“Off-river” storage, Bootawa Dam, receives water pumped from the Manning River to supply a
regional water scheme on the mid-north coast of NSW.
As part of drought planning, short term predictive modelling of future streamflow has been developed
from an analysis of the last 30 years of recorded flow data and “on-line” upstream river gauges.
In the longer view, a comparison was made of th e last 30 years of recorded flow with an analysis of
the previous 80 years of synthetic flow data. There is a downward trend in streamflow in the last 25
years. Is this likely to continue, or is it part of a cycle or some other factor?
Long term fluctuations in the Southern Oscillation Index are compared to rainfall for this region.
Estimates of sustainable yield of the scheme are dependant on many factors, including environmental flows, dam size, turbidity constraints, river pump transfer capacity, river loss, catchment rural demand, accuracy of streamflow data and future climate change.
The affect of each of these factors has been quantified and ranked according to their importance on
The $70 million upgrade of Wivenhoe Dam is being undertaken by the Wivenhoe Alliance, in close
proximity to the town of Fernvale, Queensland. As part of the Alliance’s commitment to delivering positive outcomes for the local community, it was decided part way through the project, to commit to delivering a ‘signature’ community legacy project. The team brainstormed a range of options and a decision-making matrix was used to choose the project that would best meet its objectives.
A partnership has been formed between the Alliance, Esk Shire Council and SEQWater to deliver a
master-planned project which incorporates elements such as a community information/service facility, upgrade of Fernvale Memorial Park, streetscape enhancements, improved parking and installation of shelters along the adjacent rail trail. These major partners, together with representatives of the local community, constitute the steering committee, which oversees planning of the project.
The project aims to encourage visitors to the area, to provide improved amenity and sense of pride for the region, and in turn encourage strong relationships for SEQWater in the area in which they operate.
Due to tight time frames the partnership is managing the fund raising activities, community consultation and design processes in parallel.
This paper discusses the process by which the Alliance was able to deliver this remarkable project, within a short timeframe. It also discusses how the local community has been involved and the benefits, which have resulted.
Blowering Dam was constructed in 1968 by the Snowy Mountains Hydro-Electric Authority, on behalf of the Water Conservation and Irrigation Commission. It is a large earth and rockfill embankment dam, approximately 112m high and 808m long, with a concrete chute spillway at the right abutment. The reservoir holds about 1,628GL of water that is mainly for irrigation and supplying an 80MW hydro-electric power station. The dam is owned and operated by State Water Corporation, NSW.
Revisions to the design flood estimate have highlighted the dam requiring an upgrade to cope with increased discharge rates. The NSW Department of Commerce has carried out feasibility studies of different upgrade options. The need to evaluate the hydraulic performance of the existing un-gated spillway was identified. Flow overtopping the chute walls can potentially erode the backfill behind the walls, and, the rockfill on the downstream toe of the embankment. Consequently, this may lead to significant damage of the spillway and may risk the safety of the dam.
Hydraulic analysis of the spillway using a 3-D computational fluid dynamics model was performed for various flood levels to determine the discharge coefficients and the discharge rating curve. It was also required to identify whether the chute walls need raising to contain the increased discharges. These results were compared with those calculated by other “standard” methods. Such verification provided a level of onfidence in the analysis results which were then used in the studies to assess available upgrade options.
In order to have further confidence in the analysis, the computed results were validated against physical test data and some limited information from an actual discharge. Further verification against established theory was conducted by modelling a supercritical flow through a contraction in an open-channel in order to see if the computation could predict the shock wave effect that was observed in physical models as well as full scale channels. A reasonably good correlation was obtained from all validating tests.
This paper presents some background of the proposed dam upgrade, potential upgrade options considered and details of the hydraulic modelling of the spillway. Some interesting flow behaviour caused by the shock wave will be highlighted.
This paper relates to the conference sub-themes of Dam Safety Upgrades – Management of
Risk and Due Diligence and Dam Construction.
Specifically, it relates to the changing willingness of governments to fund risk reduction in
dams compared with risk reduction in other areas.
The cost of dam safety upgrades is just one of a portfolio of risk reduction strategies
affecting the general community that governments are required to underwrite.
This paper examines the variation in acceptable risk standards between dam safety and
other areas. This may be explained in terms of what is acceptable to the community and the
courts. For instance, a corporation is likely to attempt to minimise its liability (which may
differ to minimising risk for the community). We also examine:
• a portfolio approach to safety expenditure and the implicit cost-benefit relationship;
• the impact of the asymmetric relationship between expenditure and absolute size of
potential loss; and
• the importance of a whole-of-government approach and reviewing apparent
inconsistencies in approach to risk.
There is an increasingly well-established literature on the value of a human life and
increasingly systematic approaches to the evaluation of risk and the setting of risk
standards. Risk standards are particularly explicit in the area of dam safety – they set limits
of tolerable risks for large-scale loss of life (eg. for existing dams, a loss of life of more than
10 persons with a probability of more than one in a ten thousand per annum is regarded as
unacceptable under the Australian guidelines).
However, there are significant contrasts in what is tolerated as acceptable risk between
different areas of government activity. To date, there appears to be no systematic evaluation
of the portfolio of risks or a common view on what is acceptable levels.
Changes to the estimation of extreme rainfall events resulted in significant increases in the estimates of the PMF since the original design of Wivenhoe Dam. To upgrade the dam to meet these new requirements, SEQWater (owner and operator) formed an Alliance with Leighton Contractors, Coffey Geosciences, MWH and the NSW Department of Commerce.
The option selected for the upgrade works included the construction of a new secondary spillway, upgrade of the existing gravity section, radial-gated spillway, and strengthening of the dam crest.
Value management was key throughout the project ensuring the Alliance was continually looking to
improve practices, increase cost-effectiveness and create innovative solutions for design elements of the project.
On numerous occasions when the design was challenged, the Alliance made ‘best for project’ decisions to carry out additional investigations or design work to pursue alternatives. As an example, the powerful tool of Computational Fluid Dynamics was used in the analysis and design of flow deflector plates on the existing spillway, which were an alternative to the originally designed gate locking pins. The investigation and development of this alternative resulted in significant cost savings and a more effective design solution.
This paper presents aspects of the design carried out by the Wivenhoe Alliance, lessons learned, and the way continual investigations during construction provided value for money solutions.