By Michael Raffety
Mountain Democrat 11-29-10
Big Bertha’s gone, but a couple of feet of snow replaced the big rock as the latest challenge for the Syblon Reid construction crew rebuilding Flume 9.
And cold temperatures. It was 20 degrees when the El Dorado Irrigation District inspector snowshoed in to the job site Monday morning.
Two weeks ago the new concrete flume sections were flown in by helicopter. Getting the site prepared for the flume sections was quite a chore. The previous owner of the 22.5-mile El Dorado Canal, PG&E, had laid down timbers and logs as a base for the the 150 feet of Flume 9.
After taking out the wooden flume Syblon Reid had scaled the hillside above it down to bedrock, blasting off the huge rock nicknamed Big Bertha. Then to create a stable and permanent base for the new concrete flume sections it had dug down 23 feet before it found bedrock, said Daryl Noel, EID’s hydro operations engineer.
A lot of what was dug up was old timbers and logs. EID replaced that buried timber base with an engineered compacted base. Then it had Syblon Reid pour parallel 27-inch-wide and 18-inch-deep foundation tracks on which the concrete flumes sit and are anchored by drilling in bolts.
The flume sections are reinforced by 5/8 inch rebar spaced 12 inches apart both horizontally and vertically. The flume sections are created at another site, accessible by road, where the helicopter can pick them up.
The foundation and steel reinforcing is required to meet seismic safety conditions. EID’s engineering specifications, created by Carlton Engineering, are a huge improvement over what PG&E put in. Concrete flume sections PG&E installed in the 1980s have steel that is described by EID officials as wire mesh and what looks like 1/4-inch rebar, the kind that a person could bend a 10-foot section by hand.
The flume base PG&E built is little more than several inches of concrete. On the 1 1/2-mile walk from the Alder Creek Syphon tender’s house to Flume 9 other sections of PG&E concrete flume rest on a series of concrete squares. The light steel reinforcing on PG&E’s concrete flume installations leads to cracking along the edges of the flat bottomed flumes.
A couple of weeks ago a boulder escaped and a tree fell the wrong way, damaging a couple of sections of PG&-installed concrete flume where Flume 9 was set to hook into the existing flume. It took a week to split that rock, said carpenter Brian Luce.
In the meantime one section had to be demolished and an epoxy crew had to be called in to seal the crack in the other section. That was a three-day job, according to Noel. It required a tent to be set up over the expoxy site and propane heaters to warm the concrete to 60 degrees a day before the expoxy, a day to do the epoxying and a day after for it to cure. The epoxy crew packed its supplies in by hand, including a 100-gallon propane tank.
Monday the Syblon Reid crew was constructing forms to connect the new concrete flumes to the old one on the east end and to the in-ground canal on the west end. Tuesday the rebar crew will come in a set the rebar. Shotcrete will then be delivered by helicopter as soon as the weather is clear. A storm is expected Thursday and Friday.
The crew is facing a Dec. 10 deadline and it appears they will meet it. At midnight on Dec. 10 EID will start sending water down the flume to begin generating power and feed drinking water to Water Treatment Plant 1.
Visible above the new flume 9 is netting held in place by vertical and horizontal cables and anchored in the bolts drilled 10 feet deep into the rock. The slide-prone slope has been scraped down to bedrock and a brow ditch dug above the slope to direct runoff away from the slope. A channel under the new flume will carry the brow ditch water off, Noel said.
EID’s engineered base and heavily steel reinforced concrete flumes are built to last 100 years. The canal system and four alpine reservoirs supply 30 percent of the district’s water and supplied water to El Dorado Hills while the water treatment plant there was rebuilt.