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Dam Safety & Security

Dam safety modifications continue at Folsom Dam

Work is proceeding on modifications needed to improve the safety of the Folsom Dam and Reservoir on the American River in northern California. Folsom Dam is part of the 11-powerhouse Central Valley Project, which provides hydropower, flood control, irrigation water, and drinking water to homes and businesses in northern California.

In February 2010, the U.S. Department of the Interior's Bureau of Reclamation solicited bids for modifications to spillway piers and gates. This work, which expected to cost $25 million to $50 million, will involve: refurbishing stoplogs, making seismic improvements to tainter gates, replacing trunnion pins, surveying for reinforcement and trunnion anchor location in body of pier, locating through bolts, fabricating and installing pier wraps and horizontal pier bracing, replacing part of the bridge deck required for drilling to install vertical pier anchors, and installing vertical pier anchors.

In August 2009, Reclamation awarded a $2 million contract for other modifications to Alpine Diversified of Lemoore, Calif. According to Reclamation, the work involves modifications to Dikes 4 and 6 on the north shore of Folsom Reservoir. Among other activities, the contract calls for the removal of the downstream face of both dikes to add filters and drains to control erosion. Construction work is expected to be completed in the summer of 2010. The project is needed to meet new federal safety rules, Reclamation said.

The Interior Department said in April 2009 that Reclamation would invest $22.3 million in stimulus money from the American Recovery and Reinvestment Act of 2009 to address dam safety concerns at the high-risk Folsom Dam. The work is a Joint Federal Project by Reclamation, the U.S. Army Corps of Engineers, California Department of Water Resources, and Sacramento Area Flood Control Agency.

FERC informs licensees of changes to dam security classifications

In January 2010, the Federal Energy Regulatory Commission (FERC) sent letters to owners of all dams over which it has jurisdiction, information them of potential changes in their current security classifications.

The changes in classification are a result of FERC's new Security Program for Hydropower Projects, which was released in June 2009.

Prior to this revision, all dams under FERC jurisdiction were assigned to one of three security groups – Security Groups 1, 2, and 3 – with specific requirements designated for each group. Security Group 1 dams are inspected with a high level of scrutiny by FERC. Security Group 2 dams are inspected by FERC engineers at a high level of awareness, consistent with the potential threat level. Security Group 3 dams are inspected by FERC engineers as the dams come up for scheduled dam safety inspections, from one to three years.

The original grouping was based primarily on potential consequences if the facility was successfully sabotaged. Since 9/11, national dam sector security programs have more fully developed into a risk-based evaluation that appropriately considers threat, vulnerability, and consequences, says Frank Calcagno, senior physical infrastructure security specialist with FERC.

The recent reclassification was made using information received during the 2009 FERC security inspections and using the likelihood, vulnerability, and consequence values of FERC's Dam Assessment Matrix for Security and Vulnerability Risk (DAMSAVR) evaluation. Based on risk rather than consequences alone, the number of Security Group 1 dams nationwide decreased by about 40 percent.

As a result of this change, new assessments and plans must be completed by December 31, 2010. Owners of Security Group 1 dams must submit a security assessment, vulnerability assessment, security plan, internal emergency response and rapid recovery plan, and annual security compliance certification letter. Owners of Security Group 2 dams must submit all of these documents except the vulnerability assessment. And owners of Security Group 3 dams are not required to submit any documents.

For details on the new requirements, visit the Internet: www.ferc.gov/industries/hydropower/safety/guidelines/security/securitydocumentv2.pdf.

Bonneville Dam contract awarded for seismic mitigation work

The U.S. Army Corps of Engineers has awarded a contract for seismic mitigation work at its 1,076.6-MW Bonneville Lock and Dam, on the Columbia River in Oregon, to Wildish Standard Paving Co. of Eugene, Ore.

The work entails filling the north wall of the old navigation lock (referred to as the Ambursen section) with concrete to reduce the risk of failure under design seismic loading. Monoliths 20 through 25 of the old navigation lock north wall are hollow sections and will be filled with concrete to form new gravity dam sections. The work includes foundation preparation, concrete and gravel placement, control and treatment of seepage water, anchoring, and grouting.

The contract was awarded in February 2010 and has a value of $3,182,550.

DHS offers guide to waterside barriers at dams

The U.S. Department of Homeland Security (DHS) offers Waterside Barriers Guide.

The four-page guide was developed to assist dam owners and operators in understanding the possible need for waterside barriers as part of their overall security plan, DHS says. The guide discusses waterside threats, such as individuals using a water route to gain access to a restricted area. The guide then divides waterside barriers into two categories:

– Systems, which rely on detection or interdiction to stop an aggressor (such as remote radar systems); and

– Technologies, designed to stop or incapacitate an aggressor (such as boat barriers).

The guide also discusses barrier maintenance and the likelihood of a barrier to perform effectively.

The Dams Sector Security Education Workgroup identified the need for this guide. This work group is composed of members from the Dams Sector Coordinating Council and Dams Sector Government Coordinating Council.

– To receive a copy of the guide, E-mail: dams@dhs.gov.

Corps implements new dam safety system

A new dam safety classification system is being used to screen 14 U.S. Army Corps of Engineers dams in the Omaha and Lincoln areas of Nebraska. These dams are being screened using a new risk-informed process to establish priorities for investigations and remediation work on a national basis.

The Corps of Engineers released an Engineering Circular on May 31, 2007, titled "Interim Risk Reduction Measures for Dam Safety," which defines the new Dam Safety Action Classification (DSAC) system. It places dams into five classes: DSAC I dams have the highest priority for action, and DSAC V dams the lowest.

DSAC V dams are considered safe and in compliance with all current criteria. Interim risk-reduction measure plans must be developed for all DSAC I, II, and III dams to reduce risks while long-term solutions are investigated and implemented. These interim measures include updating the emergency action plans (EAPs) and conducting training exercises with emergency management agencies. At some projects, interim risk reduction measures also may include performing repairs and installing additional instrumentation to better monitor the project.

There are four Corps-owned dams on the Papillion Creek system in the Omaha area. They are Glen Cunningham, Standing Bear, Wehrspann, and Zorinsky. Three of these four dams received a DSAC IV rating and require no interim risk-reduction measures.

Glen Cunningham received a DSAC III rating, primarily due to concerns with settlement that occurred during and shortly after construction and may have resulted in damage to the embankment of the dam. Investigations are planned to verify if the embankment has actually been damaged as a result of settlement.

There are ten Corps-owned dams on the Salt Creek system in the Lincoln area. They are Blue Stem, Branched Oak, Conestoga, Holmes Lake, Olive Creek, Pawnee, Stage Coach, Twin Lakes, Wagon Train, and Yankee Hill. Five of them – Blue Stem, Conestoga, Pawnee, Twin Lakes, and Yankee Hill – received a DSAC IV rating and require no interim risk-reduction measures.

Branched Oak, Holmes Lake, Olive Creek, Stage Coach, and Wagon Train received a DSAC III rating, primarily due to potential seepage issues along the outlet conduits. The conduit issues will be assessed and appropriate repairs made. Studies also will be performed to determine if other seepage issues exist at any of these projects.

A reevaluation to determine the amount of available freeboard resulting from an extreme precipitation event is planned at all ten of the Salt Creek dams. Such a weather event is called the probable maximum precipitation (PMP), and the probability of this event occurring is extraordinarily low. There is no evidence to suggest an emergency situation exists or is about to occur at any of the Nebraska dams with a DSAC III rating. Studies and appropriate repairs will be made at each of these dams to correct any confirmed dam safety problems.

Main spillway gate being replaced at Bond Falls Dam

To enhance the safety of its Bond Falls Dam, Upper Peninsula Power Company (UPPCO) is replacing the single main spillway gate with a remotely-operated two-gate structure. The dam, on the Ontonagon River in Michigan, was built in 1938 and impounds water for the company's 12.2-MW Victoria hydro facility.

UPPCO must increase the spillway capacity at Bond Falls to pass the inflow design flood (IDF), says John Myers, director of dam safety for UPPCO. In 2004, the company determined the IDF for this dam. This upgrade will increase capacity to 13,800 cubic feet per second (cfs) from 4,600 cfs.

UPPCO has submitted the completed design for the spillway gate replacement work. Before work can progress, the plan must be approved by UPPCO's board of directors and the Federal Energy Regulatory Commission, Myers says.

This work is anticipated to begin in May 2010 and be completed in November 2010. During this time, the elevation of the reservoir will be about 20 feet lower than the normal summer pool, Myers says.

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