The completion of a vital municipal dam near Libby will be delayed after flooding washed away thousands of yards of soil earlier this month.
Prior to the Dec. 9 flooding, engineers and local officials expected to finish the new Flower Creek Dam in February 2016, but Mayor Doug Roll said completion could be pushed back to early spring. Construction on the $8 million dam, located just south of Libby, began in 2014.
The dam will hold back the community’s water supply and replaces the original structure built in the 1940s.
Earlier this month, heavy rain resulted in flooding throughout Lincoln County. Water coming down Flower Creek began to build up and run around the dam. The water moved approximately 2,000 cubic yards of soil near the right abutment core wall. The dam itself was not damaged and missing soil will be replaced with cement.
“There was never a danger to the community or the citizens,” Rolls said of the flood. “There is flood insurance that will cover this damage and it will all be paid for.”
It’s unclear how much the repairs will cost. Roll said that some cleanup would be required around the dam site before work can continue.
The original dam was built in 1946. In 2010 it was deemed inadequate and engineers said it could be compromised by a major seismic event in the area. Morrison-Maierle completed a core sample test of the arch dam and found that the concrete strength was less than 1,000 pounds per square inch. Normal strength is between 3,000 and 4,000 pounds per square inch. If a seismic event did compromise the dam, Flower Creek and Libby could be flooded. In 2012, Lincoln County installed a new sensor and alert system at the dam. If there was a sudden drop in water behind the dam, 911 dispatchers would be notified and could view images of the site to decide if a siren should be sounded in the city.
In late 2014, the reservoir behind the dam was lowered and construction began on a new dam 85 feet downstream. Major construction began early this year. The Flower Creek Dam is part of a larger, multi-million dollar project to rebuild and repair Libby’s aging water system.