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.
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.
David M. Schaaf, P.E., Jeff Schaefer, Ph.D., P.E., P.G
The United States Army Corps of Engineers (USACE) has an inventory of over 600 dams. The main purpose of many of these dams is for flood control, but there are a significant number of dams primarily used for navigation. Additional benefits at many of these projects are provided through hydropower generation, recreation, and irrigation for farmers. Many of the dams are quite old and represent an aging infrastructure across the inventory. In addition, leaner budgets relative to the need for repairs across the aging system require that USACE invest wisely in order to efficiently use available funds to reduce the greatest risks across the inventory. Previously, individual projects with perceived deficiencies were evaluated separately by the responsible district. This evaluation was not compared in any programmatic way to other USACE dams being evaluated for deficiencies.
In order to improve the process of making risk-based decisions across the entire spectrum of USACE dams, the Screening for Portfolio Risk Assessment (SPRA) for the USACE Dam Safety Program was initiated during the summer of 2005. This effort represents the first level of a multiple phased effort to bring full scale risk assessment to the decision-making regarding making investment decisions associated with dam safety by linking engineering reliability with economic and life loss impacts on a relative scale. The SPRA effort involved the development of a tool for evaluating the relative life and economic risk of dam failures for a variety of deficiencies across the inventory of USACE dams. This paper will focus on the basic aspects of the evaluation tool as well as the process by which the screening was completed.
In Austria, special procedures for ensuring dam safety apply to dams higher than 15 m or reservoirs with a capacity of more than 500,000 m³. There are at present about 90 dams which belong to this category. The largest one is the 200 m high Kölnbrein arch dam.
In general, it is the task of the dam owner to provide for the safety of a dam. For that, he has to appoint qualified engineers, the “Dam Safety Engineers”, which are in charge of dam surveillance and maintenance. The Water Authority verifies that the owner makes the necessary provisions for dam safety. Water Authorities are the Provincial Governor and the Federal Minister of Agriculture and Forestry. The Water Authorities are supported by a governmental advisory board, the “Austrian Commission on Dams”.
Projects for new dams or for reconstruction of existing dams are examined by the Austrian Commission on Dams. Approval by the Water Authority is based on the findings of this commission. A group of a few experts of the commission accompanies the project during construction, first impounding and the final acceptance procedure. In normal operation, dam attendants carry out visual inspections and measurements. The most important instruments are measured automatically and the data are transmitted to a permanently manned control centre. The Dam Safety Engineer has to inspect the dam at least once a year. His annual report to the Water Authorities must contain an assessment of the safety of the dam. The Federal Dam Supervisory Department of the ministry checks the annual reports and carries out an in-depth inspection of the dam at least every five years.
In the case of extraordinary events, the Dam Safety Engineer has to assess the situation and he has to set appropriate measures. An Emergency Action Plan is available for all dams of the said category.
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.
The paper describes the methodology, operative techniques and organizational aspects that are used for dam safety assessment procedures. Kelag owns 15 larger dams with wall heights up to 110 m. It is necessary to monitor the aging of the structures and to check all safety equipment regularly. The manned control centre is situated at the KELAG Headquarter in Klagenfurt, which is the capital of Austria’s southern-most Province, Carinthia. KELAG is the principal electricity supplier in Carinthia, and owns several reservoirs in the Austrian Alps. The whole hydropower system has a capacity of 434 MW with an annual production of 1000 GWh. During the last century KELAG employees designed, supervised and constructed most of the structures in cooperation with the authorities. Most of the rock-fill dams have a bituminous concrete sealing on the upstream face. KELAG owns one concrete arch dam with a height of 30 m. A pendulum monitors the movement of the dam crest. This information is transmitted to both the power house and the manned control centre in Klagenfurt. Seepage is monitored at all rock-fill dams. In case of an alarm a skilled engineer has to be informed by the staff of the manned control centre. This dam safety engineer starts to check the reasons on site and manages the emergency action plan. Data has been collected since 1998 and special software is used to handle this information, carry out interpretation and safety assessments. One aim of data collection is to develop a decision support system performing online evaluation, explanation and interpretation of dam behaviour. Normally, once a year geodetic measurements are carried out at all dams.
KELAG’s experience gained in the use of automatic monitoring and risk assessment of dams is covered in this paper. The monitoring systems show the state of the structures and those showing anomalous situations requiring human intervention can be identified as soon as possible. Although the repercussions of the free market system have led to substantial staff reductions, the quality of dam surveillance has had to remain unaffected. Dam safety is guaranteed by new types of instrumentation, data transmission and data assessment. A special software has to be updated constantly.