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Dam Safety & Security

Report released on work needed at Coon Rapids Dam

A major refurbishment needs to be completed on Coon Rapids Dam to provide a 50-year or greater life span and deal with dam safety issues, and this work needs to begin as soon as possible. These are two recommendations from a recently completed assessment of the dam.

Coon Rapids Dam, on the Mississippi River in Minnesota, was built in 1913 and impounded water for a hydroelectric facility. The dam was abandoned in 1966 and subsequently taken over by the county park districts to be used as a regional recreation area.

In 1009, a concrete section of the dam broke up. The concrete was part of the downstream apron, and the resulting scour hole is about 12,000 square feet in size. It was located below the midsection of the dam about 50 feet from the gates. Although it was determined that the scour hole was not affecting the safety of the dam, repair was needed to avoid long-term damage.

Thus, the Minnesota legislature formed the Coon Rapids Regional Dam Commission in 2010 to study options and make recommendations for the future use of the dam. The seven areas of interest discussed by the commission are:

Engineering firm Stanley Consulting was hired to study whether the dam could act as an effective fish barrier and research the cost for such work. The firm’s report indicated that an improved dam structure and modified operating procedures could serve as an effective fish barrier 99.9 percent of the time. The report estimated the capital cost for improvements to the dam were about $16.9 million. The commission used the resulting report to develop its recommendations.

 

The commission developed five recommendations:

— The Coon Rapids Regional Dam Commission Report, released in February 2011, is available on the Internet at www.crdcommission.blogspot.com.

Spillway, canal work needed for 27.7-MW Minidoka

To ensure the safety of Minidoka Dam, the U.S. Department of the Interior’s Bureau of Reclamation will construct a new spillway, dikes, and canal headworks.

The 27.7-MW Minidoka Dam project is on the Snake River in Idaho. Minidoka is an 86-foot-tall zoned earthfill structure that began operating in 1909. In September 2010, Reclamation issued a record of decision calling for replacement of a spillway and canal headworks cited in an environmental impact statement for the dam.

The agency said the concrete of the 2,237-foot-long wood and concrete spillway, stoplog structure piers and canal headworks has deteriorated to the point where it could fail soon. In addition, the headworks for the canals that run on the north and south sides of the dam show visible signs of deterioration.

Reclamation will hire a contractor to furnish and construct a new south gated spillway, north and south roller-compacted-concrete dikes, north and south side canal headworks, and north and south roller-compacted-concrete overflow spillways. Work also includes modifications to the existing north gated spillway.

The work is valued at $10 million to $25 million.

Dam safety work to be performed at East Branch Dam

The U.S. Army Corps of Engineers plans to hire contractors to perform dam safety work at East Branch Dam on the Clarion River in Pennsylvania.

East Branch is a rolled earthfill embankment dam that experiences seepage problems. Dam repairs initially were performed in 1957. However, the dam has since been determined to be potentially unsafe, prompting the Corps to take precautionary measures to ensure safety of East Branch Dam, pending implementation of a formal dam safety modification program.

Work is to include exploratory and preparatory grouting and construction of a two-component, 300-foot-deep cutoff wall within the existing embankment dam.

The work is expected to cost $100,000 to $250,000.

UPPCO begins refilling reservoir behind Bond Falls Dam

Upper Peninsula Power Co. (UPPCO) began refilling of the Bond Falls Reservoir in late March.

The reservoir was drawn down about 20 feet below the normal summer pool to complete spillway construction, as required by the Federal Energy Regulatory Commission. This work, which began in May 2010, involved replacing the single main spillway gate with a remotely-operated two-gate structure to increase spillway capacity. The new capacity, designed to pass the inflow design flood, is 13,800 cubic feet per second (cfs), compared with the previous 4,600 cfs.

The dam, on the Ontonagon River in Michigan, was built in 1938 and impounds water for the 12.2-MW Victoria plant.

If snow melt and precipitation are close to normal, refilling is expected to take two years, says Virgil Schlorke, manager of regional generation for UPPCO. Once refilled after the spring runoff in 2012, the reservoir will be operated at higher levels than it was in the past.

A.V. Watkins Dam to undergo seismic evaluation

The U.S. Department of the Interior’s Bureau of Reclamation plans to perform a seismic and static issue laboratory evaluation of A.V. Watkins Dam, a 36-foot-tall, 14.5-mile-long zoned earthfill dam that forms Willard Bay Reservoir near Ogden, Utah.

Portions of the embankment were built in 1955, 1964, and 1989. The 10,000-acre Willard Bay off-channel reservoir behind the U-shaped dam was designed for a capacity of 215,000 acre-feet and usable storage area of 198,200 acre-feet.

This evaluation is needed to determine the increase in seismic risk associated with the proposed raising of the dam crest and maximum water surface elevation by 5 feet. Reclamation has developed alternatives to achieve this goal, which is designed to provide additional storage to meet future water supply needs, and begun geotechnical analyses.

This dam nearly failed in November 2006 as a result of piping and internal erosion of foundation soils. Reclamation and the Weber Basin Water Conservancy District determined a portion of A.V. Watkins Dam’s foundation had eroded, leaving a small number of 2- to 5-foot-wide sinkholes near the toe of the dam.

The evaluation is expected to be complete in the fall of 2011, at which time the results will be incorporated into the feasibility study.

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