Bronson McPherson, David Guest, Barton Maher, Ian Tanner and Amit Chanan
There is significant community interest in the potential for water supply dams to be adapted for flood mitigation, particularly for major dams located upstream of flood vulnerable populations. There may be a number of large dams which have the potential to provide significant flood mitigation benefits to Australian communities if they can be adapted for flood mitigation functionality. Other dams already provide significant flood mitigation benefits, however their limitations are not properly understood by the general public. Two major dams located near a large urban town centre prone to flooding are examined as a case study and some international cases are presented.
Flood mitigation often has a different funding source to water supply. The funding arrangements for flood mitigation dam works can be complex, considering the potential stakeholders and somewhat intangible benefits. If the community wants to use a water supply dam to provide flood mitigation then who provides the funding for the modification works?
Wark, Bob; Thomas, Louise
This paper discusses the rating curves developed for several case studies from the Pilbara and Kimberley, including the Harding Dam, Moochalabra Dam and Ophthalmia Dam. The paper will discuss the impact of underestimated rating curves on the design of infrastructure. An example has occurred at Harding Dam where the pump station was designed to be inundated at a 1:100 AEP and this is now estimated to occur at a lower AEP. The paper will also discuss methods to improve the accuracy of rating curves and the challenges associated with determining accurate rating curves.
Michael Ashley and Robert Wark
The construction of service reservoirs has been an integral part of the development of water supply systems throughout Western Australia, and many such developments have occurred in coastal regions. The porous and highly soluble limestone foundations that are found in coastal regions pose specific challenges and risks for the long term management of these structures. Minimising leakage rates has been traditionally driven by economic losses. However, it has become apparent that the leakage has caused long term structural damage to the foundations of the structures.
Based on four case studies from south west Western Australia, this paper describes the extent of the problem, investigation and testing methods, design challenges and construction issues to be considered when constructing water storages on porous foundations.
Dr Andy Hughes , Tom Wanner , Ben Jones
This paper will present the ideas formulated to safely pass the design floods for ten dams within this sensitive environment, which include the installation of new spillways and/or the raising of dam crests, whilst taking in to account the site constraints and the age of the dams, some of which are up to 300 years old. The risk assessment carried out to quantify the overall risk of the dam failures will also be discussed including the breach inundation flood modelling of central London.
The paper will focus on the engineering and environmental constraints of the project in relation to the highly urbanised area, and the challenges faced when trying to accommodate the needs of many government and high profile stakeholder bodies, and pieces of legislation, in one of the most politically sensitive parts of the country.
Peter Allen and Kevin Bartlett
One of the recommendations of the Queensland Flood Commission of Inquiry was for the introduction of a legislative requirement for all referable dams in Queensland to have Emergency Action Plans (EAPs) formally approved by the Dam Safety Regulator. Prior to this EAPs were required under the dam safety conditions applied to each referable dam and they were not formally approved. This recommendation has now been implemented as a requirement of the Water Supply (Safety and Reliability) Act 2008. This paper summarizes the emergency action planning system now applicable to Queensland’s referable dams and details the actions involved in implementing this system. It involves significant consultation between dam owners and local disaster managers and gives local disaster managers an opportunity to formally comment on EAPs prior to them being submitted for approval. Development of associated regulatory guidelines to cover all aspects of EAPs was done in order to make EAPs more consistent and more readily understood by users and other stakeholders in emergency situations. Once the guidelines had been developed, the Regulator undertook a state-wide series of seminars to raise the level of awareness of local disaster management groups and dam owners of the new requirements. The legislation also requires the publication of the approved EAPs on the department’s website to raise the public’s awareness of the risks involved and improve their responses in advance of emergency events. This represents a challenge from a public relations perspective because people will become more aware of the risks to which they are exposed. The paper summarises the Regulator’s experience in reviewing and considering the EAPs submitted for approval and it indicates some of the benefits and challenges of the ongoing program.
Shane McGrath, Phillip Cummins, and David Stewart
Dam owners and regulators now commonly use risk assessment techniques to assist with decision making for an individual dam or a portfolio of dams. In many cases risk assessment is used to select an optimal course of action in relation to ongoing safety performance of dams, including the achievement of public safety objectives. However, whilst it is an important tool, the use of risk assessment alone is not sufficient to establish that a dam is “safe”.
In modern organisations, business objectives are achieved through a systematic approach to management which described simply sets out what needs to be achieved, how the required outcomes will be delivered and audits the process and results.
In hazardous industries such as mining, chemical, nuclear and dams, it is necessary to reliably achieve business objectives such as product volumes, unit costs and workplace health and safety alongside public safety objectives. In the dams industry, dam safety management systems are now being implemented to document how the organisation satisfies its corporate and business objectives, governance responsibilities and risk management processes.
It is also common in hazardous industries that a “safety case” is required by regulators to demonstrate that the owner has identified what could go wrong at its facility, what controls are in place and that there is a system in place to ensure that the controls are reliable. Whilst dam owners may rely on a dam safety risk assessment to meet regulatory obligations and demonstrate due diligence, the results of risk assessments are not routinely documented sufficiently to satisfy a “safety case” and therefore will not fully meet the organisation’s requirements.
Many dam owners are also responsible for the safety management of other hazardous facilities, such as urban water and mining corporations which typically manage hazardous chemical installations and hazardous or toxic waste disposal. For such organisations, the corporate awareness and processes should already exist to extend the “safety case” philosophy to the management of their dams.
This paper sets out the importance of a dam “safety case”, the essential elements of a safety case and its relationship to the dam safety management system.