algies Bay and Omaha and other communities surrounding these three
major areas.
The population growth study has consolidated the population
projection data into the following areas:
•
Warkworth
•
Snells-Algies
•
Omaha
•
Tawharanui
•
Mahurangi East
•
Sandspit
•
Rainbows End
•
Sharp Road
•
Matakana
•
Matakana Valley
•
Point Wells
•
Omaha
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•
Leigh Town
•
Mathesons Bay Town
•
Leigh / Whangateau Rural
•
Buckleton Beach
•
Baddeleys Beach
•
Buckleton/ Baddeleys Rural
April 2009
HG Ref 1014-125641-01
Out of the above list, only Warkworth, Snells-Algies, Omaha, Martins Bay (part
of Mahurangi East) and Point Wells are currently serviced by public sewerage
networks. Matakana is due to be connected to Omaha WwTP shortly. The rest
of the areas are on private systems.
The Water and Sanitary Services Assessment 2005 identified that some
communities will require future public sewerage services as the existing private
on-site systems do not meet the requirements.
These include Sandspit,
Rainbows End, Leigh, Mathesons Bay, Baddeleys Beach and Buckleton Beach in
the study area. These areas are assumed to be connected to public sewerage
schemes between 2016 and 2026.
Rest of the un-reticulated areas are assumed to be serviced by on-site systems
during
the
study
period.
These
include
Sharp
Road,
Leigh/Whangateau Rural, and Buckleton/Baddeleys Rural.
Matakana
Valley,
These areas have
been excluded in this master plan study.
2.0
CONNECTED POPULATION PROJECTION
The population projection model (Revised 26 August 2008) was used for
forecasting the wastewater flow and pollutant loads in the study area between
2006 and 2051.
2.1.1
Sewerage Extension Assumptions
As discussed in Section 1.2, a number of areas are expected to be serviced by
public sewerage networks in the study period.
Considering the geographic
location of various communities to the existing wastewater treatment systems,
some connection assumptions have been made.
Table 2 summarises the public sewerage network expansion assumed for this
report.
Table 2: Public Sewerage Network Connection Assumptions
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Current Public Sewerage
Connection Status
Assumed Time for Connection
Warkworth
Connect to Warkworth WwTP
-
Snells-Algies
Connect to Snell-Algies WwTP
-
Omaha
Connect to Omaha WwTP
-
Some connected to Omaha
WwTP
Connect to Omaha WwTP in
2011
Some connected to
Snells-Algies WwTP
Assume all dwellings are
connected in 2011
Sandspit
Not connected
Connect to Snells-Algies WwTP
between 2020-2030
Rainbows End
Not connected
Assume public connection
between 2020-2030
Matakana
Connected to local wetland
Connect to Omaha in 2008/9
Point Wells
Connected to Omaha WwTP
(2008)
-
Leigh Town
Not connected
Assume public connection
between 2020-2030
Mathesons Bay
Town
Not connected
Assume public connection
between 2020-2030
Buckleton
Beach
Not connected
Assume public connection
between 2020-2030
Baddeleys
Beach
Not connected
Assume public connection
between 2020-2030
Tawharanui
Mahurangi East
Three sub-regional areas were considered in this study, they include:
a)
Warkworth
i.
b)
c)
d)
Warkworth Township
Snells-Algies
i.
Snells Beach & Algies Bay
ii.
Mahurangi East
iii.
Sandspit
Omaha
i.
Omaha & Tawharanui
ii.
Matakana
iii.
Point Wells
Others (The form of sewerage connections to be decided):
i.
Rainbows End
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ii.
Leigh Town
iii.
Mathesons Bay Town
iv.
Buckleton Beach
v.
Baddelleys Beach
April 2009
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It is noted that the connection of Sandspit to Snells-Algies WwTP is not
confirmed and will require further assessment.
2.1.2
Population Growth Projection
The population growth forecast was based on the growth model prepared by Rob
Bates (Revision 26th August 2008). The population growth figures presented in
this study is based on a gradual increase in permanent population and a steady
decline in household occupancy (from 2.6 to 2.2 people/household between
2006 and 2051).
The details of the population growth model are discussed
separately in the HGCL report titled “Population Sensitivity Analysis” (September
2008, G Anderson).
The peak summer population is the sum of permanent
population and the peak occupancy rate in the holiday homes.
The population figures presented in the report “Population Sensitivity Analysis”
are adopted as the population basis for projecting wastewater flow and pollutant
mass loads.
The population projection presented in that report used three
population growth rates (50%, 100% and 200%) to illustrate the sensitivity of
the growth rate.
Figures 2.1 to 2.3 presents the range of future connected population during the
study period (2006-2051), extracted from the population sensitivity analysis.
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Figure 2.1: Connected Population Projection of Warkworth WwTP
The connected population of Warkworth WwTP is expected to increase from
3300 to 9500 in the next 45 years. This corresponds to 190% increase of
connected population.
If the population growth rate is only 50% of the
predicted value, the connected population in 2051 is approximately 6200, a
90% increase. If the population growth rate is twice of the predicted value, the
connected population in 2051 is approximately 16300, a 400% increase.
The summer population in the area will reach 9740 in 2051. The ratio of peak
summer population to annual average population is 1.03 in 2051.
Figure 2.2: Connected Population Projection of Snells-Algies WwTP
The connected population of Senlls-Algies WwTP is expected to increase from
3700 to 5500 in the next 45 years. This corresponds to 50% increase of
connected population.
If the population growth rate is only 50% of the
predicted value, the connected population in 2051 is approximately 4300, a
16% increase. If the population growth rate is twice of the predicted value, the
connected population in 2051 is approximately 6300, a 70% increase.
The summer population in the area will be approximately 7200 in 2051, this
corresponds to 3.5% increase between 2006 and 2051.
The ratio of peak
summer population to annual average population will change from 1.9 in 2006
to 1.3 in 2051. This is because more dwellings are expected to be converted
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from being used as holiday homes to residential dwellings, and this will result in
a gradual decline of peak summer population.
Figure 2.3: Connected Population Projection of Omaha WwTP
The connected population of Omaha WwTP is expected to increase from 470 to
2400 in the next 45 years. This corresponds to 400% increase of connected
population. If the population growth rate is only 50% of the predicted value,
the connected population in 2051 is approximately 1400, a 190% increase. If
the population growth rate is twice of the predicted value, the connected
population in 2051 is approximately 2358, a 400% increase. It is understood
that the reason for similar projected connected population at 100% and 200%
growth rate in 2051 is that the number of available lots for converting from
holiday homes to permanent residential dwellings reaches saturation in 20112016 .
The summer population in the area will be approximately 4900 in 2051. This
corresponds to 8% increase between 2006 and 2051. The ratio of peak summer
population to annual average population will change from 9.8 in 2006 to 2.1 in
2051. This is because more dwellings are expected to be converted from being
used as holiday homes to residential dwellings, and this will result in a gradual
decline of peak summer population.
This master plan study only uses the 100% population growth rate for
wastewater flow and pollutant mass loads projection.
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WASTEWATER FLOW AND LOADS PROJECTION
This section describes the projection of wastewater flow and loads.
3.1
COMPARING WITH CURRENT FLOW AND LOAD DATA
Previous sewage sampling data were used for estimating the per capita
contribution rates for flow and pollutant loads.
Table 1 summarises the per capita generation rates estimated from the previous
sampling programmes.
Table 1:
Comparison of Per Capita Generation Rates
Parameters
Flow/load per capita
Warkworth
Snells
Omaha
Typical
Value
224
197
311
180-250
224
L/cap/d
-
160
145
-
224
L/cap/d
BOD5
49
48
49
65
65
g/cap/d
TSS
89
-
87
70-90
90
g/cap/d
TN
11
-
11
13-15
15
g/cap/d
NH4N
10
-
-
10
10
g/cap/d
4
-
2.9
3
4
g/cap/d
Flow (ADWF)
Flow (Summer)
TP
This
Study
Unit
Note:
1.
The per capita generation rates of Warkworth were derived from the influent sampling data
between September and October 2007 based on a population of 3273 (August 2008
Population Model).
2.
The per capita generation rates of Snells were derived from the fortnightly influent sampling
data between July 2002 and February 2003 based on a population of 3339 (August 2008
Population Model).
3.
The ADWF flow per capita generate rate of Omaha was derived from the wastewater flow
monitoring between Jan 2005 and Dec 2007 based on a population of 354 (August 2008
Population Model)
4.
The pollutant per capita generation rates of Omaha were derived from the influent sampling
data in January 2008 based on a summer population of 3412 (August 2008 Population
Model)
From Table 1, the flow per capita rate varies between 197 to 311L/cap/day.
The
higher
value
at
the
Warkworth
and
Omaha
catchment
(224
and
311L/cap/day respectively) was due to high inflow/infiltration in the catchments.
It is understood that Council intends to connect the new subdivisions with low
pressure sewer network thus no further I/I increase is expected.
Hence this
master plan study adopts a ADWF flow per capita rate of 224L/cap/day.
Instantaneous peak flow of conventional gravity connections is estimated based
on 5x instantaneous peaking factor on ADWF which is part of Rodney District
Council’s engineering standard.
The instantaneous peak flow of low pressure
sewer network is dependent on more detailed reticulation investigation which is
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beyond the scope of this study. Thus, this study only estimates the peak flow to
the treatment plant based on conventional gravity sewer connections.
The region has significant influx of holiday population during December and
January period, particularly in Snells-Algies and Omaha areas.
The estimated
flow per capita is between 145 and 160L/cap/day. This study assumes a peak
summer flow per capita of 224L/cap/day.
The BOD5 per capita rates are around 49g/cap/day. The figures are lower than
typical allowance of 65g/cap/day.
This study assumes a prudent BOD5 per
capita generation rate of 65g/cap/day.
The TSS per capita rates are ranged around 90g/cap/day.
similar than typical allowance of 70 to 90g/cap/day.
The figures are
For this project, solids
generation rate of 90g/cap/day is adopted.
The TN per capita rates are around 11 g/cap/day. The figures are slightly lower
than typical allowance between 13 and 15g/cap/day. For this study, a prudent
TN per capita rate of 15g/cap/day is adopted.
The NH4N per capita rates are around 10g/cap/day. The figure is similar than
typical allowance of 10g/cap/day. For this study, a NH4N per capita rate of
10g/cap/day is adopted.
The TP per capita rates are ranged around 3 to 4g/cap/day. The figure is higher
than typical allowance of 3g/cap/day. For this study, a TP per capita rate of
4g/cap/day is adopted.
3.2
WASTEWATER FLOW AND LOADS PROJECTION TABLES
This section presents the wastewater flow and pollutant loads for various subareas in the study area based on the connected population figures.
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Sub-Regional Area 1: Warkworth - Wastewater Flow and Pollutant Mass Loads Projection
This area encompasses major township of Warkworth and its wastewater is currently treated at Warkworth wastewater treatment plant.
Table 3 presents the wastewater flow and pollutant mass loads projection for Warkworth area.
Table 3: Warkworth Sub-Area: Flow and Loads Projection
2006
2011
2016
2021
2026
2031
2036
2041
2046
2051
Notes
Average Population
Population
3273
4026
4905
5726
6653
7290
8088
8540
9200
9466
3
733
902
1099
1283
1490
1633
1812
1913
2061
2120
3
3666
4509
5494
6413
7451
8165
9058
9564
10304
10602
AAF (m³/d)
834
1025
1249
1458
1694
1857
2060
2175
2343
2411
BOD (kg/d)
213
262
319
372
432
474
526
555
598
615
TSS (kg/d)
295
362
441
515
599
656
728
769
828
852
TN (kgN/d)
49
60
74
86
100
109
121
128
138
142
NH4N (kgN/d)
TP (kgP/d)
33
40
49
57
67
73
81
85
92
95
10
12
15
17
20
22
24
26
28
28
ADWF (m /d)
PWWF (m /d)
5x peaking factor
Peak Summer Population (Dec/Jan Period)
Population
3847
4572
5408
6187
7087
7686
8458
8873
9508
9740
862
1024
1211
1386
1588
1722
1894
1987
2130
2182
4309
5121
6057
6930
7938
8608
9472
9937
10649
10908
BOD (kg/d)
250
297
352
402
461
500
550
577
618
633
TSS (kg/d)
346
412
487
557
638
692
761
799
856
877
TN (kgN/d)
58
69
81
93
106
115
127
133
143
146
NH4N (kgN/d)
TP (kgP/d)
38
46
54
62
71
77
85
89
95
97
12
14
16
19
21
23
25
27
29
29
3
Daily Flow (m /d)
PWWF (m3/d)
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Based on the flow projection for Warkworth presented in Table 3, the estimated ADWF will reach 2120m3/day in 2051. The future annual
average flow in 2051 is around 2400m³/day, and this is estimated based on assuming the current ratio of AAF/ADWF 1.14 is unchanged.
The peak summer daily flow will increase from 862m³/day to 2182m³/day. The peak summer daily flow to annual average daily flow will
change from 1.17 to 1.03 during the study period. This is a result of a reduction of holiday homes in the area. In 2051, the difference between
annual average and peak summer condition is expected to be marginal.
The BOD5, TN and TP mass load are expected to increase to 615, 142 and 28kg/d on annual average basis.
3.2.2
Sub-Regional Area 2: Snells-Algies - Wastewater Flow and Pollutant Mass Loads Projection
Snells-Algies area comprise Snells Beach, Algies Bay, Sandspit and Mahurangi East. Sandspit is currently serviced by private onsite systems
and part of Mahurangi East (Martins Bay) is connected to the Snells-Algies WwTP.
In this study, it is assumed that Mahurangi East is all
connected to the Snells-Algies WwTP at the beginning of the study period while Sandspit will be connected to Snells-Algies WwTP in 2016.
Currently, there is no financial plan mentioned in the 2006 LTCCP to connect Sandspit to the Snells-Algies sewerage network. Table 4 presents
the wastewater flow and pollutant mass loads projection for Snells-Algies area.
Table 4: Snells-Algies Sub-Area: Flow and Loads Projection
2006
2011
2016
2021
2026
2031
2036
2041
2046
2051
Notes
Average Population
Population
3660
4163
4694
4758
4972
5025
5242
5284
5503
5532
3
820
933
1051
1066
1114
1126
1174
1184
1233
1239
3
4099
4663
5257
5329
5569
5629
5871
5918
6163
6196
BOD (kg/d)
238
271
305
309
323
327
341
343
358
360
TSS (kg/d)
329
375
422
428
447
452
472
476
495
498
TN (kgN/d)
55
62
70
71
75
75
79
79
83
83
NH4N (kgN/d)
TP (kgP/d)
37
42
47
48
50
50
52
53
55
55
11
12
14
14
15
15
16
16
17
17
ADWF (m /d)
PWWF (m /d)
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