The paper describes the development of UK guidance on reservoir drawdown capacity. The guidance provides for a consistent thought process to be used in determining the recommended capacity. A basic recommended standard is proposed for embankment dams which varies with the consequences of failure of a dam. The drawdown rate for the highest consequence dams is 5% dam height/day with an upper limit of 1m/day. Engineering judgement is used to vary this standard allowing for ‘other considerations’ including the vulnerability to rapid dam failure, surveillance and precedent practice. A different approach is proposed for concrete/masonry dam, which considers the prime purpose of drawdown being to lower the reservoir in a reasonable timeframe to permit repairs rather than rapid lowering to avert failure. The UK approach is compared with that used in Australia and suggestions made for where its use may be appropriate.
— OR —
Now showing 1-12 of 59 2982:
Oroville Dam is located on the Feather River in northern California (USA). At 234.7 m (770-ft) tall, this earth embankment is the tallest dam in the United States. With its 4.3 billion m3 (3.5 million acre-feet) of storage, Lake Oroville is the second largest reservoir in California, supplying water to cities as far south as Los Angeles. The Oroville Dam, reservoir (Lake Oroville), and hydropower plant facility is the flagship of the State Water Project (SWP), which is owned and operated by the State of California, Department of Water Resources (DWR).
Multiple-arch dam technology enjoyed a certain popularity between the fifties and seventies, but was later discontinued for practical reasons. The multiple-arch dam that is the subject of this paper is especially peculiar since it was built using prefabricated elements and a combination of several pre-stressed steel systems.
This dam consists of 17 buttressed arches with a maximum height of 35 m on a limestone and dolostone foundation. It has a crest length of 531 m and a 15 hm3 reservoir. After 55 years in operation, several apparent degradations have surfaced and a study on the safety of the dam is currently being carried out.
The main concern is the dam’s structural safety, which is apparently linked to the integrity of the post-stressed steel elements and the precast elements in the arches. This paper describes the approach chosen for the remediation study, the visual inspection, and the tests developed on the post-stressed steel and concrete, in order to feed a 3D numerical model of the structure.
Lake Buffalo located on the Buffalo River near Myrtleford in Victoria was constructed in the 1960s as a cofferdam for the then proposed Big Buffalo dam. Consequently, the dam was designed for a short life (<10 years) and design features and criteria for a permanent dam were not implemented.
Critical features include a primary spillway with three vertical lift gates, two outlet conduits located
through the spillway piers, a single upstream valve on each outlet conduit for regulation and isolation, and a multi-part bulkhead which is installed in front of the valves for inspection and maintenance.
With the continued operation of the dam beyond 60 years, upgrades appropriate to a permanent dam have been implemented, including addressing deficiencies with spillway gate hoists lifting equipment and redundancy of the outlet conduit vales. This proved challenging, as the operation of spillway structures does not readily align with industry or Australian Standards. This paper will outline the issues encountered, their resolution and the lessons learnt during this upgrade work.
Millions of dollars are spent on dam upgrade works which are often undertaken to meet the flood security requirements. Prioritisation of the dam upgrade work is based on portfolio risk assessments in which dambreak modelling is an integral part. Concurrent design flow hydrographs of tributaries downstream of dam are required for the assessment of the incremental effect of a dam break scenario. The Annual Exceedance Probability (AEP) neutral concurrent tributary flows can be estimated using a bivariate-normal distribution approach.
This paper examines the underlying assumptions made in the application of the bivariate normal distribution approach using observed and design rainfall data for Avon Dam and its downstream tributary catchments. Synthetically generated data was used to illustrate the impact of the log-normal distribution assumption on the AEP neutral concurrent tributary rainfalls. This paper suggests a modification to the bivariate-normal distribution approach to estimate more unbiased AEP neutral concurrent design rainfalls. The use of historical gridded rainfall in the estimation of inter-catchment rainfall correlation is also demonstrated.
The volume-of-fluid (VOF) technique was employed to develop a Computational Fluid Dynamics (CFD) model for comparison to physical measurements available from the Eildon Dam model in Australia for validations purposes. The water surface in the downstream chute of the spillway was observed to be mostly comprised of fully developed aerated flow. The free surface is physically measured as located between the mixing and upper zones, thus investigator judgement is critical to achieve reliable measurements. The mixing zone is also characterized by surface waves to complicate matters even further. A challenge arose to develop a post processing methodology that replicates as closely as possible the measuring technique used by the physical modeller for direct comparison of results, using a novel method which utilises Poisson probability of exceedance applied to the free surface.