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ROCK ISLAND DISTRICT

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Posted 5/2/2017

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Contact
Operations Project Manager
641-828-7522

Location
Knoxville, Iowa

Description
Project in Operation. The Red Rock Dam was constructed from 1960 to 1969 at a total cost of $88,838,600. The Project encompasses over 50,000 acres of fee land and 25,000 acres of flowage easement. The Red Rock watershed is 12,323 square miles. At normal conservation pool Lake Red Rock is 15,250 acres; Iowa's largest lake. At full flood pool it is nearly 65,000 acres, with 1,436,000 acre feet of storage. The Red Rock Dam is the largest in the Mississippi Valley Division.

Since the dam started operations in 1969, it has prevented $1,335,831,000 in damages. The dam regulates flow through fourteen sluice gates. During large magnitude floods, flow is released through five Tainter gates. Red Rock Project also includes remedial works such as the Carlisle levee, Avon levee, and the Southeast Des Moines/Southwest Pleasant Hill levee. The latter protecting over $1 billion in assets. Red Rock's regional economic impact is $13,231,000 (FY '15). The Red Rock Dam has a Dam Safety Action Classification (DSAC) rating of 4.

The dam recently became the host structure for the Red Rock Hydropower Project, a private venture to convert the flood control structure to a hydropower producer. It is financed by the Western Minnesota Municipal Power Agency, and will be operated by Missouri River Energy Services.

Status
The Red Rock Dam is approaching its 50th Anniversary of operation. It has served well, but like any important infrastructure, it needs timely maintenance to ensure that it can operate another 50 years. During the 2012 Operational Condition Assessment it was documented that the five tainter gates have a paint system failure, and that side seal angle brackets are severely corroded, some with visible section loss. If the current conditions persist, additional corrosion of the gates is likely, potentially compromising the performance of the gates, which if it occurs during a large magnitude flood, could result in greater un-prevented flood damages.

The dam is situated over a bedrock of siltstone, sandstone, limestone and coal. In some places evaporate deposits of gypsum and anhydrite were formed. Fractures in the rock has allowed groundwater to come in contact with the evaporate deposits, and causing loss of the material by solutioning. This can result in a void in the bedrock, or possible collapse of the more resistant bedrock materials. In order to prevent underseepage a grout curtain was placed in the dam foundation during construction. Remedial grouting was completed in the 1990s, and while limited in scope, high grout takes were experienced in several holes. The 2012 Periodic Assessment identified "seepage and piping through the soluble gypsum layer" as the greatest risk driver for the Red Rock Dam. Subsequent investigative borings indicate that previous grouting was only partially effective at best. An apparent sinkhole is located about 300 feet upstream of the dam, and appears to have increased in size and depth. Grouting efforts and excavations for the hydropower project confirm the presence of water bearing bedrock layers and dissolvable bedrock materials.

Failure of the Red Rock Dam would have massive consequences to downstream areas as far as Saint Charles, Missouri. The inundation area includes over $1.8 billion of infrastructure and a Population at Risk of 27,500.

The total costs include estimates for repairing and painting the five tainter gates; dam foundation exploration, modeling and analysis in support of ongoing studies to define soluble foundation extents and necessary remediation in preparation for risk assessment and design.

Authority
OM - Operations and Maintenance

Summarized Project Costs

Estimated Federal Cost  N/A 
Estimated Non-Federal Cost  N/A 
Estimated Total Project Cost  $3,100,000 
Allocations Prior to Current FY 2017 Cost  N/A 
Current FY 2017 Allocation (received to date)  N/A 
Current FY 2017 Total Capability  N/A 


Major Work Item Current Year
FY 2017:
Des Moines River Regulation Manual Update

Preliminary dam foundation analysis investigation

Five year Periodic Inspection and Operational Condition Assessment

Routine Operation and Maintenance - mowing, inspecting, exercising gates, greasing trunnion arms, etc.