2015 – Nam Ou VI: Geomembrane face rockfill dam in Laos
A. Scuero, G. Vaschetti, J. Cowland, B. Cai , L. Xuan
Nam Ou VI rockfill dam is part of the Nam Ou VI Hydropower Project under construction in Laos. The scheme includes an 88 metres high rockfill dam, designed as a Geomembrane Face Rockfill Dam (GFRD), which when completed will be the highest GFRD in Laos. The only element providing watertightness to the dam is an exposed composite PVC geomembrane, installed according to an innovative design now being increasingly adopted to construct safe rockfill dams at lower costs. The same system will shortly be installed on a water retaining embankment for a coal mine in NSW, Australia, and has been approved for a tailings dam in Queensland, Australia. At Nam Ou VI the geomembrane system is being installed in three separate stages, following construction of the dam. The first two stages have been completed, and the last stage will start in November 2015. The paper, after a brief discussion of the adopted system’s concept, advantages and precedents, focuses on the construction aspects.
Keywords: GFRD, PVC geomembrane, waterproofing, rockfill dam.
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2015 Papers
2015 – An analysis of dam safety incidents in Victoria
Learn moreMaree Dalakis, Dr Saman de Silva, Siraj Perera and Dr Gamini Adikari
This paper describes the results of a statistical and qualitative analysis on historical dam safety incidents in Victoria, the first study of its kind conducted in the State. The study investigates trends arising from qualitative dam safety incident data collected by the Department of Environment, Land, Water and Planning since the year 1996. The reported incidents are categorised based on their severity and statistical trends are identified in relation to the types of incidents common to regulated and unregulated dams, as well as common responses to incidents, including their post-incident operation. The geographical distribution of incidents across the State is also analysed to determine the effects of seismicity on dam safety incident rates. Furthermore, the unique Victorian conditions of sustained drought and subsequent flooding and their impact on incident rates are investigated through the combined analysis of geographical incident distribution and streamflow data. The incident data is further assessed according to the frequency of visual inspection and reporting of the structures in order to gauge the relative influence of these practices, and dam regulation in general, on mitigating incident risk in dams. An understanding of dam safety incident trends and the impact of inspection and reporting practices is increasingly important given the increasing expectation for dam owners to properly operate and maintain their assets with minimal resources and finances.
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Keywords: dam, safety, incident, historical, failure. -
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2015 Papers
2015 – Readiness to Impound Assessment using a Risk Based Framework – Murum Dam Case Study
Learn moreRichard Herweynen, Tim Griggs, Alan White
The Ministry of Public Utilities, Sarawak, Malaysia used an independent dam safety consultant to advise them on whether the Murum Dam was ready for impoundment. They were looking for a holistic assessment of the dam from a dam safety perspective. As a result, a risk framework was adopted to identify the key issues that needed to be addressed prior to impoundment of the Murum Dam. The process adopted which is presented in this paper, was transparent and defensible; and provided a reasoned approach for which items must be completed prior to the commencement of impoundment. As a result effort was focused on the key activities required prior to impoundment – whether this was the completion of specific works, the availability of key instrumentation to monitor the dams performance, the availability and operation of key dam safety systems, or the appropriate emergency preparedness should a dam safety incident occur during first filling. This systematic process based on a risk based approach, was a useful method of determining the dam’s readiness for impoundment, and provided an excellent way of communicating the importance of activities to the key stakeholders. The authors believe that this method is transferable to other dam projects, for an assessment of a dam’s readiness for impoundment.
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Keywords: Dam safety, risk, impoundment, reservoir filling. -
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2015 Papers
2015 – Benchmarking Dam Safety Management in Victoria
Learn moreDavid 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.
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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 -
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2015 Papers
2015 Poster – Remedial works in Bakers Gully Dams – partially decommissioning
Learn moreAida Baharestani, Dominic Kerr
North East Water (NEW) manages two reservoirs in series on Bakers Gully Creek, approximately 1.5km south of Bright in north-east Victoria. Both dams were constructed more than 100 years ago and taken out of service in the 1970s.
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The Bakers Gully dams had an unacceptable risk profile according to ANCOLD’s Limit of Tolerability.
As the dams are out of service and have no operational benefit, NEW made the decision to partially decommission the dams.
The objective of the work was to lower the consequence categories of the dams from “High C” to “Low” and increase the spillway capacities according to ANCOLD Guidelines and ultimately reduce the dam safety risks to an acceptable level.
This paper describes the different stages of the project ranging from concept design, community engagement, environmental assessment and detailed design. In particular the paper explores the complexities of balancing in cost and public safety with community and ecological values.
Keywords: Dam decommissioning, Community engagement, Severity of damage and loss -
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2015 Papers
2015 – Remedial works to reduce seepage under Visegrad HPP dam
Learn moreNikifor Petrovic, Sladoljub Pezerovic
Dam rehabilitation works at the Visegrad Hydropower Project on the River Drina in Bosnia and Herzegovina were completed in October 2014 after two years of very challenging and collaborative effort between the client, designer and contractor.
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The successfully accomplished remedial works programme was a highly complex geotechnical intervention. The dam was constructed on a karst foundation extending up to 200 m below reservoir floor level. Rates of seepage through the foundation increased over time, from 1.4 m3/s following first impoundment in 1989, to 14.7 m3/s in 2009.
The rehabilitation works comprised:
Preparatory works (site installation, work platforms, conveyer belts, electricity and water supply, drilling and grouting equipment installation);
Site investigation works (drilling of boreholes, measurements of inclination, geo-physical carotage, downhole video, underwater camera recording);
Installation of monitoring equipment and implementation of real time recording system;
Installation of inert material into a sinkhole within the storage area and into the bore holes located upstream of the dam; and
Grouting of the foundation area using different grout mixes and grouting methods.
During rehabilitation works the main achievements were:
A total of about 37,300 m3 of inert material (granular materials with different fractions from 0 to 32 mm) was installed into the foundation cracks and caverns. This was a significant achievement due to very complex geological conditions and resulted in a seepage reduction through the foundation and improvement of the overall safety and stability of the dam.
The total consumption of grouting material was in access of 2,500 tonnes of cement, bentonite, sand and additives.
After completion of the work, seepage of water through the foundation was reduced to about 4.5 m3/s.
Keywords: Seepage, remedial works, dam, grouting, inert material.