Video Courtesy of John Wilkes at Carpi USA Inc.
Florence Lake Dam in the Sierra east of Fresno is one of Southern California Edison’s most distinctive facilities because of its 58 concrete arches.
But because the dam was built at an elevation of 7,330 feet, the 92-year-old structure is subject to the stresses of freezing and thawing during the winter.
National Dam Safety Awareness Day
May 31 is National Dam Safety Awareness Day, which is commemorated to remember lessons learned from previous dam failures. Learn more about dam safety here.
In 2014, SCE began a project to mitigate erosion and leakage at the most critical arches by installing a geomembrane liner on the dam. The last of the work will resume in September.
“We routinely conduct maintenance and repairs on our dams to ensure public safety,” said Nicolas von Gersdorff, SCE’s chief dam safety engineer. “The geomembrane liner provides waterproofing and will reduce freeze-thaw damage to the concrete.”
Made of PVC (polyvinyl chloride), the liner molds to the arches like white plastic wrap, sealing them from the water. A similar liner was installed at Shaver Lake several years ago.
The liner is a relatively new development in protecting dams. In the past, various coatings or spongy concrete was used to fill in cracks or chips caused by erosion to the dam, but they weren’t as effective as the new liner material.
Installing the liner is a multi-stage process. First, crews grind down the concrete face so they have an even surface to work on. They then install a layer made up of a felt-like material. They cover that with the geomembrane which first must be heated so it will create a secure seal as it cools.
Crews have faced several challenges installing the liner. Under the dam’s permits, the water level must be maintained at 21,000 acre-feet until Sept. 1 so the lake can be used for summer recreation. The liner project requires the lake to be drained to 1,000 acre-feet.
In addition, all the liner work must be completed by Oct. 31 before winter sets in. That leaves a two-month window to do the installation.
The concrete arches, which soar as high as 15 stories, also required a unique approach. Contractor Carpi USA devised an innovative three-part scaffold so workers could reach the entire curved surface of each arch.
The last of the liner work will be completed by the end of October. The liner is expected to last 50 years.