The Little Rock District completed a Major Rehabilitation Evaluation study of Clearwater Dam to correct the seepage deficiency. The Major Rehabilitation Evaluation Report was approved in July 2004 by USACE and by the Assistant Secretary of the Army (Civil Works) in August 2004. Some seepage under earthen dams is normal, however, at Clearwater, the concern is that the seepage over the long-term is increasing and has and will continue to cause the movement of soil from the embankment. In January 2003, a sinkhole appeared in the upstream face of the dam, providing evidence that this could be occurring. Without correction, the seepage could lead to instability, especially in the case of high lake levels. The Corps of Engineers has designated Clearwater Dam as a high priority and is confident that funding will continue to be provided for the project.
The alternative recommended by the study consists of a subsurface concrete cutoff wall along the full length of the dam, extending from the top of the upstream seepage blanket down through the embankment and into the bedrock. A cutoff wall is a deep trench excavated in the soil and rock into which concrete is placed, and the result is a seepage barrier wall that should virtually cut off the subsurface seepage flow. Excavation is accomplished using specialized equipment. The trenches are usually 2' to 4' wide and can be hundreds of feet deep. They are formed in individual interconnected panels from 8' to 25' long or circular overlapping borings and, when contiguously completed, can total thousands of feet in length or perimeter. Further studies indicated the need for an investigative drilling and grouting program. This investigative drilling and grouting program will provide added resistance to seepage with the cutoff wall.
The recommended project is expected to cost $175-200M and be completed in 2013. The project will be constructed in two phases. Phase I is the investigative drilling and grouting program to determine the condition of the bedrock underlying the dam, grout the rock, and help define how deep the cutoff wall needs to be constructed. Phase II will be the cutoff wall itself. Phase I is being accomplished using two contracts. The first contract generally completes the drilling and grouting through the embankment and a short distance into the rock. This first contract was awarded in January 2006 and completed in October 2007. The second contract was awarded in August 2007 and is scheduled to complete in late 2008. The second contract will complete the drilling and grouting the prescribed depth into the rock, which will be deeper than the cutoff wall. The Phase II Cutoff Wall contract is scheduled for award in September 2008.
Phase I –
The first Phase I contract was awarded in January 2006 to Advanced Construction
Techniques, Ltd of Kettleby, Ontario. The contract completion was October
2007.
Phase I - The second Phase I contract (Phase Ib) was awarded in August
2007 to Advanced Construction Techniques. The contract is scheduled for
completion in late 2008.
Phase II – Detailed design for Phase II is being completed, using data obtained through the Phase I contracts and previous investigations. We expect to award the Phase II contract in September 2008.
• The Corps has developed and implemented several risk reduction measures to maintain confidence in the safe operation of the dam, until the major rehabilitation is completed.
• Clearwater Dam continues to function normally, and we see no evidence of imminent danger to the public. The Corps closely operates and monitors the dam, especially during high water events, to manage the risks of seepage related problems.
• The Corps has an aggressive Dam Safety Program, which includes increased visual monitoring (24/7 during extremely high pools), increased frequency of instrumentation readings, dam safety training, and emergency planning and coordination.
• During high water events in March/April 2008, the dam has functioned normally, and no visible problems have been observed at the dam. Corps personnel visually monitored the dam 24/7 to detect any problems with the dam.
• Highway H-H will continue to remain open to traffic. The cutoff wall will be constructed along a line approximately 100 feet toward the lake from the centerline of the dam, on the top of the existing berm.
• Recreation facilities or opportunities should not be affected by construction on the Major Rehabilitation project, aside from fact that we are likely to continue to disapprove deviations from the approved water control plan for the lake, which have been requested in the past to enhance recreation. The Information Center located at the Clearwater Project Office has been temporarily relocated to make room for the Corps’ construction staff during construction of the Major Rehabilitation project.
• Lake
levels are not directly affected by construction on the Major Rehabilitation
project. We do expect to continue operating under our approved water control
plan and not consider any deviation requests to raise the lake to elevation
500 during the recreation season. This is to limit risk to the dam due
to higher lake elevations until the dam is rehabilitated.
• The Phase I project consists of drilling holes through the dam
and into the underlying rock to find cavities in the rock, fill any cavities,
grout fractures in the rock, and determine how deep the cutoff wall needs
to be constructed to limit the seepage and protect the dam.
• The drilling and grouting in Phase I has found the rock underlying
the dam contains cracks and fractures. There is evidence that the drilling
and grouting is helping to seal those cracks and fractures, based on measurements
taken during the March/April 2008 high water event.
• The Phase II contract is expected to be awarded in late 2008.
This phase of the project is expected to last approximately four to five
years.
• The Corps is also continuing seismic studies on the dam because of its proximity to the New Madrid fault.
Press Releases - Latest news listed first.
CORPS
TO FOLLOW APPROVED PLAN FOR CLEARWATER LAKE LEVEL IN SUMMER
LITTLE
ROCK, Ark., May 2 - To manage water levels at Clearwater Lake in southeastern
Missouri for the forthcoming summer, the Army Corps of Engineers announced
today that the previously approved Clearwater Lake Operating Plan will
be used. This calls for the lake to transition from elevation 494 to elevation
498 beginning immediately. The plan calls for the lake to remain at elevation
498 until June 1 and then transition back to elevation 494 by early October.
More
CLEARWATER DAM REHABILITATION PROJECT UPDATE
PIEDMONT,
Mo., Jan. 30 - The ongoing rehabilitation of Clearwater Dam continues
to be a topic of discussion, so it is a fitting topic for this week's
column. Overall the dam is faring quite well as work proceeds on the major
rehabilitation project, which is scheduled to take about five more years
to complete. The project ultimately calls for construction of a concrete
cutoff wall the length of the dam, a sort of concrete dam within the earthen
dam. More
CLEARWATER
DAM MAJOR REHABILITION PROJECT UPDATE
LITTLE ROCK, Ark., Dec. 26 - Ongoing exploratory drilling as
part of the Clearwater Dam Major Rehabilitation project has detected three
pockets of sandy soil within the core of the dam. Experts are still evaluating
the cause and extent of this condition and how it might affect the performance
of the dam until the cutoff wall can be completed. They have found no
evidence of impending failure. More
CLEARWATER
DAM MAJOR REHABILITATION PROJECT (PHASE 1)
PIEDMONT,
Mo., May 30 - The first phase of the Clearwater Dam Major Rehabilitation
Project is underway. The contract for this phase the project was awarded
to ACT (Advanced Construction Techniques), which in turn sub-contracted
part of the work to Quadri Construction Company of Ellsinore, Mo. Phase
one is expected to take about one year to complete. More
FIRST
PHASE BEGINNING ON CLEARWATER DAM REHABILITATION
PIEDMONT,
Mo., March 14 - The first phase of the Clearwater Dam Major Rehabilitation
Project will get underway this month. Over the course of the next four
years or so, a concrete cutoff wall will be built through the dam into
the bedrock to make the dam good as new and keep it safe for many years
to come. More
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