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Engineers recommend projects at Clearwater Dam
PIEDMONT, Mo. -- Six independent engineers have confirmed the U.S. Army Corps of Engineers' assessment of the Clearwater Dam seepage problems and the recommended remedial projects.
Construction of a deep concrete cutoff wall that was proposed in the corps' 2004 Major Rehabilitation Evaluation Report is also recommended in the External Peer Review Panel's Clearwater Dam Consensus Report.
"The design work has been completed. We hope to award a contract by the end of September," said Tony Batey, chief of engineering and construction in the Little Rock, Ark., Army Corps of Engineers District. "It will take four to five years to complete the project."
Steve Poulos, chairman of the Peer Review Panel, Eric Halpin, special assistant for dam safety at corps headquarters in Washington, D.C., and Batey talked with reporters during a conference phone call Thursday.
The review panel also agreed with the corps that Clearwater should be classified as a Class 1 dam.
"This is the highest level of classification and means that repairs are urgently needed," Poulos said. "This class is the least safe, but it doesn't mean the dam is ready to fail."
There are six dams in the United States with a Class 1 rating.
"It started leaking back in 1950 soon after it was completed," Poulos said.
Following the 2002 flooding, a sinkhole was discovered in the dam during January 2003.
"It caused a lot of concern," Poulos said.
The corps completed a $3.6 million grout curtain project in the vicinity of the sinkhole in May 2005. A $17 million contract was awarded in January 2006 for investigative drilling and grouting along the entire length of the dam.
"It is 75 percent done. It will be completed in early 2009," Batey said.
Officials were concerned when the lake level rose quickly in March and crested only four feet below the emergency spillway in April.
"The dam performed quite well. The lake rose 50 to 60 feet in two days," Batey said. "Our staff was on site 24 hours a day, reading instruments and inspecting the dam."
He also indicated the Clearwater staff did not find any additional problems with the dam.
"They did see some reduction of seepage due to the grouting work," Batey said.
Halpin emphasized many of the review panel's findings and recommendations are already being acted upon by the corps.
"Safety is our No. 1 priority," Halpin said. "The review panel's work is one more step in the assessment process to reduce the risk to the public."
Poulos discussed the immediate, short-term and long-term remedial actions and noted a new Emergency Action Plan was completed in November.
"The Little Rock District is now in the process of updating the surveys and flood routing for the valley downstream from the dam. When these studies are complete, a new set of hydraulic calculations will be made to create inundation maps," Poulos said.
Pool restrictions based on risk analyses were established in August 2007. The report recommends interim risk analyses be prepared to estimate the degree to which the improvements change the risk of failure.
Other recommendations deal with installing more instrumentation and increasing surveillance of all features of the dam that may be deteriorating, continuation of the ongoing investigation and grouting program and extending it into the abutments, evaluation of the earthquake performance for the dam and widen the spillway to permit a larger flow than is currently possible in case the lake level reaches the spillway during periods of heavy rainfall.
"We have known for a long time the spillway is not wide enough. This will be a side benefit to the cutoff wall project," Mark Brightwell, project manager for the major rehabilitation project, said from his Little Rock office later Thursday.
He explained the flood criteria is different today than when the dam was built 60 years ago.
"We enlarged the spillway in the 1980s, but using today's flood criteria, the spillway is still not large enough," Brightwell said.
By the time the entire project is completed in 2013, the cost is expected to be nearly $200 million.