FERC dam safety program to use risk-informed decision making
The Federal Energy Regulatory Commission's (FERC) new five-year strategic plan contains goals that include the use of risk-informed decision-making in its dam safety program.
Chairman Jon Wellinghoff delivered the Strategic Plan FY 2009-2014 to congressional leaders October 1, 2009, saying FERC plans to align its strategic goals and objectives more closely with its statutory authority. The plan has two overall goals: to ensure that rates, terms, and conditions are just, reasonable, and not unduly discriminatory; and to promote development of safe, reliable, and efficient infrastructure that serves the public interest.
In fiscal year 2009, FERC explored how risk assessment methodologies could benefit its dam safety program. It determined that risk assessment could help FERC:
- – Better understand and quantify potential failure modes;
– Identify previously unidentified failure modes with high risk;
– Understand consequences of potential failure modes on life, health, and property;
– Understand the uncertainty and variability in traditional analyses;
– Understand the risk associated with a single dam or its entire inventory of dams;
– Compare the safety of different dams using a common basis, risk;
– Compare the relative contribution to risk of all failure modes at a given dam; and
– Evaluate risk reduction alternatives and effectively reduce the risk that FERC-jurisdictional dams pose to the public in quantifiable and defensible terms.
The strategic plan said FERC would develop an action plan in fiscal year 2010 that could lead to incorporating risk-informed decision-making into its dam safety program by fiscal year 2014. In fiscal year 2011, it is to prepare a portfolio risk assessment of FERC's dam inventory.
However, FERC said the risk assessment program would not replace its other more traditional methods, such as FERC staff dam inspections or independent engineering consultant inspections of dams.
FERC's Strategic Plan 2009-2014 may be obtained from the Internet at www.ferc.gov/about/strat-docs/FY-09-14-strat-plan-print.pdf.
Government awards $60 million for dam safety services
The U.S. Department of Agriculture's Natural Resources Conservation Service (NRCS) selected six companies or groups of companies to perform professional services related to dam safety assessment, design, design review, and construction management. The combined total value of the contracts is $60 million, with projects to be funded at least in part through the American Recovery and Reinvestment Act of 2009.
The six companies selected are AMEC; Black & Veatch; Gannett Fleming; HDR; URS; and a joint venture of Kleinfelder, Golder Associates, and Freese and Nichols Inc.
From 300 to 800 assessments of existing NRCS structures are anticipated, with the work involving such elements as breach inundation mapping, failure and risk analysis computations, and identification of rehabilitation alternatives. Design tasks may involve anything from engineering investigations to the development of rehabilitation construction plans and specifications. The work may involve structural, civil, geotechnical, hydraulic, and environmental engineering, as well as construction management.
The contracts are for five years, including options. The companies must provide a quick turnaround on proposals for task orders and must complete typical dam assessments within six months and typical design reviews within six weeks.
NRCS is responsible for providing technical assistance to entities of state and local governments and tribes for planning and installing watershed projects under the Watershed Protection and Flood Prevention Act.
TVA raising height of four dams for safe operation
The Tennessee Valley Authority (TVA) is raising the height of four of its dams to help reduce the risk of flooding in the event of weather more extreme than any conditions ever recorded in the region.
This work is necessary after a recent update of TVA's river modeling program determined that the maximum floodwater elevations could be higher than previously calculated if a worst-case winter rainfall were to occur in the upper part of the Tennessee Valley watershed, says Terry Johnson in TVA's communications department.
The four dams being raised are the dams at hydro projects 136-MW Cherokee, 155.6-MW Fort Loudoun, and 40-MW Watts Bar and Tellico Dam (which supplies water to the Fort Loudoun powerhouse).
To raise the dams, TVA will use Concertainers from Hesco Bastion. Concertainers are prefabricated, multi-cellular systems made of coated steel-welded mesh and lined with a non-woven polypropylene geotextile. These temporary, wall-like structures, placed on top of earthen embankments at the dam, will raise the top elevation by about 4 feet. The extra height will prevent water from overtopping and damaging the embankments, Johnson says.
TVA plans to have these structures installed by January 1, 2010, because large regional floods are most likely to occur in winter and early spring. The structures will remain in place until TVA identifies and implements a permanent solution to manage the probable maximum flood for these structures, Johnson says.
He says it will cost about $8 million to install the Concertainers on the four dams. G-UB-MK Constructors and TVA employees will perform the modifications to raise the height of the embankments. G-UB-MK has a long-term contract with TVA to perform modifications and maintenance activities at its hydro and fossil plants, Johnson says.
Corps completes stabilization work at Tuttle Creek Dam
Work is complete on the foundation stabilization being performed at Tuttle Creek Dam, reports the U.S. Army Corps of Engineers.
This modification is part of the $175 million Tuttle Creek Dam Safety Assurance Project, intended to improve the safety of the dam. The dam is a 157-foot-tall, 7,500-foot-long rolled earth and rockfill embankment structure. Without the improvements, a 5.7 to 6.6 magnitude earthquake could inflict significant damage to the dam, the Corps says.
The dam is near the Humboldt Fault, which has produced an earthquake with a magnitude of 5.1. About 13,000 people live downstream of Tuttle Creek Dam, which is on the Big Blue River in Kansas.
The foundation stabilization work performed by contractor Treviicos South Inc. of Boston consisted of building 351 underground concrete walls beneath about 1 mile of the downstream slope of the dam. Each wall is 4 feet wide, 45 feet long, and 60 feet deep. The walls will support the dam, preventing failure during an earthquake. The final wall was completed on August 31, 2009.
Other work being performed on the dam includes structural modifications of the 18 spillway gates east of the dam. The gates are being painted, and work should be complete by November 2009. Construction equipment will remain at the dam for another year to restore the downstream side of the dam and place riprap on the upstream and downstream slopes.
The Corps says the Tuttle Creek Dam Safety Assurance Project is about $75 million under budget and two years ahead of schedule.
In June 2009, the Corps received $24.4 million in American Recovery and Reinvestment Act funding, which allowed the Corps to fully fund the project to completion.