In 2015, a study was undertaken where recommendations were made to provide protection to the exposed rock in the unlined channel of the spillway at Burdekin Falls Dam. The protection included a matrix of anchor bars which extended the full 504 m width of the spillway and 25 m in the downstream direction. Over 1,200 anchors were proposed comprising 36 mm diameter bar extending up to 15 m into the foundation.
A value engineering study was undertaken in 2017 where a review of the rock scour potential was undertaken. The study was based on a methodology developed by Pells (2016) as part of a research grant funded under an Australian Research Council (ARC) Linkage Project which was jointly financed by the Federal Government of Australia, various state government bodies and engineering consultancies involved in dam design, operations and management.
This paper describes the approach taken as part of the value engineering study, the methods used in the assessment and the benefits of both innovative thinking and challenging the more traditional approach of rock scour assessment, the outcome of which resulted in a $11 m plus saving to the owner of the asset.
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.
On February 7, 2017, the gated service spillway (also known as the Flood
Control Outlet or FCO Spillway) at Oroville Dam was being used to release water
to control the Lake Oroville level according to the prescribed operations plan.
During this operation, the service spillway’s concrete chute slab failed, resulting
in the loss of spillway chute slab sections and deep erosion of underlying
foundation materials. Subsequently, as the damaged service spillway was
operated in an attempt to manage multiple risks, the project’s free overflow
emergency spillway was overtopped for the first time since the project was
completed in 1968. Significant erosion and headcutting occurred downstream of
the emergency spillway’s crest structure, leading authorities to evacuate about
188,000 people from downstream communities.
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.
Following the catastrophic failure of the bottom outlet conduits of the Massingir Dam, a rehabilitation project was launched involving the installation of steel liners and the rehabilitation of the hydromechanical equipment. This paper describes the testing of an emergency gates for possible use as a control gate to maintain supply to downstream water users. It further describes the innovative use of alternative access for concreting and other services, the use and benefits of self-compacting concrete for infill concreting between the steel liner and existing concrete and the programme and cost benefits of pressurising the steel conduit prior to concrete encasement.
Many mapped faults in the south-eastern highlands of New South Wales and Victoria are associated with apparently youthful topography, suggesting that faulting may have played a role in shaping the modern landscape. This has been demonstrated to be the case for the Lake George Fault, and may reasonably be inferred for the poorly characterised Murrumbidgee, Khancoban, Tantangara, Berridale Wrench and Tawonga faults. More than a dozen nearby major faults with similarly youthful topography are uncharacterised. In general, fault locations and extents are inconsistent across different scales of geologic mapping, and rupture lengths, slip rates and other fault behaviours remain largely unquantified. A more comprehensive understanding of these faults is required to support safety assessments for communities and large infrastructure in the region.