G. Hadzilacos, ML. Ng, K. Taske, A. Small and B. Loney
Alteration of flow patterns by constructing a dam may have an irreversible impact on ecosystems depending on the timing, duration and frequency of these flows. As part of an Environmental Impact Study, carried out for a proposed mining operation in Australia that included an earth dam on a pristine ephemeral creek, an appropriate waterway management scheme was proposed that required the establishment of measurable instream flow requirements. This paper describes an environmental flow analysis (EFA) carried out to identify flow regimes that achieve the desired ecological outcomes for the affected waterways. The EFA methodology was based on the range-of-variability approach using a calibrated rainfall-runoff model to form the hydrologic basis. The study established a relationship between flow components and ecological variables based upon which the flow requirements were estimated using a simple methodology.
2011 – A case study of an initial Environmental Flows Assessment for an earth dam on a pristine stream in Cape York
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B. Ghahreman Nejad, H. Taiebat, M. Dillon and K. Seddon
One of the causes of tailings dam failure has been seismically induced liquefaction during earthquakes. Liquefaction, if mobilised, significantly reduces the stiffness and strength of affected soils in the embankment dam or its foundation and may lead to large deformations and dam failure. This paper reports the results of seismic liquefaction assessment and deformation analyses of Bobadil tailings dam located in Tasmania. The tailings dam consists of a perimeter rockfill starter dam which has been raised in stages using the “upstream” construction method. The embankment raises (formed by clay or coarse tailings) are constructed over a foundation of previously deposited tailings in the impoundment which is potentially susceptible to liquefaction. Extensive field and laboratory tests were carried out to assess the tailings liquefaction potential and also to determine the material properties required for seismic stability and deformation analyses. Numerical modelling of seismic liquefaction and deformation analyses were carried out to predict the magnitude and pattern of deformations that may lead to uncontrolled release of tailings. The results of these analyses are presented and compared with literature report of those observed during past earthquakes.
2011 – Numerical Modelling of Seismic Liquefaction for Bobadil Tailings Dam
Craig Johnson, Mark Arnold
Toorourrong Reservoir is a small storage reservoir which was constructed in 1885 and forms an important part of Melbourne’s water supply network. As part of Melbourne Water’s dam safety upgrade program, remedial works at Toorourrong Reservoir were identified to address deficiencies in flood capacity, embankment stability and to provide protection against piping. These works included an engineered filter system, downstream stabilising berm and raising of the dam crest level by 2.3m through a combination of earthfill and a concrete parapet wall. The existing spillway also required substantial enlargement and the existing scour and outlet structures were to be reconfigured. These works were designed and undertaken by the Water Resources Alliance (WRA).
Preliminary geotechnical investigations indicated the dam was founded on soft alluvial deposits, with the potential for foundation liquefaction under earthquake loading. During the course of subsequent investigations, the full complexity of the dam foundation was realised using numerous techniques including geophysics, CPT
u probes and seismic dilatometer testing. The results of these investigations were used to develop a detailed geotechnical model and embankment design sections. A range of analytical methods were utilised to characterise the liquefaction potential of the foundation, with these making reference to recent developments in this area of practice. Through an extensive assessment and review process, the design soil properties for the foundation were established and the liquefaction potential determined.
Based on these assessments, it was found that the potential for liquefaction existed across the majority of the dam foundation, with discrete soil layers liquefying depending on the intensity of the design seismic event. Strain-weakening (sensitive) soils were also identified in the foundation. A quasi risk-based stability assessment was undertaken for a range of post-liquefaction strength parameters and FoS to determine the sensitivity of the foundation response. Stability analyses were performed which indicated that additional stabilising berms were required at several locations. However, even with these berms, the extremely low post-liquefaction strengths meant that further ground improvement was required. This was assessed further and Grouted Stone Columns (GSC) were ultimately selected as the preferred foundation improvement method for the critical design sections with GSC to be installed both upstream and downstream to reinforce the dam foundation. This is the first time GSC have been used in Australia and some key “lessons learned” will be discussed.
2011 – Toorourrong Reservoir – Small Dam, Big Problems
Bob Wark, Louise Thomas, Andrew Peek
Alkali Silica Reaction (ASR) has been by far the dominant cause identified in the deterioration of concrete caused by expansion of the pastes from an interaction with the aggregates. However the path to the identification of the presence of the deleterious effects of ASR is not always straightforward. In a recent example, the concrete spillway slabs and walls at South Dandalup Dam exhibited classic craze cracking symptoms of ASR. However when subjected to more detailed analysis the driving process was found to be delayed ettringite formation (DEF).
ASR and DEF are chemically different concrete deterioration mechanisms with physically similar manifestation, causing slow concrete expansion in the presence of moisture. ASR has been reported mostly in concrete structures constructed prior to the early 90’s when the DEF deterioration mechanism was not fully recognised. However it is possible that ASR and DEF can take place simultaneously and more extensive damage due to DEF could have occurred and remain undetected.
The paper will also describe a recent case using basalt aggregate for Stirling Dam in which the use of an accelerated mortar bar test gave an extreme reaction but the ASTM concrete prism expansion test gave a negative result. Further detailed petrographic examination provided the clues to the real cause.
The paper will describe the occurrence of the problems, compare the causes and outline the methods undertaken to investigate the issues. Alternative concrete mix designs, incorporating a high flyash content to replace ordinary Portland cement as the main pozzolanic material, have been investigated and successfully implemented. This paper describes the investigations undertaken to develop these alternate mixes, the resultant properties of the concrete and its resistance to deterioration.
2011 – Searching for Solutions to ASR
Mark R. Sinclair & Richard J. Rodd
Over the last six years there have been ongoing significant developments in the design, fabrication and particularly of the corrosion protection details for high capacity ( >13,500kN MBL ) re-stressable ground anchors used to improve stability of gravity dams. These Australian based developments and the resultant specifications and details have now become the de-facto standards adopted.
The ANCOLD Register dams to have had this generation of cables installed have included; Ross River Dam, Lake Manchester Dam, Catagunya Dam, Tinaroo Falls Dam and Wellington Dam. These projects include the highest capacity permanent ground anchors installed to date worldwide. Some smaller capacity anchors installed into dams have also benefited from this technology.
The Recent Developments and Application of Large Ground Anchors for
Lesa Delaere, Ivor Stuart, Thomas Ewing, David Marsh
As part of Wide Bay Water’s commitment to minimising environmental impacts of its water supply weirs, a “Nature Like” Fishway is under development for the Burrum No 1 Weir. This project is a fishway offset provision for the raising of Lenthalls Dam in the upper reaches of the Burrum River in Hervey Bay. The Burrum No 1 weir forms the primary pumping pool for the Hervey Bay water supply and is located at the tidal limit of the Burrum River. Understanding fish biology and behaviour is critical to the effectiveness of the design of a fishway as much as the balance between the goals of maximising fish passage versus cost, construction and operational difficulties that a fish passage solution may present.
This paper presents the aquatic ecology of the project and the inter-relationship of fish biology and river flow frequency. It discusses the fish species of the Burrum River, their behaviour, seasonal migration and criteria for successful passage. It presents the analysis of river flows with respect to frequency and headwater/tailwater relationships to weir drownout, which was complicated by the tidal flow regimes downstream of the weir. These aspects were also applied in consideration of river behaviour; low flow characteristics for fishway operation during dry seasons and drought, and high flow characteristics during the wet season and floods.
The biological needs for successful fish passage for two very different river flow characteristics were analysed. This allowed targeted design criteria and fishway solution to be developed to provide maximum benefit without causing undue cost to the project.
Burrum Weir Fishway – Fish Biology and River Flows: Two Faces