An analytical approach is presented to calculate the pull-out probability of failure of concrete lining of
plunge pools. The concrete lining is aimed to protect the plunge pool against scour where a scour hole may
endanger the stability of the dam foundation. Uplift and pressure loading of the jet are major actions on
the concrete lining. Ground anchors are used to stabilise the lining against these actions and the governing
mode of failure is the pull-out (tensile failure) of these anchors. While the anchoring design for static uplift
is straightforward, dynamic jet action introduces remarkable complexity into the design. The adopted
methodology is based on a stochastic modelling of the high velocity jet action. A bi-linear power spectral
density function is assumed based on the laboratory measurements on the scale physical models done by
the others. This loading mainly reflects the turbulent pressure fluctuations where the jet impacts the plunge
pool floor. Response of the lining, idealised as a single degree of freedom, is calculated by the random
vibration procedures which provides the most realistic structural analysis methodology. It is assumed the
lining is impervious and hence no dynamic under-pressure is developed. The analysis results provide a
probabilistic description of the anchor tensile force which enables the designer to compute the probability
of failure of the anchors knowing their ultimate strength.
Kirsty Carroll, Kelly Maslin, Richard Rodd
Melbourne Water manages over 210 retarding basins across Greater Melbourne ranging in size from 4ML to 4700 ML with embankment heights from 0.3m to 10m. Over the years the basins have been designed and constructed by a range of different owners and authorities. Varying design and construction standards with the majority of retarding basins generally being located in highly urbanised areas, has resulted in Melbourne Water having a large portfolio of assets that have potential to pose a significant risk to the downstream communities they are designed to protect.
High level hazard category assessments completed over the last10 years identified that approximately 90 structures were either High or Extreme hazard categories based on the ANCOLD Guidelines on Assessment of the Consequences of Dam Failure.
In an attempt to identify retarding basins requiring priority consideration for remedial works Melbourne Water embarked on a process of completing a dam safety risk assessment for five of the retarding basins in accordance with the ANCOLD Guidelines on Risk Assessment. The objective of the risk assessment was to develop an understanding of the key risk issues that might affect retarding basins as distinct from water supply storages, identify potential remedial works and develop a prioritised risk management strategy for the five basins considered. In completing the risk assessment there was also significant discussion about ways to streamline the process to allow assessment of the remaining basins.
This paper details the results obtained from the risk assessment, investigates the application of the base safety condition and implementation of a risk management strategy. It also looks at similarities between sites to enable common upgrades to be implemented across the range of retarding basins. This paper also discusses the need for guidelines specific to retarding basins to be developed.
How do you solve a problem like retarding basins? An asset owner’s perspective
Lesa Delaere, Ivor Stuart, Thomas Ewing, David Marsh
As part of Wide Bay Water’s commitment to minimising environmental impacts of its water supply weirs, a “Nature Like” Fishway is under development for the Burrum No 1 Weir. This project is a fishway offset provision for the raising of Lenthalls Dam in the upper reaches of the Burrum River in Hervey Bay. The Burrum No 1 weir forms the primary pumping pool for the Hervey Bay water supply and is located at the tidal limit of the Burrum River. Understanding fish biology and behaviour is critical to the effectiveness of the design of a fishway as much as the balance between the goals of maximising fish passage versus cost, construction and operational difficulties that a fish passage solution may present.
This paper presents the aquatic ecology of the project and the inter-relationship of fish biology and river flow frequency. It discusses the fish species of the Burrum River, their behaviour, seasonal migration and criteria for successful passage. It presents the analysis of river flows with respect to frequency and headwater/tailwater relationships to weir drownout, which was complicated by the tidal flow regimes downstream of the weir. These aspects were also applied in consideration of river behaviour; low flow characteristics for fishway operation during dry seasons and drought, and high flow characteristics during the wet season and floods.
The biological needs for successful fish passage for two very different river flow characteristics were analysed. This allowed targeted design criteria and fishway solution to be developed to provide maximum benefit without causing undue cost to the project.
Burrum Weir Fishway – Fish Biology and River Flows: Two Faces
David R Jeffery
In 2004 the Victorian Government announced the decision to proceed with Australia’s largest dam decommissioning project, the return of the 365,000ML capacity Lake Mokoan to a wetland.
The project has been completed and has resulted in significant river health benefits through liberating environmental flows in the Broken, Goulburn, Murray and Snowy Rivers. Decommissioning has allowed the recovery of water savings for return as environmental flow to the River Murray (30,000 ML/year) and Snowy River (21,000 ML/year).
With decommissioning complete, development of a significant wetland complex across the 8100 hectare site has commenced.
This project has been undertaken at a time when the Broken River basin was exposed to its worst drought conditions in over 100 years and within 11 years of the worst flooding experienced in the nearby Rural City of Benalla. These extremes of climatic conditions and their impacts on the local and irrigation communities have ensured considerable community and stakeholder interest in the decision to proceed with decommissioning and in the subsequent delivery of each of the project elements.
This paper provides an explanation of the drivers for the project, describes the process followed and some of the challenges experienced over the projects seven year life and presents some of the lessons learned along the way.
2011 – MOKOAN – RETURN TO WETLAND PROJECT
Robert Keogh RPEQ, CE Civil (Hon), Mal Halwala, Peter Boettcher, Renee Butterfield
SunWater is a Government Owned Corporation (GOC), operating in a competitive market on an equal commercial footing with the private sector. SunWater owns 23 referable dams. Over the last fifty years there has been significant development of the methodologies used to estimate extreme rainfall events. These have resulted in substantial increases in probable maximum flood (PMF) estimates for most of SunWater’s dams.
SunWater has undertaken a Comprehensive Risk Assessment program across its portfolio. SunWater now has a good understanding of the deficiencies and available risk reduction options for each dam under all load conditions. The total cost to rectify all deficiencies is several hundred million dollars and well beyond the financial capacity of the organisation in the short term.
ANCOLD and Regulators have different published opinions on decision making criteria for dam safety upgrades. Once the conditions for the tolerability of Societal and Individual Risk are satisfied the onus remains with the dam owner to meet the ALARP principle. The decision making process is complicated by uncertainties in inputs to risk assessments. The authors have considered these uncertainties as well as the legal implications, differing ANCOLD and Regulator requirements, and business and economic loss, in formulating the decision making process. The methodology is simplified but effective. If the process is followed the dam owner’s investments will meet ANCOLD, Regulatory, legal and business requirements.
This Paper details a logical decision making process designed to allow a non technical Board to balance social, legal and financial objectives. The process considers overall risk, tolerability, the ALARP principle, and project prioritisation. The process is being used by SunWater to determine the Acceptable Flood Capacity of each dam, which dams will be upgraded, priorities and scheduling of each upgrade.
How SunWater, as a commercial dam owner makes investment decisions for dam safety upgrades