2000 – Risk Assessment: A Complex Exercise But A Worthwhile Tool

Categories: 2000, Papers Tags: 2000, A. Ash, D.S. Bowles, R. Herweynen, Risk Assessment, S. Abbey

A. Ash, D. S. Bowles, S. Abbey and R. Herweynen

A preliminary risk assessment was undertaken of its three dams by the South East Queensland Water Board (SEQWB) in 1999. The risk assessment process used included a series of workshops that proved to be an important part of ensuring a worthwhile result. The combined expertise of the consultants together with that of staff from the Board and the Queensland’s Department of Natural Resources were used to improve the outcome. The results of the assessment showed that the process had both advantages as well as difficulties in comparison to a standards based approach for making dam safety decisions. Risk Assessment was seen to be a useful management tool for managing dam safety. It gave the owner the ability to quickly rank upgrade requirements or maintenance options on the basis of probability of failure, life safety risks and financial risks to the owner or economic risks to all stakeholders.

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Papers 2000

2000 – Mitigating Cold Water Pollution Below Dams
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B. S. Sherman

Many large Australian dams currently lack selective withdrawal capabilities and release water mainly from deep within the hypolimnion. Deep-water releases coupled with the strong thermal stratification typical of Australian reservoirs results in discharge temperatures 10 °C or more colder than would normally be expected. Cold water pollution has impacted more than 1000 km of river habitat in Australia where it is known to impair spawning, feeding and survival of many native fishes.

This report reviews alternative approaches for the mitigation of cold water pollution below dams. The underlying theory and practical limitations of operation as well as field experience (including cost) with each of the methods are discussed. Two methods in particular, suface pumps and submerged curtains, appear to offer cost-effective alternatives to the expensive retrofitting of dams with multi-level outlet structures (estimated to cost $5-35m per dam for major dams in NSW). These methods are predicted to be capable of increasing discharge temperatures by 4-10 ° throughout the range of irrigation releases without any redirection of flows, i.e. hydropower releases can be maintained at present levels. This holds the promise of restoring more desirable temperatures over hundreds of kilometres of river.
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Papers 2000

2000 – It’s More Fun When You Do It Yourself – Constructing the Lake Eppalock Main Embankment Remedial Works Project
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Steven Fox, Garry Fyfe

This paper describes some key details of the construction of the Lake Eppalock Main Embankment Remedial Works Project. This $8.25 million earthworks project was completed on a “live” storage to an accelerated program. As the dam owner Goulburn-Murray Water took the decision to directly manage the construction of these works with resultant benefits in timing, risk management and project management costs.

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Papers 2000

2000 – Dam Technology in Australia 1850-1999 – Creating the Book
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B. A. Cole

In October 2000 ANCOLD published a history of dam technology in Australia covering the 150 years in which large dams have been constructed in this country. The paper describes how this project began, the search for authors, the way the authors tackled their tasks, the peer reviews which resulted in additional chapters being written, and the archive searches for interesting photographs to illustrate the text. All this was accomplished by dam engineers including the editor. Then follows an account of the professional publication process: sub-editing, desktop publishing, proof-reading, the preparation of an index, the cover design and the printing process. Some conclusions are drawn from this first experience of book publishing.
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Papers 2000

2000 – Protecting Environment Flows While Catering for Urban Water Supply Demand – The Cowarra Off-Creek Dam Experience
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Murray Thompson and Geoff Chenhall

The Hastings District Water Supply Augmentation Scheme [HDWS] includes a 10GL off-creek storage dam, which is currently under construction and due for completion in October 2001. The Cowarra off-creek storage dam is required to meet predicted long-term urban growth demands for water supply and to ensure protection of environmental flows in the Hastings River.

Since 1985 the Hastings Council has progressively developed a strategy for the augmentation of the water supply scheme. A very successful ongoing consultation process with both the local community and key government agencies during the planning and implementation phases of this project has highlighted a number of key issues including:

“That the impact upon aquatic flora and fauna in the Hastings River should be minimised and appropriate safeguards developed by maintaining minimum river flows to ensure that the river habitat is not adversely affected”

The subsequent HDWS Environmental Impact Statement, 1995 was one of the first in NSW to recognise the importance of environmental river flows in the assessment of the aquatic ecological effects of water supply schemes. This paper to be presented to the ANCOLD Conference on Dams will detail the investigation, planning, implementation and current construction activities associated with the Cowarra Off-Creek Storage Dam.
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Papers 2000

2000 – Grahamstown Dam Stage 2 Augmentation Selection and Design of a Labyrinth Spillway and Baffle Chute
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M. B. Barker, R.M. Holroyde, J Williams and T. Qiu

Grahamstown Dam is a major water supply source for the Newcastle area and it is proposed to raise the full supply level by 2.4m from RL 10.4m to RL 12.8m. The present spillway is inadequate to pass the PMF without overtopping of the existing embankments at the new FSL and part of the raising comprises construction of a new embankment of about 10m high with a right bank spillway upstream of the existing spillway capable of passing the PMF. The Pacific Highway is located some 600m downstream of the new spillway and a 60m wide culvert below the Pacific Highway is being constructed with capacity sufficient to pass the PMF. Significant changes were made to the feasibility design for the spillway and the Pacific Highway culvert using a labyrinth spillway and a baffle chute energy dissipator respectively. Both of these designs are uncommon and the process of finalising the designs as well as some of the problems in the use of a labyrinth spillway and the cost savings realised in the use of these designs are presented.
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