Janice H. Green and Jeanette Meighen
The Probable Maximum Precipitation (PMP) is defined as ‘the theoretical greatest depth of precipitation that is physically possible over a particular catchment’. The PMP depths provided by the Bureau of Meteorology are described as ‘operational estimates of the PMP’ as they represent the best estimate of the PMP depth that can be made, based on the relatively small number of large events that have been observed and our limited knowledge of the causative mechanisms of extreme rainfalls.
Nevertheless, the magnitudes of the PMP depths provided by the Bureau are often met with scepticism concerning their accuracy when compared to large rainfall events which have been observed within catchments and which are, typically, only 20% to 25% of the PMP estimates. The recent increases in the PMP depths, resulting from the revision of the Generalised Tropical Storm Method (GTSMR), have served only to entrench this cynicism.
However, analyses of the magnitudes of the storms in the databases adopted for deriving PMP depths show that these observed storms constituted up to 76% of the corresponding GTSMR PMP depths and up to 80% of the Generalised Southeast Australia Method PMPs for the storm location. Further, comparisons of the PMP depths to large storms observed in similar climatic regions around the world indicate that the PMPs are not outliers.
The results of these analyses are presented for a range of catchment locations and sizes and storm durations and demonstrate that the PMP estimates provided by the Bureau of Meteorology are reasonable and are not unduly large.
Now showing 1-12 of 59 2970:
For many years most emergency management agencies in Australia have used a framework called Prevention, Preparedness, Response and Recovery (PPRR). This approach has worked very well in the past and has been incorporated into the more recent framework of Emergency Risk Management.
While Emergency Management Agencies use practice sessions in the form of Desktop/Tabletop Exercises and Field Exercises as part of Preparedness (the 2nd P in PPRR) these activities can suffer from a lack of engagement with the community.
State Water Corporation, a dam owner in NSW, has installed warning systems to trigger plans written by the SES to warn affected residents of possible dam failure. Although the systems are maintained and tested regularly in a technical sense, the next logical step is to encourage the affected communities to understand their role in the event of evacuation.
A joint exercise involving the NSW State Emergency Service (SES), State Water Corporation and the community, was conducted in a town in the Namoi valley in 2005 and has provided an opportunity to explore this concept. State Water Corporation is now confident that not only will the technical side of the warning system work but that residents should be more aware of their role and that of the SES and State Water Corporation.
Other benefits from the exercise are: the opportunity for improving general flood awareness in the community; the SES identifying community representatives; fine tuning procedures between and within the SES and State Water Corporation; allaying fears within the community about what is required of them in a dam failure; and demonstrating the dam owner’s duty of care to affected residents.
R. Dawson, J. Grimston, R. Cole, D. Bouma
The authors have been involved in the design and construction of several embankment dams in New Zealand over the past decade, and have considerable corporate knowledge from dams designed by the company in its 47-year history. This paper examines four dams which are relatively small to medium, ranging in height from 10 to 19 m with moderate storage volumes. Three of the dams service landfills and the fourth a wood processing mill. Such dams may provide the designer with considerable challenges due to their relatively low capital cost resulting in limited investment in geotechnical investigation at the front end of the project, with varying levels of change often required during construction due to unforeseen conditions as a result of the limited investigations.
The general arrangement and conceptual design principles for each of the dams is described followed by the field investigation and laboratory testing undertaken for each dam, together with the interpreted ground conditions.
The experiences from construction have helped to develop techniques for a balance between preliminary design, investigation, and evolution of the design and specification during construction. It is imperative to develop a sufficiently detailed preliminary design, on the basis of readily available information such as visual and geological assessment, to allow the investigation to be thoughtfully designed to allow the major assumptions to be verified. This needs to be followed by a skilfully executed geotechnical investigation with the designer advising on findings and changing direction as necessary through the investigation. An investigation trench along the full alignment of the cutoff trench (if envisaged in the design) is warranted. Earthworks specifications should be evolved early in the construction phase through compaction trials using specific plant for the site, and backed up by insitu and laboratory testing.
The Koralpe hydropower scheme is a major development on the Feistritzbach tributary of the River Drau to utilize water in a 50 MW powerhouse located in the south-eastern Carinthia, Europe. The Soboth reservoir is situated 735 m higher in a narrow valley and is created by the 85 m high Feistritzbach dam which was constructed near the border of Austria and Slovenia between 1988 and 1990. This rockfill dam is the latest addition to KELAG’s more than 15 structures and is sealed by an asphaltic core. The excellent deformability and impermeability of the asphaltic core is able to follow the deformation of the compacted rock-fill material best during construction, initial filling and operation period without any seepage. The asphaltic core was placed in three 20 cm layers per day by a specially developed placing unit from a contractor. The upstream and downstream filter zone was placed at the same time with the same machine and compacted carefully by vibrating rollers. The dam is curved in plan with a radius of 650 m and contains about 1.6 million m³ rock fill material. The surface of the downstream side was built exceeding the environmental standards of the time.The most important indicator of the normal function of a dam is the behaviour of seepage. A monitoring system of seepage, piezometers, earth pressure cells and deformation has been installed. The seepage water is monitored online at seven points of the dam base and at the access tunnel to the bottom outlet valve. Geodetic measurements on and inside the dam are done once a year. Several additional pieces of surveillance equipment were installed to observe the behaviour of the asphaltic core. The paper concentrates on the design, construction and performance of the dam with the asphaltic core.
Karen Soo Kee
Strategic resource management has never been more important than it is today with the aging of the “baby boomers” and their ongoing exodus from the workforce. The vacancies they leave in professions such as engineering are just beginning to be felt and will exponentially escalate over the next few years. Specialised professions such as dam engineering and related professions will be hit the hardest as the knowledge and skills learnt over decades are depleted.
The lack of skilled staff and in fact the lack of interest of young engineers in entering the dam industry is one of the critical challenges for today. How do we attract professional staff into the field of dam safety before the exodus creates a “black hole” that can never be filled? And how can we ensure the knowledge transfer from existing skilled staff to newer staff to retain expertise within the industry?
Another issue for resource management is that tomorrow’s workers, the “X &Y generations”, will be unlike the current and previous generations of workers. These workers will be less likely to have a mortgage, will have fewer children and be more interested in lifestyle, not career. They will be extremely confident, well educated and very mobile. The future will be a sellers market. The challenge here will not only be to attract and recruit talented workers but also to retain them.
Lawrie Schmitt and Angus Paton
As the owner of most of the large dams in South Australia the South Australian Water Corporation (SA Water) is responsible for the safety of these structures and their designed function of water supply and flood control. In order to meet these responsibilities SA Water monitors the performance of the structures using engineering deformation surveys and various forms of instrumentation. This paper outlines the instrumentation and survey monitoring undertaken at SA Water large dams and discusses the issues arising.