Department of Primary Industries, Water and Environment

Meander Dam Feasibility Study Engineering Review

Prepared by

HYDRO ELECTRIC CORPORATION ARBN 072 377 158 Report No.: TAS-106880-CR-03 4 Elizabeth St, Hobart Rev. Status: Rev. 0 Tasmania, Australia Date Issued: February 2002 Document Information

JOB/PROJECT TITLE:

Meander Dam Feasibility Studies

TITLE: Meander Dam Feasibility Studies: Desktop Review

CLIENT ORGANISATION: Department of Primary Industries Water and Environment

CLIENT CONTACT: Debbie Miller

DOCUMENT ID NUMBER: TAS-106880-CR-03 DATE: 21 February 2002 REVISION STATUS: Rev. 0 JOB/PROJECT MANAGER: Paul Southcott JOB/PROJECT NUMBER: TAS-106880

CURRENT DOCUMENT APPROVAL:

COMPILED BY: P. Southcott

REVIEWED BY: B. Knoop

APPROVED BY: L. Polglase

REVISION HISTORY:

REV DATE DESCRIPTION PREPARED REVIEWED APPROVED

Hydro Tasmania Page ii Meander Dam Feasibility Study Engineering Review Executive Summary Introduction Low summer flows in the Meander River due to extractions of water for irrigation result in the reduced ecological health of the river and restrict the growth in irrigation in the Meander Valley. The proposed Meander Dam is expected to address these two key issues bringing greater economic activity to the region and improving the environmental condition of the river.

Proposals to build a dam on the Meander River at Warners Creek go back to at least 1968 when the Rivers and Water Supply Commission recommended that the site be investigated further. Since then there have been a number of economic and technical studies undertaken of a dam at this site. The most recent was a 1995 study by Gutteridge Haskin & Davey (GHD) which examined the environmental implications of a multiple farm dam alternative to a major dam on the Meander at Warners Creek. In the Tasmanian State Budget of 2001, the government allocated money to undertake final feasibility studies of the dam, with a view to progressing the project as rapidly as possible.

The proposed dam site is at the southern end of the Meander Gorge, approximately 450 metres downstream of the confluence of the Meander River and Warners Creek (Quamby Bluff 1:25000 map sheet 4638 E468350, N5384100).

A desktop review conducted as part of this study concluded that a 50m high dam storing approximately 43,000ML was technically feasible, although it recommended that more detailed investigations be undertaken to address the issues. This engineering feasibility report is the second report and describes the detailed technical feasibility studies that have been undertaken by Hydro Tasmania on behalf of the Department of Primary Industries Water and Environment into the proposed dam. The investigations included:

§ An assessment of the geology and geotechnical conditions at the dam site, reservoir area and catchment. § An investigation into the hydrology of the catchment including basic characterisation of the hydrological parameters, catchment yield, storage yield and behaviour, and flood hydrology. § An engineering assessment of the most economic and appropriate form of dam construction for the site and preliminary design of the preferred arrangement. § An engineering assessment of the viability of a mini-hydro power station, including an assessment of possible options, and preliminary design of the preferred option.

Total demand for irrigation water is estimated as approximately 26,000ML/a consisting of 2000ML/a of current water entitlements and a preliminary estimate of the additional demand for irrigation water of 24,000ML/a, based on a farmer survey. It is concluded that a dam 50m in height storing approximately 43,000ML provided the best tradeoff between reliability and quantity of the water supplied. The estimated cost of the dam is $25m and could be constructed over a period of about 18 months.

Technical Assessment Geology The geotechnical investigations showed that the foundations of the dam would be on dolerite bedrock. The dolerite has joints and other geological structures that will require grouting and surficial treatment to make good the foundation for a dam with low potential leakage. The diversion conduit for the RCC dam is likely to be excavated in weathered to sound fresh

Hydro Tasmania TAS-106880-CR-03 Page iii Meander Dam Feasibility Study Engineering Review dolerite and the dam's stability is likely to be controlled by the presence of sheet joints. It is anticipated that some rock bolting and shotcreting may be required during construction to support this cut. There is a major fault cutting across the river downstream of the dam wall that will require shotcrete lining where encountered in the diversion cut.

The other significant feature of the site is the low saddle area - Huntsman Saddle on the left bank of the dam site. Concerns have been expressed over the potential seepage loss through this saddle area. It should be possible to operate the dam at a full supply level of 402m without significant seepage loss in this area. It is recommended that ground water monitoring be established prior to filling the reservoir and this be continued after first filling to ensure that any potential environmental impacts are identified and managed in an appropriate fashion.

Slope stability in the reservoir is a further concern for the project, since much of the storage basin is surrounded by deep talus soils derived from the surrounding Jurassic age dolerite. Landslides appear to be a common feature of the catchment area, and the concern would be the re-activation of landslides (although none have been identified within the storage) under normal operation of the reservoir which may lead to turbidity problems. This is not expected to impact on the integrity or longevity of the dam. Provision in the dam design has been made for sedimentation with a significant volume of dead storage.

Hydrology Hydrological and meterological data have been summarised for the Meander Dam site and surrounding areas. The data shows a strong seasonal influence with low flows over the summer period and high flows over the winter. Stream gauge records for the site cover the period from 1982 and 1991. The record has been extended through correlation with downstream sites to give a record length of approximately 34 years and from this the average annual catchment yield was found to be 189,000 ML.

A daily time step storage analysis model was developed that incorporated inflows, direct rainfall and evaporation, releases for environmental flows, domestic water supplies and irrigation, and spills. It was found that the reliability of supply of the irrigation water and yield from the reservoir were sensitive to the environmental releases. With trout excluded from consideration of the environmental flows, the annual yield of the reservoir with a full supply level of 402m was an additional 24,000 ML/a for irrigation with a reliability on an annual basis of 88%.

A flood routing model was developed for the catchment and a range of inflows from 1:50 AEP to the Probable Maximum Precipitation Design Flood (PMPDF) were analysed. The critical duration varies from 24 hours for the 1:50 AEP flood to 6 hours at the PMPDF. The peak inflows and outflows for the 1:50 AEP flood are 545 m3/s and 215 m3/s respectively. The corresponding values for 1:10,000AEP flood are 1680 m3/s and 1415 m3/s. It is apparent that the dam will have a significant attenuating effect on peak flows at the dam and should have a beneficial impact in reducing downstream flood impact.

Dam Engineering Three types of dam were considered: Roller Compacted Concrete (RCC), Concrete Faced Rockfill (CFR) and Earth Rockfill (ERF). On the basis of lower costs and lower construction risks, the RCC option was found to be the best solution. Preliminary design of the RCC has been undertaken and the arrangement includes:

Hydro Tasmania TAS-106880-CR-03 Page iv Meander Dam Feasibility Study Engineering Review § upstream and downstream coffer dams with a box culvert diversion conduit running along the right bank; § a RCC wall with a vertical upstream face and downstream face slope of to 1V:0.8H; § A centrally located conventional concrete spillway with 4 Flowgate spillway gates, which only operate at floods in excess of 1:400 AEP; § A multilevel offtake built into the body of the dam, with a conduit discharging through a cone dispersion valve; § Emergency dewatering facilities;

The design has taken into account environmental concerns and has a multi-level offtake to ensure the best quality water is released from the reservoir. Furthermore, screening sufficiently fine to exclude fish from the outlet works is proposed. Fish passage is to be catered for through a trapping and relocation program.

The estimated cost of design and construction of the dam is approximately $25m and the annual operating costs are estimated to be $115,000.

Mini Hydro A number of options for the mini-hydro were considered during the study, including left and right bank options, and a number of alternatives for the right bank option. It was concluded that a power station located at the base of the dam housing two horizontal axis Francis turbines of 2.85 and 1.35MW capacity is the best option. This arrangement has the potential to generate an annual average of approximately 13,000 MWh. On this basis the mini-hydro is an economically attractive addition to the project and is expected to add to the return on the investment. The estimated cost of design and construction of the mini-hydro is approximately $6.0m and the annual operating costs are estimated to be $75,000.

Overall Conclusions A 50m high RCC dam with a 43,000ML reservoir, supplying a total irrigation water demand of 26,000ML is technically feasible. Providing that the environmental and economic aspects of the project are shown to be viable, then it is recommended that the project can proceed to detailed design and construction. The approach taken could either be for a design contract followed by a construction contract, or as a single design and construct contract.

Hydro Tasmania TAS-106880-CR-03 Page v Meander Dam Feasibility Study Engineering Review Data Summary of Dam and Mini-Hydro The following is a summary of important data relating to the dam and appurtenant structures. Reference should also be made to the drawings in this report.

DAM NAME: Meander Dam

STREAM: Meander River

CATCHMENT AREA: 159 km2

DAM TYPE: Roller Compacted Concrete (RCC)

HEIGHT: 48m

CREST LENGTH: 170m

VOLUME OF DAM: 64000 m3

CREST LEVEL: S.L. 406.5m plus 1.2m high crest wall giving overall height of S.L. 407.7m. FULL SUPPLY LEVEL: S.L. 402.0m

DESIGN FLOOD LEVEL: S.L. 407.1m

FREEBOARD ABOVE DFL: 0.6m

GROSS RESERVOIR CAPACITY: 43000 ML

EFFECTIVE STORAGE CAPACITY: 41000 ML

TYPE OF SPILLWAY: Centrally located conventional spillway 28m wide with 4 Flowgate spillway gates which only operate at floods in excess of 1:400 AEP.

SPILLWAY CREST LEVEL: · Concrete sill: S.L. 398.5m · Top of gates: S.L. 402.0m

SPILLWAY CAPACITY: 1500 m3/s

TYPE OF OUTLET WORKS: · Multilevel offtake built into the dam body with five intake valves and an emergency dewatering valve. · A cone dispersion valve for irrigation releases. · A riparian flow valve.

PERIOD OF CONSTRUCTION: 18 months of site works starting in April.

PERIOD OF INITIAL FILLING: August of second year.

Hydro Tasmania TAS-106880-CR-03 Page vi Meander Dam Feasibility Study Engineering Review

The following is a summary of important data relating to the mini hydro. Reference should also be made to the drawings in this report.

POWER STATION STRUCTURE Concrete construction with removable metal roof.

STATIC HEAD: 42m

GENERATING SET: Two horizontal axis Francis turbines of 2.85 MW and 1.35 MW capacity.

RATED OUTPUT: 1.7 MVA and 3.2 MVA

RATED VOLTAGE 11 kV

MAXIMUM DISCHARGE: 12 m3/s

AVERAGE ANNUAL GENERATION: 13248 MWhr

Hydro Tasmania TAS-106880-CR-03 Page vii Meander Dam Feasibility Study Engineering Review Table of Contents

1 INTRODUCTION...... 1 2 GEOLOGY ...... 3 2.1 Introduction 3 2.2 Scope of Report 3 2.3 Review of Documentation 4 2.4 Regional Geology 4 2.4.1 General Topography 4 2.4.2 General Geology and Permeability of Dam Site 5 2.4.3 General Geology of Project Area 5 2.4.4 Fault Zones 6 2.4.5 Karstic Topography 6 2.4.6 Geomorphological Processes 6 2.4.7 Geomorphological Processes – Upstream and Downstream from Dam Site 7 2.4.8 Regional Seismicity 8 2.5 Dam Site 9 2.5.1 General 9 2.5.2 Rock Types 9 2.5.3 Geological Structure 9 2.3.5.1 Jointing 9 2.3.5.2 Faulting 10 2.5.4 Chemical Weathering 10 2.5.5 Physical Weathering 10 2.5.6 Groundwater and Permeability 10 2.5.7 Engineering Implications 11 2.7.5.1 General 11 2.7.5.2 Foundation strength and stripping depths 12 2.7.5.3 Dam foundation permeability and grouting 13 2.7.5.4 Use of excavated rock as sources of rockfill 13 2.7.5.5 Sources of additional rockfill materials for the dam type options 13 2.5.8 Risk Assessment for Dam Foundation Preparation 14 2.5.9 Diversion Tunnel or Conduit 15 2.9.5.1 General 15 2.9.5.2 Risk Assessment for Diversion Tunnel 16 2.5.10 Spillway 16 2.10.5.1 General Excavation and Support Requirements 16 2.10.5.2 Risk Assessment for Spillway 17 2.10.5.3 Erodibility 18 2.6 Borrow Materials 18 2.6.1 General Requirements 18 2.6.2 Clay Borrow 19 2.6.3 Filter Zone 19 2.7 Slope Stability - Storage Area 19 2.8 Huntsman Saddle 20 2.8.1 General 20 2.8.2 Risk Assessment 21 2.9 Conclusions 21 2.10 References 22

Hydro Tasmania TAS-106880-CR-03 Page viii Meander Dam Feasibility Study Engineering Review 3 HYDROLOGY ...... 23 3.1 Data Availability 23 3.2 Yield Analysis 25 3.3 Low Flow Frequency Analysis 26 3.4 Analysis of Storage Reliability 28 3.4.1 Approach of Analysis 28 3.4.2 Inputs to the Model 29 3.4.3 Mini Hydro Considerations 32 3.4.4 Determination of Failure/Reliability 32 3.4.5 Results 33 3.5 Estimation of Design Flood 41 3.6 References 44 4 DAM ENGINEERING...... 46 4.1 Storage Capacity 46 4.2 Alternatives Considered 46 4.2.1 Earth and rockfill dam 47 4.2.2 Concrete faced rockfill dam 48 4.2.3 Comparison of options 48 4.3 Roller Compacted Concrete Dam Arrangement 49 4.3.1 Stability checks 49 4.3.2 Foundation treatment 50 4.3.3 Materials and construction methods 50 4.3.4 Instrumentation 50 4.3.5 Site layout 51 4.3.6 Construction schedule 51 4.4 Diversion Arrangement 52 4.5 Spillway Arrangement 55 4.6 Outlet Works 58 4.7 Reservoir Drawdown 58 4.8 Operation & Maintenance 59 4.9 Data Summary 61 4.10 References 62 5 MINI HYDRO ...... 63 5.1 Introduction 63 5.2 Location of Mini Hydro Power Station 63 5.3 Turbine Selection 64 5.4 Generator System 65 5.5 Auxiliary Electrical Systems 66 5.6 Grid Connection 66 5.7 Power House Configuration 66 5.8 Economic Viability 67 5.8.1 Energy Price 67 5.8.2 Capital Cost Estimate 68 5.8.3 Annual Revenue and Expenditure 68 5.8.4 Economic Analysis 68 5.9 Project Risks 68 5.10 Data Summary 69 5.11 Conclusions 69 6 CONCLUSIONS ...... 73 6.1 Geology 73

Hydro Tasmania TAS-106880-CR-03 Page ix Meander Dam Feasibility Study Engineering Review 6.2 Hydrology 73 6.3 Dam Engineering 74 6.4 Mini Hydro 74 6.5 Overall Conclusions 75 APPENDIX A1 RESULTS OF LABORATORY TESTING...... A1 - 1 APPENDIX A2 PLAN OF GEOLOGICAL INVESTIGATIONS...... A2 - 1 APPENDIX A3 GEOLOGICAL CROSS SECTIONS AT THE DAM SITE...... A3 - 1 APPENDIX A4 TRENCH LOGS ...... A4 - 1 APPENDIX B1 CLIMATE STATISTICS...... B1 - 1 APPENDIX B2 DATA AVAILABILITY AND QUALITY...... B2 - 1 APPENDIX B3 YIELD ANALYSIS RESULTS ...... B3 - 1 APPENDIX B4 CONCEPTUAL TIME STUDIO MODEL...... B4 - 1 APPENDIX B5 FLOOD FIT HYDROGRAPHS...... B5 - 1 APPENDIX B6 DESIGN RAINFALLS ...... B6 - 1 APPENDIX B7 DESIGN FLOOD HYDROGRAPHS ...... B7 - 1 APPENDIX B8 DAVEY AND MAYNARD WATER DEMAND SURVEY...... B8 - 1 APPENDIX C1 COST ESTIMATE COMPARISON FOR THE THREE DAM TYPES C1 - 1 APPENDIX C2 DETAILED COST ESTIMATE FOR THE RCC OPTION...... C2 - 1

DRAWINGS

Hydro Tasmania TAS-106880-CR-03 Page x Meander Dam Feasibility Study Engineering Review

1 Introduction Low summer flows in the Meander River due to extractions of water for irrigation result in the reduced ecological health of the river and restrict the growth in irrigation in the Meander Valley. The proposed Meander Dam is expected to address these two key issues bringing greater economic activity to the region and improving the environmental condition of the river.

Proposals to build a dam on the Meander River at Warners Creek go back to at least 1968 when the Rivers and Water Supply Commission recommended that the site be investigated further. Since then there have been a number of economic and technical studies undertaken of a dam at this site. The most recent was a 1995 study by Gutteridge Haskin & Davey (GHD) which examined the environmental implications of a multiple farm dam alternative to a major dam on the Meander at Warners Creek. In the Tasmanian State Budget of 2001, the government allocated money to undertake final feasibility studies of the dam, with a view to progressing the project as rapidly as possible.

The proposed dam site is at the southern end of the Meander Gorge, approximately 450 metres downstream of the confluence of the Meander River and Warners Creek (Quamby Bluff 1:25000 map sheet 4638 E468350, N5384100). Previous investigation reports have proposed a dam at this site, up to 50 metres in height and storing up to 43,000 megalitres. The feasibility of a mini-hydro power station was also investigated.

This engineering feasibility report is the second in a series of a detailed feasibility studies being undertaken by Hydro Tasmania on behalf of the Department of Primary Industries Water and Environment into the proposed dam. The other documents in the series are:

§ Meander Dam Feasibility Study – Desktop Review, § Meander Dam Feasibility Study – Environmental Review, and § Meander Dam Feasibility Study – Agricultural and Economics Review

The aims of this report are:

§ To further investigate key engineering issues requiring additional investigation, as identified in the Meander Dam Desktop Feasibility report; § To assess these issues and undertake preliminary design of the dam and mini-hydro; § To estimate the costs of design, construction and operation; § To identify any technical risks associated with the project.

The report is structured into chapters covering: § Geology of the dam site and catchment; § Hydrology of the dam; § Engineering of the dam; § Engineering of the mini-hydro.

The report does not address the overall economics or environmental aspects of the project, except where these impact on the technical specification of the dam. The detailed environmental and economic analyses are included in the separate reports listed above.

Hydro Tasmania TAS-106880-CR-03 Page 1 of 75 Meander Dam Feasibility Study Engineering Review If the project is found to be feasible on engineering, economic, agricultural and environmental grounds, the information gathered during the preparation of this series of reports will be used to prepare a Development Proposal and Environmental Management Plan.

Hydro Tasmania TAS-106880-CR-03 Page 2 of 75 Meander Dam Feasibility Study Engineering Review

2 Geology

2.1 INTRODUCTION This chapter sets out our assessment of the geological and geotechnical conditions at the Meander Dam Site with respect to the feasibility of constructing an irrigation supply dam. Our assessment has focussed on the feasibility of constructing three particular types of dams at this site, ie, an earth and rock fill dam (ERF), a roller compacted concrete dam (RCC) and a concrete faced rockfill dam (CFR). Our comments although primarily directed at a ERF dam are generally also applicable to the other two alternatives.

The geotechnical investigations that were previously carried out at the site were directed primarily at the RCC and/or CFR option. Consideration is now being extended to Earth Rock Fill (ERF) options.

The purpose of this chapter is to identify those features of the geomorphology and geology at the project area, including the dam site that could affect or rule out the construction of an earth rock fill dam (ERF), or the other options (RCC, CFR) dams.

2.2 SCOPE OF REPORT The role of Coffey Geosciences Pty Ltd, (Coffey) in the Hydro Tasmania team was to assess the geotechnical conditions at the site and to provide feasibility level geotechnical design advice for the engineering studies of various dam options.

The purpose of the geotechnical assessment is to: · Assess the foundation/bedrock conditions at the proposed dam site; · Locate possible sources of dam construction materials; · Assess the spillway cut and tunnel excavation conditions.

During this project Coffey was to make recommendations on any further geotechnical investigations that may be required to progress the dam design to a construction level of detail.

Coffey’s proposed methodology was as follows: · Conduct a review of the existing Hydro Tasmania and GHD reports, plans, sections, field logging and mapping information available through Department of Primary Industries Water & Environment, Hydro Tasmania, Mineral Resources Tasmania and GHD archives. The information would be collated and summarised to allow the development of engineering geological models for the site; · Produce engineering geological and geotechnical models of the site with particular emphasis on interpretation of potential problem areas such as the spillway excavations, dam foundations, and the Huntsman Saddle area; · Conduct a site visit, including engineering assessment of the reservoir, dam and spillway sites; · Conduct a subjective geotechnical risk assessment to identify areas that could affect the overall feasibility of the dam project, and/or require further investigation or specific engineering at feasibility, or detailed design stages;

Hydro Tasmania TAS-106880-CR-03 Page 3 of 75 Meander Dam Feasibility Study Engineering Review · Specify additional investigations for feasibility level borrow investigations to find suitable low permeability material that would be required if a rock and earthfill embankment is proposed as an option; · Prepare feasibility engineering geological models and geotechnical design recommendations; · Report the findings and recommendations, with all relevant information from past investigations appended. · A potential source for low permeability borrow would be identified and further investigated by the excavation of approximately 6 test pits if an earth and rock fill dam was proposed. The test pits would be excavated using a conventional rubber tyred backhoe to depths of 3m or refusal, whichever was shallower. Disturbed samples of representative materials would be taken to assist with logging and to provide material for laboratory testing. The test pits would be excavated in the presence of a geotechnical professional from Coffey who would log the test pits, nominate sample intervals and collect samples. The pits would be backfilled immediately on completion and compacted using the backhoe wheels.

Recovered samples were to be returned to our Hobart office. Selected soil samples would be submitted to one of our NATA registered laboratories for tests comprising: · Standard compaction tests; · Atterberg limits tests; · Wet sieve grading curves; · Emerson Dispersion

A summary of the test results is included in Appendix A1.

2.3 REVIEW OF DOCUMENTATION The documentation reviewed for this report included: 1. Hydro-Electric Commission of Tasmania, (1989), “Meander River Irrigation Scheme, Meander Damsite Investigation Phase I, Site Investigation Report, Volume 1, Volume 2”, Report No. 64-W-12, Job No. 492-80005 2. Gutteridge, Haskins & Davey, 1989, “Rivers and Water Supply Commission, Meander River Dam Investigations, Preliminary Design Volume 1 – Report, April 1989, Extract pp1 – 84, No Figures .

Other documents that were checked for this report are referenced in the text where this is appropriate.

2.4 REGIONAL GEOLOGY

2.4.1 General Topography The dam site is located within a gorge through a down-faulted dolerite mass some 5km north of the Western Tiers formed from Jurassic age dolerite. A natural basin occurs between the downfaulted dolerite mass and the main escarpment of the Western Tiers. This basin forms the storage basin for the proposed dam. The Meander River traverses the basin in a generally north-easterly direction, across the relatively flat valley floor formed by the Poatina Group sedimentary rocks. The river course turns abruptly through a near horseshoe shaped curve immediately upstream from the entrance to the gorge in which the dam site is located. It then

Hydro Tasmania TAS-106880-CR-03 Page 4 of 75 Meander Dam Feasibility Study Engineering Review flows almost due north through the gorge at the dam site, then continues in a north easterly direction until it leaves the gorge over a kilometre downstream from the dam site. The abrupt change in direction and the horseshoe shaped curve referred to above have resulted in the left bank of the dam being formed by a relatively narrow ridge.

2.4.2 General Geology and Permeability of Dam Site The dam site is located at the entrance to the Meander River gorge that is about 300m deep cut through the dolerite mass between the prominent peaks of Archers Sugarloaf to the north west of the dam site and Warners Sugarloaf to the east of the dam site. The dam site is underlain by very high strength dark grey dolerite rock which is exposed as massive sheet exposures and cliffs at the proposed dam site. Appendix A2 gives the location of the investigations and Appendix A3 gives the geological cross-sections at the dam site.

Reasonably comprehensive geotechnical investigations have been carried out at the proposed Meander Dam including about 26 drillholes with associated water pressure testing and test pitting. The work has involved diamond core drilling at the dam site itself and at the Huntsman Saddle. The latter is a low saddle on the western side of the dam storage basin and could represent a potential area for seepage from the dam storage. Permeability testing of the rock mass at the proposed dam site has shown that the dolerite is a low permeability rock mass – less than 1 Lugeon (1 x 10-7 m/s). Strata close to the ground surface have been rendered more permeable by opening of jointing and physical weathering.

The storage basin for the dam is in Poatina Group of sedimentary rocks that include sandstone and minor calcareous units. Extensive permeability testing of this unit in the Huntsman Saddle area has shown permeabilities ranging generally between 2.8 x 10-6 m/sec and 6.3 x 10-7 m/sec at depths between 8.8m and 15.8 m. below the surface.

2.4.3 General Geology of Project Area The storage area of the proposed dam is a large semi-circular basin upstream of the actual gorge. It lies almost completely within the Permian age Poatina Group of fossiliferous mudstone and sandstone. Much of the storage area is obscured by Quaternary age alluvium and dolerite talus.

Topographic constraints impose restrictions on the height of dam that can be reasonably built at the site. The main restrictions are:

· The left abutment ridge at the dam site has a crest at ASL 410m to ASL 415m; the river bed at the centreline of the dam is at about ASL 360m; this difference restricts the height of dam at the selected site to about 50m. · Huntsman Saddle is a broad low lying saddle lying at ASL 409.4m, ie approximately7m above the proposed FSL 402m. The saddle is thus at the same level as the left abutment ridge, reinforcing the practical dam height of about 50m.

The Huntsman Saddle lies below the base of an old landslide to the east and Permian strata including possibly some cavernous limestone to the west. Elongated zones of seepage have been observed on the western side of the saddle where the geology comprises Permian siltstone and sandstone. The saddle represents a potential location for seepage loss from the dam storage area.

Hydro Tasmania TAS-106880-CR-03 Page 5 of 75 Meander Dam Feasibility Study Engineering Review The Jurassic age dolerite overlies the Permian age sedimentary sequence. The mass of dolerite within which the dam site is located is thought to represent a downfaulted block associated with Tertiary normal faulting.

The dolerite forms the steep topography surrounding the storage basin. The steeper topography is underlain by deep talus soils that result from normal colluvial processes as well as landsliding.

The Quaternary age sediments in the Meander River appear to be confined to the immediate vicinity of the stream and there do not appear to be extensive alluvial deposits within the storage area.

2.4.4 Fault Zones There is a major fault zone roughly at right angles to the Meander River at the dam site, located immediately upstream of the dam site. This appears to be a Tertiary age block fault that has resulted in the downfaulting of the dolerite mass that forms the actual dam site.

A second major fault zone cuts the Meander River at right angles on the immediate downstream side of the dam axis. This fault that was encountered during the geotechnical investigations for the dam is up to 10 metres wide.

2.4.5 Karstic Topography There are no known areas of karstic topography in the vicinity of the dam site or storage area. Calcareous interbeds have been described in the Huntsman Saddle area.

2.4.6 Geomorphological Processes The Meander River flows in a northeasterly direction across the gently sloping basin formed by Poatina Group sedimentary rocks. The high escarpment of the cliffs of Jurassic dolerite, are associated with prominent columnar jointing rings in the southern half of the basin. The gently sloping ground of the Poatina Group sedimentary rocks forms the northwestern quadrant of the basin and Huntsman Saddle. A downfaulted outlier of Jurassic dolerite forms the northeastern quadrant of the basin. The Meander River is joined by several other streams including the main tributary, Warners Creek, within the basin, resulting in braided stream channels and recent sediment deposits in the lowest part of the basin just upstream of the gorge.

The dolerite overlies the sub-horizontally bedded Permian Poatina Group sedimentary rocks.

Much of the basin below the escarpment has been cleared by forestry operations and there are numerous tracks and erosion scours resulting from these operations.

The geomorphological and tectonic processes resulting in the current topography and geologic conditions at the site comprise a combination of: · Permian deposition of Poatina Group sedimentary rocks. · Jurassic dolerite intrusions into the sedimentary rocks. Columnar jointing developed at this time. · Development of the precursor to the Meander River gradually eroding a channel through the Jurassic dolerite. · Tertiary age downfaulting of the dolerite mass in which the proposed dam is located.

Hydro Tasmania TAS-106880-CR-03 Page 6 of 75 Meander Dam Feasibility Study Engineering Review · Possible uplift of the dolerite mass at a rate that permitted the Meander River to cut the existing V shaped gorge in which the proposed dam is located. This assessment of uplift would account for the fresh nature of the dolerite in the Warners Sugarloaf/ Archers Sugarloaf mass and the youthful nature of the river and its gorge. Sheet jointing would have developed as the stress relief occurred during stream downcutting. · Continued weathering and erosion of the relatively weak Poatina Group sedimentary rocks in the Meander Dam basin leading to the flat valley floors and braided stream channel in the Meander Dam basin. Continued erosion of the Poatina Group sedimentary rocks continually undercuts the more resistant dolerite which fails along the near vertical columnar joints creating the prominent Western Tiers escarpment . · Talus from the undercutting of the Western Tiers escarpment weathers to clay soils and boulders, which saturates from rainfall and groundwater and develops into landslides at the base of the escarpment with sediment flowing into the Meander River. · Land clearing and forestry activities hastens the natural landslip process leaving the current topography.

2.4.7 Geomorphological Processes – Upstream and Downstream from Dam Site Downstream from the proposed dam site the Meander River continues in the youthful stream channel through the Warners Sugarloaf/ Archers Sugarloaf dolerite mass until it leaves the gorge and discharges on to the flatter agricultural land near Meander. The river in the gorge flows in a channel of dolerite bedrock with cobbles and boulder of dolerite talus. In the Meander River gorge the Meander River flows at a steeper gradient than in either the Meander Dam basin where the braided stream channels occur or in the flatter agricultural land around Meander. Because of the steeper gradient in the gorge only coarser materials such as coarse sand, gravel, cobbles and boulders are deposited. Finer materials such as clay slit and fine sand is deposited in the area of the Meander Dam basin floor or, through the process of continuing erosion is remobilised, and flushed through the narrow, relatively steep Meander River gorge as suspended solids during periodic flooding and eventually discharges at the downstream end of the gorge once the stream gradient flattens out, allowing sediments to deposit on the flatter agricultural land near Meander.

The process of temporary deposition of sediments in the Meander Dam basin, remobilisation for transport through the gorge and eventual deposition near the village of Meander reflects the sedimentary basin’s response to periodic flooding in the Meander Dam basin area. Of particular relevance to this process is the shape of the Meander Dam catchment with very steep talus slopes at the toe of the escarpment. The slopes are at slopes of about 350 to 500 at or steeper than their angle of repose, leading to active on-going undercutting of the Western Tiers escarpment. Run off from these slopes would be very rapid even in their natural undisturbed state. With forestry operations and land clearing the rate of run-off would be increased compared to the natural state accentuating the peak flow and hence the erosive capacity of the Meander River and its tributaries.

The geomorphologic processes in the catchment area upstream of the proposed dam must be described as youthful and very active in which the geomorphologic processes are dominated by periodic flooding from the steep catchment. The active processes would lead to erosion, landsliding and regular natural loss of natural flora and fauna in response to the landsliding.

Hydro Tasmania TAS-106880-CR-03 Page 7 of 75 Meander Dam Feasibility Study Engineering Review Fauna habitats in the talus slopes from the escarpment would change regularly in response to the landsliding.

The 1999 Dunnings Rivulet event focussed public attention on the landsliding and erosion potential in the area of Meander. In this event a record amount of silt was washed into the Tamar River in northern Tasmania. The yellow coloured sludge is believed to have travelled down river feeding into South Esk River from a landslide at the headwaters of Dunnings Rivulet, close the Central Plateau about 12 km south of Meander. As mentioned earlier landsliding and erosion of the landslide talus materials are a natural part of the landform development in the area of the proposed dam. Any land clearing or interference with the natural slopes will speed up the process leading to an imbalance between supply of material from the landslide areas and the erosion downstream. The implications for the proposed dam are that there will be an increased sedimentation rate if there is uncontrolled clearing in the catchment of the dam. The size and capacity of the proposed dam storage will permit the finer sediments to settle out. Spillway operation at the dam will discharge flood flows back into the river gorge downstream from the dam recreating natural flooding and erosion in the gorge but with a lower fine sediment and clay content than under natural conditions.

Active landslips are principally located on the escarpment well away from the reservoir. Thus, major landslides putting material directly into the reservoir are considered unlikely. The main impact of landsliding on storage volume will be from material transported by fluvial processes in the catchment and this will tend to limit the amount of material reaching the reservoir within its design lifetime. The finer sediments transported in suspension will tend to settle out in the reservoir although some will continue to pass through. A sediment store of 2 million cubic metres of material has been allowed for in the design of the dam. The coarser fraction landslide material would be transported as bedload at a rate defined by the carrying capacity of the stream into which the landslide ends up in. Bed load that does reach the reservoir will be deposited in the upper reaches. It is not considered that either of these will have any significant impact on the longevity of the storage.

2.4.8 Regional Seismicity In a comprehensive technical review of the Australian continent carried out by Doyle, Everingham and Sutton in 1968, (Reference 3), the main seismically active area of Tasmania was off shore to the north east of Tasmania near Flinders Island. In this area earthquakes of Magnitude of 6.0 or greater have been recorded. The next most seismically active area is the west coast area earthquakes in range of Magnitude 4.0 to 4.9 have been recorded.

Closer to the proposed dam site, a recent study of seismic microzonation in Launceston carried out by Michael-Leiba and Jensen (Reference 4), presented a tabulation of earthquakes that had caused damage in the Launceston area. Five events that have caused damage in Launceston had been reported between 1884 and 1946. These events were all off the north east coast, some 140 km to 240 km from Launceston. Seismic events along the west coast range up to about Magnitude 5.9, and were generally located at a distance of about 100km to 150 km from the proposed dam site.

For the proposed dam site it is concluded that there is a very low risk of seismic events at the dam site itself but there could be some effects from more distant earthquake centres off the north east coast.

Hydro Tasmania TAS-106880-CR-03 Page 8 of 75 Meander Dam Feasibility Study Engineering Review 2.5 DAM SITE

2.5.1 General The dam site is located within a down faulted block of Jurassic age dolerite through which the Meander River has cut a V shaped gorge with side slopes of about 350 on either side. The side slopes are thus reasonably symmetrical. The gorge is about 300m deep.

Most of the site is covered by either dolerite talus including dolerite cobbles and boulders in a red clay soil or by dolerite outcrops. When fresh, dolerite is a dark grey very high strength rock. Dolerite is exposed as massive sheet exposures and cliffs at the proposed dam site. Site clearing work and bulldozer trenching to provide access tracks to drilling platforms, was carried out as part of the original geotechnical investigations. Some erosion has apparently taken place as a result of this work, leaving a slightly higher proportion of bedrock exposure at the site than would have been the case in the natural site conditions.

The river at the dam site includes alluvium such as cobbles and boulders up to 750mm across.

2.5.2 Rock Types The predominant rock type at the dam site is Jurassic age dolerite. Dolerite has been found in all cored boreholes drilled at the site and is thought to extend to at least 50m beneath the site and immediately upstream from the proposed dam site.

Dolerite bedrock is also found within 1 to 2m below the riverbed.

2.5.3 Geological Structure

2.3.5.1 Jointing The dolerite at the site has a well-developed jointing structure. The joint patterns were assessed as part of the original geological investigations at the site. Three main joint sets were identified, being: · Joint Set A. Joints in this set are steeply dipping or vertical and are the most common structural feature of the site. These joints are columnar joints of the same origin as the prominent jointing in the Western Tiers Escarpment above the site. Columnar joints are an indication of cooling contraction at the time of formation of the dolerite. Air photo interpretation carried out at the time of the original geological investigation revealed two sets of lineaments sub-parallel to Joint Set A, suggesting a partial tectonic origin for these joints. · Joint Set B. This joint set dips generally westward at about 350, with individual joints having dips varying from 200 to 500 over their length. The joints may be continuous for over 40m in their length with spacings 15m to 30m ranging to 2m. Joint Set B appear to be classic sheet joints that can be expected in a steep V shaped gorge. · Joint Set C is a set of gently dipping to horizontal joints; the joints are roughly normal to the columnar joints and roughly sub-parallel to the original ground surface before erosion

The three sets of joints form a block pattern with joint planes at approximately orthogonal directions.

Hydro Tasmania TAS-106880-CR-03 Page 9 of 75 Meander Dam Feasibility Study Engineering Review 2.3.5.2 Faulting A major fault was revealed by the geotechnical investigations at the site. The fault trends 0900 - sub-parallel to the dam axis. The fault is 6 to 10m wide and contains clay and highly weathered rock near the ground surface.

2.5.4 Chemical Weathering The dolerite in the foundation area is described on the cored borehole logs as "slightly weathered". We have interpreted this to encompass rock that is more commonly described as "fresh". The weathering scheme used during the original geotechnical investigations ranged from Slightly Weathered to Completely Weathered.

2.5.5 Physical Weathering Of equal relevance for the foundation of the dam as the effects of chemical weathering of the dolerite, is the manner of physical weathering of the dolerite at the site. The rock mass, being a very high strength dolerite with widely spaced joints in three approximate orthogonal orientations, tends to weather preferentially along the joints leaving the interior of joint blocks unaffected by weathering. This leads to the dominant disintegration mode of failure of the rock mass being detached boulders and blocks. The size of such detached boulders and blocks ranges from less than 1m to about 2 to 3m across.

In assessing the likely foundation conditions for the dam, it is not always possible on the basis of a few isolated boreholes to distinguish with reliability the full extent of the weathered in- situ blocks and the detached boulders since there is a complete continuum between the two states.

2.5.6 Groundwater and Permeability The rock mass permeability and the groundwater levels within the rock mass are fundamental parameters for the assessment of the need and extent of foundation grouting.

In this respect the information resulting from the geotechnical investigation has limitations. In particular, the groundwater at the dam site has not been systematically recorded. There is no record of whether water levels were measured in the cored boreholes at the time of the geotechnical investigations for the dam and no record of water level measurements subsequent to the geotechnical investigation. The lack of information about the groundwater level in the left abutment ridge combined with the absence of water pressure testing in borehole DH 3 at the top of the left abutment, leaves open the possibility that the ridge could be a potential seepage zone from the dam. As part of the detailed design studies groundwater information will need to be obtained in this area to provide a basis for either accepting the ridge as a suitable foundation without treatment or extending grouting to this area.

In a broadly jointed rock mass such as exists at the site more information is needed to assess the pattern of flow in the rock mass. We have assumed that groundwater flow will be along isolated joints rather than a general flow through the rock mass.

Water pressure testing was carried out during the geotechnical drilling at the dam site. The results of this testing expressed in Lugeon Units were shown on the cored borehole logs.

Tests within 10 metres of the surface gave Lugeon values up to 30uL. More commonly the lugeon values were very low – “effectively zero". The Lugeon permeability results indicate permeabilities generally lower than the 1 to 3 Lu cut-off usually required for foundation

Hydro Tasmania TAS-106880-CR-03 Page 10 of 75 Meander Dam Feasibility Study Engineering Review grouting. There may be a number of potential permeable pathways through the near surface weathered dolerite that will require grouting or near surface foundation treatment. The need for and depth of curtain grouting is also an issue that should be considered. In general the permeability test results indicated that the rock mass at the site is of low permeability and suitable for the foundations for the proposed dam. The need for grouting of the foundations has not been discussed in the geotechnical report on the foundation investigations other than to indicate that the foundations for the cut-off for the dam will be onto slightly weathered dolerite and that 'normal consolidation grouting' will be required. This conclusion can also be applied to the three dam options.

However there are still some questions as to the watertightness of the left abutment ridge at the dam site. As mentioned earlier in this report the left abutment ridge has an unusual shape due to the location of the river immediately upstream from the dam site. There is a possibility that there has been some stress relief in the left abutment ridge leading to the opening of joints and therefore an increase in rock mass permeability. The degree to which this possible stress relief has affected the site permeability would be best assessed on the basis of additional piezometric and permeability data on the left bank. The implications of this are covered under the discussion of foundation permeability in section 2.5.7.

The presentation of the Lugeon results in summary form without details of how the tests were carried out in terms of reliability and variation of flow during the testing provides an incomplete picture of the rock mass permeability. In particular it is not possible from the summary results to ascertain. This information is available in the original records:

· The range of test pressures used, · The accuracy and reliability of the flow at each test pressure, · Whether there was any tendency to artesian flow given the steepness of the valley sides and the existence of near vertical columnar joints, and · The groundwater level at the time of testing.

Given the importance of the groundwater and permeability to the assessment of the need for and extent of foundation grouting for the dam, additional drilling and water pressure testing should be carried out as part of the detailed design process, supplemented by the installation of piezometers in left abutment boreholes.

2.5.7 Engineering Implications

2.7.5.1 General The geotechnical investigations have been sufficient to demonstrate that the foundations are suitable for either a RCC dam, a CFR dam or an ERF dam subject to detailed design studies being carried out to address specific issues. The principal geotechnical issues that have arisen from the geotechnical investigations carried out to date relate to:

· Foundation strength and stripping depths, · Dam foundation permeability and grouting, · Use of excavated rock as sources of rockfill, and · Sources of additional rockfill materials for the dam type options.

These issues are discussed in more detail below.

Hydro Tasmania TAS-106880-CR-03 Page 11 of 75 Meander Dam Feasibility Study Engineering Review 2.7.5.2 Foundation strength and stripping depths The foundations for each of the dam type options (RCC, CFR and ERF) will need to be taken to the level of the fresh to slightly weathered dolerite across the whole width of the dam. The achievement of sound groutable foundations will require removal of all soil and weathered rock. Much of this work should be achievable using bulldozer / excavator and truck techniques. Given the strength of the dolerite and the apparent absence of a significant uniformly moderately to slightly weathered zone over the whole dam footprint the foundation will have to be taken to fresh to slightly weathered rock over the whole footprint with deeper excavation in the cut-off zone. The use of bulldozer ripping alone will not be sufficient to reach material that can be effectively grouted for any of the three options. Drilling and blasting will be required to reach groutable rock in the dam cut-off zone.

The strength of the dolerite has been assessed as suitable for each of the dam type options, but there will be a different requirement for the stripping and foundation preparation for each option. A detailed comparative assessment of foundation stripping and preparation is required for each dam type option (RCC, CFR and ERF). Additional geotechnical investigations will be required at the detailed design stage to enable close definition of the foundation conditions.

For the RCC dam the key geotechnical features for the dam foundation are seen as:

· All foundations to be taken to sound in-situ high to very high strength rock – generally this will be fresh to slightly weathered rock beneath the first blocky layer to at least a depth of 2m to 3m in the abutments and up to 4 to 5m in the central valley floor; · Abrupt vertical or overhanging slopes to be removed by drilling and blasting to trim to an acceptable shape and provide a foundation that can be grouted; · Defining more reliably the average foundation excavation depth.

For the CFR dam the key geotechnical features for the dam foundation are seen as:

· All foundations to be taken to sound in-situ high to very high strength rock – generally this will be fresh to slightly weathered rock; · Plinth excavation to be taken through the upper blocky layer to at least a depth of 2m to 3m in the abutments and up to 4m to 5m in the central valley floor; · Abrupt vertical or overhanging slopes along the plinth line to be removed by drilling and blasting to trim to an acceptable shape and provide a foundation that can be grouted; · Defining more reliably the average foundation excavation depth to enable detailed design of the plinth prior to start of construction.

For the ERF dam the key geotechnical features for the dam foundation are seen as:

· All foundations to be taken to sound in-situ high to very high strength rock – generally this will be fresh to slightly weathered rock, at an average depth of 2m · Cut -off excavation to be taken through the upper blocky layer to at least a depth of 2.5m to 3m in the abutments and up to 4m to 5m in the central valley floor. · Abrupt vertical or overhanging slopes along the cut-off line to be removed by drilling and blasting to trim to an acceptable shape and provide a foundation that can be grouted and against which the core materials can be placed and compacted. · Defining more reliably the average foundation excavation depth to enable detailed design of the cut-off excavation prior to start of construction.

Hydro Tasmania TAS-106880-CR-03 Page 12 of 75 Meander Dam Feasibility Study Engineering Review Earth core foundations have very strict requirements regarding foundation shape, seam treatment, blanket grouting and surface treatment such as shotcrete, water control, dental concrete and curtain grouting.

2.7.5.3 Dam foundation permeability and grouting The Lugeon permeability results indicate permeabilities generally lower than the 1uL to 3uL cut-off usually required for foundation grouting. There may be a number of potential permeable pathways through the near surface weathered dolerite that will require grouting or near surface foundation treatment.

The principal features related to dam foundation grouting are seen as:

· The water testing has shown the rock mass in the foundation to be generally of low permeability and for the most part not requiring grouting. However, the jointed nature of the dam foundations including steeply dipping and sheet joints parallel to the river valley increases significantly the risk of individual seepage paths through the foundations. · These seepage paths will constitute water loss past the dam and the value of the water loss should be assessed against the cost of grouting. · The RCC dam will require curtain grouting to reduce uplift pressures under the dam. · The CFR dam will require curtain grouting because of the short seepage path and high hydraulic gradients that operate on the foundation. · The ERF dam provides a much wider core zone over which the seepage pressures can dissipate. If the water loss can be tolerated then the need for curtain grouting is reduced to a question of dam integrity against erosion. For such a narrow dam as proposed for this site curtain grouting is a good investment for dam protection and water loss reduction. · The depth of the curtain grouting will have to be determined by additional geotechnical investigations during the detailed design stage of the dam.

2.7.5.4 Use of excavated rock as sources of rockfill The fresh to slightly weathered dolerite appears to be suitable material for rockfill requirements for either the CFR or the ERF options. Further consideration should be given to the questions of:

· Volume of rock available from required excavations, · Suitability of material grading, · Integration of required excavations into the construction sequence as regards scheduling of supply of material, · Testing to confirm durability and suitability of the crushed dolerite rock for concrete aggregates.

The construction material requirements for each of the dam options will differ in terms of quality, sizing and program availability. These issues should be considered further in making the choice between the various dam options.

2.7.5.5 Sources of additional rockfill materials for the dam type options The needs for rockfill material will vary depending on the various dam options. The RCC option will need a reliable supply of high strength concrete aggregate material. This could be provided by the development of a new quarry within the storage area of the dam. Potential quarry sites were indicated for at the left bank ridge, and at Warners Sugarloaf, and at a further site just upstream from the dam on the right bank. This latter site was described as a

Hydro Tasmania TAS-106880-CR-03 Page 13 of 75 Meander Dam Feasibility Study Engineering Review “Rejected Quarry” in the original geotechnical investigations. Given the potential for quarry blasting to affect the integrity of constructed grout curtain works the siting of a quarry within about 500 metres of the dam should be subjected to vibration limits. The potential quarry site at the left bank ridge site immediately upstream of the dam offers the most favourable site for the quarry.

There are potential dolerite sources either well above the proposed top water level or downstream from the dam that could provide fresh dolerite but these sources would leave permanent quarry sites and may not be acceptable from an environmental viewpoint.

The ERF option will also require a suitable source of cohesive soil for use in the core of the dam, and less stringent requirements for the rockfill shell of the dam than for a CFR dam. The ERF dam will also require suitable filter materials. The alluvium in the Meander River appears to be limited in extent and is unlikely to be a suitable source of filter for the dam. Processed filter material will be required for the ERF option.

The CFR dam option also requires a suitable face underlay zone such as weathered sandstone. There needs to be a comparative study of the various potential material types for each dam option and a costed inventory or material requirements to enable a comparison between each dam option. Both dam types requires good quality material for filter zones etc

2.5.8 Risk Assessment for Dam Foundation Preparation The construction of the dam foundations and the sourcing of materials for the construction of the dam carries a number of geotechnical risks that can affect the integrity of the foundation, the integrity of the dam and the viability of the project. While no single feature has been identified in this review of the geotechnical conditions at the site there a number of factors that should be addressed as part of the detailed design,

The risks identified cover all three dam types considered for the site including the RCC, CFR and ERF options.

Some of the risks from a geotechnical viewpoint relating to the dam are: · Risk of right abutment instability resulting from movement along the sheet joints. Should such movement occur it could delay the project, require additional support measures and increase excavation quantities. · Risk of valley bulge features affecting method of construction of the dam cut-off. Valley bulge effects frequently occur in V shaped valleys where stress concentrations lead to upward heave along existing joints, even overthrust faulting can occur. Should such bulging occur then the permeability along the valley floor section of the dam can be significantly increased and the cut-off will need to be redesigned and strengthened. There has been no indication of such a feature being found during the geotechnical investigations or even indicated by the drilling and water testing carried out to date. Valley bulge should be considered as a potential risk. · Risk of deeper foundation excavation using drill and blasting to achieve the groutable foundations. · Risk of encountering other fault zones or weaknesses not found by the geotechnical investigations. · Risk of re-mobilisation of landsliding in talus materials in the clay borrow area · Risk of Increased costs resulting from greater than anticipated depth of excavation for the cut-off foundation for each type of dam considered.

Hydro Tasmania TAS-106880-CR-03 Page 14 of 75 Meander Dam Feasibility Study Engineering Review · Risk of increased foundation preparation such as blanket grouting, slurry grouting and excessive dental concrete and shotcrete placement due to foundation irregularities. · Risk of increase time and volume and hence cost of foundation grouting due to need to drill secondary, tertiary and quaternary holes should continuous permeable paths be encountered in foundation stripping. · Risk of seepage and springs that require special treatment such as drainage, grouting and materials placement.

On top of these geotechnical risks there are the normal construction risks such as flooding of the works by overtopping of the coffer dam, etc..

2.5.9 Diversion Tunnel or Conduit

2.9.5.1 General The preferred option for river diversion should the RCC dam option be selected, would comprise a diversion conduit cut into the right bank. Excavation for this conduit may involve a cut height up to 8 metres. The stability of such a cutting on the right bank would be governed to a large extent by the sheet joints.

The key geotechnical features of the conduit excavation on the right bank of the river are:

· Excavation by careful drill and blast techniques – such as pre splitting, to avoid damage to the rock mass within the dam foundation, beyond the excavation lines. · The left hand wall of the conduit will be more weathered than the right hand wall. The left hand wall of the conduit is expected to comprise blocky jointed dolerite whose integrity will have been prejudiced by the drilling and blasting in the conduit channel and by stress relief effects resulting from the removal of rock support between the conduit excavation and the river. It should be anticipated that this wall would require rock bolt support during construction as well as a shotcrete protection for the main fault zone crossing the conduit and any other weak, weathered zones. For planning purposes the excavated slope for the left wall of the conduit should be at least 0.25H:1V to 0.5H:1V. · The right hand wall of the conduit will comprise blocky jointed dolerite for the upper part of the slope. For planning purposes the excavated slope for the high wall should be at least 0.25H:1V to 0.5H:1V or locally flatter in the upper weathered zone and 0.25H:1 for the lower part of the slope. The slope is expected to expose joints in Joint Set B as the dominant joint set in the high wall. When this joint set is combined with Joint Set A there will be a potential for slope instability in the form of loose blocks, wedge failures and batter instability. Systematic rock support will be required in the more closely jointed sections of the excavation. Support by rock bolts and shotcrete / mesh is envisaged for the weathered upper sections of the slope. Support by isolated rock bolts is envisaged for the lower part of the slope. · The floor of the conduit is expected to comprise generally fresh to slightly weathered jointed dolerite. Erosion protection by shotcrete and mesh will be required where the conduit cuts the main fault zone downstream for the dam centre-line.

If a diversion tunnel is adopted the tunnel would be located beneath the right abutment of the dam. There does not appear to be much geologic advantage favouring one abutment over the other. In both locations the tunnel would be located in fresh broadly jointed dolerite and in both locations the tunnel would intersect at right angles the fault zone that has been identified. The portals of the tunnel in either location could be located in fresh dolerite. The choice of the

Hydro Tasmania TAS-106880-CR-03 Page 15 of 75 Meander Dam Feasibility Study Engineering Review right bank versus the left bank for the diversion tunnel could be made on the grounds of overall tunnel length and constructability issues such as ease of access.

Temporary portal support would require stable excavated slopes with rock bolt and mesh support; some shotcrete may be required to provide a safe stable entrance if there are weathered zones and loose / detached boulders remaining after excavation. Any materials liable to slake during exposure should be protected by shotcrete. If adverse conditions are encountered at the portal there may be a need to install a short section of steel rib supports the first 10m to 20m of the tunnel to provide a safe transition from the portal excavation to the general tunnel excavation. The steel sets would be required where the depth of the portal excavation is shallow and there remains a risk of detached joint blocks. Although the use of rockbolts, steel mesh and shotcrete should be sufficient in the portal areas to give a safe portal, it would be prudent to have steel sets on hand as a precaution for loose blocky conditions that can not be safely tunnelled.

The tunnel itself will be excavated in fresh to slightly weathered dolerite. Excavation by conventional drill and blast techniques is anticipated. The principal risk of roof instability will arise from the combination of the three joint sets that have the potential to form joint bound dolerite blocks. In the portal areas of the tunnel and those sections of the tunnel where weathering has been able to penetrate to about tunnel level there will be a tendency for the rock mass to break completely along the three joint sets. In this case there will be a risk of rock falls. Systematic tunnel support should be provided in these sections of the tunnel. At a greater depth below the surface the rock will tend to break mainly through the rock substance and the risk of rock falls is lower. In these sections individual tunnel support by way of rock bolts will be required.

In the section of the tunnel where the fault zone intersects the tunnel line the ground conditions are expected to be altered to clay and /or highly weathered rock. In this section of the tunnel - estimated as about 10 to 15m long of ground affected by the fault, reduced advance and full tunnel support by steel ribs embedded in shotcrete will be required.

2.9.5.2 Risk Assessment for Diversion Tunnel The risks for the diversion tunnel relate mainly to:

· Portal stability. · Groundwater inflow. · Extent and type of ground support specified not fully addressing the tunnel conditions liable to be encountered. Frequently tunnels are designed without sufficient geotechnical investigations being carried out at the detailed design stage. Generally during construction the tunnel can be constructed to the final lines and grades but using less efficient means increasing costs and time for completion.

2.5.10 Spillway

2.10.5.1 General Excavation and Support Requirements The spillway for the CFR and ERF dam options is located on the right abutment of the dam and extends downstream to about the point where the river recovers its north easterly direction. It is assumed that the spillway for the RCC dam will be a central overflow spillway without the need to create a long spillway cutting. The spillway will be excavated by drill and blast techniques into the slightly weathered to fresh dolerite bedrock on the right bank of Meander River.

Hydro Tasmania TAS-106880-CR-03 Page 16 of 75 Meander Dam Feasibility Study Engineering Review

The key geotechnical features of the spillway excavated on the right bank of the river are:

· Excavation by drill and blast techniques will have to achieve a reasonable degree of fragmentation of the slightly weathered to fresh dolerite bedrock if the quarried rock is to be used as source of rockfill for the dam. · Excavation should not damage the rock mass beyond the excavation lines if the spillway is to be unlined or have minimal rock support. This requirement conflicts with the need to fragment the rock as described above; in the end the needs of the stable and safe spillway structure should prevail - leading either to special blasting techniques in the spillway excavation, secondary blasting or effective wastage of the fresh rock resource. · The left hand wing wall of the spillway (the low wall of the excavation) needs to be stable and non-erodible since any failure of the wall could lead to spillage directly at the toe of the dam and thus prejudice its stability. The left hand wall of the spillway is expected to comprise blocky jointed dolerite whose integrity will have been prejudiced by the drilling and blasting in the main spillway channel and by stress relief effects resulting from the removal of rock support in the spillway channel excavation. It should be anticipated that this wall would require extensive rock bolt support during construction as well as a concrete training wall for permanent spillway operation. For planning purposes the excavated slope for the low wall should be at least 0.25H:1V to 0.5H:1V. · The right hand wall of the spillway (the high wall of the excavation) will comprise blocky jointed dolerite for the upper part of the slope. For planning purposes the excavated slope for the high wall should be at least 0.25H:1V to 0.5H:1V or locally flatter in the upper weathered zone and 0.25H:1 for the lower part of the slope. The slope is expected to expose joints in Joint Set B as the dominant joint set in the high wall. When this joint set is combined with Joint Set A there will be a potential for slope instability in the form of loose blocks, wedge failures and batter instability. Systematic rock support will be required in the more closely jointed sections of the excavation. Support by rock bolts and shotcrete / mesh is envisaged for the weathered upper sections of the slope. Support by isolated rock bolts is envisaged for the lower part of the slope. · The floor of the spillway is expected to comprise generally fresh to slightly weathered jointed dolerite. · Regular maintenance will be a feature of the unlined spillway. Frost heave, stress relief and weathering will lead to a gradual deterioration of the excavated spillway face. Any large rock falls will need to be removed from the floor of the spillway so as to avoid spillway blockage. Permanent access will be required to the spillway.

2.10.5.2 Risk Assessment for Spillway The reliable performance of the spillway is essential for the stability of the proposed dam and for environmental protection. Blockage of the spillway could result in diversion of the spillway flow during flood times and present an erosion risk to the dam embankment. In addition for the CFR and ERF dam options the spillway will be relied upon as a source of suitable rockfill for embankment construction. Thus the spillway is a key element in the dam construction. If either the CFR or ERF design option proceeds at the site, then a detailed risk assessment of the spillway should be carried out.

Some of the risks from a geotechnical viewpoint relating to the spillway are:

· Quantity and quality of rockfill from excavation fails to meet the construction requirements for the dam, leading either to the need to develop a new quarry or extend and existing one, with added costs and delays,

Hydro Tasmania TAS-106880-CR-03 Page 17 of 75 Meander Dam Feasibility Study Engineering Review · Overall slope fails to prove as stable as designed leading to recut of batters and / or slope instability during operation. · Wing wall on left-hand side of spillway requires more extensive stabilisation and extensive concrete wing wall construction. · Spillway floor is assessed to be erodible over much of its length requiring more extensive concrete paving and energy dissipation. · Construction materials from spillway excavation require more extensive secondary blasting as a consequence of the blocky nature of the dolerite resulting from careful construction techniques. · Drilling and blasting damages the rock mass behind the excavation lines in the spillway increasing support and maintenance costs.

2.10.5.3 Erodibility The geological data from the site indicates that the dam and spillway will be excavated completely in fresh to slightly weathered dolerite. The spillway should prove to be suitable source of fresh rock for the proposed dam. It may be possible to leave the lower section of the spillway unlined if the potential for erosion can be assessed. There will be a need for concrete lining in the section of the spillway where it crosses the EW fault. Erodibility in the spillway bucket area is an issue that will need to be addressed in the detailed design.

2.6 BORROW MATERIALS

2.6.1 General Requirements The rock requirements for each dam option will vary because of the different ways in which rock is incorporated into the design. For the RCC dam option the requirement will be for a reliable sound concrete aggregate material from a source with known materials properties and reliable supply. This consistency is unlikely to be available from required excavation at the site such as tunnel excavation or spillway excavation. It should be possible to integrate suitable materials from these sources into the stockpile of a processing plant if a site quarry is established close to the dam.

For the CFR dam the rock requirements will be for the supply of about 250,000 m3 of well graded, free draining rockfill. Fresh dolerite from a site quarry and from required excavation should be a suitable source for this material. Like the RCC dam the material should be of consistent quality and since it will need to be compacted in relatively thin layers, typically less than 0.5m to 1.0m thick the rock would have to be produced by controlled blasting to avoid oversized boulders. This may be a problem if it is intended to use the required excavation for the spillway as a source of rockfill. The rockfill yield from required excavation in the spillway will be controlled by the weathering and infilled soil along joints within the upper 2 to 3 m below the ground surface. The openness of the joints and the presence of weathering is expected to yield oversized boulders requiring wastage or secondary blasting unless a suitable zone can be found for these materials. For the CFR option however the proximity of the spillway excavation to the dam will make it an ideal source of rock fill from the point of view of location. Full use should be made of all suitable materials from this source even if some secondary blasting is required to avoid opening a quarry within the storage area. The use of a site quarry upstream from the dam as a source of rockfill would have restricted access to the downstream toe of the dam because of the upstream concrete plinth works and the steep gorge downstream from the dam.

Hydro Tasmania TAS-106880-CR-03 Page 18 of 75 Meander Dam Feasibility Study Engineering Review For the ERF dam, the quantity of rockfill required is 277,000 cubic metres. This type of dam would require more rockfill than the CFR dam and all rockfill needs could be provided by the spillway and tunnel excavation. Rip rap zones could be provided from oversized blasted rockfill.

2.6.2 Clay Borrow An estimated 60,000 cubic metres of core material is required for an upstream sloping core. A potential source of clay borrow pit has been located within the storage area of the dam close to the left abutment. The left bank borrow area is in an zone of deep dolerite talus at the foot of the slopes to Archers Sugarloaf. It appears to have either resulted from landslide deposits from the dolerite or to have been formed from residual soil developed over the dolerite. Eight test pits (Appendix A4) were excavated as part of the preliminary investigation of this potential source. They showed a consistent picture of a 3m to 3.5m layer of silty clay material of high plasticity. There were some boulder accumulations in the upper 1 to 1.5 of the deposit comprising rounded dolerite boulders 0.3m to 0.5m across in red brown clay. The material is considered to be an ideal source of clay fill. The clay should form an effective core for the dam embankment provided it is compacted at a moisture content at or slightly above Optimum Moisture Content (OMC). It should be anticipated that some boulders will remain in the clay when used in the ERF dam embankment; provided that the boulders are isolated or can be encompassed within the 200mm compacted clay layers in the earth core fill then the boulders should not be of concern to construction. Accumulations of boulders and cobbles that remain on the fill should be graded off the fill.

The preliminary investigations did not attempt to quantify the available resource in the borrow area. The borrow area covers an area at least 300 m long x 200 wide and is expected to have an average depth of over 3m, giving a potential resource of at least 180,000 cu.m. A borrow pit here should be capable of providing all the required earthfill for the ERF option. To proceed further with the use of this source as borrow a more systematic investigation would be required. The further investigations should also consider the stability implications of the removal of clay borrow from the toe of the deposit.

2.6.3 Filter Zone Estimated filter requirement is 13,500 cubic metres. No natural sources of suitable filter material for the proposed dam have been identified. The river is not considered to be a potential source of gravel for either direct use as filter or for processing into filters. All filter materials for the proposed ERF option will have to be obtained from crushing and screening quarried rock. The supply of filter could either be from a commercial quarry or from a crushing and screening plant set up on site to process on site rock. This could be sourced from either required excavation in the diversion tunnel and spillway or from a new site quarry.

2.7 SLOPE STABILITY - STORAGE AREA The dam storage area contains extensive deposits of talus and alluvium extending into the proposed dam storage areas. Given the nature of the area’s topography there is a potential for landslips to form or be exacerbated by the construction of the dam, although there are no known slides within the reservoir area. Such slides will not threaten the integrity of the dam and are only a potential turbidity problem. The potential for storage area slides need to be considered at the detailed design stage and operating rules formulated to minimise this risk.

Hydro Tasmania TAS-106880-CR-03 Page 19 of 75 Meander Dam Feasibility Study Engineering Review 2.8 HUNTSMAN SADDLE

2.8.1 General The geotechnical investigation carried out as part of the original investigations for the dam showed that the ground level at Huntsman Saddle is only about 7 metres above the FSL 402.2m of the proposed dam. The width over which the head of water would act when the dam is at FSL is about 200m increasing significantly as the head is lowered by a further metre and so on, due to the broad shape of the saddle. Against this background the permeability assessed by both constant head tests and Lugeon tests were reasonably high for natural sedimentary rocks. Permeability values in the centre of the saddle at Drill Hole 20, ranging generally between 2.8 x 10-6 m/sec and 6.3 x 10-7 m/sec between the surface and 15.8 m below the surface, that its from ASL 409 to ASL 393 (AHD). Tests on other holes in the saddle area gave comparable values in the upper soil layers. With the low seepage gradients operating at the saddle and the likelihood that storage level fluctuations in the dam will keep the pond level much further below the saddle level than 7 metres indicated there is a reduced potential for seepage from the reservoir. Given the relatively flat hydraulic gradients in this area it is unlikely that seepage from the dam will affect the viability of the saddle dam, but it could give rise to environmental effects such as continuous seepage in new areas and / or slip zones requiring treatment.

Although the potential for seepage through the saddle exists and the consequences of seepage although probably slight in actual water loss terms, it could have a measurable effect on the groundwater in the area. Whether this affect is to recharge depleted aquifers only to have the water seep back to the dam when storage levels fall or whether there could be observable effects outside of the dam catchment would need to be assessed on the basis of a more detailed review of the hydrology in this area. This would involve in particular, regular monitoring of water levels in the saddle area both before construction and after construction so that a pattern of groundwater behaviour in relation to rainfall and (later) storage levels in the dam can be assessed. Given that the storage levels would only remain at the FSL for relatively short periods the gradients across the saddle would be determined by a lower storage level.

During flood events the level would rise closer to the saddle crest level increasing seepage gradients substantially for short periods. For example to AEP of 1:50y is AHD 404.5m, only 4.5m below the saddle crest. The potential for seepage through the saddle would be increased during flood periods, but seepage is unlikely to develop if the water level falls within a few days. For example for a flood event of AEP of 1:10 6 y the reservoir level will be at AHD 409.8m, about 0.1m above the saddle crest.

The potential for seepage along fault zones near the Huntsman Saddle area particularly under average storage levels and flood conditions will require further examination by seepage modelling. Initially the models could use the values set out in the geotechnical report. However, should the modelling show that potential flow or recharge could give rise to potentially unacceptable effects outside of the catchment further field work may need to be carried out to better assess the groundwater parameters for use in that model.

If provision is to be made for containing the AEP of 1:10 6 y event, then there would need to be a saddle dam.

Hydro Tasmania TAS-106880-CR-03 Page 20 of 75 Meander Dam Feasibility Study Engineering Review 2.8.2 Risk Assessment The geometry and soil permeability profile identified in the Huntsman Saddle area has the potential to cause changes in the groundwater conditions in the saddle area under sustained high water levels in the storage. Modelling and possibly additional testing is required to assess the potential risks associated with the Huntsman Saddle area. Some of the risks associated with the Huntsman Saddle area are:

· The risk that seepage will occur under sustained high reservoir levels. The further risks are the risk of soil dispersion leading to tunnel erosion requiring lowered storage levels until any damage is repaired. Costs of loss of storage and repair would need to be assessed as well as any riparian risks. · The risk that seepage will occur in the currently wet and boggy areas downstream from the saddle and that the increased seepage can be directly related to the operation of the storage. There would be a need to monitor the groundwater levels and stream flows in the area to establish a reliable base line against which future performance could be measured. · The risk that remedial earthworks, such as filter layers and drainage systems may need to be installed to protect against the risk of seepage. There is a possibility that this expense may not be required if the monitoring recommended above shows that a perceived increase in seepage after construction and operation of the dam was similar to the performance of the site prior to construction of the dam.

2.9 CONCLUSIONS The geotechnical investigations show that the foundations of the dam would be on dolerite bedrock. The dolerite has joints and other geological structures that will require grouting and surficial treatment to make good the foundation for a dam with low potential leakage. The spillway and diversion tunnel can both be excavated in sound fresh dolerite which is a suitable material for such features. The excavated spoil should be suitable for use in rockfill zones for the construction of the proposed dam. There is a major fault cutting across the site that will require concrete lining where encountered in the spillway or diversion tunnel, but other than that there is the potential to leave substantial portions of the spillway and diversion tunnel unlined.

The other main feature of the site is the low saddle area - Huntsman Saddle on the left bank of the dam site. Concerns have been expressed over the potential seepage loss through this saddle area. It should be possible to operate the dam at full supply level without significant seepage loss in this area.

Slope stability in the reservoir is a further concern for the project, since much of the storage basin is surrounded by deep talus soils derived from the surrounding Jurassic age dolerite. Landslides appear to be a common feature of the catchment area, and the concern would be the re-activation of landslides (although none have been identified within the storage) under normal operation of the reservoir which may lead to turbidity problems. This is not expected to impact on the integrity or longevity of the dam. Provision in the dam design has been made for sedimentation with a significant volume of dead storage.

Hydro Tasmania TAS-106880-CR-03 Page 21 of 75 Meander Dam Feasibility Study Engineering Review 2.10 REFERENCES 1. Hydro-Electric Commission of Tasmania, (1989), “Meander River Irrigation Scheme, Meander Damsite Investigation Phase I, Site Investigation Report, Volume 1, Volume 2”, Report No. 64-W-12, Job No. 492-80005 2. Gutteridge, Haskins & Davey, 1989, “Rivers and Water Supply Commission, Meander River Dam Investigations, Preliminary Design Volume 1 – Report, April 1989, Extract pp1 – 84, No Figures . 3. Doyle, H.A., Everingham, I.B. and Sutton, D.J., (1968), “Seismicity of the Australian Continent”, Jnl Geol Soc. Aust 15(2):pp 295-312, 1968. 4. Michael-Leiba, M. and Jensen, V., (1997), “Seismic microzonation of Launceston”Australian Geological Survey.

Hydro Tasmania TAS-106880-CR-03 Page 22 of 75 Meander Dam Feasibility Study Engineering Review

3 Hydrology

3.1 DATA AVAILABILITY In order to summarise and describe the climate within the catchment and the surrounding area, data from a number of sites have been collated. Twelve rainfall sites, 5 flow sites, 4 evaporation sites and 4 temperature sites were summarised by a series of statistics. The sites used are listed in the table below. Monthly means, standard deviations, maxima and minima were calculated for each of these sites along with 10, 50 and 90th percentiles. These statistics are included in Appendix B1. Summaries of the record lengths and data qualities of the flow and rainfall sites are included in Appendix B2. Wind Roses for 4 sites have also been created, these are included in Appendix B3.

Table 3-1: Sites used for climate analysis Site No. Name Rain Flow Evap Temp Wind 18907 Meander @ Meander ü 597 Pine Tree Rivulet ü 972 Lake Augusta East ü 509 Lake Gwendy ü 16201 Fisher River ü ü ü 267 Warners Creek ü 1634 Western Creek ü 1548 Liffey ü 871 Blackwood Creek ü 941 Great Lake East ü 863 Breona ü 162 Meander @ Deloraine Bridge ü ü 541 Meander b/l Deloraine ü 18224 Jackeys Creek ü ü 18221 Meander d/s Warners ü 588 Meander a/b Warners ü 091022 Cressy Research Station (BoM) ü 091104 Launceston Airport (BoM) ü 093036 Campbell Town (BoM) ü 096015 Lake St Clair (BoM) ü 131 Lake St Clair ü 888 Cressy Research Farm ü 22 Mersey @ Kimberley ü 68 Liaweenee Canal ü 1615 Devonport Airport ü 1583 Sheffield School Farm ü 388 Launceston Airport ü

Hydro Tasmania TAS-106880-CR-03 Page 23 of 75 Meander Dam Feasibility Study Engineering Review Meander River d/s Warners Creek

25

20

Outliers 90th Percentile

15 /s) 3 10 Flow (m 5

0 10th Percentile

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month

Monthly 25th - 75th Percentiles (includes median)

Figure 3-1: Statistics for Meander River Flow - Mean, Standard Deviation (Period of record 1966 to 2001)

Mean Monthly Rainfall - Meander @ Meander (including standard deviation) 200 180 160 140 120 100 80 60 Rainfall (mm) 40 20 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 3-2: Statistics for Meander Catchment Rainfall - Mean, Standard Deviation

Hydro Tasmania TAS-106880-CR-03 Page 24 of 75 Meander Dam Feasibility Study Engineering Review

Maximum and Minimum Monthly Rainfall Meander @ Meander 250 Minimum 200 Maximum

150

100

50

0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 3-3: Statistics for Meander Catchment Rainfall - Minimum, Maximum

3.2 YIELD ANALYSIS

An inflow yield sequence to the proposed storage was required to determine the quantity of water available for the storage. The most suitable record for this analysis was the flow record at site 18224, Meander River below Warners Creek. The record at this site covers the period 27/08/1982 - 18/10/1991. In order to extend this record, a daily regression analysis was undertaken between the Meander below Warners site and the two Meander at Deloraine sites (site numbers 162, 541 Table 3-2).

The methodology used to determine the regression between the stations is that outlined in Australian Rainfall and Runoff (p201 1987 version). The major differences noted in the regression equations with the two Deloraine sites is due to the differences in time periods of the correlation with the Warners Creek site. The relationship between Jackeys Creek and the Warners Creek site was investigated, with the result that the r2 value for the Jackeys/Warners was lower than that for the Deloraine/Warners relationship. There is also a shorter period of record for the Jackeys Creek site.

Consideration has been given to the residuals at time t and at time t-1. There is no relationship between these which proves that the basic assumptions in regression analysis have not been violated. As the r2 value is high and the sites are on the same stream, any serial correlation that exists at one site will be preserved through the regression analysis.

Table 3-2: Flow Sites used in regression analysis Site No. Site Name Start Date Finish Date Equation R2 162 Meander River @ Deloraine Bridge 01/09/1954 Present 5.12x 0.91 541 Meander River below Deloraine 30/09/1968 06/08/1996 5.99x 0.9

These two sites have been used to extend the record to cover the period 1/1/1966 - 1/10/2001 (approximately 35 years).

Hydro Tasmania TAS-106880-CR-03 Page 25 of 75 Meander Dam Feasibility Study Engineering Review As the Meander below Warners site is almost at the dam site, the difference in catchment areas is negligible and therefore no further factoring of the inflow was required.

The results of the yield analysis are shown in Appendix B3, as well as in Figure 3-4 and Figure 3-5.

Long term average inflow of 189,000 ML/year is available at the dam site. The 5 and 95 percentile values of the inflow sequence are 283,000 and 121,000 Ml/year respectively.

Yearly Inflows 400000 350000 300000 250000 200000 150000 100000 Inflow (ML/year) 50000 0

1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999

Figure 3-4: Yearly Inflow Sequence

Mean Monthly Flows 40000 35000 30000 25000 20000 15000

Flow (ML/month) 10000 5000 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 3-5: Mean Monthly Inflows

3.3 LOW FLOW FREQUENCY ANALYSIS

A low flow frequency analysis to determine the 7 and 30 day low flow events for the purposes of considering drought events was undertaken. A 7 day and 30 day low flow event analysis

Hydro Tasmania TAS-106880-CR-03 Page 26 of 75 Meander Dam Feasibility Study Engineering Review was carried out using by extracting minimum yearly 7 and 30 day average values from the flow sequence. This data was plotted on log-log axes. A two parameter Weibull (or Type III Extremal) Distribution was chosen to fit the minimum flow data as recommended in Maidment (1983, p18.19). The Weibull parameters (a, b) were estimated using the Method of Moments (Kite, 1985, p134). The methodology outlined in Kite (1985, p140) was used to plot the frequency curve. Figure 3-6 shows the 7 day and 30 day low flow analyses.

The results show that for a 1 in 10 year event, the flow over a 7 day period is approximately 9 ML/day, while the 30 day period shows a flow of approximately 10ML/day.

Hydro Tasmania TAS-106880-CR-03 Page 27 of 75 Meander Dam Feasibility Study Engineering Review

7 day low flow

100

10 Flow (ML/day)

1 1 10 100 AEP (1 : X)

30 day low flow 1000

100

10 Flow (ML/day)

1 1 10 100 AEP (1 : X)

Figure 3-6: 7 and 30 Day Low Flow Frequency Analyses for dam site inflows

3.4 ANALYSIS OF STORAGE RELIABILITY

3.4.1 Approach of Analysis A storage analysis was performed to determine the capability of the proposed Meander Dam to meet the required downstream water demand. The total downstream water demand is made up of three major requirements: environmental release, town water demand and irrigation demand. To carry out the analysis a storage model was constructed in TimeStudio Modelling and run on a daily time step. The model performs a storage balance between inflows

Hydro Tasmania TAS-106880-CR-03 Page 28 of 75 Meander Dam Feasibility Study Engineering Review (described above in Section 3.2) and direct rainfall on the surface of the storage, which increase storage volume and factors that reduce storage volume including releases, evaporation and spill.

DStorage = Inflow – Outflow

S - Sprev = ( I + P ) – ( R + E + Sp ) Where S = Storage Volume Sprev = Storage Volume at previous time step I = Inflow P = Rainfall on the surface of the storage R = Total release from the storage E = Evaporation on the surface of the storage Sp = Spill

The analysis was carried out over the entire inflow sequence (35 years).

Comparison of the average inflow and estimated outflow from the storage give an indication of the accuracy of the model.

Average Annual Inflow 194000 ML Average Annual Outflow 204000 ML

The error of 5% is due to the crude nature of the storage balance, however it is considered that an error of this magnitude is appropriate for the purposes of preliminary analysis.

3.4.2 Inputs to the Model Each of the inputs to the simulation model are discussed in detail below.

Lake Surface Precipitation and Evaporation

The rain gauge at the Meander River at Meander Site (Hydro Tasmania site number 18907) was used to determine the direct rainfall on the storage. The continuous record extends back to August 1990, with daily values recorded from June 1990. For the period prior to this date, or in cases of missing record, average monthly values from the rainfall site were substituted (Appendix B1). Inflows into the reservoir were reduced by to take into account the reduction in catchment area due to creation of the reservoir.

Monthly evaporation data (Appendix B1) from the Cressy Research Site (site number 888) was used in the storage analysis. The Cressy evaporation record is that which is assumed to be the closest in 'location' as it is also situated just below the Tiers. A correction factor was applied to the evaporation estimates to take into account the differences between pan evaporation and actual evaporation from the reservoir.

Both the evaporation and rainfall inputs are dependent on the surface area of the storage at each time step. The storage volume at each time step is calculated with the relationship between volume and level coded into the model. Once the level is known, the corresponding surface area value is calculated. These storage-level and surface area-level curves are shown below.

Hydro Tasmania TAS-106880-CR-03 Page 29 of 75 Meander Dam Feasibility Study Engineering Review

6000000 90000 Surface Area 5000000 Storage 75000 ) 2 4000000 60000

3000000 45000

2000000 30000 Surface Area (m

1000000 15000 Effective Storage Capacity (ML)

0 0 362.0 368.0 374.0 380.0 386.0 392.0 398.0 404.0 410.0 Reduced Level (m)

Figure 3-7: Storage-Area-Level Curves

Environmental Release

The environmental release is given first priority for water releases from the reservoir, so if the available storage is limited the water will be allocated to environmental release first. The environmental requirements vary by month according to Table 3-3 below, and must be met to sustain fish and macroinvertebrate life downstream of the proposed dam site. The environmental flow requirements for trout spawning habitat and excluding trout spawning habitat are shown. For each month, the value adopted for modelling was the higher of the two requirements.

Table 3-3: Environmental Release Requirements

Month Including Spawning Excluding Spawning Adopted Habitat Habitat m3/s ML/month m3/s ML/month m3/s ML/month Jan 0.79 2076 0.63 1656 0.79 2076 Feb 0.42 1104 0.36 946 0.42 1104 Mar 0.33 867 0.22 578 0.33 867 Apr 1.00 2628 0.82 2155 1.00 2628 May 2.20 5782 1.90 4993 2.20 5782 Jun 2.52 6623 2.40 6307 2.52 6623 Jul 3.00 7884 2.40 6307 3.00 7884 Aug 2.95 7753 2.40 6307 2.95 7753 Sep 2.90 7621 2.40 6307 2.90 7621 Oct 2.40 6307 2.40 6307 2.40 6307 Nov 1.75 4599 1.40 3679 1.75 4599 Dec 1.37 3600 1.00 2628 1.37 3600

Hydro Tasmania TAS-106880-CR-03 Page 30 of 75 Meander Dam Feasibility Study Engineering Review *Note: the release which excludes Spawning Habitat is taken as an alternate environmental release for the sensitivity analysis.

Town Water Release

Town water obligations were taken as a high priority and combined with the environmental release in the storage model. Water is currently extracted from the Meander River for the following towns:

Deloraine <3 ML per day Westbury ~2 ML per day Exton very small supply Meander small private supply

After consideration of the figures above, a constant daily rate of 5 ML/day was included in the model as a release for town water supply.

Irrigation Demand: Water Entitlements and Additional Demand

Irrigation demand was placed into two categories, water entitlements and additional demand. Water entitlements represents all water licences currently held by irrigators on the Meander River. These water entitlements were extracted from a DPIWE database which lists all the States water licences for the year 2000. The total yearly demand required for water entitlements was found to be 1750 ML which does not include temporary licences or licences on tributaries.

Additional demand is that volume of water which irrigators would like to use if it was available from the Meander dam. This demand was determined by a survey conducted by Davey and Maynard Agricultural Consulting (Appendix B7). The additional water requirement indicated by the results of the survey was 24,000 ML. The monthly distribution of irrigation demand was determined in two stages: · The April to October (inclusive) entitlements were distributed evenly over those winter months; and · The summer allocations were determined by carrying out a water balance calculation by Davey & Maynard (Appendix B7) at Deloraine.

This distribution is shown below in Table 3-4. A loss factor of 25% was applied to the additional demand to allow for factors such as evaporation and infiltration to groundwater. The value for the loss factor was arrived at from experience in similar catchment modelling and from previous studies on this catchment.

Hydro Tasmania TAS-106880-CR-03 Page 31 of 75 Meander Dam Feasibility Study Engineering Review Table 3-4: Monthly Distribution of Irrigation Demand

Water Additional Month Entitlements (ML) Demand (ML) Jan 465 7440 Feb 375 6000 Mar 165 2640 Apr 36 0 May 36 0 Jun 36 0 Jul 36 0 Aug 36 0 Sep 36 0 Oct 36 0 Nov 165 2640 Dec 330 5280

3.4.3 Mini Hydro Considerations Giving consideration only to the extractions considered so far, during the winter months, a large proportion of available inflow will be lost to storage as spill from the reservoir. The possibility of using this excess water through a hydro turbine was investigated. A number of releases were considered and it was found that a release of 12 m3/s (1037 ML/day) could be utilised without any significant decrease in reliability of irrigation demand. This discharge is high enough to provide sufficient water for all other required releases. So whenever the mini hydro was operating in the model, the total release from the storage was taken to be 1037 ML/day.

Rules Regulating Mini Hydro Release

A set of operating rules was coded into the model to ensure that additional releases for the purposes of power generation, would not affect the reliability of the storage to meet its other release requirements. These operating rules are shown below:

· Unless the dam is spilling, the mini hydro can only operate during a period starting on the first day of April and finishing on the last day of September. · During April to August (inclusive), the mini hydro can only operate if the lake level is greater than a level 4 metres below FSL. · During September, the Mini Hydro will operate only if the lake level is greater than a level 1 metre below FSL.

These operating rules prevent excessive draw down of the storage and allow the storage to fill before commencement of the summer irrigation period.

3.4.4 Determination of Failure/Reliability

The reliability of the storage to meet the downstream water demand has been measured by determining the percentage of failures over the period of analysis. A “failure” is defined as an

Hydro Tasmania TAS-106880-CR-03 Page 32 of 75 Meander Dam Feasibility Study Engineering Review event where the available storage at a given time step is less than the required demand at that time step. There were two separate means of evaluating the failure rate:

· Average Daily Statistic – is defined as the number of days when the dam is not able to supply all of the additional irrigation demand divided by the number of days in the record. · Average Annual Statistic – is defined as the number of years where the additional irrigation demand was not met, divided by the total number of years (34 in this analysis). This gives a consistent failure count as the typical failure period is included in the middle of the accounting period.

3.4.5 Results

Determination of Characteristic Years

To provide an adequate representation of the storage response due to various inflow conditions, three characteristic calendar years were chosen for comparison. These years were selected by ranking the total annual inflow and choosing the 10th, 50th and 90th percentiles as representing a dry, typical and wet year respectively. The following years were chosen:

Condition Percentile Year Yield (ML)

Dry Year 10 1987 102605 Typical Year 50 1981 181134 Wet Year 90 1974 279688

Storage Reliability

The reliability of the storage to meet demand has been measured using the failure statistics mentioned above. The following results were obtained when running the model over the entire period of available record:

Average daily failure = 2% Average annual failure = 12%

From the results above it can be seen that once every 8 years the total irrigation demand is not released, but overall failure occurs only 2% of the time. In running the model excluding the additional demand, there are no failures. Therefore once in every 8 years irrigators would be unable to take the full additional demand.

Table 3-5 shows the time taken to fill the storage to full supply if filling were to commence at the time shown. During the period of filling, it was assumed that the water obligations were being met except for additional irrigation. Extra release for Mini Hydro operation was not made available until the storage had filled. The modified environmental release has been assumed during the filling of the reservoir. It is clear that the filling time is sensitive to the assumed closure date. If closure is after the 1st of September, the full irrigation release is much more likely not to be available in the first year of operation. In a dry year, it is almost certain that the full irrigation release will not be available.

Hydro Tasmania TAS-106880-CR-03 Page 33 of 75 Meander Dam Feasibility Study Engineering Review Table 3-5: Storage Fill Times Year Type of Year Time to Fill Start 1 Start 1 Start 1 July August September 1966 First Year Inflow Sequence 29 days 49 days 111 days 1987 'Dry Year' 349 days 326 days 295 days 1981 'Typical Year' 26 days 30 days 337 days 1974 'Wet Year' 31 days 38 days 32 days

Time Series and Duration Plots

Figure 3-8 to Figure 3-10 show time series plots derived from the simulation model for three scenarios of a dry year, typical year and a wet year respectively. Each plot includes data from some months either side of the characteristic year.

The first plot displays the inflows and outflows of the storage in a continuous format. It can be seen for all three characteristic years that the majority of the inflows take place during the winter months when irrigation demand is also at a minimum. Spill ranges from zero during the dry year to some significant events during the typical and wet years. Releases in the dry year plot are almost entirely restricted to the required releases for irrigation with only a small amount of mini hydro output. Mini hydro releases are more abundant in the typical year plot and in the wet year plot the mini hydro release remains almost constantly over the winter period.

The cumulative plots for each characteristic year give an indication of the accumulation of inflow and outflow. They also show, in each given year, whether the total inflow exceeds the total outflow or vice versa. It should be noted that the accumulation begins from the start of the trace and includes some of the previous and following years. The cumulative plot for the typical year shows that the year begins in a dry period but significant inflows during later months raise the inflow rate considerably.

The storage level plots for each characteristic year show at least some sign of draw down over the summer irrigation period. The wet year plot shows the least amount of storage drainage as high inflows were obtained during the summer period. The typical year shows two significant summer draw downs but the high inflows over the winter period raise the storage level and provide adequate water for release for the following year.

Figure 3-11 shows duration curves for storage, level and release from the proposed storage from the full simulation period. The values above the 96th percentile on the level and storage duration curves show the period of failure. The release duration curve has a stepped appearance indicating the monthly release rates from the storage. It can be seen that mini hydro release occurs about 30% of the time when release is greater than 400ML/day.

Hydro Tasmania TAS-106880-CR-03 Page 34 of 75 Meander Dam Feasibility Study Engineering Review

6000 Inflow

) Spill y

a Release D

/ 5000 L M (

w o

l 4000 f t u O

s

v 3000

w o l f n I 2000

1000

0 1987 1988 Period(01/09/1986 @ 00:00:00 to 01/03/1988 @ 00:00:00)

200000

w ) Inflow

L 150000 o l f t M ( u

e O

v i s t

v 100000 Outflow a l v u w m o l f u n I C 50000

0 1987 1988 410 Period(01/09/1986 @ 00:00:00 to 01/03/1988 @ 00:00:00) FSL

) 400 m (

l e v 390 e L

e g

a 380 r o t S 370

1987 1988 Period(01/09/1986 @ 00:00:00 to 01/03/1988 @ 00:00:00) Figure 3-8: Inflow vs Outflow and Storage Level Plots during a Dry Year.

Hydro Tasmania TAS-106880-CR-03 Page 35 of 75 Meander Dam Feasibility Study Engineering Review

5500 Inflow Spill 5000

) Release

y 4500 a D /

L 4000 M ( 3500 w o l f

t 3000 u O

2500 s v

w 2000 o l f n

I 1500

1000

500

0 1981 1982 Period(01/09/1980 @ 00:00:00 to 01/03/1982 @ 00:00:00)

250000

w 200000 ) Inflow o L l f t M ( u

e

O 150000

v i s t v a l v

u Outflow

w 100000 m o l f u n I C 50000

0 1981 1982 410 Period(01/09/1980 @ 00:00:00 to 01/03/1982 @ 00:00:00) FSL

) 400 m (

l e

v 390 e L

e g

a 380 r o t S 370

1981 1982 Period(01/09/1980 @ 00:00:00 to 01/03/1982 @ 00:00:00)

Figure 3-9: Inflow vs Outflow and Storage Level Plots during a Typical Year.

Hydro Tasmania TAS-106880-CR-03 Page 36 of 75 Meander Dam Feasibility Study Engineering Review

Inflow 6000 Spill

) Release y

a 5000 D / L M (

w 4000 o l f t u O

3000 s v

w o l

f 2000 n I

1000

0 1974 1975 Period(01/09/1973 @ 00:00:00 to 01/03/1975 @ 00:00:00)

400000

350000

w ) 300000 o L

l Inflow f t M ( u 250000 e O

v i s t

v 200000 a l v u Outflow w 150000 m o l f u n I C 100000

50000

0 1974 1975 410 Period(01/09/1973 @ 00:00:00 to 01/03/1975 @ 00:00:00) FSL

) 400 m (

l e

v 390 e L

e

g 380 a r o t S 370

1974 1975 Period(01/09/1973 @ 00:00:00 to 01/03/1975 @ 00:00:00)

Figure 3-10: Inflow vs Outflow and Storage Level Plots during a Wet Year.

Hydro Tasmania TAS-106880-CR-03 Page 37 of 75 Meander Dam Feasibility Study Engineering Review ) L M (

e g a r o t S

Percentage of Time Exceeded

Full Supply Level ) m (

l e v e L

e g a r o t S

Dead Storage Level

Percentage of Time Exceeded

Mini Hydro Release ) y a D / L M (

e s a e l e R

Percentage of Time Exceeded Figure 3-11: Storage, Level and Release Duration Curves

Hydro Tasmania TAS-106880-CR-03 Page 38 of 75 Meander Dam Feasibility Study Engineering Review

Sensitivity

Various scenarios were considered to determine which inputs contributed most to failure of the storage meeting its required releases. Figure 3-12, below, shows the effects on failure of the storage due to varying size of storage and varying additional demand. The base case results obtained above used an additional demand of 24000 ML and FSL = 402 m. Both the varying additional demand and size of storage have an affect on the reliability of the storage. Note, the daily statistic of a 0.7% failure rate at low levels of irrigation demand shown occurs during filling of the storage, before irrigation could begin.

9 Average Daily Failure Statistic 8 FSL = 399 m 7 FSL = 402 m (proposed) 6 FSL = 405 m 5 4 3 2 Failure of Supply (%) 1 0 10 15 20 25 30 Annual Additional Irrigation Demand (x1000 ML)

50 Average Annual Failure Statistic 45 FSL = 399 m 40 FSL = 402 m (proposed) 35 FSL = 405 m 30

25 20 15 10 Failure of Supply (%) 5 0 10 15 20 25 30 Annual Additional Irrigation Demand (x1000 ML)

Figure 3-12: Sensitivity Analysis – Normal Environmental Release

The sensitivity to maximum storage level and additional irrigation demand were also examined using the alternative environmental flow release, which is based on exclusion of the trout spawning requirements (as discussed in Section 3.4.2).

Hydro Tasmania TAS-106880-CR-03 Page 39 of 75 Meander Dam Feasibility Study Engineering Review

9 Average Daily Failure Statistic 8 FSL = 399 m 7 FSL = 402 m (proposed) 6 FSL = 405 m 5

4

3

Failure of Supply (%) 2

1

0 10 15 20 25 30 Annual Additional Irrigation Demand (x1000 ML)

50 Average Annual Failure Statistic 45 FSL = 399 m 40 FSL = 402 m (proposed) 35 FSL = 405 m 30 25 20

15 10 Failure of Supply (%) 5 0 10 15 20 25 30 Annual Additional Irrigation Demand (x1000 ML)

Figure 3-13 Sensitivity Analysis – Alternate Environmental Release

Hydro Tasmania TAS-106880-CR-03 Page 40 of 75 Meander Dam Feasibility Study Engineering Review

3.5 ESTIMATION OF DESIGN FLOOD

In performing the design flood analysis for Meander Dam a systematic stepwise process was adopted. The following outlines the basic steps undertaken in the analysis.

The catchment area of Meander Dam was determined and appropriate sub areas were derived to enable modelling of the rainfall runoff processes within the catchment.

A rainfall/runoff routing network was developed, using TimeStudio modelling package, for the Meander Dam catchment and was initially coded as a calibration version of the model with the catchment in the pre dam natural state. A diagram of the conceptual TimeStudio model has been provided in Appendix B4.

From the historical record, eight significantly large flood events were identified to calibrate the runoff routing parameters, including the calibration of the channel routing parameter Alpha and the non linearity exponent, ‘n’. The latter, which is required for the river reach routing, was assumed as 0.8, in line with the current best practise recommendations. Six sets of parameters were used to derive modelled hydrographs for each of the eight calibration hydrographs. Engineering judgement was used after visual inspection of the six sets of parameter fits, and a single set of parameters was adopted that was considered to best fit all of the eight calibration events. The fit hydrographs are shown in Appendix B5.

Table 3-6 Adopted Routing Parameters Alpha (a) n 1.4 0.8

Design rainfalls were estimated for the Meander Dam catchment. This was done by obtaining FORGE (focussed rainfall growth estimation technique) rainfalls for the Meander Dam catchment, together with estimates of the probable maximum precipitation (PMP). PMP Estimates were obtained from a report by the Bureau of Meteorology, (BoM, 1988). Intermediate rainfalls were interpolated using a technique recommended by the FORGE procedure. FORGE rainfall estimates were adjusted to match Australian Rainfall and Runoff (ARR, 1987) estimates at an AEP of 1:50, which is recommended best practise. The adopted design rainfalls are provided in Appendix B6.

Spatial variability of the design rainfalls was adopted using the PMP spatial pattern (BoM, 1988).

Using the calibration model and applying design rainfalls, the loss parameters for design were calibrated by comparison of the derived flow with recorded at site flood frequency information. The flood frequency curve is derived by plotting annual maxima on log-normal probability, fitted to a Log Pearson type III (LPIII) distribution. Figure 3-14 shows the recorded at site flood frequency curve together with the calibrated estimates of the modelled flow at AEPs of 1:50 and 1:100.

Hydro Tasmania TAS-106880-CR-03 Page 41 of 75 Meander Dam Feasibility Study Engineering Review

1000.0

CL =3.5, IL=10

5% Confidence Limit

100.0

Peak Discharge (cumecs) 95% Confidence Limit

10.0

1.01 1.111 1.25 2 5 10 50 100 AEP (1:Y)

Figure 3-14 At site Flood Frequency Curve based on Recorded Annual Maxima

Preburst temporal patterns for the Coastal Zone were sourced (BoM, 1999) and applied to the GSAM patterns. The use of preburst patterns allowed a single set of design losses to be applied to all exceedance probabilities.

Table 3-7 Adopted Loss Parameters Continuing Initial Loss Loss (mm) (mm/hr) 3.5 10

The calibration model was then modified to incorporate relevant design assumptions, such as the inundation of appropriate reaches, the storage characteristics and the spillway ratings for Meander Dam. The operation of the 4 'Flowgates' was also incorporated into the model. (see section 4.5) The inclusion of any release for the purposes of irrigation, environmental release or mini hydro operation was not considered due to the magnitude of such releases being small in comparison to the extreme inflow and the seasonal nature of such releases.

The storage was assumed to be at full supply level (402m AHD) at the beginning of each design event analysed.

Nine durations for each of twelve annual exceedance probabilities (AEP) were considered in the determination of the modelled inflow and outflow frequency curves presented in Figure 3-15. The changing slope of the outflow frequency curve is due to the operation of the spillway fusegates.

Hydro Tasmania TAS-106880-CR-03 Page 42 of 75 Meander Dam Feasibility Study Engineering Review

10000

Inflow 1000

Outflow

100 Peak Discharge (cumecs)

10 50 100 1000 104 105 106 107 AEP (1:Y)

Figure 3-15 Design Flood Frequency Curve

Flood magnitudes at critical durations are used to plot the frequency curves. These critical durations were found to be variable. The critical outflow duration changes from 24hrs (AEPs of 1:50 and 1:100) to 6hrs at the AEP of the PMP. The explanation for this is twofold; firstly the impact of losses reduces with increasing design rainfalls, secondly the increased flood magnitude reduces the impact of storage attenuation.

Whilst the operation of the fusegates increases the outflow (with respect to the same flood without fusegates), particularly in the probability range 1:500 to 1:105, the reservoir level is actually reduced. At an AEP of 1:104 the influence of the gates reduces the maximum flood level by 1.8m. Figure 3-16 shows the impact of the gates on the level frequency curve.

411

409 Without Fusegates Dam Crest Level 407

With Fusegates 405 Peak Level (mAHD)

403

FSL 401 50 100 1000 104 105 106 107 AEP (1:Y) Figure 3-16 Design Flood Level Frequency Curve

Hydro Tasmania TAS-106880-CR-03 Page 43 of 75 Meander Dam Feasibility Study Engineering Review

Hydrographs have been supplied at various probabilities, and are presented in Appendix B7. Table 3-8 summarises the magnitudes of Peak Inflows, Peak Outflows and Peak Levels at critical durations.

Table 3-8 Tabulated Design Flood Results AEP Peak Peak Peak (1:Y) Inflow Outflow Level (m3/s) (m3/s) (mAHD) 50 545 215 404.5 100 560 255 404.8 200 640 325 405.3 500 840 415 405.9 1000 995 730 406.1 2000 1180 990 406.2 5000 1450 1330 406.4 104 1680 1415 406.7 50x104 2265 1720 407.8 105 2530 1865 408.3 106 3400 2305 409.8 6.7x106 4060 2550 410.6

The Dam Crest Wall Level of Meander Dam is 407.7m AHD. Based on the results provided in Table 3-8 and Figure 3-16 it has been estimated that the likelihood of exceeding the Dam Crest is 1:40,000 in any given year.

3.6 REFERENCES

Bureau of Meteorology 1999. Rainfall Antecedent to Large and Extreme Bursts over Southeast Australia, Report No. HRS 06, Bureau of Meteorology, Australia.

Bureau of Meteorology, Hydrometeorological Advisory Service 1988. Preliminary Estimates of Probable Maximum Precipitation over the catchment of Meander Dam, Report No. IGPMP/06, Bureau of Meteorology.

Canterford, R.P. et al 1987. Australian Rainfall and Runoff - Volume 2. Barton, ACT: IEAust.

Gamble, S.K, Turner, K.J, Smythe, C.J, 1998. Application of the Focussed Rainfall Growth Estimation Technique in Tasmania. Hydro Electric Corporation of Tasmania (Internal Document)

Kite, G.W, `1985. Frequency and Risk Analyses in Hydrology,. Water Resources Publications, Colorado,USA

Maidment, D.R, `1992. Handbook of Hydrology, McGraw-Hill, Sydney,Australia.

Nathan, R. J. , Weinmann, P. E. 1999. Australian Rainfall and Runoff, Book VI, Estimation of large and extreme floods. Barton, ACT. IEAust.

Hydro Tasmania TAS-106880-CR-03 Page 44 of 75 Meander Dam Feasibility Study Engineering Review Pilgrim, D.H. 1987. Australian Rainfall and Runoff - Volume 1. Barton, ACT. IEAust.

Hydro Tasmania TAS-106880-CR-03 Page 45 of 75 Meander Dam Feasibility Study Engineering Review

4 Dam Engineering

4.1 STORAGE CAPACITY The chosen full supply level was derived from an evaluation of the imbalance between the natural inflow and the requirements for irrigation (present and future) and environmental releases. The capacity is essentially a compromise between the risk of falling short of demand in dry years and the cost of a higher dam.

Of the average annual catchment yield of 189,000 ML, the dam is required to deliver, over the year, about 7150 ML for existing water rights, 24,000 ML for projected additional irrigation demand and 61,000 ML for environmental flows and Deloraine water supply. The proportion of this requirement to be held in storage depends on the variability of the summer inflows. Following simulations based on the hydrological record, the annual probability of a shortfall was found to be between 35% and 3% for full supply level in the range RL 399 m to 405 m (further details are given in the hydrology chapter of this report). Given the rapid increase in storage capacity with dam height in this range, conditions favour a large dam. However, as storage levels approach the elevation of Huntsman Saddle (RL 408 m) at the northern boundary of the reservoir, it becomes substantially more expensive to contain floods. With extra storage offering diminishing returns in terms of drought risk mitigation, it is clear that RL 405 m is the maximum practical storage level. This level, however, carries additional technical risks from seepage problems at Huntsman Saddle and the left bank ridge. Levels 3 m and 6 m below this limit were chosen for comparison, with RL 402 m appearing the most promising. The live storage capacity (RL 402 – RL 380 m) for this option is 40,000 ML.

The layouts shown in the drawings are therefore based on a full supply level of RL 402 m, and in Appendix C2 there are cost comparisons for higher and lower versions of the preferred dam type.

4.2 ALTERNATIVES CONSIDERED Three layouts were studied. Two of these, a roller compacted concrete dam and a concrete faced rockfill dam, were based on the most promising options from the studies by Gutteridge, Haskins & Davey in 1989, and a further alternative was an earth and rockfill dam.

Table 4-1 Dam Arrangement Options

Dam type Spillway Diversion Outlet works

Roller compacted Central (over dam) Precast segmental Wet well against concrete (RCCD) conduit upstream face

Concrete faced Right bank Tunnel in right bank Tower with shaft into rockfill (CFRD) diversion tunnel

Earth and rockfill Right bank Tunnel in right bank Tower with shaft into (ERFD) diversion tunnel

Hydro Tasmania TAS-106880-CR-03 Page 46 of 75 Meander Dam Feasibility Study Engineering Review The above dam arrangements were compared for a full supply level of RL 402 m and a minimum drawdown level of RL 380 m. The outlet arrangements provided for withdrawal of water within 6 m of the surface anywhere within the reservoir operating range. The reason for limiting the drawdown to RL 380 m, 20 m above the riverbed, is that the storage volume below this level represents only 5% of the total volume and it is undesirable for environmental reasons to lower the pond level any further for such a small gain in utilisation. The exposure of additional areas of mudflats could lead to accelerated siltation, and there is also a cost associated with extending the outlet gates to a lower level. Given the potential slope instability some sediment storage is also required.

4.2.1 Earth and rockfill dam The dolerite around the dam site makes excellent rockfill for an embankment dam and is abundant in quantity. For the impervious core there is a deposit of clay (extremely weathered dolerite) within easy reach on the left bank. The clay is determined to be generally suitable, with low permeability and fair workability, but there would be some cost associated with removing occasional boulders. There would also be a fairly high testing component, as the material appears to be quite variable from place to place. It could be necessary to perform frequent compaction tests to set targets for compaction density in the dam.

Sandy materials for filter zones are not readily obtainable around the dam site, so this component may require some sand brought in by local suppliers, possibly mixed with processed fines from the on-site quarry. However, the filter zones constitute only about 4% of the volume of the dam, so the cost is not prohibitive.

The most economical dam configuration was considered to be one with an inclined core. This permits a steeper downstream face, with consequent savings in diversion length, and simplifies construction vehicle movements on the dam. It is also a design that is more tolerant of differential settlements in the long term.

The spillway for the earth and rockfill dam would be cut into the right bank, with a concrete crest weir totalling 70 m in length. Concrete lining is believed to be necessary only in two regions: where the chute crosses a fault about half-way down, and in an enlarged energy- dissipating region at the downstream end. Some adverse joint planes in the right-hand side of the cut might require extensive rock bolting and possible future remedial work.

The proposed diversion works consist of a tunnel located on the right bank and a cofferdam 18 m high. A range of diversion tunnel sizes from 4.25 m to 5.5 m was evaluated in combination with required cofferdam heights to determine the optimum solution. As shown in Figure 1, the most economical solution was a tunnel diameter of 4.8 m in combination with an upstream cofferdam with its crest at elevation 377.0 m.

Hydro Tasmania TAS-106880-CR-03 Page 47 of 75 Meander Dam Feasibility Study Engineering Review

2350000

2300000

2250000

2200000 Total Cost of Tunnel and Cofferdam [$]

2150000

2100000 4.00 4.25 4.50 4.75 5.00 5.25 5.50 5.75 Tunnel Diameter [m]

Figure 4-1 Diversion tunnel optimisation – tunnel diameter vs total capital cost of tunnel and upstream cofferdam

4.2.2 Concrete faced rockfill dam The concrete faced rockfill embankment, with face slopes of 1V:1.3H, is somewhat steeper than the earth and rockfill and thus saves 25% in volume. It is marginally quicker to build and less vulnerable to delays from wet weather.

Cost comparisons showed that the reduced embankment construction cost almost exactly balances the additional cost of concrete and reinforcement for the face slab. However, a further significant cost in the CFR dam is the reinforced concrete plinth, which forms the perimeter slab for the face slipforming as well as a grout cap. It entails elaborate formwork, heavy reinforcement and difficult access. Historical costs for this type of work approach $2500/m3. This raises the estimated cost of the CFR dam almost $2m above the estimate for the earth-cored alternative.

Arrangements for the diversion and spillway are almost identical to those for the earth and rockfill option, with a 4.8 m concrete-lined tunnel in the right bank and a free-overflow unlined chute spillway higher on the right bank.

4.2.3 Comparison of options In the cost comparison it was found that the earth and rockfill dam was very close to the roller compacted concrete dam in terms of direct construction cost, with the CFRD option some 7% dearer. However, when the construction schedule was considered, the additional infrastructure costs and interest during construction weighed against the ERFD proposal. The ERFD was estimated to need nine months longer to build. It also entailed greater environmental risks and ongoing maintenance costs. In the overall assessment of capitalised costs at the end of construction, there was a margin of $1.4 M (5%) in favour of the RCCD proposal. All further work was concentrated on the RCCD layout.

Hydro Tasmania TAS-106880-CR-03 Page 48 of 75 Meander Dam Feasibility Study Engineering Review 4.3 ROLLER COMPACTED CONCRETE DAM ARRANGEMENT A stability analysis was carried out to compare two alternative RCCD cross-sections and cases with and without foundation drains. Both cross-sections had vertical upstream faces; one was a simple trapezoidal section and one had a vertical downstream face in the top few metres and a less steep slope lower down.

The preferred cross-section was the latter type, with a downstream face plane that intersects the upstream face at crest level. The top part of the downstream face is vertical, the depth of the vertical portion being proportional to the crest width. The crest can thus be varied in width to suit access requirements without affecting the footprint and without much effect on the total volume of concrete. Although it is necessary to use formwork or precast panels to build the vertical part of the downstream face, the sloped section can generally be constructed without formwork. (A slope of 1V:0.8H is about the steepest slope that can be managed without formwork.)

A cost comparison between dams with and without foundation drains showed very little difference. The cost of a gallery, drains and ongoing maintenance is offset by about 25% extra concrete if drains are not used. However, there is a strong argument for installing a gallery for inspection and maintenance purposes. In this case there is only a small incremental cost associated with the installation of drainage facilities. The recommended arrangement therefore shows a drainage gallery extending over about two thirds of the length of the dam. The smaller cross sections at the abutments are stable without drains.

4.3.1 Stability checks The dam cross sections were checked for overturning stability under flood loading to RL 407.1 m as well as for a pseudostatic earthquake load using a seismic coefficient of 0.2 and a water load to FSL. In both cases the factor of safety against overturning exceeds 1.6. The dam is also stable for a flood loading up to the 1:400 AEP level with the drains blocked, i.e. with uplift intensity varying linearly from headwater pressure at the upstream face to tailwater pressure at the downstream toe.

The analysis followed the recommendations of the Guidelines on design criteria for concrete gravity dams and the Guidelines for design of dams for earthquake issued by ANCOLD (Australian National Committee on Large Dams) – Refs. 1 & 2. Seismic studies for Trevallyn Dam (to the east of Meander) and Cethana Dam (to the west) have predicted peak ground accelerations of 0.15 g and 0.20 g respectively for an average exceedence probability of 1 in 10,000. Because of the fleeting nature of such accelerations it is normal to adopt a lower figure for the seismic coefficient in a pseudostatic analysis; the stability check thus establishes that seismic stability is not a significant design constraint.

Sliding failure was not analysed as a separate mode above foundation level because it is reasonably easy to key the dam into the foundation, preventing sliding at the interface, and between concrete lifts it is necessary to develop a tension crack over virtually the full area before the upper part is free to slide. For this to occur, the dam would have to have failed the overturning stability test described above, even though the consequent failure might be a sliding one.

However, a third potential mode of sliding failure (distinct from sliding at or above the foundation contact) is on a joint plane within the rock mass under the dam. This could occur where a sub-horizontal joint slopes upwards in the downstream direction; where a horizontal joint allows a shallow thickness of rock above it to buckle under compressive loading in the

Hydro Tasmania TAS-106880-CR-03 Page 49 of 75 Meander Dam Feasibility Study Engineering Review downstream direction; or where joints intersecting the spillway plunge pool allow a short length of dam (at its deepest section) to slide independently of the stable portions nearer the abutments. Risks of this sort are not much reduced by broadening the base of the dam; there is more to be gained by deepening the foundation excavation. This allows questionable joints to be bypassed, until the depth is such that the risk of joints “daylighting” downstream is eliminated. It also increases the passive resistance of remaining material in contact with the downstream side of the foundation excavation. Hence the recommendation in the geology chapter (Section 2.5.7.2) that foundations should be stripped to high to very high strength rock, possibly 4 to 5 m deep in the valley floor.

4.3.2 Foundation treatment Foundation investigations indicated that the dolerite rock has ample strength to support a concrete gravity dam. A modest amount of grouting will be required to seal up the more open joints near the surface along the upstream foundation contact zone, but this is not a major operation compared to the concrete production for the main body of the dam.

4.3.3 Materials and construction methods It is envisaged that the concrete for the dam will be produced on site. This will involve crushing dolerite rock and stockpiling various gradings before re-blending the rock particles together with cement in a pug mill. It would be feasible to use rock quarried from various miscellaneous excavations such as the power station or the spillway plunge pool, but with the difficulty of excluding weathered material and the double handling involved, there are unlikely to be any worthwhile savings. The alternatives are to open a quarry at a suitable nearby rock exposure, or to supply the aggregates from existing commercial quarry operations in the district.

Various methods can be adopted for forming the dam faces, placing the concrete mixture and applying roller compaction. It has been assumed in the cost estimates that the following methods will be used: · Vertical faces will be formed with precast panels; · The sloping downstream face will be formed with modified kerb placing equipment; · A series of concrete contraction joints will be formed to split the dam into distinct blocks. Embedded water stops will be placed at the upstream face of the contraction joints. · Precast panel joints in the upstream face will be sealed with waterstop; · The primary water barrier just behind the upstream face will be achieved by vibrating grout into the lean RCC mix; · Substantial quantities of conventional concrete will be used for encasing pipes and surfacing the spillway chute. A contractor might have alternative methods for many operations but we believe the cost differences would be minor. The main economies are to be achieved in the efficient production and placing of the dam concrete.

4.3.4 Instrumentation Permanent instrumentation is fairly simple for a concrete dam. A leakage measuring weir is advisable, or possibly two if it is difficult to find a suitable central location. A set of survey targets should be installed along the crest, along with reference pillars on either abutment. To

Hydro Tasmania TAS-106880-CR-03 Page 50 of 75 Meander Dam Feasibility Study Engineering Review check on the effectiveness of the foundation drains it would also be recommended to install a set of piezometers, say eight instruments, in boreholes in the drainage zone just below the base of the dam. It is not proposed to install any internal devices (inclinometers, plumblines) for deformation monitoring.

For measuring temperature rises in the concrete during construction, an array of temperature probes can be laid and connected to a data logger. This would probably be needed only in the early stages, during the warmer months and until the behaviour of the concrete was well understood.

As well as dam safety monitoring, some instrumentation will relate to the operation of the dam. A reservoir level probe will be fitted and the signal relayed by telephone to the valve control centre, along with indicators of which gates and valves are open. The water level at a flow measuring weir downstream of the dam would also be continuously monitored.

All instrumentation related to the remote monitoring of hydropower equipment is considered separately.

4.3.5 Site layout It is envisaged that the major construction operations will be upstream of the dam site. An area for stockpiling materials can be established on the right bank, east of Warners Creek, and the pug mill can be placed on a bench on the right bank at about full supply level. Conveyors should be used as far as possible to transport concrete onto the dam, minimising the amount of traffic driving onto the working surface. Ramps are still needed for regular access by mobile cranes and delivery of materials such as precast components and fuel.

The outlet shaft, spillway training walls and spillway chute surface will be constructed incrementally, alternating with the placement of RCC in adjoining areas. The main floors and walls of the power station can be constructed concurrently with the dam, but installation of pipework and most mechanical equipment should be deferred until the dam is nearing full height. This is primarily to avoid excessive flood risk.

4.3.6 Construction schedule A rough schedule has been prepared, and this forms the basis of the calculation of interest during construction. It provides for a total project duration of 24 months (excluding the development approval procedure). The schedule comprises 6 months for design and 18 months of site works. To economise on the river diversion system it would be necessary to begin work in the autumn or winter, diverting the flow in October. This is shown in the chart below. The main dam concrete placing would take place from December to July, with remaining crest, spillway and outlet works extending over a further two months. Reservoir filling would begin in August of the second year.

Since the diversion conduit is to be used for the main outlet pipe, much of the work involving the main release valve and the hydro plant can only proceed after the diversion plug is installed. Work in the powerhouse might therefore continue somewhat longer, but the basic completion of the scheme is scheduled for 2 months after diversion closure, i.e. in October of the second year.

If it is not practicable to schedule the construction as proposed here, with the river initially diverted in spring, then the design flow capacity will have to be increased substantially. A thorough analysis demands an assessment of the monthly exceedence probabilities for a given

Hydro Tasmania TAS-106880-CR-03 Page 51 of 75 Meander Dam Feasibility Study Engineering Review capacity at a few crucial stages of construction and comparing the expected value of losses against the cost of greater flow capacity. However, as a rule of thumb for initial sizing it may be assumed that during concrete placing the probability of overtopping should be limited to 15% per month. Thus, for example, if the start was delayed three months and the first embankment concrete was placed in March, then it might be June before the dam was high enough to increase the diversion capacity substantially. Estimating a peak outflow of 120 m3/s for a pond level of RL 370 m, the required conduit cross-section would need to be about 50% greater than the minimum size proposed here, or around 4 m x 4 m. The additional cost, including excavation, inlet concrete, stoplogs and plug, is estimated at $380,000.

Figure 4-2 Construction schedule for RCC dam

4.4 DIVERSION ARRANGEMENT Alternatives proposed in previous studies were a tunnel in the right bank for the CFR dam and a box-culvert type conduit under the RCC dam. The conduit could be considerably smaller than the tunnel for two reasons: · the concrete dam would be much better able to withstand overtopping during construction; and · the shorter construction schedule of an RCC dam allows the period of vulnerability to be limited to a few months in the drier part of the year. (For a given monthly exceedence probability, the flow in summer is roughly half that of the winter months.) The diversion conduit for the RCC dam can also be substantially shorter than that needed for an embankment dam. It is feasible for the conduit to pass through the body of the dam without special design precautions. For the embankment alternatives, particularly the earth and rockfill, it is preferable to use a tunnel to avoid problems of differential settlement (and the potential for “piping” along the conduit) and to keep the work site clear.

The chosen diversion capacity for the RCCD proposal was 65 m3/s, which entails an overtopping risk of about 15% per month in summer. It is expected that the main dam would rise above the upstream cofferdam about 5 months after diversion, and the conduit would then accept progressively greater flows up to 150 m3/s with the dam at full height. In the winter months, inflows of 120–170 m3/s will have a similar probability of occurrence to the 65 m3/s in summer, but by that stage the risk of overtopping will be substantially reduced because of the available storage volume upstream of the dam. For summer floods not exceeding the cofferdam crest level of RL 368 m, the available storage of 100 ML (100,000m3) has little effect in attenuating the peak of the flow (see storage curve Figure 1). In winter, with the dam constructed to RL 380 m or more, the available storage capacity will have increased to more than 2000 ML (2 million m3). This will control incoming floods, and the risk of overtopping will diminish greatly.

Hydro Tasmania TAS-106880-CR-03 Page 52 of 75 Meander Dam Feasibility Study Engineering Review

Table 4-2 Estimated flood flows, summer and winter Average recurrence Winter Summer Monthly exceedence interval (Jun-Oct) (Nov-May) probability (yrs) (m3/s) (m3/s)

20 450 270 0.008 10 385 222 0.017 5 321 175 0.033 2 236 112 0.080 1 173 65 0.154

The preferred diversion conduit was a single box culvert located on the right bank and passing through the dam body at the extreme right of the riverbed. A range of box culvert sizes between 3.0 m and 3.6 m was modelled in combination with cofferdam heights to determine the optimum solution. As seen from Figure 4-4, the most economic solution was a 3.3 m box culvert in combination with an upstream cofferdam with its crest at elevation RL 368.0 m. The diversion conduit arrangement is shown in Drawing No. A1-11666.

405

400

395

390

385 RL (m) 380

375

370

365

360 0 5000 10000 15000 20000 25000 30000 35000 40000 45000 ML

Figure 4-3 Storage curve

Hydro Tasmania TAS-106880-CR-03 Page 53 of 75 Meander Dam Feasibility Study Engineering Review

940000

930000

920000

910000

900000

890000 Total Cost of Culvert and Cofferdam [$] 880000

870000

860000 2.80 2.90 3.00 3.10 3.20 3.30 3.40 3.50 3.60 3.70 3.80 Culvert Size [m]

Figure 4-4 Diversion culvert optimisation – culvert size vs total capital cost of culvert and upstream cofferdam

The diversion conduit would sometimes flow full, so it is necessary to anchor it or weigh it down to prevent uplift. The diversion terminates just downstream of the power station works; it is intended that the plunge pool be excavated after diversion closure.

A downstream cofferdam is needed, but with the fairly steep riverbed downstream of the dam its crest level can be 6 m lower than the upstream cofferdam, at RL 362 m. Cofferdam construction materials are readily available in the vicinity of the dam site. The upstream cofferdam is a rockfill embankment with an impervious zone of silty clays, which can be obtained from ample deposits located in the left bank a few hundred metres upstream of the site. The downstream cofferdam can be constructed with the same materials. In this case it may be simpler to build the entire dam of the available silty clays, since this structure may have to retain water on both the downstream and upstream sides. When an overtopping flood abates, the tailwater will recede quickly, but the space between the dam and the downstream cofferdam may remain flooded.

Because both cofferdams are likely to be overtopped during the construction of the RRCD, they will need to be resistant to erosion. The preferred method is to use conventional earth and rockfill construction for the cofferdams, but with downstream facings of rock-filled gabions.

To fill the reservoir, diversion closure is achieved by inserting stoplogs into slots provided at the base of the upstream face. The box culvert units upstream of this point could be reclaimed if desired. The diversion plug is constructed in the first few metres of conduit, within the body of the dam (in the plane of the grout curtain). Access at this stage is only from downstream, since the storage level will rise rapidly in the first few days of reservoir filling.

Hydro Tasmania TAS-106880-CR-03 Page 54 of 75 Meander Dam Feasibility Study Engineering Review 4.5 SPILLWAY ARRANGEMENT In the previous studies by Gutteridge, Haskins & Davey proposals were presented for three alternative spillway layouts in connection with the RCC dam. The central crest spillway was clearly the cheapest of these options, i.e., as originally proposed, but it required a greater flood rise because of the limited overflow crest width available. For the current study an additional option of a 35 m wide spillway equipped with emergency gates was considered. This arrangement would allow a flood rise of 4.5 m (from FSL 402 m to maximum flood level 406.5 m), the same as that associated with the free-overflow spillways with a 70 m overflow crest length. In this arrangement, the concrete spillway crest level would be set about 3 m below FSL and a row of gates would retain the additional water to full supply level. The gates would be capable of withstanding overtopping by 4 m, which allows floods with an annual exceedence probability (AEP) of up to 1 in 500 to pass. In extreme floods, the gates would then progressively open to allow much greater flows to pass with only a small incremental rise in reservoir level.

The emergency gate option was costed and found to be cheaper than an additional left or right bank spillway and chute excavated in rock. Such a spillway option is similar in price to building the dam 2.1 m higher and providing a small flood levee at Huntsman Saddle. Compared to the latter alternative, the gated spillway has two major advantages:

· There is no need to remove dwellings and prohibit building construction at levels between RL 407 m and 409 m around the storage, an area of some 45 hectares; and · It offers the option of building the dam to a full supply level of RL 399 m with an uncontrolled spillway and subsequently raising the storage to the desired final level at relatively little expense.

The proposed layout therefore incorporates emergency gates along the spillway crest. These could take various forms, but are basically unpowered gates, activated by water pressure and triggered by filling or draining a ballast tank. The gates could wash away in extreme floods (with Hydroplus Fusegates, for example) or fold into a recess in the spillway crest, as illustrated in the accompanying drawings. This arrangement is based on a design from a South African company, Flowgate Projects, which offers a cantilever gate that can seal against adjacent segments without requiring intermediate piers. The gates would be of epoxy or polyamine coated steel, and can be designed with varying degrees of manual override to either permit manual release at lower flood levels or prevent inadvertent premature opening of the gates. It is recommended that the spillway gates be thoroughly inspected and tested (if possible) on at least an annual basis to ensure safe ongoing operation of the dam.

In the layout shown in the accompanying drawings the width of the spillway has been reduced from 35 m to 28 m in order to provide space at the dam toe for the proposed powerhouse. This demands a few compromises that raise the cost slightly above the preferred dimensions, but the required flood capacity is adequately catered for. The spillway sill is lowered to RL 398.5 m and the flood level for the 1:20,000 AEP flood rises to RL 407.1 m. The probability of releasing the flood gates increases marginally, from 0.2% per annum (1 in 500) to 0.25% (1 in 400). The gates are in four sections, each 7 m wide, and they open at levels between RL 406.0 m and 406.3 m. The latter level is not exceeded until a flood of about 1:5000 AEP occurs. Various floods have been routed through the storage to ensure that the outflow does not exceed the inflow at any stage. Examples are given in the chapter on hydrology in this report.

Hydro Tasmania TAS-106880-CR-03 Page 55 of 75 Meander Dam Feasibility Study Engineering Review The required spillway capacity is determined by reference to the ANCOLD Guidelines on selection of acceptable flood capacity for dams (Ref. 3). Although the guidelines recommend a study of risk exposure under various floods, there is a “fallback” method which relates the maximum allowable probability of the dam crest flood to the Incremental Flood Hazard Category (IFHC) of the dam.

An approximate conservative assessment the Population at Risk was found to be approximately 100. The ANCOLD guidelines would put this in the High C category and the estimated economic losses also put the dam firmly in the High C category. Thus the acceptable design flood should have an AEP of less than 1:10,000. The assessment was based on the limited information that could be obtained from the existing 1:25,000 maps. At the detailed design stage it is appropriate that a more detailed analysis take place using surveyed cross-sections at Meander and Deloraine. In the unlikely event that this detailed analysis indicates that the population exceeds 100, then the appropriate category would be High A and the dam would be required to pass a PMPDF. Preliminary analysis shows that this is possible by allowing the flood to pass over the crest walls (ie less than a 2m above the crest walls) and by amouring the abutments to ensure that erosion does not destabilise the dam. It is estimated that this additional protection would cost approximately $250,000.

The proposed dam crest level is RL 406.5m. With a 1.2 m parapet wall, this offers 1.1 m freeboard for the 1:10,000 AEP flood and 0.6 m freeboard for the 1:20,000 AEP flood. Overtopping is imminent with an AEP of 1 in 40,000. A concrete dam can withstand some overtopping, so there would still be a substantial margin of safety against outright failure.

A flip bucket at the bottom of the spillway chute disperses the discharge over a considerable length of the riverbed. Since the most severe floods are expected to be short in duration, the main concern with potential erosion involves the more frequent or prolonged floods that may only result in 10 or 20 percent of the rated discharge. A plunge pool extending for 80 m beyond the flip bucket is provided to absorb the residual energy of the flow and minimise the risk of rocks and gravel being washed downstream. This is adequate to contain the hydraulic jump associated with flows up to the 1:100 AEP level. Figure 4-5 shows the spillway discharge (i.e. the flood flow attenuated by storage effects) as a function of annual exceedance probability and Figure 4-6 shows the approximate water level downstream of the plunge pool. In the cost estimates we have compared the arrangement described above with a smaller and larger dam (full supply levels 399, 402 and 405 m - see Appendix C2). The smaller dam requires larger spillway gates or, alternatively, a greater range of flood rise, because of the reduced flood attenuation due to the smaller reservoir surface area. The higher dam also requires larger gates – in this case significantly larger, since the flood rise is curtailed by the level of Huntsman Saddle. The gates must not only permit the passage of a greater flow, but they must open much more frequently. The proposed gates are therefore fully powered gates with automatic actuation and a backup power supply. This adds about $1.7m to the cost and reinforces the view that the lower supply level of RL 402 is close to the maximum economically feasible level.

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2000

1800

1600

1400

1200

1000

800 Spillway flow (m3/s)

600

400

200

0 1 10 100 1000 10000 100000 AEP (1:X)

Figure 4-5 Spillway discharge vs annual exceedence probability (plotted as inverse, 1/AEP)

366

365

364

363

362 Tailwater Level [m]

361

360

359 0 200 400 600 800 1000 1200 1400 1600 Discharge [cumecs]

Figure 4-6 Tailwater level vs spillway discharge

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4.6 OUTLET WORKS The outlet works comprise the following: · Five intake valves at levels RL 377m to RL 400 m; · An emergency dewatering valve at RL 363.3 m; · A trashrack spanning the five intake levels (RL 377m to RL 397m). · A manifold and delivery pipe within the dam; · A cone dispersion valve for irrigation releases; · A riparian flow valve;

To ensure acceptable water quality, irrigation and environmental releases from the Meander Reservoir have to be drawn off at levels that vary with reservoir water level. A multi-level intake arrangement is therefore necessary. Two options were considered for the intake:

(i) A multi-level intake tower with baulks (gates not offering full sealing). The “wet well” tower would be placed against the upstream face of the dam at the diversion conduit location. (ii) A multi-level intake incorporated in the body of the dam, employing valves located within a dry well in the dam.

In both cases irrigation and environmental discharges are released through the steel outlet conduit installed in the diversion culvert, with control by a cone dispersion valve at the downstream end.

The cost estimates were similar for each alternative, but option (ii) was preferred on the grounds of easier maintenance. The selected waterway configuration consists of five 1.6 m diameter horizontal intakes feeding a vertical manifold located in the dam body. The manifold is mounted above the diversion conduit and connects through an elbow to the bottom outlet pipe within the conduit. Irrigation and environmental discharges are released through a cone dispersion valve located at the downstream end of the bottom outlet conduit.

The waterway configuration has been selected to give the most economical sizing consistent with allowable flow velocities and low head losses to enable utilisation for hydropower development. Details of the multi-level intakes and irrigation outlet are shown in Drawing No. B1-08542.

4.7 RESERVOIR DRAWDOWN A bottom outlet is provided for reservoir drawdown in case of an emergency. The intake for reservoir drawdown is located at a higher level (from riverbed) than for river diversion to allow some dead storage for sedimentation. The bottom outlet discharge-rating curve is shown in Figure 4-7. The valve is of 1.6 m diameter and feeds the main outlet pipe, with outflow either through the cone dispersion valve or through the hydropower turbines.

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405

400

395

390

385

Reservoir Elevation [m] 380

375

370

365 0 5 10 15 20 25 30 35 Bottom Outlet Discharge [cumecs] Figure 4-7 Bottom Outlet Discharge Rating Curve.

Reservoir drawdown times for different reservoir inflow conditions, using the bottom outlet and the cone dispersion valve, are as follows:

For periods of average inflow: 20 days For periods of high inflow: 60 days

4.8 OPERATION & MAINTENANCE Ongoing operating costs fall broadly into four categories:

· Day-to-day flow monitoring and discharge control; · Routine maintenance and repairs; · Safety inspections and monitoring; · Environmental controls and fishery management.

It is assumed that the daily regulation of outflows will be performed remotely, but in view of varying demand and weather conditions, as well as seasonal environmental requirements, this control cannot be pre-programmed and automated. The cost of routine management is dependent on the organisation responsible for the dam, so the amounts in the cost estimate are only a rough approximation of the likely cost.

Routine maintenance will consist of frequent checks on the correct operation of valves and inspections of the intake trashracks for accumulated debris. It is expected that corrective action will be needed only occasionally, so there is no provision for a permanent trashrack rake and associated machinery. The choice of concrete as the main material renders the dam virtually maintenance-free, but there will still be occasional repairs to walkways, galleries, valves, etc and very infrequent painting of the spillway gates (approximately every 15 to 20

Hydro Tasmania TAS-106880-CR-03 Page 59 of 75 Meander Dam Feasibility Study Engineering Review years). The access roads will be unsealed, and will need occasional clearing of culverts and trimming of vegetation.

Routine safety inspections are recommended in the ANCOLD guidelines on dam safety management (Ref. 4) at a twice-weekly frequency for checks by maintenance staff, yearly for inspections by dam engineers, and five-yearly for comprehensive safety reviews. Work associated with these inspections would include monitoring and review of piezometer readings, leakage flows, annual deformation surveys and annual inspections of the spillway gates. Possible additional studies might arise from exceptional floods or earth tremors.

Environmental requirements are spelt out in an accompanying report. The main routine cost that enters into the feasibility study is the trapping and transport of migrating fish at certain times of the year. The scope of this undertaking is not clear at present and may be subject to changes. A sum of $20,000 per year has been tentatively entered into the cost estimate, but this would need to be reviewed at an early stage if investigations proceed.

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4.9 DATA SUMMARY The following is a summary of important data relating to the dam and appurtenant structures. Reference should also be made to the drawings in this report.

DAM NAME: Meander Dam

STREAM: Meander River

CATCHMENT AREA: 159 km2

DAM TYPE: Roller Compacted Concrete (RCC)

HEIGHT: 48m

CREST LENGTH: 170m

VOLUME OF DAM: 64000 m3

CREST LEVEL: S.L. 406.5m plus 1.2m high crest wall giving overall height of S.L. 407.7m. FULL SUPPLY LEVEL: S.L. 402.0m

DESIGN FLOOD LEVEL: S.L. 407.1m

FREEBOARD ABOVE DFL: 0.6m

GROSS RESERVOIR CAPACITY: 43000 ML

EFFECTIVE STORAGE CAPACITY: 41000 ML

TYPE OF SPILLWAY: Centrally located conventional spillway 28m wide with 4 Flowgate spillway gates which only operate at floods in excess of 1:400 AEP.

SPILLWAY CREST LEVEL: · Concrete sill: S.L. 398.5m · Top of gates: S.L. 402.0m

SPILLWAY CAPACITY: 1500 m3/s

TYPE OF OUTLET WORKS: · Multilevel offtake built into the dam body with five intake valves and an emergency dewatering valve. · A cone dispersion valve for irrigation releases. · A riparian flow valve.

PERIOD OF CONSTRUCTION: 18 months of site works starting in April.

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PERIOD OF INITIAL FILLING: August of second year.

4.10 REFERENCES 1. ANCOLD (Australian National Committee on Large Dams), Guidelines on design criteria for concrete dams, November 1991. 2. ANCOLD (Australian National Committee on Large Dams), Guidelines for design of dams for earthquake, August 1998. 3. ANCOLD (Australian National Committee on Large Dams), Guidelines on selection of acceptable flood capacity for dams, March 2000. 4. ANCOLD (Australian National Committee on Large Dams), Guidelines on dam safety management, January 1994.

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5 Mini Hydro

5.1 INTRODUCTION The incorporation of mini hydropower generation in the Meander Valley Irrigation Scheme has been considered in several of the feasibility studies carried out in the past.

In 1984, the Hydroelectric Corporation (HEC) considered the addition of a hydropower station to the then Warners Creek Scheme which had a reservoir storage of only 15000 megalitres. The cost of required additional structures exceeded the value of energy generated making the scheme uneconomical.

In a review carried out in 1987, of a proposed project configuration with 43000 megalitre storage, HEC recommended provision be made for incorporation of a mini hydropower station at the Meander Dam as an addition to the Meander Valley Irrigation Scheme.

In November 1994 Gutteridge Haskins and Davey (GHD) considered several options for provision of irrigation to the Meander Valley. Two “dam” options (with the dam located downstream of Warners Creek on the Meander River and named Scheme A and Scheme B) were considered. Scheme A consisted of a 43000 megalitre storage dam with irrigation channels taking off from a control weir downstream of the dam. Scheme B was a 13000 megalitre storage with no irrigation channels, irrigation releases being let down river and users pumping their requirements off the river. Incorporation of hydropower in Schemes A and B was considered and found marginally economical with Scheme A and uneconomical with Scheme B.

All these studies indicated that provision of a mini hydropower station downstream of the Meander Dam was practical but that economic viability depended on reservoir storage, operational constraints and assumed value of energy.

Recent changes in the economics of power generation, particularly that of renewable energy generation together with proposed changes to the electricity market, makes development of mini hydro more viable.

Options for development of a mini hydropower station in conjunction with the Meander Dam have been considered in this context.

5.2 LOCATION OF MINI HYDRO POWER STATION Location and configuration of the mini hydropower development are governed by options for utilising the head and flows developed and available at the dam. These options are affected by existing topography, geological conditions, and type of dam and its configuration including location of spillway and outlets works, all impacting on the feasibility and economy of the development.

The dam type selected for the Meander Irrigation Scheme is a roller-compacted concrete (RCC) dam. The river diversion and bottom outlets are located on the right bank of the

Hydro Tasmania TAS-106880-CR-03 Page 63 of 75 Meander Dam Feasibility Study Engineering Review Meander River, location being determined by the geology and topography of the dam site. The spillway is located over the crest of the dam.

With the given configuration of headworks, two broad options for location of the mini hydro power station downstream of the dam were investigated. These were: (a) power station located on the left bank with independent waterway; (b) power station located on the right bank utilising a waterway common with the bottom outlet. The right bank option was the most economical. Existing topography and geological conditions would entail a much larger volume of excavation on the left bank in addition to requiring an independent power penstock. A sub-option of the right bank location, with the power station located some distance away from the dam was also investigated. Location of the power station approximately 40m downstream of the dam, while reducing excavation, required extension of the spillway right hand guidewall to protect the power station and also a longer power penstock however, and was thus uneconomical.

The optimal location of the power station is considered to be at the dam toe, adjacent to the spillway and on the right bank as shown on Drawing No. A1-11666. The proposed location will minimise excavation and utilise a single common waterway for irrigation and environmental releases, hydro power and reservoir drawdown, thus giving the most economical arrangement.

5.3 TURBINE SELECTION Power generation potential is a function of available net head and discharge at the site. These in turn are functions of reservoir level, friction losses through the water conveyance system, and irrigation and other releases from the reservoir.

The Meander Dam creates a reservoir with full supply level 402.0m and a minimum operating pool of 380.0m. The primary function of the Meander Reservoir is to supply water for irrigation. Water available for power generation is therefore limited to irrigation and environmental releases at all times except during high reservoir inflows and spillage.

Analysis of stream flow duration for the period of flow record indicated that the range of potential releases from the reservoir is quite broad (0 to 25m3/s). Sequential streamflow routing (SSR) using the time series of inflows (attenuated by reservoir storage) was carried out for maximum hydro power discharges values in the range 5 to 15m3/s to determine the optimal maximum discharge. The target was to maximise return with the mini hydro station operating as part of the Tasmanian electricity grid. The use of one or more turbines to utilise the range of flows was considered taking account of constraints imposed on reservoir operation by irrigation demand and reliability.

At lower discharges in the range 5 to 6m3/s, annual average energy generated is of the order of 10500MWhr while at higher discharges in the range 10 to 15m3/s energy generated is of the order of 14500MWhr. Economic analysis shows that NPV values increase for the higher flows while Benefit/Cost ratios lower and then increase to similar values with increase of flow. The NPV values for flows in the range 12 to 15m3/s are approximately $1M greater than those at the lower range.

Analysis of reservoir outflows for the two cases show that with lower flows through the turbines, water loss through spillage amounts to approximately 30% while losses reduce to

Hydro Tasmania TAS-106880-CR-03 Page 64 of 75 Meander Dam Feasibility Study Engineering Review approximately 10% at the higher flows. Provision for higher discharge capacities at the dam also allow capacity to meet peaking requirements for irrigation.

A maximum turbine discharge of 12m3/s was selected as the turbine design flow as higher discharges did not reduce spillage loss greatly and spillage could be managed by prudent reservoir management.

Given the available net head of approximately 42m and flow variation, a configuration of two horizontal axis Francis turbines of 2.85MW and 1.35MW capacity were selected so as to fully utilise the range of available flows. With a maximum discharge of 12m3/s, the larger turbine would utilise flows in the range of 4 to 8m3/s while the smaller would operate in the range 2 to 4m3/s. The system was then simulated using the relevant efficiency curves to derive long term generation at Meander. The average annual generation is 13248 MWhr, although this is limited by the accuracy of the storage analysis model to +/-5%.

The horizontal arrangement of the turbine and generator provides ease of access for maintenance. The arrangement also allows the turbine bearings to be supported from the foundations rather than providing the casing thickening and stiffeners that are required in a vertical arrangement. The turbines would be fitted with mechanical seals to provide minimal maintenance requirements.

Flow control through the Francis turbines is achieved by a adjustable inlet guide vanes. Some conservatism has been employed in the design and with a set level (the level between machine centreline and the tailwater level in the station tailrace discharge), of 3 metres being used in determining the turbine performance. Higher set levels increase the propensity of the turbine to cavitate and thus limits the performance range. There are opportunities to improve this in the design phase. There are also opportunities to reduce the costs of the Power House Building by the use of a combined two runner generating set. This employs two turbines driving a single generator and requires a smaller footprint than shown in Drawing No. B1- 08544.

5.4 GENERATOR SYSTEM

The Generator System will consist of:

§ Two(2) Generators with rated outputs of 1.7MVA and 3.2MVA at 11kV. § 11kV Indoor Switchboard. § Protection and Control System. § Remote Control and monitoring via phone line dial up system. This will provide the station with the ability to adjust flow settings and allow the local control system to monitor and adjust guide vane settings to maintain flows and startup and shutdown operations.

The output from the Generators will be stepped up to the local network rated voltage of 22kV by an 11/22kV 5.0MVA outdoor pad mounted Power Transformer. The Transformer will be either a dry or oil type. At this power rating, oil transformers are approximately 70% the cost of dry type units, however installation and maintenance requirements for oil units are greater and consequently the overall cost difference between the two types is generally low.

Hydro Tasmania TAS-106880-CR-03 Page 65 of 75 Meander Dam Feasibility Study Engineering Review 5.5 AUXILIARY ELECTRICAL SYSTEMS Station Services, such as lighting, heating, ventilation, switchgear operating mechanisms and pumps, will be supplied from an indoor AC distribution board connected to a 22/0.415kV 100kVA pole mounted Power Transformer installed at the Station end of a new 22kV grid connection feeder.

Essential Station Services, such as Generator Circuit Breaker trip coils and associated relays, control and communications equipment, will be supplied from an indoor DC distribution board connected to a single Charger and Battery system.

5.6 GRID CONNECTION The Mini Hydro generation will be connected to Aurora Energy’s local 22kV Network via a new 22kV overhead distribution line extension of Aurora’s Railton No.2 Feeder. Three (3) different points of connection between a new distribution line extension and the existing local feeder have been identified by Aurora Energy, however one of these would require consent from Transend and so was not investigated further. The following grid connection options describe the route and also identify augmentation requirements for Aurora’s existing network.

Option (1)

A feeder extension from existing local 22kV spur line to the Meander Mini-Hydro Station. The extension route would run between Archers Sugarloaf and the new dam, and along an existing transmission line easement up to the point where the easement meets the 22kV spur line. The length of this proposed route is approximately 2.4km. Augmentation would be required from the spur line back to Barbers Road line via Huntmans Road line.

Option (2)

A feeder extension from Barbers Road line to the Meander Mini-Hydro Station. The extension route would run between Archers Sugarloaf and the new dam, and along an existing transmission line easement up to the point where the easement meets the Barbers Road line. The length of this proposed route is approximately 4.82km. Augmentation would not be required.

Option 2 is recommended for grid connection since the implementation is simpler and preferred by Aurora Energy. The cost of option 2 is higher due to the greater length of new transmission line and it would be worthwhile to re-examine option 1 during the detailed design stage.

5.7 POWER HOUSE CONFIGURATION The power station has been located so as to utilise the irrigation and bottom outlet conduit as the power penstock and minimise excavation. This has been achieved by provision of a trifurcation on the bottom outlet conduit, enabling the irrigation/environmental release valve to be located against the spillway chute right-hand training wall.

The horizontal axis Francis turbines have been placed with the draft tubes discharging vertically into the tailrace. Turbine floor level is at El 360.0m and centerline is set at El 362.0m. The downstream wall of the power station has been taken to El 364.5m giving adequate protection from inundation of critical electrical components for spillway discharges

Hydro Tasmania TAS-106880-CR-03 Page 66 of 75 Meander Dam Feasibility Study Engineering Review up to an AEP of 1:4000. The power station superstructure is of concrete construction with a removable metal roof to enable easy access for maintenance and repair to machinery. Power station layout and detail is shown on Drawing No. B1-08544.

The offset layout provides for the space savings, this and other arrangements could be explored further in the detailed design phase.

Ancillary equipment such as dewatering system, fire detection, and communication equipment are provided in the Power Station Building. Adequate equipment spacing and access has been provided for ease of maintenance. The Guard Valve and the Inlet Isolation Valve provide isolation from the dam for turbine maintenance.

During power station maintenance or where excess flows are required the turbines can be bypassed and water released by the use of an energy dissipating valve. The energy dissipating valve is required to limit cavitation damage in the valve and avoid damage to the spillway or stream downstream of the valve. The type utilised is a fixed cone dispersion valve.

5.8 ECONOMIC VIABILITY The economic viability of the mini hydro development depends on its cost and its revenue.

As regards costs, the advantage of incorporating a mini hydro generation at Meander Dam is that its cost is only the incremental costs directly due to the mini hydro station and its appurtenances. These costs are based on the preliminary general arrangement shown in Drawing No B1-08544 and used to assess the economics of power generation.

5.8.1 Energy Price In the recent past, several factors have affected the price of energy.

In the renewable energy sector, the Commonwealth Government’s Mandatory Renewable Energy Target commenced in April 2001. Under this legislation, electricity retailers and other large electricity purchasers are required to source a minimum of two percent of electricity purchases from accredited renewable sources over a ten-year period. In addition, the Sustainable Energy Development Authority of New South Wales has initiated the Green Power Scheme. Under this scheme, renewable energy retailers gain accreditation of their renewable energy products and thereby gain a premium.

The mandated renewables premium and Green Power accreditation is expected to add $20 to $30 per MWhr to the value of hydropower generation.

In the energy market, the interconnection of Tasmania and Victoria through the Basslink and participation of Tasmania in the wholesale electricity market will enable energy produced during peaking hours to receive a higher tariff. The peaking premium is expected to add between $5 to $10 per MWhr to hydropower generation.

The future energy price will therefore consist of three components, viz; the base price, the renewables premium, and the peaking premium, as follows:

Base Price $35 - $40 per MWhr Renewables Premium $20 - $30 per MWhr Peaking Premium $05 - $10 per MWhr

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The anticipated range of energy prices applicable to the Meander mini hydropower project is therefore in the range $40 to $80 per MWhr. A value of $60 per MWhr has been used as the base case for economic analysis.

5.8.2 Capital Cost Estimate

The capital costs associated with mini hydro development have been estimated on a conservative basis. Costs of 35% of pipe-work and valves have been added as premium to the costs of the mini hydro development to allow for increased dimensions above those required for purely irrigation and environmental releases. The capital cost of the development is $6.0M.

5.8.3 Annual Revenue and Expenditure

The long-term average generation at the Meander mini hydro power station obtained as the result of detailed simulation is approximately 13248 MWhr. The average annual gross revenue based on a tariff of $60 per MWhr is estimated at $794,880. Based on experience at Hydro Tasmania the expected annual operation and maintenance cost is in the range $25000 to $75000. A conservative value of $75000/a has been adopted as O&M costs in analysis.

5.8.4 Economic Analysis

Analysis was carried out using a 60-year planning horizon and several real pre-tax discount rate scenarios using values of the capital costs, revenues and expenditures detailed above. The results are as tabulated below.

Discount Rate 8.6% Benefit/Cost Ratio 1.34 NPV $M 2.3 Cost $/MWhr 44.9

5.9 PROJECT RISKS

The risks to successful implementation the mini hydro development can be categorised as technical inadequacies, cost over runs, and schedule over runs. A risk analysis matrix is given in Table 5-1.

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5.10 DATA SUMMARY The following is a summary of important data relating to the mini hydro. Reference should also be made to the drawings in this report.

POWER STATION STRUCTURE Concrete construction with removable metal roof.

STATIC HEAD: 42m

GENERATING SET: Two horizontal axis Francis turbines of 2.85 MW and 1.35 MW capacity.

RATED OUTPUT: 1.7 MVA and 3.2 MVA

RATED VOLTAGE 11 kV

MAXIMUM DISCHARGE: 12 m3/s

AVERAGE ANNUAL GENERATION: 13248 MWhr

5.11 CONCLUSIONS

Examination of the technical and economic viability of constructing a mini hydro power station at Meander Dam show that installation of two Francis turbines is feasible. Using a lower bound value of power sales at $60/MWhr and a relatively high discount rate of 8.6% shows that the Net Present value of the development is $2.3M the benefit cost ratio is 1.3 and cost of production is $45/MWhr. Thus the potential benefits are significant. It is therefore recommended that development of the mini hydro power station be implemented in conjunction with the Meander Dam.

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Table 5-1 RISK FACTOR LIKELIHOOD IMPACT CONTAINMENT MONITORING AND RESPONSIBILITY CONTROL Technical/Quality L H · Inflows and demand based Quality Assurance Design Consultant on observation. Period of Assessment of record extended by Machine Output catchment correlation · Conservative estimates of Incorrect power output made · Output checked against previous estimates Technical/Quality L M · Tolerance allowed in Supplied efficiency curves Project Manager efficiency curves Output of · Contractor to provide turbine/generator performance data with tender below specification · Penalties for low efficiency Technical/Quality L L · Use single contract for both Contract Specification Project Manager works Tolerances between Civil and Electro- Mechanical Installation not met Technical/Quality L H · Design building to be water- Design, Contract Specification Project Manager proof against high spillway Inundation due to high dischages by setting floor spillway discharges and wall elevations above flood level and to required watertightness

Cost Overrun L M · Based cost on current budget Costing System, Design, Contract Project Manager price Specification Electro-Mechanical · Obtain comparative prices Supply and Installation from several independent suppliers · No requirement for highly specialised or sophisticated equipment · Fixed price contract · Well defined scope of works · Contingency allowed Cost Overrun L M · Civil works straightforward Costing System, Design, Contract Project Manager and not complicated Specification Civil Works · Unforeseen conditions unlikely

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· Well defined scope of works · Contingency allowed

RISK FACTOR LIKELIHOOD IMPACT CONTAINMENT MONITORING AND RESPONSIBILITY CONTROL Cost Overrun L M · Well defined scope of design Project Management System, Project Manager and supervision Contract Specification Design/Site · Regular update of progress Supervision · Establish management contract · Establish design and build contract

Schedule Overrun M M · Approval requirement to be Project management Project Manager defined early Delay in receiving · Application documents to be development approval prepared as early in project review process as possible Schedule Overrun M M · Limit overseas scope of Design, Contract Specification, Project Manager supply Project Management Delay due to reliance · Obtain packaged aggregates on overseas electro- mechanical suppliers Schedule Overrun L M · Commence manufacture as Design, Contract Specification, Project Manager early as possible Project Management Delay due to local · Provide adequate lead time electro-mechanical supply Schedule Overrun L L · Civil works straightforward Design, Contract Specification, Project Manager · Unforeseen conditions Project Management Delay due to civil unlikely works construction · Detailed programme to be submitted by contractor · Civil works can commence well in advance of electro- mechanical supply and will not be on critical path · Offer bonus for early completion, liquidated damages for delays Schedule Overrun L L · Offer bonus for early Design, Contract Specification, Project Manager completion, liquidated Project Management Delay due to electro- damages for delays · Potential to commence

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mechanical installation electro-mechanical works in advance of civil works and commissioning

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6 Conclusions Engineering investigations have been undertaken into the feasibility of proposed Meander Dam on the Meander River at Warners Creek. The investigations included:

§ An assessment of the geology and geotechnical conditions at the dam site, reservoir area and catchment. § An investigation into the hydrology of the catchment including basic characterisation of the hydrological parameters, catchment yield, storage yield and behaviour, and flood hydrology. § An engineering assessment of the most economic and appropriate form of dam construction for the site and preliminary design of the preferred arrangement. § An engineering assessment of the viability of a mini-hydro power station, including an assessment of possible options, and preliminary design of the preferred option.

A preliminary estimate of additional demand for irrigation water of 24,000ML/a, based on a farmer survey conducted by Davey and Maynard Pty Ltd, was used as the basis for selecting the size of the storage. It is concluded that a full supply level of 402m provided the best tradeoff between reliability and quantity of the water supplied, although this will be further addressed in the economic analysis.

6.1 GEOLOGY The geotechnical investigations showed that the foundations of the dam would be on dolerite bedrock. The dolerite has joints and other geological structures that will require grouting and surficial treatment to make good the foundation for a dam with low potential leakage. The diversion conduit for the RCC dam is likely to excavated in weathered to sound fresh dolerite and the dam's stability is likely to be controlled by the presence of sheet joints. It is anticipated that some rock bolting and shotcreting may be required during construction to support this cut. There is a major fault cutting across the river downstream of the dam wall that will require shotcrete lining where encountered in the diversion cut.

The other significant feature of the site is the low saddle area - Huntsman Saddle on the left bank of the dam site. Concerns have been expressed over the potential seepage loss through this saddle area. It should be possible to operate the dam at a full supply level of 402m without significant seepage loss in this area. It is recommended that ground water monitoring be established prior to filling the reservoir and this be continued after first filling to ensure that any potential environmental impacts are identified and managed in an appropriate fashion.

Slope stability in the reservoir is a further concern for the project, since much of the storage basin is surrounded by deep talus soils derived from the surrounding Jurassic age dolerite. Landslides appear to be a common feature of the catchment area, and the concern would be the re-activation of landslides (although none have been identified within the storage) under normal operation of the reservoir which may lead to turbidity problems. This is not expected to impact on the integrity or longevity of the dam. Provision in the dam design has been made for sedimentation with a significant volume of dead storage.

6.2 HYDROLOGY Hydrological and meterological data have been summarised for the Meander Dam site and surrounding areas. The data shows a strong seasonal influence with low flows over the summer

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period and high flows over the winter. Stream gauge records for the site cover the period from 1982 and 1991. The record has been extended through correlation with downstream sites to give a record length of approximately 34 years and from this the average annual catchment yield was found to be 189,000 ML.

A daily time step storage analysis model was developed that incorporated inflows, direct rainfall and evaporation, releases for environmental flows, domestic water supplies and irrigation, and spills. It was found that the reliability of supply of the irrigation water and yield from the reservoir were sensitive to the environmental releases. With trout excluded from consideration of the environmental flows, the annual yield of the reservoir with a full supply level of 402m was an additional 24,000ML for irrigation with a reliability on an annual basis of 92%.

A flood routing model was developed for the catchment and a range of inflows from 1:50 AEP to the Probable Maximum Precipitation (PMDF) were analysed. The critical duration varies from 24 hours for the 1:50 AEP flood to 6 hours at the PMPDF. The peak inflows and outflows for the 1:50 AEP flood are 545 m3/s and 215 m3/s respectively. The corresponding values for 1:10,000AEP flood are 1680 m3/s and 1415 m3/s. It is apparent that the dam will have a significant attenuating effect on peak flows at the dam and should have a beneficial impact in reducing downstream flood impact.

6.3 DAM ENGINEERING Three types of dam were considered: Roller Compacted Concrete (RCC), Concrete Faced Rockfill (CFR) and Earth Rockfill (ERF). On the basis of lower costs and lower construction risks, the RCC option was found to be the best solution. Preliminary design of the RCC has been undertaken and the arrangement includes:

§ upstream and downstream coffer dams with a box culvert diversion conduit running along the right bank; § a RCC wall with a vertical upstream face and downstream face slope of to 1V:0.8H; § A centrally located conventional concrete spillway with 4 Flowgate spillway gates, which only operate at floods in excess of 1:400 AEP; § A multilevel offtake built into the body of the dam, with a conduit discharging through a cone dispersion valve; § Emergency dewatering facilities;

The design has taken into account environmental concerns and has a multi-level offtake to ensure the best quality water is released from the reservoir. Furthermore, screening sufficiently fine to exclude fish from the outlet works is proposed. Fish passage is to be catered for through a trapping and relocation program.

The estimated cost of design and construction of the dam is approximately $25m and the annual operating costs are estimated to be $115,000.

6.4 MINI HYDRO A number of options for the mini-hydro were considered during the study, including left and right bank options, and a number of alternatives for the right bank option. It was concluded that a power station located at the base of the dam housing two horizontal axis Francis turbines of 2.85 and 1.35MW capacity is the best option. This arrangement has the potential to generate an annual average of approximately 13,000 MWh. On this basis the mini-hydro is an economically attractive addition to the project and is expected to add to the return on the investment. The

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estimated cost of design and construction of the mini-hydro is approximately $6.0m and the annual operating costs are estimated to be $75,000.

6.5 OVERALL CONCLUSIONS The technical feasibility of a 50m high RCC dam with a full supply level of 402m, supplying an additional 24,000ML/a of irrigation water has been demonstrated. Providing that the environmental and economic aspects of the project are shown to be viable, then it is recommended that the project can proceed to detailed design and construction. The approach taken could either be for a design contract followed by a construction contract, or as a single design and construct contract.

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Appendix A1 Results of Laboratory Testing

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Appendix A2 Plan of Geological Investigations

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Appendix A3 Geological Cross Sections at the Dam Site

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Appendix A4 Trench Logs

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Appendix B1 Climate Statistics

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Table B.0-1 Rainfall sites - Averages, Maximums and Percentiles RAINFALL (mm) Meander Pine Tree Lake Lake Fisher Warners Western Liffey Blackwood Great Breona Meander River Rivulet Augusta E Gwendy River Creek Creek Creek Lake E @ Deloraine (18907) (597) (972) (509) (16201) (267) (1634) (1548) (871) (941) (863) (162) AVERAGES January 59.1 78.3 61.0 121.4 67.6 101.4 60.6 49.9 49.2 70.2 73.2 67.8 February 59.1 61.3 49.0 105.4 112.9 92.2 52.6 56.0 52.1 55.6 78.0 48.2 March 77.7 87.3 69.8 98.7 119.0 64.9 73.8 60.2 65.9 81.0 91.0 44.8 April 62.8 105.1 82.5 96.0 96.4 151.4 97.3 82.5 99.7 99.6 130.2 59.3 May 87.3 146.3 97.9 160.2 207.3 173.4 121.4 107.3 110.2 116.1 175.5 70.9 June 109.9 156.3 96.8 162.5 212.4 199.0 116.4 108.9 107.1 114.2 184.4 97.8 July 136.3 208.0 118.9 167.4 241.6 251.8 150.2 139.1 139.4 159.4 238.0 99.3 August 131.7 193.7 110.4 187.3 287.8 223.2 146.5 134.6 140.2 147.1 221.5 101.9 September 103.1 149.1 103.2 178.0 249.9 184.4 112.8 106.8 107.2 118.1 177.5 89.7 October 86.8 119.1 92.5 139.1 181.8 179.1 97.5 98.4 92.4 95.8 149.7 63.1 November 91.4 86.1 69.6 130.2 160.8 160.3 74.8 66.3 70.7 77.0 108.4 68.4 December 73.5 92.3 72.9 113.6 151.6 141.1 86.5 68.9 71.9 86.8 108.1 50.9 MONTHLY MAX January 104.6 166.8 218.6 304.1 112.2 143.4 132.3 174.9 145.8 242.8 185.9 173.0 February 130.0 196.0 168.4 200.2 208.6 204.2 246.0 169.4 229.7 273.6 269.0 99.4 March 151.2 265.9 206.0 233.4 166.6 114.4 230.2 257.6 232.8 294.7 298.4 110.4 April 153.4 269.6 206.6 128.8 162.8 315.2 258.0 306.2 281.8 438.0 361.1 134.4 May 141.6 393.8 203.0 318.2 359.7 257.2 259.6 388.5 369.2 267.6 474.2 155.4 June 158.4 286.0 190.4 267.0 299.6 357.9 266.6 290.2 231.1 228.9 387.6 134.8 July 200.1 369.4 219.2 283.4 504.4 302.8 316.7 295.5 307.9 387.0 499.3 198.4 August 203.4 388.2 228.5 304.0 431.0 274.8 287.3 380.9 315.8 333.6 540.9 200.2 September 191.2 363.8 217.3 345.0 337.8 204.8 208.8 254.4 232.2 304.2 416.6 145.2 October 129.6 285.0 199.0 169.6 251.0 206.0 193.2 249.6 245.3 216.3 333.6 139.4 November 149.0 176.8 144.4 237.4 249.4 242.0 163.9 183.8 162.6 183.8 328.5 131.8 December 108.9 236.7 192.8 206.0 287.7 237.8 231.5 217.4 219.2 231.1 331.5 141.2 PERCENTILES 10 153.5 215.4 145.2 225.7 258.0 252.2 171.8 160.1 164.1 179.0 275.0 120.1 50 86.1 110.8 81.3 129.3 144.3 162.9 92.5 80.5 83.5 91.8 122.4 65.7 90 36.1 44.4 36.3 71.2 76.3 63.1 37.5 29.1 33.5 33.7 53.4 31.0

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Table B.0-2 Rainfall Sites - Minimums and Standard Deviations RAINFALL (mm) Meander Pine Tree Lake Lake Fisher Warners Western Liffey Blackwood Great Breona Meander River Rivulet Augusta E Gwendy River Creek Creek Creek Lake E @ Deloraine (18907) (597) (972) (509) (16201) (267) (1634) (1548) (871) (941) (863) (162) MONTHLY MIN January 25.4 16.8 0.0 28.4 42.2 29.2 7.1 2.5 7.7 5.1 3.6 31.0 February 1.0 2.1 0.0 28.6 25.0 16.8 3.2 0.0 0.0 0.0 0.0 13.4 March 22.0 6.4 4.3 33.8 77.1 16.4 5.1 0.0 0.8 4.8 18.5 7.4 April 14.6 12.8 20.7 61.8 62.2 38.2 15.1 0.0 4.1 8.1 8.7 22.4 May 10.6 15.4 17.4 64.8 96.2 79.6 17.8 11.6 16.2 9.0 0.8 23.6 June 77.0 47.3 0.0 106.4 150.4 119.8 48.2 7.1 31.2 25.1 25.5 71.8 July 60.2 63.9 41.6 67.2 84.6 163.4 46.3 32.2 34.6 47.0 60.6 47.4 August 54.2 65.1 29.2 0.2 119.0 121.6 41.4 27.7 46.4 21.7 40.4 35.0 September 42.0 14.0 17.6 94.2 121.8 170.0 20.9 15.9 21.4 24.1 74.1 30.0 October 48.6 28.6 0.0 102.8 128.2 134.8 21.4 22.4 19.9 12.9 31.9 22.2 November 38.0 8.4 0.0 71.4 99.4 115.2 23.3 7.6 17.6 14.8 28.5 29.8 December 27.6 9.7 0.0 23.6 84.4 46.2 12.1 0.3 8.2 4.4 5.6 8.6 STD. DEVIATION January 30.2 39.8 43.3 89.6 29.3 44.6 33.4 34.3 32.2 53.0 44.5 42.2 February 49.5 44.8 40.0 58.1 92.0 63.4 49.7 43.6 54.3 56.8 57.3 28.9 March 53.6 68.4 52.1 63.2 44.4 39.5 52.0 50.8 50.3 65.6 56.7 37.0 April 49.7 55.8 45.3 27.8 39.9 114.3 56.9 62.2 64.5 78.9 82.7 36.2 May 46.9 83.5 51.0 86.5 129.3 67.1 59.8 71.0 70.8 68.8 96.2 46.4 June 32.8 52.8 36.2 53.3 57.7 83.4 51.6 57.5 49.5 47.7 97.0 19.5 July 53.7 81.0 57.9 75.1 165.8 48.8 61.5 62.9 66.6 73.0 122.0 50.4 August 56.6 77.9 45.7 104.5 133.0 52.2 56.0 72.2 60.3 66.2 114.4 54.6 September 55.6 90.1 55.0 84.5 91.6 15.5 56.1 55.7 58.0 72.8 82.8 37.5 October 29.9 58.0 46.4 21.5 53.7 38.6 50.3 57.2 48.0 51.4 79.1 33.9 November 44.6 41.2 31.5 50.7 72.4 57.7 33.8 39.5 35.7 42.0 69.4 33.1 December 36.5 66.6 49.0 53.6 79.8 89.1 57.4 46.1 48.8 66.8 75.0 39.2

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Table B.0-3 Flow Site statistics

FLOW (m3/s) Fisher Meander Meander Meander Jackeys Meander Fisher Meander Meander Meander Jackeys Meander River @ Deloraine b/l Deloraine a/b Warners Creek d/s Warners River @ Deloraine b/l Deloraine a/b Warners Creek d/s Warners (16201) (162) (541) (588) (18221) (18224) (16201) (162) (541) (588) (18221) (18224) AVERAGES MONTHLY MAX January 0.63 2.88 4.35 1.53 0.18 2.00 29.00 44.88 142.30 85.99 3.57 80.95 February 0.36 3.09 3.12 0.90 0.11 0.57 17.44 129.70 176.10 37.67 2.32 7.19 March 0.54 3.86 3.92 3.02 0.11 1.61 24.42 216.20 224.70 208.10 8.99 153.90 April 1.28 6.27 7.57 4.85 0.22 4.30 25.46 139.00 202.50 179.00 16.13 237.10 May 2.28 14.12 12.50 6.54 0.44 6.44 26.08 320.10 213.70 252.80 19.14 167.10 June 2.44 14.27 16.44 7.13 0.83 8.17 20.46 145.90 244.70 134.70 20.60 192.10 July 2.87 23.37 24.60 9.04 1.29 11.49 32.42 287.20 252.30 200.20 25.51 260.50 August 3.06 28.18 25.83 9.04 1.34 9.45 25.34 328.30 433.20 183.00 19.43 193.30 September 2.91 20.83 18.93 8.98 1.13 9.13 22.78 390.80 224.90 283.20 40.00 366.30 October 2.01 12.09 13.01 4.95 0.65 6.02 26.01 130.60 350.00 273.10 19.40 337.60 November 1.12 7.24 7.40 2.80 0.35 3.26 26.33 216.70 162.40 102.20 9.44 81.19 December 0.89 4.40 5.83 2.83 0.25 2.95 23.01 112.80 185.40 235.50 6.23 51.72 MONTHLY MIN STD. DEVIATION January 0.03 0.03 0.22 0.07 0.01 0.18 0.59 3.26 3.49 1.28 0.18 1.45 February 0.01 0.05 0.19 0.05 0.00 0.13 0.37 3.70 3.62 0.60 0.14 0.24 March 0.00 0.03 0.15 0.05 0.00 0.14 0.55 4.49 4.14 2.36 0.17 2.04 April 0.00 0.07 0.19 0.06 0.00 0.13 0.88 6.86 5.46 2.36 0.37 4.27 May 0.19 0.05 0.51 0.51 0.01 0.39 1.08 10.40 7.19 2.95 0.30 2.94 June 0.19 0.05 0.61 0.90 0.01 0.39 0.59 9.00 7.17 2.54 0.42 3.07 July 0.09 0.10 2.82 0.92 0.17 1.45 1.31 14.44 11.49 5.11 0.60 4.98 August 0.03 0.13 2.92 1.09 0.12 1.37 1.00 10.94 9.77 3.39 0.81 4.61 September 0.24 1.59 1.82 1.08 0.10 0.82 1.11 9.20 9.41 3.80 0.57 5.05 October 0.20 0.13 0.36 0.40 0.09 0.84 1.18 7.06 9.11 2.97 0.46 4.07 November 0.11 0.11 0.51 0.21 0.03 0.40 0.63 6.09 5.38 2.29 0.24 1.59 December 0.07 0.07 0.36 0.16 0.01 0.32 0.65 4.95 4.73 2.89 0.23 2.02 PERCENTILES 10 3.57 26.95 27.47 10.94 1.45 12.52 50 1.41 8.54 8.82 4.14 0.35 4.39 90 0.17 1.04 1.35 0.65 0.04 0.54

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Table B.0-4 Evaporation Statistics

EVAPORATION (mm) Cressy Research Launceston Campbell Lake Lake Cressy Lake Cressy Station Airport Town St. Clair St. Clair Research Farm St. Clair Research Farm (091022) (091104) (093036) (096015) (131) (888) (131) (888) AVERAGES STANDARD DEVIATION January 6.0 6.9 6.1 3.6 3.6 6.0 0.8 0.7 February 5.7 6.4 5.6 3.8 3.6 5.7 0.7 0.6 March 3.8 4.6 3.5 2.8 2.7 3.8 0.5 0.5 April 2.3 2.7 2.2 1.9 1.8 2.2 0.4 0.2 May 1.2 1.5 1.2 1.2 1.2 1.2 0.4 0.1 June 0.8 0.9 0.7 0.9 0.8 0.7 0.4 0.2 July 0.9 1.0 1.0 0.8 0.8 0.8 0.5 0.1 August 1.3 1.6 1.5 1.1 1.0 1.4 0.4 0.1 September 2.2 2.5 2.3 1.6 1.5 2.3 0.5 0.2 October 3.3 3.8 3.4 2.3 2.3 3.3 0.6 0.4 November 4.4 5.1 4.2 2.8 2.7 4.4 0.5 0.6 December 5.3 6.5 5.7 3.3 3.1 5.3 1.1 0.7 Lake Cressy Lake Cressy Lake Cressy St. Clair Research Farm St. Clair Research Farm St. Clair Research Farm (131) (888) (131) (888) (131) (888) MONTHLY MAX MONTHLY MIN PERCENTILES January 5.0 7.4 1.4 4.6 10 113.2 182.5 February 4.5 6.0 2.2 4.4 50 60.2 110.1 March 3.7 4.6 1.5 2.9 90 21.7 44.4 April 2.5 2.5 1.1 1.6 May 1.9 1.4 0.6 0.9 June 1.4 1.2 0.2 0.5 July 2.5 1.1 0.3 0.7 August 2.1 1.6 0.4 1.1 September 2.3 2.6 0.8 2.0 October 3.3 4.1 1.3 2.7 November 3.7 6.0 1.7 3.7 December 4.6 6.5 0.1 3.7

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Table B.0-5 Temperature Statistics

TEMPERATURE (oC) Mersey Fisher Liawenee Mersey Fisher Liawenee @ Kimberley River Canal @ Kimberley River Canal (22) (16201) (68) (22) (16201) (68) AVERAGES MONTHLY MAX January 17.8 11.4 11.8 33.9 25.9 13.6 February 19.1 11.4 12.3 35.3 27.1 14.0 March 16.1 8.7 9.0 31.8 25.9 10.2 April 11.6 5.3 5.9 27.5 21.6 7.3 May 10.0 3.7 4.3 23.5 13.4 5.9 June 7.9 2.1 2.4 21.7 11.5 3.8 July 7.8 1.4 1.9 20.0 10.3 2.8 August 8.7 1.8 2.2 21.1 13.1 3.8 September 11.0 3.2 3.4 25.4 16.2 5.0 October 12.5 4.7 5.4 27.1 18.8 6.5 November 15.0 7.3 7.2 28.6 24.0 10.5 December 16.6 9.0 9.5 33.0 27.9 12.1 MONTHLY MIN STD. DEVIATION January 2.9 -7.8 9.3 0.8 1.0 1.5 February 2.2 -1.0 10.0 0.2 1.5 1.5 March 1.5 -1.7 7.8 0.5 0.5 0.9 April -2.4 -12.2 4.5 0.7 0.3 1.0 May -3.5 -12.2 3.4 1.0 0.9 0.8 June -3.3 -8.0 1.6 0.5 0.7 0.7 July -3.6 -9.2 0.3 0.1 0.8 0.8 August -3.0 -9.5 0.8 0.7 0.8 0.9 September -2.0 -8.6 1.7 0.2 0.8 1.2 October -1.3 -9.3 4.1 0.4 1.0 0.8 November -1.1 -12.2 5.4 2.0 1.6 1.6 December 1.9 -1.4 7.8 0.4 0.5 1.4 PERCENTILES 10 16.9 11.7 12.0 50 10.9 5.1 5.4 90 7.7 1.7 1.8

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Appendix B2 Data Availability and Quality

SITE PERIOD OF RECORD Meander River @ Meander Pine Tree Rivulet Lake Augusta E Lake Gwendy Fisher River Warners Creek Western Creek Liffey Blackwood Creek Great Lake East Breona Meander River @ Delorain Bridge 1930 1950 1970 1990 2010 1910 1920 1940 1960 1980 2000 Figure B2.1: Data Availability for Rainfall Records

SITE PERIOD OF RECORD

Fisher River u/s Lake Mackenzie Meander River @ Deloraine Bridge Meander River b/l Deloraine Jackeys Creek Meander River d/s Warners Creek Meander River a/b Warners Creek 1970 1980 1990 2000 2010 1960 Figure B2.2: Data Availability for Flow Records

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Table B2.1: Data Quality summary for Rainfall Records

Site Name Period of Record Variable Data Quality 0-32 33-150 151-255 Comments 18907 Meander River 11/07/1990 - Present 1 49.9% 0.7% 49.5% Missing Record: 13/7/93 - 10/12/98. Otherwise good quality @ Meander data. 597 Pine Tree Rivulet 02/04/1969 - Present 1 94.0% 1.7% 4.4% Missing Record: 6 months Jul 96, 2 months Jan 91. Several gaps of up to a month present. Some estimation of data. 972 Lake Augusta E 15/07/1971 - Present 1 96.2% 0.6% 3.2% Missing Record: 6 months Jan 73, 2 months Nov 73, 7 months Sept 78. Several gaps of up to a month present. 509 Lake Gwendy 23/04/1992 - Present 1 90.8% 2.4% 6.7% Missing Record: 2 months Jul 92, 3 months Aug 94. Couple of gaps of up to a month. 16201 Fisher River 05/12/1973 - Present 1 14.8% 0.3% 84.8% 1 month of data then a large gap. Record really begins 23/2/97. Plenty of gaps in the data throughout the record. 267 Warners Creek 31/05/1988 - 25/07/1994 1 87.6% 0.0% 12.4% Missing Record: 2 months Dec 88, Oct 89 and Aug 91, 1.5 months Sept 90. 1634 Western Creek 01/05/1964 - 31/12/1991 10 100.0% 0.0% 0.0% Good quality data.

1548 Liffey 01/01/1916 - 31/12/1991 10 80.0% 0.0% 20.0% Missing Record: 31/5/46 - 1/6/54, 31/7/58 - 1/7/59, 30/4/60 - 1/10/61, 30/9/62 - 1/1/65. 4 months Jan 60. 871 Blackwood Creek 01/03/1955 - 31/12/1991 10 99.0% 0.0% 1.0% Missing Record: 3 months Oct 86, some smaller gaps exist.

941 Great Lake East 01/10/1965 - Present 1 100.0% 0.0% 0.0% Generally good quality data.

863 Breona 16/01/1920 - 31/12/1987 10 74.1% 0.0% 25.9% Record really begins 1/8/36. Missing Record: 31/7/63 - 1/12/64 6 months Jan 67. Gaps of up to 5 months through record. 162 Meander River 08/08/1991 - Present 1 93.8% 3.2% 3.0% Missing Record: 3 months May 93, some smaller gaps exist in @ Deloraine Br the data.

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Table B2.2: Data and Rating Quality Summary for Flow Records

Site Name Period of Record Data Quality Flow Rating

0-32 33-150 151-255 Comments Quality Rating Changes Gauged to

Fisher River Some gaps in data in late 23 lower 16201 u/s Lake Mackenzie 05/12/1972 - Present 96.9% 1.1% 2.0% 1970's of up to a month. 33 upper 2 11 m3/s Otherwise good quality. Meander River Missing record from 1/1/76 to 13-33 162 @ Deloraine Bridge 01/01/1966 - Present 9.6% 21.8% 68.6% 1/8/96. Some gaps in early lower 3 350 m3/s record. Affected by rating. 44 upper Meander River 13 lower 541 b/l Deloraine 30/09/1968 - 06/08/1996 97.2% 2.8% 0.0% Generally good quality data. 23-44 8 350 m3/s upper Almost a year of missing 18221 Jackeys Creek 01/04/1982 - 30/08/2001 95.9% 0.5% 3.6% record in 1997. Otherwise 13 2 7 m3/s good quality data. Meander River 2 week gap in record in March 18224 d/s Warners Ck 27/08/1982 - 18/10/1991 100.0% 0.0% 0.0% 1991. Otherwise good 23 17 175 m3/s quality data. Meander River Quality affected by upper end 23 lower 588 a/b Warners Ck 31/12/1972 - 22/02/1985 62.9% 37.1% 0.0% of the flow rating. 44 upper 4 19 m3/s

Hydro Tasmania TAS-106880-CR-01 Page B2 - 3 Meander Dam Feasibility Studies

Appendix B3 Yield Analysis Results

Month 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 Jan 245 680 1714 3468 12743 8589 3150 12977 12512 Feb 67 180 4972 20223 605 7549 4471 3294 3835 1606 Mar 1969 347 10088 8352 1560 1466 1419 7307 9483 19437 Apr 5196 109 34318 8702 8679 9861 2009 17877 24431 8467 May 11605 59 52591 14050 9599 27497 2181 34054 24899 36572 Jun 5892 3186 47199 10932 15161 38470 4818 35839 34563 22440 Jul 49882 12272 30653 40433 41931 12962 23549 37449 45362 72841 Aug 28545 34274 77578 45203 63834 40852 46862 51482 38036 37026 Sep 40313 13820 25286 16932 24237 32891 13482 32413 48068 28491 Oct 9834 19680 33416 4621 17584 39190 5200 23214 17279 28991 Nov 8736 3850 21489 4765 8057 19570 3697 11308 7217 27351 Dec 5597 2907 5031 2425 5447 16676 772 20939 13538 4367

Total 167716 90928 343301 178351 200162 259727 117049 278327 279688 300101

Month 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 Jan 4549 4285 743 3969 1531 2134 898 755 10469 2230 Feb 3015 1682 2800 3012 1033 1181 1129 351 1936 2045 Mar 6345 13316 1254 3981 3133 2419 6082 541 15875 7439 Apr 6172 7837 6848 16431 18083 9511 7128 11729 12542 2739 May 14363 33796 15137 7131 17359 7407 13101 13648 15695 26800 Jun 16928 22338 8299 14692 24079 19721 14929 24449 25133 22089 Jul 10888 16538 26685 33662 44148 53927 12202 11683 33202 18544 Aug 24320 37990 26475 34443 29324 49197 9145 27066 43326 35200 Sep 17365 5839 23053 28910 46321 16256 26507 30724 52740 13490 Oct 7897 4743 16756 44964 10849 15238 3871 7912 22855 9263 Nov 4231 2001 7958 11798 4362 3061 2403 13904 5613 6186 Dec 15548 2889 6899 3849 5743 1082 4316 6003 9067 19577

Total 131620 153254 142907 206841 205966 181134 101711 148765 248452 165602

Month 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 Jan 8163 8652 1569 9423 1217 4348 4569 5896 13850 7788 Feb 1577 1210 683 1263 1929 1232 3814 10091 7834 6545 Mar 813 3045 393 5009 685 412 1767 8781 1508 638 Apr 15579 2974 4678 37228 7533 3397 14742 4416 2562 3856 May 20615 20681 17789 23606 7962 2873 30693 6308 20083 12405 Jun 11914 14178 33422 26591 8066 20070 26623 14772 23991 22553 Jul 46457 15612 38150 41208 43069 21987 34903 32805 20142 22969 Aug 13537 11088 28350 15605 23290 38556 31859 44233 20126 31402 Sep 23225 4923 26045 25120 12567 17911 26810 22931 7318 19738 Oct 30458 6746 32704 18294 9700 6631 32386 12905 8514 7848 Nov 6635 8998 10568 5738 13424 8480 27244 16878 5153 3906 Dec 11504 4498 8248 3723 2878 7352 18336 15872 913 3127

Total 190476 102605 202600 212808 132320 133249 253747 195888 131993 142774

Hydro Tasmania TAS-106880-CR-03 Page B3 - 1 Meander Dam Feasibility Studies

Month 1996 1997 1998 1999 2000 2001 Jan 17933 6663 333 1860 875 784 Feb 11476 2766 1409 14253 2858 466 Mar 19857 1716 183 15355 2888 6448 Apr 15302 2405 4023 5773 2013 5426 May 6835 48503 4773 16074 17014 8129 Jun 34883 22537 20826 29135 12520 20821 Jul 35111 15496 42124 26635 52589 9177 Aug 73065 26234 33677 38740 17314 39150 Sep 47696 29245 45142 25865 33588 27042 Oct 18178 8105 23756 9109 23670 Nov 5003 3411 12436 6133 15641 Dec 4564 2125 7006 1608 1678

Total 289902 169205 195690 190537 182647

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Appendix B4 Conceptual Time Studio Model

Damsite A M D L K B C F H 1 J

I E

G

Sub Area (km2) Reach Length (km) A 19.6 A®Jn 3.8 B 16.7 B®C 4.5 C 12.5 C®Jn 2.6 Jn®D 1.5 D 5.5 D®Jn 2.1 E 14.1 E®F 5.5 F 12.8 F®Jn 3.0 G 15.7 G®H 6.5 H 11.6 H®Jn 2.7 I 11.4 I®J 5.5 J 5.4 J®Jn 2.0 K 24.7 K®Jn 3.7 L 2.3 Jn®L 0.9 M 8.6 L®Jn 1.2 Jn®Damsite®Drowne 2.0 d M®Damsite 1.6

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Appendix B5 Flood Fit Hydrographs The following are the fit hydrographs used to calibrate the Meander extreme flood model. Start and finish times have been removed so as not to unintentionally bias particular events. X axis values are given in hours and Y axis values are given in m3/s. Each hydrograph has been determined using an Alpha of 1.4 and an ‘n’ of 0.8.

250 Modelled Actual 200

150

100

50

0 0 5 10 15 20 25 30 35 40

300 Modelled Actual 250

200

150

100

50

0 0 10 20 30 40 50 60 70 80

Hydro Tasmania TAS-106880-CR-03 Page B6 - 1 Meander Dam Feasibility Studies

300 Modelled 250 Actual

200

150

100

50

0 0 10 20 30 40 50 60 -50

200 Modelled 180 Actual 160 140 120 100 80 60 40 20 0 0 10 20 30 40 50 60 70 80

Hydro Tasmania TAS-106880-CR-03 Page B6 - 2 Meander Dam Feasibility Studies

200 Modelled 180 Actual 160 140 120 100 80 60 40 20 0 0 10 20 30 40 50 60

250 Modelled Actual 200

150

100

50

0 0 20 40 60 80 100 120

-50

Hydro Tasmania TAS-106880-CR-03 Page B6 - 3 Meander Dam Feasibility Studies

250 Modelled Actual 200

150

100

50

0 0 20 40 60 80 100 120 140

250 Modelled Actual 200

150

100

50

0 0 10 20 30 40 50 60

-50

Hydro Tasmania TAS-106880-CR-03 Page B6 - 4 Meander Dam Feasibility Studies

Appendix B6 Design Rainfalls

Design Rainfalls (mm) AEP Duration (hrs) (1:Y) 3 4 5 6 12 24 36 48 72 50 56 65 73 79 114 156 182 202 226 100 62 72 81 88 126 173 201 222 249 200 69 80 90 99 141 192 223 245 276 500 81 94 105 115 165 223 257 281 316 1000 92 106 119 131 187 251 287 313 350 2000 104 121 136 149 213 283 322 350 389 5000 124 144 161 176 252 331 373 403 445 10000 139 162 181 198 283 369 415 447 491 50000 179 206 231 252 356 462 520 557 606 1.00E+05 196 227 252 275 388 503 567 608 659 1.00E+06 256 293 322 348 480 633 730 788 844 6.70E+06 301 339 369 394 530 720 860 940 1000

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Appendix B7 Design Flood Hydrographs

600

500 Inflow

400 /s) 3 300 Flow (m 200 Outflow

100

0 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92 96 Time (hrs)

1:100 Flood Hydrographs

900

800 Inflow 700

600 /s) 3 500

400 Flow (m 300 Outflow 200

100

0 0 4 8 12 16 20 24 28 32 36 40 44 48 Time (hrs)

1:500 Flood Hydrographs

Hydro Tasmania TAS-106880-CR-03 Page B7 - 1 Meander Dam Feasibility Studies

1200

1000 Inflow

800 /s) 3 600 Flow (m 400 Outflow

200

0 0 4 8 12 16 20 24 28 32 36 40 44 48 Time (hrs)

1:1000 Flood Hydrographs

1800

1600 Inflow 1400

1200 /s) 3 1000

800 Flow (m 600 Outflow 400

200

0 0 4 8 12 16 20 24 28 32 36 40 44 48 Time (hrs)

1:10,000 Flood Hydrographs

Hydro Tasmania TAS-106880-CR-03 Page B7 - 2 Meander Dam Feasibility Studies

2000

1800 Inflow 1600

1400

1200 /s) 3 1000

Flow (m 800

600 Outflow

400

200

0 0 4 8 12 16 20 24 28 32 36 40 44 48 Time (hrs)

1:20,000 Flood Hydrographs

3500

3000 Inflow

2500 /s)

3 2000

1500 Flow (m

1000 Outflow

500

0 0 4 8 12 16 20 24 28 32 36 40 44 48 Time (hrs)

1: 6.7x106 (AEP of PMP) Flood Hydrographs

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APPENDIX B8 Davey and Maynard Water Demand Survey

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APPENDIX C1 Cost Estimate Comparison for the Three Dam Types

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APPENDIX C2 Detailed Cost Estimate for the RCC Option

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