Refilling at Taum Sauk to begin early next year

By PAULA BARR
Daily Journal Staff Writer

Published: Saturday, November 21, 2009
Updated: Saturday, November 21, 2009 1:46 PM CST

Nearly four years since the dam failed and released 1.3 billion gallons of water from the Upper Taum Sauk Reservoir, the new dam wall is completed.

Ozark Constructors crews finished the final section of roller-compacted concrete (RCC) Nov. 13 and are removing equipment from within the confines of the dam, according to Ameren spokesman Brianne Lindemann.

“We are finishing electrical and instrumentation installations, installation of the floor surface and installation of the grout curtain,” Lindemann explained. “We anticipate beginning the refill program by the end of January or early February.”

The RCC placement began on Oct. 10, 2007. The completed dam is comprised of more than 2.8 million cubic yards of RCC.

The rebuilt project employed more than 800 people at the height of construction. At this point, construction is still on schedule to allow the electric plant to be fully operational in early 2010. Once the reservoir is completed, it is expected to be the largest RCC dam in North America.

The flat top of the dam walls are 84 feet above the 55-acre basin. The dam was being built in sections, with smooth interior walls and outside walls that form large steps. One section is slightly lower than the rest to serve as an overflow release structure. Should mechanical failure or other causes allow the water rise too high, the stairs on the release structure will diffuse the energy of any water that overflows. That overflow will be directed down the mountain on uninhabited Ameren land and into the Black River.

 The new reservoir is built on the footprint of the previous dam, which failed at 5:15 a.m. Dec. 14, 2005. A 700-foot-long breach in the northwest corner of the reservoir released its contents, sending a raging flood of water down the side of the mountain, through Johnson’s Shut-Ins State Park, and into the East Fork of the Black River during a 25-minute period.

The water ripped up trees and soil from its path, dropped car-sized boulders into the campground and swept the ranger’s house from its foundation. The ranger, his wife, and their three children were carried across the road into a field, where they later were rescued.

It pulverized the soil into silt so fine it remained suspended in the water of the lower reservoir. Since then, Ameren has worked to restore the damaged state park and clean the silt from the water.

Construction on the new dam began in 2007 with a new design. The old, rock-fill dam had been constructed on soil and weathered rock and was made of rock that came from blasting on the mountain. The outside sloped up to a parapet, which is a low wall that encircled the reservoir.

The new dam is built on bedrock and is made of RCC, which contains fly ash, is drier than traditional concrete and was made on site in three plants. It was laid down in 18 inch layers, each of which was compacted with rollers until it was about 12 inches thick. Shut off valves with backups are expected to keep the water from rising too close to the top.

The new reservoir will have continuous video camera and staff monitoring by people on-site as well as in St. Louis and the Osage plant.

Plant manager Dave Fitzgerald plans to monitor the dam daily from the gallery, a walkway around the reservoir that runs inside the base of the dam. High-tech equipment will monitor water leaks, cracks or other occurrences that could become a problem.

Data from that equipment, as well as from drain lines that come from the top of the reservoir to the gallery and from the gallery into the ground, will help Chief Dam Engineer Tom Hollenkamp determine whether it will be necessary to shut down production to fix a problem.

The plant will have a production capacity of 440 megawatts through two pump turbines, which is about one-third of the electricity generated by the Callaway Plant. Startup will take about 10 minutes compared to several hours for coal-generated plants, he added.

Once the reservoir is completed, water will be pumped up the mountain from the Lower Reservoir to the Upper Reservoir during off-peak times for electricity usage, usually from 11 p.m. to 7 a.m. To generate electricity during afternoon peak times, the water will be sent back down the mountain to the lower reservoir.

Paula Barr is a reporter for the Daily Journal and can be reached at 573-431-2010, ext. 172 or at pbarr@dailyjournalonline.com.

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