Lynnwood’s circular cover is largest in the world
Alderwood Water and Wastewater District (AWWD) in Lynnwood, Wash., is home to the world’s largest circular water reservoir cover. Measuring 375 feet in diameter, the aluminum dome was installed last summer as part of a $4.5 million improvement project that included protecting the reservoir from environmental contamination.
AWWD’s Reservoir No. 1 stores 28 million gallons of water. Prior to being covered, it had to be drained and cleaned annually to rid it of leaves and other debris. With the roof, that process needs to be repeated every five years rather than every year.
Gardena, Calif.-based Temcor constructed the cover. The company first drained the reservoir then built the roof from the center out, starting with a 218-foot tower. Following construction of the tower, the company assembled the roof frame, raising the frame five to six feet off the reservoir floor each time it completed a strut ring.
The tower held the completed frame as workers installed 85 stainless steel columns (85 inches in diameter and 45 feet tall) to support the dome. With the columns in place, the roof was lowered into place and secured. From start to finish, the project took four-and-a-half months.