Flowers Creek Dam History

• Concrete dam constructed in 1946 for Pacific Power & Light
• Company. City of Libby purchased dam in 1986.
• Primary purpose: City of Libby Municipal water
• Dam Height: 59 feet
• Dam Storage: 285 acre-feet
• Dam Classification: High Hazard

Project History

Since originally constructed, the dam has exhibited significant leakage on the dam face through numerous construction joints, resulting in considerable carbonation and iron leachate buildup.  This was likely from substandard original concrete with high water-to-cement ratio. The dam was repaired in 1966 in areas of the upstream and downstream face with higher quality concrete.  In 1995, a synthetic liner was installed on the upstream face to reduce the seepage. In 2009, an inspection revealed seepage was becoming more of a problem. The DNRC recommended that the City perform core drilling to determine concrete strength.  Numerous core samples were taken in 2010 and the results of the sampling showed that the effective strength of the concrete was less than 1000 psi which resulted in a risk of failure during seismic events or if the reservoir level is cycled or drained.  As a result of the findings, the City of Libby began a substantial effort to analyze the existing dam, and looked at numerous alternatives for water sources and water storage for the City. Over a several year effort, it was decided to replace the existing dam with a new concrete gravity structure downstream of the existing dam.

Work Breakdown

• Lower reservoir
• Downstream cofferdam construction
• Existing dam demolition
• Construction of new mass-concrete gravity dam

Project Funding

The total cost of the project is $11,511,000. To finance the project, the City of Libby used numerous grant and loan programs. Acquisition of grants and loans were obtained with assistance by the lead engineering consultant:

• USDA RD Loan: $3,690,000
• USDA RD Grant: $5,140,000
  • RD Loan/Grants are project dependent and are proportional largely based on population and median household income. The terms of the loan included a 40 year repayment at a 3.25% interest rate.

• Department of Commerce - TSEP Construction Grant: $750,000
  • Required 100% Match (Cash, Loan, Other Grants)
• Department of Commerce – CDBG Grant: $450,000
  • Requires 25% Match (Cash, Loan, Grants, In-Kind Work)

• DNRC RRGL Grant: $100,000
• DNRC RRGL Loan: $800,000
  • The terms of the loan included a 20 year repayment at a 3.00% interest rate
• City of Libby: $581,000
  • In-kind (administration), preliminary engineering and design engineering fees

Project Status & Results

• Construction began in December 2014 with drawdown of reservoir
• Project is anticipated to be substantially complete in November 2015
• Due to size and scale of project, numerous permits, authorizations, licenses and acts needed to be acquired and/or met prior to construction occurring

• Public outreach and involvement has been crucial for support of the project

Project Partners

Owner: City of Libby

Lead Design Engineer: Morrison-Maierle

Prime Contractor: Johnson-Wilson Constructors, Inc.