2012 – Sediment Monitoring in Lake Argyle confirms success of Ord catchment management
Robert Wark, R.N.M. Nixon
Sediment inflows to Lake Argyle, the reservoir formed by the construction of the Ord River Dam, were seen as a significant threat to the Ord Irrigation Project when the scheme was being developed through the 1960s. Sediment monitoring was built into the operation of Lake Argyle when the Ord River Dam was completed in 1971. The paper describes the strategies that have been in place to assess sediment loads and monitor sediment build up in the reservoir.
Spectacular reduction in sediment flows has been achieved through developing a comprehensive catchment management program. The program commenced in the early 1960s and was adapted and modified as progress was made. The paper describes the steps taken to identify the areas of the catchment at risk, the measures implemented and the current status of the catchment.
A key feature of the catchment management program has been the willingness to critically review progress and adapt the program. A variety of sediment tracing techniques have been used to help confirm the sources of sediment in the catchment, and the paper describes these, and the broad range of results and how they have helped direct the work on catchment management.
Keywords: Sediment, monitoring, catchment management, Lake Argyle, Ord River
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2012 Papers
2012 – Justifiable Maintenance – Reliability Centred Maintenance of Dam and Weir Assets
Learn moreSteven Hare, Daniel Masters, Phil Farnik
State Water Corporation, New South Wales’ bulk water delivery business, is enhancing its maintenance planning and execution through a maintenance improvement project. This project incorporates a Reliability Centred Maintenance (RCM) analysis of water infrastructure assets including dams, weirs and pipelines and refining current maintenance procedures.
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The project aims to address inconsistencies in maintenance frequencies and applications that have resulted from historically managing assets at a regional level. This project, coupled with State Water’s new “functional based” organisational structure, is expected to yield an effective and consistent preventive maintenance program across the organisation. The project is also expected to increase the reliability of critical dam infrastructure and aid in maintaining safe operation of the organisation’s assets.
This paper briefly describes the history of maintenance, principles of RCM, project implementation aspects and early outcomes. These outcomes include the reduction of maintenance frequencies on non safety critical assets with low failure rates, elimination of ineffective tasks and standardisation of maintenance frequencies on equipment common to all dam sites.
Keywords: Reliability centred maintenance, dams, weirs -
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2012 Papers
2012 – Diversion Design for Dam Construction
Learn moreTim Griggs and Richard Herweynen
The river diversion is an important aspect to be considered in the design of a dam. It generally consists of an upstream cofferdam, river diversion conduit and downstream cofferdam and allows the dam to be constructed in a dry section of river.
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This paper reviews the diversion design adopted at three recent Australian roller compacted concrete (RCC) dams and comments on the effectiveness of the design in providing risk mitigation during the construction of each of these dams. The dams considered are Paradise Dam (2005), Meander Dam (2007) and Wyaralong Dam (2011).
Rather than selecting an arbitrary design flood for the diversion, a risk-based assessment was used that generally resulted in a relatively low design capacity. Even though there were cases where the diversion capacity was exceeded, it is considered that the risk based design process provided an economical diversion design for these recent Australian dams.
Keywords: Diversion, roller compacted concrete dam, RCC. -
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2012 Papers
2012 – Angat Multipurpose Dam Remedial Works Project
Learn moreJohn Grimston, David Leong, Robin Dawson
The Angat Multipurpose Project, originally constructed in the 1960’s, is located 60 km north-east of Manila, and provides power, irrigation and domestic water supply and flood mitigation. The major water-retaining structures of the scheme are a 131 m high main rockfill dam and a 55 m high rockfill saddle dam.
Previous seismology studies have identified the presence of a possible branch of the West Valley Fault crossing under the saddle dam. If the fault dislocated, the branch under the saddle dam could produce horizontal and vertical shear displacements. Further, earthquake shaking poses a risk outside the fault zone. If the main dam/saddle dam were to fail in such an event, there would be major consequences in respect to both the water supply (serves a population of approximately 10 million) and the large population living below the dams. The dams are thus in the highest hazard category under any internationally accepted standard.
A study to investigate the dam safety aspects and identify remediation works which would bring the seismic performance of the main dam/saddle dam system up to an acceptable level was undertaken and included:- Investigations and topographic survey of main dam/saddle dam
- seismic dynamic response studies
- review of current Probable Maximum Flood (PMF) to assess spillway capacity
- preparation of remedial actions plan for dam remedial works
- dam break analysis
- preparation of Emergency Action Plan
- site specific seismic hazard assessment
- preparation of concept design for remedial works including Design-Build contract documentation.
The main conclusions were:
- the peak PMF inflow into Angat reservoir is now estimated to be 12,000 m3/s compared with the previous PMF estimate of 8400 m3/s
- the ultimate discharge capacity of the spillway before the dam is overtopped at the abutments (assuming zero freeboard) is 7,180 m3/s
- the spillway capacity is just short of the PMF standard and, the ultimate capacity of the spillway corresponds with about a 70,000 year return period flood event based on consideration of flood and volume frequency analyses of historical floods
- an auxiliary spillway would be needed to safely pass the PMF
- the main dam/saddle dam require remediation due to the potentially high degree of seismic shaking and the potential for fault dislocation under the saddle dam.
Keywords: Dam, Remedial, Seismic, Fault, Spillway.
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2012 Papers
2012 – Innovation in the Design and Construction of the Enlarged Cotter Dam
Learn moreMartin Weir
The Enlarged Cotter Dam project was selected as a key component in securing the future water supply for Canberra and the ACT region. The RCC gravity dam, when completed, will stand 84m high and will be the largest of its kind in Australia.
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The dam was designed, and is currently being constructed, under the Alliance contract model. The collaboration this model brings between the owner and the design and construction teams facilitated a drive in innovation from the design through to the construction stages of the project. The focus of this paper is on some of the key innovative aspects of the project, for consideration on future RCC and dam projects.
Investigation was made into the placement of RCC in 400mm layers, compared to the industry adopted standard of placement in 300mm thick layers. Whilst full scale trials demonstrated that placement in 400mm thick layers was not detrimental to the quality of the RCC, the benefits in terms of increased production were never fully realised due to adverse weather and the geometry of the dam placement area. Some issues were also encountered with regards to the compaction of the GERCC on the dam faces. The results do however suggest that the method warrants consideration on future RCC projects.
The construction of the dam’s secondary spillway included a waterstop installation in a constrained RCC placement zone. By developing an arrangement that could hold the waterstop in place and induce the movement joint in the correct location, this arrangement simplified what could have been a complicated procedure in an already time consuming placement area.
The start of RCC placement was at risk of further delay on account of the extensive mass concrete pours required to level the dam foundation. A conventionally vibrated concrete mix, made from the existing site won RCC materials, was designed so that it could be produced from the RCC batch plant. This method of concrete production, combined with an efficient means of delivering the concrete to the pour area, accelerated the placement process and reduced the cost of construction.
Keywords: RCC, dam, construction. -
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2012 Papers
2012 – Negotiating the Geological Structure of the Enlarged Cotter Dam Site During the Abutment Excavation Period
Learn moreAndrew Barclay, Greg Kotze
The Enlarged Cotter Dam (ECD) is under construction on the Cotter River, 18km west of Canberra. The new dam comprises an 85m high roller compacted concrete gravity dam, located 120m downstream of an existing 31m high concrete dam. This paper describes the geological structures that prevail at the site and their significance with respect to design and construction considerations.
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Geological mapping has confirmed that the abutment slopes are characterised by zones of prominent rock outcrop and thin mantles of colluvial soil that form overall slope angles of 45 degrees. The Cotter River valley in the ECD area has been eroded through a geological sequence of Early to Late Silurian age, comprised predominantly of porphyritic rhyolite and lapilli tuffs of the Walker Volcanics.
Geotechnical investigations for the ECD were extensive and comprehensive. The results obtained have enabled the compilation of a detailed geological model of the dam site. Particular attention was paid to defining, characterising and kinematically analysing prominent geological structures, including intersecting sheared or crushed seams and zones that traverse the dam footprint.
Prominent geological structures that were encountered during the abutment excavation had significant design and construction implications for:
Abutment stripping and foundation preparations;
Rock slope stabilisation;
The foundation of the intake tower that comprises a 66m high concrete structure; and
The foundations for 1 x 56m high and 2 x 78m high tower cranes that required positioning on the steep abutment slopes during construction.
This paper highlights the importance of understanding the geological origin, nature and distribution of rockmass defects within a complex rock foundation. Site specific construction requirements and engineering design solutions used to successfully negotiate adverse geological structures are described.
Keywords: Dam, Roller Compacted Concrete, Geological Structures, Abutment, Foundation.