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For many years, engineers associated with the design, construction and operation of large dams have been undertaking environmental effects studies in association with their projects in the belief that they were thereby satisfying their obligation to the community whose interests they served. With increasing environmental consciousness of the community in developed countries, methods have been developed one by one for assessing environmental impacts of various kinds, and techniques have been developed for abating them.
However, the issue in November of the report of the World Commission on Dams (WCD) has focussed attention not only on the importance of bigger issues such as regional ecology, national economic disbenefits and social dislocation, but also on the vulnerability of dams to social and political hindsight.
This paper develops the above background, and shows why some excellently conceived techniques developed in the early 1970’s were capable of identifying almost all imaginable environmental impacts of dam projects, but were not applied in such a way as to deal adequately with the larger issues. It is argued that tools for dealing with all known issues now exist, but that responsible and competent application of the tools are not equivalent to successful application of them. d A new approach is suggested both to upgrade the quality of the decision and to make successful adoption of a soundly based decision more likely to withstand long term critical appraisal, by expressly recognising these decisions as ethical ones.Learn more
Dr Bradford Sherman, Dr Phillip Ford, Allison Mitchell, Gary Hancock
Recent reports from the World Commission on Dams have highlighted the relative lack of knowledge regarding the release of greenhouse gases (GHGs) from reservoirs. In order to be considered eligible to receive carbon credits in the future, hydropower facilities probably will be assessed using some sort of life cycle analysis of net GHG emissions.
Unfortunately, empirical data regarding GHG emissions is available only for a few reservoirs none of which are located in temperate or semi-arid climates.
We report preliminary observations on the vertical distributions of methane and carbon dioxide in Chaffey Reservoir (Tamworth, NSW) and Dartmouth Reservoir, two temperate zone reservoirs located in southeastern Australia. In Chaffey, the diffusive methane flux from the hypolimnion to the epilimnion (where it is oxidised by bacteria) was estimated to be 220-1760 mg-CH, m’ d’. Operation of a destratification system released 43 t of CH, to the atmosphere in 3 days. The carbon dioxide flux to the atmosphere via the surface of Dartmouth was 21-168 mg-CO, m’ d’, and 530 mg-CO, m° d’ through the turbine. The impact on GHG emissions of common reservoir management techniques such as destratification and hypolimnetic oxygenation is discussed.Learn more
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.Learn more
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.Learn more
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.Learn more
Bill Hakin, Phillip Solomon, Peter Siers Bruce Goddard
Lyell Dam is located on the Coxs River near Lithgow NSW Australia. It was constructed in 1982 to supply cooling water to Delta Electricity’s Mt. Piper and Wallerawang power stations.
In 1994 the storage capacity of the dam was increased by 7,500 Ml by raising the embankment height and installing two 3.5m high inflatable rubber dams on an enlarged and slightly raised spillway sill. Two significant failures of the rubber dams in 1997 and 1999, led the dam owner to seek an alternative method of maintaining the increased Full Supply Level (FSL) whilst still providing spillway capacity for the design flood. Although the lost storage has a certain strategic value to Delta Electricity, the main reason for restoring the capacity to its former level was to preserve the environmental and recreational use of the reservoir for the local community.
Following a detailed review of options, Delta Electricity chose to regain the former FSL with the Hydroplus Fusegate System. Because of the freeboard available at Lyell dam it was possible to design the Fusegates such that none tip before the 20 000 AEP flood.
In order to derive accurate as-built levels and dimensions of the existing spillway, new laser scanning methods were utilised to create a digital 3-D model of its complex shape.
The water retaining concrete Fusegates were poured in-situ and designed without anti-crack reinforcement. This innovation was only possible by use of a special design mix and careful temperature control/monitoring during concrete placing.
This is the first installation of the Hydroplus Fusegate System in Australia. The paper examines the philosophy of approach and various unique methods used in the application of the System during the design and construction stages.Learn more
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.Learn more
Tim Waldron, K D Murray and Allan Crichton
The City of Hervey Bay is a growing tourist community that is located a comfortable 3½ hour drive north of Brisbane. To meet the growing water demands of the community, Wide Bay Water Corporation required the raising of its sole water supply – Lenthalls Dam.
At the time of the option study, Queensland dam owners were aware of their obligation to manage their dams to minimise adverse environmental impacts but detailed Environmental Flow Objectives were still being developed.
This required a solution for the raising of Lenthalls Dam that provided maximum flexibility while, at the same time, being cost effective.
A range of solutions and new technologies were investigated. Using a Risk Management methodology, the Crest Gate system developed in South Africa was adopted.Learn more
Subsequently, draft Environmental Flow Objectives have been set and the use of a gated system has been beneficial in meeting post-winter flow objectives.
Tony McCormick, John Grimston, Robin Dawson
Project Aqua is a proposed hydroelectric and irrigation resource sharing development on the Lower Waitaki River in New Zealand’s South Island. The NZ $1 billion project aims to deliver approximately 540 MW peak power at an economically viable price, while minimising environmental and social impacts. Application of traditional hydro concepts in historical studies for the same reach has not provided an economic solution. The current proposal challenges conventional thinking in many areas with innovative concepts allowing a significantly lower cost while not sacrificing safety or flexibility.
Development of storage may involve high social and environmental impacts. No significant storage is needed for Project Aqua as the operation of existing upstream dams can be modified to provide for peaking demand and maintenance of minimum flows. The river intake offers innovative features with its very low profile structure. The concept allows a departure from the traditional barrage or dam diversion and maintains an open braid for jet boat and fish passage. This concept has proven to be a major feature in the overall project progression to the current stage.
The largest impact component of the scheme is the eight canals designed to carry 340 cumecs over 63 km through six power stations. Cuts and fills form the canals with locally derived materials used for the embankments and lining. Expensive lining has been minimised by balancing flow exchange with groundwater through the cut and fill sections.
Feasibility design has been completed and resource consents are currently being sought. This paper will cover the significant design features and impacts.Learn more
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 toLearn more
assist with the long-term monitoring of the dam.
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.Learn more
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.Learn more