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.
Jared Deible, John Osterle, Charles Weatherford, Tom Hollenkamp, Matt Frerking
The original rockfill dike, constructed in 1963 to form the Upper Reservoir at the Taum Sauk Pump Storage Project near Lesterville, MO failed on December 14, 2005. The Upper Reservoir has been completely rebuilt as a 2.83 million cubic yard (2.16 million cubic meters) Roller Compacted Concrete (RCC) Dam in compliance with FERC Regulations. The project is the largest RCC project constructed in the USA and is the first pumped storage project to utilize an RCC water retaining structure. The project is owned and operated by AmerenUE and consists of an Upper Reservoir and a Lower Reservoir connected by a vertical shaft, rock tunnel, and penstock. The Powerhouse has two pump-turbines with a total generation capacity of 450MW.
A refill plan was developed to monitor the performance of the dam during the first refill. Because it is a pumped storage project with no natural inflow, the reservoir level can be raised and lowered with reversible pump turbines. The refill plan includes hold points when the dam s performance will be assessed at eight reservoir levels. Monitoring of the performance of the dam is done through instrumentation readings and visual inspections. Inspections check for alignment changes, leakage, seepage, cracking, or any other unusual or changed conditions. Instrumentation monitored during the refill program includes piezometers, seepage weirs, survey monuments, and joint meters. The level control system for the project was also evaluated during the refill program. This paper summarizes the monitoring and inspections conducted during the refill and the performance of the dam during this period, and the performance of the dam during the initial period after the refill program.
Glen Hobbs, Robert Rigg, Alan Hobbs, Adam Butler
Maintenance errors and associated non-conformances are becoming increasingly recognised as a source of system failures in a wide range of industries. Research in other industries has shown that errors often arise in response to local factors beyond the control of the maintainer. Various dam ‘incidents’ have been attributed to maintenance errors. In Australia we have been fortunate with few serious dam safety events. However, the dam operating and maintenance environment is changing dramatically.
A survey of dam maintenance personnel was recently undertaken in Australia. The survey was in the form of 49 questions that asked participants to state how frequently a situation occurred. This survey format has previously been used in other industries; thus allowing a comparison of dam maintenance with other high-risk industries such as rail infrastructure, oil and gas, and airline maintenance.
A number of ‘error-producing’ conditions have been identified and survey results indicate a high level of poor procedures/documentation and supervision; highlighting the need for accurate and appropriate manuals and supervision of tasks. These and other factors are leading to instances of maintenance non-compliance, which may threaten the reliability and safety of equipment. The survey has revealed that trade training needs to be addressed. However, occupational safety issues are low; indicating a positive approach to a safe working environment. The paper also discusses the responses to specific maintenance questions relevant to the dam industry.
Ben Greentree, David Bamforth, Matthew O’Rourke and James Willey
A series of relatively small floods occurring between end of construction in 1978 and late 1980s caused extensive and dramatic rock erosion to the very steep unlined section of the Googong Dam spillway. Following a review of hydraulic performance at larger floods, the spillway’s future erosion potential was evaluated and it became clear that extensive remedial work was required. A detailed design was developed comprising the retro-fitting of a full concrete-lined chute, the raising and extension of the spillway chute walls, strengthening of the upstream training walls and excavation of a large plunge pool. The Googong Dam has an ANCOLD hazard rating of ‘extreme’ because of its location upstream of Queanbeyan and Canberra.
In early 2008, the Bulk Water Alliance (BWA), comprising ACTEW Corporation Ltd, (in cooperation with ActewAGL) (the Owner), GHD Pty Ltd (the Designer) and Abigroup Contractors Pty Ltd in joint venture with John Holland Pty Ltd (the Constructors) was formed to deliver a package of water security projects for the ACT, one of which is the Googong Dam Spillway Upgrade.
After preparation of a construction methodology and target outturn cost (TOC), the project was approved by the Actew Board and construction commenced in February 2009. Completion is due in late 2010. A number of significant geotechnical, structural and logistical challenges were encountered during construction, resulting in major changes to the construction methodology necessitating design changes. The changes were incorporated within the original TOC, without instigating scope change contractual claims and while still maintaining spillway functionality in line with Owner operational requirements.
This paper presents delivery phase challenges that necessitated construction methodology and design changes to achieve best for project outcomes; how these challenges were overcome through genuine innovation reliant on a collaborative effort by all the Alliance partners; and how the contractual framework of the Alliance was essential for the change management process to be successful.
David S. Bowles, Loren R. Anderson, Michael E. Ruthford, David C. Serafini, Sanjay S. Chauhan, Utah State University, Logan, Utah, U.S. Army Corps of Engineers, Sacramento, CA
In 2005 the Sacramento District of the US Army Corps of Engineers implemented an operating restriction to reduce the risk of an earthquake-induced failure of Success Dam, which could cause significant life loss and property damage. This paper describes an update of the 2004 risk-based evaluation of operating restrictions for Lake Success, which incorporated new information obtained by the District and enabled a re-evaluation of the level of the operating restriction and provided a basis for a possible modification of the restriction.
A RISK-BASED RE-EVALUATION OF RESERVOIR OPERATING RESTRICTIONS TO REDUCE THE RISK OF FAILURE FROM EARTHQUAKE AND PIPING
Kristen Sih, Peter Hill, Susan Ryan, Siraj Perera
Although ANCOLD provides guidance on good dam safety practices, in Australia it is the State and Territory Governments’ role to protect the public from dam safety incidents and in many cases these jurisdictions have legally binding regulations in place that dam owners must adhere to. This paper presents a comparative analysis of the dam safety regulations currently in place for Australian states, as well as selected international jurisdictions. The limit of applicability of the regulations, number of dams regulated, content of the regulations and powers and responsibilities of the regulator are all compared. It was found that there is a large range within each of these categories with regulatory approaches varying from light-handed and objective based, to highly prescriptive. The extent to which risk management principles are used in the regulations for each jurisdiction has also been investigated. It was found that in jurisdictions where higher hazard category dams account for a higher proportion of dams being regulated, risk analysis is included in the regulations. Finally, the ANCOLD societal risk criteria and ALARP considerations have been compared and contrasted with those from international jurisdictions and other hazardous industries.