Nihal Vitharana, Nuno Ferreira
The raising and/or stabilising of existing concrete gravity dams by continuous concrete buttressing is a viable solution and, in some cases, it is the only solution available. There are few medium-large dams in Australia currently under consideration for raising with continuous buttressing.
Two of the major issues to be surmounted are: (a) the existing dam should not be subjected to cracking (particularly on the upstream face) due to heat-hydration effects, and (b) the requirement for the two dam bodies to resist the hydrostatic and other loadings as a monolith (unified dam).
However, there is great need for understanding the mechanisms involved in selecting an appropriate heat-of-hydration model and in calculating thermal stresses rationally. Due to such lack of understanding, expensive precautions, mostly with compounding conservatisms, would be adopted in concept and detailed designs eg. shear-keys on the interface, artificial cooling, post-grouted interface, anchor bars at the interface, concrete with high cement contents. On the other hand, unsafe designs could be the result.
The paper discusses these issues highlighting that a rational approach can be adopted to economise the design and construction processes. An example is also presented to demonstrate how the potential for temperature-induced cracking in new and old dam bodies can be evaluated with reduced uncertainty by considering all the mechanisms involved in a holistic way.
Keywords: Heat-of-Hydration modelling, raising concrete dams, thermal stresses, concrete buttressing
This paper discusses the common environmental issues and requirements project lenders have when financing hydropower dam projects in developing countries. The environmental specialist’s role, as part of the Lender’s Technical Advisor team, is discussed throughout the main phases of project finance (credit approval, financial close, lending/construction and loan repayment/operation). Further, how environmental issues are reviewed and monitored, thereby minimising reputational risks to the lenders are outlined.
Lenders typically consider hydropower dam financing, especially reservoir schemes, as high reputational risk loans. Finance is usually syndicated and although most international lenders are Equator Principles signatories or use the International Financing Corporations (IFC) Performance Standards, some lenders have additional environmental guidelines and requirements to enable financing. These differences are discussed.
Common environmental concerns include loss of habitat of endangered and/or threatened species, changes to river flows, erosion and sediment control during construction, and the minimisation and disposal of project wastes.
These issues are discussed drawing on the author’s experience in monitoring environmental issues of hydropower projects in Asia Pacific and Africa, including both smaller run-of-river schemes and larger storage reservoir projects.
Keywords: Environment, impacts, project financing, concerns, lenders, lenders technical advisor.
Nicole Anderson and Nihal Vitharana
A large number of aging concrete dams in Australia may not meet the requirements of modern dam safety practices. In addition, there is an ever-increasing demand for the supply of water. Continuous concrete buttressing is a method of strengthening existing dams which allows the dam to be raised to augment the storage capacity at an incremental cost.
This paper explores the key design considerations involved in concrete-buttressing existing concrete gravity dams. Critical aspects considered include storage level during construction, interface drainage, interface shear transfer, the relative strength of existing and new concrete and the behaviour during the heating and cooling phases of the heat-of-hydration. The discussions will be of relevance to asset owners and water authorities faced with upgrading existing dams in a time where there is an increasing demand for security of supply of water resources.
David Stewart, Shane McGrath & Siraj Perera
Dam safety in Victoria is overseen by the Department of Environment, Land, Water and Planning on behalf of the relevant Minister and under the Water Act. For each of the 19 state-owned Water Corporations, Government has issued a Statement of Obligations which describes all responsibilities of the Corporation, including specific reference to dam safety management and ANCOLD Guidelines.
These Corporations report annually to the Department on their compliance with all their obligations, including dam safety management. In late 2014, 13 Water Corporations along with the Department commissioned a comparative benchmarking study of dam safety management practices across the state. This work was facilitated by the VicWater Dams Industry Working Group. The study used a rapid assessment method against 14 separate criteria for dam safety management, based on the Statements of Obligations, guidance notes developed by the Department, ANCOLD Guidelines, the ICOLD Draft Bulletin on Dam Safety Management, good governance principles and examples of best practice from other jurisdictions.
The study involved assessment of background data, site inspections and discussions with various individuals of each owner, including a range of field staff, dam safety staff, Executive Managers, Managing Directors and Board Directors. The benchmarking study covered 142 dams of Significant, High and Extreme Consequence Category throughout Victoria.
The results of the benchmarking study have been extremely useful for individual dam owners and for the Department to understand areas where good practice is in place and also where there is potential for improvement of individual programs. The study also provides a measure of assurance of the current status of dam safety management practices and areas where regulatory practices could be better focused. It also reinforced the importance of strong industry networks such as ANCOLD and VicWater for knowledge transfer, capacity development and sustainability of dam safety management practices.
This paper presents the methodology used for the benchmarking study and its broader findings. It also highlights good practice considerations for dam owners, regulators and other dam safety practitioners.
Keywords: Dam Safety Management, Governance, Benchmarking
David Brett, Robert Longey, Jiri Herza
The independent expert review panel for the Mount Polley Tailings Storage Facility failure came out strongly recommending changes to the technology of tailings dams in British Columbia (and by inference, world-wide). The Panel had examined the historical risk profile of tailings dams in British Columbia and recommended, amongst other things, that best available technology (BAT) be adopted for tailings disposal. Examples of BAT, described by the panel, included “dry-stacking” of filtered, unsaturated, compacted tailings and reduction in the use of water covers in a closure setting. The recommended technologies would require a major shift in current practice and raises many questions, such as:
– Are these recommendations appropriate in Australia?
– Does this signal the end of the tailings dams as we know them?
– Do the current Australian National Committee on Large Dams Guidelines (ANCOLD) apply to these new BAT technologies?
– If not, is there a role for ANCOLD in setting standards for the future?
This paper discusses the Mt Polley tailings dam failure and searches for answers to these questions. In particular, this paper reviews the background to “dry-stacking’, to explore the implications for the Australian mining industry.
Keywords: Tailings Dam, Dry Stacking, Best Available Technology