John Grimston, Robin Dawson
The Ambuklao and Binga Hydro-Electric Power Projects are located in Luzon, Philippines and were privatised in early 2008 after public bidding. Ambuklao dam forms an impoundment on the Agno River. The nearest city, Baguio, is approximately 45km or 1.5hrs drive away. The key headworks feature is an embankment central core rockfill dam and reaches a maximum height of some 129 m above the bed of the Agno River. A gated spillway is located at the left abutment, with a steep chute and flip bucket. Binga dam forms an impoundment approximately 20 km downstream of the Ambuklao dam. The rockfill embankment with an inclined clay core reaches a height of about 107 m above the bed of the Agno River. The spillway is located at the left abutment.
Heavy tropical rains and typhoons can cause very high flows in the rivers leading into the Ambuklao and Binga reservoirs. PMF peak flow is 11,600 cumecs. Due to the steep slopes surrounding the reservoir and along the access roads to the Binga Dam, landslides can create a hazard in the reservoir or for emergency access to the dam. There are numerous active faults in the area, including the Abra, Digdig and Philippines Faults (the latter being one of the most active faults around the Philippines). The region around the dams is capable of and has experienced earthquakes with a magnitude of 7.8 on the Richter Scale. This was demonstrated by the 1990 earthquake (7.8 magnitude) and caused minor damage to the dam structures.
The Project owner commenced rehabilitation implementation planning immediately after purchasing the facilities aimed at reactivating the Ambuklao plant’s 75MW capacity (inoperable since 1999 due to reservoir siltation issues triggered by the 1990 earthquake) and increasing it to 105MW. Rehabilitation at the Binga plant will increase capacity from it’s current 100MW to 120MW. The overall rehabilitation works include plant, intakes, associated tunnels, etc. This paper will focus primarily on the dam and spillway related rehabilitation, studies and design including review of the PMF and spillway capacity for both dams, Ambuklao innovative upstream face rehabilitation, Ambuklao spillway studies and rehabilitation and Binga spillway works and reservoir sedimentation studies.
2011 – Refurbishment of Ambuklao and Binga Hydro Power Dams and Appurtenant Works
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The enlargement of the Cotter Dam is being undertaken by ACTEW to provide a greater security of water supply to Canberra. The project involves constructing a larger, higher new dam wall immediately downstream of the existing Cotter Dam, to allow the present dam to continue functioning and supplying water while construction is underway. The project raised a number of environmental issues partly because the Cotter Dam currently supports a self-sustaining population of (endangered) Macquarie Perch, and because the Bendora Dam, upstream of Cotter Dam, contains a breeding population of (endangered) Trout Cod. Bendora Dam will not be physically affected by the works on Cotter Dam, but its operations may be altered. An ecological risk analysis was conducted to identify critical environmental risks that would need to be investigated and managed or ameliorated and management strategies were put in place to reduce risks. ACTEW have adopted an adaptive management approach to the project, but in order to implement that approach it is necessary to conduct effective monitoring of the fish populations of concern. These potentially include the two endangered species, as well as potential predators (such as cormorants) and competitors (such as trout). Power analysis has been used as a tool to evaluate whether it is feasible to monitor key populations sufficiently rigorously to be able to confidently detect a change (either an increase or decrease in a population). For Macquarie Perch and trout it should be possible to detect population changes statistically with a logistically feasible monitoring program.
2011 – Using risk analysis, power analysis and adaptive management to minimise ecological impacts of the Cotter Dam enlargement
Richard R. Davidson, Joergen Pilzand Bruce Brown
Recent earthquakes in Chile, New Zealand and Japan have created a new focus on the safe design of tailings dams in seismic regions of the world. Building sand and rockfill embankments to sustain large ground motions and provide crucial drainage of excess pore pressures remain daunting challenges at each site. Are conventional hydraulic deposition practices still viable? What new technologies can be considered? Addressing seismic stability of existing upstream method tailings dams whether currently in operation or closed is stretching our seismic geotechnical engineering profession to its limits of understanding of behaviour. Creating a safe, secure environmental storage must also be integrated with the geotechnical and hydrologic concerns. Is there a viable risk context to consider these competing issues? This paper will raise these issues within the international context and suggest a prudent path forward.
2011 – The Challenges of Building Tailings Dams in Seismic Regions
Paul Somerville, Hong Kie Thio
There is a large degree of uncertainty as to the true state of nature (i.e. epistemic uncertainty) regarding many aspects of seismic hazard analysis. Such differences are often highlighted by differences between alternative models put forth by different model proponents. This epistemic uncertainty is treated by giving weight to all viable alternative models through the use of logic trees in probabilistic seismic hazard analysis, rather than just using a preferred model. This paper reviews epistemic uncertainties that arise from alternative distributed earthquake source models; alternative models for the recurrence of earthquakes on those sources; alternative approaches to including active faults; alternative models for the recurrence of earthquakes on active faults; alternative ground motion prediction models for Australia; and alternative methods for incorporating site response. It also reviews alternative representations of the design response spectrum for the development of ground motion time histories.
2011 – Recent Developments in Seismic Hazard Analysis
Craig Messer, Francisco Lopez, and Manoj Laxman
The Enlarged Cotter Dam is a new 80m high Roller Compacted Concrete Dam being constructed to augment the water supply for the Canberra region. Due to the size of the main dam and the extreme climatic variations in the ACT, where temperatures range from sub zero in winter to in excess of forty degrees in summer, it is expected that significant stresses will be generated during the cooling of the structure. For this reason it is essential that an understanding of the magnitude of these stresses is developed through the initial strength development period and at critical periods such as the first and second winter when the temperature differential between ambient conditions and the core of the structure may be greatest. The development of thermal stress within the structure has critical impacts on both the RCC mix design and the dam construction equipment and methodology.
For the Enlarged Cotter Dam, thermal stresses were investigated using both two and three dimensional finite element transient heat transfer analyses, making use of the thermal properties derived from laboratory testing including instrumented thermal blocks, as well as established literature. Modelling of the thermal stresses in the dam required the development of time dependent concrete properties, such as strength, stiffness and heat generation, with the latter based on test results and calibrated to actual measured values. Additionally, site dependent conditions for ambient temperature, external conduction, convection and radiation factors, dam foundation temperatures and restraint, dam construction sequence, formwork, joint spacing, insulation and timing of reservoir filling were also modelled.
Initial thermal modelling of the dam demonstrated that significant tensile stresses and potential cracking could develop within the structure, at both early and mature concrete ages. Subsequent analyses were developed to investigate methods of reducing these stresses to within acceptable limits. This paper presents the results of the thermal analyses, including the methods to be employed during and after construction to minimise cracking without impacting construction costs and even optimising the speed of construction.
Finite Element Transient Thermal Analysis of the Enlarged Cotter Dam
T. Mortimer, J. McNicol, P. Keefer, W. Ludlow
CS Energy’s Kogan Creek Coal Mine located in the Surat Basin in Queensland, services the 750MW coal fired, Kogan Creek Power Station. Strip mining generates large volumes of mine waste which is typically used to construct waste dumps. Recent work at the mine has focused on using mine waste to construct an ash storage facility to store ash that is piped over 5 km from the power station as a dense phase slurry. The use of mine waste to construct the ash storage facility provides significant cost and time savings, however a range of design, construction and operation issues needed to be addressed to operate a facility of this type.
This paper describes some of the key design, construction and operation considerations for the ash storage facility. Design considerations include pipeline transport through environmentally sensitive areas, addressing the stability of the embankment and the use of a partial LLDPE geomembrane lining system to reduce the risk of seepage from the storage. Construction considerations include post construction (pre ash deposition) floor treatment to reduce potential settlement. Operational considerations include ash slurry deposition, water management of the decant pond and progressive rehabilitation of the final landform.
2011 – Design, Construction and Operation of a Partially Lined, Ash Storage Facility Constructed from Mine Waste