Dam Safety & Security

Corps awards contract for Center Hill grout curtain

The U.S. Army Corps of Engineers awarded an $87.4 million contract to Kiewit–A.C.T. to install a grout curtain seepage barrier at 135-MW Center Hill Dam. The dam is on the Caney Fork River in DeKalb County, Tenn. The Corps’ Nashville District made the award.

Kiewit-A.C.T., of Little Rock, Ark., is a joint venture of Kiewit Southern Co., a subsidiary of Kiewit Corp., and Advanced Construction Techniques Ltd. It was chosen in a solicitation that estimated the price for the two-year contract would be $50 million to $100 million.

The 250-foot-tall dam consists of a 1,382-foot-long concrete section and 778-foot-long earth embankment. The contractor is to install an 800-foot-long grout curtain into the rock foundation of the main dam embankment, build a work surface near the crest of the earthen embankment portion of the dam, and install a 3,500-foot-long grout curtain into the rock foundation at the left rim of the dam. Kiewit-A.C.T. also is to plug an area beneath the grout line on the left rim.

The dam, near Lancaster, Tenn., has a history of seepage problems that have worsened in recent years. It is among six dams the Corps identified as having a high risk of failure. In 2006, the Corps approved a $240 million rehabilitation plan that includes the grouting work. Work to improve the dam’s long-term reliability could be completed in 2014, the Corps said.

Reclamation awards $5.5 million for Deer Creek Dam rehab

The Bureau of Reclamation awarded a $5.5 million seismic modification contract to PNK Constructors LLC for 5-MW Deer Creek Dam in Utah.

PNK, of Coalville, Utah, will perform the final stage of a multi-phase project that includes improvements to the spillway control structure and raising the dam crest, Reclamation said. The work is scheduled for completion in late fall or early winter 2008, according to Reclamation and the Provo River Water Users Association, which operates and maintains the dam under contract to Reclamation.

Reclamation launched the multi-phase project to modify the 235-foot-tall, 1,300-foot-long zoned earthfill dam and spillway structure in 2003 to enable it to withstand a large seismic event.

Deer Creek Dam, the main feature of the Provo River project, was completed in 1941. The dam stores water for municipal and irrigation needs of Utah and Salt Lake counties.

Deer Creek Dam improvements are being conducted as part of Reclamation’s Safety of Dams Program, which involves regular inspections of dams throughout 17 states in the western U.S. to identify and correct deficiencies and improve seismic performance.

U.S. completes dam-break studies of Hawaii dams

The U.S. Army Corps of Engineers completed detailed dam-break studies of ten Hawaii dams identified as being of special concern primarily due to downstream urban development.

The State Dam Safety Office will use the reports in following up with dam owners and emergency preparedness agencies, Dam Safety Officer Edwin Matsuda said.

Sen. Daniel Inouye, D-Hawaii, secured $2 million in funds for the studies following the 2006 failure of Kaloko Reservoir Dam on the island of Kauai, in which seven people died. The Corps initiated the studies in January 2007, choosing dams from a list prepared by the Hawaii Department of Land and Natural Resources’ Dam Safety Program.

The Corps evaluated various hydrologic and dam failure scenarios, and analyzed hydraulics that resulted from maps of downstream areas that could be adversely affected.

Consulting firms assisted the Corps in the work, including Tetra Tech, PB Americas in joint venture with Northwest Hydraulic Consultants, SSFM International in joint venture with WEST Consultants, and Oceanit Laboratories.

The reports cover engineering models of possible dam failures due to extreme loading scenarios. The state said hazard maps in each report could be used to help classify a dam’s hazard potential but added they are not evacuation maps.

The Corps transmitted reports of the studies to the Department of Land and Natural Resources for: Nuuanu Dam No. 4 and Wahiawa Dam on Oahu; Twin, Waita, Elua, Aepo, Puu Lua, Reservoir 24, and Upper Kapahi reservoirs on Kauai; and Kualapuu Reservoir on Molokai.

The department posted the reports on its website, http://hawaii.gov/dlnr. The link address is http://hawaii.gov/ dlnr/reports-1/dam-break-studies.

The department’s Hawaii Inventory of Dams listed 133 dams: 53 on Kauai; 16 on Oahu; 51 on Maui, Molokai, and Lanai; and 13 on the island of Hawaii. The state categorized 75 dams as high risk, 21 as significant risk, 20 as low risk, and 17 as dams of an undetermined risk.

City awards contract for Lake Wohlford Dam study

The city of Escondido, Calif., expects to receive a consultant’s report in July outlining mitigation options to prevent liquefaction of Lake Wohlford Dam in the event of a major earthquake at the 1.7-MW Escondido hydroelectric project.

The city council authorized a $195,800 contract in January for GEI Consultants Inc. to study ways to mitigate potential liquefaction of the dam’s hydraulic fill. GEI previously examined the potential for liquefaction under contracts totaling $258,400.

The studies and field and laboratory testing conducted by GEI determined the hydraulic fill in the upstream slope of the dam has the potential to liquefy during a maximum credible earthquake of 7.5 magnitude on the Elsinore fault. The rockfill portion of the dam was determined to be able to withstand an earthquake of that magnitude.

The Escondido project includes the 1.7-MW Bear Valley power plant, on San Luis Rey River and Escondido Creek in San Diego County. Lake Wohlford Dam was built of rock in 1895, reaching a height of 76 feet. In 1924, authorities used silt and sand to add 24 feet. However, the city said the silt and sand materials were not evenly mixed.

In a filing with the Federal Energy Regulatory Commission, the city sets out design and construction activities to remediate the dam. The city plans to submit a draft design report by Nov. 30, 2008, and plans and specifications by Dec. 31, 2009. Once plans and specifications are approved, the project will be advertised for bids, the city said.

The city said it intends to start remediation work by July 29, 2010, and finish construction by July 28, 2011.

While remediation is investigated, the city said it would continue to operate the reservoir below the elevation of 1,460 feet – 20 feet below the spillway crest.

U.S. tests seismic stability of 1.4-MW Wanship Dam

Crews with the Bureau of Reclamation conducted test drilling to evaluate the seismic stability of Wanship Dam, a 175-foot-tall, 2,015-foot-long earthfill dam in Utah’s 5.7-MW Weber Basin project.

Information collected from the field exploration program will be used for risk assessments and to determine performance parameters of the dam. Reclamation said it is working in cooperation with Weber Basin Water Conservancy District, which operates and maintains the project.

Drill crews and geologists drilled several test holes in the zoned earthfill dam. Investigators will evaluate the potential for liquefaction of foundation alluvial materials in the event of an earthquake that could compromise the dam’s integrity.

Wanship Dam, 1.5 miles south of Wanship on the Weber River, impounds Rockport Lake, a 62,120-acre-foot reservoir. The dam provides storage for irrigation water and power generation. Wanship power plant has a single 1.4-MW turbine-generator. The Weber Basin project has a second development, 4.3-MW Gateway power plant.

The work is being conducted under the authority of the Safety of Dams Act of 1978, which ensures Reclamation dams receive periodic examinations and evaluations for early detection of potential dam safety problems.

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