David Ho, Karen Riddette, Michael Hogg, Jayanta Sinha and John Roberts
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 confidence 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.
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Ian Cordery, Peter S. Cloke
Scientists advocate more hydrological monitoring but in most regions publicly funded monitoring is in
steady decline. The lack of measured data at dam sites means there are many designs for new dams and remedial work that are insufficiently supported by factual information. Unfortunately data –free modelling exercises will usually produce favourable results – favourable to the modeller’s purposes, but not necessarily favourable to the determination of physical reality or truth. In these days of the popularity of modelling it is common to find decisions being made based on model studies for which little or no local data were available for model calibration or verification. How can the ‘large dam’ fraternity encourage (ensure) more data use? Causes of lack of data are many. For example governments fund data collection but others need the data, and data collection is a long-term activity that produces few benefits in the short term. Some years ago it was shown that hydrological data collection and archiving provided benefits to the community of at least nine times the costs of the data.
The real costs of comprehensive data collection are not large but examples will be given of the huge
costs, mainly due to the need to allow for uncertainty, that result from unavailability of data. Those
who understand this problem need to explain it to their communities, politicians and CEOs in a clear,
unmistakably persuasive manner, and to demand an increase in data collection. If we do not, no one
The Ross River Dam, designed in the early seventies, does not meet current dam safety criteria for overtopping and piping within the embankment or the foundation. The dam comprises a 40m long concrete overflow spillway flanked by a central core rockfill embankment of 130 m on the right bank and 170m on the left bank with a 7620 m long left bank earth fill embankment, which has no internal filter zones for piping protection. The embankment was extensively assessed and treated forfoundation deficiencies in 1982, and further assessed in 20002002 for appropriate upgrade options.
This paper describes the process of validation of the detailed design using Risk Based Design Criteria. This process included data mining for historical performance and original design intention,
comparison of the original design against current and historical investigations and assessment of the upgrades using the large volume of data available from previous work. A design team comprising specialist hydrologists, hydrogeologists, geologists, geotechnical and dams engineers worked within a risk assessment framework at all stages of the design to ensure the design was validated using the design Validation Model. This process incorporated assessment of crest level based on flood risk and wave overtopping, review of 2D and 3D seepage models to assess piping and foundation erosion potential, assessment of fissured soils within the embankment foundation for structural stability and evaluation of spillway model testing for potential spillway failure modes.
Stuart Macnish, Nikki Bennett
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.
David S. Bowles, Loren R. Anderson, Terry F. Glover, Sanjay S. Chauhan, Ronn S. Rose
A risk assessment was performed for the Sacramento District of the U.S. Army Corps of Engineers to explore the justification for imposing an operating restriction on Lake Success to reduce the probability and consequences of an Earthquake-induced dam failure. The potential for both a sudden overtopping failure and a delayed “seepage erosion through cracks” failure were considered.
The risk assessment focused on the seismic performance of the dam, the potential life loss and economic consequences of Earthquake-induced dam failure, and the estimated residual risk and degree of risk-based justification for the Existing operating regime, a range of Potential Operating Restrictions, and an Indicative Improved Warning and Evacuation System. Risk assessment inputswere supported by seismic deformation analyses under various Earthquake loadings and pool elevations, dam break-inundation modelling, and reservoir simulation.
Evaluations against tolerable risk guidelines from the USBR, ANCOLD, and the UK HSE, together with insights into the relationship between pool elevation and dam failure risk, provided important inputs for the decision to implement an operating restriction.
Mike Taylor, Jonathan Jensen and Greg Branson
Pykes Creek Dam is a 33 m high, 22,120 ML embankment dam, 72 km west of Melbourne owned and operated by Southern Rural Water.
The outlet works include a 30 m high “wet” outlet tower near the upstream toe of the dam on the right
abutment with its lower half comprising a concrete lined shaft excavated in rock. A 1.5 m diameter
concrete lined tunnel extends 30 m upstream from the base of the tower to a reinforced concrete inlet structure.
The only controls upstream of the downstream toe of the dam comprised 2 guard gates located on the downstream side of the tower, operated manually by means of handwheels from the top of the tower.
Major deficiencies with the outlet works included:
A major constraint in addressing these deficiencies was that any remedial works needed to be
undertaken without draining the reservoir or interfering with the releases required for downstream
consumers, including irrigators in Werribee and Bacchus Marsh.The paper describes how all of the deficiencies have been addressed with no interruption to supply, by means of a collaborative effort between the dam owner, the consulting engineer, and 5 separate contractors, with the dam owner playing a leading role.