Part 1: Inside look at the Reservoir – Take a look at this massive project’s construction, from the inside! It’s a once-in-a-lifetime peek inside a 50 million gallon water tank …
It’s not a huge parking lot they’re building, here, atop Powell Butte – it’s part of the roof of Portland Water Bureau’s Powell Butte Reservoir No. 2.
Story and photos by David F. Ashton
If there’s a massive earthquake, there’s a good chance now that the Portland Water Bureau (PWB) Powell Butte Reservoir No. 2 will survive it, keeping greater Portland supplied with drinking water.
That’s just one of the amazing facts East Portland News learned during a March 11 visit to the “Powell Butte Reservoir Project Phase 2”.
With columns in place, workers prepare to put the roof on the final open quarter of the new Powell Butte Reservoir No. 2.
> See our August 1, 2012 update story, with links to many past stories: CLICK HERE for a photographic history of this project – from early planning sessions onward.
During the last visit, the floors, and many of the support columns had been poured, and some of the massive pipe work had begun.
PWB Senior Engineering Associate and Assistant Construction Manager Rick Lapp and PWB Public Information Manager Tim Hall stand next to what will be a vent shaft – one of the above-ground features that will be visible after the project has been completed.
“Reservoir No. 1 may withstand a minor earthquake,” said PWB Senior Engineering Associate and Assistant Construction Manager Rick Lapp, walking us out from the offices, and onto a section of finished roof, along with our guide, PWB Public Information Manager Tim Hall.
“It was built to standards when it was constructed was built starting in 1979, and went operational in 1981,” Lapp said. “Reservoir No. 2 is designed to ride out a strong earthquake, and to keep Portland ‘in water’.”
With 540 columns – 20 foot on-center, Reservoir No. 2, supporting the concrete roof, which will eventually be covered with earth – it’s a solid structure.
These monolithic 30 ft. columns will soon support the roof of Reservoir No. 2 in this cell. Note the “rebar” reinforcing steel sticking out of the top of each column – it will be embedded in the roof, when the concrete is poured.
Making sure each of the columns are constructed so they “meet code”, Special Inspector Dick Stroh, and Quality Control Inspector Alex Colt, do a “reinforcement inspection” before the other half of the form is bolted into place and the concrete is poured.
“The way it’s constructed, the columns are tied and poured into the floor, and the roof is tied and poured into the columns,” Lapp pointed out. “So the whole thing is one continuous structure, instead of pieces that are hooked together.”
Constructing it as a continuous structure helps in another way he added, “There aren’t any cracks or crevices inside the cells (tanks), making them much easier to flush and clean.”
Keeping “Portland in water” during an emergency is one reason for the colossal project.
Another reason is to help keep up with Portland’s increasing thirst for clean water.
“On a hot day, Reservoir No. 1 will ‘turn over’ its 50,000,000 gallon capacity almost four times,” Lapp noted. “That means the system is taking in from the Bull Run Headworks – and sending out from Powell Butte – about 200 million gallons in a 24 hour, period.”
Add to this the fact that some of Portland’s beloved-but-aging open-air reservoirs on Mt. Tabor and in Washington Park must be decommissioned, “It’s easy to see why the additional 50,000,000 gallon capacity of Reservoir No. 2 is necessary.”
One feels dwarfed, standing in these cavernous cells.
Behind the scaffolding is the Inlet Pipe – where water, fresh from Bull Run, enters a cell.
As we walked inside one of the 25,000,000-gallon “cells”, we beheld a water pipe large enough to stand in.
The massive pipe runs the width of the tank, and elbows at a right angle at the outlet, causing the water to swirl and circulate in the cell until it exits through an outlet pipe in the floor, where it heads out to customers.
“And handling this massive amount of water is all done through valves,” Lapp reminded. “That’s right, there are no pumps. “It comes from our ‘headworks’ at Bull Run, and is fed, by gravity, to Powell Butte, and then on to Mount Tabor. And then there’s another line that goes all the way to Beaverton, and that supplies them with about half of their water.”
Soon, this Overflow Pipe’s opening will be embedded in the wall of a cell in Reservoir No. 2.
Near the top of each cell, built into the wall, is another big pipe – it’s 78 inches in diameter – called the Overflow Pipe. “There is a weir wall on the other side of the main wall that channels the water away during an ‘over-low event’,” Lapp explained.
“But, we haven’t overflowed Reservoir No. 1 in, well, years. We know an overflow event would affect Johnson Creek, so we keep the water level in each cell from four to eight feet below the overflow level all the times.”
Overflow and drain pipes converge on this pumping station, now under construction.
As we drove away from the main project site, Lapp showed off the new pumping station – and, down the way, the de-coronation structure under construction.
“There is a big pump in the bottom of the pumping station, so when we must empty a cell, we can pump the water to the top of the Butte, and irrigate a great deal of the land here,” Lapp said.
And, because our water is “finished” – chlorinated – at the Bull Run Headworks, they’re also building a de-coronation system for overflowing water.
Any chlorinated water leaving the reservoirs, headed for Johnson Creek, will pass through the de-coronation system being constructed in this underground vault.
“When water goes through this structure, it’ll flow through floor-to-ceiling columns inside the vault that are filled with, in most cases, ascorbic acid, to neutralize the chlorine,” Lapp instructed.
“The water that goes off to Johnson Creek will be chlorine-free, so there’s nothing [in the water] to burn fishes’ gills. It’s all about the salmon.”
Both of these systems are purposely oversized, he added. “In the future, when they build a third or a fourth reservoir, they won’t have to tear up the ground again; the piping is already installed.”
The project is on schedule to be completed in April of 2014.
If it weren’t heavily overcast and raining, Mt. Hood would be seen in the background of this photo of the project.
Coming next week …
Part 2: Powell Butte Park Restored
© 2013 David F. Ashton ~ East Portland News