Over the next several months, the 25-million gallon underground reinforced concrete reservoir being built a top Kelly Butte in Southeast Portland will begin to rise from the ground.
The 394 by 296 foot underground reservoir will be constructed as two separate cells, each with a capacity of 12.5 million gallons. The two cells will operate independently of one another, providing the Portland Water Bureau with the ability to efficiently clean out or repair one side or the other, all while keeping the system in service.
By mid-September, crews overseen by the Portland Water Bureau and contactor Hoffman Construction Company had completed the excavation of the reservoir’s footprint. Starting in October, truck loads of concrete were brought onto the site and offloaded into a concrete pump truck that began pouring the 266 20-foot-by-20 foot squares that will comprise the floor of the reservoir.
The floor is being poured in a checker-board pattern which will allow for a precision watertight seal and help control shrinkage cracking. The reservoir’s floor is scheduled to be completely poured by spring 2014.
In conjunction with the floor pours, supporting columns are in the process of being constructed using metal forms. Upon completion, 252 columns will support the roof of the reservoir.
After the Kelly Butte Reservoir is brought online in 2015, every five years Water Bureau crews will drain, inspect and wash down each cell.
The construction of the reservoir, along with the intricate network of underground piping, multiple vaults and an overflow basin, will allow Portland to comply with federal LT2 rules. The Kelly Butte Reservoir will serve not only east Portland, but it will also be a stopover to supply water to the Washington Park reservoir and southwest Portland area water storage tanks.