Best Water/Environment: Haiwee Power Plant Penstock Replacement Project
Owner: Los Angeles Dept. of Water and Power
Lead Design Firm: Golder Associates
General Contractor: Barnard Construction Co.
The Haiwee Power Plant Penstock project, in the remote Owens Valley in the Eastern Sierras, involved replacing 9,420 ft of carbon-steel riveted penstock. Originally installed in the early 1900s, the gravity-fed penstock carries water from the South Haiwee Dam to the Haiwee Power Plant and is part of Los Angeles Aqueduct No. 1, which brings water 233 miles to the city. A previously collapsed section of penstock was restored in the 1980s but was distorted due to numerous longitudinal creases and folds.
Crews had to cut nearly 2,000 ft of the old penstock into sections before removing it and abating more than 1,800 ft of those sections because of asbestos in their exterior coating. The new penstock is 84-in.-dia, bell-and-spigot, fiberglass-reinforced polymer (FRP) pipe. More than 170 oversize truckloads of the pipe were transported from plants in Washington and Alabama.
Compared with carbon steel, FRP pipe is much lighter and easier to handle and was a more cost-efficient option for meeting the project’s design criteria. FRP also provides superior corrosion resistance from internal corrosion and external corrosive soils.
“We had a small window, the low-flow period from January to March, to take the penstock out of service,” says Ed Congdon, Los Angeles Dept. of Water and Power project manager. “To make it worse, we had a record snowpack year, so we had to cut short our outage and complete the tie-ins. We made some cofferdams to flow water in the bypass channel and lower the reservoir level.”
Coordinating design and environmental issues and regulatory requirements was probably the project’s most challenging aspect. “We had to have a biologist, an archaeologist and Native American monitors on site the whole time,” says Congdon.