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Dam Safety & Security

BC Hydro studies ways to fix 67.5-MW Strathcona Dam

BC Hydro says it could cost as much as C$70 million (US$66 million) to mitigate piping and seismic risks at 67.5-MW Strathcona Dam.

The earthfill dam was constructed in British Columbia in the 1950s. BC Hydro previously acknowledged the dam did not meet modern-day standards. The utility said internal erosion within the dam core could occur. Over time, erosion could result in sinkholes or subsidence of the crest and lead to dam overtopping, it said.

In its 2007-2010 service plan, BC Hydro said it is studying how to best mitigate piping and seismic risks at the dam. The utility said in addition to possible internal erosion and degradation in the dam, the concrete intake structure, the adjoining conduit through the base of the dam, the dam itself, and the spillway might be at significant risk in an earthquake.

BC Hydro estimates the total cost for a Strathcona Dam seismic and seepage project could range from C$50 million to C$70 million (US$47 million to US$66 million). It has set a targeted completion date of 2010 for the work.

In 2005, BC Hydro upgraded the dam’s crest to provide the Campbell River hydroelectric system with increased capacity to accommodate extreme floods. The Strathcona Dam powerhouse is one of three generating stations in the utility’s Campbell River System, on Vancouver Island.

California dam owner plans spillway remediation

The Placer County Water Agency is moving forward with plans to expand its ability to handle the probable maximum flood (PMF) at L.L. Anderson Dam, part of the 223.753-MW Middle Fork American River project in California.

The water agency plans to modify the dam’s spillway to safely pass an inflow of 59,100 cubic feet per second (cfs) for the PMF. The existing inflow is 15,000 cfs.

The Federal Energy Regulatory Commission accepted the water agency’s plan and schedule for the spillway work.

The water agency’s schedule includes a Potential Failure Mode Analysis session in October 2007 to review remedial repair options. Engineering is to be completed in December 2008. Construction is to begin in April 2010 and end in December 2010.

Work calls for adding 30 feet to the width of the 40-foot-wide spillway for the 231-foot-tall, 2,700-foot-long dam. Spillway gates also could be replaced or new gates added.

MWH is serving as engineer on the $20 million program.

Contractor provides security for 2,079-MW Hoover Dam

Wackenhut Corp. is continuing to provide security services to the federal government for the 2,078.8-MW Hoover Dam, on the Colorado River in Arizona and Nevada.

Wackenhut, of Palm Beach Gardens, Fla., has performed security work at Hoover Dam since 2002, under the direction of the Hoover Dam Police Department, the principal law enforcement authority at the dam.

The U.S. Department of Interior’s Bureau of Reclamation awarded a $3.1 million contract to Wackenhut, extending services to June 30, 2008.

Wackenhut is providing security at Hoover Dam Highway 93 vehicle inspection checkpoints in Nevada and in Arizona. Employees also are stationed at several other locations around the dam and the dam’s Visitors Center.

Another contractor, Sim-G Technologies LLC of Washington, D.C., recently engineered, designed, and installed upgrades to electronic security systems at Hoover, as well as to Reclamation’s 255-MW Davis in Arizona and 120-MW Parker in California. That work was performed under terms of a $4.96 million contract.

Board of consultants assists in safety review of Ashton Dam

PacifiCorp Energy said a board of consultants is assisting the utility in ensuring the continued safe operation of the 60-foot-tall Ashton Dam. The dam is part of the 7.35-MW Ashton-St. Anthony hydroelectric project in Idaho.

In December 2004, observations by operators at the dam led to concerns about the condition of the structure. PacifiCorp lowered the reservoir behind the dam about 5 feet to allow closer inspection and monitoring. Additional survey monuments were installed.

Officials from PacifiCorp and the Federal Energy Regulatory Commission (FERC) concluded the additional monitoring would permit the reservoir to be raised 3 feet to accommodate irrigation withdrawal and recreational access. However, the officials determined the reservoir should be held at that elevation to ensure the dam’s safety until a thorough evaluation could be completed.

PacifiCorp reports the drawdown has had minimal effects on generation and water control.

In 2005, in conjunction with the Federal Energy Regulatory Commission’s independent consultant safety inspection and report process, a potential failure modes analysis (PFMA) was conducted. A result of the PFMA was a recommendation for a more extensive investigation of the dam’s construction history and performance.

“As we progressed through an evaluation of the dam’s construction history and performance, and the development of a remediation plan, it became obvious that we needed the opinion of experts to answer questions regarding what course of action will best ensure the continued safe operation of the project,” said Roger Raeburn, PacifiCorp Energy’s manager of hydro asset planning and dam safety. Consequently, at FERC’s request, PacifiCorp said it is retaining a board of consultants.

The board consists of two geotechnical engineers and an engineering geologist consultant. All have extensive experience with the design, construction, and evaluation of embankment dams. The board will assist with a review of methods and materials used in the dam’s original construction. It also will review the performance of the dam since it was completed in 1914. And, the board will look into the need for any remediation measures to ensure the dam will continue to safely function.

Raeburn says if it is determined some form of remediation is required, the board is expected to participate in the development and oversee implementation of that work.

The Ashton hydro plant sits on Henry’s Fork of the Snake River, about 2 miles west of Ashton, Idaho. The dam is a rock- and earth-filled structure featuring a 70-foot-wide concrete intake and 82-foot-long spillway. The project began operating in 1914, and was purchased and expanded in 1925 by Utah Power. PacifiCorp acquired Utah Power in 1989.

PacifiCorp Energy consists of the generation, power supply, and mining operations of PacifiCorp. The utility group is part of MidAmerican Energy Holdings Co.

Spillway work in progress at Utah’s Scofield Dam

Gerber Construction of Lehi, Utah, is modifying the Scofield Dam spillway on behalf of Utah’s Carbon Water Conservancy District. The work is being performed under terms of a $7 million contract awarded by the Bureau of Reclamation.

Reclamation said the cost of all modifications planned for the 99-foot tall, 574-foot-long zoned earthfill dam would total about $7 million, or about $3 million less than the $10 million once estimated.

Tasks specified in the contract include replacement of the dam’s concrete spillway chute, the gatehouse on the dam crest, and the highway bridge over Scofield Dam.

The portion of the job under the Safety of Dams program will cost $5.8 million, of which Reclamation will pay 85 percent and the conservancy district 15 percent. The Utah Department of Transportation and the water conservancy district are paying for non-dam-safety work. The transportation department will pay $670,000 for highway work. The district will pay $350,000 for the control house.

Reclamation said it would conduct a pre-construction meeting with the contractor to outline tasks related to Safety of Dams work and other work at the dam. Work is scheduled to begin in early July, and all the work is to be completed in spring 2009.

Scofield Dam is located on the Price River, a tributary of the Green River, about 22 miles northwest of Price, Utah. Construction of the dam began in 1943 and was completed in 1946. It is the principal feature of the Scofield project, which provides seasonal and long-term regulation of the Price River for supplemental irrigation of about 26,000 acres of land, protection from floods, and water for fish propagation.

AMEC named to provide flood map services

The Federal Emergency Management Agency (FEMA) awarded a five-year, $40 million contract to AMEC for flood map modernization services for a region that consists of five states and Washington, D.C.

The Region III contract calls for AMEC, a project management and services company, to provide digital flood insurance rate maps, hydrologic and hydraulic floodplain modeling, coastal flooding analyses, community floodplain ordinance reviews and updates, multi-risk analyses, and post-disaster support.

In the event of a disaster in Region III, which includes the District of Columbia, Delaware, Maryland, Pennsylvania, Virginia, and West Virginia, AMEC could assist the federal government in developing disaster recovery maps. AMEC also could be called upon to address specialized flood risk situations, including dam breaks.

The contract replaces an expiring $10 million contract. It is the largest contract FEMA has awarded AMEC, which also provides FEMA mapping services for state partners in Alabama, Indiana, Kansas, Kentucky, Missouri, North Carolina, North Dakota, South Dakota, and Utah.

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