David Ryan, Sean Fleming
The Connors River Dam and Pipeline Project comprises the construction of a 367,540 ML storage on the Connors River located in central Queensland and a 130 km pipeline capable of delivering annually 49,500 ML of high priority water to the rapidly expanding Central Queensland Coalfields. The dam also has the capacity to supply water for the downstream agricultural sector.
Key outcomes of SunWater’s recent business case investigations included the identification of a strategy that would deliver the project in parallel with the construction programs currently being developed by the coal mining sector, the delivery of a quality product with high certainty cost and the ability to supply water at a commercially attractive rate. Construction activity is currently scheduled to commence in mid 2011, with commissioning of the works early 2014.
The paper outlines the project details, the design features of the dam and pipeline and the contract strategy adopted in an attempt to deliver the project on time and within budget.
Keywords: Roller Compacted Concrete, Early Contractor Involvement, Design and Construction.
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Brendan Sheehan, Chris Topham, Alan White, Rowenna Lagden
Darwin Dam is a 21m high embankment dam constructed on a geologically complex foundation that includes karst limestone features. The dam retains the top 15m of Lake Burbury on Tasmania’s west coast, and borders the Tasmanian Wilderness World Heritage Area. Defensive design of the dam addressed the key failure modes of piping through the complex foundations of limestone, sandstone, gravels and silts, and guarding against sinkholes forming in the limestone foundations. During construction, a comprehensive range of instruments were installed in the dam and foundation, as a long term means of monitoring this structure. A range of surveillance data has been collected since lake filling and this data, along with historic geological investigation information, was used to develop a three dimensional (3D) geological model of the dam and
foundation with phreatic profiles. The software used was a commercially available geographical information system. This tool has assisted Hydro Tasmania to better understand and manage the dam. The paper outlines the need for a 3D model, the methodology for development of the model, resources required, limitations and lessons learned. The benefits of the model, such as aiding understanding of foundation behaviour, assisting with interpretation of surveillance data, supporting decision making, and potential use during incident response are also discussed.
Keywords: Three dimensional, computer model, karst foundation, geology, hydrogeology ,dam surveillance
Cat McConkey, Zarmina Nasir, Rachel Caoil
The Enlarged Cotter Dam (ECD) is the first major project to be assessed and approved under the new planning regime in the Australian Capital Territory (ACT). ACTEW chose the ECD as its highest priority option in securing Canberra’s water supply for the future because of its relative economic benefit to the community, reliability of water supply, technical feasibility and comparatively low environmental impact.
The planning and construction of large dams has been reduced from a typical 10 plus years to four years in the ACT and surrounds for the ECD. Australian and International Dam design and construction has significantly developed from a time when dam approvals focused on engineering, economics and constructability to now include regulatory planning processes that seek to reconcile environmental, social and economic impacts.
This paper explores and contrasts the experience of securing approvals for the ECD in 2009 to past experiences of dam planning approvals and consultation processes.
C.Johnson, D.Stephens, M.Arnold and N.Vitharana
As part of Melbourne Water’s dam safety upgrade program, emergency release capacity is being investigated at a number of dams. Recent work undertaken by the Water Resources Alliance (WRA) for Melbourne Water has highlighted the lack of current Australian guidelines for appropriate emergency release capacity. With no relevant ANCOLD Guidelines, current practice still references the 1990 USBR guidelines which relate the length of time to empty a reservoir to the hazard and risk associated with dam failure. As hazard category assessment criteria has been improved since and dam design and safety standards are more stringent, the applicability of the USBR criteria in today’s environment is under consideration.
With the prevailing climatic conditions requiring the augmentation of Melbourne’s water supplies, the Tarago Reservoir was recently brought back into service. However, the dam lacked adequate emergency and environmental release capacity, with this being critical to manage construction flood risk for a pending filter raising project. Through an analysis of recorded inflow data, it was evident the existing scour facility had insufficient capacity to handle the recorded inflows, and would not be able to maintain the reservoir at an appropriate level during the proposed works. The length of time to empty the reservoir for the existing scour facility and the preferred scour upgrade option were calculated and it was found that by providing a new 1200mm scour facility, USBR emptying times were met or exceeded. The enlarged outlet capacity was also required to meet the new environmental flow requirements for the dam.
The paper will review international guidelines, share the experience of several Australian water authorities in assigning emergency release capacity for their dams, and discuss the specific work undertaken to provide suitable emergency release capacity at Tarago Reservoir for Melbourne Water.
M. Tooley, N. Anderson, N. Vitharana, G. McNally, C. Johnson and D. Moore
There is a significant stock of aging concrete dams in Australia which would not meet the requirements of the current recognised dam safety practices applicable to concrete gravity dams.
In this paper, field and laboratory investigations undertaken for two concrete gravity dams are presented, these being Middle River Dam and Warren Dam both owned and operated by the South Australian Water Corporation. The field investigations included a comprehensive drilling program recovering core samples ranging in diameter from 61mm (HQ) to 95mm (4C), continuous imaging (RAAX) of the drilled holes and installation of piezometers. Geological logging of the holes and mapping of the unlined spillway were also undertaken. The laboratory program included the testing of concrete lift joints and concrete samples in direct tension, shear and compression.
Concrete in Middle River Dam is suffering from extensive Alkali Aggregate Reaction (AAR), and consequently a suite of laboratory testing is being undertaken to determine the current level of deterioration and residual reactivity so that potential future AAR-induced expansion can be incorporated into any upgrade design solution.
The main purpose of the study is to determine whether site-specific parameters can be used to re-assess the stability of these two dams as calculations, based on the current standards, have shown that the dams have exceeded the allowable factors of safety values at the storage water levels experienced to date.
The findings may be useful to dam designers and owners faced with the upgrading of concrete dams, where traditional assumptions can result in no upgrade or an upgrade costing several million dollars.
Aric Torreyson, Krey Price, Bob Hall
In a 2004 feasibility study, the U.S. Army Corps of Engineers (Corps) and Ventura County Watershed Protection District (VCWPD) recommended decommissioning Matilija Dam, a concrete arch dam originally constructed to a 60-metre height in 1948. A decade after its completion, the United States Bureau of Reclamation (USBR) constructed the Ventura River Project, comprising additional facilities designed to meet the growing water demand of Ventura County. Robles Diversion Dam, a 7-metre high by 160-metre long diversion structure located downstream of Matilija Dam, was built under the Ventura River Project to feed Lake Casitas, a water supply reservoir that serves as an integral part of the overall project.
Due to extreme sedimentation, Matilija Dam no longer serves its intended water supply and flood control purposes. In addition to the loss of storage capacity, other issues surround the dam, including adverse environmental impacts from its continued operation, seismic considerations, and structural concerns. These concerns led to the decision to decommission the dam as an essential step in rehabilitating key ecosystems in the Ventura River Catchment and reducing future risks to public safety. According to current estimates, 5 million cubic metres of sediment has accumulated behind the dam and will need to be removed in conjunction with the dam decommissioning; minimising the associated downstream impacts has been the subject of additional government studies.
The USBR determined through detailed hydrologic, hydraulic, and sediment transport analyses, including numerical and physical modelling, that the existing Robles Diversion Dam was not capable of passing the increased sediment load expected to result from the removal of Matilija Dam. To increase the sediment transport capacity across its spillway, the existing diversion dam requires modification. Under contract with the Corps, Tetra Tech and its subcontractors are completing the design plans for the Robles Diversion Dam modifications.
This paper presents unique aspects of the Robles Diversion Dam modifications, including sediment management procedures guided by numerical and physical model results and issues associated with the design of a rock ramp spillway and high-flow fishway, expansion of the existing spillway gate structure, and raising of the dam embankment. The rehabilitation efforts reduce impacts to the migration of endangered fish species and allow for the eventual removal of Matilija Dam, which is the ultimate goal in the effort to balance engineered structures with a natural river setting. When completed, the project will provide fish passage to the upper catchment for the first time in over sixty years.