Panel urges immediate steps to avert Center Hill failure
An independent panel of experts urged immediate action to avert catastrophic failure of the U.S. Army Corps of Engineers’ 135-MW Center Hill Dam on Tennessee’s Caney Fork River.
A panel report said significant potential exists for catastrophic failure of the 250-foot-tall concrete and earthen embankment structure under normal operating conditions. The report confirmed findings of an earlier Corps in-house report on uncontrolled seepage that has existed since at least the late 1960s.
“The continued progression of this piping will eventually cause loss of the reservoir through large cavities in the abutments, under the concrete section of the dam, or it will cause collapse of the embankment section as sinkholes develop in the upstream slope resulting in rapid erosion, breach of the dam, and loss of the reservoir,” the report said.
Because it is impossible to estimate when the dam might fail, the panel urged immediate action to reduce risks to the public. It said investigations, grouting, and construction of other remedial measures must be expedited.
Short term: Lower reservoir, expedite grouting
The panel recommends immediate lowering of the reservoir level as far as possible while still operating and providing most project benefits. It recommends keeping the pool level at or below elevation 620 to 630 all year.
The panel also recommends completing a planned grouting program for the main embankment dam, saddle dam, left abutment, and right abutment rim as soon as possible. It said the remedial action is necessary to reduce the risk of dam failure and to establish an appropriate restricted reservoir level.
The panel said grouting should employ the newest methods to make sure a grout curtain seepage barrier is effective, and that important information on foundation conditions is collected for design of a proposed cutoff wall.
Long term: Consider RCC dam at new location
In the longer term, the panel of experts recommends reconsideration of previous dam repair proposals, including possible dam replacement at a site upstream or downstream from the current location. The panel noted the Corps previously ruled out building a new dam, concluding the economic consequences of removing the existing dam, treating the foundation, and building a new dam would devastate surrounding communities.
Options could include a new roller-compacted-concrete dam or partial or full removal and replacement of the existing embankment dam. The panel said a cutoff wall installed from the foundation level would have a much longer life than one installed from the embankment crest and that a concrete dam would be much more resistant to erosion than present embankments.
Center Hill Dam, near Lancaster, Tenn., consists of a 1,382-foot-long concrete section and 778-foot-long earth embankment. It is among six dams, including 270-MW Wolf Creek Dam in Kentucky, that the Corps previously identified as being critically near failure or possessing extremely high life or economic risk.
U.S. performs safety check of 250-MW Yellowtail Dam
The U.S. Department of Interior’s Bureau of Reclamation is investigating structural conditions at 250-MW Yellowtail Dam in Montana as part of a periodic dam safety evaluation.
The investigation, under Reclamation’s Safety of Dams program, was to continue into November at Yellowtail, part of the government’s Pick-Sloan Missouri Basin project.
The examination involves drilling from the crest of the dam in the vicinity of the left abutment. No change in reservoir operations is anticipated during drilling, the agency said.
Comprising 1.5 million cubic yards of concrete, the thin-arch dam is 525 feet tall, with a crest length of 1,480 feet. Four 12-foot-diameter penstocks supply four 87,500-horsepower Francis turbines with 62.5-MW generators in a dam toe powerhouse.
Yellowtail was completed in 1966 on the Bighorn River about 45 miles west of Hardin, in south-central Montana. Reclamation operates and maintains the multi-purpose dam for irrigation water, flood control, and power generation.
ASDSO recognizes work on Massachusetts dam rehab
The Association of State Dam Safety Officials (ASDSO) selected Cobble Mountain Reservoir Dam in Granville, Mass., as its 2007 rehabilitation project of the year. Springfield, Mass., Water and Sewer Commission owns the dam.
The dam was completed in 1931 to provide drinking water for the city of Springfield and surrounding communities.
In 2001, Camp Dresser & McKee Inc. (CDM), Wethersfield, Conn., was hired to design a rehabilitation of the high-pressure outlet works facility in the dam’s diversion tunnel. The outlet works operate under 200 feet of static head.
CDM came up with a plan to replace two 42-inch by 30-inch differential needle valves and to rehabilitate two 40-inch guard valves. In 2005, R.H. White Construction of Auburn, Mass., was awarded a contract to do that work.
R.H. White replaced the needle valves with 30-inch-diameter jet-flow gates, which discharge directly into the 1,500-foot-long, 12-foot-diameter diversion tunnel.
Steel-Fab Inc., Fitchburg, Mass., built the jet-flow gates.
ASDSO said innovative design solutions showed resourcefulness in planning and execution. The association also praised the effective partnering efforts by a water utility, engineering consulting firm, general contractor, and a metal fabricating contractor.
ASDSO presented the award for the 2007 National Rehabilitation Project of the Year during its annual conference in September, in Austin, Texas.
ASDSO names other award recipients
During the conference, ASDSO also presented four merit awards for outstanding contributions to dam safety on regional levels:
– Mount Mansfield Co./Stowe Mountain Resort, Stowe, Vt., for leadership in promoting dam safety (Northeast);
– Spartanburg Water System, Spartanburg, S.C., for work to improve Lake Blalock, protect the public, and ensure a plentiful water supply for its customers (Southeast);
– James Hegarty of consulting engineering firm Prein & Newhof, Grand Rapids, Mich., for his involvement in the design and study of dam removal (Midwest); and
– Upper Brushy Creek Water Control and Improvement District, Round Rock, Texas, for innovative and cost-effective methods to confront the challenge to public safety posed by low-to-high hazard potential dams (West).
Additionally, ASDSO presented a national merit award to former Rep. Sue Kelly, R-N.Y., for her leadership in reauthorizing the National Dam Safety Program.
New officers lead dam safety association
Mark Ogden of Ohio is the new president of the Association of State Dam Safety Officials (ASDSO). Ogden took office during the organization’s 2007 annual meeting in September in Austin, Texas. He succeeds Jim Gallagher of New Hampshire, now immediate past president.
Also serving as 2007-2008 ASDSO officers are Rob Martinez of Nevada (president-elect), Bob Finucane of Vermont (secretary), and David Gutierrez of California (treasurer).
Ogden has been active in ASDSO for many years, serving not only as an association officer (past secretary, treasurer and president-elect) but also as conference program committee chairman and information technology advisory committee member. He is administrator and dam safety engineer for the Ohio Department of Natural Resources.
Martinez previously served as ASDSO’s secretary. He is chief of engineering and dam safety for the Nevada Division of Water Resources.
Finucane, chief of the Vermont Dam Safety and Hydrology Section, served as an ASDSO representative to the Brazilian Congress on Large Dams, sponsored by the Brazilian National Committee of the International Commission on Large Dams (ICOLD).
Gutierrez heads the California Division of Safety of Dams and recently chaired the Model State Dam Safety Program Update committee.
Dam safety group names 2007 scholarship winners
The Association of State Dam Safety Officials (ASDSO) selected two winners of its annual scholarship program.
Salvador Varela, a construction management major at Boise State University in Idaho, and Josh Goodall, a civil engineering major at Oregon State University, each will receive a $5,000 scholarship for the 2007-2008 school year.
ASDSO recognized the two undergraduates at the organization’s annual conference, Sept. 9-13, in Austin, Texas.
Varela, a native of Rexburg, Idaho, has helped develop estimates for Washington Group International projects, including Olmsted Dam, during summer employment. His career plans include becoming a dam safety official.
In addition to his studies, Goodall, of Bend, Ore., is a teacher’s assistant at OSU. He has interned at Kennedy/Jenks Consultants, working on a variety of water and wastewater projects, including storm drainage for the City of the Dalles.
Following undergraduate studies, Goodall plans to obtain a master’s degree in structural engineering, with a focus on large infrastructure designs, including bridges and dams.
CEATI taps Tjoumas to advise Dam Safety Interest Group
Constantine “Gus” Tjoumas joins the CEA Technologies (CEATI) Dam Safety Interest Group as a technology adviser. Tjoumas retired as the director of the Federal Energy Regulatory Commission’s Division of Dam Safety & Inspections in January 2007.
In his new job, Tjoumas will: develop the group’s strategic direction and prospective projects the group will sponsor; provide technical guidance to consortiums on dam monitoring, data collection, and gate reliability; and conduct a survey of participants’ needs and interests. He also is to prepare a report on major developments in the dam safety field.
The Dam Safety Interest Group is one of five CEATI interest groups in the area of electrical generation. Its members are dam owners from North America and elsewhere who jointly sponsor research and development projects to assess and improve safety.
Topics and issues addressed by the group include: risk assessment; geophysical methods in diagnosing and monitoring embankment dams; erosion and piping; reliability and discharge facilities; ice loadings; probability of extreme floods; emergency preparedness; and testing of embedded anchors.
Gary Salmon, an international consultant who previously worked at BC Hydro, where he was director of dam safety, led the interest group until his death in October 2007 (see next page).
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