Technical Note 2 - Orange City Council...2019/10/04 · TECHNICAL NOTE 2 ORANGE WATER RESOURCES ORANGE CITY COUNCIL OCC_IWCM_TECHNICAL NOTE 2_FINAL.DOCX This report has been prepared

TECHNICAL NOTE 2

ORANGE WATER RESOURCES

PREPARED FOR

ORANGE CITY COUNCIL

MAY 2013

TECHNICAL NOTE 2

ORANGE WATER RESOURCES

PREPARED FOR

ORANGE CITY COUNCIL

TECHNICAL NOTE 2 ORANGE WATER RESOURCES

ORANGE CITY COUNCIL IWCM EVALUATION STUDY

PREPARED FOR:

ORANGE CITY COUNCIL

MAY 2013

POSTAL ADDRESS PO BOX 1963 ORANGE NSW 2800 LOCATION 154 PEISLEY STREET ORANGE NSW 2800 TELEPHONE 02 6393 5000 FACSIMILE 02 6393 5050 EMAIL [email protected] WEB SITE WWW.GEOLYSE.COM


ORANGE CITY COUNCIL

OCC_IWCM_TECHNICAL NOTE 2_FINAL.DOCX

This report has been prepared by Geolyse Pty Ltd for Orange City Council and may only be used and relied on by Orange City Council for the purposes for which it was prepared. The preparation of this report has been in accordance with the project brief provided by the client and has relied upon the information, data and results provided or collected from the sources and under the conditions outlined in the report. Geolyse otherwise disclaims responsibility to any person other than Orange City Council for liability howsoever arising from or in connection with this report. Geolyse also excludes implied warranties and conditions, to the extent legally possible. The opinions, conclusions and recommendations in this report are based on conditions encountered and information reviewed at the date of preparing this report. Geolyse has no responsibility or obligation to update this report to account for events or changes occurring subsequent to the date that the report was prepared. Geolyse reserves the right, at any time with or without notice, to amend, modify or retract any part or all of the report including any opinions, conclusions, or recommendations contained therein. Unauthorised use of this report in any form whatsoever is strictly prohibited.

Report Title: IWCM EVALUATION STUDY

Project: Orange City Council IWCM

Client: Orange City Council

Report Ref.: OCC_IWCM_Technical Note 2_Final.docx

Status: Final

Issued: May 2013

Next review: June 2018

Cover Photos:

Main – Suma Park Dam spillway (Source: OCC)

Top – Suma Park Reservoir (Source: Kerry Fragar)

Middle 1 – Stormwater harvesting batch pond (Source: Kerry Fragar)

Middle 2 – Orange STP Trickling Filter (Source: OCC)

Bottom – Harvested stormwater discharging to holding pond (Source: Martin Haege)


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CONTENTS ABBREVIATIONS .................................................................................................... VII

INTRODUCTION ........................................................................................................ 1 1.1 BACKGROUND .................................................................................................................. 1 1.2 SCOPE OF TECHNICAL NOTE 2 ...................................................................................... 2 1.3 LIMITATION OF TECHNICAL NOTE 2 .............................................................................. 2 1.4 REPORT STRUCTURE ...................................................................................................... 2 1.5 STUDY TEAM ..................................................................................................................... 3 1.6 ACKNOWLEDGEMENT ..................................................................................................... 3

METHODOLOGY ....................................................................................................... 4 2.1 INTRODUCTION ................................................................................................................ 4 2.2 SECURE YIELD .................................................................................................................. 4

2.2.1 WHAT IS SECURE YIELD? ................................................................................ 4 2.2.2 BASELINE SECURE YIELD ............................................................................... 5 2.2.3 5/10/10 VS 5/10/20 .............................................................................................. 6 2.2.4 APPROACH ........................................................................................................ 7

2.3 ORANGE WATER BALANCE MODEL ............................................................................... 7

2.3.1 DESCRIPTION .................................................................................................... 7 2.4 CLIMATE CHANGE ............................................................................................................ 9 2.5 FINANCIAL ANALYSIS..................................................................................................... 10

2.5.1 NET PRESENT VALUE .................................................................................... 10 2.5.2 TYPICAL RESIDENTIAL BILL .......................................................................... 10

2.6 GREENHOUSE GAS ........................................................................................................ 10 2.7 COMPARISON OF OPTIONS .......................................................................................... 11

WATER RESOURCES ............................................................................................ 12 3.1 INTRODUCTION .............................................................................................................. 12 3.2 SURFACE WATER ........................................................................................................... 12

3.2.1 INTRODUCTION ............................................................................................... 12 3.2.2 GOSLING CREEK DAM .................................................................................... 13 3.2.3 SPRING CREEK DAM ...................................................................................... 16 3.2.4 SUMA PARK DAM ............................................................................................ 18 3.2.5 LAKE CANOBOLAS .......................................................................................... 26 3.2.6 MACQUARIE RIVER TO ORANGE PIPELINE ................................................. 29 3.2.7 BURRENDONG DAM TO ORANGE PIPELINE ............................................... 40 3.2.8 MULYAN CREEK DAM ..................................................................................... 42 3.2.9 CADIA VALLEY OPERATIONS WATER INFRASTRUCTURE ........................ 50 3.2.10 MANAGING STORAGE EVAPORATION ......................................................... 50 3.2.11 LONG LIST RECOMMENDATIONS ................................................................. 51

3.3 STORMWATER ................................................................................................................ 52

3.3.1 EXISTING STORMWATER HARVESTING SCHEMES ................................... 52 3.3.2 BLACKMANS SWAMP CREEK 100% TRIGGER ............................................ 63 3.3.3 BLACKMANS SWAMP CREEK STAGE 2 ........................................................ 65 3.3.4 BLACKMANS SWAMP CREEK STAGE 3 ........................................................ 69 3.3.5 BLACKMANS SWAMP CREEK MAXIMUM HARVESTING ............................. 72 3.3.6 DOWNSTREAM STORMWATER HARVESTING ISSUES .............................. 75 3.3.7 UPSTREAM STORMWATER HARVESTING ................................................... 75 3.3.8 NORTHERN SUBURBS STORMWATER HARVESTING (BEER ROAD) ....... 79 3.3.9 LONG LIST RECOMMENDATIONS ................................................................. 81

3.4 RAINWATER TANKS ....................................................................................................... 81


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3.4.1 INTRODUCTION ............................................................................................... 81 3.4.2 RAINWATER TANK REBATE POLICY............................................................. 82 3.4.3 ASSESSMENT OF RAINWATER TANKS ........................................................ 82 3.4.4 RESULTS .......................................................................................................... 85 3.4.5 USE OF RAINWATER TANKS AS A WATER SUPPLY OPTION .................... 88 3.4.6 SUMMARY ........................................................................................................ 89 3.4.7 LONG LIST RECOMMENDATION .................................................................... 89

3.5 GROUNDWATER ............................................................................................................. 89 3.5.1 SPRING HILL AND LUCKNOW ........................................................................ 89 3.5.2 EXISTING GROUNDWATER RESOURCES FOR ORANGE .......................... 90 3.5.3 POTENTIAL GROUNDWATER RESOURCES ................................................ 91 3.5.4 LONG LIST RECOMMENDATIONS ................................................................. 95

3.6 TREATED EFFLUENT...................................................................................................... 95 3.6.1 DESCRIPTION .................................................................................................. 95 3.6.2 VOLUME ........................................................................................................... 95 3.6.3 INDIRECT POTABLE REUSE .......................................................................... 99 3.6.4 LONG LIST RECOMMENDATIONS ............................................................... 108

3.7 REGIONAL WATER RESOURCES ............................................................................... 108

3.7.1 CENTROC STUDY.......................................................................................... 108 3.7.2 LAKE ROWLANDS.......................................................................................... 109 3.7.3 MOLONG CREEK DAM .................................................................................. 112 3.7.4 LONG LIST RECOMMENDATIONS ............................................................... 112

3.8 OTHER ........................................................................................................................... 112

3.8.1 LUCKNOW MINE – REFORM SHAFT............................................................ 112 3.8.2 BROWNS CREEK MINE ................................................................................. 113 3.8.3 WATER CARTING .......................................................................................... 117 3.8.4 LONG LIST RECOMMENDATIONS ............................................................... 119

3.9 DEMAND MANAGEMENT ............................................................................................. 119

3.9.1 INTRODUCTION ............................................................................................. 119 3.9.2 RESTRICTION FREQUENCY AND DURATION ............................................ 120 3.9.3 CONSERVATION WATER PRICING .............................................................. 121 3.9.4 LONG LIST RECOMMENDATIONS ............................................................... 122

ASSESSMENT OF OPTIONS ................................................................................ 123 4.1 INTRODUCTION ............................................................................................................ 123 4.2 WATER SECURITY ........................................................................................................ 123

4.2.1 COMPARING SECURE YIELD WITH DEMAND ............................................ 123 4.2.2 SENSITIVITY OF PROJECTIONS .................................................................. 125

4.3 BUSINESS AS USUAL WATER SECURITY.................................................................. 127 4.4 FUTURE WATER SUPPLY OPTIONS ........................................................................... 130

4.4.1 UPDATE SINCE PRG MEETING 3 ................................................................. 130 4.4.2 LONG LIST OF OPTIONS .............................................................................. 131 4.4.3 SHORT LIST OPTIONS .................................................................................. 134 4.4.4 EVALUATION OF SHORT LISTED OPTIONS ............................................... 135

CONCLUSIONS AND RECOMMENDATIONS ...................................................... 138 5.1 CONCLUSIONS .............................................................................................................. 138 5.2 RECOMMENDATIONS................................................................................................... 138

REFERENCES ........................................................................................................ 139

APPENDICES


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APPENDIX A Quote for Rainwater Tank Installation

APPENDIX B IBL Solutions Reports

APPENDIX C Climate Change Modelling Results

APPENDIX D QBL Results

TABLES Table 1.1 – Study team ........................................................................................................................... 3 Table 2.1 – Comparison of secure yield rules ......................................................................................... 6 Table 3.1 – Supply from external sources for assessment of raising Suma Park Dam ........................ 22 Table 3.2 – Secure yield results for raising Suma Park Dam ............................................................... 23 Table 3.3 – Summary of Option SW1: raise Suma Park Dam by 1.0 m ............................................... 26 Table 3.4 – Lake Canobolas scheme performance .............................................................................. 28 Table 3.5 – Summary of Option SW2: Lake Canobolas ....................................................................... 29 Table 3.6 – Comparison of actual and modelled annual water consumption – 2000 to 2010 analysis 37 Table 3.7 – River flow and extraction – 2000 to 2010 analysis ............................................................. 38 Table 3.8 – Macquarie pipeline average annual operating costs .......................................................... 38 Table 3.9 – Summary of Option SW3: Macquarie River to Orange pipeline ........................................ 39 Table 3.10 – Burrendong Dam pipeline – preliminary cost estimates ................................................... 41 Table 3.11 – Summary of Option SW4: Burrendong Dam to Orange pipeline ..................................... 42 Table 3.12 – Conceptual Mulyan Creek Dam Stage-Storage-Surface Area Data ................................ 46 Table 3.13 – Mulyan Creek Dam – preliminary cost estimates ............................................................. 49 Table 3.14 – Summary of Option SW5: Mulyan Creek Dam ................................................................ 49 Table 3.15 – Average storage evaporation loss .................................................................................... 50 Table 3.16 – BSCSHS Operating Rules ............................................................................................... 57 Table 3.17 – BSCSHS Staging ............................................................................................................. 58 Table 3.18 – PCSHS Operating Rules .................................................................................................. 59 Table 3.19 – Summary of harvest volumes from approved stormwater harvesting schemes .............. 62 Table 3.20 – Summary of harvest volumes from stormwater harvesting schemes on 100% trigger .... 63 Table 3.21 – Summary of Option SH0: BSCSHS Stage 1b .................................................................. 65 Table 3.22 – Summary of harvest volumes from BSCSHS Stage 2 ..................................................... 67 Table 3.23 – BSCSHS Stage 2 – preliminary cost estimates ............................................................... 68 Table 3.24 – Summary of Option SH1: BSCSHS Stage 2 .................................................................... 68 Table 3.25 – Summary of harvest volumes from BSCSHS Stage 3 ..................................................... 70 Table 3.26 – BSCSHS Stage 3 – preliminary cost estimates ............................................................... 71 Table 3.27 – Summary of Option SH2: BSCSHS Stage 3 .................................................................... 72 Table 3.28 – Summary of harvest volumes from maximum BSCSHS .................................................. 73 Table 3.29 – Maximum BSCSHS – preliminary cost estimates ............................................................ 74 Table 3.30 – Summary of Option SH3: Maximum BSCSHS ................................................................. 74 Table 3.31 – Upstream harvesting results ............................................................................................ 77 Table 3.32 – Upstream stormwater harvesting – preliminary cost estimates ....................................... 78 Table 3.33 – Summary of Option SH4: Upstream stormwater harvesting ............................................ 78 Table 3.34 – Upstream stormwater harvesting – preliminary cost estimates ....................................... 80 Table 3.35 – Summary of Option SH5: Upstream stormwater harvesting (Beer Road) ....................... 80 Table 3.36 – Tank Rebate Policy ST061 – rebate schedule ................................................................. 82 Table 3.37 – Household water demand profile used for rainwater tank modelling ............................... 82 Table 3.38 – Assumptions and Input to the rainwater tank model ........................................................ 83 Table 3.39 – Tank and installation costs – Scenario 1 ......................................................................... 84 Table 3.40 – Tank and installation costs – Scenarios 2 and 3 .............................................................. 84 Table 3.41 – Summary of rainwater tank financial analysis .................................................................. 87 Table 3.42 – Summary of Option RW1: Rainwater tanks ..................................................................... 89 Table 3.43 – Orange town water supply bores ..................................................................................... 90 Table 3.44 – Summary of Option GW1: Bores ...................................................................................... 91 Table 3.45 – Annual effluent transfer to CVO ....................................................................................... 98


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Table 3.46 – Spring Hill and Lucknow effluent production forecast ...................................................... 99 Table 3.47 – Summary of Option E1: Non-membrane IPR scheme ................................................... 101 Table 3.48 – Summary of Option E2: Membrane IPR scheme ........................................................... 102 Table 3.49 – Orange STP storm flow storage ..................................................................................... 105 Table 3.50 – STP storm flow capture – preliminary cost estimates .................................................... 106 Table 3.51 – Summary of Option E5: STP storm flow recovery scheme ............................................ 107 Table 3.52 – Summary of Option R1: Pipeline from augmented Lake Rowlands ............................... 111 Table 3.53 – Estimated capital costs for Browns Creek mine to Orange water transfer system ........ 116 Table 3.54 – Summary of Option O2: Browns Creek mine water transfer .......................................... 116 Table 3.55 – Water cartage options .................................................................................................... 118 Table 3.56 – Water cartage summary of capital and operating costs ................................................. 119 Table 3.57 – Orange forecast water demand – BAU .......................................................................... 122 Table 3.58 – Orange forecast water demand – high level demand management .............................. 122 Table 4.1 – Existing water system secure yield .................................................................................. 124 Table 4.2 – Water supply management strategy infrastructure options.............................................. 127 Table 4.3 – Long list options ............................................................................................................... 131 Table 4.4 – Short-listed water security options ................................................................................... 135

FIGURES Figure 1: Water balance model schematic ......................................................................................... 8 Figure 2: Surface water catchments ................................................................................................ 14 Figure 3: Gosling Creek Reservoir stage-storage curve .................................................................. 15 Figure 4: Spring Creek Reservoir stage-storage curve.................................................................... 17 Figure 5: Suma Park Reservoir stage-storage curve ....................................................................... 19 Figure 6: Suma Park Dam storage-yield curve ................................................................................ 25 Figure 7: Modelled additional Suma Park Dam storage during critical drought period .................... 25 Figure 8: Lake Canobolas connection options ................................................................................. 27 Figure 9: Proposed Macquarie River pipeline .................................................................................. 31 Figure 10: Macquarie River catchments ............................................................................................ 32 Figure 11: Modelled Macquarie River flow duration curve (Geolyse, 2012) ...................................... 34 Figure 12: FDC impact for 12/34 rule ................................................................................................. 35 Figure 13: Monthly Macquarie River flow data (Scenario B) – January 2000 to December 2010 ..... 36 Figure 14: Combined storage behaviour: 2000 to 2010 analysis ...................................................... 37 Figure 15: Conceptual pipeline route from Burrendong Dam to Orange ........................................... 41 Figure 16: Conceptual Mulyan Creek Dam, catchment ..................................................................... 44 Figure 17: Mulyan Creek mass curve of inflow to proposed dam ...................................................... 45 Figure 18: Mulyan Creek Dam storage-demand relationship ............................................................ 45 Figure 19: Conceptual Mulyan Creek Dam ........................................................................................ 46 Figure 20: Potential annual demand supplied by 1,350 ML Mulyan Creek Dam ............................... 47 Figure 21: Conceptual demand supplied through Federation Drought period for Mulyan Creek Dam................................................................................................................................... 47 Figure 22: Preliminary hydraulic grade line and pipe sizes ............................................................... 48 Figure 23: Stormwater harvesting infrastructure ................................................................................ 52 Figure 24: Stormwater harvesting catchments .................................................................................. 55 Figure 25: BSCSHS Stage 1 scheme layout ..................................................................................... 56 Figure 26: NSW Office of Water approval framework – Water quality ............................................... 61 Figure 27: BSCSHS Stage 1 flow duration curves ............................................................................. 64 Figure 28: BSCSHS Stage 2 conceptual offline wetland system ....................................................... 66 Figure 29: BSCSHS Stage 2 flow duration curves ............................................................................. 67 Figure 30: BSCSHS Stage 3 conceptual harvesting weir .................................................................. 69 Figure 31: BSCSHS Stage 3 flow duration curves ............................................................................. 71 Figure 32: Maximum BSCSHS flow duration curves ......................................................................... 73 Figure 33: Upstream stormwater harvesting locations....................................................................... 76 Figure 34: Potential northern suburbs stormwater harvesting (Beer Road) ...................................... 79 Figure 35: Rainwater Tank Analysis – Potential Household Water Saving ....................................... 85 Figure 36: Scenario 1 – Rainwater tank size comparison for outside use only ................................. 86 Figure 37: Scenario 2 – Rainwater tank size comparison for outside and toilet use ......................... 86 Figure 38: Scenario 3 – Rainwater Tank Size Comparison for Outside, Toilet Use and Washing

Machine ............................................................................................................................ 87 Figure 39: Orange water supply bores ............................................................................................... 90


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Figure 40: Forecast total annual effluent production – city of Orange, medium growth .................... 96 Figure 41: Forecast total annual effluent production – city of Orange, high growth .......................... 96 Figure 42: BAU treated effluent production and availability ............................................................... 98 Figure 43: IPR non-membrane treatment train ................................................................................ 100 Figure 44: IPR membrane treatment train ....................................................................................... 102 Figure 45: Average household water use, kL/year .......................................................................... 108 Figure 46: Potential pipeline from Lake Rowlands to Orange ......................................................... 110 Figure 47: Browns Creek mine to Orange pipeline route options .................................................... 115 Figure 48: Water security for existing water supply infrastructure – no climate change .................. 125 Figure 49: Water security for existing water supply infrastructure – with climate change ............... 126 Figure 50: Water security with BAU water supply infrastructure – no climate change .................... 129 Figure 51: Water security with BAU water supply infrastructure – with climate change .................. 130


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Orange City Council’s Integrated Water Cycle Management

Integrated Water Cycle Management (IWCM) is a 30 year strategic planning tool that enables Orange City Council to manage urban water services in a holistic manner and in accordance with best management practice. It brings together water supply, sewerage and stormwater within a catchment context, identifies current and potential future issues relating to planning and service delivery and examines how these issues can best be addressed.

IWCM Evaluation Study

The IWCM Evaluation Study lists all urban water service targets and identifies all the issues relating to planning and service delivery for urban water supply, sewerage and stormwater over the next 30 years. It examines what issues:

• can be addressed by existing or formally adopted actions and capital works – the Business as Usual scenario; or

• remain to be addressed in the IWCM Strategy.

Technical Notes

The IWCM Evaluation Study is supported by a number of Technical Notes that provide detailed supporting information and analysis. Findings from the technical work are presented in the relevant sections of the IWCM Evaluation Study.

Technical Note 1: IWCM Targets and Community Objectives

This Technical Note details the relevant targets and community objectives for the delivery of urban water services for Orange City Council.

Technical Note 2: Orange Water Resources

This Technical Note presents details of the various water resources considered by Orange City Council to provide long term water security including: surface water, stormwater, rainwater, groundwater, treated effluent, regional supplies and other solutions. It defines secure yield and how it relates to long term water security. It also includes an analysis of how climate change may impact on the secure yield.

Technical Note 3: Potable Water Demand and Effluent Production

This Technical Note describes the assessment of future potable water needs and effluent production for Orange and the villages of Lucknow and Spring Hill. Demand projections are based on consideration of historical demand, demand drivers and demand management.

Technical Note 4: Typical Residential Bill Analysis

This Technical Note defines what the Typical Residential Bill (TRB) is and details the modelling undertaken to determine the TRB and the impact of current and proposed actions and capital works.


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ABBREVIATIONS ABS Australian Bureau of Statistics

BAU Business as usual

CVO Cadia Valley Operations

D/S Downstream

DEUS Department of Energy, Utilities and Sustainability

DoP Department of Planning

DPWS Department of Public Works and Services

EA Emergency Authorisation issued under Section 22A of the Water Act 1912

ERP Estimated Residential Population

GPT Gross Pollutant Trap

GL Gigalitre (1,000 megalitres)

ha Hectares

IPR Indirect potable reuse

IWCM Integrated Water Cycle Management

kL Kilolitre (1,000 litres)

kWhr Kilowatt hour

L Litre (1,000 millilitres)

LGA Local Government Area

L/s Litres per second

LEP Local Environmental Plan

mg/L Milligrams per litre

m3/hr Cubic metres per hour

mL Millilitre

ML Megalitre (1 million litres or 1,000 kilolitres)

ML/day Megalitres per day

m Metre

mm Millimetres

NOW NSW Office of Water

NPV Net Present Value

OCC Orange City Council

pa Per annum

QBL Quadruple bottom line (environmental, social, economic and governance)

REF Review of Environmental Factors

STP Sewage Treatment Plant (works)

TBL Triple bottom line (environmental, social and economic)

TRB Typical Residential Bill

µg/L Micrograms per litre

U/S Upstream

UV Ultraviolet

WTP Water Treatment Plant (works)

WWTP Wastewater Treatment Plant (or STP)


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Introduction

1.1 BACKGROUND A hydrology study completed in 1990 determined that the secure yield for the Orange surface water system, including the storages of Suma Park, Spring Creek and Gosling Creek Reservoirs was 7,800 ML/year (Public Works, 1990). This formed the basis of the volumetric water entitlement issued under the Water Management Act, 2000 for the Orange water supply.

The city’s annual water demand reached 7,120 ML in 2002. Since that time, Orange City Council has introduced substantial demand management and efficiency measures that have reduced annual water consumption. Despite this, the experience during the 2000 to 2010 drought period indicated that Orange’s water supply was not as secure as indicated by the 1990 study.

The Integrated Water Cycle Management (IWCM) Concept Study (MWH, 2007) identified that the system secure yield needed to be updated. NSW Water Solutions was engaged by Orange City Council to undertake this review.

The initial results of the secure yield review became available to Council in February 2008 and showed a dramatic reduction in the secure yield from the 1990 figure of 7,800 ML/year to 3,500 ML/year1.

The 2008 secure yield review used an extended climate data set that covered the period 1890 to 2007. The dramatic reduction in the calculated secure yield was put down to the influence of the Federation Drought (1895 to 1902), which was the critical drought period in the analysis, and improved streamflow modelling2. It was also considered at the time that the lower secure yield was being reflected in the current situation where the extended drought period from 2000 was putting pressure on the city’s water resources. It was evident that the city’s secure yield was less than the current and estimated future water demand.

Council has made some significant ground with demand management. The current unrestricted annual water demand with these measures in place is 5,400 ML/year (refer to Technical Note 3) and it is forecast that demand will remain at or around this level for the next 10 years despite continued forecast population growth. This indicates Council is expecting the community to become more water efficient.

Orange City Council adopted a comprehensive Strategic Water Supply Strategy at its meeting of 19 November 2009. The strategic objective of the strategy is:

To establish a broad based water supply strategy for the next 50 years and beyond which focuses on ongoing water conservation, quality and demand management and the provision of key water supply infrastructure at least 10 years in advance of projected demand.

The ultimate aim of the strategy is to see fewer restrictions, improved security, and capacity for ongoing growth.

In 2007, Orange City Council commenced investigation of a range of alternative water supply sources that lead to the development of stormwater harvesting on Blackmans Swamp Creek. The 2009 strategy continued on from this work and included a range of local and regional water supply infrastructure options that would be considered as part of a future water supply system.

This Technical Note presents a comprehensive review of water resources in and around Orange that have been considered for future water supply augmentation. 1 This initial study result has since been updated. The revised secure yield for the existing catchment and storages based on the 5/10/10 rule is 3,400 ML/year. 2 The dramatic reduction in secure yield has since been confirmed through numerous analyses and revisions undertaken throughout the IWCM Evaluation Study.


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This review applies to the Orange water supply only. The villages of Spring Hill and Lucknow are supplied from groundwater sources and modelling of this system (as presented in Technical Note 3) indicates adequate supplies for the next 50 years.

1.2 SCOPE OF TECHNICAL NOTE 2 This Technical Note presents details of the various water sources considered by Orange City Council to provide long term water security including: surface water, stormwater, rainwater, groundwater, treated effluent, regional supplies, other emergency solutions and demand management.

For each viable water source option, the Technical Note provides an assessment of:

• how it would work;

• the potential increase in secure yield;

• the effectiveness of the option;

• capital and annual operating cost and Net Present Value (NPV);

• how the option would impact on the Typical Residential Bill (TRB);

• potential operational greenhouse gas emissions; and

• approvals and licencing requirements, possible issues and likely approvals timeframes.

Six water supply infrastructure components are currently included in Council’s Business as Usual (BAU) scenario. These were adopted by Council in its 2009 Strategic Water Supply Strategy. The ability of these components to provide water security for the next 50 years is assessed with and without climate change.

1.3 LIMITATION OF TECHNICAL NOTE 2 This report presents a preliminary evaluation of technically feasible options to increase the city’s secure yield. It is a broad, high level strategic evaluation and seeks to identify those options that could be considered as part of Council’s water supply system. The options short-listed from this assessment would be subject to further detailed analysis, environmental assessment and legislative approvals/licencing. As such, the numbers presented in this report are subject to change and should not be taken as final. For example, the assessment of how much a certain option may be able to provide in terms of average annual supply or secure yield may change during the detailed environmental approvals stage due to some yet to be identified environmental constraint.

1.4 REPORT STRUCTURE This report is structured as follows:

• Section 2 provides an outline of the methodology used to assess various water supply options. This section includes a description of secure yield and climate change modelling and defines the metrics used to compare water supply options;

• Section 3 provides a description of the water supply options considered throughout preparation of the IWCM Evaluation Study including costs and potential to improve the city’s secure yield;

• Section 4 provides an assessment of the BAU water supply components and short lists other viable options for future consideration; and

• Section 5 provides the conclusions and recommendations.


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1.5 STUDY TEAM Table 1.1 outlines the study team and their respective roles.

Table 1.1 – Study team

Organisation Role

Geolyse Pty Ltd • Project management • Background data collation • Analysis of data • Assessment and modelling of options • Financial modelling • Coordination of secure yield modelling • Assessment and reporting

NSW Water Solutions • Secure yield modelling • Climate Change modelling

1.6 ACKNOWLEDGEMENT The secure yield modelling undertaken for options considered in this assessment was undertaken by NSW Water Solutions (Mr Peter Cloke and Mr Chee Chen).


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Methodology

2.1 INTRODUCTION This section provides an outline of the methodology used to assess various water supply options. A range of metrics were used to allow comparison of viable water source options. These included:


• capital and annual operating costs and Net Present Value (NPV);

• how the option would impact on the Typical Residential Bill (TRB); and

• potential operational greenhouse gas emissions.

Climate change assessment was undertaken for the water supply components of the Business as Usual (BAU) scenario.

The methodology used to derive each metric is provided in the following sections.

2.2 SECURE YIELD

2.2.1 WHAT IS SECURE YIELD?

Orange City Council is using secure yield as a quantitative measure for comparing various water supply options. The secure yield assessments are undertaken by NSW Water Solutions and the following description of this method is provided by Cloke (undated).

The procedure for sizing water supply systems on a security of supply basis (secure yield) arose from experiences during the severe 1979 to 1983 drought. Previous methods of sizing did not reflect the performance of the system as perceived by the consumer who tends to view the system’s performance in terms of annual water charges and the frequency, duration and severity of restrictions on the use of water.

The key considerations for the procedure were that:

• it is neither practical, economic nor environmentally responsible to provide “restriction free” water supply systems;

• a trade-off is necessary between the security of supply provided (i.e. the relative lack of restrictions) and the associated capital and operating costs;

• they should allow comparison of alternative water supply schemes which are operationally satisfactory (i.e. restrictions are not of excessive frequency, duration or severity); and

• adequate storage should be available to allow the operating authority to manage the scheme during drought periods.

The procedures result in a defined term called “Secure Yield”. The secure yield is considered to be the annual demand that can be supplied from the system while satisfying the following conditions:

a) Duration of restrictions does not exceed 5% of the time;

b) Frequency of restrictions does not exceed 10% of years (i.e. 1 year in 10 on average); and

c) Severity of restrictions does not exceed 10%. Systems must be able to meet 90% of the unrestricted water demand (i.e. 10% average reduction in consumption due to water restrictions) through a repetition of the worst recorded drought, commencing with the storage drawn down to the level at which restrictions need to be imposed to satisfy a) and b) above.


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Secure yield is defined as the highest annual water demand that can be supplied from a water supply system while meeting the above 5/10/10 rule.

The above guidelines for sizing of water supply systems on a security of supply basis were developed to enable sizing and comparison of alternative water supply schemes that should be satisfactory from an operational point of view. The guidelines seek to provide schemes that are operationally satisfactory so that:

• restrictions are neither of excessive duration nor too frequent; and

• adequate capacity is available to allow the operating authority to manage the scheme during drought periods.

Previously, secure yield was based on a ‘5/10/20 rule’. This meant that a 20% reduction in consumption would be required through a repetition of the worst recorded drought. State Government performance monitoring data shows that the overall water consumption has fallen and it is considered that it would be much more difficult to achieve a 20% reduction in consumption than it was 20 years ago. Accordingly, in February 2009 the NSW Office of Water agreed to base future planning in non-metropolitan NSW on being able to achieve an average of a 10% reduction in consumption through a repetition of the worst drought commencing with the storage already drawn down to satisfy the restriction duration and frequency criteria in a) and b) above. Thus the NSW ‘5/10/20 rule’ has been superseded by a ‘5/10/10 rule’.

The level of security that is appropriate for sizing of headworks for country water supplies may vary with the size of the town, the nature of its industries and the cost of providing that security. The duration, frequency and level of restrictions implied by the 5/10/10 rule are considered to be a reasonable basis for sizing of water supply headworks on a security of supply basis.

2.2.2 BASELINE SECURE YIELD

Numerous secure yield runs have been undertaken by NSW Public Works (NSW Water Solutions) during the course of the IWCM Evaluation Study and investigations of alternate water sources.

The initial secure yield analysis was reported in February 2008, which indicated the existing catchment with a Suma Park Reservoir volume of 18,000 ML had a secure yield of 3,500 ML/year. This was based on the 5/10/20 rule. This was the first report that showed a dramatic reduction from the secure yield calculated in 1990 of 7,800 ML/year.

The 2008 analysis used an extended climate data set that covered the period 1890 to 2007. The dramatic reduction in the calculated secure yield was put down to the influence of the Federation Drought (1895 to 1902). If the Federation Drought period is removed from the analysis, the secure yield is 4,500 ML/year (based on 5/10/20 rule).

In November 2009, some sensitivity testing was undertaken that examined the impact of the frequency and duration of restrictions. Based on the results of this analysis and consideration of the influence of the Federation Drought, it was considered that the base secure yield of 3,500 ML/year from the February 2008 report was too conservative, and Council adopted a figure of 4,000 ML/year. This was reported in the Water Projects Updated Report – November 2009 (Orange City Council, 2009).

Bathymetric survey of Suma Park Reservoir was completed in July 2010. This revealed that the volume at Full Supply Level (FSL) is 17,290 ML (i.e. 710 ML less than used in the secure yield modelling).

Around the same time, Council was considering raising Suma Park Dam in conjunction with dam safety upgrade works. Secure yield analyses were undertaken to examine the effect of increasing the volume of Suma Park Reservoir using the 5/10/20 rule with the following results:

• Suma Park Reservoir volume 17,290 ML (existing): secure yield = 3,450 ML/year;

• Suma Park Reservoir volume 18,970 ML (1.0 m raise): secure yield = 3,600 ML/year; and

• Suma Park Reservoir volume 20,760 ML (2.0 m raise): secure yield = 3,800 ML/year.


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This showed that increasing the dam FSL by 1.0 m from the existing FSL would increase the secure yield by 150 to 200 ML/year.

Further secure yield modelling was undertaken for a Suma Park Reservoir volume of 18,970 ML (i.e. assuming a 1.0 m raise) based on the 5/10/20 rule. This gave a value of 3,600 ML/year which was reported in the Water Strategy Update Report – December 2010 (Orange City Council, 2010).

The increased dam volume (i.e. 1.0 m raise) was then analysed using the 5/10/10 rule (which is now being adopted for all secure yield analyses) and the secure yield was found to be 3,400 ML/year. Therefore, adopting the 5/10/10 rule reduced the secure yield by 200 ML/year compared to the 5/10/20 rule for a Suma Park Reservoir volume of 18,970 ML.

Further analyses were based on a Suma Park Reservoir volume of 18,970 ML (i.e. assuming a 1.0 m raise) as various options were assessed.

At the time of preparation of the August 2011 report titled Orange Emergency Drought Connection Macquarie Pipeline Update (Orange City Council, 2011) there had been no secure yield analysis of the existing Suma Park Reservoir volume (i.e. 17,290 ML) using the 5/10/10 rule. Therefore based on the relationship derived from the 5/10/20 modelling for the three different Suma Park Reservoir volumes, it was assumed that the secure yield for the existing reservoir volume would be 3,250 ML/year (i.e. 150 ML/year less than that determined for a 1.0 m raise).

Further secure yield assessment was undertaken in September 2011 that examined a range of water supply options, three Suma Park Reservoir volumes (existing, 1.0 m and 2.0 m raises) and modified environmental flow rules. In addition, the operating rules associated with Gosling Creek Dam were reviewed and added to the analysis.

The September 2011 analysis adopted the 5/10/10 rule and gave the following results:

• Suma Park Reservoir volume 17,290 ML (existing): secure yield = 3,400 ML/year;

• Suma Park Reservoir volume 18,970 ML (1.0m raise): secure yield = 3,600 ML/year; and

• Suma Park Reservoir volume 20,760 ML (2.0m raise): secure yield = 3,800 ML/year.

Therefore, the secure yield for the existing catchment, Gosling Creek and Spring Creek reservoirs and Suma Park Reservoir with a volume of 17,290 ML, based on the 5/10/10 rule is 3,400 ML/year.

2.2.3 5/10/10 VS 5/10/20

As discussed above, the secure yield modelling was initially based on a 5/10/20 rule. This meant that a 20% reduction in consumption would be required through a repetition of the worst recorded drought. However, in accordance with best practice, Orange City Council adopted the 5/10/10 rule which is now included in Council’s water supply level of service.

The secure yield modelling undertaken in the early part of the IWCM Evaluation Study has provided results that can be compared to see the effect of the two rules. These results are summarised in Table 2.1 along with the assumptions used for each modelling run.

Table 2.1 – Comparison of secure yield rules

Secure yield assumptions Secure Yield, ML/year

5/10/20 5/10/10 Difference

Base system: Suma Park Reservoir volume 18,970 ML (1.0 m raise) Spring Creek Reservoir, Gosling Creek Reservoir

3,600 3,400 200

Base system plus: Blackmans Swamp Creek and Ploughmans Creek harvesting on 100% trigger Bores adding 1.1 ML/day

5,400 5,000 400


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2.2.4 APPROACH

2.2.4.1 Secure Yield Modelling

NSW Water Solutions have developed a secure yield model for the Orange water supply system. The secure yield model uses climate data for the period 1890 to 2007. The secure yield model includes the surface water catchments of Spring Creek Dam (including Gosling Creek Dam) and Suma Park Dam. This represents the existing natural catchment and water supply system and excludes any external supply sources.

Inflow from additional water sources being considered such as groundwater bores and stormwater harvesting are provided as a daily flow series and water is added from these schemes depending on defined operating rules as detailed below:

• Stormwater harvesting – the Orange water balance model (refer to Section 2.3) was used to generate daily stormwater harvesting volumes assuming there is no limitation in the operation of these schemes with regards to the volume in Suma Park Reservoir. The input from these schemes is controlled by the secure yield model with input only being added if the volume in Suma Park Reservoir is less than nominated trigger levels;

• Groundwater bores – a constant daily flow based on the volume available from the bores added whenever Suma Park Reservoir is less than 100%; and

• Macquarie River to Orange pipeline – the daily river flow series was linked to the secure yield model and water transferred based on defined operating rules, e.g. transfer 12 ML/day whenever the level in Suma Park Reservoir was less than 90% and flow in the river greater than 34 ML/day.

2.2.4.2 Estimated Secure Yield

Not all options were assessed using the NSW Water Solutions secure yield model due to time and budget constraints. Analysis of numerous secure yield model results indicated that it was the federation drought that defined the secure yield for Orange. This was typically a 5.5 to 6 year period from 1894 to 1900 when the combined storage was below full supply level.

An estimate of the potential secure yield increase for an external supply option could be derived by calculating how much additional water the option could have added through the critical drought period and dividing this by the length of the critical drought. The Orange water balance model (refer to Section 2.3) was used for these calculations.

The use of estimated secure yield is noted as required.

2.3 ORANGE WATER BALANCE MODEL

2.3.1 DESCRIPTION

The integrated daily water balance model developed to assess the Blackmans Swamp Creek Stormwater Harvesting Scheme, the Ploughmans Creek Stormwater Harvesting Scheme and other water augmentation schemes being considered by Orange City Council was used for this study. The schematic layout of this model is shown on Figure 1. The integrated water balance model is used to: • Examine various options for supplementing the city’s raw water supplies;

• Quantify the expected benefits of each scheme either as a stand-alone project or in combination with other schemes; and

• Calculate the changes in downstream flow regimes in the Summer Hill Creek and Ploughmans Creek systems resulting from the various options.

The model uses a daily time step and includes the following main components.


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Catchment Streamflow

Catchment runoff calculations are used to generate a daily streamflow series which is used as inflow to the various storages in the model. The Model for Urban Stormwater Improvement Conceptualisation (MUSIC) is used to generate streamflow for urban areas while the catchment inflow series used for the secure yield modelling is used for the major water supply dams.

Figure 1: Water balance model schematic

Storage Balances

A daily balance is undertaken for each storage (i.e. wetlands, harvest weirs, water storages) in the system using the following:

• Inflows - streamflow (which includes spill from upstream storages where applicable)

- direct rainfall added to the storage water surface (based on stage-surface area relationships)

- inflow from alternate sources such as bores, Macquarie River

• Outflows - spill

- evaporative losses from the water surface (based on stage-surface area relationships)

- extractions (water demand, pumps for harvesting schemes, environmental releases)

Storage at the end of a day is the storage at the start of the day plus the inflows minus the outflows.


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Climate Data

The water system model is used as a tool to compare the performance of various options to supplement the city’s water raw water supplies. The model uses daily rainfall patterns derived from actual rainfall data from 1890 to 2007. This simply means that the modelling compares options assuming that we receive the same rainfall patterns as observed over the past 118 years, for another 118 years. Year 1 in the model is 1890 climate; Year 118 is 2007 climate.

Water Demand

The water balance model includes the water demand for the city.

The water demand in Year 1 of the model was set at 5,400 ML/year (refer to Technical Note 3) and it was assumed to increase with population growth at a rate of 0.8% per annum. The growth rate is based on the medium growth population forecast defined in Technical Note 3.

The daily water demand in the water balance model is restricted in accordance with Council’s adopted water restriction policy that links the level of restriction to the combined water storage volume in Suma Park and Spring Creek Reservoirs.

2.4 CLIMATE CHANGE While secure yield allows for meeting demand with restrictions through a much worse drought than has occurred since 1890, consideration needs to be given to possible changes from climate change. This study uses the approach proposed in NSW Office of Water’s draft proposed policy for assessing the impact of climate change on non-metropolitan water supplies as described in Samra and Cloke (2010).

Climate change data were obtained from the NSW Office of Water’s 2008 data set which provides historical and future climate change series for the year 2030 based on the A1B warming scenario; a mid-range warming scenario. The following daily climate data were obtained for the catchment:

• rainfall;

• evapotranspiration;

• minimum temperature; and

• maximum temperature.

The historical and climate change data sets covered the period January 1986 to December 2006

The approach required four modelling steps:

1. Daily rainfall and evapotranspiration data were used in the secure yield model to produce 15 sets of inflow data for the system storages.

2. Daily rainfall and evapotranspiration data were used in the stormwater harvesting model to produce 15 sets of climate changed daily harvesting values.

3. Daily rainfall, evapotranspiration and temperature data were used in the Scenario B Macquarie River catchment model to produce 15 sets of climate changed daily streamflow at the proposed offtake point for this option.

4. The above data sets were used as input to the Orange secure yield model to determine climate changed secure yield.

It was assumed for the climate change assessment that the inflow from the bores would not change.

The climate change analysis covered the period January 1896 to December 2006 (rather than 1890 to 2007) as it was constrained by the available climate change data.


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Climate change modelling was limited to components of the BAU scenario.

The projected impacts of climate change in 2030 on the average annual rainfall, streamflow and evapotranspiration compared to the historical data sets for Orange are as follows:

• Median average annual rainfall is expected to decrease by 2%, with models ranging from a reduction of 7% to an increase of 7%;

• Median average annual streamflow is expected to decrease by 15%, with models ranging from a reduction of 31% to an increase of 22%; and

• Median evapotranspiration is expected to increase by 2%, with models ranging from no change to an increase of 4%.

2.5 FINANCIAL ANALYSIS

2.5.1 NET PRESENT VALUE

The Net Present Value (NPV) of capital and operating costs were determined for each scheme. The NPV calculations were based on the following assumptions:

• 7% discount rate;

• 50 year assessment period;

• 15% contingency on capital costs; and

• 15% cost on capital components for survey, design, engineering and supervision.

All NPV results are presented in $2010/2011.

It should be noted that all cost estimates provided in this document are strategic planning level assessments that would require further refinement during concept and detailed design phases. As such, they should only be relied upon for the purposes of making comparisons between options.

2.5.2 TYPICAL RESIDENTIAL BILL

The Typical Residential Bill (TRB) is defined as follows (Water Services Association of Australia, 2010):

TRB = Residential sewerage charge + residential water fixed charge + special levies + residential water usage charge for the average residential consumption

Orange City Council does not have any special levies for water or sewerage.

A financial model was developed to examine the impact of proposed water security options on the TRB for Orange. A full description of this model is provided in Technical Note 4.

2.6 GREENHOUSE GAS Operational greenhouse gas emissions were calculated from the estimated electricity consumption which was converted to carbon dioxide equivalents using the NSW Pool Coefficient.

The NSW Pool Coefficient is the average greenhouse gas emissions intensity of electricity sent to customers in the State. For 2011 the Pool Coefficient is 0.975 tonnes of carbon dioxide equivalent per megawatt hour (http://greenhousegas.nsw.gov.au/documents/FS-Comp-PoolCoeff-Oct11.pdf).

http://greenhousegas.nsw.gov.au/documents/FS-Comp-PoolCoeff-Oct11.pdf


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2.7 COMPARISON OF OPTIONS The above analyses were used to define the following measures for each feasible water supply option:

• Capital costs: a direct measure of the estimated capital costs;

• Operating costs: a direct measure of the estimated annual operating costs;

• NPV – capital costs: the present value of capital costs in $2010/2011 that takes into account timing of capital expenditure;

• NPV – operating costs: the present value of operating costs in $2010/2011 that expresses 50 years of operating in current dollars;

• Potential increase in secure yield (ML/year);

• Total cost of secure yield supplied: this was calculated as the total present value of the option divided by the present value of the secure yield supplied. This measure was derived for capital, operating and total cost. It is used as a measure of the effectiveness of the option with units of $ per ML increase in secure yield;

• Change in TRB if adopted: this was the step change in the TRB if the option was implemented within realistic timeframes commencing in 2010/2011; and

• Greenhouse gas emissions: calculated for operating power costs only.

In addition to the above measures, comment is provided on potential issues and the likely timeframe to implement each feasible option. The likely timeframe relates to the approval/licensing process as well as construction and commissioning.


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Water Resources

3.1 INTRODUCTION This section provides a description of water resources that are available in Orange and the surrounding region that could form part of Orange’s water supply system. The section presents assessment of a range of potential water sources which are identified with the following prefixes:

• SW – surface water;

• SH – stormwater;

• RW – rainwater tanks;

• GW – groundwater;

• E – Effluent;

• R – Regional water sources; and

• O – Other options including mines and water carting.

Demand management (D) is also considered as an approach to improving the water security.

For each viable water source option, the report provides an assessment of:

• how it would work;


• the effectiveness of the option;

• capital and annual operating cost and NPV;

• how the option would impact on the TRB;

• potential operational greenhouse gas emissions; and

• approvals and licencing requirements, possible issues and likely approvals timeframes.

3.2 SURFACE WATER

3.2.1 INTRODUCTION

Surface water is the primary source of town water supply for Orange. The Orange LGA has six major creek catchments:

• Blackmans Swamp Creek;

• Ploughmans Creek;

• Spring Creek/Brandy Creek;

• Gosling Creek;

• Upper Summer Hill Creek; and

• Lower Summer Hill Creek.

These catchments are shown in Figure 2. All of the catchments, except for Ploughmans Creek, run into the lower Summer Hill Creek catchment and onto Lewis Ponds Creek which joins the Macquarie River. Ploughmans Creek joins with Broken Shaft Creek and then becomes the Bell River. The Bell River joins the Macquarie River at Wellington.


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The major water storage is formed by Suma Park Dam, located on Summer Hill Creek, approximately 4 km east of Orange. The catchment area to Suma Park Dam includes the two other reservoirs (Spring Creek and Gosling Creek) and feeder creeks mostly situated to the south and south-east of the city’s urban area (refer to Figure 2).

3.2.2 GOSLING CREEK DAM

3.2.2.1 Background

The original village of Orange was serviced by water reserves on Blackmans Swamp Creek and private wells. After years of concern over the unreliability of Blackmans Swamp Creek as a water supply, the Council in 1877 attempted to persuade the State Government to finance a more permanent and secure supply of water.

Gosling Creek Dam was constructed in 1890 specifically for the purpose of providing Orange’s first water supply reservoir. The supply was said, then, to be good for the next twenty years.

In 1918 the Meadow Creek system, later renamed Lake Canobolas, was built. Water was pumped to Orange via the 2 ML service tank on Cargo Road, by two pumps powered by coal gas engines. This system was used on a regular basis until about 1935; then on an intermittent basis in dry periods until the end of World War II. Water from both Gosling Creek and Lake Canobolas was unfiltered and untreated and the water quality was poor. It was commonplace at the time for householders to use alum to clarify water before washing clothes.

Gosling Creek Reservoir was not abandoned altogether and did continue to provide the drinking water supply for Bloomfield Hospital. Further, overflow from Gosling Creek Reservoir has, and continues, to drain to Spring Creek Reservoir which remains a functioning component of the city’s drinking water supply scheme.

The Gosling Creek Dam is now used for recreation and irrigation purposes. Newcrest Mining was granted a licence from the Department of Water and Energy in August 2007 to draw water from Gosling Creek Dam up to a maximum volume of 450 ML, for a maximum period of three months. Over this period of time, only 90 ML was utilised.

3.2.2.2 Catchment and Storage Volume

Gosling Creek Dam sits on Gosling Creek south of Orange (refer to Figure 2). The catchment area upstream of the dam is 18.82 km2.

Gosling Creek Dam is a concrete structure with a maximum wall height of 8 m. The reservoir capacity was first calculated in 1890 as 650 ML. However due to silting the reservoir has been recalculated in 2007 to have a capacity of 524 ML. The reservoir has a surface area of about 17 ha at full supply level (FSL).

The stage-storage curve for Gosling Creek Reservoir is provided in Figure 3.


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Figure 2: Surface water catchments


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Figure 3: Gosling Creek Reservoir stage-storage curve

3.2.2.3 Dams Safety Act, 1978

Gosling Creek Dam is a prescribed dam under Schedule 1 of the Dams Safety Act, 1978. The Dams Safety Committee (DSC) can require owners of prescribed dams to do things to ensure the safety of their dams.

Gosling Creek Dam has the following consequence categories:

• Sunny Day Consequence Category (SDCC) Low

• Flood Consequence Category (FCC) Significant

The latest dam surveillance report was completed in 2005 and found that the dam is performing satisfactorily.

3.2.2.4 Operation

Water can be drawn through two floating trunnions (300 mm and 450 mm in diameter) into a 600 mm diameter outlet pipe controlled by a 450 mm valve located on the downstream side of the wall. Water can be drawn from the storage at a set level below the fluctuating storage level. There is a 600 mm scour valve below the outlet pipe and pump which supplies the irrigation system for the recreation reserve. The service main control and scour valves are operated from ground level and cannot be operated when the reservoir is above dam crest level and spilling.

Gosling Creek Reservoir is part of the Orange water supply system with water transferred in very specific circumstances. Specifically, water is transferred from the reservoir to Spring Creek Reservoir according to the following rules:

• Release trigger – water is transferred when the combined storage levels of the city’s two main reservoirs (Suma Park and Spring Creek Reservoirs) are at or estimated to reach 25% of their full supply level within the short term based on existing drawdown rates of the city’s combined water supplies; and

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• Cease release trigger – transfer stopped when the storage in Gosling Creek Reservoir reaches 50%.

The above rules provide access to about 262 ML of stored water plus any inflows occurring at the time.

The cease release trigger is based on a Council resolution. However an environmental impact assessment undertaken for the emergency transfer of water in 2009 found that the storage could be drawn down to 10% without significant adverse environmental impact (Geolyse, 2009a). This would provide access to a further 150 ML of stored water (plus any inflows occurring at the time).

3.2.2.5 Options for Additional Water Supply

Gosling Creek Dam forms the upper most storage in the system and therefore fills first in response to catchment runoff before spilling to Spring Creek Reservoir. Stored water is used when the city’s main storages are drawn down.

There are no realistic options for increasing the capacity of Gosling Creek Reservoir, or significant benefits in operating the storage in a different manner.

3.2.3 SPRING CREEK DAM

3.2.3.1 Background

Spring Creek Dam was constructed in 1931 along with the Spring Creek Water Treatment Plant (WTP) and became the main water supply for Orange at the time. Sixteen years later, in 1947, the Spring Creek Dam wall was raised and, following a partial embankment failure in 1966, reconstruction work was undertaken and completed in 1969.

Spring Creek Reservoir was drawn down in March 2000 to allow safety upgrade works to be undertaken on the main embankment and spillway. These works were completed in March 2007. The Spring Creek WTP was decommissioned in 2000 as it was unable to access water from the storage during the dam upgrade works. This plant is unlikely to be used again.


Spring Creek Dam is located at the junction of Spring Creek and Gosling Creek, downstream of Gosling Creek Dam (refer to Figure 2). Inflow to Spring Creek Reservoir includes Gosling Creek (the overflow from Gosling Creek Dam), Brandy Creek and Spring Creek. The catchment area upstream of the dam is 65.57 km2 which includes the Gosling Creek Dam catchment.

Spring Creek Dam is a composite dam, consisting of an earth fill embankment with a concrete core and has a height of 16 m and a crest length of 206 m. The dam has a storage capacity of 4,449 ML and surface area of 97.5 ha at FSL.

The stage-storage curve for Spring Creek Reservoir is provided in Figure 4.


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Figure 4: Spring Creek Reservoir stage-storage curve


Spring Creek Dam is a prescribed dam under Schedule 1 of the Dams Safety Act, 1978. The Dams Safety Committee (DSC) can require owners of prescribed dams to do things to ensure the safety of their dams.

Spring Creek Dam has the following consequence categories:

• SDCC High C

• FCC High C

The latest dam surveillance report was completed in 2001 and found that while the dam was performing satisfactorily there could be no guarantee that this would continue into the future. A concept design report was subsequently completed to address safety issues and upgrading works completed in 2007.

3.2.3.4 Operation

The Spring Creek WTP sourced raw water from the reservoir, treated and distributed this water to the water reticulation system. This plant had a capacity of 10 ML/day but was decommissioned in 2000 when the storage was drawn down to facilitate the dam safety upgrade works. Since that time, all potable water has been supplied from the Icely Road WTP.

Spring Creek Reservoir is now operated as part of the combined water storage. Prudent water management maintains stored water higher in the system as it requires energy to move water uphill. Therefore Spring Creek Reservoir is used for water storage with water being transferred to Suma Park Reservoir when the downstream storage falls to less than 25%.

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3.2.3.5 Options for Additional Water Supply

There are no realistic options for increasing the capacity of Spring Creek Reservoir, or significant benefits in operating the storage in a different manner.

A feasibility study for de-silting the storage on the back end of the upgrade works and while the reservoir was essentially empty was undertaken in March 2007 (Geolyse, 2007). Undertaking this activity would increase the dam storage capacity and the conditions under which this activity could be physically undertaken are infrequent and short lived – that is, it was seen as opportune while the dam was empty, which (hopefully) would not occur again within the short term.

De-silting the dam would entail removal of the sediment deposited on top of the (then) natural ground surface since the dam was built. The rate and concentration of deposition would vary spatially; with a concentration closer to the original stream beds and behind the wall. Test pits were excavated across the floor of the storage and it was estimated that the de-silting would remove an average of 200 mm across the floor area (approximately 74 ha). This would yield 148,000 m3 of sediment; providing an additional 148 ML of storage: a 3% increase in capacity, the equivalent to about 10 days average water supply for the city of Orange (Geolyse, 2007).

The logistics, costs and approvals process of this operation were considered. It was estimated that the direct economic cost of de-silting 148,000 m3 (in situ) of material ranged from between $3.5 to $5.3 million. This equates to a cost of between $22,680 and $35,760 for each additional megalitre of storage obtained.

Secure yield modelling undertaken for the IWCM Evaluation Study for the raising of Suma Park Dam (refer to Section 3.2.4.5) shows that storage volume increases of over 1,600 ML only increased the system secure yield by around 200 ML/year. Based on this result, the potential 148 ML additional storage gained by de-silting Spring Creek Reservoir would not have a significant impact on the system secure yield.

The option of de-silting Spring Creek Reservoir (Option SW8) was ruled out at the time the storage was drawn down. It would be even more expensive to do now that the dam is full.

3.2.4 SUMA PARK DAM

3.2.4.1 Background

Persistent water shortages remained following the increase in capacity of Spring Creek Reservoir. A new dam, Suma Park Dam, was constructed on Summer Hill Creek to the north-east of the city. This dam was completed in 1962 and provided a reservoir with a capacity of 18,100 ML (see comment below regarding revised storage volume).

The Icely Road WTP was completed in 1959 and sourced its raw water from the Suma Park Reservoir. The capacity of the Icely Road WTP was increased in 1966 to 20 ML/day. More works commenced in 1981 to double the capacity of the Icely Road WTP with construction completed in 1985. It now has a capacity of 38 ML/day and is the main water treatment plant for the city’s water supply system.

Suma Park Dam creates the main water supply reservoir for Orange.


Suma Park Dam is located on Summer Hill Creek approximately 2.5 km upstream of its confluence with Blackmans Swamp Creek (refer to Figure 2). Inflow to Suma Park Reservoir includes Gosling Creek (the overflow from Spring Creek Dam), Dairy Creek and Summer Hill Creek. The total catchment area upstream of the dam is 178.49 km2 of which 112.92 km2 (63%) is downstream of the Spring Creek Dam catchment.


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Suma Park Dam has the following components:

• a main dam consisting of a 30.5 m high concrete arch dam with a central ungated spillway. The crest length of the main wall is about 208 m. Discharge over the spillway is dissipated in a plunge pool at the base of the dam;

• a 6 m high, 160 m long earth fill saddle dam located about 400 m west of the main dam; and

• outlet works consisting of an intake tower about 5 m upstream of the main dam wall that conveys water to the pump station approximately 300 m downstream which delivers water to Icely Road WTP.

Initial stage-storage data showed that Suma Park Reservoir stored approximately 18,100 ML at FSL. A detailed bathymetric survey was undertaken in July 2010 and a new stage-storage curve developed for the reservoir. Further detailed survey was conducted on the main wall and spillway section as part of the safety upgrade works. This determined that the minimum spillway level is RL 842.31 m AHD. From this data the revised capacity of Suma Park Reservoir at FSL is 17,290 ML.

The original and revised stage-storage curves for Suma Park Reservoir are shown in Figure 5. The revised data shows that the storage has a surface area of 159.5 ha at FSL.

Figure 5: Suma Park Reservoir stage-storage curve


Suma Park Dam is a prescribed dam under Schedule 1 of the Dams Safety Act, 1978. The Dams Safety Committee (DSC) can require owners of prescribed dams to do things to ensure the safety of their dams.

Suma Park Dam has the following consequence categories:

• SDCC High B

• FCC High B

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The latest dam surveillance report was completed in 2001 and found that while the dam was performing satisfactorily there could be no guarantee that this would continue into the future. The spillway capacity of Suma Park Dam does not meet standards recommended by the NSW Dam Safety Committee (NSW DSC) and the Australian National Committee on Large Dams (ANCOLD) therefore an upgrade to the dam is planned.

3.2.4.4 Suma Park Dam Upgrade

Engineering consultants are currently undertaking the concept, detailed design and documentation for the safety upgrade works. Council is seeking a realistic, innovative, cost-effective solution to address the risks presented by Suma Park Dam in both the short and long term by combining a staged construction approach with an effective flood warning system.

Upgrade of the dam will be undertaken in two stages:

• Stage 1: upgrade of the dam to achieve appropriate capacity within the dam to safely pass the 1 in 1,000,000 Annual Exceedance Probability (AEP) flood (note that this was originally to upgrade the dam to safety pass the 1 in 100,000 AEP flood; however this was revised to the 1 in 1,000,000 AEP flood after a review of the catchment hydrology); and

• Stage 2: works to achieve a negligible risk level with regards to dam safety.

The concept and detailed design work is addressing Stage 1 of the dam upgrade works.

A review of the catchment flood hydrology was completed as part of the concept phase. This demonstrated that the upgraded Spring Creek Dam has a significant effect on attenuating flood inflows to Suma Park Dam. It was therefore feasible to upgrade the spillway of Suma Park Dam to accommodate the 1 in 1,000,000 year flood for the Stage 1 upgrade. The concept design for the Stage 1 upgrade includes (Entura, 2011a):

• Stage 1A: a 2.3 m high parapet wall on the downstream side of the crest of the non-overflow sections of the main concrete wall; and

• Stage 1B: a three bay fuseplug spillway at the location of the saddle dam up to 5.25 m high.

The estimated project costs for these stages are:

• Stage1A $2.7 million

• Stage 1B $5.4 million

• Total Stage 1 $8.1 million

Earthquake analysis demonstrated that the upgraded dam would retain a sufficient factor of safety following damage from the maximum design earthquake and that no additional strengthening was required. It was concluded that at the completion of Stage 1A and Stage 1B works the dam will satisfy the NSW DSC’s requirements for negligible dam safety risk with no further upgrade (Entura, 2011a). In effect, the Stage 2 objectives have been achieved with the Stage 1 works and no further works are required.

3.2.4.5 Raising Suma Park Dam

Description

Following review of the concept design prepared for the Stage 1 upgrade works, Council commissioned an assessment of the technical, cost and program implications of raising the FSL of Suma Park Dam. This assessment examined the implications of a 1.0 m and 2.0 m increase in FSL (Entura, 2011b).

The main findings from this assessment are (Entura, 2011b):

• a 1.0 m raising of FSL by raising the concrete spillway and providing a larger fuse plug auxiliary spillway poses no insurmountable technical issues;


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• raising the FSL by greater than 1.0 m should not be considered as the stresses in the existing concrete arch dam wall would exceed allowable limits;

• raising the FSL by 1.0 m inundates properties not belonging to Council and land acquisition would be required;

• an Environmental Impact Statement (EIS) is likely to be required to identify any environmental issues and obtain the required statutory approvals for raising the FSL; and

• the EIS and property acquisition is likely to take a minimum of 12 months.

The estimated capital costs of including a 1.0 m increase in the FSL in association with the Stage 1 dam safety upgrade works gave the following cost breakdown:

• Stage1A $4.1 million

• Stage 1B $6.9 million

• Total Stage 1 $11.0 million

With an allowance for an additional $0.65 million for approvals and land acquisition, the additional cost to increase the FSL by 1.0 m is $3.55 million.

A 2.0 m increase would cost an additional $6.86 million; however as noted above, a 2.0 m increase in FSL is not technically feasible and no more than a 1.0 m increase should be considered for the dam (Entura, 2011b).

There would be no annual operating costs for the dam raising option, apart from routine dam maintenance and inspection which is already undertaken.

Raising Suma Park Dam is included in Council’s BAU scenario.

Assessment of Secure Yield

The benefit of increased storage capacity in Suma Park Reservoir was assessed using secure yield modelling. This assessment considered:

• inflow from the existing catchment;

• the potential input from other external catchment water sources including bores, stormwater harvesting and the proposed Macquarie River to Orange pipeline; and

• possible changes in environmental flow releases from Suma Park Dam.

The secure yield analyses used the following Suma Park Reservoir volumes:

• Current spillway level (842.31 mAHD); volume = 17,290 ML

• Raise 1.0 m (843.31 mAHD); volume = 18,970 ML

• Raise 2.0 m (844.31 mAHD); volume = 20,760 ML

Suma Park Dam is licenced under Part II of the Water Act, 1912. Condition (6) of the current licence (80SL046857) includes an environmental flow release requirement as follows:

(6) Subject to condition (7), the licensee shall release into the watercourse downstream of the dam a flow of water equivalent to 12 litres per second or to the flow entering the storage of the dam for the time being, whichever is the lesser.

The licence is currently being reviewed as part of the public enquiry being handled by the Orange District Land Board. The draft licence proposes an amendment to condition (6) as follows:

(6) Subject to condition (7), the licensee must release into the watercourse downstream of the dam a flow of water equivalent to 2 megalitres per day for a total of 176 consecutive days commencing 1 November each year and ending 25 April each following year (being a total of 352 megalitres).


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These two conditions were assessed in the secure yield modelling as Environmental Flow Rule (EFR) 1 and 2 respectively.

The secure yield analysis included input from a number of external sources in addition to the natural catchment inflow. The results presented include input from the external sources listed in Table 3.1.

Table 3.1 – Supply from external sources for assessment of raising Suma Park Dam

Variable

BSC100PC/100 Daily input from the Blackmans Swamp Creek and Ploughmans Creek stormwater harvesting schemes added to Suma Park Dam whenever the storage in the dam is less than 100%

Bores75 (1) A daily inflow of 0.2 ML/day to Suma Park Dam only when the storage is less than 100%

MR12/30 (2) Add 12 ML/day to Suma Park Dam when: 1. Volume in Suma Park Dam is 30 ML/day

Bores300 An additional inflow from the bores of 0.62 ML/day to Suma Park Dam only when the storage is less than 100%. This is additional to Bores75 i.e. the total bore inflow is 0.82 ML/day (or 300 ML/year).

BSC2 Daily input from the Blackmans Swamp Creek Stage 2 and Ploughmans Creek stormwater harvesting schemes added to Suma Park Dam whenever the storage in the dam is less than 100%

Lake Rowlands Adding a daily inflow of 2.66 ML/day (972 ML/year) to Suma Park Dam only when the storage is less than 100%

(1) At the time of undertaking this assessment, the existing groundwater bores were licensed to extract 75 ML/year. New licences were granted in early 2012 increasing the annual extraction limit to 462 ML/year.

(2) At the time of undertaking this assessment, Th

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Technical Note 2 - Orange City Council...2019/10/04 · TECHNICAL NOTE 2 ORANGE WATER RESOURCES ORANGE CITY COUNCIL OCC_IWCM_TECHNICAL NOTE 2_FINAL.DOCX This report has been prepared