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D. S. Bowles

Portfolio risk assessment (PRA) can now be considered to be a standard of practice in Australia. In this paper various advances in the state-of-the-practice for performing PRA’s are reviewed, including some pitfalls and limitations. The uses of PRA outcomes by owners are discussed, along with some ways to improve the value derived from PRAs. The challenges that are common in seeking to achieve an integration of the PRA process into the owner’s dam safety management program and with broader business processes, and the importance of targeting PRA outcomes to an owner’s specific business needs, are emphasised.

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2000 Papers

2000 – Advances in the Practice and Use of Portfolio Risk Assessment
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D. S. Bowles

Portfolio risk assessment (PRA) can now be considered to be a standard of practice in Australia. In this paper various advances in the state-of-the-practice for performing PRA’s are reviewed, including some pitfalls and limitations. The uses of PRA outcomes by owners are discussed, along with some ways to improve the value derived from PRAs. The challenges that are common in seeking to achieve an integration of the PRA process into the owner’s dam safety management program and with broader business processes, and the importance of targeting PRA outcomes to an owner’s specific business needs, are emphasised.

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2000 Papers

2000 – Ben Boyd Dam: A Case Study in Incident Management
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P.W. Heinrichs and R. Fell

Ben Boyd Dam, a 29 m high earthfill embankment built in 1978, has had an unusual history. In 1979, a number of seeps developed during first filling with water 5 m below FSL indicating unexpectedly high pressures. Investigations concluded the coarse filter permeability was very low due to excess fines. Remedial works in 1982 included a drainage filter beyond the toe and a new stability berm above. New piezometers were installed, including several in the blanket filters in the existing dam. These later indicated up to 10.5 m head in isolated areas within the filter. Pump out tests partially lowered the water level in the standpipes but in 1995 the water level rose by 4 m back to its previous high level. All this during a period of relatively low rainfall. Stability analyses were carried out and further investigations in 1999 concluded that apart from general leakage from the foundation abutment into the filters, the rise in pressures was due to leakage from a riser hole from one of the nearby foundation piezometers. A potential for piping along the piezometer tubes within the dam was also identified.

This situation was managed without resort to costly capital works, because it was concluded that the pressures from the vertical riser were not a potential failure mode, and potential piping failure would be adequately handled by the existing chimney drain, intersecting the piezometer tubes trench. Any potential piping failure would also give warning signs which increased frequency of monitoring (now in place) would pick up in time to allow lowering of the storage.
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2000 Papers

2000 – Capping of Very Low Strength Tailings Using Woven Geotextile and Geosynthetic Clay Liner
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Ross Stewart

This paper describes the use of a high strength woven geotextile and preloading to stabilise the surface of a very low strength tailings pond, and the incorporation of a geosynthetic clay liner (GCL) within the final capping design to complete closure. The pond, which contains tin and copper tailings, formed the lower tailings containment area of a three-tiered tailings storage, located directly above the Wild River in North Queensland. Stabilising the lower pond (area 2,500 m2), which contained tailings of “zero strength” in the central area involved the placement of a woven geotextile over the surface, which was anchored around the perimeter. The placement of finger berms (preloading fill) on the geotextile was successful without exceeding the bearing capacity of the tailings overall. Settlements of the berms were closely monitored to allow the system to support construction plant. After the finger berms were joined, they were widened until the area was covered. A sand layer was then placed over the area followed by a GCL to form an impermeable barrier prior to the placement of clay and topsoil.
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2000 Papers

2000 – Dam Remedial Works in Western Australia
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Robert Wark, Nihal Vitharana and Michael Somerford

This paper reviews the history of dam remedial works on publicly-owned dams in Western Australia over the last 40 years. Projects have ranged from refurbishment of the facilities, through capacity upgrades to complete reconstruction. Major work has been undertaken on at least thirty dams. Most of these dams are now owned by Western Australia’s Water Corporation. The Corporation continues to undertake remedial works where necessary and now has a strategy in place for an on-going program of remedial works.

The paper outlines the scope of the work undertaken and why the work was required. The current status of the Corporation’s planning for an on-going remedial works program is also reported.
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2000 Papers

2000 – Dam Technology in Australia 1850-1999 – Creating the Book
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B. A. Cole

In October 2000 ANCOLD published a history of dam technology in Australia covering the 150 years in which large dams have been constructed in this country. The paper describes how this project began, the search for authors, the way the authors tackled their tasks, the peer reviews which resulted in additional chapters being written, and the archive searches for interesting photographs to illustrate the text. All this was accomplished by dam engineers including the editor. Then follows an account of the professional publication process: sub-editing, desktop publishing, proof-reading, the preparation of an index, the cover design and the printing process. Some conclusions are drawn from this first experience of book publishing.
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2000 Papers

2000 – Development in Non-Linear Finite Element Analysis for Dam Safety Management
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A.J. Crichton, A.W. Ford, and J.T. Williams

Developments in finite element analysis software are allowing more scope for their use in the stability review of Australia’s ageing dam population. Until recently, model simulation of structural discontinuities were outside the scope of routine dam safety assessment. Current state of the art finite element software puts complex joint modelling tools within the reach of the practicing dam engineer.

This paper describes the use of non-linear finite element techniques to assess the structural adequacy of the Julius Dam, a 26.5 m high multiple arch buttress dam in North-western Queensland. This structure impounds 127,000 ML behind its 399 m crest length for the Mt Isa water supply. The assessment of the structural adequacy included using non linear contact elements to model the sliding between adjacent arch barrels. Contact elements are able to simulate friction on an interface by allowing force transfer by friction under compression with no tensile strength. This tool is invaluable for assessing formed joints or defects within existing structures, as is demonstrated in the paper.
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2000 Papers

2000 – Development of a Comprehensive Approach to Consequence Assessment
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P.I. Hill, D. Cook, R.J. Nathan, P.A. Crowe, J.H. Green, N. Mayo

This paper describes the development of a comprehensive approach to estimating the consequences of failure of a dam. The approach considers separately the consequences in terms of potential loss of life, economic loss and damage to the environment and the development and application of the method involved professionals from a wide range of disciplines. The method has been applied to 28 dams in NSW.
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2000 Papers

2000 – Embankment Dam Rehabilitation with Granular Filters
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Mark Locke, Buddhima Indraratna, Phillip Cummins and Gamini Adikari

ABSTRACT: Australia has a large number of older embankment dams, which have been in service and performed adequately for over 50 years. However, current industry practice in embankment dam design predicts that the granular filters within these dams may not be adequate. This may require refurbishment of the dam by retro-fitting a new filter to ensure the continued safety of the structure. This paper outlines the potential problems with older embankment dam designs, and the reasons for constructing a new filter. Potential problems may include inadequate or non-existent filters, risk of failure due to earthquake, piping, or excessive foundation seepage. Design methods for granular filters are described briefly, concentrating on whether an existing filter is adequate, and the potential improvement by constructing a new filter. Construction issues for placing filters on existing dams are also discussed.

A new analytical method, developed to describe the time dependent erosion and filtration within embankment dams, is described briefly. The model predicts particle erosion, transport and retention based on fundamental fluid mechanics and geotechnical concepts. The application of this model to the design of filters for new and existing dams will be described. The predictions of such analytical modelling can give a designer a significantly clearer picture of the purpose of a granular filter, the extent of core erosion that can be expected, and the effect of retrofitting a new filter to an existing dam.
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2000 Papers

2000 – Environmental Challenges in Constructing the Warragamba Dam Auxiliary Spillway
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Pieter van Breda, Peter Walton, Kate Lenertz and Tim Sheridan

The Warragamba Dam Auxiliary Spillway Project, designed to manage floodwaters up to a Probable Maximum Flood event, was approved by the NSW Minister for Urban Affairs and Planning on February 12, 1998. An Environmental Impact Statement prepared for this project predicted that noise, dust (suspended and deposited), blasting, vibration, water quality and revegetation would be the significant environmental issues requiring management throughout the construction phase.

The closest residents are approximately 200m from the construction activity. The works must not interfere with the operation of the Dam, which stores 80% of Sydney’s drinking water and the integrity of the existing infrastructure must be maintained at all times. The approved proposal was to emplace the 2.2Mm3 of spoil excavated to create the spillway in an area 25 ha by 20m high on top of a ridge on the left bank adjoining the Blue Mountains National Park. This created visual impact and rehabilitation challenges.

Although the contract for this project was primarily performance based, strict environmental clauses were incorporated to manage these priority issues. Noise and dust modelling were required from each pre-qualified Tenderer, to demonstrate capability of compliance with NSW Environment Protection Authority requirements. This formed part of the tender assessment. Criteria were also developed for revegetation, specifying numbers of endemic trees, shrubs and grasses per 400m2 of spoil emplacement in order to create a floral community similar to the existing adjacent National Park.

The implementation of these requirements and the development of a site Environmental Management Plan by the Sydney Catchment Authority, Australian Water Technologies and Abigroup Contractors, whilst maintaining productivity, has proven to be a working example of the benefits of Partnering.
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2000 Papers

2000 – Grahamstown Dam Stage 2 Augmentation Selection and Design of a Labyrinth Spillway and Baffle Chute
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M. B. Barker, R.M. Holroyde, J Williams and T. Qiu

Grahamstown Dam is a major water supply source for the Newcastle area and it is proposed to raise the full supply level by 2.4m from RL 10.4m to RL 12.8m. The present spillway is inadequate to pass the PMF without overtopping of the existing embankments at the new FSL and part of the raising comprises construction of a new embankment of about 10m high with a right bank spillway upstream of the existing spillway capable of passing the PMF. The Pacific Highway is located some 600m downstream of the new spillway and a 60m wide culvert below the Pacific Highway is being constructed with capacity sufficient to pass the PMF. Significant changes were made to the feasibility design for the spillway and the Pacific Highway culvert using a labyrinth spillway and a baffle chute energy dissipator respectively. Both of these designs are uncommon and the process of finalising the designs as well as some of the problems in the use of a labyrinth spillway and the cost savings realised in the use of these designs are presented.
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2000 Papers

2000 – Harvey Dam Environmental Management
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Michael Somerford, Michelle Northover and Steve Wilke

Western Australia’s Water Corporation is constructing the Stirling-Harvey Redevelopment Scheme, a $275 million scheme to supplement Perth’s public supply. A major component of the scheme is the construction of the Harvey Dam, a 45 metre high, earth core rockfill dam.

The main environmental issues associated with the construction of the Harvey Dam are related to construction and traffic noise, blast vibration and dust generated during the construction period. Appropriate environmental management is required to minimise noise and dust emissions because of nearby schools, town site, residences and horticultural activities.

The new reservoir will commence filling in 2002. It will inundate several private properties, farming land, an area of pine plantation and six sites of cultural and heritage significance.

This paper discusses the management and monitoring strategies associated with the construction of the new dam. It also describes the initiatives that the Water Corporation has undertaken to ensure that adverse impacts of the project on the environment are minimised.
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2000 Papers

2000 – Hume Dam Rehabilitation – An Owner’s Perspective
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David Dole and Brian Haisman

The $75 million remedial works at Hume Dam on the Murray River near Albury have been of national significance. The rehabilitation program associated with the structure itself and with its appurtenant works is now in the final steps of construction. The authors summarise this program with an emphasis not on technical details, but on decision processes. Equity in this dam is, in effect, held in equal parts by three State governments and by the Commonwealth government. At the same time, in response to the national water reform agenda, the governments have agreed upon new cost sharing arrangements that more nearly reflect the value of services to each government. The particular problems of decision-making within this evolving inter-State environment are discussed.

Lessons from experiments with application of risk analysis are discussed. Finally, the matter of adequacy of the structure for extreme floods is still under consideration. Hume Dam will presently pass the Design Flood developed in accord with Book VI (1999) of Australian Rainfall and Runoff, and the Dam Crest Flood has been estimated to have an annual exceedance probability of 1:110,000. _ Retrofitting a spillway to pass the estimated Probable Maximum Flood will double the cost of remedial works and is estimated at 10 times the cost of similar capacity built into original construction. The authors discuss the public policy elements of this pending decision.
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2000 Papers

2000 – It’s More Fun When You Do It Yourself – Constructing the Lake Eppalock Main Embankment Remedial Works Project
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Steven Fox, Garry Fyfe

This paper describes some key details of the construction of the Lake Eppalock Main Embankment Remedial Works Project. This $8.25 million earthworks project was completed on a “live” storage to an accelerated program. As the dam owner Goulburn-Murray Water took the decision to directly manage the construction of these works with resultant benefits in timing, risk management and project management costs.

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2000 Papers

2000 – Lyell Dam Rubber Dam Incidents
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I. R. Forster

Lyell Dam is a concrete-faced rockfill dam, located on the Coxs River, near Lithgow, NSW. The dam forms part of the Coxs River Water Supply Scheme, which supplies water to Delta Electricity’s Wallerawang and Mount Piper Power Stations. In 1994, the spillway capacity of the dam was upgraded, and the storage augmented with the addition of two 40 m long by 3.5 m high inflatable rubber dams to the spillway crest. An automatic deflation system, controlled by a programmable logic controller, was installed to provide a staged bag deflation sequence during flooding, and hence minimise the downstream impact of rubber dam operation.

Although the rubber dams and control system initially operated as designed, more recently, two uncontrolled bag deflations have occurred, which have caused flooding downstream and loss of significant storage volumes. In the first incident, a spontaneous uncontrolled deflation of the rubber dams released about 1600 ML, before the bags re-inflated automatically. An investigation revealed that the incident was most likely the result of design deficiencies in the control system. Recommendations were made for improvements to the system.

During the most recent deflation, one of the rubber dams failed by spontaneous rupture, and approximately 6000 ML of water was released from the dam. The Dam Safety Emergency Plan was activated to ensure persons at risk downstream were notified of the impending flood wave. A post- failure inspection of the ruptured bag suggested that the likely cause of failure was a manufacturing defect, which allowed air to penetrate the layers of rubber forming the bag. The rupture most likely occurred when the resulting air pocket expanded on exposure to the sun.

The paper examines the two deflation incidents in detail, and analyses the emergency response to the second incident.
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2000 Papers

2000 – Mitigating Cold Water Pollution Below Dams
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B. S. Sherman

Many large Australian dams currently lack selective withdrawal capabilities and release water mainly from deep within the hypolimnion. Deep-water releases coupled with the strong thermal stratification typical of Australian reservoirs results in discharge temperatures 10 °C or more colder than would normally be expected. Cold water pollution has impacted more than 1000 km of river habitat in Australia where it is known to impair spawning, feeding and survival of many native fishes.

This report reviews alternative approaches for the mitigation of cold water pollution below dams. The underlying theory and practical limitations of operation as well as field experience (including cost) with each of the methods are discussed. Two methods in particular, suface pumps and submerged curtains, appear to offer cost-effective alternatives to the expensive retrofitting of dams with multi-level outlet structures (estimated to cost $5-35m per dam for major dams in NSW). These methods are predicted to be capable of increasing discharge temperatures by 4-10 ° throughout the range of irrigation releases without any redirection of flows, i.e. hydropower releases can be maintained at present levels. This holds the promise of restoring more desirable temperatures over hundreds of kilometres of river.
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2000 Papers

2000 – Protecting Environment Flows While Catering for Urban Water Supply Demand – The Cowarra Off-Creek Dam Experience
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Murray Thompson and Geoff Chenhall

The Hastings District Water Supply Augmentation Scheme [HDWS] includes a 10GL off-creek storage dam, which is currently under construction and due for completion in October 2001. The Cowarra off-creek storage dam is required to meet predicted long-term urban growth demands for water supply and to ensure protection of environmental flows in the Hastings River.

Since 1985 the Hastings Council has progressively developed a strategy for the augmentation of the water supply scheme. A very successful ongoing consultation process with both the local community and key government agencies during the planning and implementation phases of this project has highlighted a number of key issues including:

“That the impact upon aquatic flora and fauna in the Hastings River should be minimised and appropriate safeguards developed by maintaining minimum river flows to ensure that the river habitat is not adversely affected”

The subsequent HDWS Environmental Impact Statement, 1995 was one of the first in NSW to recognise the importance of environmental river flows in the assessment of the aquatic ecological effects of water supply schemes. This paper to be presented to the ANCOLD Conference on Dams will detail the investigation, planning, implementation and current construction activities associated with the Cowarra Off-Creek Storage Dam.
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