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David J. Walland, Jeanette Meighen, Catherine Beesley, Karin Xuereb

The method for estimating Probable Maximum Precipitation in areas of Australia affected by tropical storms has been revised. The method that it replaces, designed in the 1970s is considered outdated and based on limited data.

The entire Bureau rainfall record has been examined objectively for the largest rainfall events. These events have been analysed and modified to enable storm transposition across a large region. The modifications are based on local topography, moisture and location. Once the storm data is transposed to a single location it can be meaningfully compared and used to construct an upper estimate on the possible rainfall. This estimate can then be used in conjunction with information about a specific catchment in order to estimate Probable Maximum Precipitation at that location.

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2002 Papers

2002 – A New Method for Estimating Probable Maximum Precipitation in Tropical Australia
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David J. Walland, Jeanette Meighen, Catherine Beesley, Karin Xuereb

The method for estimating Probable Maximum Precipitation in areas of Australia affected by tropical storms has been revised. The method that it replaces, designed in the 1970s is considered outdated and based on limited data.

The entire Bureau rainfall record has been examined objectively for the largest rainfall events. These events have been analysed and modified to enable storm transposition across a large region. The modifications are based on local topography, moisture and location. Once the storm data is transposed to a single location it can be meaningfully compared and used to construct an upper estimate on the possible rainfall. This estimate can then be used in conjunction with information about a specific catchment in order to estimate Probable Maximum Precipitation at that location.
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2002 Papers

2002 – Assessing The Likelihood Of Concentrated Leaks Leading To Failure In Concrete Faced Rockfill Dams
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P. H. Southcott, R. Herweynen and R. Fell

Hydro Tasmania is in the process of undertaking a Portfolio Risk Assessment of its 54 referable dams, of which 14 are concrete faced rockfill dams. One of the potential failure modes identified during the study so far is a concentrated leak developing in the face slab or joints of the slab, leading to failure of the dam. Current methodologies for assessment of piping failures through embankment dams are considered inadequate for this failure mode. This paper discusses an event tree methodology developed from the work of Foster and Fell (1999) and Foster et al (2001) to address this failure mode. The key aspect of this method is identifying the factors that influence the likelihood of initiating a concentrated leak through the perimetric, vertical and crest wall joints and through the face slab concrete. It is concluded that for the vast majority of well designed and constructed concrete faced rockfill dams that a concentrated leak leading to failure is very unlikely.
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2002 Papers

2002 – Awoonga Alliance – Awoonga Dam Raising Stage 1
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H. Morrison, J. Leckie, P. Richardson, R Paton

Awoonga Dam is a 40 metre high concrete faced rockfill dam on the Boyne River near Gladstone in Central Queensland. The dam supplies domestic and industrial water to the Gladstone region and the Callide Power Station. Stage 1 will increase FSL by 10 metres to EL 40, which increases storage capacity from 289,000 ML to 777,000 ML. To provide for future industrial growth in the region, the dam design facilitates future raising up to a nominated FSL of EL 62, in a number of stages.

The project consists of:
- Raising the rockfill embankment by 11 metres
- Providing upstream face protection
- Raising the mass concrete spillway by 10 metres
- Provision for future raising
- New outlet for environmental releases
- Relocation of the Boyne Valley Highway
- Relocation of the Monto Rail Line
- Relocation of 49 km of HV power line
- Relocation of 3 km of telecommunications
Significant savings were realised by adopting the alliances project delivery method, resulting in completion 5 months ahead of program and more than 10% under budget.

This paper details development of the project under the alliance and outlines some of the lessons learnt.
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2002 Papers

2002 – Catagunya Dam – Corrosion Assessment of Fully Grouted Post-Tensioned Anchors
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R.I. Herweynen and A.M. Hughes

Hydro Tasmania has a number of dams which were designed and constructed in the 1950-70s
with fully grouted, post-tensioned anchors. The method used was leading edge in its day,
however, it does not achieve the cable protection of modern methods which provide two barriers
against corrosion and are monitorable. Hydro Tasmania has developed and employed an
innovative program to ascertain the integrity and remaining life of the cables and to prepare
long term management plans for its cabled dams.

An international panel was set-up to provide guidance on the overall issue, assist in developing
a sound methodology for assessing the corrosion of the anchors and advise on long-term
monitoring. To focus the efforts, Catagunya Dam was adopted as the pilot dam, as the stability
of this dam is very much dependent on the integrity of the anchors. This paper will provide a
brief overview of the project to date but will focus in detail on the main components of the
corrosion assessment of the anchors, namely:
- In situ ground water testing over the entire valley section using holes drilled for piezometers.
- Laboratory testing carried out by CAPCIS in the UK to simulate potential corrosion rates
  using actual ground water samples collected.
- In situ potentiostatic polarisation testing used to determine instantaneous corrosion rates forthe test anchors.
The paper also provides a brief summary of the instrumentation installed at Catagunya Dam to
assist with the long-term monitoring of the dam.
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2002 Papers

2002 – Dartmouth Regulating Dam – Increasing the Full Supply Level
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Russell Hawken, Peter Buchanan, Doug Connors, Bill Hakin

Dartmouth Regulating Dam is located on the Mitta Mitta River, approximately 8 km downstream of
Dartmouth Dam. The dam is a 23 m high concrete gravity structure with a 60 m long central spillway
section. The dam forms the storage required for regulating releases from the Dartmouth Power
Station back to the Mitta Mitta River, so as to satisfy environmental requirements. Dartmouth
Regulating Dam and Power Station are owned and operated by Southern Hydro Limited, the largest
hydropower generator in Victoria.

To allow greater flexibility in their generation and hence a better response to the peaks in electricity
demand, Southern Hydro investigated the possibility of increasing the full supply level of the dam.
After an initial assessment of the economic benefits a detailed review of raising options was
undertaken, including different proprietary products and conventional spillway gates. Following this
review it was concluded that the Hydroplus System would provide the greatest benefits when all
aspects of the raising were considered, including dam safety, long term reliability, maintenance and
cost.

This paper discusses the reasons for the raising of the full supply level, the approvals process
undertaken and the technical issues addressed during the design stage, including the required
modifications to the dam and the appropriate sizing of the Hydroplus Fusegates.
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2002 Papers

2002 – Environmental Flows-The South Australian Water Corporation Perspective
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G.W. Ashman, C.M. Hamilton and N.J. Hall

Consideration of the need to accommodate environmental flows in the operation of major dams is a relatively new requirement in South Australia. Recognition of environmental water requirements has been promoted through the COAG water industry reforms and the State Water Resources Act. The South Australian Water Corporation is working with other Government agencies on environmental flow projects that will potentially involve three of the Corporation’s large dams. This presentation will summarise the work done to date on establishing environmental flow releases from these storages. The presentation will give the SA Water perspective on the regulatory, environmental, social and operational aspects of the environmental flow issue.
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2002 Papers

2002 – Experimental Investigation of the Rate of Piping Erosion of Soils in Embankment Dams
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C.F. Wan, R. Fell, M.A. Foster

This paper presents the findings of experimental investigation of the rate of piping erosion of soils conducted at the University of New South Wales.

Two tests, namely the Slot Erosion Test and the Hole Erosion Test, have been developed to study the erosion characteristics of a soil. The erosion characteristics are described by the Erosion Rate Index, which indicates the rate of erosion due to fluid traction, and the Critical Shear Stress, which represents the minimum shear stress when erosion starts. Results of the two laboratory erosion tests are strongly correlated. Values of the Erosion Rate Index span from 0 to 6, indicating that two soils can differ in their rates of erosion by up to 106 times. Coarse-grained soils, in general, are less erosion-resistant than fine-grained soils. The Erosion Rate Indices of coarse-grained cohesionless soils show good correlation with the fines and clay contents, and the degree of saturation of the soils, whereas the Erosion Rate Indices of fine-grained cohesive soils show moderately good correlation with the degree of saturation. The absence of smectites and vermiculites, and apparently the presence of cementing materials, such as iron oxides, improves the erosion resistance of a fine-grained soil.

The Hole Erosion Test is proposed as a simple index test for quantifying the rate of piping erosion in a soil, and for finding the approximate Critical Shear Stress corresponding to initiation of piping erosion. Knowledge of these erosion characteristics of the core soil of an embankment dam aids assessment of the likelihood of dam failure due to piping erosion in a risk assessment process.
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2002 Papers

2002 – Harvey Dam Project- Risk Management Strategies
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Bob Wark, Colin Bradbury, Michael Somerford and Michelle Rhodes

The Harvey Dam project is a major component of the Water Corporation’s Stirling-Harvey Redevelopment Scheme, which was developed to provide potable water to Perth. The scheme will deliver 34 GL/annum or about 10% of Perth’s supply. The project timetable was tight. The decision to proceed with the scheme, made in June 1998, required Harvey Dam to be ready to impound water by June 2002.

Construction of the Harvey Dam was complicated by the following:
- The tight project timeline;
- The dam is located about 1.6km upstream of Harvey townsite and its population of 3000 people;
- Strict environmental constraints applied to construction noise, dust, blast vibrations and construction traffic;
- Variable ground conditions required flexibility within the contract in both the extent and type of ground treatment required;
- The need to maintain irrigation supplies throughout the construction period, from the existing aged Harvey Weir, which was located immediately upstream of the proposed dam; and
- The need to safely discharge floods at all stages of dam construction.
These and other issues required the development of risk management strategies for the project. The construction risks were allocated within the contract to provide for an equitable sharing of risk between the Contractor and the Principal. The paper describes the development and implementation of the risk management strategies and what lessons have been learnt from the process.
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2002 Papers

2002 – Implications of Cold Water Releases for Freshwater Fish Populations
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Tom Ryan, Charles Todd and Simon Nicol

The potential impacts of cold water releases on the downstream thermal regime include: reducing the seasonal temperature range (lowering of the maximum and raising the minimum); reducing the diurnal temperature variation; rapid temperature changes; and delaying the seasonal warming of stream temperatures. Recent investigations have identified at least 20 large dams within Victoria, that have the potential to release cold water from below the hypolimnium. A monitoring program is currently being implemented in Victoria to identify the occurrence of cold water releases and to estimate the extent of the downstream impacts.

Cold water releases have been shown to impact the biological processes within aquatic ecosystems and consequently reduce the natural productivity. The physiological development of native freshwater fish can be impacted in a number of ways. Growth and reproductive development of adult fish is impacted while the survival of eggs and larvae can also be retarded. As a result, the sustainability and viability of native fish populations are greatly compromised.

Using stream temperature data from the Mitta Mitta River downstream of Dartmouth Dam, the decline of the native fish populations, due to cold water releases, can be demonstrated under current operating conditions. The decline in population numbers can be further demonstrated with the use of a simple age-based population model for Murray Cod. The spawning opportunity and survival of egg and larvae can be improved for Murray Cod by increasing the overall spring release temperatures by 2, 4, 6 and 8 oC. The population model adjusted for these thermal improvements, results in increased survival prospects for the Murray Cod population.
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2002 Papers

2002 – Interim Raising of Main Creek Tailings Dam by Upstream Construction
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David Brett, Anton van Velden and Phil Soden

The Main Creek Tailings Dam is a 60m high earth and rockfill dam constructed during the early 1980’s to store tailings from the Savage River Mine on Tasmania’s west coast. The dam served the mine well for nearly 20 years, storing around 32 million m3 of tailings, but has required raising due to the expanded mining plans of the current operators, Australian Bulk Minerals (ABM). ABM believe that the mine could require a further 60 million m3 of tailings storage over the next twenty years at increased production levels. This could be stored in the Main Creek Dam by raising it by around 35m. In the medium term this scale of raising would be feasible using waste rock product from ongoing mining but in the short term of several years an interim solution would be required. The feasibility of upstream construction on the tailings beach was reviewed and found feasible for
a maximum 12m in 4 lifts.

Of critical concern were
- The strength of tailings materials in the wet environment
- The seismicity of the site and potential for liquefaction, and
- The practicality of construction without failing the material
The paper discusses the investigation and design phases of the dam and describes the issues arising during construction recently completed over the period January to April 2002. The use of pore pressure, shear strength changes and tailings beach movement monitoring to control construction is discussed.
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2002 Papers

2002 – Inundation Risk Reduction Adjacent to Awoonga Dam
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D. Ryan

Awoonga Dam is located near the town of Gladstone in central Queensland. The dam is on the Boyne River, and supplies water for domestic and industrial use in the Gladstone area. It is also used for recreation including swimming, boating, fishing, sailing and water skiing.

Awoonga Dam was completed in 1984. It has a storage capacity of 289,000Ml, and a submerged area of 3,450ha. The dominant land use in the catchment area is open grazing and includes the Mount Castle Tower National Park. A limestone quarry is also adjacent to the reservoir
The Gladstone Area Water Board (GAWB) own and operate Awoonga Dam. In 1999, the decision was made to raise the existing structure using a staged construction program.

Included in the first stage was the protection of a limestone quarry, which is operated by Frost Enterprises Pty Ltd, and is adjacent to the reservoir. The quarry would be partially inundated unless some form of protection was provided.

This paper provides an outline of the investigation undertaken, the options considered and the solution provided to protect the quarry, hereafter referred to as Frost Quarry.
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2002 Papers

2002 – Karapiro Dam Stability Enhancement Project – Construction
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R.M. Dawson, A. Orange

Karapiro dam is the last in a line of hydro-electric dams on the Waikato River, in New Zealand’s North Island. Investigations identified a potential deficiency in parts of the dam under seismic loading. Detailed investigations and analysis narrowed the deficiency to a low strength clay seam under the concrete gravity left abutment structure. An innovative approach was taken to solving the stability problems at minimum cost, without lowering the storage lake, which would have had significant environmental and social impacts. The process of design and construction was overviewed by an international board of review.

Construction was completed in three main stages with further investigation and design refinement between. The main contract was completed over about eight months and included detailed concrete mix and pour schedule design to control stress development due to temperature gradients for the 2000 + cubic metres of mass concrete placed. While the extent of work was relatively small, the quality control, programming, and presence of a full reservoir throughout demanded a high degree of communication and co-operation between the Principal, Designer and Constructor. Despite some surprises during construction, the project was completed within budget and formed strong bonds between all those involved. This paper briefly describes the design process, and focuses on construction, from the point of view of the Owner, Constructor and the Designer.
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2002 Papers

2002 – Lake Daylesford Dam: Safety Review Following Overtopping
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Mike Taylor, Paul Maisano and Rod Conway

Daylesford Dam forms an ornamental lake, known locally as Lake Daylesford, situated on Wombat Creek within the heart of Daylesford in Victoria. It is a focus of the local tourism industry and is vitally important to the Daylesford community as a recreational, social and environmental asset, with important heritage value.
On 24 October 2000, the 12m high embankment was overtopped following heavy rainfall and was in danger of breaching. This could have resulted in loss of the dam and lake, downstream damage to roads and the environment and possible loss of life. The overtopping of the dam prompted the Hepburn Shire Council, land manager for the dam, to initiate a safety review of the dam as well as the commissioning of a Dam Surveillance Program and a Dam Safety Emergency Plan.

The spillway is of the side-channel type with a 30m long concrete sill at the entrance discharging into a 5m wide unlined trough and chute. The existing spillway can only accommodate a peak flow of 24m3/s, which represents an AEP of less than 1 in 20. The required flood capacity in terms of the latest ANCOLD guidelines on spillway adequacy is for an AEP of 1 in 1 000 which equates to 120m3/s.
Following discussions with Hepburn Shire Council, and an evaluation of public usage of the Lake Daylesford area, it was assessed that the following constraints apply when considering options for increasing spillway capacity:
- A lowering of the full supply level is not an option due to existing shoreside development.
- Any raising of the embankment should be kept to a minimum as the crest forms a cross-roads for a large number of pathways and hiking trails.
- Due to the heritage value of the dam, changes to the appearance of the structure should be minimised.
- Due to the high level of recreational use of the site, the remedial works should be compatible with minimising any disruption to the use of the area by the public during construction.
The proposed solution includes the following:
- Widening the unlined spillway trough and lowering the invert.
- Utilising rock from the spillway excavation for a stabilising fill on the downstream face with a filter zone to reduce the risk of piping failure, with a modest ( <1 m) raising of the embankment crest.
- Reconstructing the spillway crest and access bridge.
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2002 Papers

2002 – Managing Uncertainty in a Dam Environment
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Nathan Juchau

Water storage dams influence the lives of a large number of people. This influence may be through provision of essential water supply or risk of dam failure during sunny day or extreme flood scenarios. It is therefore imperative that these structures are managed in a responsible with a clear understanding of the associated uncertainty. In view of the large capital cost of the structures involved, this understanding is important to ensure that, where necessary,
practical and cost effective solutions are achieved. The NSW Dams Safety Committee largely regulates the management of dams in New South Wales, however, dam owners have the opportunity to display individual initiative in this process.

The Hunter Water Corporation (HWC) is a water authority based in Newcastle, New South Wales, responsible for the supply of water and wastewater services for over 470,000 people. HWC has realised, as a responsible dam owner, that safety improvements are a continuum over the life of the structure. Chichester Dam is an example of this on-going safety improvement process that is illustrated through the principle of ALARP in a risk assessment approach.
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2002 Papers

2002 – Meeting Modern Seismic Criteria Using The Time-History Method of Analysis For An Existing Dam
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J. Matthews, A. Crichton, G. Gibson

Glenmaggie Dam is a 37m high concrete gravity dam, which was constructed from 1919 to 1927. A
design review, which was carried out in line with ANCOLD Guidelines, (SMEC 1999) indicated that the dam did not meet the ANCOLD Guidelines for earthquake. This was despite the fact that the dam was stabilised in 1989 by the addition of 70 post-tensioned ground anchors. Faced with the possibility of having to perform a major upgrade to the dam, Southern Rural Water opted to undertake a more detailed assessment of the seismic loads and to carry out further analysis of the dam using the time history method. The time history method uses an accelerogram to model the forces acting on the structure throughout the earthquake and takes into account the continually changing direction of these forces. It can also be used to determine the size of any permanent
displacements caused by the earthquake, which can then be compared to the maximum allowable permanent deformation of the dam to determine if they are acceptable. The study was carried out by GHD Pty Ltd and also utilised updated seismic information for the dam site provided by the Seismology Research Centre and a geological assessment of the local faults by the URS Corporation. This paper discusses the methods used to determine the seismic loads; the techniques used in the study and the outcomes and follows the process from a dam owner’s perspective.
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2002 Papers

2002 – Meeting Referable Dam and Water Management Requirements of the Queensland Water Act – A ‘How To’ Guide
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R.A. Ayre and T. L. McGrath

The regulatory environment of Queensland’s water resources has changed significantly within the last few years as a consequence of the passing of the Water Act 2000. SunWater, as the owner of referable dams and the operator of water infrastructure, is required to observe the provisions of the new Act.

SunWater has undertaken dam failure analyses of a number of its dams in accordance with the new guidelines prepared by the Department of Natural Resources and Mines. The results of these assessments are being used as part of a portfolio risk assessment of its assets to help prioritise refurbishment activities. Aspects within the guidelines relate to various ANCOLD publications, with a focus on the consequence of failure for determining incremental hazard categories and appropriate design standards for spillway adequacy.

SunWater also operates its schemes under the provisions of Interim Resource Operation Licenses (IROLs). As part of Government’s water planning process, SunWater is required to submit proposed water management arrangements for its schemes. SunWater develops these arrangements, which include operation, water trading, and monitoring rules, to meet its business objectives and the objectives of government. With government approval, these proposed arrangements will translate to the provisions of Resource Operation Licenses when the Resource Operation Planning (ROP) process is completed.

This paper describes SunWater’s experience and approach to meeting regulatory requirements in the above areas.
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