Gary Hargraves, Russ McConnell and John Ruffini
The acceptance of the use of generalised methods for estimating extreme rainfall has resulted in a growth of the Probable Maximum Flood (PMF) estimates that spillways of dams are required to pass. In many cases spillways were not designed with spare capacity and are incapable of safely passing the new PMF estimates. Dealing effectively with the potential for dams to cause damage and loss requires a risk management approach. Such an approach requires more reliable tools for estimation of rainfall. This paper examines the issues, the progress made, and outlines further work and options for clarifying risk.
Dr Judy Henderson
Against a background of several decades of increasingly polarised and acrimonious debate, the World Commission on Dams (WCD) was established in 1998 with a two year mandate to review the development effectiveness of dams, assess alternatives for water resources and energy development and develop internationally acceptable criteria and guidelines for future decision- making. This report discusses the role of large dams in development and the challenges of water resource management in the future. T the work program of the WCD is outlined and progress to date on fulfilling its mandate.
Robert E Saunders
The vast majority of dams in Australia are relatively small affairs. For example, approximately 90% of Queensland’ referable dams are less than 15 m in height. Most of these dams are owned by small communities, mining companies or farmers, many of which have smaller operations than those of Australia’s larger dam owners. In many cases the dam represents the owner’s sole source of water supply.
Many smaller dam owners are unaware of the key factors affecting the safety and best management of their facilities. Added to this is a general lack of understanding of dam related issues by the community at large. This often leads to significant owner and community concerns (and conflicts) that have the potential to jeopardise the viability, or worse, the safety of a project. The relative importance of the dam to the smaller dam owner often exacerbates these issues.
This paper serves to illustrate, by way of example, a consultant’s viewpoint of some of the issues encountered on small dam projects and suggests actions that the dams industry as whole could take to improve the situation.
ANCOLD Environmental Guidelines have been under preparation for a considerable time. A brief for their preparation followed a resolution by the ANCOLD executive in 1991] that:
“ANCOLD should be seen by the profession and the community as a credible and informed source of information on the risks and benefits associated with dam projects.”
Why the guidelines were initiated, why they have taken the time they have to prepare and what they cover are described in this paper.
To the author’s knowledge, they are the only guidelines of their type, addressing the environmental effects of dams and associated works. It is hoped that they generate substantive debate. This paper initiates the public comments phase.
The paper has two purposes:
° = To introduce the guidelines ° To use the guidelines to introduce this environmental issues session of this conference
Javad Tabatabaei! and Christopher Zoppou
Cotter Dam was constructed in 1912 to 19m and was raised to 31m in 1949. Due to its close proximity to a popular recreational resort, it is considered as a high hazard dam. It forms a storage with a capacity of only 4500ML and receives flows from a catchment area of 482km?. Concern about the ageing and structural integrity of Cotter Dam was expressed as early as 1967. There has also been a major revision of the Probable Maximum Flood (PMF) and new earthquake requirements for the dam. All these factors have contributed to the decision to undertake remedial works on the dam. The remedial work could be interrupted by flows over the spillway. This would increase the cost of the works because the construction equipment must be removed and reinstated (de/remobilisation) when there are flows over the spillway. Additional costs are also incurred for each day the construction equipment remains idle (standby). The total tender price therefore includes the cost associated with the remedial work as well as any standby and de/remobolisations. Risk analysis was used to establish the frequency the reservoir water level exceeds the spillway level. The risk analysis was used to select the successful remedial works tender.
Buddhima Indraratna, Mark Locke and Gamini Adikari
The main objectives of the filter are to prevent erosion of the dam core, permit controlled passage of seepage flow through the dam and facilitate dissipation of excess pore pressures in the core. In most designs of dam filters, empirical methods based on particle size ratios have been used. These empirical rules are developed through extensive laboratory tests. Although the empirical rules benefit from directly or indirectly incorporating most factors affecting filtration, they cannot be extrapolated for distinctly different soils and do not describe the time dependent changes that occur within the filter medium.
Mathematical models can be formulated to explain the fundamental physics of particle interaction and migration, within a framework of well defined geohydraulic constraints. Considering the mass flow and momentum conservation principles; time dependent changes in particle size distributions, mass flow rates, retention capacity and base soil erosion rates can be simulated.
This paper reviews various empirical and mathematical models, based on the authors experience. A novel approach to large scale filtration is highlighted based on testing actual soil and filter materials from an Australian dam, in a new 500mm diameter apparatus.