David Ho, Karen Boyes, Shane Donohoo and Brian Cooper
Many dam structures in Australia were designed and built in the 1950s and 60s with limited hydrological information. As a result existing spillway structures are under-sized for today’s revised probable maximum floods (PMF). Potential problems such as the generation of excessive negative pressure over spillway crest under increased flood condition could be encountered. This may cause instability or cavitation damage to the spillway. The raised flow profile may also have adverse impacts on crest bridges and gate structures.
Historically, physical models have been constructed in hydraulic laboratories to study these behaviours, but they are expensive, time-consuming and there are many difficulties associated with scaling effects. Today, with the use of high-performance computers and more efficient computational fluid dynamics (CFD) codes, the behaviour of hydraulic structures can be investigated numerically in reasonable time and expense.
This paper describes the two- and three-dimensional CFD modelling of spillway behaviour under rising flood levels. The results have been validated against published data and good agreement was obtained. The technique has been applied to investigate several spillway structures in Australia.
An energy and water company spends $8 million on maintenance each year. This work is defined and scheduled through a maintenance management system, part of an enterprise solution that cost the company over $2 million for licence fees, management consulting and installation.
The company has an ageing asset base and has been spending $18 million annually on capital improvements. The work activities are selected to meet safety requirements, enhance reliability, improve plant and upgrade customer service, and are defined, prioritised and scheduled on Word and Excel, which are standard applications on the desks of the company’s engineers and accountants.
This company is a composite (typical) of many in the energy and water business.
The most significant business decisions that owners usually have to make are capital spending commitments to modernise energy and water assets. To be successful, strategies have to be devised to meet the overall strategic objectives of the business, and processes adopted based on a fully functional and integrated asset planning system.
‘Aptus’ is a web-based planning application built specifically for asset intensive businesses. It enables a consistent analytical framework using engineering knowledge and the dam owner’s financial criteria, to provide new perspectives and support strategic planning and decision making with triple bottom line reporting. Aptus is a proven resource to maximize the value of the asset portfolio and sustain the business into the future.
The main iron ore body at Cockatoo Island in the West Kimberleys forms a cliff face plunging steeply into the sea. It was mined by BHP down to low tide level, but the tidal range of 10 metres hampered operations. Being a very pure and sought after ore, various investigations were made to determine methods of extracting the ore below the sea. A coffer dam into the sea was investigated with the conclusion that the soft marine sediments and apparent artesian groundwater in the foundation posed a major risk and high costs.
The mine was sold to a smaller company who proceeded to win useful ore from the island. They also eyed off the undersea ore and approached GHD to use soft ground technology developed for the Derby Tidal Power Project. The soft marine sediments and apparent artesian groundwater conditions were investigated.
The paper describes the design processes involved to achieve dam stability in a space limited by lease boundaries and the desire to maximise the amount of ore that could be accessed. A key to the process was the development of construction techniques and core placement procedures that could cope with the tidal range. Timing aspects were crucial and were controlled by observations of an extensive array of instruments installed for control purposes.
In 1998, ANCOLD Guidelines entitled “Guidelines for Design of Dams for Earthquake” was issued. The Guideline mainly deals with the seismic aspects of dams and only a basic reference is made to the seismic assessment of intake towers in Section 8.3. Although the much needed and pioneering step taken to introduce this Guideline is to be appreciated and it has covered the seismic aspects of dams, some confusion does exist amongst dam / structural engineers in assessing the seismic performance of concrete intake towers. This is mainly due to the fact the behaviour of reinforced concrete intakes towers is quite different from that of earth or concrete gravity dams. This confusion could potentially lead to gross overestimate of the inertia loads on concrete intake towers resulting in unnecessary expenditure in investigation and remedial works.
The energy dissipation due to inelastic hysteresis behaviour of concrete members results in a great reduction in the inertia loads compared with those calculated with traditional “elastic” analysis methods. This consequently results in significant reductions in bending moments and shear forces on the tower and its foundation. It is very important to understand the basic behaviour of reinforced concrete, considering the composite action of concrete, longitudinal & hoop reinforcing steel, before embarking in sophisticated dynamic analysis the outputs of which are highly dependent on the input parameters
The authors have developed a methodology in which the hysteresis energy dissipation due to the inelastic behaviour of concrete intake towers is considered. Various criteria were defined for serviceability and ultimate failure modes such as excessive deflection, spalling of concrete, buckling of reinforcing steel. The confinement effect of hoop steel on the core concrete is also considered.
This paper will present the fundamental aspects of seismic behaviour of reinforced concrete structures with practical cases as applied to intake towers. The results showed that the current methods adopted by various Dam Authorities in Australia are cursory and the energy dissipation aspect should be considered, in conjunction with expert advice, before undertaking any remedial works.
The paper highlights the fundamental importance of correct data selection and storage for the quality of Asset Management demanded for today’s water industry infrastructure.
In developing this theme, the concept of Risk driven maintenance is introduced to focus attention on those issues that not only the identify the appropriate data to be collected and stored, but also, by way of illustrated examples, the direct relevance and application of reliability engineering principles in Risk Analysis.
The author’s principle objective is to demonstrate that the historical data on reliability, condition and performance must be supported with detailed costing information if any worthwhile outcomes are to be forthcoming from analysis.
Hydro Tasmania has recently developed a Dam Safety Emergency Plan, which covers 54 referable dams throughout Tasmania. A major contribution was the development of the Pieman River flood warning system. The flood warning system is a computer-based model that forecasts the hydrological situation of the catchment up to 48 hours into the future and alarms the appropriate personnel when a flood event is imminent. The Pieman River catchment experiences some of the highest average annual rainfalls in Tasmania and contains dams in the High Hazard category. The flood warning system was developed using Hydstra Modelling™ (formerly TimeStudio), which links directly to the Hydstra TSM™ database. This package offers powerful automation tools that enable the Pieman River flood warning system to operate, alert personnel and display results on Hydro Tasmania’s internal website with no manual involvement. With its maintenance free operation and user-friendly interfaces, the Pieman River flood warning system is an effective contribution towards the overall risk management package of the Pieman River Power Development