Tech Notes

Issue 3 and Volume 16.

Modifications to high-head gates reduce downpull

Specific modifications to high-head leaf gates can reduce downpull forces in both the open and closed type of gate. This is the primary finding of research commissioned by VA Tech Hydro GmbH and carried out by the Institute of Hydraulic Engineering at Vienna University of Technology. The goal of this research was to reduce downpull forces on gates, which, in turn, will decrease the cost of hydraulic hoist equipment needed to open these gates.

Downpull results from the magnitude of the vertical hydrodynamic downward force on a gate. In many cases, the downpull acting on a gate is higher than the dead weight of the gate. Although moderate downpull is desirable to securely close the gate under emergency conditions, too much downpull can increase the required size, and thus cost, of the hoist equipment.

Researchers considered open (girdered) and closed (smooth) gate construction. Results for each are as follows:

    For open gate construction, perforating the bottom girder reduces downpull forces. This perforation helps balance the greater pressure on the upper side of the bottom girder with the lower pressure on the bottom side of the girder. Reduction in hydrodynamic forces ranged from 6 percent when perforations were 6.3 percent of the total girder area to 80 percent when perforations were 40 percent of the girder area.

    For closed gate construction, perforation canals added from the top to the bottom of the gate reduce downpull forces. These canals are designed to compensate for suction forces at the bottom girder by transferring them to the top of the gate. Downpull forces on the perforated gate were reduced by about 80 percent.

The hydraulic tests were carried out at the institute on gate models with a scale of 1:25. Researchers varied several geometric and hydraulic parameters during these investigations, including gate dimensions, upstream and downstream water levels, and opening ratios.

The institute is using the results of this research to develop a computer-based database to determine hoist forces on high-head gates.

IEEE releases standards for hydroelectric power

The Institute of Electrical and Electronics Engineers Inc. (IEEE) announces availability of its Hydroelectric Power Standards. The standards cover hydro generation, operation, maintenance, and testing. The content of the standards was developed by the Hydroelectric Power Subcommittee of the IEEE Power Engineering Society’s Energy Development and Power Generation Committee.

The standards, in pdf file format on a CD-Rom, are a collection of ten active standards, guides, and recommended practices. Users of the CD-Rom can search the full text of a single standard or search all standards at the same time.

The enhanced edition, called VuSpec, contains the complete collection of active standards, but also provides access to two related standards and four archived standards. This CD-Rom contains both pdf and html files. Other bonus features include:

    A browser interface with links and navigation;

    An electronic glossary of terms with official definitions;

    Multiple search modes for quick finds or complete searches through all the content at once;

    A hyperlinked foreword by the IEEE Hydroelectric Power Subcommittee, describing the intent and application of the standards; and

    A bibliography of more than 85 reference papers on machine design, control features, and plant layouts, with full text of eight of the papers.

Click here to enlarge image

– The active standards (STDVU128) are available for US$215 for IEEE members and affiliates and US$240 for non-members. The VuSpec edition (STDVU129) is available for US$330 for members and affiliates and US$365 for non-members. To order, contact customer service at (1) 800-678-4333; or visit the Internet: www.ieee.org.

ICOLD Forum: Risk assessment for dams

The increase in the complexity of decision-making for dams – to meet societal demands for transparency and accountability – requires an improved approach to their economical and safe operation, maintenance, and overall management, say members of the International Commission on Large Dams’ Committee on Dam Safety. Risk assessment should be considered a tool that can be applied to assist dam owners in solving challenges related to dam safety management.

In the face of growing public scrutiny, the traditional standards-based approach to the task of allocating limited resources for the operation, repair, or improvement of dams is, by itself, becoming increasingly inadequate. The principles of risk assessment are logical and sound. However, the technique itself is still in the development phase. Its application to dams is strongly conditioned to cultural differences between countries. Thus, it is not possible to propose a risk assessment framework that would be suitable for all countries, committee members say.

With regard to risk assessment and its application to dam safety management, discussion must take place to develop a generally accepted position. The result will be a valuable additional tool to assist engineers, owners, and regulators in meeting their obligations with regard to dam safety.

ICOLD offers a technical bulletin on the topic of risk assessment for dams. Bulletin 130, Risk Assessment in Dam Safety Management – A Reconnaissance of Benefits, Methods and Current Applications, was prepared by the ICOLD Committee on Dam Safety. This committee is made up of 29 members from 28 countries.

The bulletin provides an introduction to the principles and terminology of risk assessment. Sections cover:

    Risk assessment in the context of dam safety management, including the reasons to undertake risk assessments to supplement the traditional approach to risk management;

    Principles of risk assessment, including how it is performed;

    Work being done by various countries in applying risk assessment to dams; and

    A glossary providing common and/or preferred terminology, to assist in discussing risk assessment.

To order this 276-page bulletin for 52 euros (US$70), visit www.icold-cigb.org and click on Publications, then Bulletins.

– ICOLD is a nongovernmental organization that provides a forum for the exchange of knowledge and experience in dam engineering. The organization leads the profession in ensuring that dams are built safely, efficiently, economically, and without detrimental effects on the environment. To learn more about ICOLD activities, contact Michel De Vivo, Secretary-General, ICOLD 151, Bd Haussmann, Paris 75008 France; (33) 1-40426824; E-mail: secretaire. [email protected]