Dr. Mark Locke, Jiri Herza
Gördes Dam is a nickel and cobalt mine tailings dam situated in a seismically active zone in Manisa Province, Western Turkey. The dam is a conventional cross valley earthfill structure with a fully lined storage basin. The starter embankment with a maximum height of 50 m will be raised in downstream lifts to an ultimate height of 90 m. The total storage capacity is 19 million m3. Construction of the starter embankment is planned to commence in late 2012 and the dam will be commissioned in June 2013.
The tailings will be discharged from the dam crest and return water will be collected by a floating decant pump at the opposite site of the storage. Decant water has high calcium sulphate levels and will require treatment before re-use in the plant or release. The tailings contain about 33 % of solids and are classified as high plasticity silts and clays with more than 90 % of particles passing the 0.075 mm sieve.
The dam is founded on a complex formation of altered sedimentary and metamorphic rocks including mudstones, siltstones, limestones and serpentines. The mudstone blocks, the predominant foundation materials, are juxtaposed with siltstones and serpentines via a complex arrangement of faults. Where exposed, the mudstones are highly to completely weathered with a well-developed structure of smooth bedding surfaces leading to anisotropic strength characteristics. Several landslides, likely associated with the anisotropic character of the mudstones, were identified within the area including a significant landslide under the upstream shoulder of the dam.
Mining development in Turkey has a complex legislative environment. There is also standard practice which is not legislated but expected, this can be considerably different to normal design practice in Australia. The Turkish legislation is based on waste management guidelines and may be more appropriate to landfills than large tailings storages. The legislation is very prescriptive in some aspects and silent in others, with little consideration of risk or consequence based design.
This paper discusses the design difficulties associated with the challenging foundation conditions, which have been magnified by the requirements and limitations embedded in the approval documentation and the legislative environment in Turkey. It will also address some of the key differences between the design philosophy in Australia and in Turkey with a focus on the major risk elements of the design.
Keywords: Tailings, Turkey, Liner, HDPE, Nickel laterite
Krey Price, David Moore, John Palensky
Cold water pollution (CWP) occurs when dam releases draw from lower-temperature regions of a reservoir, potentially impacting fish survivability in downstream waterways. Declining fish populations along the Missouri River have prompted recent investigations into solutions for CWP prevention.
Fort Peck Dam is an 80-metre high, 7-kilometre long dam located along the Missouri River; completed in 1940, it is one of the world’s oldest and largest hydraulically filled earthen dams and is listed on the U.S. National Historic Register. Inflow temperatures to Fort Peck Reservoir are significantly warmer than the outflow temperatures through the dam during the months of March through August. A water temperature of 18°C has been identified as critical for spawning and recruitment of locally threatened fish species; however, downstream temperatures typically remain below 14°C during critical time periods. This difference is due to the current deep-water withdrawal from Fort Peck Reservoir.
Ten alternatives were proposed to increase the temperature of the discharge, and an options analysis narrowed the results to a single, preferred alternative that consisted of a flexible, submerged weir around the intake. This paper documents the design efforts undertaken for temperature control measures at Fort Peck Dam, including a description of the modelling methods, design criteria, and effectiveness of the submerged weir alternative.
The use of a submerged weir to increase discharge temperatures relies on the process of passing warmer water from the upper portion of the water column over the weir crest into the intake area, rather than drawing from the bottom of the reservoir. For reservoirs with fluctuating levels, such as those at Fort Peck Dam, a flexible curtain can be suspended a set distance from the water surface using a float system, with the bottom of the curtain anchored to the lake bottom with ballast and cables. The crest elevation is set relative to the thermocline; as the lake level fluctuates, the flexible curtain folds and unfolds in response.
The impacts of CWP are increasingly recognised as an environmental risk worldwide. This paper draws upon the results of similar, implemented projects around the world, including a comparison to cold water pollution prevention measures and costs that have been assessed by CSIRO for application to Australian reservoirs.
Keywords: Cold water pollution, reservoir stratification, thermocline, curtain, fish health
David Stephens, Kristen Sih, Peter Hill, Rory Nathan, David Dole
The spring and summer of 2010-11 were characterised by severe flooding affecting much of Victoria. In a number of cases, communities downstream of large dams developed to supply water for irrigation and critical human and stock needs were significantly impacted. Following the floods, the Victorian Government commissioned the Victorian Floods Review (VFR) to consider the total warning and response to these floods. Whilst dam operations were not specifically included in the terms of reference, overwhelming community interest lead to the VFR commissioning a high level review of the way a number of key dams were operated during the floods. This review identified some of the inherent tensions in the legislative framework for water harvesting, storage and dam safety in Victoria. These tensions were often matched by the conflicting expectations of the public living immediately downstream of the dams versus those dependent on the water resource stored in the dams. The final report of the VFR was handed down in December 2011 and contained a number of recommendations specifically for dam owners. These recommendations are reviewed and discussed in light of both the legal and public relations ramifications for owners and operators of large water supply dams. An overview is also given of the operational constraints to downstream flood mitigation facing many dam owners. Such constraints are typically imposed by the type of dam (i.e. fixed crest), relatively small storage and outlet capacities when compared to flood volumes and limitations on the reliability of forecast rainfall information. Some possible ways of overcoming these constraints are identified and discussed.
Keywords: Flood, mitigation, Victorian Floods Review
Gurmeet Singh, Nanda Nandakumar, Md Atiquzzaman, Andrew Richardson
This paper describes the flood modelling of the Lachlan River floodplain and highlights the impacts of complex terrain and concurrent tributary flows on river hydraulics for extreme design flood event. This study was undertaken as part of Portfolio Risk Assessment of dams operated by State Water Corporation.
It is demonstrated how a one dimensional/two dimensional coupled model can provide realistic spatial distribution of hydraulic parameters for consequence assessment and emergency flood risk management.
Keywords: 1D/2D coupled hydraulic model, time to peak, duration of flooding, rate of rise.
Mike Phillips, Kelly Maslin
A spillway upgrade conceptual design and selection process was undertaken to identify options for upgrading the Dartmouth Dam to pass the Probable Maximum Flood (PMF). A number of upgrade options were investigated, including variations of dam raise heights and spillway modifications. One of the options, the piano key weir, was initially developed from the limited available publications on the weir design, and further developed with the use of a 1:60 scale model. The piano key weir, a variation of the labyrinth weir, is a passive spillway that utilises a total weir length several times that of the effective spillway width. For the Dartmouth Dam study, the piano key weir design that was developed consisted of a 7-cycle, 9 m high structure, with a total weir length of nearly 600 m, or more than 6 times the existing effective spillway width of 91 m. The spillway was designed to pass the routed PMF outflow of approximately11,500 m3/s with a head of approximately 11 m.
The piano key weir design was developed using the following analyses:
Initial 1:60 scale physical model of the piano key weir based on published papers on piano key weirs and design manuals for labyrinth weirs;
Structural analysis and weir member sizing using initial physical model results;
Computational Fluid Dynamics (CFD) modelling to improve the hydraulic efficiency of the weir for the range of flows;
Revised 1:60 scale physical model of the piano key weir; and
Confirmation of conceptual structure design.
This paper describes the process of developing the piano key weir option for the Dartmouth Dam spillway and lessons learned.
Keywords: Piano key weir, CFD, spillway, physical model
Louise Thomas, Graeme Mann, Alex Gower
Mundaring Weir is a 41m high concrete gravity dam that was built in c.1900 to supply water to the Western Australian goldfields towns of Coolgardie and Kalgoorlie. The dam was raised by 9.75 metres in c.1950 and impounds a reservoir of 63.5 GL. The c.1900 cast iron outlet works and c.1950 mild steel outlet works are still in operation without any significant modification or refurbishment since installation.
Mundaring Weir remains the principal storage for the Goldfields and Agricultural Water Supply (G&AWS). To meet the increasing demand and improve water quality in the G&AWS, the West Australian Water Corporation is upgrading the outlet works, constructing a new pump station and a water treatment plant.
The paper discusses: condition assessments undertaken; basis for refurbishment and the selection and design, including hydraulic modelling, of a staged upgrade of aged outlet structures; and ensuring these works can be undertaken without impacting on supply during the course of the works.
Keywords: Outlet Works, Asset Condition Assessment, Mundaring Weir