Retarding Basin Fundamentals (April 2013) – MODULE 1 TO 4
Retarding basins are becoming increasingly important elements in urban flood planning throughout Australia but it is evident that many basins have not been implemented in line with modern day “risk management” approaches. Accordingly, as part of its Professional Development program, and in advance of its proposed Guideline on Retarding Basins due out in 2014, the Australian National Committee on Large Dams (ANCOLD) is planning a series of seminars across Australia on Retarding Basin Fundamentals. The seminars are being provided to assist basin owners, and their professional staff and advisors, to plan, implement and operate their basins in a safe and effective manner consistent with various Government and “duty of care” obligations.
The one day seminars are being presented by leading dam safety and risk management professionals including:
Richard Rodd- dams consultant with over 40 years experience in dam and basin design, construction, operation and maintenance.
Kelly Maslin – dams consultant with over 15 years experience in dams and risk management.
Norm Himsley – dams consultant and member of NSW Dam Safety Committee with over 40 years experience in dam and basin design, construction, operation and maintenance.
Includes access to the following videos:
$60.00 - $80.00
Stephen Newman, Kelly Maslin
Lake Bellfield is a reserve storage for the Wimmera Mallee Water (WMW) Stock and Domestic System in North Western Victoria, constructed between 1963 and 1967. The dam is located on Fyans Creek approximately 3 km upstream from Halls Gap in an area of high tourist value and is rated in the Extreme category under ANCOLD guidelines. The dam consists of an earth and rockfill embankment 745 m long with a maximum height of 57 metres and retains a reservoir with a storage capacity of 78,500 ML.
Previous studies and a subsequent physical model study confirmed that the existing spillway does not meet the requirements of the current ANCOLD guidelines. The current flood capacity is approximately 40% of the Probable Maximum Flood. A range of potential upgrade options to pass the PMF were evaluated with a 1.9 metre composite earthfill and downstream concrete parapet wall raise in combination with spillway lowering of 3.4 metres selected. Construction of this option was completed in early 2003.
This paper describes the key features of the investigation and design including:
Since publication in 2003, the ANCOLD Guidelines for Risk Assessment have reached broad acceptance and use in Australia. In practice, dam owners use the principles of risk assessment to drive business investment decisions. As the guidelines undergo revision, it is timely to assess whether our practices need to evolve to more holistically consider all types of consequences, rather than our current focus on loss of life, in decision-making. This paper aims to prompt dam owners and consultants alike to re-assess our focus on loss of life in risk assessment decision-making, and whether we should more meaningfully consider alternative or broader indicators.
An industry survey was undertaken which found that large dam owners are generally happy with the current system of dam safety decision making. However, the survey responses did identify difficulties in relation to justifying investment below the limit of tolerability that are subject to ALARP principles. In a small number of cases, dam owners found it difficult to justify investment when life safety was not important.
Building on the industry survey and subsequent discussions with practitioners, this paper discusses how the current approach to risk based decision making may result in sub optimal decision making. Further it is discussed how there is an important role that economics should play in providing a universally accepted framework for assessing trade-offs and providing consistent evidence to support decision making.
Dam Types, Foundation & Construction (November 2014) – MODULES 1 to 5 (Full Seminar)
COURSE OBJECTIVES AND OUTLINE
This short course is designed to provide sound basic understanding into dam types, foundations and construction, their key issues and considerations including investigations and design and addressing new and existing dams and associated upgrades.
It will begin with looking at all the various types of embankment and concrete dams, their issues and considerations as a lead into choosing or reviewing dam type and associated upgrade including risk assessment, historical performance and basic monitoring for dam safety.
Next foundations types and associated investigations, design and construction key aspects will be covered in view of the importance of this component for both new and existing dams.
To round off basic dam understanding the final sessions will concentrate on preliminary and common construction considerations and in particular construction of embankment and concrete dam walls.
David Guest, George Samios, Richard Rodd
Tenterfield Creek Dam is a 15m high concrete gravity structure that was constructed in 1930 and raised by 1.83m and stabilised using 97 post-tensioned ground anchors in 1974.Recent stability assessments concluded that the dam does not satisfy the ANCOLD Guidelines for Stability of Gravity Dams and that the situation is likely to deteriorate given the questionable performance of the post-tensioning cables and on the grounds of continuing corrosion and demonstrated loss of load.Tenterfield Shire Council is committed to improving the stability of the dam to meet the requirements of the NSW Dam sSafety Committee and engaged Public Works Advisory to assist them achieve this outcome.
Public Works Advisory prepared a dam upgrade options study which selected two options for further consideration. The estimated costs of the two preferred options were found to be potentially close;therefore Tenterfield Shire Council requested that both options be taken to detail design and tender stage to allow the market to indicate which option was in-fact better value.Factors other than construction costs were also considered in the options evaluation process and these factors influenced the selection outcome. The two upgrade options of lowest cost were the conventional gravity dam strengthen solutions i.e. installation of new post-tensioned ground anchors and downstream mass concrete buttressing. The decision to proceed to tender with two options was supported by the other key funding stakeholder, DPI Water.
This paper provides some unique insight on the comparison of conventional upgrade options for concrete gravity dams and also examines some interesting design aspects encounter edduring the design development process
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.