Wolf Creek Dam

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The Sustainability of Experience —
Investing in the Human Factor

28th Annual USSD Conference
Portland, Oregon, April 28 - May 2, 2008

Hosted by
Portland General Electric

On the Cover
Portland General Electric’s North Fork Dam, on the Clackamas River southeast of Portland, is a thin, variable-radius concrete arch dam with a maximum height of 207 feet and a thickness varying from 32 feet at the base to 8 feet at the crest. The spillway is a 200-foot-long gated ogee-type structure with a 250-foot-long reinforced concrete chute discharging into the tailrace. The spillway is controlled by three, 50-foot-wide by 37.5-foot-high tainter gates. The powerhouse contains two generating units capable of producing 54 MW of power. A fish ladder is located on right side of the dam.

U.S. Society on Dams
Vision
To be the nation's leading organization of professionals dedicated to advancing the role of dams for the benefit of society.
Mission — USSD is dedicated to:
• Advancing the knowledge of dam engineering, construction, planning, operation, performance, rehabilitation, decommissioning, maintenance, security and safety; • Fostering dam technology for socially, environmentally and financially sustainable water resources systems;

• Providing public awareness of the role of dams in the management of the nation's water resources;
• Enhancing practices to meet current and future challenges on dams; and • Representing the United States as an active member of the International Commission on Large Dams (ICOLD).

The information contained in this publication regarding commercial projects or firms may not be used for advertising or promotional purposes and may not be construed as an endorsement of any product or from by the United States Society on Dams. USSD accepts no responsibility for the statements made or the opinions expressed in this publication.

Copyright © 2008 U.S. Society on Dams
Printed in the United States of America
Library of Congress Control Number: 2008924523
ISBN 978-1-884575-42-6
U.S. Society on Dams
1616 Seventeenth Street, #483
Denver, CO 80202
Telephone: 303-628-5430
Fax: 303-628-5431
E-mail: stephens@ussdams.org
Internet: www.ussdams.org

SEEPAGE ANALYSIS AT WOLF CREEK DAM:
STUDYING THE DIAGNOSTIC EFFECTIVENESS OF AUDIO
FREQUENCY DOMAIN MAGNETICS IN KARST ENVIRONMENTS
Val Kofoed1
Paul Rollins2
ABSTRACT
As part of an ongoing rehabilitation effort at Wolf Creek Dam, a sixty-year old structure on the Cumberland River, the US Army Corps of Engineers Nashville District recently employed a new seepage-diagnosis tool that uses Controlled Source - Audio Frequency Domain Magnetics (CS- AFDM). In this procedure, electrodes are strategically placed on the up and downstream sides of an earthen embankment dam. When the electrodes are charged, the electrical current gathers in areas of highest water concentration while emitting a distinctive magnetic field (Biot-Savart Law). That field is then captured by a specially tuned receiver, and the received data is used to generate both two-dimensional maps and three-dimensional models of the water flow in the surrounding area. The maps and models show where the dam may be compromised by developing seeps. If seepage is detected, these resources provide remediation teams with the information necessary to begin stemming the water flow.

This technology carries great promise. By using electrical currents and magnetic fields— rather than drawing down reservoirs or drilling—to analyze the seepage paths, CSAFDM procedures can avoid much of the disruption and delay entailed in more traditional analytical techniques. Though still new, the use of CS-AFDM in the diagnostic imaging of embankment dams has been tested with sufficient frequency and in a sufficiently diverse set of circumstances to begin drawing some general conclusions about its overall utility. This paper will detail the latest developments in the evolution of this technology, focusing in...
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